Phase 2 scaffold: mitra online status & pairing logic

Add mitra online/offline status with heartbeat-based auto-offline,
customer-mitra pairing via Valkey pub/sub blast, session management,
and control center dashboard with real-time stats.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/src/services/session.service.js

@@ -0,0 +1,149 @@
+import { getDb } from '../db/client.js'
+import { publish } from '../plugins/valkey.js'
+
+const sql = getDb()
+
+export const getActiveSessionByCustomer = async (customerId) => {
+  const [session] = await sql`
+    SELECT cs.id, cs.customer_id, cs.mitra_id, cs.status, cs.created_at, cs.paired_at,
+      m.display_name AS mitra_display_name
+    FROM chat_sessions cs
+    LEFT JOIN mitras m ON m.id = cs.mitra_id
+    WHERE cs.customer_id = ${customerId}
+      AND cs.status IN ('active', 'pending_payment')
+    ORDER BY cs.created_at DESC LIMIT 1
+  `
+  return session
+}
+
+export const getActiveSessionsByMitra = async (mitraId) => {
+  const sessions = await sql`
+    SELECT cs.id, cs.customer_id, cs.status, cs.created_at, cs.paired_at,
+      c.display_name AS customer_display_name
+    FROM chat_sessions cs
+    INNER JOIN customers c ON c.id = cs.customer_id
+    WHERE cs.mitra_id = ${mitraId}
+      AND cs.status IN ('active', 'pending_payment')
+    ORDER BY cs.created_at DESC
+  `
+  return sessions
+}
+
+export const endSession = async (sessionId, endedBy) => {
+  const [session] = await sql`
+    UPDATE chat_sessions
+    SET status = 'completed', ended_at = NOW(), ended_by = ${endedBy}
+    WHERE id = ${sessionId} AND status IN ('active', 'pending_payment')
+    RETURNING id, customer_id, mitra_id, status, ended_at, ended_by
+  `
+
+  if (!session) {
+    throw Object.assign(new Error('Session not found or already ended'), {
+      code: 'SESSION_NOT_ACTIVE', statusCode: 409,
+    })
+  }
+
+  // Notify both parties
+  await publish(`session:${sessionId}:status`, {
+    type: 'session_ended',
+    session_id: sessionId,
+    ended_by: endedBy,
+  })
+
+  return session
+}
+
+export const rerouteSession = async (sessionId, newMitraId) => {
+  // Get current session
+  const [current] = await sql`
+    SELECT id, customer_id, mitra_id, status FROM chat_sessions
+    WHERE id = ${sessionId} AND status IN ('active', 'pending_payment')
+  `
+
+  if (!current) {
+    throw Object.assign(new Error('Session not found or not active'), {
+      code: 'SESSION_NOT_ACTIVE', statusCode: 409,
+    })
+  }
+
+  // Verify new mitra is online
+  const [newMitraStatus] = await sql`
+    SELECT is_online FROM mitra_online_status WHERE mitra_id = ${newMitraId}
+  `
+  if (!newMitraStatus?.is_online) {
+    throw Object.assign(new Error('Target mitra is not online'), {
+      code: 'MITRA_NOT_ONLINE', statusCode: 422,
+    })
+  }
+
+  const oldMitraId = current.mitra_id
+
+  // Update session with new mitra (forced assignment)
+  const [session] = await sql`
+    UPDATE chat_sessions
+    SET mitra_id = ${newMitraId}
+    WHERE id = ${sessionId}
+    RETURNING id, customer_id, mitra_id, status
+  `
+
+  const [newMitra] = await sql`
+    SELECT display_name FROM mitras WHERE id = ${newMitraId}
+  `
+
+  // Notify customer about reroute
+  await publish(`session:${sessionId}:status`, {
+    type: 'rerouted',
+    session_id: sessionId,
+    mitra_display_name: newMitra.display_name,
+  })
+
+  // Notify old mitra session removed
+  if (oldMitraId) {
+    await publish(`mitra:${oldMitraId}:requests`, {
+      type: 'session_rerouted',
+      session_id: sessionId,
+    })
+  }
+
+  // Notify new mitra about new session
+  await publish(`mitra:${newMitraId}:requests`, {
+    type: 'session_assigned',
+    session_id: sessionId,
+  })
+
+  return session
+}
+
+export const listSessions = async ({ page = 1, limit = 20, status } = {}) => {
+  const offset = (page - 1) * limit
+  const conditions = status
+    ? sql`WHERE cs.status = ${status}`
+    : sql``
+
+  const items = await sql`
+    SELECT cs.id, cs.customer_id, cs.mitra_id, cs.status, cs.created_at, cs.paired_at, cs.ended_at, cs.ended_by,
+      c.display_name AS customer_display_name,
+      m.display_name AS mitra_display_name
+    FROM chat_sessions cs
+    INNER JOIN customers c ON c.id = cs.customer_id
+    LEFT JOIN mitras m ON m.id = cs.mitra_id
+    ${conditions}
+    ORDER BY cs.created_at DESC
+    LIMIT ${limit} OFFSET ${offset}
+  `
+  const [{ count }] = await sql`SELECT COUNT(*) FROM chat_sessions cs ${conditions}`
+  return { items, total: Number(count), page, limit }
+}
+
+export const getSessionById = async (sessionId) => {
+  const [session] = await sql`
+    SELECT cs.id, cs.customer_id, cs.mitra_id, cs.status, cs.created_at, cs.paired_at, cs.ended_at, cs.ended_by,
+      c.display_name AS customer_display_name,
+      m.display_name AS mitra_display_name
+    FROM chat_sessions cs
+    INNER JOIN customers c ON c.id = cs.customer_id
+    LEFT JOIN mitras m ON m.id = cs.mitra_id
+    WHERE cs.id = ${sessionId}
+  `
+  return session
+}