// skill-ops.mjs — Spor B / B3: skill-lifecycle operation PLANNERS (lag-4-analog
// at skill granularity). The pure core APPLIES NOTHING and reads no disk: it
// returns { entry, diff, guardrail }. The operator gate (decisions.json) records
// the PENDING entry; a later approved apply-session performs any skills/ mutation.
//
// Sesjon 16 ships merge_skills only (operator priority). sanitize/retire/create
// follow in S17+ as further planners that emit the same kind of gated entry.
//
// Inherited arkitektur-invariant: detection/verification/transformation never
// write to skills/ directly — only via the ledger after the operator gate.
// Destructive ops carry mandatory guardrails that PROVE curated value is
// preserved (ref-file count-invariant + set-equality) and refuse (ok=false)
// when two reference files would clobber on the same target path.

import { readdirSync, existsSync, statSync } from 'node:fs';
import { join, relative, sep } from 'node:path';
import {
  loadDecisions,
  saveDecisions,
  recordAction,
} from '../../kb-update/lib/decisions-io.mjs';

export const MERGE_OPERATION = 'merge_skills';

// ---------------------------------------------------------------------------
// Pure core — planMergeSkills
// ---------------------------------------------------------------------------

/**
 * Plan a skill merge: `absorbed` is retired into `absorber`. Pure; mutates
 * nothing; reads no disk. Reference identity is the references/-relative path
 * (e.g. "rag-architecture/x.md"): two files sharing that identity across the
 * two skills would clobber on merge — the guardrail catches that and fails.
 *
 * @param {string} absorber  skill that survives and receives all references
 * @param {string} absorbed  skill that is retired; its refs move under absorber
 * @param {{ skillRefs?: Record<string,string[]>, descriptions?: Record<string,string>,
 *           categorySkill?: Record<string,string>, decided_at?: string|null,
 *           note?: string }} [ctx]
 * @returns {{ entry: object, diff: object, guardrail: object }}
 */
export function planMergeSkills(absorber, absorbed, ctx = {}) {
  if (!absorber || !absorbed || absorber === absorbed) {
    throw new Error(`planMergeSkills: cannot merge a skill into itself (${absorber} / ${absorbed})`);
  }
  const skillRefs = ctx.skillRefs ?? {};
  const descriptions = ctx.descriptions ?? {};
  const categorySkill = ctx.categorySkill ?? {};

  const aRefs = skillRefs[absorber] ?? [];
  const bRefs = skillRefs[absorbed] ?? [];
  const aSet = new Set(aRefs);

  // Collision = a references-relative path present under BOTH skills. On merge
  // the absorbed copy would overwrite the absorber copy (or vice versa): a
  // silent loss of curated content. The guardrail must surface and reject it.
  const collisions = [...new Set(bRefs.filter((r) => aSet.has(r)))].sort();

  // Post-merge identity set = union of both ref sets by references-relative path.
  const postSet = new Set([...aRefs, ...bRefs]);
  const expectedPostCount = aRefs.length + bRefs.length; // no-loss target
  const postCount = postSet.size;
  const countInvariant = postCount === expectedPostCount; // holds iff no collision
  const setEquality = [...aSet, ...new Set(bRefs)].every((r) => postSet.has(r)) && collisions.length === 0;

  const guardrail = {
    method:
      'no curated value lost: postSet = union(absorber refs, absorbed refs) by references-relative path. ' +
      'count-invariant = postCount === absorber+absorbed (fails on collision); ' +
      'set-equality = every source ref survives AND no two map to the same target.',
    preCountAbsorber: aRefs.length,
    preCountAbsorbed: bRefs.length,
    expectedPostCount,
    postCount,
    countInvariant,
    setEquality,
    collisions,
    ok: countInvariant && setEquality && collisions.length === 0,
  };

  const fileMoves = bRefs.map((r) => ({
    from: `skills/${absorbed}/references/${r}`,
    to: `skills/${absorber}/references/${r}`,
  }));

  const taxonomyReassignments = Object.keys(categorySkill)
    .filter((category) => categorySkill[category] === absorbed)
    .sort()
    .map((category) => ({ category, from: absorbed, to: absorber }));

  const diff = {
    fileMoves,
    taxonomyReassignments,
    descriptionReconciliation: {
      absorber: descriptions[absorber] ?? null,
      absorbed: descriptions[absorbed] ?? null,
      note: 'Descriptions must be reconciled manually / by judge — the planner does not auto-merge semantic scope.',
    },
    retire: absorbed,
  };

  const entry = {
    operation_type: MERGE_OPERATION,
    status: 'pending',
    decided_at: ctx.decided_at ?? null, // never Date.now() in a pure lib
    targets: { absorber, absorbed },
    guardrail,
    note:
      ctx.note ??
      `Dry-run: merge ${absorbed} -> ${absorber} (${guardrail.ok ? 'guardrail OK' : 'GUARDRAIL FAILED'}). Applies nothing.`,
  };

  return { entry, diff, guardrail };
}

// ---------------------------------------------------------------------------
// Impure shell — read-only disk load + gated ledger write
// ---------------------------------------------------------------------------

/** Recursively list references/-relative .md paths (POSIX separators) under one skill. */
function listSkillRefs(refDir) {
  const out = [];
  if (!existsSync(refDir)) return out;
  const walk = (dir) => {
    for (const e of readdirSync(dir, { withFileTypes: true })) {
      const p = join(dir, e.name);
      if (e.isDirectory()) walk(p);
      else if (e.isFile() && e.name.endsWith('.md')) out.push(relative(refDir, p).split(sep).join('/'));
    }
  };
  walk(refDir);
  return out.sort();
}

/**
 * Read-only: { skill -> [references-relative .md paths] } for every skill dir
 * that has a references/ folder.
 * @param {string} skillsDir absolute path to the skills/ root
 * @returns {Record<string,string[]>}
 */
export function loadSkillRefs(skillsDir) {
  const out = {};
  for (const e of readdirSync(skillsDir, { withFileTypes: true })) {
    if (!e.isDirectory()) continue;
    const refDir = join(skillsDir, e.name, 'references');
    if (existsSync(refDir) && statSync(refDir).isDirectory()) out[e.name] = listSkillRefs(refDir);
  }
  return out;
}

/**
 * Drive a merge dry-run against real disk: load refs read-only, plan the merge,
 * and (only with write:true) record the PENDING entry in decisions.json. Writes
 * NOTHING under skills/ — the destructive apply is a separate approved step.
 * @param {string} absorber
 * @param {string} absorbed
 * @param {{ skillsDir: string, dataDir: string, write?: boolean, decided_at?: string|null,
 *           descriptions?: Record<string,string>, categorySkill?: Record<string,string> }} opts
 * @returns {{ entry: object, diff: object, guardrail: object }}
 */
export function runMergePlan(absorber, absorbed, opts) {
  const { skillsDir, dataDir, write = false, decided_at = null, descriptions, categorySkill } = opts;
  const skillRefs = loadSkillRefs(skillsDir);
  const result = planMergeSkills(absorber, absorbed, { skillRefs, descriptions, categorySkill, decided_at });
  if (write) {
    const ledger = recordAction(loadDecisions(dataDir), result.entry);
    saveDecisions(ledger, dataDir);
  }
  return result;
}