using MeterVault.Core.Analysis;
using MeterVault.Core.Analysis.Costing;
using MeterVault.Core.Analysis.Coverage;
using MeterVault.Core.Analysis.Quantities;
using MeterVault.Core.Analysis.Totals;
using MeterVault.Core.Analysis.Virtual;
using MeterVault.Core.Domain;
using MeterVault.Core.Normalization;
using MeterVault.Infrastructure.Analysis;
using MeterVault.Infrastructure.Persistence;
using Microsoft.EntityFrameworkCore;

namespace MeterVault.Infrastructure.Costing;

/// <summary>
/// One cost request from catalog to priced result: which lines, standing charges and manual costs the scope holds, the
/// quantities they need (read once, through the analysis reader), and their prices (the Core calculator).
/// </summary>
/// <remarks>
/// <para>
/// The order is fixed: catalog, tariffs, manual costs and categories are loaded once → the bill is classified with the
/// tariff book (D-35) → the scope becomes pricing groups (a type's bill, a category, a meter) → the buckets are planned
/// and cut into local months (D-36) → the quantities of every meter any group prices are read in one reader pass → each
/// group is priced twice: per bucket, and over the period's own months for its total.
/// </para>
/// <para>
/// A figure that is the sum of several groups (the portfolio: every type's bill plus the global standing charge and the
/// meterless manual costs) is added up with <see cref="CostAmount.Sum"/>, so it reconciles with its parts exactly.
/// </para>
/// </remarks>
internal sealed class BillRun
{
    private readonly MeterVaultDbContext _db;
    private readonly AnalysisReader _reader;
    private readonly CostAnalysisRequest _request;
    private readonly ResolvedPeriod _period;
    private readonly TimeZoneInfo _zone;
    private readonly string _currency;
    private readonly DateOnly _today;

    private readonly HashSet<int> _notCosted = [];
    private readonly Dictionary<int, DateOnly?> _firstData = [];
    private readonly List<AnalysisProblem> _quantityProblems = [];

    /// <summary>A catalog the caller already loaded and wants this run to reuse (A-40); null to load one.</summary>
    private readonly AnalysisCatalog? _sharedCatalog;

    private AnalysisCatalog _catalog = null!;
    private TariffBook _book = null!;
    private TotalsClassification _full = null!;
    private List<ManualCost> _manual = [];
    private List<CostCategory> _categories = [];
    private Dictionary<int, IReadOnlyList<int>> _virtualSources = [];

    private BucketPlan _plan = null!;
    private AnalysisBucket _periodBucket = null!;
    private IReadOnlyList<CostPart> _displayParts = [];
    private IReadOnlyList<CostPart> _periodParts = [];
    private Dictionary<int, IReadOnlyList<BucketValue>> _displayValues = [];
    private Dictionary<int, IReadOnlyList<BucketValue>> _periodValues = [];
    private Dictionary<int, IReadOnlyList<BucketValue>> _displaySpans = [];
    private Dictionary<int, IReadOnlyList<BucketValue>> _periodSpans = [];
    private Dictionary<int, AnalysisSeries> _series = [];

    public BillRun(
        MeterVaultDbContext db, AnalysisReader reader, CostAnalysisRequest request, string currency, AnalysisCatalog? catalog = null)
    {
        _db = db;
        _reader = reader;
        _request = request;
        _period = request.Period;
        _zone = reader.Zone;
        _currency = currency;
        _today = PeriodResolver.LocalDate(_period.Now, _zone);
        _sharedCatalog = catalog;
    }

    private bool WantsCategories =>
        _request.Scope.Kind == CostScopeKind.Category || (_request.Scope.Kind == CostScopeKind.Portfolio && _request.IncludeCategories);

    public async Task<CostAnalysis> ExecuteAsync(CancellationToken cancellationToken)
    {
        await LoadAsync(WantsCategories, cancellationToken).ConfigureAwait(false);
        if (ScopeFor() is not { } scope)
        {
            return Refused(EmptyPlan(), CostRefusal.UnknownScope);
        }

        var plan = await PlanAsync(scope, cancellationToken).ConfigureAwait(false);
        if (plan.Refused)
        {
            return Refused(plan, CostRefusal.TooManyPoints);
        }

        _plan = plan;
        _periodBucket = PeriodBucket.Of(_period);
        _displayParts = CostCalculator.Parts(plan.Buckets);
        _periodParts = CostCalculator.Parts([_periodBucket]);
        await ReadQuantitiesAsync(scope, cancellationToken).ConfigureAwait(false);
        await LoadServiceAsync(cancellationToken).ConfigureAwait(false);

        foreach (var group in scope.AllGroups())
        {
            Price(group);
        }

        return Compose(scope);
    }

    /// <summary>What a scope has data for (D-19): its priced meters' coverage and its manual costs, without pricing.</summary>
    public async Task<CostAvailability> AvailabilityAsync(CancellationToken cancellationToken)
    {
        await LoadAsync(WantsCategories, cancellationToken).ConfigureAwait(false);
        if (ScopeFor() is not { } scope)
        {
            return CostAvailability.None;
        }

        var metered = await _reader.QuantityAvailabilityAsync(_db, _catalog, scope.AvailabilityMeters, _period.Now, cancellationToken)
            .ConfigureAwait(false);
        return Availability(metered, scope.ManualInScope);
    }

    // ------------------------------------------------------------------------------------------------ loading

    private async Task LoadAsync(bool categories, CancellationToken cancellationToken)
    {
        // The catalog is a snapshot of meters, tanks, links and rollup states; a caller that reads several figures of
        // one page from it (the Overview's bill and its comparison) passes the one it already holds, so they answer
        // from the same snapshot and the load is not repeated (A-40).
        _catalog = _sharedCatalog ?? await AnalysisCatalog.LoadAsync(_db, _zone, cancellationToken).ConfigureAwait(false);

        // One tariff load per request; ordered so that the book's deterministic tie-break never depends on the plan.
        var tariffs = await _db.Tariffs.AsNoTracking().OrderBy(t => t.Id).ToListAsync(cancellationToken).ConfigureAwait(false);
        _book = TariffBook.Create(tariffs, _currency);
        _full = _catalog.Classify(_book.HasMeterScopedUnitPrice);
        _virtualSources = _catalog.TotalsMeters.Where(m => m.IsVirtual).ToDictionary(m => m.Id, m => m.VirtualSources);

        _manual = await _db.ManualCosts.AsNoTracking().OrderBy(c => c.Id).ToListAsync(cancellationToken).ConfigureAwait(false);
        if (categories)
        {
            _categories = await _db.CostCategories.AsNoTracking()
                .Include(c => c.Members)
                .OrderBy(c => c.Sort)
                .ThenBy(c => c.Id)
                .ToListAsync(cancellationToken)
                .ConfigureAwait(false);
        }
    }

    // ------------------------------------------------------------------------------------------------ scope → groups

    /// <summary>The scope as pricing groups, or null when its meter or category does not exist.</summary>
    private ScopePlan? ScopeFor()
    {
        var scope = _request.Scope;
        switch (scope.Kind)
        {
            case CostScopeKind.Portfolio:
            {
                var plan = new ScopePlan { AvailabilityMeters = [.. _full.BillItems.Order()], ManualInScope = [.. _manual] };
                foreach (var type in TypesWithMeters())
                {
                    plan.Types.Add((type, TypeGroup(type)));
                }

                plan.Portfolio = new PricingGroup();
                if (_book.HasAnyInScope(TariffComponent.BasePrice, TariffScope.Global, null))
                {
                    plan.Portfolio.Rows.Add(new StandingChargeKey(TariffScope.Global, null));
                }

                plan.Portfolio.Manual.AddRange(_manual.Where(c => c.MeterId is not { } id || _catalog.Find(id) is null));
                if (_request.IncludeCategories)
                {
                    plan.Categories = PlanCategories();
                }

                return plan;
            }

            case CostScopeKind.EnergyType:
            {
                var type = scope.Id!.Value;
                var plan = new ScopePlan
                {
                    AvailabilityMeters = [.. _full.ForType(type).Billing.Items.Order()],
                    ManualInScope = [.. _manual.Where(c => MeterType(c.MeterId) == type)],
                };
                plan.Types.Add((type, TypeGroup(type)));
                return plan;
            }

            case CostScopeKind.Meter:
            {
                if (_catalog.Find(scope.Id!.Value) is not { } meter)
                {
                    return null;
                }

                var (group, info) = MeterGroup(meter);
                return new ScopePlan
                {
                    Single = group,
                    Meter = info,
                    AvailabilityMeters = [meter.Id],
                    ManualInScope = [.. group.Manual],
                    OwnSemantics = !meter.IsVirtual,
                };
            }

            default:
            {
                if (_categories.Find(c => c.Id == scope.Id) is null)
                {
                    return null;
                }

                var categories = PlanCategories();
                var entry = categories.Entries[scope.Id!.Value];
                return new ScopePlan
                {
                    Single = entry.Group,
                    CategoryEntry = entry,
                    Categories = categories,
                    AvailabilityMeters = entry.Cover.CoverMeterIds,
                    ManualInScope = [.. entry.Group.Manual],
                };
            }
        }
    }

    private IEnumerable<int> TypesWithMeters() => _catalog.Meters.Values.Select(m => m.EnergyTypeId).Distinct().Order();

    private int? MeterType(int? meterId) => meterId is { } id && _catalog.Find(id) is { } meter ? meter.EnergyTypeId : null;

