import { NextRequest, NextResponse } from 'next/server'
import { getServerSession } from 'next-auth'
import { authOptions } from '@/lib/auth'
import { prisma } from '@/lib/db'

export async function GET(request: NextRequest) {
  try {
    const session = await getServerSession(authOptions)
    if (!session?.user) {
      return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
    }

    const now = new Date()
    const today = new Date(now.getFullYear(), now.getMonth(), now.getDate())
    const weekAgo = new Date(today.getTime() - 7 * 24 * 60 * 60 * 1000)
    const monthAgo = new Date(today.getTime() - 30 * 24 * 60 * 60 * 1000)

    // Fetch all data in parallel
    const [
      // Task counts by status
      tasksByStatus,
      // Task counts by priority
      tasksByPriority,
      // Task counts by department
      tasksByDepartment,
      // Overdue tasks
      overdueTasks,
      // Tasks due today
      dueTodayTasks,
      // Tasks due this week
      dueThisWeekTasks,
      // User workload (tasks per assignee)
      userWorkload,
      // Recently completed tasks (last 7 days)
      recentlyCompleted,
      // Tasks created in last 30 days
      tasksCreatedLast30Days,
      // Tasks completed in last 30 days
      tasksCompletedLast30Days,
      // Total tasks
      totalTasks,
      // Active users
      activeUsers,
    ] = await Promise.all([
      // Tasks by status
      prisma.task.groupBy({
        by: ['status'],
        _count: { id: true },
      }),
      // Tasks by priority
      prisma.task.groupBy({
        by: ['priority'],
        _count: { id: true },
      }),
      // Tasks by department
      prisma.task.groupBy({
        by: ['department'],
        _count: { id: true },
      }),
      // Overdue tasks (past due, not completed)
      prisma.task.count({
        where: {
          dueDate: { lt: today },
          status: { notIn: ['COMPLETED', 'CANCELLED', 'NA'] },
        },
      }),
      // Due today
      prisma.task.count({
        where: {
          dueDate: {
            gte: today,
            lt: new Date(today.getTime() + 24 * 60 * 60 * 1000),
          },
          status: { notIn: ['COMPLETED', 'CANCELLED', 'NA'] },
        },
      }),
      // Due this week
      prisma.task.count({
        where: {
          dueDate: {
            gte: today,
            lt: new Date(today.getTime() + 7 * 24 * 60 * 60 * 1000),
          },
          status: { notIn: ['COMPLETED', 'CANCELLED', 'NA'] },
        },
      }),
      // User workload - tasks assigned per user
      prisma.user.findMany({
        where: { isActive: true },
        select: {
          id: true,
          displayName: true,
          email: true,
          department: true,
          taskAssignments: {
            include: {
              task: {
                select: {
                  id: true,
                  status: true,
                  priority: true,
                  dueDate: true,
                },
              },
            },
          },
        },
      }),
      // Recently completed
      prisma.task.count({
        where: {
          status: 'COMPLETED',
          completedAt: { gte: weekAgo },
        },
      }),
      // Tasks created last 30 days
      prisma.task.count({
        where: {
          createdAt: { gte: monthAgo },
        },
      }),
      // Tasks completed last 30 days
      prisma.task.count({
        where: {
          status: 'COMPLETED',
          completedAt: { gte: monthAgo },
        },
      }),
      // Total tasks
      prisma.task.count(),
      // Active users with task assignments
      prisma.user.count({
        where: {
          isActive: true,
          taskAssignments: { some: {} },
        },
      }),
    ])

    // Calculate user-level metrics
    const userMetrics = userWorkload.map((user) => {
      const tasks = user.taskAssignments.map((a) => a.task)
      const activeTasks = tasks.filter(
        (t) => !['COMPLETED', 'CANCELLED', 'NA'].includes(t.status)
      )
      const completedTasks = tasks.filter((t) => t.status === 'COMPLETED')
      const overdue = activeTasks.filter(
        (t) => new Date(t.dueDate) < today
      )
      const highPriority = activeTasks.filter(
        (t) => t.priority === 'HIGH' || t.priority === 'URGENT'
      )

      return {
        id: user.id,
        name: user.displayName || user.email,
        department: user.department,
        totalAssigned: tasks.length,
        activeTasks: activeTasks.length,
        completedTasks: completedTasks.length,
        overdueTasks: overdue.length,
        highPriorityTasks: highPriority.length,
        completionRate:
          tasks.length > 0
            ? Math.round((completedTasks.length / tasks.length) * 100)
            : 0,
      }
    })

    // Sort users by active tasks (highest workload first)
    userMetrics.sort((a, b) => b.activeTasks - a.activeTasks)

    // Calculate summary metrics
    const totalActive = tasksByStatus
      .filter((s) => !['COMPLETED', 'CANCELLED', 'NA'].includes(s.status))
      .reduce((sum, s) => sum + s._count.id, 0)

    const totalCompleted = tasksByStatus.find((s) => s.status === 'COMPLETED')?._count.id || 0

    const completionRate = totalTasks > 0 ? Math.round((totalCompleted / totalTasks) * 100) : 0

    // Calculate workload distribution
    const avgTasksPerUser = activeUsers > 0 ? Math.round(totalActive / activeUsers) : 0
    const maxWorkload = Math.max(...userMetrics.map((u) => u.activeTasks), 0)
    const minWorkload = Math.min(...userMetrics.filter((u) => u.activeTasks > 0).map((u) => u.activeTasks), 0)

    // Format status breakdown
    const statusBreakdown = {
      notStarted: tasksByStatus.find((s) => s.status === 'NOT_STARTED')?._count.id || 0,
      inProgress: tasksByStatus.find((s) => s.status === 'IN_PROGRESS')?._count.id || 0,
      completed: totalCompleted,
      blocked: tasksByStatus.find((s) => s.status === 'BLOCKED')?._count.id || 0,
      na: tasksByStatus.find((s) => s.status === 'NA')?._count.id || 0,
      cancelled: tasksByStatus.find((s) => s.status === 'CANCELLED')?._count.id || 0,
    }

    // Format priority breakdown
    const priorityBreakdown = {
      low: tasksByPriority.find((p) => p.priority === 'LOW')?._count.id || 0,
      medium: tasksByPriority.find((p) => p.priority === 'MEDIUM')?._count.id || 0,
      high: tasksByPriority.find((p) => p.priority === 'HIGH')?._count.id || 0,
      urgent: tasksByPriority.find((p) => p.priority === 'URGENT')?._count.id || 0,
    }

    // Format department breakdown
    const departmentBreakdown = tasksByDepartment.reduce(
      (acc, d) => {
        acc[d.department] = d._count.id
        return acc
      },
      {} as Record<string, number>
    )

    return NextResponse.json({
      summary: {
        totalTasks,
        activeTasks: totalActive,
        completedTasks: totalCompleted,
        completionRate,
        overdueTasks,
        dueTodayTasks,
        dueThisWeekTasks,
        activeUsers,
        avgTasksPerUser,
        maxWorkload,
        minWorkload,
      },
      trends: {
        recentlyCompleted,
        tasksCreatedLast30Days,
        tasksCompletedLast30Days,
        velocity: tasksCompletedLast30Days, // Tasks completed per 30 days
      },
      breakdowns: {
        status: statusBreakdown,
        priority: priorityBreakdown,
        department: departmentBreakdown,
      },
      userWorkload: userMetrics,
    })
  } catch (error) {
    console.error('Workload KPI API error:', error)
    return NextResponse.json({ error: 'Internal server error' }, { status: 500 })
  }
}