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 VideoFrame? _run;          // the wide scrollable run (dev preview only)
    private double _offsetPx;
    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 TICKS (creator ruling 2026-10-30: "the point is, it's a ticker… so,
    /// tick"). True for the product, and the dev simulation uses the same path — so what the
    /// creator previews is what ships.</summary>
    public bool Scroll { get; set; } = true;

    /// <summary>Marquee speed in pixels per second — the creator's dial (a read-speed choice, not a
    /// styling one).</summary>
    public double PixelsPerSecond { get; set; } = DefaultPixelsPerSecond;

    public const double DefaultPixelsPerSecond = 120;
    public const double MinPixelsPerSecond = 20;
    public const double MaxPixelsPerSecond = 200;   // creator cap: faster than this is unreadable

    /// <summary>Advances the scroll by <paramref name="seconds"/>. The strip is a marquee: one
    /// measured run, cropped to a moving window, so a tick is a row-wise byte copy rather than a
    /// re-rasterisation.</summary>
    public void Advance(double seconds, double? pixelsPerSecond = null)
    {
        if (!Scroll) return;
        _offsetPx += seconds * (pixelsPerSecond ?? PixelsPerSecond);
    }

    /// <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 (Scroll)
            {
                if (_run is null || fingerprint != _tilesFingerprint)
                {
                    _tilesFingerprint = fingerprint;
                    _run = ScoreboardRenderer.RenderRun(tiles, _style);
                }
                return _run is null ? null : ScoreboardRenderer.Crop(_run, (int)_offsetPx, ScoreboardRenderer.Width);
            }

            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;
        _run = null;
        _tilesFingerprint = null;
    }
}