    /// <summary>A type's bill (D-34, D-35): its lines, its own standing charge (D-40), the manual costs of its meters (D-41).</summary>
    private PricingGroup TypeGroup(int type)
    {
        var billing = _full.ForType(type).Billing;
        var group = new PricingGroup { EnergyTypeId = type, Basis = billing.Basis };
        foreach (var line in billing.Lines)
        {
            group.Lines.AddRange(Expand(line, billing.SeparatelyBilled));
        }

        if (_book.HasAnyInScope(TariffComponent.BasePrice, TariffScope.EnergyType, type))
        {
            group.Rows.Add(new StandingChargeKey(TariffScope.EnergyType, type));
        }

        group.Rows.AddRange(MeterFeeRows(type, group.Lines));
        group.Manual.AddRange(_manual.Where(c => MeterType(c.MeterId) == type));
        return group;
    }

    /// <summary>
    /// A-18: the meter-scoped standing charges of a type's physical meters that no line of <paramref name="lines"/>
    /// accrues — a PV or house meter behind the billed grid meter — each as a row of its own on its meter, so a meter fee
    /// is charged once, on its meter (D-40), rather than dropped because its meter is not a bill line.
    /// </summary>
    private List<StandingChargeKey> MeterFeeRows(int type, IEnumerable<LineSpec> lines)
    {
        var lined = lines.Select(l => l.MeterId).ToHashSet();
        return [.. _catalog.Meters.Values
            .Where(m => m.EnergyTypeId == type && !m.IsVirtual && !lined.Contains(m.Id)
                && _book.HasAnyInScope(TariffComponent.BasePrice, TariffScope.Meter, m.Id))
            .Select(m => m.Id)
            .Order()
            .Select(id => new StandingChargeKey(TariffScope.Meter, id))];
    }

    /// <summary>
    /// A meter's own cost (D-39 for virtual meters): the line the bill prices it with, else a view at its unit price or
    /// its feed-in credit; a virtual meter by its cost rule. Its manual costs go with it (D-41).
    /// </summary>
    private (PricingGroup Group, MeterCostInfo Info) MeterGroup(AnalysisMeter meter)
    {
        var group = new PricingGroup();
        group.Manual.AddRange(_manual.Where(c => c.MeterId == meter.Id));
        var line = _full.LineOf(meter.Id);

        if (!meter.IsVirtual)
        {
            var own = OwnLines(meter);
            group.Lines.AddRange(own.Lines);

            // A meter the scope prices no quantity of (a generation meter) still carries its own fee (A-18).
            if (own.Lines.Count == 0 && _book.HasAnyInScope(TariffComponent.BasePrice, TariffScope.Meter, meter.Id))
            {
                group.Rows.Add(new StandingChargeKey(TariffScope.Meter, meter.Id));
            }

            return (group, new MeterCostInfo(meter.Id, own.Rule, own.OnBill, own.Reason, []));
        }

        if (meter.Formula is null)
        {
            return (group, Info(MeterCostRule.None, line is not null, MeterNotCostedReason.NotEvaluable));
        }

        var rule = meter.CostRule switch
        {
            VirtualCostRule.SourceCosts => MeterCostRule.SourceCosts,
            VirtualCostRule.OwnQuantity => MeterCostRule.OwnQuantity,
            _ => MeterCostRule.None,
        };

        // A stored source-costs rule over a nested difference is taken as none (A-15), and a generation result is never
        // billed (D-34): say why rather than "no rule".
        var notCosted = rule != MeterCostRule.None ? MeterNotCostedReason.None
            : meter.Validation?.CostRuleProblem is not null ? MeterNotCostedReason.SourcesNotPureSum
            : meter.Quantity.Kind == QuantityKind.Generation ? MeterNotCostedReason.Generation
            : MeterNotCostedReason.NoCostRule;

        if (line is not null)
        {
            group.Lines.AddRange(Expand(line, SeparatelyBilledOf(meter.EnergyTypeId)));
            IReadOnlyList<int> billedSources = rule == MeterCostRule.SourceCosts
                ? [.. group.Lines.Select(l => l.MeterId).Distinct().Order()]
                : [];
            return (group, new MeterCostInfo(meter.Id, rule, true, notCosted, billedSources));
        }

        if (rule == MeterCostRule.SourceCosts)
        {
            if (CostSourcesOf(meter.Id) is not { } sourceIds)
            {
                return (group, Info(MeterCostRule.None, false, MeterNotCostedReason.SourcesNotPureSum));
            }

            var lines = SourceLines(meter, [], []);
            if (lines.Count == 0)
            {
                // D-39 adds the sources' own costs; generation and runtime sources have none (D-34).
                return (group, Info(MeterCostRule.None, false, NotCostedReasonOf(sourceIds)));
            }

            group.Lines.AddRange(lines);
            return (group, new MeterCostInfo(meter.Id, rule, false, notCosted, [.. lines.Select(l => l.MeterId).Distinct().Order()]));
        }

        if (rule == MeterCostRule.OwnQuantity)
        {
            group.Lines.Add(new LineSpec(meter.Id, meter.EnergyTypeId, BillLineKind.UnitPrice, meter.Quantity.Unit, [], null));
        }

        return (group, new MeterCostInfo(meter.Id, rule, false, notCosted, []));

        MeterCostInfo Info(MeterCostRule costRule, bool onBill, MeterNotCostedReason reason = MeterNotCostedReason.None) =>
            new(meter.Id, costRule, onBill, reason, []);
    }

    /// <summary>
    /// What a physical meter's own scope prices: its line on the bill; otherwise a view by what it measures — its
    /// consumption at its unit price, its export as a feed-in credit — or nothing, and why (generation and operating time
    /// are never billed, D-34).
    /// </summary>
    private OwnCost OwnLines(AnalysisMeter meter)
    {
        if (_full.LineOf(meter.Id) is { } line)
        {
            return new OwnCost([.. Expand(line, SeparatelyBilledOf(meter.EnergyTypeId))], MeterCostRule.BillLine, true, MeterNotCostedReason.None);
        }

        return meter.Quantity.Kind switch
        {
            QuantityKind.Consumption => new OwnCost(
                [new LineSpec(meter.Id, meter.EnergyTypeId, BillLineKind.UnitPrice, meter.Quantity.Unit, [], null)],
                MeterCostRule.UnitPriceView, false, MeterNotCostedReason.None),
            QuantityKind.Export => new OwnCost(
                [new LineSpec(meter.Id, meter.EnergyTypeId, BillLineKind.FeedIn, meter.Quantity.Unit, [], null)],
                MeterCostRule.FeedInView, false, MeterNotCostedReason.None),
            QuantityKind.Generation => new OwnCost([], MeterCostRule.None, false, MeterNotCostedReason.Generation),
            QuantityKind.Runtime => new OwnCost([], MeterCostRule.None, false, MeterNotCostedReason.Runtime),
            _ => new OwnCost([], MeterCostRule.None, false, MeterNotCostedReason.NoCostRule),
        };
    }

    /// <summary>Why a sum whose sources price nothing has no cost: all generation, all operating time, or no rule at all.</summary>
    private MeterNotCostedReason NotCostedReasonOf(IReadOnlyList<int> sourceIds)
    {
        var kinds = sourceIds.Select(id => _catalog.Meters[id].Quantity.Kind).Distinct().ToList();
        return kinds switch
        {
            [QuantityKind.Generation] => MeterNotCostedReason.Generation,
            [QuantityKind.Runtime] => MeterNotCostedReason.Runtime,
            _ => MeterNotCostedReason.NoCostRule,
        };
    }

    private IReadOnlyList<SeparatelyBilledMeter> SeparatelyBilledOf(int type) => _full.ForType(type).Billing.SeparatelyBilled;

