using System.Globalization;

namespace ytLive.Services;

/// <summary>
/// TASK 64: the key's settings for one layer, in the app's own terms. <see cref="Color"/> is the
/// screen as the creator's camera saw it (whatever the detector measured), not a canonical green.
/// </summary>
public sealed record ChromaKeyOptions(
    bool Enabled,
    string Color,
    double Similarity,
    double Softness,
    bool Spill,
    ChromaScreen Screen = ChromaScreen.Green)
{
    public static readonly ChromaKeyOptions Off = new(false, "#00B140", 0.12, 0.08, true);

    /// <summary>Creator-facing defaults when a detector suggestion is accepted: a little
    /// tolerance around the measured colour, a soft edge, and spill cleanup on.</summary>
    public static ChromaKeyOptions For(ChromaKeySuggestion suggestion)
        => new(true, suggestion.ColorHex ?? "#00B140", 0.12, 0.08, true, suggestion.Screen);

    /// <summary>Identifies this look, so decode sessions can be shared per look rather than
    /// duplicated per layer (two layers keyed identically reuse one decoder).</summary>
    public string Signature => Enabled
        ? FormattableString.Invariant(
            $"{Color.ToUpperInvariant()}|{Similarity:0.###}|{Softness:0.###}|{Spill}|{Screen}")
        : "off";
}

/// <summary>
/// TASK 64: builds the ffmpeg filter chain for a clip. Keying happens IN THE DECODE PIPE, not in
/// this process: the bundled ffmpeg keys with slices of its own CPU cost, emits straight-alpha
/// BGRA (verified against the shipped binary: keyed pixels come out with alpha 0), and — the
/// point — the pipe is upstream of BOTH consumers (the shared preview bitmap and the compositor's
/// frame), so the creator's preview and the stream cannot disagree.
/// <para>Order matters: scale first (cheaper, and the edge is computed at output size), then key,
/// then despill, then force BGRA so the alpha survives the pipe.</para>
/// </summary>
public static class VideoFilterChain
{
    /// <summary>The video half of a clip's `-vf`. Unkeyed clips keep the old single-scale chain.</summary>
    public static string BuildVideo(int width, int height, ChromaKeyOptions? key = null)
    {
        var scale = $"scale={width}:{height}";
        if (key is not { Enabled: true }) return scale;

        var parts = new List<string>(4)
        {
            scale,
            $"colorkey={NormalizeColor(key.Color)}:{Number(key.Similarity)}:{Number(key.Softness)}",
        };
        if (key.Spill)
            parts.Add($"despill=type={(key.Screen == ChromaScreen.Blue ? "blue" : "green")}");
        parts.Add("format=bgra");
        return string.Join(",", parts);
    }

    /// <summary>ffmpeg takes `0xRRGGBB`. Anything unparseable falls back to the app default
    /// rather than producing a filter string ffmpeg would reject at spawn time.</summary>
    private static string NormalizeColor(string? hex)
    {
        var value = (hex ?? string.Empty).Trim();
        if (value.StartsWith("0x", StringComparison.OrdinalIgnoreCase)) value = value[2..];
        if (value.StartsWith('#')) value = value[1..];
        if (value.Length != 6) return "0x00B140";
        foreach (var c in value)
            if (!Uri.IsHexDigit(c)) return "0x00B140";
        return "0x" + value.ToUpperInvariant();
    }

    private static string Number(double value)
        => Math.Clamp(value, 0, 1).ToString("0.###", CultureInfo.InvariantCulture);
}