/**
 * TaskQueue Stream Definition
 *
 * Manages global task queue state for concurrency control.
 * Tracks running tasks count and queued task list.
 *
 * @see Requirements 10.1, 10.4
 */

import { defineStream } from '@motia/core'
import { z } from 'zod'

// Maximum concurrent tasks
export const MAX_CONCURRENT = 4

// Task queue state schema
export const TaskQueueStateSchema = z.object({
  runningCount: z.number().min(0).max(MAX_CONCURRENT),
  maxConcurrent: z.number().default(MAX_CONCURRENT),
  queue: z.array(z.string()), // sessionId list in FIFO order
})
export type TaskQueueState = z.infer<typeof TaskQueueStateSchema>

/**
 * Create initial queue state
 */
export function createInitialQueueState(): TaskQueueState {
  return {
    runningCount: 0,
    maxConcurrent: MAX_CONCURRENT,
    queue: [],
  }
}

/**
 * Check if a new task can run immediately
 */
export function canRunImmediately(state: TaskQueueState): boolean {
  return state.runningCount < state.maxConcurrent
}

/**
 * Get queue position for a session (1-based, null if not in queue)
 */
export function getQueuePosition(
  state: TaskQueueState,
  sessionId: string
): number | null {
  const index = state.queue.indexOf(sessionId)
  return index === -1 ? null : index + 1
}

// Define the taskQueue stream (global, single instance)
export const taskQueueStream = defineStream({
  name: 'taskQueue',
  schema: TaskQueueStateSchema,
  persistence: {
    enabled: true,
  },
})