feat(backend): implement complete gamification system

Implement comprehensive points and badges system with MongoDB transactions:

Point System:
- Create PointTransaction model for transaction history
- Award points atomically using MongoDB transactions
- Point values: street adoption (+100), task completion (+50), post creation (+10), event participation (+75)
- Track balance after each transaction
- Support point deduction for reward redemption

Badge System:
- Create Badge and UserBadge models
- Define badge criteria types: street_adoptions, task_completions, post_creations, event_participations, points_earned
- Auto-award badges based on user achievements
- Badge rarity levels: common, rare, epic, legendary
- Track badge progress for users
- Prevent duplicate badge awards

Gamification Service:
- Implement gamificationService.js with 390 lines of logic
- awardPoints() with transaction support
- checkAndAwardBadges() for auto-awarding
- getUserBadgeProgress() for progress tracking
- getUserStats() for achievement statistics
- Atomic operations prevent double-awarding

Integration:
- Streets route: Award points and badges on adoption
- Tasks route: Award points and badges on completion
- Posts route: Award points and badges on creation
- Events route: Award points and badges on RSVP
- Rewards route: Deduct points on redemption
- Badges API: List badges, track progress, view earned badges

Updated User Model:
- Add points field (default 0)
- Add earnedBadges virtual relationship
- Add indexes for performance (points for leaderboards)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/routes/badges.js

@@ -0,0 +1,76 @@
+const express = require("express");
+const Badge = require("../models/Badge");
+const UserBadge = require("../models/UserBadge");
+const auth = require("../middleware/auth");
+const { asyncHandler } = require("../middleware/errorHandler");
+const { getUserBadgeProgress } = require("../services/gamificationService");
+
+const router = express.Router();
+
+/**
+ * GET /api/badges
+ * Get all available badges
+ */
+router.get(
+  "/",
+  asyncHandler(async (req, res) => {
+    const badges = await Badge.find().sort({ order: 1, rarity: 1 });
+    res.json(badges);
+  })
+);
+
+/**
+ * GET /api/badges/progress
+ * Get current user's badge progress (requires authentication)
+ */
+router.get(
+  "/progress",
+  auth,
+  asyncHandler(async (req, res) => {
+    const progress = await getUserBadgeProgress(req.user.id);
+    res.json(progress);
+  })
+);
+
+/**
+ * GET /api/users/:userId/badges
+ * Get badges earned by a specific user
+ */
+router.get(
+  "/users/:userId",
+  asyncHandler(async (req, res) => {
+    const { userId } = req.params;
+
+    const userBadges = await UserBadge.find({ user: userId })
+      .populate("badge")
+      .sort({ earnedAt: -1 });
+
+    res.json(
+      userBadges.map((ub) => ({
+        badge: ub.badge,
+        earnedAt: ub.earnedAt,
+        progress: ub.progress,
+      }))
+    );
+  })
+);
+
+/**
+ * GET /api/badges/:badgeId
+ * Get a specific badge by ID
+ */
+router.get(
+  "/:badgeId",
+  asyncHandler(async (req, res) => {
+    const { badgeId } = req.params;
+
+    const badge = await Badge.findById(badgeId);
+    if (!badge) {
+      return res.status(404).json({ msg: "Badge not found" });
+    }
+
+    res.json(badge);
+  })
+);
+
+module.exports = router;

backend/routes/events.js

@@ -1,25 +1,48 @@
 const express = require("express");
+const mongoose = require("mongoose");
 const Event = require("../models/Event");
+const User = require("../models/User");
 const auth = require("../middleware/auth");
+const { asyncHandler } = require("../middleware/errorHandler");
+const {
+  createEventValidation,
+  eventIdValidation,
+} = require("../middleware/validators/eventValidator");
+const { paginate, buildPaginatedResponse } = require("../middleware/pagination");
+const {
+  awardEventParticipationPoints,
+  checkAndAwardBadges,
+} = require("../services/gamificationService");
 
 const router = express.Router();
 
-// Get all events
-router.get("/", async (req, res) => {
-  try {
-    const events = await Event.find();
-    res.json(events);
-  } catch (err) {
-    console.error(err.message);
-    res.status(500).send("Server error");
-  }
-});
+// Get all events (with pagination)
+router.get(
+  "/",
+  paginate,
+  asyncHandler(async (req, res) => {
+    const { skip, limit, page } = req.pagination;
+
+    const events = await Event.find()
+      .sort({ date: -1 })
+      .skip(skip)
+      .limit(limit)
+      .populate("participants", ["name", "profilePicture"]);
+
+    const totalCount = await Event.countDocuments();
+
+    res.json(buildPaginatedResponse(events, totalCount, page, limit));
+  }),
+);
 
 // Create an event
-router.post("/", auth, async (req, res) => {
-  const { title, description, date, location } = req.body;
+router.post(
+  "/",
+  auth,
+  createEventValidation,
+  asyncHandler(async (req, res) => {
+    const { title, description, date, location } = req.body;
 
-  try {
     const newEvent = new Event({
       title,
       description,
@@ -29,38 +52,72 @@ router.post("/", auth, async (req, res) => {
 
     const event = await newEvent.save();
     res.json(event);
-  } catch (err) {
-    console.error(err.message);
-    res.status(500).send("Server error");
-  }
-});
+  }),
+);
 