    /// <summary>
    /// A bill line as priced lines. A physical meter is its own line. A virtual meter counted by an override (D-23) is
    /// priced by its cost rule (D-39): its own quantity, or its sources' metered costs — one line per source, each at
    /// its own price, never the sum repriced; with the rule <c>none</c> it is left out and reported.
    /// </summary>
    private IEnumerable<LineSpec> Expand(BillLine line, IReadOnlyList<SeparatelyBilledMeter> separately, bool report = true)
    {
        var meter = _catalog.Meters[line.MeterId];
        if (!meter.IsVirtual || meter.CostRule == VirtualCostRule.OwnQuantity)
        {
            return [new LineSpec(meter.Id, meter.EnergyTypeId, line.Kind, meter.Quantity.Unit, line.Deductions, null)];
        }

        if (meter.CostRule == VirtualCostRule.SourceCosts)
        {
            return SourceLines(meter, line.Deductions, separately);
        }

        if (report)
        {
            _notCosted.Add(meter.Id);
        }

        return [];
    }

    /// <summary>
    /// D-39 <c>sourceCosts</c>: each physical source priced the way its own scope prices it (A-15) — a consumption source
    /// at its unit price (or its bill line), an export source as a feed-in credit, a generation or runtime source not at
    /// all — once per source the formula's weights name (<see cref="CostSourcesOf"/>). A separately billed subsection the
    /// bill takes out of the sum is taken out of the source it runs through.
    /// </summary>
    private List<LineSpec> SourceLines(AnalysisMeter meter, IReadOnlyList<BillDeduction> deductions, IReadOnlyList<SeparatelyBilledMeter> separately)
    {
        var sources = CostSourcesOf(meter.Id) ?? [];
        var perSource = sources.Select(_ => new List<BillDeduction>()).ToList();
        foreach (var deduction in deductions)
        {
            var through = separately.FirstOrDefault(s => s.MeterId == deduction.MeterId && s.SubtractFromMeterId == meter.Id)?.ThroughMeterId;
            var index = through is { } t ? Math.Max(0, sources.ToList().IndexOf(t)) : 0;
            if (perSource.Count == 0)
            {
                break;
            }

            var factor = UnitFactor(deduction.MeterId, sources[index]) ?? deduction.UnitFactor;
            perSource[index].Add(new BillDeduction(deduction.MeterId, factor));
        }

        var lines = new List<LineSpec>();
        for (var i = 0; i < sources.Count; i++)
        {
            var own = OwnLines(_catalog.Meters[sources[i]]).Lines;
            for (var j = 0; j < own.Count; j++)
            {
                lines.Add(own[j] with { Deductions = j == 0 ? [.. own[j].Deductions, .. perSource[i]] : own[j].Deductions, ForMeterId = meter.Id });
            }
        }

        return lines;
    }

    /// <summary>
    /// The physical sources whose metered costs a <c>sourceCosts</c> meter adds (D-39): the meters its formula's weights
    /// name — each once, so <c>m1 + m1 - m1 + m2</c> is m1 and m2 — through nested pure sums. Null when a nested source
    /// is not a pure sum: its sources' costs would include a subtrahend's (A-15).
    /// </summary>
    private List<int>? CostSourcesOf(int virtualId)
    {
        var result = new List<int>();
        var visiting = new HashSet<int>();
        return Collect(virtualId) ? result : null;

        bool Collect(int id)
        {
            if (_catalog.Find(id) is not { } meter)
            {
                return true;
            }

            if (!meter.IsVirtual)
            {
                result.Add(id);
                return true;
            }

            if (meter.Formula is not { IsPureSum: true, Coefficients: { } weights } || !visiting.Add(id))
            {
                return false;
            }

            foreach (var source in weights.Keys.Order())
            {
                if (!Collect(source))
                {
                    return false;
                }
            }

            visiting.Remove(id);
            return true;
        }
    }

    private IReadOnlyList<int> SourcesOf(int virtualId) =>
        [.. (_virtualSources.GetValueOrDefault(virtualId) ?? []).Where(id => _catalog.Find(id) is { IsVirtual: false })];

    private double? UnitFactor(int from, int to)
    {
        var fromUnit = _catalog.Meters[from].Quantity.Unit;
        var toUnit = _catalog.Meters[to].Quantity.Unit;
        return Units.AreSame(fromUnit, toUnit) ? 1d : Units.ConversionFactor(fromUnit, toUnit);
    }

    // ------------------------------------------------------------------------------------------------ categories (D-42)

    /// <summary>
    /// Every category's cover, the parts of the bill each holds, which categories are slices of the bill and which are
    /// overlapping views, and the composition's groups.
    /// </summary>
    private CategoryPlan PlanCategories()
    {
        var plan = new CategoryPlan();
        var billRows = BillRows();
        var members = _categories.ToDictionary(c => c.Id, ExpandMembers);
        var covers = _categories.Select(c => CategoryCover.Compute(_full, c.Id, members[c.Id])).ToList();
        var report = CategoryCover.CheckOverlap(_full, covers);

        var manualClaims = _manual.ToDictionary(c => c.Id, c => ClaimsOf(c, members));
        var rowClaims = billRows.ToDictionary(r => r, r => _categories.Where(c => HoldsRow(c, r, members[c.Id])).Select(c => c.Id).ToList());

        // A slice of the bill shares nothing with another slice: two line-disjoint categories claiming the same manual
        // cost or standing charge would add it twice, so both become views.
        var views = new HashSet<int>(report.OverlappingViewIds);
        var candidates = _categories.Select(c => c.Id).Where(id => !views.Contains(id)).ToHashSet();
        foreach (var claimants in manualClaims.Values.Concat(rowClaims.Values))
        {
            var slices = claimants.Where(candidates.Contains).ToList();
            if (slices.Count > 1)
            {
                views.UnionWith(slices);
            }
        }

        plan.Overlaps = Overlaps(report, manualClaims, rowClaims);
        var disjoint = _categories.Select(c => c.Id).Where(id => !views.Contains(id)).ToHashSet();

        foreach (var (category, cover) in _categories.Zip(covers))
        {
            var group = new PricingGroup();
            var separately = cover.SeparatelyBilled;
            foreach (var line in cover.Lines)
            {
                group.Lines.AddRange(Expand(line, cover.LiesOutsideBill ? separately : SeparatelyBilledOf(_catalog.Meters[line.MeterId].EnergyTypeId)));
            }

            // A meter's own fee accrues on its line where the category prices one (A-18); only a meter without one needs its row.
            group.Rows.AddRange(rowClaims
                .Where(r => r.Value.Contains(category.Id))
                .Select(r => r.Key)
                .Where(r => r.Scope != TariffScope.Meter || !group.Lines.Exists(l => l.MeterId == r.ScopeId)));
            group.Manual.AddRange(_manual.Where(c => manualClaims[c.Id].Contains(category.Id)));
            plan.Entries[category.Id] = new CategoryEntry(category, cover, group, views.Contains(category.Id));
        }

        // Uncategorized: the bill lines and manual costs no slice holds; standing charges no slice holds are rows of their own.
        var categorized = disjoint.SelectMany(id => plan.Entries[id].Cover.CoverMeterIds).ToHashSet();
        plan.UncategorizedMeterIds = [.. _full.BillItems.Where(id => !categorized.Contains(id)).Order()];
        foreach (var id in plan.UncategorizedMeterIds)
        {
            plan.Uncategorized.Lines.AddRange(Expand(_full.LineOf(id)!, SeparatelyBilledOf(_catalog.Meters[id].EnergyTypeId)));
        }

        plan.Uncategorized.Manual.AddRange(_manual.Where(c => !manualClaims[c.Id].Exists(disjoint.Contains)));
        foreach (var row in billRows.Where(r => !rowClaims[r].Exists(disjoint.Contains)))
        {
            var group = new PricingGroup();
            group.Rows.Add(row);
            plan.RowSlices.Add((row, group));
        }

        plan.Disjoint = [.. _categories.Where(c => disjoint.Contains(c.Id)).Select(c => c.Id)];
        return plan;
    }

