import type { Asset } from "@core/asset";
import type { ScreenRect, WebGlRendererContext } from "./types";

export type ImageTextureRenderer = {
  syncAssets(assets: readonly Asset[]): void;
  render(asset: Asset, rect: ScreenRect, clipRect?: ScreenRect): boolean;
  dispose(): void;
};

type TextureState =
  | { status: "loading"; image: HTMLImageElement }
  | { status: "ready"; texture: WebGLTexture }
  | { status: "error" };

type TextureEntry = {
  source: string;
  current: TextureState;
  previousTexture?: WebGLTexture;
};

export function createImageTextureRenderer(context: WebGlRendererContext, invalidate: () => void): ImageTextureRenderer {
  const { gl } = context;
  const program = createProgram(gl);
  const positionLocation = gl.getAttribLocation(program, "a_position");
  const texCoordLocation = gl.getAttribLocation(program, "a_texCoord");
  const samplerLocation = gl.getUniformLocation(program, "u_image");
  const positionBuffer = gl.createBuffer();
  const texCoordBuffer = gl.createBuffer();
  const textures = new Map<string, TextureEntry>();
  let disposed = false;

  if (!positionBuffer || !texCoordBuffer || !samplerLocation) throw new Error("Failed to create image texture renderer");

  gl.bindBuffer(gl.ARRAY_BUFFER, texCoordBuffer);
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 1]), gl.STATIC_DRAW);

  return {
    syncAssets(assets) {
      const activeIds = new Set(assets.map((asset) => asset.id));
      for (const [assetId, entry] of textures) {
        if (!activeIds.has(assetId)) {
          disposeEntry(gl, entry);
          textures.delete(assetId);
        }
      }
    },
    render(asset, rect, clipRect) {
      const drawRect = clipRect ? intersectScreenRects(rect, clipRect) : rect;
      if (!drawRect || drawRect.w <= 0 || drawRect.h <= 0) return true;

      const entry = getTextureEntry(context, textures, asset, invalidate, () => disposed);
      const texture = renderableTexture(entry);
      if (!texture) return false;

      gl.enable(gl.SCISSOR_TEST);
      gl.scissor(drawRect.x, context.canvas.height - drawRect.y - drawRect.h, drawRect.w, drawRect.h);
      gl.enable(gl.BLEND);
      gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA);
      gl.useProgram(program);

      gl.activeTexture(gl.TEXTURE0);
      gl.bindTexture(gl.TEXTURE_2D, texture);
      gl.uniform1i(samplerLocation, 0);

      gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
      gl.bufferData(gl.ARRAY_BUFFER, rectVertices(context.canvas, rect), gl.DYNAMIC_DRAW);
      gl.enableVertexAttribArray(positionLocation);
      gl.vertexAttribPointer(positionLocation, 2, gl.FLOAT, false, 0, 0);

      gl.bindBuffer(gl.ARRAY_BUFFER, texCoordBuffer);
      gl.enableVertexAttribArray(texCoordLocation);
      gl.vertexAttribPointer(texCoordLocation, 2, gl.FLOAT, false, 0, 0);

      gl.drawArrays(gl.TRIANGLES, 0, 6);
      gl.disable(gl.BLEND);
      return true;
    },
    dispose() {
      disposed = true;
      for (const entry of textures.values()) disposeEntry(gl, entry);
      gl.deleteBuffer(positionBuffer);
      gl.deleteBuffer(texCoordBuffer);
      gl.deleteProgram(program);
    },
  };
}

function getTextureEntry(
  context: WebGlRendererContext,
  textures: Map<string, TextureEntry>,
  asset: Asset,
  invalidate: () => void,
  isDisposed: () => boolean,
): TextureEntry {
  const cached = textures.get(asset.id);
  if (cached && cached.source === asset.source) return cached;

  if (cached) {
    if (cached.current.status === "ready") {
      if (cached.previousTexture) context.gl.deleteTexture(cached.previousTexture);
      cached.previousTexture = cached.current.texture;
    } else {
      disposeState(context.gl, cached.current);
    }
    cached.source = asset.source;
    cached.current = loadTextureState(context, asset, cached, invalidate, isDisposed);
    return cached;
  }

  const entry: TextureEntry = { source: asset.source, current: { status: "error" } };
  entry.current = loadTextureState(context, asset, entry, invalidate, isDisposed);
  textures.set(asset.id, entry);
  return entry;
}

