// lib/util/research-loop-cap.mjs
// Stateful, default-off cost cap for the /trekresearch bounded conversation
// loop (Phase 4.5 dimension discovery + Phase 5 loop turns).
//
// Three properties the plan review required:
//   (a) Default-off — VOYAGE_STORM_ENABLED must be '1'; otherwise the budget
//       is 0 regardless of effort. This IS the decline branch: doing nothing
//       leaves the mechanism off, and adopt is flipping this one constant.
//   (b) The cap counts itself — allowTurn() derives used-turn count from an
//       append-only JSONL ledger, never from a caller-supplied number. A cap
//       that asks the caller how many turns it has used is not a cap. Each
//       grant additionally claims a turn SLOT with O_EXCL, so the bound holds
//       when several callers decide at once instead of only when they queue.
//   (c) Correct size bound — worst case is max_conv_turns × max_total_dimensions,
//       where max_total_dimensions is the WHOLE list (interview + discovered)
//       under settings.json:16's cap of 8 — not × discovered-only.
//
// CLAUDE_PLUGIN_DATA absent => fall back to ~/.claude/voyage. The variable is
// EMPTY in the Bash tool's process env (measured in a live plugin-enabled
// session), and the Phase 5 bash snippet is this module's only caller — so
// denying on its absence denied turn 1 of every real run. The root is resolved
// in code rather than demanded of the environment, and hooks/scripts/
// pre-agent-cap.mjs resolves it through the SAME function, so the writer and
// the reader can never disagree about where the ledger lives.
//
// The fail-closed stance covers both directions of ledger IO: a ledger that
// cannot be WRITTEN denies the turn, and a ledger that exists but cannot be
// READ denies it too. Only ENOENT counts as zero turns spent, because that is
// the legitimate first-turn state. This module is a budget control, not
// telemetry — the opposite of lib/stats/event-emit.mjs's fail-open.
//
// CLI shim, two modes:
//   node lib/util/research-loop-cap.mjs --run-id ID --dimension D --effort E
//   → JSON: { ok, used, budget, reason? }   (exit 0 = granted, exit 1 = denied)
//
//   node lib/util/research-loop-cap.mjs --check-dimensions N
//   → JSON: { ok, count, ceiling, reason? } (exit 0 = within, exit 1 = rejected)
//   The second axis of the bounded-cost NFR. Phase 4.5 never calls the budget
//   gate, so this mode requires no run id, effort or STORM flag — but it reads
//   the SAME MAX_TOTAL_DIMENSIONS the budget is sized against.

import { existsSync, mkdirSync, appendFileSync, readFileSync, writeFileSync } from 'node:fs';
import { dirname, join } from 'node:path';
import { homedir } from 'node:os';

export const MAX_CONV_TURNS = 3;
export const MAX_TOTAL_DIMENSIONS = 8; // settings.json:16 maxDimensions — whole list, not discovered-only

const LEDGER_FILENAME = 'trekresearch-loop-ledger.jsonl';
const CLAIM_DIRNAME = 'trekresearch-loop-claims';

export function isStormEnabled(env = process.env) {
  return env.VOYAGE_STORM_ENABLED === '1';
}

