// ── event_run_log — SQL only ───────────────────────────────────────────────
//
// EVENTS.md § Observability. "Why didn't phase 3 start?" must be a query, and
// `activity_log.detail` is TEXT and unqueryable, which is why this table exists
// beside the audit log rather than instead of it. Both are written: the audit of
// WHO published WHAT goes to `activity_log`, the diagnosis goes here.
//
// **`kind` is a closed set enforced here rather than an ENUM in the DDL.** The
// set grows with almost every later phase — conditions in Phase 5, cap draws in
// Phase 6, ledger movements in Phase 8 — and an ENUM change is a table alter
// this project has no migration system for. A constant in a file is the same
// guarantee with a cheaper hinge.

const log = require('../../utils/logger')('events')
const { query } = require('../../utils/db')
const { parseJson } = require('./eventJson')

// Phase 1's kinds. Later phases append; nothing here is ever renamed, because a
// stored row would then name a kind no reader knows.
const KINDS = [
  'run.created',      // an occurrence was materialised
  'run.status',       // a status transition, with from/to
  'phase.entered',    // a phase's steps were materialised
  'step.status',      // a step transition, with the module's answer
  'note',             // a human action taken from the admin surface
  // Phase 2's, all five of them answers to a question an operator asks out
  // loud. `run.blocked` in particular is the whole reason this table exists
  // rather than a server log line: "it did not start because run 37 holds
  // invasion:Yew" is a fact with two run ids in it, and it has to be
  // queryable from the run that did NOT start.
  'run.blocked',      // an occurrence held off: another run has its concurrency key
  'run.health',       // a health change, which is not a status change
  'step.retry',       // a step failed transiently and will be attempted again
  'step.parked',      // a step is waiting on a human and nothing is holding it
  'phase.completed',  // every step of a phase reached a terminal status
  // Phase 5's four. `condition.evaluated` is written for BOTH outcomes (§
  // Observability), and the non-matching one is the more valuable of the two on
  // the night: "the boss did spawn, in Britain" and "no boss has spawned" are
  // different answers to the same question and look identical without it.
  'phase.gate',          // a phase opened an advance gate, with what it waits for
  'condition.evaluated', // a firing was tested against a gate, matched or not
  'phase.advanced',      // a gate opened: on a firing, on its deadline, or forced
  // Phase 6's three. `step.refused` is the one worth naming separately from
  // `step.status`: a refusal is not a failure, and an operator reading a run that
  // stopped needs to see at a glance that nothing is broken -- the deployment
  // simply does not permit what the author asked for.
  'run.budget',       // the caps this run was seeded with, and which switch set each
  'step.refused',     // a step was not permitted: disabled, or over a cap
  'version.verified', // a dry run passed against a version, unlocking scheduled starts
  // Phase 8's six, and every one of them is an answer to "what did this event
  // leave behind". `resource.recorded` is written at the ANSWER rather than at
  // the placeholder, because a placeholder is a promise and the operator's
  // question is about the world.
  'resource.recorded',  // a step reported what it created or borrowed, and it is ledgered
  'resource.orphaned',  // a module reports a ledgered resource is no longer in force
  'cleanup.reverted',   // a group of resources came back
  'cleanup.failed',     // a group did not, with the reason and how it was left
  'cleanup.swept',      // one pass over a run's ledger, and what it found
  'cleanup.retry',      // a human cleared the attempt counter and asked again
]

const hydrate = (row) => row && { ...row, detail: parseJson(row.detail, null) }

const listForRun = async (runId, { limit = 500 } = {}) => {
  const n = Math.min(Math.max(Number(limit) || 500, 1), 2000)
  return (
    await query(`SELECT * FROM event_run_log WHERE run_id = ? ORDER BY at DESC, id DESC LIMIT ${n}`, [
      runId,
    ])
  ).map(hydrate)
}

/**
 * Write one line. **Never throws.**
 *
 * The diagnostic log is what an operator reads when something has already gone
 * wrong, so a failure to write it must not become a second failure on top of the
 * first — a runner that aborted a run because it could not record why would be
 * the worst possible reading of "observability". The same posture
 * `uoLinkClient.js` takes: answer, do not throw.
 */
async function write({ runId, stepId = null, kind, phase = null, detail = null }) {
  if (!KINDS.includes(kind)) {
    // A programming error, not an operational one, and it is louder than a
    // silent drop for exactly that reason.
    log.warn('event run log: unknown kind', { kind, runId })
    return false
  }
  try {
    await query(
      'INSERT INTO event_run_log (run_id, step_id, kind, phase, detail) VALUES (?, ?, ?, ?, ?)',
      [runId, stepId, kind, phase, detail === null ? null : JSON.stringify(detail)],
    )
    return true
  } catch (err) {
    log.error('event run log write failed', { runId, kind, message: err.message })
    return false
  }
}

/**
 * Delete log lines belonging to runs that are both TERMINAL and older than
 * `before`, a bounded number at a time.
 *
 * The schema comment beside `idx_evlog_at` parked this sweep here, and it is the
 * rule Engagement Phase 14 arrived at applied to a second high-cardinality table:
 * **only terminal rows are eligible.** A run still in flight keeps every line it
 * has, however old — the log's whole job is answering "why didn't phase 3 start?"
 * about a run that is, right now, not starting phase 3, and a horizon that could
 * reach a live run would delete the answer while the question was still open.
 *
 * `LIMIT` makes one call a bounded amount of work rather than a table-sized
 * transaction; the timer runs again and takes the next slice. The join is on the
 * run's terminal status rather than on a precomputed id list so that a run which
 * reached a terminal state between the two would not be missed.
 */
const pruneTerminal = async (before, limit = 5000) => {
  const n = Math.min(Math.max(Number(limit) || 5000, 1), 50_000)
  const result = await query(
    `DELETE l FROM event_run_log l
       JOIN event_runs r ON r.id = l.run_id
      WHERE r.status IN ('completed','cancelled','failed','missed')
        AND COALESCE(r.ended_at, r.updated_at) < ?
      LIMIT ${n}`,
    [before],
  )
  return Number(result?.affectedRows || 0)
}

module.exports = { KINDS, listForRun, write, pruneTerminal }