/**
 * This script automatically generates src/core/lib/HTMLEntities.mjs, the shared
 * HTML entity lookup tables used by the "To HTML Entity" and "From HTML Entity"
 * operations.
 *
 * The data is derived from the vendored WHATWG named character reference set
 * (src/core/vendor/htmlEntities/entity.json, from
 * https://html.spec.whatwg.org/entities.json) so the
 * two operations cannot drift apart and every entity is spec-conformant:
 *
 *   - HTML_ENTITY_REVERSE_LOOKUP (decode) is every single-code-point spec name.
 *   - HTML_ENTITY_LOOKUP (encode) picks one canonical name per code point via a
 *     deterministic tiebreak, overridden by htmlEntityOverrides.mjs where a
 *     specific historical name is preferred.
 *
 * @author roberson-io [michaelroberson@gmail.com]
 * @copyright Crown Copyright 2026
 * @license Apache-2.0
 */

/* eslint no-console: ["off"] */

import path from "path";
import fs from "fs";
import process from "process";
import { fileURLToPath } from "url";
import { HTML_ENTITY_CANONICAL_OVERRIDES } from "./htmlEntityOverrides.mjs";

const scriptDir = path.dirname(fileURLToPath(import.meta.url));

if (!fs.existsSync(path.join(process.cwd(), "src/core/lib"))) {
    console.log("\nCWD: " + process.cwd());
    console.log("Error: generateHTMLEntities.mjs should be run from the project root");
    console.log("Example> node src/core/config/scripts/generateHTMLEntities.mjs");
    process.exit(1);
}

const SPEC = JSON.parse(fs.readFileSync(
    path.join(scriptDir, "..", "..", "vendor", "htmlEntities", "entity.json"), "utf8"));

// Build code point -> [spec names] for single-code-point, semicolon-terminated
// references (the representable subset; multi-code-point entities are skipped).
const codePointNames = {};
for (const [key, val] of Object.entries(SPEC)) {
    if (!key.endsWith(";") || val.codepoints.length !== 1) continue;
    const name = key.slice(1, -1); // strip leading "&" and trailing ";"
    (codePointNames[val.codepoints[0]] ??= []).push(name);
}

// Deterministic canonical-name tiebreak: prefer a lower-case name, then the
// shortest, then alphabetical. Overridden per code point where a specific
// historical name is preferred.
const isAllUpper = s => s === s.toUpperCase() && s !== s.toLowerCase();

/**
 * Choose the single canonical entity name for a code point.
 *
 * @param {number} codePoint - the Unicode code point being encoded
 * @param {string[]} names - all valid WHATWG names for that code point
 * @returns {string} the canonical name to emit when encoding
 */
function canonicalName(codePoint, names) {
    const override = HTML_ENTITY_CANONICAL_OVERRIDES[codePoint];
    if (override !== undefined) {
        if (!names.includes(override))
            throw new Error(`Override &${override}; is not a spec name for code point ${codePoint} (spec: ${names})`);
        return override;
    }
    return [...names].sort((a, b) =>
        (isAllUpper(a) - isAllUpper(b)) ||
        (a.length - b.length) ||
        (a < b ? -1 : a > b ? 1 : 0)
    )[0];
}

const forward = {};   // code point -> canonical name (encode)
const reverse = {};   // name -> code point (decode, every spec name)
for (const [cpStr, names] of Object.entries(codePointNames)) {
    const cp = Number(cpStr);
    forward[cp] = canonicalName(cp, names);
    for (const name of names) reverse[name] = cp;
}

// Decode-only aliases = spec names that are not the canonical encode name.
const aliases = {};
for (const [name, cp] of Object.entries(reverse)) {
    if (forward[cp] !== name) aliases[name] = cp;
}

// --- emit -----------------------------------------------------------------
const fwdEntries = Object.keys(forward).map(Number).sort((a, b) => a - b)
    .map(cp => `    ${cp}: "${forward[cp]}",`).join("\n").replace(/,$/, "");
const aliasEntries = Object.keys(aliases).sort()
    .map(n => `    ${JSON.stringify(n)}: ${aliases[n]},`).join("\n").replace(/,$/, "");

const code = `/**
 * THIS FILE IS AUTOMATICALLY GENERATED BY src/core/config/scripts/generateHTMLEntities.mjs
 *
 * HTML entity lookup tables shared by the "To HTML Entity" and "From HTML Entity"
 * operations, derived from the WHATWG named character reference set
 * (https://html.spec.whatwg.org/entities.json). Do not edit by hand — change the
 * vendored src/core/vendor/htmlEntities/entity.json or htmlEntityOverrides.mjs
 * and regenerate.
 *
 * @author roberson-io [michaelroberson@gmail.com]
 * @copyright Crown Copyright ${new Date().getUTCFullYear()}
 * @license Apache-2.0
 */

/**
 * Canonical lookup: Unicode code point -> entity name (without "&" and ";"),
 * used for ENCODING. One canonical name per code point.
 */
export const HTML_ENTITY_LOOKUP = {
${fwdEntries}
};

/**
 * Legacy / alias names that only DECODE (spelling variants, deprecated names,
 * box-drawing aliases, etc.); not used for encoding.
 */
export const HTML_ENTITY_DECODE_ALIASES = {
${aliasEntries}
};

/**
 * Derived reverse lookup: entity name -> code point, used for DECODING. Built
 * from the canonical lookup plus the legacy aliases.
 */
export const HTML_ENTITY_REVERSE_LOOKUP = {...HTML_ENTITY_DECODE_ALIASES};
for (const codePoint in HTML_ENTITY_LOOKUP) {
    HTML_ENTITY_REVERSE_LOOKUP[HTML_ENTITY_LOOKUP[codePoint]] = Number(codePoint);
}
`;

fs.writeFileSync(path.join(process.cwd(), "src/core/lib/HTMLEntities.mjs"), code);
console.log(`generateHTMLEntities: ${Object.keys(forward).length} encode names, ` +
    `${Object.keys(reverse).length} decode names, ${Object.keys(aliases).length} aliases, ` +
    `${Object.keys(HTML_ENTITY_CANONICAL_OVERRIDES).length} overrides applied.`);