using System.Globalization;

namespace MeterVault.Integration.Tests.Performance;

/// <summary>
/// The environment switches of the performance measurement (brief §9.10, D-56). Everything is opt-in: without
/// <c>METERVAULT_PERF=1</c> the performance facts are skipped, so the normal suite neither runs nor slows down.
/// </summary>
/// <remarks>
/// <list type="table">
/// <item><term>METERVAULT_PERF</term><description><c>1</c> runs the performance facts.</description></item>
/// <item><term>METERVAULT_PERF_LABEL</term><description>Names the result files (<c>results-&lt;label&gt;.md</c>); default <c>local</c>.</description></item>
/// <item><term>METERVAULT_PERF_OUT</term><description>Where results go; default <c>%TEMP%/mv_analysis/perf</c>.</description></item>
/// <item><term>METERVAULT_PERF_RUNS</term><description>Measured runs per scenario (default 10), after <c>METERVAULT_PERF_WARMUP</c> warm-ups (default 2).</description></item>
/// <item><term>METERVAULT_PERF_DB</term><description>A connection string to use instead of a fresh container. A database that already holds
/// the dataset is reused as it is (no load, no rebuild), so a re-run on a quiet machine only measures.</description></item>
/// <item><term>METERVAULT_PERF_LOAD_DB</term><description>For the loader fact: an app-migrated database (old or new schema) to load the raw
/// dataset into, for the page-level comparison.</description></item>
/// <item><term>METERVAULT_PERF_NOW</term><description>For the loader fact: the instant the dataset ends at (ISO 8601); default the current time.</description></item>
/// <item><term>METERVAULT_PERF_SCALE</term><description>Scales every meter group (default 1 = 1,000 meters); only for quick trial runs.</description></item>
/// <item><term>METERVAULT_PERF_NOTE</term><description>Free text copied into the report (e.g. "machine busy with other builds").</description></item>
/// </list>
/// </remarks>
internal sealed record PerfSettings(
    bool Enabled,
    string Label,
    string OutputDirectory,
    int Runs,
    int Warmup,
    string? Database,
    string? LoadDatabase,
    DateTimeOffset? Now,
    double Scale,
    string? Note)
{
    public const string EnabledVariable = "METERVAULT_PERF";

    public const string LoadDatabaseVariable = "METERVAULT_PERF_LOAD_DB";

    public static PerfSettings Current { get; } = Read();

    private static PerfSettings Read()
    {
        static string? Env(string name) => Environment.GetEnvironmentVariable(name) is { Length: > 0 } value ? value.Trim() : null;

        static int Int(string name, int fallback) =>
            int.TryParse(Env(name), NumberStyles.Integer, CultureInfo.InvariantCulture, out var value) && value >= 0 ? value : fallback;

        var scale = double.TryParse(Env("METERVAULT_PERF_SCALE"), NumberStyles.Float, CultureInfo.InvariantCulture, out var s) && s > 0 ? s : 1;
        DateTimeOffset? now = DateTimeOffset.TryParse(Env("METERVAULT_PERF_NOW"), CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal, out var n)
            ? n.ToUniversalTime()
            : null;

        return new PerfSettings(
            Enabled: Env(EnabledVariable) == "1",
            Label: Env("METERVAULT_PERF_LABEL") ?? "local",
            OutputDirectory: Env("METERVAULT_PERF_OUT") ?? Path.Combine(Path.GetTempPath(), "mv_analysis", "perf"),
            Runs: Math.Max(1, Int("METERVAULT_PERF_RUNS", 10)),
            Warmup: Int("METERVAULT_PERF_WARMUP", 2),
            Database: Env("METERVAULT_PERF_DB"),
            LoadDatabase: Env(LoadDatabaseVariable),
            Now: now,
            Scale: scale,
            Note: Env("METERVAULT_PERF_NOTE"));
    }
}

/// <summary>A fact that runs only with <c>METERVAULT_PERF=1</c>; otherwise it is reported as skipped.</summary>
[AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
public sealed class PerfFactAttribute : FactAttribute
{
    public PerfFactAttribute()
    {
        if (!PerfSettings.Current.Enabled)
        {
            Skip = $"Performance measurement; set {PerfSettings.EnabledVariable}=1 to run it.";
        }
    }
}

/// <summary>
/// A fact that runs only with <c>METERVAULT_PERF=1</c> and a target database in <c>METERVAULT_PERF_LOAD_DB</c>: it loads
/// the synthetic raw dataset into a database an app has migrated, for the page-level before/after comparison.
/// </summary>
[AttributeUsage(AttributeTargets.Method, AllowMultiple = false)]
public sealed class PerfLoadFactAttribute : FactAttribute
{
    public PerfLoadFactAttribute()
    {
        if (!PerfSettings.Current.Enabled || PerfSettings.Current.LoadDatabase is null)
        {
            Skip = $"Loads the synthetic dataset into an existing database; set {PerfSettings.EnabledVariable}=1 and {PerfSettings.LoadDatabaseVariable}.";
        }
    }
}