/**
 * 任务状态机：平台强制的规则只在这里写一遍。
 *
 * `transition()` 是纯函数：只返回新任务与要做的副作用（持有记录、托管动作、事件、job），
 * 由 service 在锁住任务行的同一个事务里执行。它不读库、不读时钟。
 *
 * 不在这里判的规则（需要读其它表，由 service 在同一事务里保证）：
 * 重复报名（vk_task_entries UNIQUE）、转让请求是否 pending 且指向 actor、验收 checks 与清单的覆盖关系。
 */

import { rarityForReward } from './rarity.js'
import { TASK_STATUSES } from './task.js'

/** 除发布（新建，见 `publishStatus`）外的全部动作。 */
export const TASK_ACTIONS = Object.freeze([
  'approve',
  'reject_approval',
  'claim',
  'enter',
  'cancel',
  'open_expire',
  'edit',
  'checkpoint',
  'checkpoint_miss',
  'release',
  'hold_timeout',
  'transfer_accept',
  'submit',
  'accept',
  'reject',
  'review_auto_accept',
  'contest_close',
  'select_winner',
  'dispute',
  'resolve',
])

/** 每个 Agent 同时持有的计件活上限。 */
export const MAX_ACTIVE_HOLDS = 3

const HOUR_MS = 3600_000

/**
 * @typedef {import('./task.js').Task} Task
 *
 * @typedef {{
 *   task: Task,
 *   guild: { checkpoint_interval_sec: number, piece_review_window_sec: number, contest_review_window_sec: number },
 *   publisher_owner_user_id: string,
 *   entry_count: number,
 * }} TaskState 任务行 + 所属公会的时间规则 + 发布方 Agent 的主人 + 擂台赛当前报名数，由 service 在事务内读出。
 *
 * @typedef {{ kind: 'agent', agent_id: string, owner_user_id: string, max_rarity: number, active_hold_count: number, is_entrant: boolean }} AgentActor
 * @typedef {AgentActor | { kind: 'lead', user_id: string } | { kind: 'operator', user_id: string } | { kind: 'worker' }} Actor
 *
 * @typedef {(
 *   { type: 'approve' } | { type: 'reject_approval' } | { type: 'claim' } | { type: 'enter' } | { type: 'cancel' } |
 *   { type: 'open_expire' } | { type: 'edit', add_reward: number, deadline_at: Date|null } | { type: 'checkpoint' } |
 *   { type: 'checkpoint_miss' } | { type: 'release' } | { type: 'hold_timeout' } | { type: 'transfer_accept' } |
 *   { type: 'submit' } | { type: 'accept' } | { type: 'reject' } | { type: 'review_auto_accept', winner_agent_id: string|null } |
 *   { type: 'contest_close' } | { type: 'select_winner', winner_agent_id: string } | { type: 'dispute' } |
 *   { type: 'resolve', outcome: 'settled'|'refunded', winner_agent_id: string|null }
 * )} Action
 *
 * @typedef {(
 *   { type: 'hold_start', agent_id: string } |
 *   { type: 'hold_end', reason: 'submitted'|'released'|'timeout'|'transferred' } |
 *   { type: 'hold_checkpoint' } |
 *   { type: 'entry_add', agent_id: string } |
 *   { type: 'entry_remove', agent_id: string } |
 *   { type: 'dispute_close', agent_id: string } |
 *   { type: 'escrow_topup', amount: number } |
 *   { type: 'escrow_refund' } |
 *   { type: 'escrow_settle', winner_agent_id: string } |
 *   { type: 'dispute_open', opened_by_agent_id: string } |
 *   { type: 'event', event_type: string, target_agent_id: string|null } |
 *   { type: 'job', kind: string, run_at: Date }
 * )} Effect `event.target_agent_id` 为 null 表示发给整个公会。
 *
 * @typedef {{ ok: true, task: Task, effects: Effect[] } | { ok: false, code: 'state_conflict'|'rule_violation'|'forbidden', hint: string }} TransitionResult
 */

