using Minint.Core.Models;

namespace Minint.Core.Services.Impl;

public sealed class PaletteService : IPaletteService
{
    public int FindColor(MinintDocument document, RgbaColor color)
    {
        var palette = document.Palette;
        for (int i = 0; i < palette.Count; i++)
        {
            if (palette[i] == color)
                return i;
        }
        return -1;
    }

    public int EnsureColor(MinintDocument document, RgbaColor color)
    {
        int idx = FindColor(document, color);
        if (idx >= 0)
            return idx;

        idx = document.Palette.Count;
        document.Palette.Add(color);
        return idx;
    }

    public void CompactPalette(MinintDocument document)
    {
        var palette = document.Palette;
        if (palette.Count <= 1)
            return;

        // 1. Collect indices actually used across all layers
        var usedIndices = new HashSet<int> { 0 }; // always keep transparent
        foreach (var layer in document.Layers)
        {
            foreach (int idx in layer.Pixels)
                usedIndices.Add(idx);
        }

        // 2. Build new palette and old→new mapping
        var oldToNew = new int[palette.Count];
        var newPalette = new List<RgbaColor>(usedIndices.Count);

        // Index 0 (transparent) stays at 0
        newPalette.Add(palette[0]);
        oldToNew[0] = 0;

        for (int i = 1; i < palette.Count; i++)
        {
            if (usedIndices.Contains(i))
            {
                oldToNew[i] = newPalette.Count;
                newPalette.Add(palette[i]);
            }
            // unused indices don't get a mapping — they'll never be looked up
        }

        // 3. If nothing was removed, skip the remap
        if (newPalette.Count == palette.Count)
            return;

        // 4. Replace palette
        palette.Clear();
        palette.AddRange(newPalette);

        // 5. Remap all pixel arrays
        foreach (var layer in document.Layers)
        {
            var px = layer.Pixels;
            for (int i = 0; i < px.Length; i++)
                px[i] = oldToNew[px[i]];
        }
    }
}