/**
 * The OTHER cost ceiling: how large the whole dimension list may get after
 * Phase 4.5 discovery has appended to it.
 *
 * The bounded-cost NFR asks for explicit ceilings on both axes. The turn axis
 * had a constant, a ledger-backed reader and a PreToolUse enforcer; the
 * discovery axis had only a sentence in Phase 4.5 prose — a cap nothing reads,
 * which is the failure mode the operator decision on brief_reviewer_iter_cap
 * warned about. This is the reader.
 *
 * The ceiling is MAX_TOTAL_DIMENSIONS on purpose: the value that sizes the turn
 * budget IS settings.json:16's maxDimensions, and a second constant for the same
 * number is how two readers end up enforcing different bounds.
 *
 * Accepts the dimension list or its count, because Phase 4.5 has the list and
 * the CLI has a number. A count that cannot be read is REJECTED — a cost ceiling
 * that waves through what it cannot measure is not a ceiling.
 *
 * @param {string[]|number|string} dimensions
 * @param {{ceiling?: number}} [opts]
 * @returns {{ok: boolean, count: number|null, ceiling: number, reason?: string}}
 */
export function checkDimensionCeiling(dimensions, opts = {}) {
  const ceiling = Number.isFinite(opts.ceiling) ? opts.ceiling : MAX_TOTAL_DIMENSIONS;
  const count = Array.isArray(dimensions) ? dimensions.length : Number(dimensions);
  if (dimensions === null || dimensions === undefined || !Number.isInteger(count) || count < 0) {
    return { ok: false, count: null, ceiling, reason: 'unreadable_dimension_count' };
  }
  if (count > ceiling) {
    return { ok: false, count, ceiling, reason: 'ceiling_exceeded' };
  }
  return { ok: true, count, ceiling };
}

/**
 * Coerce TREKRESEARCH_MAX_CONV_TURNS. NaN, empty, negative, zero, Infinity, or
 * any fraction that floors below 1 all fall back to MAX_CONV_TURNS — never to
 * unbounded, and never to 0.
 *
 * The floor is applied BEFORE the `<= 0` guard, not after. Flooring afterwards
 * let '0.5' and '0.9' clear a guard written against the raw value and then
 * become 0, making the budget 0 × MAX_TOTAL_DIMENSIONS = 0: every turn denied
 * and the loop silently dead rather than bounded. A cap of 0 is not a narrower
 * cap, it is an off switch that the documented fallback promises not to be.
 */
export function resolveMaxConvTurns(env = process.env) {
  const raw = env.TREKRESEARCH_MAX_CONV_TURNS;
  if (raw === undefined || raw === null || raw === '') return MAX_CONV_TURNS;
  const n = Math.floor(Number(raw));
  if (!Number.isFinite(n) || n <= 0) return MAX_CONV_TURNS;
  return n;
}

/**
 * The one data root for everything this loop writes: the turn ledger and the
 * PreToolUse scope marker. CLAUDE_PLUGIN_DATA when the harness provides it,
 * ~/.claude/voyage when it does not — which is the case in every Bash tool
 * invocation today.
 */
export function resolveDataRoot(env = process.env) {
  const dir = env.CLAUDE_PLUGIN_DATA;
  if (dir && typeof dir === 'string' && dir.length > 0) return dir;
  const home = env.HOME && env.HOME.length > 0 ? env.HOME : homedir();
  return join(home, '.claude', 'voyage');
}

export function resolveLedgerPath(env = process.env) {
  return join(resolveDataRoot(env), LEDGER_FILENAME);
}

/**
 * Where the per-turn claim files live. A claim is the ATOMIC record that a turn
 * slot is taken; the ledger is the readable record of what that turn was for.
 *
 * The claim exists because the ledger alone cannot bound the loop. Counting the
 * ledger and then appending is read-then-write: N callers that all observe
 * `used == budget - 1` all decide to grant, and the bound is exceeded by N-1 —
 * precisely the concurrent case (several agents spawned in one message) that
 * allowTurn's own comment named as the reason it had to be append-only.
 *
 * Claim files are empty, at most `budget` per run, and never cleaned up — the
 * same standing as the ledger itself, which also grows for the life of the data
 * root. Two consequences worth stating rather than discovering: reusing a
 * runId across runs finds its slots already taken and denies, and two runIds
 * that collide after filename sanitisation block each other. Both err toward
 * denying a turn, which is the safe direction for a budget control.
 */
export function resolveClaimDir(env = process.env) {
  return join(resolveDataRoot(env), CLAIM_DIRNAME);
}

function claimFileName(runId, slot) {
  return `${String(runId).replace(/[^A-Za-z0-9._-]/g, '_')}-${slot}.claim`;
}