/**
 * 发布时的初始状态：公会开启发布前审核且发布方是公司 Agent 时先进待审核。
 * @param {{ require_lead_approval: boolean, publisher_role: 'company'|'member' }} input
 * @returns {'open'|'pending_approval'}
 */
export function publishStatus({ require_lead_approval, publisher_role }) {
  switch (publisher_role) {
    case 'company':
      return require_lead_approval ? 'pending_approval' : 'open'
    case 'member':
      return 'open'
    default:
      throw new Error(`Unhandled publisher role: ${publisher_role}`)
  }
}

/**
 * @param {TaskState} state
 * @param {Action} action
 * @param {Actor} actor
 * @param {Date} now
 * @returns {TransitionResult}
 */
export function transition(state, action, actor, now) {
  const { task } = state
  if (!TASK_ACTIONS.includes(action.type)) throw new Error(`Unhandled action: ${action.type}, id: ${task.id}`)
  const handlers = TRANSITIONS[task.status]
  if (handlers === undefined) throw new Error(`Unhandled status: ${task.status}, id: ${task.id}`)
  const handler = handlers[action.type]
  if (handler === undefined) return fail('state_conflict', `Task is ${task.status}; ${action.type} is not allowed. Re-fetch the task.`)
  return handler(state, /** @type {any} */ (action), actor, now)
}

/** @typedef {(state: TaskState, action: any, actor: Actor, now: Date) => TransitionResult} Handler */

/** @type {Record<import('./task.js').TaskStatus, Partial<Record<Action['type'], Handler>>>} */
const TRANSITIONS = {
  pending_approval: {
    approve({ task }, _action, actor) {
      if (actor.kind !== 'lead') return notAllowed('Only the guild lead can approve.')
      return ok({ ...task, status: 'open' }, [event('task.published', null), ...openJobs(task)])
    },
    reject_approval({ task }, _action, actor) {
      if (actor.kind !== 'lead') return notAllowed('Only the guild lead can reject.')
      return ok({ ...task, status: 'cancelled' }, [{ type: 'escrow_refund' }])
    },
  },

  open: {
    claim(state, _action, actor, now) {
      const { task } = state
      if (task.template !== 'piecework') return fail('rule_violation', 'This task is a contest; use enter.')
      const refused = takerRefusal(state, actor)
      if (refused !== null) return refused
      const taker = /** @type {AgentActor} */ (actor)
      if (taker.active_hold_count >= MAX_ACTIVE_HOLDS) return fail('state_conflict', `You already hold ${MAX_ACTIVE_HOLDS} piecework tasks.`)
      return ok(hold(state, taker.agent_id, now), [
        { type: 'hold_start', agent_id: taker.agent_id },
        event('task.claimed', task.publisher_agent_id),
        ...checkpointJobs(state, now),
        job('hold_timeout', task.deadline_at),
      ])
    },
    enter(state, _action, actor) {
      const { task } = state
      if (task.template !== 'contest') return fail('rule_violation', 'This task is piecework; use claim.')
      const refused = takerRefusal(state, actor)
      if (refused !== null) return refused
      return ok({ ...task, status: 'in_contest' }, [{ type: 'entry_add', agent_id: /** @type {AgentActor} */ (actor).agent_id }])
    },
    cancel({ task }, _action, actor) {
      if (!isPublisher(task, actor)) return notAllowed('Only the publisher can cancel.')
      return ok({ ...task, status: 'cancelled' }, [{ type: 'escrow_refund' }])
    },
    open_expire({ task }, _action, actor, now) {
      if (actor.kind !== 'worker') return notAllowed('Only the platform can expire a task.')
      if (now < task.deadline_at) return fail('state_conflict', 'Deadline has not passed.')
      return ok({ ...task, status: 'cancelled' }, [{ type: 'escrow_refund' }])
    },
    edit({ task }, action, actor) {
      if (!isPublisher(task, actor)) return notAllowed('Only the publisher can edit.')
      if (!Number.isSafeInteger(action.add_reward) || action.add_reward < 0) throw new Error(`edit.add_reward invalid: ${action.add_reward}, id: ${task.id}`)
      if (action.add_reward === 0 && action.deadline_at === null) return fail('rule_violation', 'Nothing to change: add reward or extend the deadline.')
      if (action.deadline_at !== null && action.deadline_at <= task.deadline_at) return fail('rule_violation', 'The deadline can only be extended.')
      const reward = task.reward + action.add_reward
      const next = { ...task, reward, rarity: rarityForReward(reward), deadline_at: action.deadline_at === null ? task.deadline_at : action.deadline_at }
      return ok(next, [
        ...(action.add_reward === 0 ? [] : [/** @type {Effect} */ ({ type: 'escrow_topup', amount: action.add_reward })]),
        ...(action.deadline_at === null ? [] : openJobs(next)),
      ])
    },
  },

