// taxonomy.mjs — Loader + accessors for data/domain-taxonomy.json (lag 0).
// Zero dependencies. The taxonomy is the single source of truth for in-domain
// classification: which sitemaps to poll, which URLs are relevant, which
// skill/category owns content, and update priority. poll-sitemaps,
// discover-new-urls and report-changes READ this instead of embedding copies.

import { readFileSync, writeFileSync, renameSync, existsSync, mkdirSync } from 'node:fs';
import { join, dirname } from 'node:path';
import { fileURLToPath } from 'node:url';

const __dirname = dirname(fileURLToPath(import.meta.url));
const DEFAULT_DATA_DIR = join(__dirname, '..', 'data');

/**
 * Load the domain taxonomy from disk.
 * @param {string} [dataDir] — defaults to ../data/ relative to lib/
 * @returns {object} parsed taxonomy
 */
export function loadTaxonomy(dataDir = DEFAULT_DATA_DIR) {
  const path = join(dataDir, 'domain-taxonomy.json');
  return JSON.parse(readFileSync(path, 'utf8'));
}

/**
 * Save the domain taxonomy atomically (write to .tmp, then rename) — mirrors
 * saveDecisions. The taxonomy is lag-0 truth and is normally read-only; the ONE
 * writer is the gated merge-apply path (Sesjon 19), which repoints category
 * ownership from an absorbed skill to its absorber. Detection scripts must NOT
 * import this.
 * @param {object} tax — taxonomy object to persist
 * @param {string} [dataDir]
 */
export function saveTaxonomy(tax, dataDir = DEFAULT_DATA_DIR) {
  if (!existsSync(dataDir)) mkdirSync(dataDir, { recursive: true });
  const path = join(dataDir, 'domain-taxonomy.json');
  const tmp = path + '.tmp';
  writeFileSync(tmp, JSON.stringify(tax, null, 2) + '\n', 'utf8');
  renameSync(tmp, path);
}

/**
 * Repoint category ownership for a skill merge. Pure — returns a new taxonomy,
 * mutates nothing. For each { category, from, to }, the category's owner is
 * changed to `to` ONLY when it currently equals `from` (defensive: a category
 * already repointed, or absent, is a no-op — never clobbered). All other fields
 * survive untouched.
 * @param {object} tax
 * @param {Array<{category: string, from: string, to: string}>} reassignments
 * @returns {object} new taxonomy
 */
export function applyCategoryReassignments(tax, reassignments) {
  const next = { ...tax.category_skill };
  for (const { category, from, to } of reassignments) {
    if (next[category] === from) next[category] = to;
  }
  return { ...tax, category_skill: next };
}

/**
 * Add category ownership for a NEW skill (create_skill, Sesjon 20). Pure —
 * returns a new taxonomy, mutates nothing. For each { category, skill }, the
 * category is assigned to `skill` ONLY when it is currently UNOWNED (absent):
 * an existing owner is never clobbered (a create must not steal a sibling's
 * category — that would be a merge, a different gated op). Additive counterpart
 * to applyCategoryReassignments: reassign repoints an owned category, add claims
 * an unowned one. The same gated apply-path is the only writer.
 * @param {object} tax
 * @param {Array<{category: string, skill: string}>} additions
 * @returns {object} new taxonomy
 */
export function applyCategoryAdditions(tax, additions) {
  const next = { ...tax.category_skill };
  for (const { category, skill } of additions) {
    if (next[category] === undefined) next[category] = skill;
  }
  return { ...tax, category_skill: next };
}

/**
 * Target sitemap child-name prefixes to scan/poll.
 * @param {object} tax
 * @returns {string[]}
 */
export function getSitemapPrefixes(tax) {
  return tax.sitemap_prefixes;
}

/**
 * Canonical owning skill for a KB category (physical-disk truth).
 * @param {object} tax
 * @param {string} category
 * @returns {string|null} skill directory name, or null if unknown
 */
export function getCategorySkill(tax, category) {
  return tax.category_skill[category] ?? null;
}

/**
 * Build a URL classifier mirroring discover-new-urls semantics:
 * exclude wins; first include match → { skill, category } with skill DERIVED
 * from the canonical category_skill map (no embedded skill assignments).
 * @param {object} tax
 * @returns {(url: string) => ({skill: string|null, category: string}|null)}
 */
export function makeClassifier(tax) {
  const include = tax.relevance.include.map((r) => ({
    re: new RegExp(r.pattern),
    category: r.category,
  }));
  const exclude = tax.relevance.exclude.map((p) => new RegExp(p));

  return function classifyUrl(url) {
    if (exclude.some((re) => re.test(url))) return null;
    for (const rule of include) {
      if (rule.re.test(url)) {
        return { skill: tax.category_skill[rule.category] ?? null, category: rule.category };
      }
    }
    return null;
  };
}

/**
 * Build a course classifier for the Learn Platform API course-detection spore
 * (C3). course_products maps an in-domain product slug → category; the owning
 * skill is DERIVED from category_skill (never stored redundantly), exactly as
 * makeClassifier derives skill for URL classification — so the slug→skill path
 * cannot diverge from the canonical category ownership. The FIRST in-domain
 * product in the list wins; a course whose products are all out-of-domain (no
 * slug in course_products) returns null and is therefore not a lead.
 * @param {object} tax
 * @returns {(products: string[]) => ({skill: string|null, category: string}|null)}
 */
export function makeCourseClassifier(tax) {
  const map = tax.course_products ?? {};
  return function classifyCourse(products) {
    if (!Array.isArray(products)) return null;
    for (const slug of products) {
      const category = map[slug];
      if (category) {
        return { skill: tax.category_skill[category] ?? null, category };
      }
    }
    return null;
  };
}

/**
 * Build a file-priority function mirroring report-changes getFilePriority:
 * ordered regex rules over the lowercased path; first match wins; else default.
 *
 * A file with NO "Last updated:" header (hasDate=false) cannot have its currency
 * verified, so it lands in the dedicated `dateless` tier ('unverified') instead
 * of inheriting a path-based priority — otherwise dateless files flood the
 * critical bucket and drown the genuinely-stale critical files (carry-forward B).
 * hasDate defaults to true so existing single-arg callers keep path-based scoring.
 * @param {object} tax
 * @returns {(filePath: string, hasDate?: boolean) => string}
 */
export function makePriorityFn(tax) {
  const rules = tax.priority.rules.map((r) => ({ re: new RegExp(r.match), priority: r.priority }));
  const fallback = tax.priority.default;
  const datelessTier = tax.priority.dateless ?? fallback;

  return function getFilePriority(filePath, hasDate = true) {
    if (!hasDate) return datelessTier;
    const lower = filePath.toLowerCase();
    for (const r of rules) {
      if (r.re.test(lower)) return r.priority;
    }
    return fallback;
  };
}