/**
 * Renders the site's favicons and web manifest from its emoji. The `icons`
 * task (`api/scripts/generate-icons.ts`) runs it before the server starts, so
 * the emoji can change without a rebuild.
 *
 * The glyph comes from Twemoji as plain vector paths, so rendering it needs no
 * emoji font, which the Alpine runtime image lacks.
 *
 * @module
 */

import { initWasm, Resvg } from "@resvg/resvg-wasm";
import { fetchTwemojiSvg } from "../remote/twemoji.ts";

const PNG_SIZES = [16, 32, 48, 64, 96, 128, 192, 256, 512];
const APPLE_SIZE = 180;
const ICO_SIZES = [16, 32, 48];

/**
 * Returns the name Twemoji files `emoji` under: its codepoints in hex, joined
 * with "-", without variation selectors (FE0F) unless the emoji is a ZWJ
 * sequence. `lib/index-html.ts` also uses it as the icon URLs' cache-busting
 * version.
 */
export function emojiToCodepoint(emoji: string): string {
  const cleaned = emoji.includes("‍") ? emoji : emoji.replace(/️/g, "");
  return [...cleaned].map((ch) => ch.codePointAt(0)!.toString(16)).join("-");
}

let wasmReady: Promise<unknown> | undefined;
function ensureWasm(): Promise<unknown> {
  if (!wasmReady) {
    const wasmUrl = new URL(
      import.meta.resolve("@resvg/resvg-wasm/index_bg.wasm"),
    );
    wasmReady = Deno.readFile(wasmUrl).then((bytes) => initWasm(bytes));
  }
  return wasmReady;
}

function renderPng(svg: string, size: number, background?: string): Uint8Array {
  const resvg = new Resvg(svg, {
    fitTo: { mode: "width", value: size },
    background,
  });
  return resvg.render().asPng();
}

/** Packs PNG images into an .ico file, which may hold PNGs as they are. */
function buildIco(images: { size: number; png: Uint8Array }[]): Uint8Array {
  const HEADER = 6;
  const ENTRY = 16;
  const offsetBase = HEADER + ENTRY * images.length;
  const total = offsetBase + images.reduce((sum, i) => sum + i.png.length, 0);
  const buf = new Uint8Array(total);
  const dv = new DataView(buf.buffer);
  dv.setUint16(2, 1, true); // type: icon
  dv.setUint16(4, images.length, true);
  let offset = offsetBase;
  images.forEach((img, idx) => {
    const e = HEADER + idx * ENTRY;
    buf[e] = img.size >= 256 ? 0 : img.size; // width (0 means 256)
    buf[e + 1] = img.size >= 256 ? 0 : img.size; // height
    dv.setUint16(e + 4, 1, true); // color planes
    dv.setUint16(e + 6, 32, true); // bits per pixel
    dv.setUint32(e + 8, img.png.length, true); // size of image data
    dv.setUint32(e + 12, offset, true); // offset of image data
    buf.set(img.png, offset);
    offset += img.png.length;
  });
  return buf;
}

function buildManifest(siteName: string, bgColor: string): string {
  const manifest = {
    name: siteName,
    short_name: siteName,
    start_url: "/",
    display: "standalone",
    background_color: bgColor,
    theme_color: bgColor,
    icons: [
      { src: "/favicon.svg", type: "image/svg+xml", sizes: "any" },
      { src: "/favicon-192x192.png", type: "image/png", sizes: "192x192" },
      {
        src: "/favicon-512x512.png",
        type: "image/png",
        sizes: "512x512",
        purpose: "any maskable",
      },
    ],
    share_target: {
      action: "/",
      method: "GET",
      params: { url: "share_url", title: "share_title", text: "share_text" },
    },
  };
  return JSON.stringify(manifest, null, 2) + "\n";
}

/**
 * Passed to {@link generateSiteIcons} by `api/scripts/generate-icons.ts`, from
 * the site's config.
 */
export interface GenerateSiteIconsOptions {
  emoji: string;
  /** Created if missing. */
  outDir: string;
  siteName: string;
  /** Fills the Apple touch icon, and the manifest's theme and background. */
  bgColor: string;
}

/**
 * Writes `favicon.svg`, `favicon.ico`, `favicon-<size>x<size>.png` (16 to 512),
 * `apple-touch-icon.png` and `manifest.webmanifest` into `opts.outDir`, the
 * directory the site's static files are served from.
 *
 * @throws {Error} When the emoji's glyph can't be fetched.
 */
export async function generateSiteIcons(
  opts: GenerateSiteIconsOptions,
): Promise<void> {
  const { emoji, outDir, siteName, bgColor } = opts;
  const svg = await fetchTwemojiSvg(emoji, emojiToCodepoint(emoji));
  await ensureWasm();

  await Deno.mkdir(outDir, { recursive: true });
  const out = (name: string) => `${outDir}/${name}`;

  await Deno.writeTextFile(out("favicon.svg"), svg);

  const pngs = new Map<number, Uint8Array>();
  for (const size of PNG_SIZES) pngs.set(size, renderPng(svg, size));
  for (const size of PNG_SIZES) {
    await Deno.writeFile(out(`favicon-${size}x${size}.png`), pngs.get(size)!);
  }
  // iOS draws a transparent touch icon on black.
  await Deno.writeFile(
    out("apple-touch-icon.png"),
    renderPng(svg, APPLE_SIZE, bgColor),
  );
  await Deno.writeFile(
    out("favicon.ico"),
    buildIco(ICO_SIZES.map((size) => ({ size, png: pngs.get(size)! }))),
  );
  await Deno.writeTextFile(
    out("manifest.webmanifest"),
    buildManifest(siteName, bgColor),
  );
}