using System.Globalization;

namespace MeterVault.Core.Tests.Analysis;

/// <summary>Frozen instants and zones for the period tests — nothing here reads the wall clock.</summary>
internal static class AnalysisClock
{
    public static readonly TimeZoneInfo Berlin = TimeZoneInfo.FindSystemTimeZoneById("Europe/Berlin");

    public static readonly TimeZoneInfo NewYork = TimeZoneInfo.FindSystemTimeZoneById("America/New_York");

    /// <summary>An unambiguous local wall-clock time in <paramref name="zone"/>, as an instant.</summary>
    public static DateTimeOffset At(TimeZoneInfo zone, int year, int month, int day, int hour = 0, int minute = 0)
    {
        var wall = new DateTime(year, month, day, hour, minute, 0, DateTimeKind.Unspecified);
        Assert.False(zone.IsInvalidTime(wall), $"{wall:s} does not exist in {zone.Id}");
        Assert.False(zone.IsAmbiguousTime(wall), $"{wall:s} is ambiguous in {zone.Id}; give the offset");
        return new DateTimeOffset(wall, zone.GetUtcOffset(wall));
    }

    /// <summary>A local wall-clock time with an explicit offset — for the hour an autumn fold repeats.</summary>
    public static DateTimeOffset At(int year, int month, int day, int hour, int minute, int offsetHours) =>
        new(year, month, day, hour, minute, 0, TimeSpan.FromHours(offsetHours));

    public static DateTimeOffset Utc(int year, int month, int day, int hour = 0, int minute = 0) =>
        new(year, month, day, hour, minute, 0, TimeSpan.Zero);

    public static DateOnly Day(int year, int month, int day) => new(year, month, day);

    public static DateOnly Iso(string date) => DateOnly.ParseExact(date, "yyyy-MM-dd", CultureInfo.InvariantCulture);

    public static DateTimeOffset IsoInstant(string instant) =>
        DateTimeOffset.ParseExact(instant, "yyyy-MM-dd'T'HH:mm'Z'", CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal);

    /// <summary>The wall clock an instant shows in <paramref name="zone"/>, for readable assertions.</summary>
    public static string Wall(DateTimeOffset instant, TimeZoneInfo zone) =>
        TimeZoneInfo.ConvertTime(instant, zone).ToString("yyyy-MM-dd HH:mm zzz", CultureInfo.InvariantCulture);
}