// ── Dispatching one step to one action ─────────────────────────────────────
//
// EVENTS.md §F. This is the boundary between the runner and code core did not
// write, and it exists as its own file because it has exactly one job: call
// `perform()` and turn whatever comes back — an envelope, a lie, a throw, a
// promise that never settles — into one of four classifications the runner knows
// how to act on.
//
// **§F's load-bearing rule, and the reason none of this is inlined into the
// runner: no shape a failure can take may read as success.** A rejected promise,
// a throw, a timeout, a non-object and a missing `ok` are all
// `{ ok: false, retry: true }`. That is the inverse of `registerTeamProvider`'s
// default, deliberately — a team provider that refuses leaves core showing what
// it already had, because staleness is cheap, whereas an action that half-ran and
// was recorded as `done` is a world change nothing will ever come back for.
//
// **The timeout is the module contract's, not this file's opinion.** Every action
// declares `budgetMs` at registration and the registry bounds it there; here it
// is enforced. Without it a module whose `perform()` awaits a socket that never
// answers holds a step's claim until the lease expires, and the reclaim then
// re-dispatches it — which is how one wedged sidecar becomes an infinite loop
// rather than a failed step.

const registries = require('../modules/registries')
const log = require('../utils/logger')('events')

// What a classification can be. `parked` is Phase 2's addition and it is the one
// outcome that is neither terminal nor a retry: the action succeeded, and the
// step is not finished, because something outside this system has to happen next.
const OUTCOMES = ['done', 'parked', 'retry', 'terminal']

// The upper bound on `holdFor`, in seconds. A wait is a scheduling instruction,
// not a lease, so this is generous — but it is bounded, because an action that
// answers `holdFor: 1e9` would park the phase past the heat death of the shard
// and the step that did it would look, in the console, exactly like one that
// worked.
const MAX_HOLD_SECONDS = 7 * 24 * 60 * 60

// The upper bound on a module's `detail`, in bytes of serialised JSON. It lands
// in `event_run_log.detail` and is read back by the run console, so it is a
// diagnostic line rather than a data channel — a module with more to say than
// this has a table of its own to say it in. Dropped rather than truncated when it
// is over: a truncated JSON object is not a JSON object, and a console that
// rendered half of one would be a second bug on top of the first.
const MAX_DETAIL_BYTES = 4096

/**
 * A module's own account of what a successful step actually did.
 *
 * Optional, module-opaque, and **never interpreted by core** — it is carried to
 * the run log and rendered, and nothing here or in the runner reads a key out of
 * it. That is the whole contract: a module knows things about its own verb that
 * core cannot compute and has no other way to say. `uo.item.grant` is the case
 * that forced it — a grant reaches the players a run's ledger holds, and *which
 * of them missed out* is knowable only to the module and reported nowhere else,
 * so an operator saw a step marked `done` and never learned four of twelve got
 * nothing.
 *
 * **Anything wrong with it is dropped and logged, never a failure.** A step that
 * did what it was asked must not be re-run because its module's commentary was
 * malformed — that would be a world write repeated for a log line. Same posture
 * `participants` takes, and for the same reason.
 */
function safeDetail(detail, actionId) {
  if (detail === undefined || detail === null) return null

  // Objects only. The column is JSON and the console renders keys, so a bare
  // string or a number has nothing to render under — and core inventing a key to
  // put it beneath would be core interpreting it after all.
  if (typeof detail !== 'object' || Array.isArray(detail)) {
    log.warn('action detail is not an object', { action: actionId, type: typeof detail })
    return null
  }

  let encoded
  try {
    encoded = JSON.stringify(detail)
  } catch (err) {
    // A circular reference, or a `toJSON` that throws. Reaching the runner would
    // make the INSERT throw instead, inside the one write that is documented
    // never to.
    log.warn('action detail could not be serialised', { action: actionId, message: err.message })
    return null
  }
  if (encoded === undefined) {
    log.warn('action detail serialised to nothing', { action: actionId })
    return null
  }
  if (Buffer.byteLength(encoded, 'utf8') > MAX_DETAIL_BYTES) {
    log.warn('action detail is too large', {
      action: actionId,
      bytes: Buffer.byteLength(encoded, 'utf8'),
      max: MAX_DETAIL_BYTES,
    })
    return null
  }

  // Re-parsed rather than passed through, so what the runner writes is a plain
  // JSON value with no getters, no prototype and no live reference into whatever
  // the module still holds.
  return JSON.parse(encoded)
}

/**
 * Run `fn()` under a deadline.
 *
 * The loser of the race is not cancelled — JavaScript has no such thing, and a
 * `perform()` still awaiting a socket keeps awaiting it. What the deadline buys
 * is that the RUNNER stops waiting, which is the half that matters: the step is
 * classified, the claim is released, and the tick moves on. A late answer from
 * the abandoned call lands on a step that has already been written, and the
 * idempotency key is what makes the retry that follows safe on the game side.
 */
function withDeadline(fn, ms, actionId) {
  let timer = null
  const deadline = new Promise((resolve) => {
    timer = setTimeout(
      () => resolve({ __timedOut: true, error: `${actionId} exceeded its ${ms}ms budget` }),
      ms,
    )
    if (timer.unref) timer.unref()
  })
  return Promise.race([Promise.resolve().then(fn), deadline]).finally(() => {
    if (timer) clearTimeout(timer)
  })
}