    /// <summary>
    /// The standing-charge rows of the whole bill: each type with meters and a base price, the meter fees no bill line
    /// accrues (A-18, as <see cref="TypeGroup"/> adds them), and the global one.
    /// </summary>
    private List<StandingChargeKey> BillRows()
    {
        var rows = new List<StandingChargeKey>();
        foreach (var type in TypesWithMeters())
        {
            if (_book.HasAnyInScope(TariffComponent.BasePrice, TariffScope.EnergyType, type))
            {
                rows.Add(new StandingChargeKey(TariffScope.EnergyType, type));
            }

            var lines = _full.ForType(type).Billing.Lines.SelectMany(l => Expand(l, SeparatelyBilledOf(type), report: false));
            rows.AddRange(MeterFeeRows(type, lines));
        }

        if (_book.HasAnyInScope(TariffComponent.BasePrice, TariffScope.Global, null))
        {
            rows.Add(new StandingChargeKey(TariffScope.Global, null));
        }

        return rows;
    }

    /// <summary>A category's members with type members expanded to every meter of the type, known meters only, ascending.</summary>
    private IReadOnlyList<int> ExpandMembers(CostCategory category)
    {
        var ids = new SortedSet<int>();
        foreach (var member in category.Members)
        {
            if (member.MeterId is { } meterId && _catalog.Find(meterId) is not null)
            {
                ids.Add(meterId);
            }

            if (member.EnergyTypeId is { } type)
            {
                ids.UnionWith(_catalog.Meters.Values.Where(m => m.EnergyTypeId == type).Select(m => m.Id));
            }
        }

        return [.. ids];
    }

    /// <summary>
    /// The categories a manual cost belongs to (D-41): its own category, else every category holding its meter.
    /// </summary>
    private List<int> ClaimsOf(ManualCost cost, Dictionary<int, IReadOnlyList<int>> members)
    {
        if (cost.CategoryId is { } categoryId)
        {
            return members.ContainsKey(categoryId) ? [categoryId] : [];
        }

        return cost.MeterId is { } meterId
            ? [.. _categories.Where(c => members[c.Id].Contains(meterId)).Select(c => c.Id)]
            : [];
    }

    /// <summary>
    /// D-42: a type's standing charge joins a category that holds the whole type — the type itself, or every physical
    /// meter of it; the global one a category that holds every billed meter.
    /// </summary>
    private bool HoldsRow(CostCategory category, StandingChargeKey row, IReadOnlyList<int> members)
    {
        var set = members.ToHashSet();
        if (row.Scope == TariffScope.Global)
        {
            return _full.BillItems.Count > 0 && _full.BillItems.All(set.Contains);
        }

        if (row.Scope == TariffScope.Meter)
        {
            // A meter's own fee goes with its meter (D-40, D-42).
            return set.Contains(row.ScopeId!.Value);
        }

        var type = row.ScopeId!.Value;
        if (category.Members.Any(m => m.EnergyTypeId == type))
        {
            return true;
        }

        var physical = _catalog.Meters.Values.Where(m => m.EnergyTypeId == type && !m.IsVirtual).Select(m => m.Id).ToList();
        return physical.Count > 0 && physical.All(set.Contains);
    }

    private static List<CostCategoryOverlap> Overlaps(
        CategoryOverlapReport report,
        Dictionary<int, List<int>> manualClaims,
        Dictionary<StandingChargeKey, List<int>> rowClaims)
    {
        var pairs = new SortedDictionary<(int, int), (SortedSet<int> Meters, SortedSet<int> Manual, List<StandingChargeKey> Rows)>();

        (SortedSet<int> Meters, SortedSet<int> Manual, List<StandingChargeKey> Rows) Pair(int a, int b)
        {
            var key = a < b ? (a, b) : (b, a);
            if (!pairs.TryGetValue(key, out var pair))
            {
                pairs[key] = pair = ([], [], []);
            }

            return pair;
        }

        foreach (var overlap in report.Overlaps)
        {
            Pair(overlap.CategoryId, overlap.OtherCategoryId).Meters.UnionWith(overlap.SharedMeterIds);
        }

        foreach (var (manualId, claimants) in manualClaims)
        {
            ForEachPair(claimants, (a, b) => Pair(a, b).Manual.Add(manualId));
        }

        foreach (var (row, claimants) in rowClaims)
        {
            ForEachPair(claimants, (a, b) => Pair(a, b).Rows.Add(row));
        }

        return [.. pairs.Select(p => new CostCategoryOverlap(p.Key.Item1, p.Key.Item2, [.. p.Value.Meters], [.. p.Value.Manual], p.Value.Rows))];

        static void ForEachPair(List<int> ids, Action<int, int> action)
        {
            for (var i = 0; i < ids.Count; i++)
            {
                for (var j = i + 1; j < ids.Count; j++)
                {
                    action(ids[i], ids[j]);
                }
            }
        }
    }

    // ------------------------------------------------------------------------------------------------ plan and quantities

    /// <summary>
    /// The buckets (D-05): the caller's plan, the size asked for, or auto from the coverage of the priced meters. A line
    /// without any tariff has no cost to chart, so its resolution (a tank's months-long dipstick intervals) does not
    /// coarsen the chart; only when nothing has a tariff do all lines decide.
    /// </summary>
    private async Task<BucketPlan> PlanAsync(ScopePlan scope, CancellationToken cancellationToken)
    {
        if (_request.Plan is { } given)
        {
            return given;
        }

        var lines = scope.AllGroups().SelectMany(g => g.Lines).ToList();
        var withPrice = lines.Where(HasAnyPrice).ToList();
        var priced = (withPrice.Count > 0 ? withPrice : lines).Select(l => l.MeterId).Distinct().Order().ToList();
        if (_request.Bucket != BucketSize.Auto || priced.Count == 0)
        {
            return BucketPlanner.Plan(_period, _request.Bucket, maxPoints: _request.MaxPoints);
        }

        var request = new AnalysisRequest(AnalysisScope.ForMeters(priced), _period)
        {
            MaxPoints = _request.MaxPoints,
            MaxSeries = int.MaxValue,
            QuantitiesOnly = true,
        };
        return await _reader.PlanAsync(_db, _catalog, request, cancellationToken).ConfigureAwait(false);
    }

    private bool HasAnyPrice(LineSpec line) => line.Kind switch
    {
        BillLineKind.FeedIn => _book.HasAny(TariffComponent.FeedIn, line.MeterId, line.EnergyTypeId),
        BillLineKind.OwnPrice => _book.HasAnyInScope(TariffComponent.UnitPrice, TariffScope.Meter, line.MeterId),
        _ => _book.HasAny(TariffComponent.UnitPrice, line.MeterId, line.EnergyTypeId),
    };

    /// <summary>
    /// Reads every meter the groups price (with the subsections they deduct, and the meters the availability is taken
    /// from) per local-month part (D-36): once for the buckets' parts, and — only when they differ — once for the
    /// period's own months, which the total is priced from.
    /// </summary>
    private async Task ReadQuantitiesAsync(ScopePlan scope, CancellationToken cancellationToken)
    {
        var lines = scope.AllGroups().SelectMany(g => g.Lines).ToList();
        List<int> ids =
        [
            .. lines.Select(l => l.MeterId)
                .Concat(lines.SelectMany(l => l.Deductions.Select(d => d.MeterId)))
                .Concat(lines.SelectMany(l => BasisCheckOf(l)?.UseMeterIds ?? []))
                .Concat(scope.AvailabilityMeters)
                .Where(id => _catalog.Find(id) is not null)
                .Distinct()
                .Order(),
        ];
        if (ids.Count == 0)
        {
            return;
        }

        var contributors = !scope.OwnSemantics;
        var display = await ReadPartsAsync(ids, _displayParts, _plan.Buckets, _plan.Size, contributors, cancellationToken).ConfigureAwait(false);
        _series = display;
        _displayValues = display.ToDictionary(p => p.Key, p => p.Value.Values);

        if (SameParts())
        {
            _periodValues = _displayValues;
        }
        else
        {
            var period = await ReadPartsAsync(ids, _periodParts, [_periodBucket], _periodBucket.Size, contributors, cancellationToken).ConfigureAwait(false);
            _periodValues = period.ToDictionary(p => p.Key, p => p.Value.Values);
        }