  claimed: {
    checkpoint(state, _action, actor, now) {
      if (!isHolder(state.task, actor)) return notAllowed('Only the current holder can post a checkpoint.')
      return ok({ ...state.task, next_checkpoint_due_at: checkpointDue(state, now), missed_checkpoints: 0 }, [
        { type: 'hold_checkpoint' },
        event('task.checkpoint', null),
        ...checkpointJobs(state, now),
      ])
    },
    checkpoint_miss(state, _action, actor, now) {
      const { task } = state
      if (actor.kind !== 'worker') return notAllowed('Only the platform can record a missed checkpoint.')
      const due = /** @type {Date} */ (task.next_checkpoint_due_at)
      if (now < due) return fail('state_conflict', 'Checkpoint is not overdue.')
      if (task.missed_checkpoints >= 1) return released(task, 'timeout', now)
      // 第一次缺失只告警：从原到期时刻顺延一个间隔。
      return ok({ ...task, next_checkpoint_due_at: checkpointDue(state, due), missed_checkpoints: 1 }, checkpointJobs(state, due))
    },
    release({ task }, _action, actor, now) {
      if (!isHolder(task, actor)) return notAllowed('Only the current holder can release.')
      return released(task, 'released', now)
    },
    hold_timeout({ task }, _action, actor, now) {
      if (actor.kind !== 'worker') return notAllowed('Only the platform can time out a hold.')
      if (now < task.deadline_at) return fail('state_conflict', 'Deadline has not passed.')
      return released(task, 'timeout', now)
    },
    transfer_accept(state, _action, actor, now) {
      const refused = takerRefusal(state, actor)
      if (refused !== null) return refused
      const taker = /** @type {AgentActor} */ (actor)
      if (taker.agent_id === state.task.holder_agent_id) return fail('state_conflict', 'You already hold this task.')
      if (taker.active_hold_count >= MAX_ACTIVE_HOLDS) return fail('state_conflict', `You already hold ${MAX_ACTIVE_HOLDS} piecework tasks.`)
      return ok(hold(state, taker.agent_id, now), [
        { type: 'hold_end', reason: 'transferred' },
        { type: 'hold_start', agent_id: taker.agent_id },
        ...checkpointJobs(state, now),
      ])
    },
    submit(state, _action, actor, now) {
      if (!isHolder(state.task, actor)) return notAllowed('Only the current holder can submit.')
      return ok(...submitted(state, now, [{ type: 'hold_end', reason: 'submitted' }]))
    },
  },

  in_contest: {
    enter(state, _action, actor) {
      const refused = takerRefusal(state, actor)
      if (refused !== null) return refused
      if (/** @type {AgentActor} */ (actor).is_entrant) return fail('state_conflict', 'You have already entered this contest.')
      return ok(state.task, [{ type: 'entry_add', agent_id: /** @type {AgentActor} */ (actor).agent_id }])
    },
    submit({ task }, _action, actor) {
      if (actor.kind !== 'agent' || !actor.is_entrant) return notAllowed('Enter the contest before submitting.')
      // 提交封存到截止，不通知发布方。
      return ok(task, [])
    },
    // 参赛者退赛：撤掉自己的报名与提交；最后一个人退出后任务回到 open。
    release({ task, entry_count }, _action, actor) {
      if (actor.kind !== 'agent' || !actor.is_entrant) return notAllowed('Only an entrant can withdraw from a contest.')
      return ok(entry_count <= 1 ? { ...task, status: 'open' } : task, [{ type: 'entry_remove', agent_id: actor.agent_id }])
    },
    contest_close(state, _action, actor, now) {
      const { task } = state
      if (actor.kind !== 'worker') return notAllowed('Only the platform can close a contest.')
      if (now < task.deadline_at) return fail('state_conflict', 'Deadline has not passed.')
      const reviewDue = new Date(now.getTime() + state.guild.contest_review_window_sec * 1000)
      return ok({ ...task, status: 'reviewing', review_due_at: reviewDue }, [event('task.submitted', task.publisher_agent_id), ...reviewJobs(reviewDue)])
    },
  },

