import Anthropic from '@anthropic-ai/sdk'

/**
 * Netlify Functions v2 handler.
 *
 * Proxies a request from the React frontend to a Claude Console-defined
 * Managed Agent via the /v1/sessions endpoints. The agent's model, system
 * prompt, tools, MCP servers, and skills are configured in the Console and
 * referenced here by ID. We open the SSE event stream first, then send a
 * `user.message` event, and pipe each `agent.message` text block to the
 * client through a ReadableStream so we never hit Netlify's 26-second
 * synchronous execution limit.
 */

// All Managed Agents endpoints require this beta header.
const MANAGED_AGENTS_BETA = 'managed-agents-2026-04-01'

// ---------------------------------------------------------------------------
// Anthropic client (reused across warm Lambda invocations)
// ---------------------------------------------------------------------------
let _client
function getClient() {
  if (_client) return _client
  if (!process.env.ANTHROPIC_API_KEY) {
    throw new Error('Server is missing ANTHROPIC_API_KEY')
  }
  _client = new Anthropic({
    apiKey: process.env.ANTHROPIC_API_KEY,
    defaultHeaders: { 'anthropic-beta': MANAGED_AGENTS_BETA },
  })
  return _client
}

// ---------------------------------------------------------------------------
// Handler
// ---------------------------------------------------------------------------
export default async (req /*, context */) => {
  if (req.method !== 'POST') {
    return new Response('Method Not Allowed', { status: 405 })
  }

  let payload
  try {
    payload = await req.json()
  } catch {
    return new Response('Invalid JSON body', { status: 400 })
  }

  const {
    stationName = '',
    stationLocation = '',
    stationWebsite = '',
  } = payload || {}

  // Server-side URL validation (mirrors the client-side regex).
  const URL_REGEX =
    /^(https?:\/\/)?([\w-]+\.)+[\w-]{2,}(\/[\w\-._~:/?#[\]@!$&'()*+,;=%]*)?$/i
  if (!URL_REGEX.test(stationWebsite)) {
    return new Response('Invalid station website URL', { status: 400 })
  }

  // Read env vars at request time (Netlify makes them available per-invocation).
  const AGENT_ID = process.env.ANTHROPIC_AGENT_ID
  const ENVIRONMENT_ID = process.env.ANTHROPIC_ENVIRONMENT_ID
  const VAULT_IDS = (process.env.ANTHROPIC_VAULT_IDS || '')
    .split(',')
    .map((s) => s.trim())
    .filter(Boolean)

  const missing = []
  if (!AGENT_ID) missing.push('ANTHROPIC_AGENT_ID')
  if (!ENVIRONMENT_ID) missing.push('ANTHROPIC_ENVIRONMENT_ID')
  if (missing.length) {
    return new Response(`Server is missing env var(s): ${missing.join(', ')}`, {
      status: 500,
    })
  }

  let client
  try {
    client = getClient()
  } catch (err) {
    return new Response(
      `Failed to initialize agent: ${err.message || err}`,
      { status: 500 },
    )
  }

  const userMessage = `Here is a new public media station intake:

- Station Name: ${stationName}
- Station Location: ${stationLocation}
- Station Website: ${stationWebsite}

Please follow your instructions to produce the funding outlook brief.`

  // ----- Create the session -----
  let session
  try {
    const sessionParams = {
      agent: AGENT_ID,
      environment_id: ENVIRONMENT_ID,
    }
    if (VAULT_IDS.length) sessionParams.vault_ids = VAULT_IDS
    session = await client.beta.sessions.create(sessionParams)
  } catch (err) {
    return new Response(
      `Failed to create session: ${err.message || err}`,
      { status: 500 },
    )
  }

  // ----- Open the event stream BEFORE sending the user message -----
  // (Stream-first ensures we don't miss any events the agent emits.)
  let upstream
  try {
    upstream = await client.beta.sessions.events.stream(session.id)
  } catch (err) {
    return new Response(
      `Failed to open session event stream: ${err.message || err}`,
      { status: 500 },
    )
  }

  // ----- Send the kickoff user.message event -----
  try {
    await client.beta.sessions.events.send(session.id, {
      events: [
        {
          type: 'user.message',
          content: [{ type: 'text', text: userMessage }],
        },
      ],
    })
  } catch (err) {
    return new Response(
      `Failed to send user message: ${err.message || err}`,
      { status: 500 },
    )
  }

  // ----- Pipe agent.message text blocks to the client -----
  const encoder = new TextEncoder()
  const seenEventIds = new Set()
  const stream = new ReadableStream({
    async start(controller) {
      try {
        for await (const event of upstream) {
          if (event.id) {
            if (seenEventIds.has(event.id)) {
              // Still need to evaluate terminal events even if seen.
            } else {
              seenEventIds.add(event.id)
              if (event.type === 'agent.message' && Array.isArray(event.content)) {
                for (const block of event.content) {
                  if (block?.type === 'text' && block.text) {
                    controller.enqueue(encoder.encode(block.text))
                  }
                }
              } else if (event.type === 'session.error') {
                const msg = event.error?.message || 'unknown session error'
                controller.enqueue(encoder.encode(`\n\n[session error: ${msg}]`))
              }
            }
          }

          // Terminal-state gate.
          if (event.type === 'session.status_terminated') break
          if (
            event.type === 'session.status_idle' &&
            event.stop_reason?.type !== 'requires_action'
          ) {
            break
          }
        }
        controller.close()
      } catch (err) {
        controller.enqueue(
          encoder.encode(`\n\n[stream error: ${err.message || err}]`),
        )
        controller.close()
      }
    },
    cancel() {
      // If the client disconnects, abort the upstream stream.
      try {
        upstream.controller?.abort?.()
      } catch {
        /* ignore */
      }
    },
  })

  return new Response(stream, {
    status: 200,
    headers: {
      'Content-Type': 'text/plain; charset=utf-8',
      'Cache-Control': 'no-cache, no-transform',
      'X-Accel-Buffering': 'no',
    },
  })
}

export const config = {
  path: '/.netlify/functions/agent-proxy',
}