/**
 * Minimal Express API: /api/agent, /health.
 * No DB, no auth. CORS allowed for frontend. Production-ready env (PORT, CORS_ORIGIN).
 */

const express = require('express')
const cors = require('cors')

const PORT = Number(process.env.PORT) || 8080
const CORS_ORIGIN = process.env.CORS_ORIGIN || 'http://localhost:3000'

const app = express()

app.use(cors({ origin: CORS_ORIGIN }))
app.use(express.json())

/** Build OpenAI client and full prompt from request body. Returns { openai, modelId, fullPrompt } or { error }. */
function buildAgentRequest(body) {
  const { prompt, context, contextNodes, connection: conn, reasoning } = body ?? {}
  const reasoningEnabled = Boolean(reasoning)
  let baseURL = process.env.AI_BASE_URL?.trim() || null
  let apiKey = process.env.OPENAI_API_KEY?.trim() || null
  let modelId = process.env.AI_MODEL?.trim() || (baseURL ? 'local-model' : 'gpt-4o-mini')
  if (conn && typeof conn === 'object') {
    const c = conn
    const provider = c.provider === 'openai' ? 'openai' : 'local'
    if (provider === 'local') {
      baseURL = (typeof c.baseURL === 'string' && c.baseURL.trim()) ? c.baseURL.trim() : baseURL
      apiKey = (typeof c.apiKey === 'string' && c.apiKey.trim()) ? c.apiKey.trim() : (apiKey || 'lm-studio')
    } else {
      baseURL = null
      apiKey = (typeof c.apiKey === 'string' && c.apiKey.trim()) ? c.apiKey.trim() : apiKey
    }
    if (typeof c.model === 'string' && c.model.trim()) modelId = c.model.trim()
  }
  if (!baseURL && !apiKey) {
    return { error: 'No AI configured. Set connection in Settings (AI) or env: OPENAI_API_KEY or AI_BASE_URL.' }
  }
  const basePrompt = [
    typeof prompt === 'string' ? prompt : 'No prompt provided.',
    context && typeof context === 'string' ? `\n\nAdditional context:\n${context}` : '',
    Array.isArray(contextNodes) && contextNodes.length > 0
      ? `\n\nContext from connected nodes:\n${contextNodes.map((n) => (n.content != null ? n.content : `${n.id}: (no content)`)).join('\n\n')}`
      : '',
  ].join('')
  const fullPrompt = reasoningEnabled
    ? basePrompt + '\n\nRespond in exactly two markdown sections. First: "## Reasoning" with your step-by-step reasoning. Then: "## Output" with only the final answer. No preamble.'
    : basePrompt + '\n\nRespond with structured markdown only. No preamble.'
  const { createOpenAI } = require('@ai-sdk/openai')
  const openai = createOpenAI({
    apiKey: apiKey || 'lm-studio',
    ...(baseURL && { baseURL, compatibility: 'compatible' }),
  })
  return { openai, modelId, fullPrompt }
}

/** POST /api/agent — run AI agent; body: { prompt, context?, contextNodes?, connection? }; returns { markdown }. */
app.post('/api/agent', async (req, res) => {
  try {
    const built = buildAgentRequest(req.body)
    if (built.error) return res.status(503).json({ error: built.error })
    const { generateText } = await import('ai')
    const result = await generateText({
      model: built.openai(built.modelId),
      prompt: built.fullPrompt,
    })
    const markdown = result?.text ?? ''
    res.json({ markdown })
  } catch (err) {
    console.error('Agent error:', err)
    res.status(500).json({ error: err?.message ?? 'Agent request failed' })
  }
})

/** POST /api/agent/stream — same as /api/agent but streams plain text (markdown) chunks. */
app.post('/api/agent/stream', async (req, res) => {
  try {
    const built = buildAgentRequest(req.body)
    if (built.error) return res.status(503).json({ error: built.error })
    const { streamText } = await import('ai')
    const result = streamText({
      model: built.openai(built.modelId),
      prompt: built.fullPrompt,
    })
    res.setHeader('Content-Type', 'text/plain; charset=utf-8')
    res.setHeader('Transfer-Encoding', 'chunked')
    result.pipeTextStreamToResponse(res)
  } catch (err) {
    console.error('Agent stream error:', err)
    res.status(500).json({ error: err?.message ?? 'Agent request failed' })
  }
})

/** Health check for Docker / orchestration */
app.get('/health', (req, res) => {
  res.status(200).json({ ok: true })
})

app.listen(PORT, '0.0.0.0', () => {
  console.log(`Backend listening on port ${PORT} (CORS: ${CORS_ORIGIN})`)
})