function loadTextureState(
  context: WebGlRendererContext,
  asset: Asset,
  entry: TextureEntry,
  invalidate: () => void,
  isDisposed: () => boolean,
): TextureState {
  const image = new Image();
  const source = asset.source;
  image.onload = () => {
    if (isDisposed() || entry.source !== source) return;
    const texture = createTexture(context.gl, image);
    if (entry.previousTexture) context.gl.deleteTexture(entry.previousTexture);
    entry.previousTexture = undefined;
    entry.current = { status: "ready", texture };
    invalidate();
  };
  image.onerror = () => {
    if (isDisposed() || entry.source !== source) return;
    entry.current = { status: "error" };
    invalidate();
  };
  image.src = source;
  return { status: "loading", image };
}

function renderableTexture(entry: TextureEntry): WebGLTexture | undefined {
  if (entry.current.status === "ready") return entry.current.texture;
  return entry.previousTexture;
}

function disposeEntry(gl: WebGL2RenderingContext, entry: TextureEntry) {
  disposeState(gl, entry.current);
  if (entry.previousTexture) gl.deleteTexture(entry.previousTexture);
}

function disposeState(gl: WebGL2RenderingContext, state: TextureState) {
  if (state.status === "ready") {
    gl.deleteTexture(state.texture);
    return;
  }
  if (state.status === "loading") {
    state.image.onload = null;
    state.image.onerror = null;
  }
}

function intersectScreenRects(a: ScreenRect, b: ScreenRect): ScreenRect | undefined {
  const x1 = Math.max(a.x, b.x);
  const y1 = Math.max(a.y, b.y);
  const x2 = Math.min(a.x + a.w, b.x + b.w);
  const y2 = Math.min(a.y + a.h, b.y + b.h);
  if (x2 <= x1 || y2 <= y1) return undefined;

  return { x: x1, y: y1, w: x2 - x1, h: y2 - y1 };
}

function createTexture(gl: WebGL2RenderingContext, image: HTMLImageElement) {
  const texture = gl.createTexture();
  if (!texture) throw new Error("Failed to create image texture");

  gl.bindTexture(gl.TEXTURE_2D, texture);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
  gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, false);
  gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, image);

  return texture;
}

function rectVertices(canvas: HTMLCanvasElement, rect: ScreenRect) {
  const x1 = (rect.x / canvas.width) * 2 - 1;
  const x2 = ((rect.x + rect.w) / canvas.width) * 2 - 1;
  const y1 = 1 - (rect.y / canvas.height) * 2;
  const y2 = 1 - ((rect.y + rect.h) / canvas.height) * 2;

  return new Float32Array([x1, y1, x2, y1, x1, y2, x1, y2, x2, y1, x2, y2]);
}

function createProgram(gl: WebGL2RenderingContext) {
  const vertexShader = compileShader(
    gl,
    gl.VERTEX_SHADER,
    `#version 300 es
    in vec2 a_position;
    in vec2 a_texCoord;
    out vec2 v_texCoord;
    void main() {
      gl_Position = vec4(a_position, 0.0, 1.0);
      v_texCoord = a_texCoord;
    }`,
  );
  const fragmentShader = compileShader(
    gl,
    gl.FRAGMENT_SHADER,
    `#version 300 es
    precision mediump float;
    uniform sampler2D u_image;
    in vec2 v_texCoord;
    out vec4 outColor;
    void main() {
      outColor = texture(u_image, v_texCoord);
    }`,
  );
  const program = gl.createProgram();
  if (!program) throw new Error("Failed to create image shader program");

  gl.attachShader(program, vertexShader);
  gl.attachShader(program, fragmentShader);
  gl.linkProgram(program);
  gl.deleteShader(vertexShader);
  gl.deleteShader(fragmentShader);

  if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
    const message = gl.getProgramInfoLog(program) ?? "Unknown program link error";
    gl.deleteProgram(program);
    throw new Error(message);
  }

  return program;
}

function compileShader(gl: WebGL2RenderingContext, type: number, source: string) {
  const shader = gl.createShader(type);
  if (!shader) throw new Error("Failed to create shader");

  gl.shaderSource(shader, source);
  gl.compileShader(shader);
  if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
    const message = gl.getShaderInfoLog(shader) ?? "Unknown shader compile error";
    gl.deleteShader(shader);
    throw new Error(message);
  }

  return shader;
}