  submitted: {
    accept({ task }, _action, actor, now) {
      if (!isPublisher(task, actor)) return notAllowed('Only the publisher can review.')
      const holder = /** @type {string} */ (task.holder_agent_id)
      return ok(settle(task, now), [{ type: 'escrow_settle', winner_agent_id: holder }, event('task.accepted', holder)])
    },
    review_auto_accept({ task }, _action, actor, now) {
      if (actor.kind !== 'worker') return notAllowed('Only the platform can auto-accept.')
      if (now < /** @type {Date} */ (task.review_due_at)) return fail('state_conflict', 'Review window has not expired.')
      const holder = /** @type {string} */ (task.holder_agent_id)
      return ok(settle(task, now), [
        { type: 'escrow_settle', winner_agent_id: holder },
        event('task.auto_accepted', task.publisher_agent_id),
        event('task.auto_accepted', holder),
      ])
    },
    reject({ task }, _action, actor, now) {
      if (!isPublisher(task, actor) || actor.kind !== 'agent') return notAllowed('Only the publisher can review.')
      const holder = /** @type {string} */ (task.holder_agent_id)
      // 第 3 次驳回直接进仲裁。
      if (task.rework_count >= 2) return ok({ ...task, status: 'disputed' }, disputeEffects(actor.agent_id, now))
      return ok({ ...task, status: 'rework', rework_count: task.rework_count + 1, review_due_at: null }, [event('task.rejected', holder)])
    },
    dispute: openDispute,
    release: holderRelease,
  },

  reviewing: {
    select_winner({ task }, action, actor, now) {
      if (!isPublisher(task, actor)) return notAllowed('Only the publisher can select a winner.')
      return ok(settle(task, now), [{ type: 'escrow_settle', winner_agent_id: action.winner_agent_id }, event('task.accepted', action.winner_agent_id)])
    },
    review_auto_accept({ task }, action, actor, now) {
      if (actor.kind !== 'worker') return notAllowed('Only the platform can auto-accept.')
      if (now < /** @type {Date} */ (task.review_due_at)) return fail('state_conflict', 'Review window has not expired.')
      // 没有任何提交全部通过清单：退款。
      if (action.winner_agent_id === null) return ok({ ...task, status: 'refunded' }, [{ type: 'escrow_refund' }, event('task.auto_accepted', task.publisher_agent_id)])
      return ok(settle(task, now), [
        { type: 'escrow_settle', winner_agent_id: action.winner_agent_id },
        event('task.auto_accepted', task.publisher_agent_id),
        event('task.auto_accepted', action.winner_agent_id),
      ])
    },
    dispute: openDispute,
  },

  rework: {
    submit(state, _action, actor, now) {
      if (!isHolder(state.task, actor)) return notAllowed('Only the current holder can submit.')
      return ok(...submitted(state, now, []))
    },
    dispute: openDispute,
    release: holderRelease,
  },

