import {
  Injectable,
  NotFoundException,
  ForbiddenException,
  BadRequestException,
} from '@nestjs/common';
import { PrismaService } from '../prisma/prisma.service';
import { CreateMessageDto } from './dto';
import { ConnectionStatus, MessageStatus, MessageType, UserRole } from '@prisma/client';

@Injectable()
export class MessagesService {
  constructor(private readonly prisma: PrismaService) {}

  /**
   * Validate if a user can message an agent (must have ACCEPTED connection)
   */
  async validateCanMessage(userId: string, agentProfileId: string): Promise<boolean> {
    const connection = await this.prisma.connectionRequest.findUnique({
      where: {
        userId_agentProfileId: {
          userId,
          agentProfileId,
        },
      },
    });

    return connection?.status === ConnectionStatus.ACCEPTED;
  }

  /**
   * Get or create a conversation between user and agent
   */
  async getOrCreateConversation(userId: string, agentProfileId: string) {
    // Validate connection first
    const canMessage = await this.validateCanMessage(userId, agentProfileId);
    if (!canMessage) {
      throw new ForbiddenException(
        'You can only message agents with accepted connection requests',
      );
    }

    // Check if conversation already exists
    let conversation = await this.prisma.conversation.findUnique({
      where: {
        userId_agentProfileId: {
          userId,
          agentProfileId,
        },
      },
      include: {
        agentProfile: {
          select: {
            id: true,
            firstName: true,
            lastName: true,
            avatar: true,
            headline: true,
            userId: true,
            user: {
              select: {
                isOnline: true,
                lastSeenAt: true,
              },
            },
          },
        },
        user: {
          select: {
            id: true,
            isOnline: true,
            lastSeenAt: true,
            userProfile: {
              select: {
                firstName: true,
                lastName: true,
                avatar: true,
              },
            },
          },
        },
      },
    });

    // Create new conversation if it doesn't exist
    if (!conversation) {
      conversation = await this.prisma.conversation.create({
        data: {
          userId,
          agentProfileId,
        },
        include: {
          agentProfile: {
            select: {
              id: true,
              firstName: true,
              lastName: true,
              avatar: true,
              headline: true,
              userId: true,
              user: {
                select: {
                  isOnline: true,
                  lastSeenAt: true,
                },
              },
            },
          },
          user: {
            select: {
              id: true,
              isOnline: true,
              lastSeenAt: true,
              userProfile: {
                select: {
                  firstName: true,
                  lastName: true,
                  avatar: true,
                },
              },
            },
          },
        },
      });
    }

    // Transform to include otherParty (for the user, other party is the agent)
    return {
      ...conversation,
      unreadCount: conversation.userUnreadCount,
      otherParty: {
        id: conversation.agentProfile.id,
        userId: conversation.agentProfile.userId,
        name: `${conversation.agentProfile.firstName || ''} ${conversation.agentProfile.lastName || ''}`.trim() || 'Agent',
        avatar: conversation.agentProfile.avatar,
        headline: conversation.agentProfile.headline,
        isOnline: conversation.agentProfile.user?.isOnline || false,
        lastSeenAt: conversation.agentProfile.user?.lastSeenAt || null,
      },
    };
  }

  /**
   * Create a new message in a conversation
   */
  async createMessage(
    conversationId: string,
    senderId: string,
    dto: CreateMessageDto,
  ) {
    // Verify conversation exists and user is part of it
    const conversation = await this.prisma.conversation.findUnique({
      where: { id: conversationId },
      include: {
        agentProfile: {
          select: { userId: true },
        },
      },
    });

    if (!conversation) {
      throw new NotFoundException('Conversation not found');
    }

    // Check if sender is part of the conversation
    const isUser = conversation.userId === senderId;
    const isAgent = conversation.agentProfile.userId === senderId;

    if (!isUser && !isAgent) {
      throw new ForbiddenException('You are not part of this conversation');
    }

    // Create the message
    const message = await this.prisma.message.create({
      data: {
        conversationId,
        senderId,
        content: dto.content,
        messageType: dto.messageType || MessageType.TEXT,
        fileUrl: dto.fileUrl,
        fileName: dto.fileName,
        fileSize: dto.fileSize,
        mimeType: dto.mimeType,
        status: MessageStatus.SENT,
      },
      include: {
        sender: {
          select: {
            id: true,
            role: true,
            userProfile: {
              select: {
                firstName: true,
                lastName: true,
                avatar: true,
              },
            },
            agentProfile: {
              select: {
                firstName: true,
                lastName: true,
                avatar: true,
              },
            },
          },
        },
      },
    });

