import { DuplicateTransactionIdError, createTransaction } from '@tanstack/db'
import { OutboxTransactionNotFoundError } from '../outbox/OutboxManager'
import { DefaultRetryPolicy } from '../retry/RetryPolicy'
import { NonRetriableError } from '../types'
import type { KeyScheduler } from './KeyScheduler'
import type { OutboxManager } from '../outbox/OutboxManager'
import type {
  OfflineConfig,
  OfflineTransaction,
  TransactionSignaler,
} from '../types'

const HANDLED_EXECUTION_ERROR = Symbol(`HandledExecutionError`)

function toError(value: unknown): Error {
  return value instanceof Error ||
    Object.prototype.toString.call(value) === `[object Error]`
    ? (value as Error)
    : new Error(String(value))
}

export class TransactionExecutor {
  private scheduler: KeyScheduler
  private outbox: OutboxManager
  private config: OfflineConfig
  private retryPolicy: DefaultRetryPolicy
  private isExecuting = false
  private executionPromise: Promise<void> | null = null
  private offlineExecutor: TransactionSignaler
  private retryTimer: ReturnType<typeof setTimeout> | null = null
  private fatalError: Error | null = null

  constructor(
    scheduler: KeyScheduler,
    outbox: OutboxManager,
    config: OfflineConfig,
    offlineExecutor: TransactionSignaler,
  ) {
    this.scheduler = scheduler
    this.outbox = outbox
    this.config = config
    this.retryPolicy = new DefaultRetryPolicy(
      Number.POSITIVE_INFINITY,
      config.jitter ?? true,
    )
    this.offlineExecutor = offlineExecutor
  }

  async execute(transaction: OfflineTransaction): Promise<void> {
    this.assertHealthy()
    this.scheduler.schedule(transaction)
    await this.executeAll()
  }

  async executeAll(): Promise<void> {
    this.assertHealthy()
    if (this.isExecuting) {
      return this.executionPromise!
    }

    this.isExecuting = true
    this.executionPromise = this.runExecution()

    try {
      await this.executionPromise
    } finally {
      this.isExecuting = false
      this.executionPromise = null
      this.scheduleNextRetry()
    }
  }

  private async runExecution(): Promise<void> {
    while (this.scheduler.getPendingCount() > 0) {
      if (!this.canExecute()) {
        break
      }

      const transaction = this.scheduler.getNext()

      if (!transaction) {
        break
      }

      await this.executeTransaction(transaction)
    }
  }

  private async executeTransaction(
    transaction: OfflineTransaction,
  ): Promise<void> {
    try {
      const terminalError =
        transaction.outboxPhase === `rejection-pending`
          ? this.getTerminalError(transaction)
          : undefined
      this.scheduler.markStarted(transaction)

      if (!transaction.outboxPhase) {
        try {
          await this.runMutationFn(transaction)
        } catch (error) {
          const err = toError(error)

          await this.handleError(transaction, err)
          ;(err as any)[HANDLED_EXECUTION_ERROR] = true
          throw err
        }
      }

      // A successful provider call can outlive this executor. Persist that
      // fact before removal so a restarted executor only retries deletion.
      const deletionPending: OfflineTransaction = transaction.outboxPhase
        ? transaction
        : { ...transaction, outboxPhase: `deletion-pending` }
      try {
        await this.removeSettledTransaction(
          deletionPending,
          !transaction.outboxPhase,
        )
      } catch (error) {
        const storageError = error as Error
        this.offlineExecutor.rejectTransaction(
          transaction.id,
          terminalError ?? storageError,
        )
        throw storageError
      }

      if (terminalError) {
        this.offlineExecutor.rejectTransaction(transaction.id, terminalError)
      } else {
        this.offlineExecutor.resolveTransaction(transaction.id, undefined)
      }
    } catch (error) {
      if (
        error !== null &&
        typeof error === `object` &&
        (error as Record<symbol, unknown>)[HANDLED_EXECUTION_ERROR] === true
      ) {
        return
      }

      throw error
    }
  }

  private async runMutationFn(transaction: OfflineTransaction): Promise<void> {
    const mutationFn = this.config.mutationFns[transaction.mutationFnName]

    if (!mutationFn) {
      const errorMessage = `Unknown mutation function: ${transaction.mutationFnName}`

      if (this.config.onUnknownMutationFn) {
        this.config.onUnknownMutationFn(transaction.mutationFnName, transaction)
      }

      throw new NonRetriableError(errorMessage)
    }

    // Mutations are already PendingMutation objects with collections attached
    // from the deserializer, so we can use them directly
    const transactionWithMutations = {
      id: transaction.id,
      mutations: transaction.mutations,
      metadata: transaction.metadata ?? {},
    }

    await mutationFn({
      transaction: transactionWithMutations as any,
      idempotencyKey: transaction.idempotencyKey,
    })
  }

