introduced supabase and experiment management UI (#23)

* introduced supabase and experiment management UI

* fixing cookie import

web/src/app/api/session/route.ts

@@ -1,13 +1,12 @@
 import { NextRequest, NextResponse } from 'next/server';
 import { randomUUID } from 'crypto';
-import { getSession, createSession } from '@/lib/sessionStore';
+import { getSession, createSession, setExperiment } from '@/lib/sessionStore';
 
 const COOKIE_NAME = 'phantom_session_id';
 const isProd = process.env.NODE_ENV === 'production';
 
 export async function GET(req: NextRequest) {
     try {
-        // check for existing session cookie
         const existingSession = req.cookies.get(COOKIE_NAME)?.value;
 
         if (existingSession) {
@@ -18,13 +17,11 @@ export async function GET(req: NextRequest) {
             });
         }
 
-        // mint new session id
         const sessionId = randomUUID();
         createSession(sessionId);
 
         const res = NextResponse.json({ sessionId, experimentId: undefined });
 
-        // set httpOnly cookie with security flags
         res.cookies.set({
             name: COOKIE_NAME,
             value: sessionId,
@@ -32,7 +29,7 @@ export async function GET(req: NextRequest) {
             sameSite: 'lax',
             secure: isProd,
             path: '/',
-            maxAge: 60 * 60 * 24 * 30, // 30 days
+            maxAge: 60 * 60 * 24 * 30,
         });
 
         return res;
@@ -44,3 +41,52 @@ export async function GET(req: NextRequest) {
         );
     }
 }
+
+export async function POST(req: NextRequest) {
+    try {
+        const body = await req.json();
+        const { experimentId } = body;
+
+        if (!experimentId) {
+            return NextResponse.json(
+                { error: 'experimentId is required' },
+                { status: 400 }
+            );
+        }
+
+        let sessionId = req.cookies.get(COOKIE_NAME)?.value;
+
+        if (!sessionId) {
+            sessionId = randomUUID();
+            createSession(sessionId);
+        }
+
+        setExperiment(sessionId, experimentId);
+
+        const res = NextResponse.json({
+            sessionId,
+            experimentId,
+            success: true
+        });
+
+        if (!req.cookies.get(COOKIE_NAME)) {
+            res.cookies.set({
+                name: COOKIE_NAME,
+                value: sessionId,
+                httpOnly: true,
+                sameSite: 'lax',
+                secure: isProd,
+                path: '/',
+                maxAge: 60 * 60 * 24 * 30,
+            });
+        }
+
+        return res;
+    } catch (err: any) {
+        console.error('session update error:', err);
+        return NextResponse.json(
+            { error: err.message || 'unknown error' },
+            { status: 500 }
+        );
+    }
+}