import type { Artboard } from "@core/artboard";
import type { Asset } from "@core/asset";
import type { Rect } from "@core/geometry";
import type { Layer } from "@core/layer";
import { getLayerMask } from "@core/layer-mask-utils";

export async function downloadArtboardPng(artboard: Artboard, assets: readonly Asset[]) {
  const width = Math.max(1, Math.round(artboard.bounds.w));
  const height = Math.max(1, Math.round(artboard.bounds.h));
  const canvas = document.createElement("canvas");
  canvas.width = width;
  canvas.height = height;

  const context = canvas.getContext("2d");
  if (!context) throw new Error("Canvas 2D is not available");

  if (artboard.backgroundColor !== "transparent") {
    context.fillStyle = artboard.backgroundColor;
    context.fillRect(0, 0, width, height);
  }

  const maskLayerIds = collectMaskLayerIds(artboard.layers);
  context.save();
  context.translate(-artboard.bounds.x, -artboard.bounds.y);
  for (const layer of renderStack(artboard.layers)) await drawLayer(context, layer, artboard.layers, assets, artboard.bounds, { maskLayerIds });
  context.restore();

  const url = canvas.toDataURL("image/png");
  const link = document.createElement("a");
  link.href = url;
  link.download = `${safeFilename(artboard.name)}.png`;
  link.click();
}

async function drawLayer(
  context: CanvasRenderingContext2D,
  layer: Layer,
  layerTree: readonly Layer[],
  assets: readonly Asset[],
  artboardBounds: Rect,
  options: { maskLayerIds: ReadonlySet<string>; ignoreOwnMask?: boolean },
) {
  if (!layer.visible || (!options.ignoreOwnMask && options.maskLayerIds.has(layer.id))) return;

  const layerMask = getLayerMask(layer);
  if (!options.ignoreOwnMask && layerMask?.enabled) {
    const maskLayer = findLayer(layerTree, layerMask.maskLayerId);
    if (!maskLayer) return;
    await drawMaskedLayer(context, layer, maskLayer, layerTree, assets, artboardBounds);
    return;
  }

  context.save();
  context.globalAlpha *= layer.opacity;

  if (layer.type === "group") {
    for (const child of renderStack(layer.children)) await drawLayer(context, child, layerTree, assets, artboardBounds, options);
    context.restore();
    return;
  }

  const asset = assets.find((candidate) => candidate.id === layer.assetId);
  if (!asset) {
    context.restore();
    return;
  }

  const image = await loadImage(asset.source);
  context.drawImage(
    image,
    layer.transform.position.x,
    layer.transform.position.y,
    asset.intrinsicSize.w * layer.transform.scale.x,
    asset.intrinsicSize.h * layer.transform.scale.y,
  );
  context.restore();
}

async function drawMaskedLayer(
  context: CanvasRenderingContext2D,
  layer: Layer,
  maskLayer: Layer,
  layerTree: readonly Layer[],
  assets: readonly Asset[],
  artboardBounds: Rect,
) {
  const layerCanvas = createArtboardCanvas(artboardBounds);
  const layerContext = translatedContext(layerCanvas, artboardBounds);
  await drawLayer(layerContext, layer, layerTree, assets, artboardBounds, { maskLayerIds: new Set(), ignoreOwnMask: true });
  layerContext.restore();

  const maskCanvas = createArtboardCanvas(artboardBounds);
  const maskContext = translatedContext(maskCanvas, artboardBounds);
  await drawLayer(maskContext, maskLayer, layerTree, assets, artboardBounds, { maskLayerIds: new Set(), ignoreOwnMask: true });
  maskContext.restore();

  const compositeContext = layerCanvas.getContext("2d");
  if (!compositeContext) return;
  compositeContext.globalCompositeOperation = "destination-in";
  compositeContext.drawImage(maskCanvas, 0, 0);
  compositeContext.globalCompositeOperation = "source-over";

  context.drawImage(layerCanvas, artboardBounds.x, artboardBounds.y);
}

function renderStack(layers: readonly Layer[]) {
  return [...layers].reverse();
}

function createArtboardCanvas(bounds: Rect) {
  const canvas = document.createElement("canvas");
  canvas.width = Math.max(1, Math.round(bounds.w));
  canvas.height = Math.max(1, Math.round(bounds.h));
  return canvas;
}

function translatedContext(canvas: HTMLCanvasElement, bounds: Rect) {
  const context = canvas.getContext("2d");
  if (!context) throw new Error("Canvas 2D is not available");
  context.save();
  context.translate(-bounds.x, -bounds.y);
  return context;
}

function collectMaskLayerIds(layers: readonly Layer[], ids = new Set<string>()) {
  for (const layer of layers) {
    const layerMask = getLayerMask(layer);
    if (layerMask) ids.add(layerMask.maskLayerId);
    if (layer.type === "group") collectMaskLayerIds(layer.children, ids);
  }
  return ids;
}

function findLayer(layers: readonly Layer[], layerId: string): Layer | undefined {
  for (const layer of layers) {
    if (layer.id === layerId) return layer;
    if (layer.type === "group") {
      const child = findLayer(layer.children, layerId);
      if (child) return child;
    }
  }
  return undefined;
}

function loadImage(source: string) {
  return new Promise<HTMLImageElement>((resolve, reject) => {
    const image = new Image();
    image.onload = () => resolve(image);
    image.onerror = () => reject(new Error("Failed to load image for export"));
    image.src = source;
  });
}

function safeFilename(name: string) {
  return name.trim().replace(/[^a-z0-9-_]+/gi, "-").replace(/^-+|-+$/g, "") || "artboard";
}