        // A-16: where a priced line's part is unresolved inside a bucket of several months, read the bucket whole too.
        List<int> spanned =
        [
            .. lines.Where(HasAnyPrice)
                .SelectMany(l => l.Deductions.Select(d => d.MeterId).Prepend(l.MeterId))
                .Where(id => _catalog.Find(id) is not null)
                .Distinct()
                .Order(),
        ];
        if (NeedsSpans(_displayParts, _displayValues, spanned))
        {
            _displaySpans = await ReadSpansAsync(spanned, _plan.Buckets, _plan.Size, contributors, cancellationToken).ConfigureAwait(false);
        }

        if (NeedsSpans(_periodParts, _periodValues, spanned))
        {
            _periodSpans = await ReadSpansAsync(spanned, [_periodBucket], _periodBucket.Size, contributors, cancellationToken).ConfigureAwait(false);
        }
    }

    /// <summary>True when a meter's part is unresolved inside a bucket that has several parts (A-16).</summary>
    private static bool NeedsSpans(IReadOnlyList<CostPart> parts, Dictionary<int, IReadOnlyList<BucketValue>> values, IReadOnlyList<int> ids)
    {
        var multi = parts.GroupBy(p => p.BucketIndex).Where(g => g.Count() > 1).Select(g => g.Key).ToHashSet();
        if (multi.Count == 0)
        {
            return false;
        }

        return ids.Any(id => values.GetValueOrDefault(id) is { } series
            && parts.Select((part, index) => (part, index)).Any(p => multi.Contains(p.part.BucketIndex) && series[p.index].Status == BucketStatus.Unresolved));
    }

    /// <summary>The meters' values over whole buckets, one per bucket (A-16).</summary>
    private async Task<Dictionary<int, IReadOnlyList<BucketValue>>> ReadSpansAsync(
        IReadOnlyList<int> ids, IReadOnlyList<AnalysisBucket> buckets, BucketSize size, bool contributors, CancellationToken cancellationToken)
    {
        List<CostPart> whole = [.. buckets.Select((b, i) => new CostPart(i, b.FirstDay, b.EndDay))];
        var read = await ReadPartsAsync(ids, whole, buckets, size, contributors, cancellationToken).ConfigureAwait(false);
        return read.ToDictionary(p => p.Key, p => p.Value.Values);
    }

    private async Task<Dictionary<int, AnalysisSeries>> ReadPartsAsync(
        IReadOnlyList<int> ids,
        IReadOnlyList<CostPart> parts,
        IReadOnlyList<AnalysisBucket> buckets,
        BucketSize size,
        bool contributors,
        CancellationToken cancellationToken)
    {
        List<AnalysisBucket> partBuckets = [.. parts.Select(p => PartBucket(p, buckets[p.BucketIndex]))];
        var request = new AnalysisRequest(AnalysisScope.ForMeters(ids), _period)
        {
            Plan = new BucketPlan(size, size, partBuckets, partBuckets.Count, Refused: false, Suggested: null),
            MaxSeries = int.MaxValue,
            AsContributors = contributors,
            QuantitiesOnly = true,
        };

        var result = await _reader.ReadAsync(_db, _catalog, request, cancellationToken).ConfigureAwait(false);
        foreach (var problem in result.Problems)
        {
            if (!_quantityProblems.Exists(p => p.Kind == problem.Kind && p.MeterId == problem.MeterId && p.Virtual?.Kind == problem.Virtual?.Kind))
            {
                _quantityProblems.Add(problem);
            }
        }

        return result.Series.Where(s => s.MeterId is not null).ToDictionary(s => s.MeterId!.Value);
    }

    /// <summary>
    /// A part as a bucket the reader sums: its local days, clipped to its bucket's instants (the last part of a to-date
    /// bucket ends at now), with its bucket's size, so it resolves exactly as its bucket would (D-14).
    /// </summary>
    private AnalysisBucket PartBucket(CostPart part, AnalysisBucket bucket)
    {
        var start = GapAttribution.LocalMidnight(part.FirstDay, _zone);
        var end = GapAttribution.LocalMidnight(part.EndDay, _zone);
        var from = start > bucket.From ? start : bucket.From;
        var to = end < bucket.To ? end : bucket.To;
        return new AnalysisBucket(part.FirstDay, part.EndDay, from, to < from ? from : to, bucket.Size);
    }

    /// <summary>
    /// True when the buckets' parts are the period's months, evaluated alike: the same days, and sizes that resolve
    /// them the same way (a month and a year both resolve by month).
    /// </summary>
    private bool SameParts()
    {
        if (_displayParts.Count != _periodParts.Count)
        {
            return false;
        }

        static bool Monthly(BucketSize size) => size is BucketSize.Month or BucketSize.Year;
        var sizesAgree = _plan.Size == _periodBucket.Size || (Monthly(_plan.Size) && Monthly(_periodBucket.Size));
        return sizesAgree && _displayParts.Zip(_periodParts).All(p => p.First.FirstDay == p.Second.FirstDay && p.First.EndDay == p.Second.EndDay);
    }

    /// <summary>
    /// The first data day of every physical meter, for standing-charge service periods (D-40) — read only when there is
    /// a base price to accrue.
    /// </summary>
    private async Task LoadServiceAsync(CancellationToken cancellationToken)
    {
        if (!_book.Tariffs.Any(t => t.Component == TariffComponent.BasePrice))
        {
            return;
        }

        var ids = _catalog.Meters.Values.Where(m => !m.IsVirtual).Select(m => m.Id).ToList();
        if (ids.Count == 0)
        {
            return;
        }

        await _db.Database.OpenConnectionAsync(cancellationToken).ConfigureAwait(false);
        var runs = await AnalysisQueries.CoverageAsync(_db.Database.GetDbConnection(), ids, cancellationToken).ConfigureAwait(false);
        foreach (var id in ids)
        {
            _firstData[id] = AvailableRange.OfRuns(runs.GetValueOrDefault(id) ?? [], _period.Now, _zone)?.FirstDay;
        }
    }

    private ServicePeriod? MeterService(int meterId)
    {
        if (_catalog.Find(meterId) is not { } meter)
        {
            return null;
        }

        return meter.IsVirtual
            ? ServicePeriod.Span(SourcesOf(meterId).Distinct().Select(MeterService))
            : ServicePeriod.ForMeter(meter.Meter.InstalledAt, meter.Meter.RetiredAt, _firstData.GetValueOrDefault(meterId));
    }

    private ServicePeriod? RowService(StandingChargeKey row) =>
        row.Scope == TariffScope.Meter
            ? MeterService(row.ScopeId!.Value)
            : ServicePeriod.Span(_catalog.Meters.Values
                .Where(m => !m.IsVirtual && (row.Scope == TariffScope.Global || m.EnergyTypeId == row.ScopeId))
                .Select(m => MeterService(m.Id)));

    // ------------------------------------------------------------------------------------------------ pricing

    /// <summary>Prices a group per bucket and over the period's own months.</summary>
    private void Price(PricingGroup group)
    {
        var rows = group.Rows
            .Select(r => new StandingChargeScope(r.Scope, r.ScopeId, RowService(r)))
            .ToList();
        var bucketLines = group.Lines.Select(l => Line(l, _displayParts, _displayValues, _plan.Buckets, _displaySpans, group.BasisGaps)).ToList();
        var totalLines = group.Lines.Select(l => Line(l, _periodParts, _periodValues, [_periodBucket], _periodSpans, group.BasisGaps)).ToList();

        group.ByBucket = CostCalculator.Calculate(new CostRequest(_plan.Buckets, _today, _book, bucketLines, rows, group.Manual));
        group.OverPeriod = CostCalculator.Calculate(new CostRequest([_periodBucket], _today, _book, totalLines, rows, group.Manual));
        foreach (var line in group.ByBucket.Lines.Concat(group.OverPeriod.Lines).Where(l => l.MonthsWithPriceChangeInsideInterval.Count > 0))
        {
            Months(group.PriceChanges, line.MeterId).UnionWith(line.MonthsWithPriceChangeInsideInterval);
        }

        for (var i = 0; i < group.Lines.Count; i++)
        {
            var spec = group.Lines[i];
            var buckets = group.ByBucket.Lines[i];
            var total = group.OverPeriod.Lines[i];
            var perBucket = new double?[_plan.Buckets.Count];
            for (var p = 0; p < _displayParts.Count; p++)
            {
                if (bucketLines[i].Quantities[p] is { IsKnown: true, Amount: { } amount })
                {
                    var index = _displayParts[p].BucketIndex;
                    perBucket[index] = (perBucket[index] ?? 0) + amount;
                }
            }

            var known = totalLines[i].Quantities.Where(q => q.IsKnown).Select(q => q.Amount!.Value).ToList();
            group.Figures.Add(new CostLineFigure(
                spec.MeterId,
                _catalog.Meters[spec.MeterId].Name,
                spec.EnergyTypeId,
                spec.Kind,
                spec.Unit,
                buckets.Buckets,
                total.Total,
                perBucket,
                known.Count > 0 ? known.Sum() : null)
            {
                Deductions = spec.Deductions,
                MonthsWithoutOwnPrice = total.MonthsWithoutOwnPrice,
                ForMeterId = spec.ForMeterId,
            });
        }

        foreach (var (buckets, total) in group.ByBucket.StandingCharges.Zip(group.OverPeriod.StandingCharges))
        {
            group.RowFigures.Add(new StandingChargeFigure(
                buckets.Scope, buckets.ScopeId, buckets.Buckets, total.Total, RowService(new StandingChargeKey(buckets.Scope, buckets.ScopeId))));
        }
    }

