/**
 * Rasterizes the favicon artwork and writes favicon-png.generated.ts, so that
 * serving a favicon needs no rasterizer at runtime. Running this when the
 * output already matches leaves the file alone, which is what lets a test
 * check that the committed output is current.
 */

import { Resvg } from "@resvg/resvg-js";
import { faviconSvg } from "./favicon-artwork.ts";
import { FAVICON_FACES, type FaviconFace } from "./favicon-types.ts";

const OUTPUT = new URL("./favicon-png.generated.ts", import.meta.url);
const BASE64_LINE_LENGTH = 80;

function renderFavicons(): Record<FaviconFace, Uint8Array> {
  const rendered = {} as Record<FaviconFace, Uint8Array>;
  for (const face of FAVICON_FACES) {
    rendered[face] = new Uint8Array(
      new Resvg(faviconSvg(face), {
        font: { loadSystemFonts: false },
        fitTo: { mode: "width", value: 32 },
      }).render().asPng(),
    );
  }
  return rendered;
}

async function assetVersion(
  rendered: Record<FaviconFace, Uint8Array>,
): Promise<string> {
  const encoded = FAVICON_FACES.map((face) =>
    `${face}\0${rendered[face].toBase64()}`
  ).join("\0");
  const digest = new Uint8Array(
    await crypto.subtle.digest("SHA-256", new TextEncoder().encode(encoded)),
  );
  return Array.from(digest, (byte) => byte.toString(16).padStart(2, "0")).join(
    "",
  );
}

function pngProperty(face: FaviconFace, png: Uint8Array): string {
  const encoded = png.toBase64();
  const chunks: string[] = [];
  for (let offset = 0; offset < encoded.length; offset += BASE64_LINE_LENGTH) {
    chunks.push(encoded.slice(offset, offset + BASE64_LINE_LENGTH));
  }
  const value = chunks.map((chunk, index) => {
    const indent = index === 0 ? "    " : "      ";
    const suffix = index === chunks.length - 1 ? "" : " +";
    return `${indent}${JSON.stringify(chunk)}${suffix}`;
  }).join("\n");
  return `  ${JSON.stringify(face)}: decodePng(\n${value},\n  ),`;
}

async function generatedSource(
  rendered: Record<FaviconFace, Uint8Array>,
): Promise<string> {
  const version = await assetVersion(rendered);
  const properties = FAVICON_FACES.map((face) =>
    pngProperty(face, rendered[face])
  ).join("\n");
  return `/**
 * Holds every favicon face as a PNG, rendered from the source artwork in
 * favicon-artwork.ts. Generated by \`deno task regenerate-favicons\`, which
 * overwrites whatever is here.
 */

function decodePng(encoded: string): Uint8Array {
  return Uint8Array.fromBase64(encoded);
}

export const FAVICON_VERSION =
  ${JSON.stringify(version)};

export const FAVICON_PNG = {
${properties}
} as const;
`;
}

async function currentOutput(
  output: string | URL,
): Promise<string | undefined> {
  try {
    return await Deno.readTextFile(output);
  } catch (error) {
    if (error instanceof Deno.errors.NotFound) return undefined;
    throw error;
  }
}

export async function regenerateFavicons(
  output: string | URL = OUTPUT,
): Promise<boolean> {
  const source = await generatedSource(renderFavicons());
  if (source === await currentOutput(output)) {
    console.log("Dashboard favicons are already up to date.");
    return false;
  }
  await Deno.writeTextFile(output, source);
  console.log(`Regenerated ${FAVICON_FACES.length} dashboard favicons.`);
  return true;
}

if (import.meta.main) await regenerateFavicons();