pmc-funder-tool/netlify/functions/agent-proxy.js

import Anthropic from '@anthropic-ai/sdk'

/**
 * Netlify Functions v2 handler.
 *
 * Proxies a request from the React frontend to the Anthropic Messages API,
 * configured for a Managed Agent workflow. We pipe `content_block_delta`
 * events directly to the client through a ReadableStream so we never hit
 * Netlify's 26-second synchronous execution limit.
 */

// ---------------------------------------------------------------------------
// Managed Agent configuration
// ---------------------------------------------------------------------------
// The Managed Agent ID is supplied via the ANTHROPIC_AGENT_ID env var. The
// agent's system prompt and model are defined in the Claude Console and used
// by default. ANTHROPIC_MODEL and ANTHROPIC_SYSTEM_PROMPT may optionally
// override them.

// ---------------------------------------------------------------------------
// 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,
  })
  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 })
  }

  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.`

  // ----- Build the streaming request -----
  // The Managed Agent's system prompt and model (configured in the Claude
  // Console) are used by default. Optional env vars can override them.
  const streamArgs = {
    model: process.env.ANTHROPIC_MODEL || 'claude-opus-4-6',
    max_tokens: 600000,
    messages: [
      {
        role: 'user',
        content: [{ type: 'text', text: userMessage }],
      },
    ],
  }
  if (process.env.ANTHROPIC_AGENT_ID) {
    streamArgs.agent_id = process.env.ANTHROPIC_AGENT_ID
  }
  if (process.env.ANTHROPIC_SYSTEM_PROMPT) {
    streamArgs.system = process.env.ANTHROPIC_SYSTEM_PROMPT
  }

  const upstream = client.messages.stream(streamArgs)

  // ----- Pipe content_block_delta events straight to the client -----
  const encoder = new TextEncoder()
  const stream = new ReadableStream({
    async start(controller) {
      try {
        for await (const event of upstream) {
          if (
            event.type === 'content_block_delta' &&
            event.delta?.type === 'text_delta' &&
            event.delta.text
          ) {
            controller.enqueue(encoder.encode(event.delta.text))
          }

          // Surface an explicit message if the agent decides to call a tool.
          // (Managed Agents may emit `input_json_delta` or `tool_use` blocks.)
          if (
            event.type === 'content_block_delta' &&
            event.delta?.type === 'input_json_delta' &&
            event.delta.partial_json
          ) {
            controller.enqueue(
              encoder.encode(
                `\n\n_[agent requested tool input: ${event.delta.partial_json}]_\n\n`,
              ),
            )
          }
        }
        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 Anthropic request.
      upstream.controller?.abort?.()
    },
  })

  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',
}