// transform.mjs — Lag 4: TRANSFORMASJON (doc → KB-fil). Pure helper library that
// turns an approved, fetched Microsoft Learn document into a KB reference file in
// the plugin's house format. It is the deterministic spine the LLM destillation
// (commands/kb-update.md, transform-prompt.md) hangs on:
//
//   buildKbHeader   — the mandatory header block (Status + Source obligatory)
//   validateKbFile  — enforce the mandatory-field contract on any candidate file
//   buildChange     — construct the lag-5 `change` object (the lag-4 → lag-5 seam)
//   resolveTargetPath — route the file to its owning skill via the taxonomy (lag 0)
//
// ARCHITECTURE INVARIANT (spec §83): this lib NEVER writes. It returns content,
// verdicts and paths; applying a file is the operator gate's job, after lag 5
// (verify-out) has cleared it. Mirrors decisions-io / verify-out: pure functions,
// no write-util imports. The only dependency is kb-headers (read-only parser) so
// validateKbFile uses the SAME source detection as build-registry — one source of
// truth for "what counts as a Source header" (the top-500-byte region).

import { parseSourceHeader } from './kb-headers.mjs';
import { getCategorySkill } from './taxonomy.mjs';

// Mandatory header fields. Status is obligatory per spec ("status-felt obligatorisk");
// Source is what lets lag 3 backfill authority_source and lag-5 rule 3 eventually fire.
const REQUIRED_META = ['title', 'status', 'category', 'source', 'lastUpdated'];

/**
 * Build the deterministic KB-file header block. Status and Source live IN the
 * header (top 500 bytes) so kb-headers.parseSourceHeader and the "Last updated:"
 * scanner can see them — the old bottom-of-file source section was invisible to
 * those scanners, which is why authority_source coverage was 0%.
 *
 * @param {{title: string, status: string, category: string, source: string,
 *          lastUpdated: string}} meta
 * @returns {string} the header block, ending with the `---` rule + trailing newline
 * @throws if any mandatory field is missing/empty
 */
export function buildKbHeader(meta) {
  const m = meta ?? {};
  const missing = REQUIRED_META.filter((k) => {
    const v = m[k];
    return v === undefined || v === null || String(v).trim() === '';
  });
  if (missing.length) {
    throw new Error(`buildKbHeader: missing mandatory field(s): ${missing.join(', ')}`);
  }
  return (
    `# ${m.title}\n\n` +
    `**Last updated:** ${m.lastUpdated}\n` +
    `**Status:** ${m.status}\n` +
    `**Category:** ${m.category}\n` +
    `**Source:** ${m.source}\n\n` +
    `---\n`
  );
}

const RE_TITLE = /^#\s+\S/m;
const RE_LAST_UPDATED = /\*\*Last updated:\*\*\s*[\d-]+/i;
const RE_STATUS = /\*\*Status:\*\*\s*\S/i;

/**
 * Validate that a candidate KB file carries the mandatory contract: a title, a
 * "Last updated:" header (so it is never dateless → never the 'unverified' bucket),
 * a Status field, and a Source header in the scannable region. Used by the gate
 * before a transformed file may be written.
 *
 * @param {string} content — full file content
 * @returns {{valid: boolean, missing: string[]}}
 */
export function validateKbFile(content) {
  const s = String(content ?? '');
  const missing = [];
  if (!RE_TITLE.test(s)) missing.push('title');
  if (!RE_LAST_UPDATED.test(s)) missing.push('last_updated');
  if (!RE_STATUS.test(s)) missing.push('status');
  if (parseSourceHeader(s) === null) missing.push('source');
  return { valid: missing.length === 0, missing };
}

/**
 * Construct the lag-5 `change` object from a transformation result — the explicit,
 * documented seam between lag 4 and lag 5. Decouples lag 4's field names from
 * verify-out's, and supplies the safe defaults lag 5 expects (no refutations yet;
 * authority_source null until lag 3 backfills it).
 *
 * @param {{field: string, oldValue?: string, newValue: string, sourceUrl?: string,
 *          authoritySource?: string|null, refutations?: Array}} t
 * @returns {{field: string, old_value: string, new_value: string,
 *            source_url: string|null, authority_source: string|null, refutations: Array}}
 */
export function buildChange(t) {
  const o = t ?? {};
  return {
    field: o.field ?? '',
    old_value: o.oldValue ?? '',
    new_value: o.newValue ?? '',
    source_url: o.sourceUrl ?? null,
    authority_source: o.authoritySource ?? null,
    refutations: Array.isArray(o.refutations) ? o.refutations : [],
  };
}

/**
 * Resolve where a transformed file belongs, routing via the taxonomy's canonical
 * category → skill map (physical-disk truth — this is what replaced
 * category-skill-map.json). Returns null for an unknown category so the caller
 * must gate rather than silently misroute.
 *
 * @param {object} tax — loaded domain taxonomy
 * @param {string} category
 * @param {string} filename — kebab-case .md filename
 * @returns {string|null} repo-relative path, or null if the category is unknown
 */
export function resolveTargetPath(tax, category, filename) {
  const skill = getCategorySkill(tax, category);
  if (!skill) return null;
  return `skills/${skill}/references/${category}/${filename}`;
}