import { NextRequest, NextResponse } from "next/server"
import prisma from "@/lib/prisma"
import { getAuthUser } from "@/lib/auth"
import { sendMessageSchema, parseBody } from "@/lib/validations"
import { checkRateLimit, getClientIdentifier } from "@/lib/rate-limit"
import { sanitizeText } from "@/lib/api-utils"

// GET - Get conversations for current user (fixed N+1 with participant include)
export async function GET(request: NextRequest) {
    try {
        const authUser = await getAuthUser()
        if (!authUser) {
            return NextResponse.json(
                { error: "Authentication required" },
                { status: 401 }
            )
        }

        const conversations = await prisma.conversation.findMany({
            where: {
                OR: [
                    { participant1: authUser.id },
                    { participant2: authUser.id },
                ],
            },
            orderBy: { lastActivity: "desc" },
            include: {
                messages: {
                    orderBy: { createdAt: "desc" },
                    take: 1,
                },
                _count: {
                    select: {
                        messages: {
                            where: {
                                isRead: false,
                                senderId: { not: authUser.id },
                            },
                        },
                    },
                },
            },
        })

        // Get other participant info (batch query instead of N+1)
        const participantIds = conversations.map(c =>
            c.participant1 === authUser.id ? c.participant2 : c.participant1
        )

        const users = await prisma.user.findMany({
            where: { id: { in: participantIds } },
            select: {
                id: true,
                name: true,
                username: true,
                image: true,
            },
        })
        const userMap = new Map(users.map(u => [u.id, u]))

        const conversationsWithUsers = conversations.map(conv => {
            const otherId = conv.participant1 === authUser.id ? conv.participant2 : conv.participant1
            return {
                ...conv,
                otherUser: userMap.get(otherId) || null,
                unreadCount: conv._count.messages,
                lastMessage: conv.messages[0] || null,
            }
        })

        return NextResponse.json({ conversations: conversationsWithUsers })
    } catch (error) {
        console.error("Error fetching conversations:", error)
        return NextResponse.json(
            { error: "Failed to fetch conversations" },
            { status: 500 }
        )
    }
}

// POST - Start a new conversation or send message (rate limited, validated, sanitized)
export async function POST(request: NextRequest) {
    try {
        const authUser = await getAuthUser()
        if (!authUser) {
            return NextResponse.json(
                { error: "Authentication required" },
                { status: 401 }
            )
        }

        // Rate limit
        const identifier = getClientIdentifier(request, authUser.id)
        const rateLimit = await checkRateLimit(`messages:${identifier}`, true)
        if (!rateLimit.success) {
            return NextResponse.json({ error: rateLimit.error }, { status: 429 })
        }

        const body = await request.json()
        const parsed = parseBody(sendMessageSchema, body)
        if (!parsed.success) return parsed.response

        const { recipientId, content } = parsed.data

        if (recipientId === authUser.id) {
            return NextResponse.json(
                { error: "Cannot message yourself" },
                { status: 400 }
            )
        }

        // Sanitize content
        const sanitizedContent = sanitizeText(content, 5000)
        if (!sanitizedContent) {
            return NextResponse.json(
                { error: "Message content cannot be empty" },
                { status: 400 }
            )
        }

        // Find or create conversation — always sort IDs for consistent unique constraint
        const [p1, p2] = [authUser.id, recipientId].sort()

        let conversation = await prisma.conversation.findUnique({
            where: {
                participant1_participant2: { participant1: p1, participant2: p2 },
            },
        })

        if (!conversation) {
            conversation = await prisma.conversation.create({
                data: {
                    participant1: p1,
                    participant2: p2,
                },
            })
        }

        // Create message
        const message = await prisma.message.create({
            data: {
                content: sanitizedContent,
                senderId: authUser.id,
                conversationId: conversation.id,
            },
        })

        // Update conversation
        await prisma.conversation.update({
            where: { id: conversation.id },
            data: {
                lastMessage: sanitizedContent,
                lastActivity: new Date(),
            },
        })

        return NextResponse.json({ conversation, message })
    } catch (error) {
        console.error("Error sending message:", error)
        return NextResponse.json(
            { error: "Failed to send message" },
            { status: 500 }
        )
    }
}