All files / src/app/api/analytics/ab-test route.ts

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/**
 * A/B Test API Route
 *
 * Handles A/B test variant assignment and conversion tracking.
 * GET - Get variant assignment for a visitor
 * POST - Track conversion
 */

import { NextRequest, NextResponse } from 'next/server';
import { z } from "zod";
import { prisma } from "@/lib/prisma";
import { logger } from "@/lib/logging";
import {
  withErrorHandling,
  successResponse,
  ApiError,
  ApiSuccessResponse,
  ApiErrorResponse } from "@/lib/api";
import { Prisma } from "@prisma/client";

// Schema for conversion tracking
const conversionSchema = z.object({
  experiment: z.string().min(1),
  visitorId: z.string().min(1).max(50),
  variant: z.string().min(1),
  value: z.number().optional()});

interface VariantResponse {
  variant: string | null;
  config?: Prisma.JsonValue;
}

/**
 * GET - Get variant assignment for a visitor
 */
async function handleGet(
  request: NextRequest
): Promise<NextResponse<ApiSuccessResponse<VariantResponse> | ApiErrorResponse>> {
  const { searchParams } = new URL(request.url);
  const experimentName = searchParams.get("experiment");
  const visitorId = searchParams.get("visitorId");

  if (!experimentName || !visitorId) {
    throw ApiError.badRequest("Missing experiment or visitorId parameter");
  }

  // Check for existing assignment
  const existingAssignment = await prisma.aBTestAssignment.findFirst({
    where: {
      experiment: { name: experimentName },
      visitorId},
    include: { variant: true }});

  if (existingAssignment) {
    return successResponse({
      variant: existingAssignment.variant.name,
      config: existingAssignment.variant.config});
  }

  // Get experiment
  const experiment = await prisma.aBTestExperiment.findUnique({
    where: { name: experimentName, status: "RUNNING" },
    include: { variants: true }});

  if (!experiment) {
    // Experiment not found or not running
    return successResponse({ variant: null });
  }

  // Check traffic percentage
  if (experiment.trafficPercent < 100) {
    const random = Math.random() * 100;
    if (random > experiment.trafficPercent) {
      // Visitor not included in experiment
      return successResponse({ variant: null });
    }
  }

  // Assign variant based on weights
  const totalWeight = experiment.variants.reduce((sum, v) => sum + v.weight, 0);
  let random = Math.random() * totalWeight;
  let selectedVariant = experiment.variants[0];

  for (const variant of experiment.variants) {
    random -= variant.weight;
    if (random <= 0) {
      selectedVariant = variant;
      break;
    }
  }

  // Create assignment
  await prisma.aBTestAssignment.create({
    data: {
      experimentId: experiment.id,
      variantId: selectedVariant.id,
      visitorId}});

  // Increment impressions
  await prisma.aBTestVariant.update({
    where: { id: selectedVariant.id },
    data: { impressions: { increment: 1 } }});

  logger.info(`A/B test assignment: ${experimentName} -> ${selectedVariant.name}`, {
    category: "API",
    experimentId: experiment.id,
    variantId: selectedVariant.id,
    visitorId});

  return successResponse({
    variant: selectedVariant.name,
    config: selectedVariant.config});
}

export const GET = withErrorHandling(handleGet);

/**
 * POST - Track conversion for A/B test
 */
async function handlePost(
  request: NextRequest
): Promise<NextResponse<ApiSuccessResponse<{ alreadyConverted?: boolean }> | ApiErrorResponse>> {
  const body = await request.json();
  const data = conversionSchema.parse(body);

  // Find the assignment
  const assignment = await prisma.aBTestAssignment.findFirst({
    where: {
      experiment: { name: data.experiment },
      visitorId: data.visitorId,
      variant: { name: data.variant }},
    include: { variant: true }});

  if (!assignment) {
    throw ApiError.notFound("Assignment");
  }

  // Don't update if already converted
  if (assignment.converted) {
    return successResponse({ alreadyConverted: true });
  }

  // Update assignment as converted
  await prisma.aBTestAssignment.update({
    where: { id: assignment.id },
    data: {
      converted: true,
      convertedAt: new Date(),
      conversionValue: data.value}});

  // Increment variant conversions
  await prisma.aBTestVariant.update({
    where: { id: assignment.variantId },
    data: { conversions: { increment: 1 } }});

  logger.info(`A/B test conversion: ${data.experiment} -> ${data.variant}`, {
    category: "API",
    visitorId: data.visitorId,
    value: data.value});

  return successResponse({});
}

export const POST = withErrorHandling(handlePost);