    /// <summary>
    /// A line's net quantity per part (D-35): its meter's value less the subsections billed on their own that month. A
    /// month the type's billing basis has no meter in service for is unknown, not the grid meter's zero (A-17). Buckets
    /// read whole (A-16) give the line its spans.
    /// </summary>
    private CostLine Line(
        LineSpec spec,
        IReadOnlyList<CostPart> parts,
        Dictionary<int, IReadOnlyList<BucketValue>> values,
        IReadOnlyList<AnalysisBucket> buckets,
        Dictionary<int, IReadOnlyList<BucketValue>> spanValues,
        Dictionary<int, SortedSet<DateOnly>> basisGaps)
    {
        var own = values.GetValueOrDefault(spec.MeterId);
        var basis = BasisCheckOf(spec);
        var quantities = new List<CostQuantity>(parts.Count);
        var gapBuckets = new HashSet<int>();
        for (var p = 0; p < parts.Count; p++)
        {
            var part = parts[p];
            if (basis is not null && IsBasisGap(basis, part, p, values))
            {
                quantities.Add(CostQuantity.Unknown(part, BucketStatus.Missing));
                Months(basisGaps, spec.MeterId).Add(part.Month);
                gapBuckets.Add(part.BucketIndex);
                continue;
            }

            var value = own?[p] ?? BucketValue.Missing();
            List<(BucketValue Value, double Factor)> deducted = [];
            foreach (var deduction in spec.Deductions)
            {
                if (_book.HasOwnUnitPrice(deduction.MeterId, part.Month))
                {
                    deducted.Add((values.GetValueOrDefault(deduction.MeterId)?[p] ?? BucketValue.Missing(), deduction.UnitFactor));
                }
            }

            quantities.Add(Net(part, value, deducted));
        }

        var service = _book.HasAnyInScope(TariffComponent.BasePrice, TariffScope.Meter, spec.MeterId) ? MeterService(spec.MeterId) : null;
        return new CostLine(spec.MeterId, spec.EnergyTypeId, spec.Kind, spec.Unit, quantities, service)
        {
            Spans = Spans(spec, parts, buckets, spanValues, gapBuckets),
        };
    }

    /// <summary>
    /// A line's quantity over each bucket of several parts that was read whole (A-16), net of the subsections billed on
    /// their own — only where the same subsections are taken out in every month of the bucket — and never over a bucket
    /// holding a basis gap.
    /// </summary>
    private List<CostSpan>? Spans(
        LineSpec spec,
        IReadOnlyList<CostPart> parts,
        IReadOnlyList<AnalysisBucket> buckets,
        Dictionary<int, IReadOnlyList<BucketValue>> spanValues,
        HashSet<int> gapBuckets)
    {
        if (spanValues.GetValueOrDefault(spec.MeterId) is not { } own)
        {
            return null;
        }

        var spans = new List<CostSpan>();
        foreach (var bucket in parts.GroupBy(p => p.BucketIndex).Where(g => g.Count() > 1))
        {
            var index = bucket.Key;
            if (gapBuckets.Contains(index) || index >= own.Count)
            {
                continue;
            }

            var applied = bucket
                .Select(part => spec.Deductions.Where(d => _book.HasOwnUnitPrice(d.MeterId, part.Month)).Select(d => d.MeterId).ToHashSet())
                .ToList();
            if (!applied.TrueForAll(set => set.SetEquals(applied[0])))
            {
                continue;
            }

            var deducted = spec.Deductions
                .Where(d => applied[0].Contains(d.MeterId))
                .Select(d => (spanValues.GetValueOrDefault(d.MeterId)?[index] ?? BucketValue.Missing(), d.UnitFactor))
                .ToList();
            var whole = new CostPart(index, buckets[index].FirstDay, buckets[index].EndDay);
            var net = Net(whole, own[index], deducted);
            spans.Add(new CostSpan(index, net.Amount, net.Availability));
        }

        return spans.Count > 0 ? spans : null;
    }

    /// <summary>
    /// A-17: for a grid-import line of a type billed on its grid import, the grid meters whose service decides the basis,
    /// and the use meters whose data shows a month the basis misses. Null for any other line, and when no billed grid
    /// meter has an install or retire date (then it covers every month).
    /// </summary>
    private BasisCheck? BasisCheckOf(LineSpec spec)
    {
        if (spec.Kind != BillLineKind.UnitPrice || spec.ForMeterId is not null)
        {
            return null;
        }

        var totals = _full.ForType(spec.EnergyTypeId);
        var billing = totals.Billing;
        if (billing.Basis != BillingBasis.GridImport || !billing.BilledMeterIds.Contains(spec.MeterId))
        {
            return null;
        }

        var grids = billing.BilledMeterIds.Select(id => _catalog.Meters[id].Meter).ToList();
        var use = totals.MetersIn(TotalsMeasure.Use).Where(id => _catalog.Find(id) is { IsVirtual: false }).ToList();
        if (use.Count == 0 || grids.TrueForAll(m => m.InstalledAt is null && m.RetiredAt is null))
        {
            return null;
        }

        return new BasisCheck([.. grids.Select(m => (m.InstalledAt ?? DateOnly.MinValue, m.RetiredAt ?? DateOnly.MaxValue))], use);
    }

    /// <summary>
    /// True when some day of <paramref name="part"/> has no billed grid meter in service while a use meter in service
    /// that month measured something (A-17): the grid meter's known zero would pass the use off as free.
    /// </summary>
    private bool IsBasisGap(BasisCheck basis, CostPart part, int index, Dictionary<int, IReadOnlyList<BucketValue>> values)
    {
        var covered = true;
        for (var day = part.FirstDay; day < part.EndDay && covered; day = day.AddDays(1))
        {
            covered = basis.GridService.Exists(w => w.First <= day && day <= w.Last);
        }

        if (covered)
        {
            return false;
        }

        return basis.UseMeterIds.Any(id =>
        {
            var meter = _catalog.Meters[id].Meter;
            var inService = (meter.InstalledAt ?? DateOnly.MinValue) < part.EndDay && (meter.RetiredAt ?? DateOnly.MaxValue) >= part.FirstDay;
            var value = values.GetValueOrDefault(id)?[index];
            return inService && value is not null && value.Status != BucketStatus.Missing
                && !(value.Status == BucketStatus.Available && value.Value is { } amount && Math.Abs(amount) <= ProvenanceRules.Epsilon);
        });
    }

    private static SortedSet<DateOnly> Months(Dictionary<int, SortedSet<DateOnly>> map, int meterId)
    {
        if (!map.TryGetValue(meterId, out var months))
        {
            map[meterId] = months = [];
        }

        return months;
    }

    /// <summary>
    /// A meter's value less deducted values: unknown as soon as any of them is (the strictest status wins, as for a
    /// virtual difference, D-27), partial when any is partial.
    /// </summary>
    internal static CostQuantity Net(CostPart part, BucketValue value, IReadOnlyList<(BucketValue Value, double Factor)> deducted)
    {
        if (deducted.Count == 0)
        {
            return value.Value is { } plain && value.Status is BucketStatus.Available or BucketStatus.Partial
                ? CostQuantity.Known(part, plain, value.Status)
                : CostQuantity.Unknown(part, UnknownStatus(value.Status));
        }

        var all = deducted.Select(d => d.Value).Prepend(value).ToList();
        foreach (var status in (ReadOnlySpan<BucketStatus>)[BucketStatus.Pending, BucketStatus.Invalid, BucketStatus.Unresolved])
        {
            if (all.Exists(v => v.Status == status))
            {
                return CostQuantity.Unknown(part, status);
            }
        }

        if (all.Exists(v => v.Value is null || v.Status is not (BucketStatus.Available or BucketStatus.Partial)))
        {
            return CostQuantity.Unknown(part, BucketStatus.Missing);
        }

        var net = value.Value!.Value - deducted.Sum(d => d.Value.Value!.Value * d.Factor);
        return CostQuantity.Known(part, net, all.Exists(v => v.Status == BucketStatus.Partial) ? BucketStatus.Partial : BucketStatus.Available);
    }

    private static BucketStatus UnknownStatus(BucketStatus status) =>
        status is BucketStatus.Available or BucketStatus.Partial ? BucketStatus.Missing : status;