    // Update conversation with last message info and unread counts
    const truncatedContent =
      dto.content.length > 255 ? dto.content.substring(0, 252) + '...' : dto.content;

    await this.prisma.conversation.update({
      where: { id: conversationId },
      data: {
        lastMessageAt: new Date(),
        lastMessageText: truncatedContent,
        // Increment unread count for the other party
        ...(isUser
          ? { agentUnreadCount: { increment: 1 } }
          : { userUnreadCount: { increment: 1 } }),
      },
    });

    return message;
  }

  /**
   * Get all conversations for a user (either as user or agent)
   */
  async getConversations(userId: string, role: UserRole) {
    let conversations;

    if (role === UserRole.AGENT) {
      // Get agent profile for this user
      const agentProfile = await this.prisma.agentProfile.findUnique({
        where: { userId },
      });

      if (!agentProfile) {
        return [];
      }

      conversations = await this.prisma.conversation.findMany({
        where: { agentProfileId: agentProfile.id },
        include: {
          user: {
            select: {
              id: true,
              isOnline: true,
              lastSeenAt: true,
              userProfile: {
                select: {
                  firstName: true,
                  lastName: true,
                  avatar: true,
                },
              },
            },
          },
          messages: {
            take: 1,
            orderBy: { createdAt: 'desc' },
          },
        },
        orderBy: { lastMessageAt: 'desc' },
      });

      // Map to include unread count from agent perspective
      return conversations.map((conv) => ({
        ...conv,
        unreadCount: conv.agentUnreadCount,
        otherParty: {
          id: conv.user.id,
          name: `${conv.user.userProfile?.firstName || ''} ${conv.user.userProfile?.lastName || ''}`.trim() || 'User',
          avatar: conv.user.userProfile?.avatar,
          isOnline: conv.user.isOnline,
          lastSeenAt: conv.user.lastSeenAt,
        },
      }));
    } else {
      // Regular user
      conversations = await this.prisma.conversation.findMany({
        where: { userId },
        include: {
          agentProfile: {
            select: {
              id: true,
              firstName: true,
              lastName: true,
              avatar: true,
              headline: true,
              userId: true,
              user: {
                select: {
                  isOnline: true,
                  lastSeenAt: true,
                },
              },
            },
          },
          messages: {
            take: 1,
            orderBy: { createdAt: 'desc' },
          },
        },
        orderBy: { lastMessageAt: 'desc' },
      });

      // Map to include unread count from user perspective
      return conversations.map((conv) => ({
        ...conv,
        unreadCount: conv.userUnreadCount,
        otherParty: {
          id: conv.agentProfile.id,
          userId: conv.agentProfile.userId,
          name: `${conv.agentProfile.firstName || ''} ${conv.agentProfile.lastName || ''}`.trim() || 'Agent',
          avatar: conv.agentProfile.avatar,
          headline: conv.agentProfile.headline,
          isOnline: conv.agentProfile.user.isOnline,
          lastSeenAt: conv.agentProfile.user.lastSeenAt,
        },
      }));
    }
  }

  /**
   * Get messages for a conversation with pagination
   */
  async getMessages(
    conversationId: string,
    userId: string,
    page: number = 1,
    limit: number = 50,
  ) {
    // Verify user is part of the conversation
    const conversation = await this.prisma.conversation.findUnique({
      where: { id: conversationId },
      include: {
        agentProfile: {
          select: { userId: true },
        },
      },
    });

    if (!conversation) {
      throw new NotFoundException('Conversation not found');
    }

    const isUser = conversation.userId === userId;
    const isAgent = conversation.agentProfile.userId === userId;

    if (!isUser && !isAgent) {
      throw new ForbiddenException('You are not part of this conversation');
    }

    const skip = (page - 1) * limit;

    const [messages, total] = await Promise.all([
      this.prisma.message.findMany({
        where: { conversationId },
        include: {
          sender: {
            select: {
              id: true,
              role: true,
              userProfile: {
                select: {
                  firstName: true,
                  lastName: true,
                  avatar: true,
                },
              },
              agentProfile: {
                select: {
                  firstName: true,
                  lastName: true,
                  avatar: true,
                },
              },
            },
          },
        },
        orderBy: { createdAt: 'desc' },
        skip,
        take: limit,
      }),
      this.prisma.message.count({ where: { conversationId } }),
    ]);

    return {
      messages: messages.reverse(), // Return in chronological order
      pagination: {
        page,
        limit,
        total,
        pages: Math.ceil(total / limit),
      },
    };
  }