  disputed: {
    resolve({ task }, action, actor, now) {
      if (actor.kind !== 'operator') return notAllowed('Only platform operators can resolve a dispute.')
      const notify = [event('dispute.resolved', task.publisher_agent_id), ...(task.holder_agent_id === null ? [] : [event('dispute.resolved', task.holder_agent_id)])]
      switch (action.outcome) {
        case 'settled':
          if (action.winner_agent_id === null) throw new Error(`resolve.winner_agent_id missing for settled, id: ${task.id}`)
          return ok(settle(task, now), [{ type: 'escrow_settle', winner_agent_id: action.winner_agent_id }, ...notify])
        case 'refunded':
          return ok({ ...task, status: 'refunded' }, [{ type: 'escrow_refund' }, ...notify])
        default:
          throw new Error(`Unhandled outcome: ${action.outcome}, id: ${task.id}`)
      }
    },
    // 持有人在仲裁中放弃：争议随之关闭，任务回到看板。
    release({ task }, _action, actor, now) {
      if (!isHolder(task, actor) || actor.kind !== 'agent') return notAllowed('Only the current holder can release.')
      const reopened = reopen(task, now)
      return ok(reopened, [{ type: 'dispute_close', agent_id: actor.agent_id }, ...releaseEffects(task, reopened, 'released')])
    },
  },

  settled: {},
  cancelled: {},
  refunded: {},
}

if (Object.keys(TRANSITIONS).length !== TASK_STATUSES.length) throw new Error('TRANSITIONS must cover every task status')

/**
 * 持有人放弃已提交或返工中的任务：只要还没结算，都可以释放回看板。
 * @type {Handler}
 */
function holderRelease({ task }, _action, actor, now) {
  if (!isHolder(task, actor)) return notAllowed('Only the current holder can release.')
  return released(task, 'released', now)
}

/** @type {Handler} */
function openDispute({ task }, _action, actor, now) {
  if (actor.kind !== 'agent') return notAllowed('Only the publisher or a taker can open a dispute.')
  const isParty = actor.agent_id === task.publisher_agent_id || actor.agent_id === task.holder_agent_id || actor.is_entrant
  if (!isParty) return notAllowed('Only the publisher or a taker can open a dispute.')
  return ok({ ...task, status: 'disputed' }, disputeEffects(actor.agent_id, now))
}

/**
 * 接单方通用校验：必须是 Agent、不能接自己或同主人 Agent 的任务、稀有度不超过等级上限。
 * @param {TaskState} state
 * @param {Actor} actor
 * @returns {TransitionResult|null}
 */
function takerRefusal({ task, publisher_owner_user_id }, actor) {
  if (actor.kind !== 'agent') return notAllowed('Only agents can take tasks.')
  if (actor.agent_id === task.publisher_agent_id || actor.owner_user_id === publisher_owner_user_id) {
    return fail('state_conflict', 'You cannot take a task published by you or by another agent of your owner.')
  }
  if (task.rarity > actor.max_rarity) return fail('rule_violation', `Task rarity ${task.rarity} is above your level cap ${actor.max_rarity}.`)
  return null
}

/**
 * @param {Task} task
 * @param {Actor} actor
 */
function isPublisher(task, actor) {
  return actor.kind === 'agent' && actor.agent_id === task.publisher_agent_id
}

/**
 * @param {Task} task
 * @param {Actor} actor
 */
function isHolder(task, actor) {
  return actor.kind === 'agent' && actor.agent_id === task.holder_agent_id
}

/**
 * @param {TaskState} state
 * @param {Date} from
 */
function checkpointDue(state, from) {
  return new Date(from.getTime() + state.guild.checkpoint_interval_sec * 1000)
}

/**
 * @param {TaskState} state
 * @param {string} agentId
 * @param {Date} now
 * @returns {Task}
 */
function hold(state, agentId, now) {
  return { ...state.task, status: 'claimed', holder_agent_id: agentId, next_checkpoint_due_at: checkpointDue(state, now), missed_checkpoints: 0 }
}

/**
 * @param {Task} task
 * @param {'released'|'timeout'} reason
 * @param {Date} now
 * @returns {TransitionResult}
 */
function released(task, reason, now) {
  const reopened = reopen(task, now)
  return ok(reopened, releaseEffects(task, reopened, reason))
}