    // ------------------------------------------------------------------------------------------------ result

    private CostAnalysis Compose(ScopePlan scope)
    {
        var groups = scope.Groups().ToList();
        var buckets = Enumerable.Range(0, _plan.Buckets.Count)
            .Select(b => CostAmount.Sum(groups.Select(g => g.ByBucket.Totals[b])))
            .ToList();
        var total = CostAmount.Sum(groups.Select(g => g.OverPeriod.Total));

        var manual = new ManualCostFigure(
            [.. groups.SelectMany(g => g.ByBucket.ManualCosts.Bookings).OrderBy(b => b.Day).ThenBy(b => b.ManualCostId)],
            AfterToday(groups),
            [.. Enumerable.Range(0, _plan.Buckets.Count).Select(b => CostAmount.Sum(groups.Select(g => g.ByBucket.ManualCosts.Buckets[b])))],
            CostAmount.Sum(groups.Select(g => g.OverPeriod.ManualCosts.Total)));

        var warnings = Warnings(groups);
        var result = new CostAnalysis(
            _request,
            _plan,
            _book.Currency,
            buckets,
            total,
            [.. groups.SelectMany(g => g.Figures)],
            [.. groups.SelectMany(g => g.RowFigures)],
            manual,
            Availability(MeteredAvailability(scope), scope.ManualInScope),
            Attention(scope, total, manual, warnings))
        {
            Warnings = warnings,
            QuantityProblems = _quantityProblems,
            EnergyTypes = [.. scope.Types.Select(t => new EnergyTypeCostFigure(
                t.EnergyTypeId, t.Group.Basis, t.Group.ByBucket.Totals, t.Group.OverPeriod.Total, [.. t.Group.Lines.Select(l => l.MeterId).Distinct()]))],
            Meter = scope.Meter,
        };

        if (scope.Categories is { } categories)
        {
            if (scope.CategoryEntry is { } entry)
            {
                result = result with { Category = Figure(entry, categories) };
            }
            else
            {
                result = result with { Composition = Composition(categories) };
            }
        }

        return result;
    }

    private CategoryComposition Composition(CategoryPlan plan)
    {
        var slices = new List<CompositionSlice>();
        foreach (var id in plan.Disjoint)
        {
            var entry = plan.Entries[id];
            slices.Add(new CompositionSlice(CompositionSliceKind.Category, id, null, entry.Group.ByBucket.Totals, entry.Group.OverPeriod.Total)
            {
                MeterIds = entry.Cover.CoverMeterIds,
                ManualCostIds = [.. entry.Group.Manual.Select(c => c.Id)],
            });
        }

        slices.Add(new CompositionSlice(CompositionSliceKind.Uncategorized, null, null, plan.Uncategorized.ByBucket.Totals, plan.Uncategorized.OverPeriod.Total)
        {
            MeterIds = plan.UncategorizedMeterIds,
            ManualCostIds = [.. plan.Uncategorized.Manual.Select(c => c.Id)],
        });

        foreach (var (row, group) in plan.RowSlices)
        {
            slices.Add(new CompositionSlice(CompositionSliceKind.StandingCharge, null, row, group.ByBucket.Totals, group.OverPeriod.Total));
        }

        return new CategoryComposition(
            slices,
            [.. _categories.Select(c => Figure(plan.Entries[c.Id], plan))],
            plan.Overlaps,
            [.. Enumerable.Range(0, _plan.Buckets.Count).Select(b => CostAmount.Sum(slices.Select(s => s.Buckets[b])))],
            CostAmount.Sum(slices.Select(s => s.Total)));
    }

    private static CategoryCostFigure Figure(CategoryEntry entry, CategoryPlan plan)
    {
        var id = entry.Category.Id;
        return new CategoryCostFigure(
            id,
            entry.Category.Name,
            entry.Category.ColorHex,
            entry.Category.Sort,
            entry.Cover,
            entry.Group.ByBucket.Totals,
            entry.Group.OverPeriod.Total)
        {
            IsOverlappingView = entry.IsView,
            OverlapsWith = [.. plan.Overlaps
                .Where(o => o.CategoryId == id || o.OtherCategoryId == id)
                .Select(o => o.CategoryId == id ? o.OtherCategoryId : o.CategoryId)
                .Distinct()
                .Order()],
            ManualCostIds = [.. entry.Group.Manual.Select(c => c.Id)],
            StandingCharges = entry.Group.Rows,
        };
    }

    /// <summary>
    /// The manual costs of the figure that start after today but inside the range the period names (D-41, compare
    /// D-04): the buckets stop at now, so they are in none, and are reported rather than silently left out.
    /// </summary>
    private List<int> AfterToday(IEnumerable<PricingGroup> groups)
    {
        var last = _period.Preset == PeriodPreset.AllHistory ? DateOnly.MaxValue : _period.NominalLastDay();
        return
        [
            .. groups.SelectMany(g => g.Manual)
                .Where(c => c.PeriodStart > _today && c.PeriodStart >= _period.FirstDay && c.PeriodStart <= last)
                .Select(c => c.Id)
                .Concat(groups.SelectMany(g => g.OverPeriod.ManualCosts.AfterTodayIds))
                .Distinct()
                .Order(),
        ];
    }

    /// <summary>The coverage of the scope's priced meters, from the series the quantities were read with.</summary>
    private AvailableRange? MeteredAvailability(ScopePlan scope) =>
        AvailableRange.Union(scope.AvailabilityMeters.Select(id => _series.GetValueOrDefault(id)?.Availability), _zone);

    /// <summary>D-19: the priced meters' coverage and the manual costs' start days up to today, and the latest month of either.</summary>
    private CostAvailability Availability(AvailableRange? metered, IReadOnlyList<ManualCost> manual)
    {
        var days = manual.Where(c => c.PeriodStart <= _today).Select(c => c.PeriodStart).ToList();
        AvailableRange? manualRange = null;
        if (days.Count > 0)
        {
            var from = GapAttribution.LocalMidnight(days.Min(), _zone);
            var to = GapAttribution.LocalMidnight(days.Max().AddDays(1), _zone);
            manualRange = AvailableRange.Of(from, to < _period.Now ? to : _period.Now, _zone) ?? AvailableRange.Of(from, to, _zone);
        }

        var range = AvailableRange.Union([metered, manualRange], _zone);
        LatestPeriod? latest = null;
        if (range is not null)
        {
            var month = range.LatestMonth;
            var byMeters = metered?.LatestMonth == month;
            var byManual = manualRange?.LatestMonth == month;
            latest = new LatestPeriod(month, byMeters && byManual ? LatestPeriodBasis.Both : byManual ? LatestPeriodBasis.Manual : LatestPeriodBasis.Meters);
        }

        return new CostAvailability(metered, manualRange, range, latest);
    }

    /// <summary>Tariffs applied with an unchecked unit, each once with the first month it priced.</summary>
    private static List<TariffWarning> Warnings(IEnumerable<PricingGroup> groups) =>
        [.. groups
            .SelectMany(g => g.OverPeriod.Warnings)
            .GroupBy(w => (w.TariffId, w.Component, w.Issue, w.MeterId))
            .Select(g => g.MinBy(w => w.FirstMonth)!)
            .OrderBy(w => w.FirstMonth)
            .ThenBy(w => w.TariffId)
            .ThenBy(w => w.MeterId ?? int.MaxValue)];