/**
 * Try to take turn slot `slot` for `runId`. `wx` is O_CREAT|O_EXCL: the kernel
 * decides the winner, so exactly one caller can ever create a given slot file.
 *
 * @returns {boolean} true when this caller took the slot, false when it was already taken
 * @throws on any IO error other than EEXIST — the caller turns that into a denial
 */
function claimSlot(claimDir, runId, slot) {
  try {
    writeFileSync(join(claimDir, claimFileName(runId, slot)), '', { flag: 'wx' });
    return true;
  } catch (e) {
    if (e && e.code === 'EEXIST') return false;
    throw e;
  }
}

/**
 * Read one run's turn count off the append-only ledger.
 *
 * ENOENT is 0 turns spent — the legitimate first-turn state, and the reason
 * this cannot simply throw on every read failure. Every OTHER read error
 * (EISDIR, EACCES, EIO) THROWS, because returning 0 from an unreadable ledger
 * re-granted the full budget on every call: unbounded, and the exact
 * silently-grant-unlimited failure this module's header argues against three
 * lines above the code that did it. The missing-directory case already failed
 * closed; this makes the unreadable-file case agree with it.
 *
 * The `existsSync` pre-check is deliberately gone: readFileSync's own ENOENT
 * carries the same information without a second syscall that can disagree with
 * the read that follows it.
 *
 * Exported so hooks/scripts/pre-agent-cap.mjs counts through this exact
 * function. A reader and a writer with private copies of the counting rule are
 * how a hook ends up enforcing a different bound than the gate it backs.
 *
 * Two counts, deliberately separate. `granted` is turns handed out. `exhausted`
 * is tombstones — records this gate wrote when it DENIED a turn. A tombstone is
 * not a turn and must never consume budget; it exists so the PreToolUse hook can
 * tell "turn B is in flight" (granted == budget, no tombstone) apart from "the
 * gate already said no and something kept going" (tombstone present).
 *
 * @param {string} ledgerPath
 * @param {string} runId
 * @returns {{granted: number, exhausted: number}}
 * @throws when the ledger exists but cannot be read
 */
export function readLedger(ledgerPath, runId) {
  let text;
  try {
    text = readFileSync(ledgerPath, 'utf-8');
  } catch (e) {
    if (e && e.code === 'ENOENT') return { granted: 0, exhausted: 0 };
    const err = new Error(`ledger unreadable at ${ledgerPath}: ${e.message}`);
    err.code = 'VOYAGE_LEDGER_UNREADABLE';
    throw err;
  }
  let granted = 0;
  let exhausted = 0;
  for (const line of text.split('\n')) {
    if (!line) continue;
    try {
      const rec = JSON.parse(line);
      if (rec.runId !== runId) continue;
      if (rec.exhausted === true) exhausted++;
      else granted++;
    } catch { /* skip malformed lines */ }
  }
  return { granted, exhausted };
}

/**
 * Record that this run has been denied a turn for budget.
 *
 * Best effort on purpose: the denial itself is already the correct answer, so a
 * ledger that cannot take the tombstone must not turn a denial into a grant. The
 * tombstone only strengthens the harness-level backstop.
 */
function markExhausted(ledgerPath, runId, now) {
  try {
    appendFileSync(ledgerPath, JSON.stringify({ ts: now.toISOString(), runId, exhausted: true }) + '\n');
  } catch { /* best effort — see above */ }
}

/**
 * Decide whether one more research-loop turn may run.
 *
 * Phase 4.5/5 may spawn several agents in a single message, so the decision has
 * to survive concurrent callers. It does that by CLAIMING a turn slot with
 * O_EXCL (see claimSlot) and only then appending to the ledger. The comment
 * that used to sit here asserted "append-only: never read-modify-write" as if
 * appending were itself the concurrency guarantee — but the decision path was
 * count-then-append, which is read-then-write, so the claim was unsupported by
 * the code beneath it. The kernel now picks the winner for each slot.
 *
 * @param {{runId: string, dimension: string, effort: string}} args
 * @param {{env?: object, now?: Date}} [opts]
 * @returns {{ok: boolean, used: number, budget: number, reason?: string}}
 */
export function allowTurn({ runId, dimension, effort } = {}, opts = {}) {
  const env = opts.env || process.env;
  const now = opts.now || new Date();