/**
 * 任务回到 open（未结算前，持有人在任何状态都可以放弃）。若此时已过截止，按原先给的工期（created_at → deadline_at）从现在起重新计时，
 * 否则任务既接不了也不会过期，会卡死。
 * @param {Task} task
 * @param {Date} now
 * @returns {Task}
 */
function reopen(task, now) {
  const deadline = now < task.deadline_at ? task.deadline_at : new Date(now.getTime() + (task.deadline_at.getTime() - task.created_at.getTime()))
  // 新接手的人从零开始计返工次数。
  return { ...task, status: 'open', deadline_at: deadline, holder_agent_id: null, next_checkpoint_due_at: null, missed_checkpoints: 0, rework_count: 0, review_due_at: null }
}

/**
 * @param {Task} task
 * @param {Date} now
 * @returns {Task}
 */
function settle(task, now) {
  return { ...task, status: 'settled', settled_at: now }
}

/**
 * @param {TaskState} state
 * @param {Date} now
 * @param {Effect[]} before
 * @returns {[Task, Effect[]]}
 */
function submitted(state, now, before) {
  const { task } = state
  const reviewDue = new Date(now.getTime() + state.guild.piece_review_window_sec * 1000)
  return [
    { ...task, status: 'submitted', next_checkpoint_due_at: null, missed_checkpoints: 0, review_due_at: reviewDue },
    [...before, event('task.submitted', task.publisher_agent_id), ...reviewJobs(reviewDue)],
  ]
}

/**
 * @param {Task} task 释放前的任务
 * @param {Task} reopened 释放后的任务
 * @param {'released'|'timeout'} reason
 * @returns {Effect[]}
 */
function releaseEffects(task, reopened, reason) {
  return [
    { type: 'hold_end', reason },
    event('task.released', /** @type {string} */ (task.holder_agent_id)),
    event('task.released', task.publisher_agent_id),
    // 截止被顺延时要按新截止重新排「过期无人接」。
    ...(reopened.deadline_at.getTime() === task.deadline_at.getTime() ? [] : openJobs(reopened)),
  ]
}

/**
 * @param {string} openedBy
 * @param {Date} now
 * @returns {Effect[]}
 */
function disputeEffects(openedBy, now) {
  return [{ type: 'dispute_open', opened_by_agent_id: openedBy }, job('dispute_arbitrate', now)]
}

/**
 * 任务上板后的到期 job：过期无人接；擂台赛另加到点关闭。
 * @param {Task} task
 * @returns {Effect[]}
 */
function openJobs(task) {
  switch (task.template) {
    case 'piecework':
      return [job('open_expire', task.deadline_at)]
    case 'contest':
      return [job('open_expire', task.deadline_at), job('contest_close', task.deadline_at)]
    default:
      throw new Error(`Unhandled template: ${task.template}, id: ${task.id}`)
  }
}

/**
 * @param {TaskState} state
 * @param {Date} from
 * @returns {Effect[]}
 */
function checkpointJobs(state, from) {
  const due = checkpointDue(state, from)
  return [job('checkpoint_warn', new Date(due.getTime() - HOUR_MS)), job('checkpoint_miss', due)]
}

/**
 * @param {Date} reviewDue
 * @returns {Effect[]}
 */
function reviewJobs(reviewDue) {
  return [job('review_warn', new Date(reviewDue.getTime() - 2 * HOUR_MS)), job('review_auto_accept', reviewDue)]
}

/**
 * @param {string} eventType
 * @param {string|null} targetAgentId
 * @returns {Effect}
 */
function event(eventType, targetAgentId) {
  return { type: 'event', event_type: eventType, target_agent_id: targetAgentId }
}

/**
 * @param {string} kind
 * @param {Date} runAt
 * @returns {Effect}
 */
function job(kind, runAt) {
  return { type: 'job', kind, run_at: runAt }
}

/**
 * @param {Task} task
 * @param {Effect[]} effects
 * @returns {TransitionResult}
 */
function ok(task, effects) {
  return { ok: true, task, effects }
}

/**
 * @param {'state_conflict'|'rule_violation'|'forbidden'} code
 * @param {string} hint
 * @returns {TransitionResult}
 */
function fail(code, hint) {
  return { ok: false, code, hint }
}

/**
 * @param {string} hint
 * @returns {TransitionResult}
 */
function notAllowed(hint) {
  return fail('forbidden', hint)
}