    /// <summary>The cost attention items (D-53) of the result.</summary>
    private List<CostAttention> Attention(ScopePlan scope, CostAmount total, ManualCostFigure manual, IReadOnlyList<TariffWarning> warnings)
    {
        var items = new List<CostAttention>();
        items.AddRange(total.MissingPrices.Select(m => new CostAttention(CostAttentionKind.MissingPrice, m.MeterId) { Price = m }));
        items.AddRange(warnings.Select(w => new CostAttention(CostAttentionKind.UnverifiedTariffUnit, w.MeterId) { Warning = w }));

        if (manual.AfterTodayIds.Count > 0)
        {
            items.Add(new CostAttention(CostAttentionKind.ManualCostAfterToday, null) { ManualCostIds = manual.AfterTodayIds });
        }

        var foreign = manual.Bookings.Where(b => b.CurrencyMismatch).Select(b => b.ManualCostId).Distinct().Order().ToList();
        if (foreign.Count > 0)
        {
            items.Add(new CostAttention(CostAttentionKind.ManualCostCurrency, null) { ManualCostIds = foreign });
        }

        items.AddRange(_notCosted.Order().Select(id => new CostAttention(CostAttentionKind.VirtualNotCosted, id)));

        var groups = scope.Groups().ToList();
        foreach (var (kind, map) in new[]
                 {
                     (CostAttentionKind.PriceChangeInsideInterval, Merge(groups.Select(g => g.PriceChanges))),
                     (CostAttentionKind.BillingBasisGap, Merge(groups.Select(g => g.BasisGaps))),
                 })
        {
            items.AddRange(map.OrderBy(m => m.Key).Select(m => new CostAttention(kind, m.Key) { FirstMonth = m.Value.Min, LastMonth = m.Value.Max }));
        }

        items.AddRange(_full.Problems
            .Where(p => p.Kind is TotalsProblemKind.UnusedMeterPrice or TotalsProblemKind.SeparateBillingUnitMismatch && InScope(scope, p.MeterId))
            .Select(p => new CostAttention(CostAttentionKind.BillingConfiguration, p.MeterId) { Totals = p }));

        // A category whose members give it no line — calculated views, generation, operating hours (D-39, D-42) — reads
        // empty; say why rather than let it pass for a category without data (A-22).
        IEnumerable<CategoryEntry> entries = scope.CategoryEntry is { } own
            ? [own]
            : scope.Categories?.Entries.Values.OrderBy(e => e.Category.Sort).ThenBy(e => e.Category.Id) ?? Enumerable.Empty<CategoryEntry>();
        foreach (var entry in entries)
        {
            if (entry.Cover.CoverMeterIds.Count == 0 && entry.Cover.AnalysisOnlyMeterIds.Count > 0)
            {
                items.Add(new CostAttention(CostAttentionKind.CategoryPricesNothing, entry.Cover.AnalysisOnlyMeterIds[0])
                {
                    CategoryId = entry.Category.Id,
                    MeterIds = entry.Cover.AnalysisOnlyMeterIds,
                });
            }
        }

        return items;
    }

    private static Dictionary<int, SortedSet<DateOnly>> Merge(IEnumerable<Dictionary<int, SortedSet<DateOnly>>> maps)
    {
        var merged = new Dictionary<int, SortedSet<DateOnly>>();
        foreach (var (meter, months) in maps.SelectMany(m => m))
        {
            Months(merged, meter).UnionWith(months);
        }

        return merged;
    }

    /// <summary>Whether a meter's billing problem belongs to the scope: its meter, its category's members, its type, or anything.</summary>
    private bool InScope(ScopePlan scope, int meterId)
    {
        if (scope.Meter is { } meter)
        {
            return meterId == meter.MeterId;
        }

        if (scope.CategoryEntry is { } entry)
        {
            return entry.Cover.MemberIds.Contains(meterId);
        }

        return scope.Portfolio is not null || scope.Types.Exists(t => t.EnergyTypeId == _catalog.Find(meterId)?.EnergyTypeId);
    }

    private CostAnalysis Refused(BucketPlan plan, CostRefusal refusal) =>
        new(
            _request,
            plan,
            _currency,
            [],
            CostAmount.Empty,
            [],
            [],
            new ManualCostFigure([], [], [], CostAmount.Empty),
            CostAvailability.None,
            [])
        {
            Refusal = refusal,
        };

    private BucketPlan EmptyPlan()
    {
        var size = _request.Bucket == BucketSize.Auto ? BucketSize.Day : _request.Bucket;
        return new BucketPlan(_request.Bucket, size, [], 0, Refused: false, Suggested: null);
    }

    // ------------------------------------------------------------------------------------------------ plans

    /// <summary>One priced line: whose quantity, in which unit, how, less what.</summary>
    private sealed record LineSpec(
        int MeterId,
        int EnergyTypeId,
        BillLineKind Kind,
        string Unit,
        IReadOnlyList<BillDeduction> Deductions,
        int? ForMeterId);

    /// <summary>What a physical meter's own scope prices, and how its cost is named.</summary>
    private sealed record OwnCost(List<LineSpec> Lines, MeterCostRule Rule, bool OnBill, MeterNotCostedReason Reason);

    /// <summary>The service windows of a type's billed grid meters (inclusive local days) and its use meters (A-17).</summary>
    private sealed record BasisCheck(List<(DateOnly First, DateOnly Last)> GridService, IReadOnlyList<int> UseMeterIds);

    /// <summary>Lines, standing-charge rows and manual costs priced together, and their priced figures.</summary>
    private sealed class PricingGroup
    {
        public int? EnergyTypeId { get; init; }

        public BillingBasis Basis { get; init; }

        public List<LineSpec> Lines { get; } = [];

        public List<StandingChargeKey> Rows { get; } = [];

        public List<ManualCost> Manual { get; } = [];

        public CostResult ByBucket { get; set; } = null!;

        public CostResult OverPeriod { get; set; } = null!;

        public List<CostLineFigure> Figures { get; } = [];

        public List<StandingChargeFigure> RowFigures { get; } = [];

        /// <summary>Per line meter: the months whose interval could not be priced because the price changes inside it (A-16).</summary>
        public Dictionary<int, SortedSet<DateOnly>> PriceChanges { get; } = [];

        /// <summary>Per grid meter: the months its type's grid basis missed while use was measured (A-17).</summary>
        public Dictionary<int, SortedSet<DateOnly>> BasisGaps { get; } = [];
    }

    private sealed record CategoryEntry(CostCategory Category, CategoryCoverResult Cover, PricingGroup Group, bool IsView);

    /// <summary>Every category's figure and the bill's composition by them.</summary>
    private sealed class CategoryPlan
    {
        public Dictionary<int, CategoryEntry> Entries { get; } = [];

        public IReadOnlyList<int> Disjoint { get; set; } = [];

        public PricingGroup Uncategorized { get; } = new();

        public IReadOnlyList<int> UncategorizedMeterIds { get; set; } = [];

        public List<(StandingChargeKey Row, PricingGroup Group)> RowSlices { get; } = [];

        public IReadOnlyList<CostCategoryOverlap> Overlaps { get; set; } = [];

        /// <summary>The groups the composition prices (every category, Uncategorized, the rows of their own).</summary>
        public IEnumerable<PricingGroup> Groups() =>
            Entries.Values.Select(e => e.Group).Append(Uncategorized).Concat(RowSlices.Select(r => r.Group));
    }

    /// <summary>A scope as pricing groups: the groups its figure adds up, and whatever else it prices alongside.</summary>
    private sealed class ScopePlan
    {
        public List<(int EnergyTypeId, PricingGroup Group)> Types { get; } = [];

        public PricingGroup? Portfolio { get; set; }

        public PricingGroup? Single { get; init; }

        public MeterCostInfo? Meter { get; init; }

        public CategoryEntry? CategoryEntry { get; init; }

        public CategoryPlan? Categories { get; set; }

        public IReadOnlyList<int> AvailabilityMeters { get; init; } = [];

        public IReadOnlyList<ManualCost> ManualInScope { get; init; } = [];

        /// <summary>A physical meter's own page: outside its service period it has no data, as its quantity says.</summary>
        public bool OwnSemantics { get; init; }

        /// <summary>The groups whose sum is the scope's figure.</summary>
        public IEnumerable<PricingGroup> Groups()
        {
            if (Single is not null)
            {
                yield return Single;
                yield break;
            }

            foreach (var (_, group) in Types)
            {
                yield return group;
            }

            if (Portfolio is not null)
            {
                yield return Portfolio;
            }
        }

        /// <summary>Everything the request prices: the scope's groups, and for the portfolio the composition's.</summary>
        public IEnumerable<PricingGroup> AllGroups() =>
            Single is null && Categories is not null ? Groups().Concat(Categories.Groups()) : Groups();

    }
}