  if (!isStormEnabled(env)) {
    return { ok: false, used: 0, budget: 0, reason: 'storm_disabled' };
  }
  if (effort !== 'high') {
    return { ok: false, used: 0, budget: 0, reason: 'effort_not_high' };
  }
  if (!runId || !dimension) {
    return { ok: false, used: 0, budget: 0, reason: 'missing_args' };
  }

  const maxConvTurns = resolveMaxConvTurns(env);
  const budget = maxConvTurns * MAX_TOTAL_DIMENSIONS;

  const ledgerPath = resolveLedgerPath(env);
  let ledger;
  try {
    ledger = readLedger(ledgerPath, runId);
  } catch (e) {
    return { ok: false, used: 0, budget, reason: `ledger-read-failed: ${e.message}` };
  }
  const used = ledger.granted;

  // Already tombstoned: this run is over. Short-circuit so a hammered gate
  // neither walks every slot again nor appends a second tombstone.
  if (ledger.exhausted > 0) {
    return { ok: false, used, budget, reason: 'budget_exhausted' };
  }
  // Claim a turn SLOT before spending anything. The ledger count only says
  // where to start looking; the claim is what makes the grant exclusive. Slot
  // numbers are bounded by `budget`, and each can be created exactly once, so
  // the total number of grants for a run can never exceed the budget however
  // many callers arrive at once.
  const claimDir = resolveClaimDir(env);
  let slot = used + 1;
  let claimed = false;
  try {
    mkdirSync(claimDir, { recursive: true });
    while (slot <= budget) {
      if (claimSlot(claimDir, runId, slot)) { claimed = true; break; }
      slot++;
    }
  } catch (e) {
    return { ok: false, used, budget, reason: `claim-failed: ${e.message}` };
  }
  if (!claimed) {
    markExhausted(ledgerPath, runId, now);
    return { ok: false, used, budget, reason: 'budget_exhausted' };
  }

  try {
    const dir = dirname(ledgerPath);
    if (!existsSync(dir)) mkdirSync(dir, { recursive: true });
    appendFileSync(ledgerPath, JSON.stringify({ ts: now.toISOString(), runId, dimension, effort, slot }) + '\n');
  } catch (e) {
    return { ok: false, used, budget, reason: `ledger-write-failed: ${e.message}` };
  }

  return { ok: true, used: slot, budget };
}

// ---- CLI shim ----------------------------------------------------------------

function parseArgs(argv) {
  const out = {};
  for (let i = 0; i < argv.length; i++) {
    const a = argv[i];
    if (a === '--run-id') out.runId = argv[++i];
    else if (a === '--dimension') out.dimension = argv[++i];
    else if (a === '--effort') out.effort = argv[++i];
    else if (a === '--check-dimensions') out.checkDimensions = argv[++i];
  }
  return out;
}

if (import.meta.url === `file://${process.argv[1]}`) {
  const args = parseArgs(process.argv.slice(2));

  // The dimension ceiling is a Phase 4.5 concern, and Phase 4.5 never calls the
  // budget gate — so this branch must not inherit the gate's preconditions
  // (run id, effort, STORM flag). It is a pure bound on list size.
  if (args.checkDimensions !== undefined) {
    const result = checkDimensionCeiling(args.checkDimensions);
    process.stdout.write(JSON.stringify(result) + '\n');
    process.exit(result.ok ? 0 : 1);
  }

  if (!args.runId || !args.dimension || !args.effort) {
    process.stdout.write(JSON.stringify({
      ok: false,
      reason: 'usage: research-loop-cap.mjs --run-id ID --dimension D --effort standard|high|low',
    }) + '\n');
    process.exit(1);
  }
  const result = allowTurn(args);
  process.stdout.write(JSON.stringify(result) + '\n');
  process.exit(result.ok ? 0 : 1);
}