  private async handleError(
    transaction: OfflineTransaction,
    error: Error,
  ): Promise<void> {
    let shouldRetry: boolean
    let hookFailure: Error | undefined
    if (error instanceof NonRetriableError) {
      shouldRetry = false
    } else {
      let decision: boolean | undefined
      try {
        decision = this.config.shouldRetry?.(error, transaction.retryCount)
        if (decision !== undefined && typeof decision !== `boolean`) {
          // An async hook is invalid, but its rejection must stay row-local.
          void Promise.resolve(decision).catch(() => {})
          throw new TypeError(
            `OfflineConfig.shouldRetry must return true, false, or undefined`,
          )
        }
      } catch (hookError) {
        hookFailure = toError(hookError)
      }
      if (hookFailure) {
        shouldRetry = false
      } else {
        shouldRetry =
          decision ??
          this.retryPolicy.shouldRetry(error, transaction.retryCount)
      }
    }

    if (!shouldRetry) {
      const terminalError = hookFailure ?? error
      const rejectionPending: OfflineTransaction = {
        ...transaction,
        outboxPhase: `rejection-pending`,
        lastError: {
          name: terminalError.name,
          message: terminalError.message,
          stack: terminalError.stack,
        },
      }
      if (hookFailure) {
        console.warn(
          `Retry decision failed for transaction ${transaction.id}:`,
          hookFailure,
          `Named mutation function error:`,
          error,
        )
      } else {
        console.warn(`Transaction ${transaction.id} failed permanently:`, error)
      }
      try {
        await this.removeSettledTransaction(rejectionPending, true)
      } catch (storageError) {
        this.offlineExecutor.rejectTransaction(transaction.id, terminalError)
        throw storageError
      }

      this.offlineExecutor.rejectTransaction(transaction.id, terminalError)
      return
    }

    const delay = Math.max(
      0,
      this.retryPolicy.calculateDelay(transaction.retryCount),
    )
    const updatedTransaction: OfflineTransaction = {
      ...transaction,
      retryCount: transaction.retryCount + 1,
      nextAttemptAt: Date.now() + delay,
      lastError: {
        name: error.name,
        message: error.message,
        stack: error.stack,
      },
    }

    this.scheduler.updateTransaction(updatedTransaction)

    try {
      await this.outbox.update(transaction.id, updatedTransaction)
    } catch (persistError) {
      // Public removal can finish while the named mutation function runs.
      // The removed row cannot be retried, but its caller still owns the
      // provider failure and later queued work must be able to run.
      if (persistError instanceof OutboxTransactionNotFoundError) {
        this.scheduler.markCompleted(transaction)
        this.offlineExecutor.rejectTransaction(transaction.id, error)
        return
      }
      throw persistError
    } finally {
      this.scheduler.markFailed(transaction)
    }
  }

  private async removeSettledTransaction(
    transaction: OfflineTransaction,
    persistMarker: boolean,
  ): Promise<void> {
    try {
      if (persistMarker) {
        try {
          await this.outbox.update(transaction.id, transaction)
        } catch (error) {
          // A public removal can finish while the provider is still running.
          if (!(error instanceof OutboxTransactionNotFoundError)) throw error
        }
      }
      await this.outbox.remove(transaction.id)
      this.scheduler.markCompleted(transaction)
    } catch (error) {
      const storageError = toError(error)
      this.fatalError = storageError
      this.scheduler.markFailed(transaction)
      this.clearRetryTimer()
      throw storageError
    }
  }

  assertHealthy(): void {
    if (this.fatalError) throw this.fatalError
  }

  private getTerminalError(transaction: OfflineTransaction): Error {
    if (!transaction.lastError)
      throw new Error(`Terminal transaction ${transaction.id} has no error`)
    const { name, message, stack } = transaction.lastError
    const error =
      name === `NonRetriableError`
        ? new NonRetriableError(message)
        : new Error(message)
    error.name = name
    error.stack = stack
    return error
  }

  async loadPendingTransactions(): Promise<void> {
    let removedIds: Array<string> = []
    await this.outbox.withAll((transactions) => {
      const { isOfflineEnabled } = this.offlineExecutor
      if (!isOfflineEnabled) return
      const providerPending = transactions.filter(
        (transaction) => !transaction.outboxPhase,
      )
      const selectedProvider = this.config.beforeRetry
        ? this.config.beforeRetry(providerPending)
        : providerPending
      const selectedById = new Map(selectedProvider.map((tx) => [tx.id, tx]))
      const filteredTransactions = transactions.flatMap((transaction) => {
        if (transaction.outboxPhase) return [transaction]
        const selected = selectedById.get(transaction.id)
        return selected ? [selected] : []
      })

