using System.Globalization;

namespace Godosa.Core.Runs;

/// <summary>Shared run flags: <c>--deterministic [seed]</c> (fixed step, seeded streams), <c>--digest [every=N]</c>
/// (state hash lines), <c>--headless</c> (no window; implies deterministic). <see cref="Seed"/> null = the game's default.</summary>
public sealed record RunFlags(bool Deterministic = false, ulong? Seed = null, bool Digest = false, int DigestEvery = 0, bool Headless = false)
{
    public ulong SeedOr(ulong fallback) => Seed ?? fallback;

    /// <summary>Consumes the run flag at <paramref name="i"/> (and its optional value, advancing <paramref name="i"/>);
    /// false when <c>args[i]</c> is no run flag.</summary>
    public static bool TryTake(IReadOnlyList<string> args, ref int i, ref RunFlags flags)
    {
        string? next = i + 1 < args.Count ? args[i + 1] : null;
        switch (args[i])
        {
            case "--deterministic":
                flags = flags with { Deterministic = true };
                if (next != null && ulong.TryParse(next, NumberStyles.None, CultureInfo.InvariantCulture, out var seed))
                    (flags, i) = (flags with { Seed = seed }, i + 1);
                return true;
            case "--digest":
                flags = flags with { Digest = true };
                if (next != null && next.StartsWith("every=", StringComparison.Ordinal))
                {
                    if (!int.TryParse(next.AsSpan(6), NumberStyles.None, CultureInfo.InvariantCulture, out var every) || every < 1)
                        throw new ArgumentException($"--digest {next}: every=N needs N ≥ 1");
                    (flags, i) = (flags with { DigestEvery = every }, i + 1);
                }
                return true;
            case "--headless":
                flags = flags with { Headless = true, Deterministic = true };
                return true;
            default:
                return false;
        }
    }
}