/**
 * Turn a raw `perform()` answer into
 * `{ outcome, error?, holdSeconds?, resources?, participants? }`.
 *
 * Exported and pure, so the classification rules are testable without a registry,
 * a database or a clock — which matters because they are the rules that decide
 * whether a world change is recorded as having happened.
 */
function classify(result, actionId) {
  if (result && result.__timedOut) {
    // Transient by default: a timeout says nothing about whether the action ran.
    // That ambiguity is exactly what the idempotency key exists to resolve, and
    // resolving it on the game side is Phase 11's protocol work — until then a
    // retry is the honest choice and the risk class decides what happens when the
    // retries run out.
    return { outcome: 'retry', error: result.error }
  }
  if (result === null || typeof result !== 'object' || Array.isArray(result)) {
    return { outcome: 'retry', error: `${actionId} answered with no envelope` }
  }
  if (result.ok !== true) {
    // `retry` must be opted into. An action that means "this will never work"
    // says `retry: false`, and an envelope that forgot to say anything gets the
    // benefit of the doubt on the transient question but not on the success one.
    const retry = result.retry !== false
    return {
      outcome: retry ? 'retry' : 'terminal',
      error: result.error ? String(result.error) : `${actionId} refused`,
    }
  }

  // ── The two success shapes that are not "finished" ──
  //
  // Both were settled by the org lead on 2026-09-02, and both are envelope
  // members rather than special cases keyed on an action id, so that the runner
  // never names a verb. `core.cue` and `core.wait` reach them through the same
  // door Phase 7 opens to a module's own long-running action.
  if (result.await === 'human') {
    return {
      outcome: 'parked',
      error: null,
      resources: result.resources || [],
      participants: result.participants || [],
      detail: safeDetail(result.detail, actionId),
    }
  }

  let holdSeconds = 0
  if (result.holdFor !== undefined && result.holdFor !== null) {
    const n = Number(result.holdFor)
    if (!Number.isFinite(n) || n < 0) {
      return { outcome: 'terminal', error: `${actionId} answered a bad holdFor "${result.holdFor}"` }
    }
    holdSeconds = Math.min(Math.floor(n), MAX_HOLD_SECONDS)
  }

  // `participants` rides beside `resources` and on the same two success shapes
  // (Phase 10). It is carried rather than interpreted here: what a member key
  // means is the module's business, and this file's whole job is to know
  // nothing about the verb it just called.
  return {
    outcome: 'done',
    error: null,
    holdSeconds,
    resources: result.resources || [],
    participants: result.participants || [],
    // On the same two success shapes as `resources` and `participants`, and for
    // the same reason: `await: 'human'` is a success, and a cue's confirm
    // finishes the step without a second dispatch, so this is the only moment
    // its module could ever have said anything.
    detail: safeDetail(result.detail, actionId),
  }
}

/**
 * Dispatch one step. Never throws.
 *
 * `verify` rides through to `perform()` unchanged (§I's dry run, Phase 6's
 * route): `verify === true` means validate and report, change nothing. It is
 * passed from here rather than being a separate code path so that the dry run
 * exercises the real dispatcher — a dry run down a second path is a dry run of
 * the second path.
 */
async function dispatchStep(step, { run, actor = null, verify = false } = {}) {
  const action = registries.eventAction(step.action_id)
  if (!action) {
    // §L, verbatim: "a step naming one fails terminal with the module named, and
    // the run degrades rather than claiming success. Never a silent skip." The
    // module was uninstalled or failed to boot between publish and now — publish
    // refuses a dormant step, so this cannot be an authoring mistake.
    return { outcome: 'terminal', error: `no module registers "${step.action_id}"`, dormant: true }
  }

  const envelope = {
    runId: run.id,
    stepId: step.id,
    idempotencyKey: step.idempotency_key,
    scope: run.scope || '',
    params: step.params || {},
    actor,
    verify: Boolean(verify),
  }

  let raw
  try {
    raw = await withDeadline(() => action.perform(envelope), action.budgetMs, action.id)
  } catch (err) {
    // A module should not throw, and if one does it is a transient failure rather
    // than a crashed tick — announceWorker's posture with its legs, and the
    // reason one bad module cannot stop every other run on the deployment.
    log.warn('event action threw', { action: action.id, run: run.id, step: step.id, message: err.message })
    return { outcome: 'retry', error: err.message }
  }

  const classification = classify(raw, action.id)
  if (step.action_version && action.version !== step.action_version) {
    // Not a refusal: the step was authored against an older declaration and the
    // module has moved on. The editor is where that becomes a warning (§F); here
    // it is recorded, so a run that behaved oddly can be explained afterwards by
    // reading the log rather than by guessing.
    classification.actionVersionDrift = { authored: step.action_version, registered: action.version }
  }
  return classification
}

module.exports = { dispatchStep, classify, withDeadline, safeDetail, OUTCOMES, MAX_HOLD_SECONDS, MAX_DETAIL_BYTES }