// Shared helpers for the font manifest builder and verifier (Node only).
import { createHash } from "node:crypto";
import { readdirSync, readFileSync, statSync } from "node:fs";
import path from "node:path";
import { fileURLToPath } from "node:url";
import * as fontkit from "fontkit";

export const ROOT = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "../..");
export const FONTS_DIR = path.join(ROOT, "public/fonts");
export const MANIFEST_PATH = path.join(FONTS_DIR, "manifest.json");

export const sha256 = (bytes) => createHash("sha256").update(bytes).digest("hex");

/** Folders under public/fonts that hold bundled families (everything that is a directory). */
export function familyFolders() {
  return readdirSync(FONTS_DIR)
    .filter((name) => statSync(path.join(FONTS_DIR, name)).isDirectory())
    .sort();
}

export function ttfFiles(folder) {
  return readdirSync(path.join(FONTS_DIR, folder))
    .filter((name) => /\.ttf$/i.test(name))
    .sort();
}

/** First four bytes as a tag: "\0\1\0\0" is reported as "0x00010000". */
export function sfntTag(bytes) {
  const b = bytes.subarray(0, 4);
  if (b[0] === 0 && b[1] === 1 && b[2] === 0 && b[3] === 0) return "0x00010000";
  return String.fromCharCode(...b);
}

/** Raw OS/2 fsType (fontkit only exposes decoded flags). */
function rawFsType(bytes) {
  const dv = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength);
  const numTables = dv.getUint16(4);
  for (let i = 0; i < numTables; i++) {
    const rec = 12 + i * 16;
    const tag = String.fromCharCode(bytes[rec], bytes[rec + 1], bytes[rec + 2], bytes[rec + 3]);
    if (tag === "OS/2") return dv.getUint16(dv.getUint32(rec + 8) + 8);
  }
  return null;
}

/** Reads a TTF with fontkit and returns the facts the manifest records. */
export function inspectFont(folder, file) {
  const bytes = new Uint8Array(readFileSync(path.join(FONTS_DIR, folder, file)));
  const font = fontkit.create(Buffer.from(bytes));
  if (font.fonts) throw new Error(`${folder}/${file}: font collections are not supported`);
  const os2 = font["OS/2"];
  return {
    bytes,
    tag: sfntTag(bytes),
    variable: Boolean(font.directory?.tables?.fvar),
    // Name ID 16 (typographic family) groups SemiBold etc. under the base family.
    familyName: font.name?.records?.preferredFamily?.en ?? font.familyName,
    info: {
      file,
      weight: os2.usWeightClass,
      style: os2.fsSelection.italic || os2.fsSelection.oblique ? "italic" : "normal",
      sha256: sha256(bytes),
      fsType: rawFsType(bytes),
      upm: font.unitsPerEm,
      ascent: font.ascent,
      descent: font.descent,
      lineGap: font.lineGap,
      capHeight: font.capHeight,
      xHeight: font.xHeight,
      hasRupee: font.hasGlyphForCodePoint(0x20b9),
      hasTabularNums: font.availableFeatures.includes("tnum"),
    },
  };
}

export const WEIGHT_WORDS = {
  Thin: 100, ExtraLight: 200, Light: 300, Regular: 400, Italic: 400, Text: 450,
  Medium: 500, SemiBold: 600, Bold: 700, ExtraBold: 800, Black: 900,
};