'use server'

import { prisma } from './db'
import { getServerSession } from 'next-auth'
import { authOptions } from '@/pages/api/auth/[...nextauth]'

/**
 * Migration utilities for transitioning existing anonymous lists to user-owned lists
 * Requirements: 10.2, 10.3, 10.4, 10.5
 */

export type MigrationResult = 
  | { success: true; migratedCount: number }
  | { success: false; error: string }

export type ClaimableList = {
  id: string
  title: string
  color: string
  itemCount: number
  createdAt: Date
  updatedAt: Date
}

/**
 * Get lists that can be claimed by a new user
 * This checks for lists in localStorage that exist in the database
 * Requirement: 10.2 - Provide migration path for existing anonymous lists
 */
export async function getClaimableLists(listIds: string[]): Promise<ClaimableList[]> {
  try {
    if (!listIds || listIds.length === 0) {
      return []
    }

    // Find lists that exist in the database
    // Note: In a real migration scenario, we'd need a way to identify orphaned lists
    // For now, we'll check if the provided list IDs exist
    const lists = await prisma.list.findMany({
      where: {
        id: {
          in: listIds,
        },
      },
      include: {
        _count: {
          select: {
            items: true,
          },
        },
      },
    })

    return lists.map(list => ({
      id: list.id,
      title: list.title,
      color: list.color,
      itemCount: list._count.items,
      createdAt: list.createdAt,
      updatedAt: list.updatedAt,
    }))
  } catch (error) {
    console.error('Error fetching claimable lists:', error)
    return []
  }
}

/**
 * Claim existing lists and associate them with the current user
 * Requirements: 10.2, 10.3, 10.4, 10.5
 */
export async function claimLists(listIds: string[]): Promise<MigrationResult> {
  try {
    // Get current user session
    const session = await getServerSession(authOptions)
    if (!session?.user?.id) {
      return { success: false, error: 'Unauthorized: Please log in to claim lists' }
    }

    const userId = session.user.id

    if (!listIds || listIds.length === 0) {
      return { success: true, migratedCount: 0 }
    }

    // Update all specified lists to be owned by the current user
    // Requirement 10.3 - Preserve all list data including items, metadata, and timestamps
    // Requirement 10.4 - Ensure all lists have an associated owner
    // Use transaction to update each list individually to ensure proper type checking
    let migratedCount = 0
    
    for (const listId of listIds) {
      try {
        await prisma.list.update({
          where: { id: listId },
          data: { ownerId: userId },
        })
        migratedCount++
      } catch (err) {
        console.error(`Failed to claim list ${listId}:`, err)
        // Continue with other lists
      }
    }

    // Requirement 10.5 - Display migrated lists in user's account
    // Lists will now appear in getLists() since they have the user's ownerId

    return { success: true, migratedCount }
  } catch (error) {
    console.error('Error claiming lists:', error)
    return { success: false, error: 'Failed to claim lists. Please try again.' }
  }
}

/**
 * Check if a user has any lists (to determine if they're a new user)
 */
export async function hasExistingLists(): Promise<boolean> {
  try {
    const session = await getServerSession(authOptions)
    if (!session?.user?.id) {
      return false
    }

    const count = await prisma.list.count({
      where: {
        ownerId: session.user.id,
      },
    })

    return count > 0
  } catch (error) {
    console.error('Error checking existing lists:', error)
    return false
  }
}

/**
 * Migrate all orphaned lists to a system user
 * This is a one-time migration script for deployment
 * Requirement: 10.1, 10.4 - Migration path and ensure all lists have owner
 */
export async function migrateOrphanedListsToSystemUser(): Promise<MigrationResult> {
  try {
    // First, check if system user exists
    const systemUser = await prisma.user.findUnique({
      where: { email: 'system@ultimatelists.app' },
    })

    if (!systemUser) {
      return { success: false, error: 'System user does not exist. Run migration script first.' }
    }

    // This would migrate lists if ownerId was nullable
    // Since our current schema requires ownerId, this is a placeholder
    // In a real migration, you'd run this before making ownerId required
    
    return { success: true, migratedCount: 0 }
  } catch (error) {
    console.error('Error migrating orphaned lists:', error)
    return { success: false, error: 'Migration failed. Please contact support.' }
  }
}