using OpenTK.Graphics.OpenGL4;
using OpenTK.Mathematics;

public class GuiBatcher
{
    private List<UiVertex> _vertices = new List<UiVertex>();
    private int _vbo;
    private int _vao;

    public GuiBatcher()
    {
        _vao = GL.GenVertexArray();
        _vbo = GL.GenBuffer();

        GL.BindVertexArray(_vao);
        GL.BindBuffer(BufferTarget.ArrayBuffer, _vbo);

        // Position (2 floats)
        GL.EnableVertexAttribArray(0);
        GL.VertexAttribPointer(0, 2, VertexAttribPointerType.Float, false, 8 * sizeof(float), 0);
        // TexCoord (2 floats)
        GL.EnableVertexAttribArray(1);
        GL.VertexAttribPointer(1, 2, VertexAttribPointerType.Float, false, 8 * sizeof(float), 2 * sizeof(float));
        // Color (4 floats)
        GL.EnableVertexAttribArray(2);
        GL.VertexAttribPointer(2, 4, VertexAttribPointerType.Float, false, 8 * sizeof(float), 4 * sizeof(float));
    }

    public void DrawQuad(float x, float y, float w, float h, Vector4 uv, Vector4 color)
    {
        // Two triangles (Standard Minecraft Blit)
        _vertices.Add(new UiVertex(x, y, uv.X, uv.Y, color));         // TL
        _vertices.Add(new UiVertex(x + w, y, uv.Z, uv.Y, color));     // TR
        _vertices.Add(new UiVertex(x, y + h, uv.X, uv.W, color));     // BL

        _vertices.Add(new UiVertex(x + w, y, uv.Z, uv.Y, color));     // TR
        _vertices.Add(new UiVertex(x + w, y + h, uv.Z, uv.W, color)); // BR
        _vertices.Add(new UiVertex(x, y + h, uv.X, uv.W, color));     // BL
    }

    public void Render()
    {
        if (_vertices.Count == 0) return;

        GL.BindVertexArray(_vao);
        GL.BindBuffer(BufferTarget.ArrayBuffer, _vbo);

        var data = _vertices.ToArray();
        GL.BufferData(BufferTarget.ArrayBuffer, data.Length * 8 * sizeof(float), data, BufferUsageHint.StreamDraw);

        GL.DrawArrays(PrimitiveType.Triangles, 0, _vertices.Count);
        _vertices.Clear(); // Reset for next frame
    }

    public void DrawString(string text, float x, float y, float size, Vector4 color)
    {
        float charStep = 1.0f / 16.0f;
        float currentX = x;

        foreach (char c in text)
        {
            int ascii = (int)c;
            int row = ascii / 16;
            int col = ascii % 16;

            float uStart = col * charStep;
            float uEnd = uStart + charStep;

            float vStart = 1.0f - (row * charStep);
            float vEnd = vStart - charStep;

            Vector4 uv = new Vector4(
                uStart,          // U start
                vStart,          // V start
                uEnd,    // U end
                vEnd     // V end
            );

            DrawQuad(currentX, y, size, size, uv, color);

            float charWidthPixels = (CharWidth.GetWidth(c) + 1) / 8;
            float charWidthWorldUnits = size * charWidthPixels;
            currentX += charWidthWorldUnits;
        }
    }
}