using System.Collections.Generic;
using ytLive.Models;

namespace ytLive.Services.Compositor;

/// <summary>Turns the session's tallies into the strip frame, and keeps the raster until a displayed
/// value actually moves.
///
/// <para>The cache is the point: a strip re-rasterised every tick would be the most expensive layer
/// the compositor carries, for pixels that did not change. `ScoreboardRecorder.Changed` only fires
/// on a visible change, so the presenter rebuilds only then.</para></summary>
public sealed class ScoreboardPresenter
{
    private readonly ScoreboardRecorder _recorder;
    private VideoFrame? _frame;
    private string? _tilesFingerprint;
    private ScoreboardStyle _style;
    private ScoreboardTiles _tiles = ScoreboardTiles.None;

    public ScoreboardPresenter(ScoreboardRecorder recorder, ScoreboardStyle style)
    {
        _recorder = recorder;
        _style = style;
        _recorder.Changed += Invalidate;
    }

    /// <summary>The strip frame for the current tallies, or null when nothing is enabled/shown.</summary>
    public VideoFrame? Frame
    {
        get
        {
            var tiles = _tiles.Build(_recorder.State);
            var fingerprint = $"{_tiles.CacheKey}|{string.Join('|', tiles)}|{_style}";
            if (_frame != null && fingerprint == _tilesFingerprint) return _frame;

            _tilesFingerprint = fingerprint;
            _frame = ScoreboardRenderer.Render(tiles, _style);
            return _frame;
        }
    }

    public void SetTiles(ScoreboardTiles tiles)
    {
        _tiles = tiles;
        Invalidate();
    }

    public void SetStyle(ScoreboardStyle style)
    {
        _style = style;
        Invalidate();
    }

    /// <summary>Drops the cached raster so the next read rebuilds it.</summary>
    public void Invalidate()
    {
        _frame = null;
        _tilesFingerprint = null;
    }
}