// Example OAuth 2.1 with PKCE flow
import { createHash, randomBytes } from 'crypto'

// Generate code verifier and challenge
const codeVerifier = randomBytes(32).toString('base64url')
const codeChallenge = createHash('sha256')
  .update(codeVerifier)
  .digest('base64url')

// Step 1: Authorization URL
const authUrl = `https://shark-mcp.example.com/oauth/authorize?` +
  `response_type=code&` +
  `client_id=${credentials?.client_id}&` +
  `redirect_uri=${encodeURIComponent(redirectUri)}&` +
  `code_challenge=${codeChallenge}&` +
  `code_challenge_method=S256&` +
  `scope=read%20write`

// Step 2: Exchange code for token
const tokenResponse = await fetch('/oauth/token', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    grant_type: 'authorization_code',
    client_id: 'mcp_agent_abc123def456789',
    client_secret: 'sk_agent_xyz789uvw012345678901234567890abcdef',
    code: authorizationCode,
    redirect_uri: redirectUri,
    code_verifier: codeVerifier
  })
})

const { access_token } = await tokenResponse.json()

// Step 3: Use token for MCP requests
const mcpResponse = await fetch('/mcp/request_loan_terms', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${access_token}`,
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
    wallet_address: '0x...',
    principal_amount: 1000,
    term_days: 30
  })
})

// Example MCP tool implementation
import { Server } from '@modelcontextprotocol/sdk/server/index.js'
import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js'

const server = new Server(
  { name: 'shark-lending', version: '1.0.0' },
  { capabilities: { tools: {} } }
)

// Register loan request tool
server.setRequestHandler(CallToolRequestSchema, async (request) => {
  if (request.params.name === 'request_loan') {
    const response = await fetch('https://shark-mcp.example.com/mcp/request_loan_terms', {
      method: 'POST',
      headers: {
        'Authorization': `Bearer ${process.env.SHARK_ACCESS_TOKEN}`,
        'Content-Type': 'application/json'
      },
      body: JSON.stringify({
        wallet_address: request.params.arguments.wallet_address,
        principal_amount: request.params.arguments.amount,
        term_days: request.params.arguments.term_days || 30,
        agent_token: 'mcp_agent_abc123def456789'
      })
    })
    
    return { content: [{ type: 'text', text: await response.text() }] }
  }
})

// Start server
const transport = new StdioServerTransport()
await server.connect(transport)