      // The retry hook is user code and may synchronously revoke replay rights.
      if (!this.offlineExecutor.isOfflineEnabled) return

      const newlyLoaded = filteredTransactions.filter((transaction) =>
        this.scheduler.schedule(transaction),
      )

      removedIds = providerPending
        .filter(({ id }) => !selectedById.has(id))
        .map(({ id }) => id)
      removedIds = this.scheduler.removePendingTransactions(removedIds)

      // Restore optimistic state for loaded transactions
      // This ensures the UI shows the optimistic data while transactions are pending
      this.restoreOptimisticState(
        newlyLoaded.filter(
          (transaction) => transaction.outboxPhase !== `rejection-pending`,
        ),
      )

      // Reset retry delays for all loaded transactions so they can run immediately
      this.resetRetryDelays()

      // Schedule retry timer for loaded transactions
      this.scheduleNextRetry()
    })

    if (removedIds.length > 0) {
      const error = new NonRetriableError(`Transaction excluded by beforeRetry`)
      await Promise.all(
        removedIds.map(async (id) => {
          try {
            await this.outbox.remove(id)
            this.offlineExecutor.rejectTransaction(id, error)
          } catch (cleanupError) {
            console.warn(
              `Failed to remove transaction excluded by beforeRetry:`,
              id,
              cleanupError,
            )
          }
        }),
      )
    }
  }

  /**
   * Restore optimistic state from loaded transactions.
   * Creates internal transactions to hold the mutations so the collection's
   * state manager can show optimistic data while waiting for sync.
   */
  private restoreOptimisticState(
    transactions: Array<OfflineTransaction>,
  ): void {
    for (const offlineTx of transactions) {
      if (offlineTx.mutations.length === 0) {
        continue
      }

      try {
        // Create a restoration transaction that holds mutations for optimistic state display.
        // It will never commit - the real mutation is handled by the offline executor.
        const restorationTx = createTransaction({
          id: offlineTx.id,
          autoCommit: false,
          mutationFn: async () => {},
        })

        restorationTx.applyMutations(offlineTx.mutations)

        // Register with each affected Collection. If one cannot track it, roll
        // it back, so no Collection keeps a restoration nothing will settle.
        try {
          // The serializer resolves every mutation's Collection or throws.
          for (const mutation of offlineTx.mutations) {
            if (mutation.collection._state.trackTransaction(restorationTx))
              mutation.collection._state.recomputeOptimisticState(true)
          }
        } catch (error) {
          // A secondary rollback settles only this restoration; it must not
          // roll back the user's live transactions on the same keys.
          restorationTx.rollback({ isSecondaryRollback: true })
          throw error
        }

        this.offlineExecutor.registerRestorationTransaction(
          offlineTx.id,
          restorationTx,
        )
      } catch (error) {
        // A live transaction with this id already shows these mutations.
        if (error instanceof DuplicateTransactionIdError) continue
        console.warn(
          `Failed to restore optimistic state for transaction ${offlineTx.id}:`,
          error,
        )
      }
    }
  }

  clear(): void {
    this.scheduler.clear()
    this.clearRetryTimer()
  }

  pause(): void {
    // Retain queued work and let the issued call finish its acknowledgment.
    this.clearRetryTimer()
  }

  getPendingCount(): number {
    return this.scheduler.getPendingCount()
  }

  private scheduleNextRetry(): void {
    // Clear existing timer
    this.clearRetryTimer()

    if (this.fatalError || !this.canExecute()) {
      return
    }

    const nextRetryTime = this.getNextRetryTime()

    if (nextRetryTime === null) {
      return // No transactions pending retry
    }

    const delay = Math.max(0, nextRetryTime - Date.now())

    this.retryTimer = setTimeout(() => {
      this.executeAll().catch((error) => {
        console.warn(`Failed to execute retry batch:`, error)
      })
    }, delay)
  }

  private getNextRetryTime(): number | null {
    const allTransactions = this.scheduler.getAllPendingTransactions()

    if (allTransactions.length === 0) {
      return null
    }

    // Later transactions cannot overtake the FIFO head, even if they are ready.
    return allTransactions[0]!.nextAttemptAt
  }

  private clearRetryTimer(): void {
    if (this.retryTimer) {
      clearTimeout(this.retryTimer)
      this.retryTimer = null
    }
  }

  private canExecute(): boolean {
    return (
      this.offlineExecutor.isOfflineEnabled && this.offlineExecutor.isOnline()
    )
  }

  getRunningCount(): number {
    return this.scheduler.getRunningCount()
  }

  resetRetryDelays(): void {
    const allTransactions = this.scheduler.getAllPendingTransactions()
    const updatedTransactions = allTransactions.map((transaction) => ({
      ...transaction,
      nextAttemptAt: Date.now(),
    }))

    this.scheduler.updateTransactions(updatedTransactions)
  }
}