import { createOpenAI } from '@ai-sdk/openai'
import { convertToModelMessages, stepCountIs, streamText, type UIMessage } from 'ai'
import { NextResponse } from 'next/server'
import { z } from 'zod'
import { validatePascalAgentAccess } from '@/lib/pascal-agent-access'
import { getPascalAgentConfig } from '@/lib/pascal-agent-config'
import { createPascalAgentMcpSession } from '@/lib/pascal-agent-mcp'
import { buildPascalAgentPrompt } from '@/lib/pascal-agent-prompt'
import { getPascalHostIdentity } from '@/lib/pascal-host-identity'
import { getSceneOperations } from '@/lib/scene-store-server'

export const dynamic = 'force-dynamic'
export const maxDuration = 600
export const runtime = 'nodejs'

const requestSchema = z.object({
  messages: z.array(z.unknown()).min(1).max(100),
  sceneId: z
    .string()
    .min(1)
    .max(64)
    .regex(/^[a-z0-9]+(?:-[a-z0-9]+)*$/),
})

const AGENT_ERROR_MESSAGE = 'AI design agent is temporarily unavailable. Please try again.'
const SCENE_ERROR_MESSAGE = 'The current scene could not be loaded.'

function accessErrorResponse(result: ReturnType<typeof validatePascalAgentAccess>) {
  if (result === 'missing_proxy_secret') {
    return NextResponse.json({ error: 'agent_proxy_not_configured' }, { status: 503 })
  }
  if (result === 'unauthorized') {
    return NextResponse.json({ error: 'unauthorized' }, { status: 401 })
  }
  return null
}

export function GET(request: Request) {
  const accessError = accessErrorResponse(validatePascalAgentAccess(request.headers))
  if (accessError) return accessError
  const identity = getPascalHostIdentity(request.headers)
  if (!identity.allowed) {
    return NextResponse.json({ error: 'host_user_required' }, { status: 401 })
  }
  const config = getPascalAgentConfig()
  return NextResponse.json({
    configured: config.configured,
    maxSteps: config.maxSteps,
    model: config.model,
  })
}

export async function POST(request: Request) {
  const accessError = accessErrorResponse(validatePascalAgentAccess(request.headers))
  if (accessError) return accessError
  const identity = getPascalHostIdentity(request.headers)
  if (!identity.allowed) {
    return NextResponse.json({ error: 'host_user_required' }, { status: 401 })
  }
  const config = getPascalAgentConfig()
  if (!config.configured) {
    return NextResponse.json(
      {
        error: 'agent_not_configured',
        message: 'Configure PASCAL_AGENT_API_KEY before using the AI design agent.',
      },
      { status: 503 },
    )
  }

  let body: unknown
  try {
    body = await request.json()
  } catch {
    return NextResponse.json({ error: 'invalid_json' }, { status: 400 })
  }

  const parsed = requestSchema.safeParse(body)
  if (!parsed.success) {
    return NextResponse.json(
      { error: 'invalid_request', details: parsed.error.issues },
      { status: 400 },
    )
  }

  const operations = await getSceneOperations()
  const storedScene = await operations.loadStoredScene(parsed.data.sceneId)
  if (!storedScene || (identity.userId && storedScene.ownerId !== identity.userId)) {
    return NextResponse.json(
      { error: 'scene_unavailable', message: SCENE_ERROR_MESSAGE },
      { status: 404 },
    )
  }

  const abortSignal = AbortSignal.any([request.signal, AbortSignal.timeout(config.totalTimeoutMs)])
  let session: Awaited<ReturnType<typeof createPascalAgentMcpSession>>
  try {
    session = await createPascalAgentMcpSession({
      abortSignal,
      sceneId: parsed.data.sceneId,
      stepTimeoutMs: config.stepTimeoutMs,
    })
  } catch (error) {
    console.error('Pascal agent could not load the requested scene.', error)
    return NextResponse.json(
      { error: 'scene_unavailable', message: SCENE_ERROR_MESSAGE },
      { status: 404 },
    )
  }
  const provider = createOpenAI({
    apiKey: config.apiKey,
    baseURL: config.baseUrl,
    name: 'pascal-agent',
  })

  let finalized = false
  const finalize = async (save: boolean) => {
    if (finalized) return
    finalized = true
    try {
      if (save && !abortSignal.aborted) {
        await session.saveDraft(abortSignal)
      }
    } finally {
      await session.close()
    }
  }

  try {
    const result = streamText({
      abortSignal,
      maxOutputTokens: 1600,
      messages: convertToModelMessages(parsed.data.messages as UIMessage[]),
      model: provider.chat(config.model),
      onAbort: async () => finalize(false),
      onError: async () => finalize(false),
      onFinish: async () => finalize(true),
      stopWhen: stepCountIs(config.maxSteps),
      system: buildPascalAgentPrompt({
        sceneId: parsed.data.sceneId,
        sceneName: session.sceneName,
      }),
      temperature: 0.2,
      tools: session.tools,
    })

    return result.toUIMessageStreamResponse({
      onError: (error) => {
        console.error('Pascal agent stream failed.', error)
        return AGENT_ERROR_MESSAGE
      },
    })
  } catch (error) {
    await finalize(false)
    console.error('Pascal agent failed before streaming.', error)
    return NextResponse.json(
      { error: 'agent_failed', message: AGENT_ERROR_MESSAGE },
      { status: 500 },
    )
  }
}