// decisions-io.mjs — Read/write + pure helpers for data/decisions.json (lag 2).
// The decision ledger is the ONLY write-authorized bridge between detection and
// the KB/registry: discovery READS it to filter, the operator gate WRITES it.
// Zero dependencies. Atomic writes via .tmp + rename (mirrors registry-io).
//
// Dedup policy = A (operatør 2026-06-19): isDecided(url) is true for ANY ledger
// entry (pending | approved | rejected). Discovery re-proposes only URLs that
// are entirely absent from the ledger; everything the operator has touched —
// approved, rejected, or explicitly deferred (pending) — stays off the list.

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');

/**
 * Empty ledger scaffold.
 *
 * Two parallel collections, both written ONLY through the operator gate:
 *   - decisions — URL-keyed (Spor A): which Microsoft Learn page belongs where.
 *   - actions   — skill-keyed (Spor B / B3): skill-lifecycle ops (merge_skills,
 *                 sanitize_skill, retire_skill, create_skill). Additive: version
 *                 stays 1, and a pre-action ledger on disk normalizes cleanly
 *                 (loadDecisions backfills the missing actions key).
 * @returns {{version: number, updated_at: string|null, decisions: object, actions: object}}
 */
export function createLedger() {
  return { version: 1, updated_at: null, decisions: {}, actions: {} };
}

/**
 * Load the decision ledger from disk. Backward-compatible: a ledger written
 * before the action layer existed (no `actions` key) is normalized to `{}` so
 * callers never have to guard against undefined.
 * @param {string} [dataDir] — defaults to ../data/ relative to lib/
 * @returns {object} parsed ledger or empty scaffold
 */
export function loadDecisions(dataDir = DEFAULT_DATA_DIR) {
  const path = join(dataDir, 'decisions.json');
  if (!existsSync(path)) return createLedger();
  const led = JSON.parse(readFileSync(path, 'utf8'));
  if (!led.actions) led.actions = {};
  return led;
}

/**
 * Save the decision ledger atomically (write to .tmp, then rename).
 * This is the gate's write path — detection scripts must NOT import it.
 * @param {object} ledger
 * @param {string} [dataDir]
 */
export function saveDecisions(ledger, dataDir = DEFAULT_DATA_DIR) {
  if (!existsSync(dataDir)) mkdirSync(dataDir, { recursive: true });
  const path = join(dataDir, 'decisions.json');
  const tmp = path + '.tmp';
  writeFileSync(tmp, JSON.stringify(ledger, null, 2) + '\n', 'utf8');
  renameSync(tmp, path);
}

/**
 * Has the operator already decided on this URL? Policy A: any entry counts.
 * @param {object} ledger
 * @param {string} url — normalized URL
 * @returns {boolean}
 */
export function isDecided(ledger, url) {
  return Boolean(ledger.decisions && ledger.decisions[url]);
}

/**
 * Record a decision for a URL. Pure — returns a new ledger, does not mutate.
 * @param {object} ledger
 * @param {string} url — normalized URL
 * @param {{status: string, decided_at?: string, suggested_skill?: string|null,
 *          suggested_category?: string, note?: string}} decision
 * @returns {object} new ledger
 */
export function recordDecision(ledger, url, decision) {
  return {
    ...ledger,
    updated_at: decision.decided_at ?? ledger.updated_at,
    decisions: { ...ledger.decisions, [url]: { ...decision } },
  };
}

/**
 * Drop candidates the operator has already decided on (policy A).
 * Discovery applies this before emitting its report.
 * @param {object} ledger
 * @param {Array<{url: string}>} candidates
 * @returns {Array<{url: string}>} candidates with no ledger entry
 */
export function filterUndecided(ledger, candidates) {
  return candidates.filter((c) => !isDecided(ledger, c.url));
}

// ===========================================================================
// Skill-level action layer (Spor B / B3) — additive, mirrors the URL helpers.
// Detection/transformation produce a PENDING action entry; only the gate writes
// it. recordAction never mutates skills/ — it records a proposal in the ledger.
// ===========================================================================

/**
 * Deterministic dedup key for a skill-lifecycle action. merge_skills is keyed
 * symmetrically on the pair (merging A<-B and B<-A dedup to the same key);
 * single-skill ops (sanitize/retire/create) are keyed by their one target.
 * @param {{operation_type: string, targets?: object}} entry
 * @returns {string}
 */
export function actionKey(entry) {
  const op = entry.operation_type;
  const t = entry.targets ?? {};
  if (op === 'merge_skills') {
    const pair = [t.absorber, t.absorbed].filter(Boolean).sort();
    return `merge_skills:${pair.join('+')}`;
  }
  const single = t.skill ?? t.name ?? t.absorber ?? '?';
  return `${op}:${single}`;
}

/**
 * Has the operator already decided on this action? Policy A: any entry
 * (pending | approved | rejected) counts — mirrors isDecided for URLs.
 * @param {object} ledger
 * @param {string} key — from actionKey()
 * @returns {boolean}
 */
export function isActionDecided(ledger, key) {
  return Boolean(ledger.actions && ledger.actions[key]);
}

/**
 * Record a skill-lifecycle action. Pure — returns a new ledger, does not mutate.
 * Keyed by actionKey(entry). Leaves the URL-keyed decisions map untouched.
 * @param {object} ledger
 * @param {{operation_type: string, status: string, decided_at?: string|null,
 *          targets?: object, guardrail?: object, note?: string}} entry
 * @returns {object} new ledger
 */
export function recordAction(ledger, entry) {
  const key = actionKey(entry);
  return {
    ...ledger,
    updated_at: entry.decided_at ?? ledger.updated_at,
    actions: { ...(ledger.actions ?? {}), [key]: { ...entry } },
  };
}

/**
 * List recorded actions, optionally filtered by status.
 * @param {object} ledger
 * @param {string|null} [status] — when given, keep only entries with this status
 * @returns {Array<object>}
 */
export function listActions(ledger, status = null) {
  const all = Object.values(ledger.actions ?? {});
  return status ? all.filter((a) => a.status === status) : all;
}

/**
 * Transition a recorded action to a new status. Pure — returns a new ledger,
 * does not mutate. Every other field (targets, guardrail, note) is preserved.
 * This is the apply-path's one write primitive (Sesjon 18): after a successful
 * skills/ mutation it flips the operator-approved entry approved -> applied,
 * keeping the entry as an audit record (policy A dedup still holds).
 * @param {object} ledger
 * @param {string} key — from actionKey()
 * @param {string} status — new status (e.g. 'approved', 'applied')
 * @param {string|null} [decided_at] — when given, advances the entry date + updated_at
 * @returns {object} new ledger
 * @throws if no action exists under `key`
 */
export function setActionStatus(ledger, key, status, decided_at = null) {
  const existing = ledger.actions?.[key];
  if (!existing) throw new Error(`setActionStatus: no action recorded under key "${key}"`);
  return {
    ...ledger,
    updated_at: decided_at ?? ledger.updated_at,
    actions: {
      ...ledger.actions,
      [key]: { ...existing, status, decided_at: decided_at ?? existing.decided_at },
    },
  };
}