  /**
   * Mark messages as read in a conversation
   */
  async markMessagesAsRead(conversationId: string, userId: string) {
    const conversation = await this.prisma.conversation.findUnique({
      where: { id: conversationId },
      include: {
        agentProfile: {
          select: { userId: true },
        },
      },
    });

    if (!conversation) {
      throw new NotFoundException('Conversation not found');
    }

    const isUser = conversation.userId === userId;
    const isAgent = conversation.agentProfile.userId === userId;

    if (!isUser && !isAgent) {
      throw new ForbiddenException('You are not part of this conversation');
    }

    // Update all unread messages from the other party
    await this.prisma.message.updateMany({
      where: {
        conversationId,
        senderId: { not: userId },
        status: { not: MessageStatus.READ },
      },
      data: {
        status: MessageStatus.READ,
        readAt: new Date(),
      },
    });

    // Reset unread count for this user
    await this.prisma.conversation.update({
      where: { id: conversationId },
      data: isUser ? { userUnreadCount: 0 } : { agentUnreadCount: 0 },
    });

    return { success: true };
  }

  /**
   * Update user's online status
   */
  async updateOnlineStatus(userId: string, isOnline: boolean) {
    await this.prisma.user.update({
      where: { id: userId },
      data: {
        isOnline,
        lastSeenAt: isOnline ? undefined : new Date(),
      },
    });
  }

  /**
   * Mark a message as delivered
   */
  async markMessageDelivered(messageId: string) {
    return this.prisma.message.update({
      where: { id: messageId },
      data: {
        status: MessageStatus.DELIVERED,
        deliveredAt: new Date(),
      },
    });
  }

  /**
   * Get conversation by ID with full details
   */
  async getConversationById(conversationId: string, userId: string) {
    const conversation = await this.prisma.conversation.findUnique({
      where: { id: conversationId },
      include: {
        agentProfile: {
          select: {
            id: true,
            firstName: true,
            lastName: true,
            avatar: true,
            headline: true,
            userId: true,
            user: {
              select: {
                isOnline: true,
                lastSeenAt: true,
              },
            },
          },
        },
        user: {
          select: {
            id: true,
            isOnline: true,
            lastSeenAt: true,
            userProfile: {
              select: {
                firstName: true,
                lastName: true,
                avatar: true,
              },
            },
          },
        },
      },
    });

    if (!conversation) {
      throw new NotFoundException('Conversation not found');
    }

    const isUser = conversation.userId === userId;
    const isAgent = conversation.agentProfile.userId === userId;

    if (!isUser && !isAgent) {
      throw new ForbiddenException('You are not part of this conversation');
    }

    // Transform to include otherParty based on who is requesting
    if (isUser) {
      // User is viewing - other party is agent
      return {
        ...conversation,
        unreadCount: conversation.userUnreadCount,
        otherParty: {
          id: conversation.agentProfile.id,
          userId: conversation.agentProfile.userId,
          name: `${conversation.agentProfile.firstName || ''} ${conversation.agentProfile.lastName || ''}`.trim() || 'Agent',
          avatar: conversation.agentProfile.avatar,
          headline: conversation.agentProfile.headline,
          isOnline: conversation.agentProfile.user?.isOnline || false,
          lastSeenAt: conversation.agentProfile.user?.lastSeenAt || null,
        },
      };
    } else {
      // Agent is viewing - other party is user
      return {
        ...conversation,
        unreadCount: conversation.agentUnreadCount,
        otherParty: {
          id: conversation.user.id,
          name: `${conversation.user.userProfile?.firstName || ''} ${conversation.user.userProfile?.lastName || ''}`.trim() || 'User',
          avatar: conversation.user.userProfile?.avatar,
          isOnline: conversation.user.isOnline,
          lastSeenAt: conversation.user.lastSeenAt,
        },
      };
    }
  }

  /**
   * Get total unread count for a user across all conversations
   */
  async getTotalUnreadCount(userId: string, role: UserRole) {
    if (role === UserRole.AGENT) {
      const agentProfile = await this.prisma.agentProfile.findUnique({
        where: { userId },
      });

      if (!agentProfile) {
        return 0;
      }

      const result = await this.prisma.conversation.aggregate({
        where: { agentProfileId: agentProfile.id },
        _sum: { agentUnreadCount: true },
      });

      return result._sum.agentUnreadCount || 0;
    } else {
      const result = await this.prisma.conversation.aggregate({
        where: { userId },
        _sum: { userUnreadCount: true },
      });

      return result._sum.userUnreadCount || 0;
    }
  }
}