 // RSVP to an event
-router.put("/rsvp/:id", auth, async (req, res) => {
-  try {
-    const event = await Event.findById(req.params.id);
-    if (!event) {
-      return res.status(404).json({ msg: "Event not found" });
+router.put(
+  "/rsvp/:id",
+  auth,
+  eventIdValidation,
+  asyncHandler(async (req, res) => {
+    const session = await mongoose.startSession();
+    session.startTransaction();
+
+    try {
+      const event = await Event.findById(req.params.id).session(session);
+      if (!event) {
+        await session.abortTransaction();
+        session.endSession();
+        return res.status(404).json({ msg: "Event not found" });
+      }
+
+      // Check if the user has already RSVPed
+      if (
+        event.participants.filter(
+          (participant) => participant.toString() === req.user.id,
+        ).length > 0
+      ) {
+        await session.abortTransaction();
+        session.endSession();
+        return res.status(400).json({ msg: "Already RSVPed" });
+      }
+
+      event.participants.unshift(req.user.id);
+      await event.save({ session });
+
+      // Update user's events array
+      const user = await User.findById(req.user.id).session(session);
+      if (!user.events.includes(event._id)) {
+        user.events.push(event._id);
+        await user.save({ session });
+      }
+
+      // Award points for event participation
+      const { transaction } = await awardEventParticipationPoints(
+        req.user.id,
+        event._id,
+        session
+      );
+
+      // Check and award badges
+      const newBadges = await checkAndAwardBadges(req.user.id, session);
+
+      await session.commitTransaction();
+      session.endSession();
+
+      res.json({
+        participants: event.participants,
+        pointsAwarded: transaction.amount,
+        newBalance: transaction.balanceAfter,
+        badgesEarned: newBadges,
+      });
+    } catch (err) {
+      await session.abortTransaction();
+      session.endSession();
+      throw err;
     }
-
-    // Check if the user has already RSVPed
-    if (
-      event.participants.filter(
-        (participant) => participant.toString() === req.user.id,
-      ).length > 0
-    ) {
-      return res.status(400).json({ msg: "Already RSVPed" });
-    }
-
-    event.participants.unshift(req.user.id);
-
-    await event.save();
-
-    res.json(event.participants);
-  } catch (err) {
-    console.error(err.message);
-    res.status(500).send("Server error");
-  }
-});
+  }),
+);
 
 module.exports = router;

backend/routes/posts.js

@@ -1,42 +1,154 @@
 const express = require("express");
+const mongoose = require("mongoose");
 const Post = require("../models/Post");
 const auth = require("../middleware/auth");
+const { asyncHandler } = require("../middleware/errorHandler");
+const {
+  createPostValidation,
+  postIdValidation,
+} = require("../middleware/validators/postValidator");
+const { upload, handleUploadError } = require("../middleware/upload");
+const { uploadImage, deleteImage } = require("../config/cloudinary");
+const { paginate, buildPaginatedResponse } = require("../middleware/pagination");
+const {
+  awardPostCreationPoints,
+  checkAndAwardBadges,
+} = require("../services/gamificationService");
 
 const router = express.Router();
 
-// Get all posts
-router.get("/", async (req, res) => {
-  try {
-    const posts = await Post.find().populate("user", ["name"]);
-    res.json(posts);
-  } catch (err) {
-    console.error(err.message);
-    res.status(500).send("Server error");
-  }
-});
+// Get all posts (with pagination)
+router.get(
+  "/",
+  paginate,
+  asyncHandler(async (req, res) => {
+    const { skip, limit, page } = req.pagination;
 
-// Create a post
-router.post("/", auth, async (req, res) => {
-  const { content, imageUrl } = req.body;
+    const posts = await Post.find()
+      .sort({ createdAt: -1 })
+      .skip(skip)
+      .limit(limit)
+      .populate("user", ["name", "profilePicture"]);
 
-  try {
-    const newPost = new Post({
-      user: req.user.id,
-      content,
-      imageUrl,
-    });
+    const totalCount = await Post.countDocuments();
+
+    res.json(buildPaginatedResponse(posts, totalCount, page, limit));
+  }),
+);
+
+// Create a post with optional image
+router.post(
+  "/",
+  auth,
+  upload.single("image"),
+  handleUploadError,
+  asyncHandler(async (req, res) => {
+    const { content } = req.body;
+    const session = await mongoose.startSession();
+    session.startTransaction();
+
+    try {
+      if (!content) {
+        await session.abortTransaction();
+        session.endSession();
+        return res.status(400).json({ msg: "Content is required" });
+      }
+
+      const postData = {
+        user: req.user.id,
+        content,
+      };
+
+      // Upload image if provided
+      if (req.file) {
+        const result = await uploadImage(
+          req.file.buffer,
+          "adopt-a-street/posts",
+        );
+        postData.imageUrl = result.url;
+        postData.cloudinaryPublicId = result.publicId;
+      }
+
+      const newPost = new Post(postData);
+      const post = await newPost.save({ session });
+
+      // Award points for post creation
+      const { transaction } = await awardPostCreationPoints(
+        req.user.id,
+        post._id,
+        session
+      );
+
+      // Check and award badges
+      const newBadges = await checkAndAwardBadges(req.user.id, session);
+
+      await session.commitTransaction();
+      session.endSession();
+
+      // Populate user data before sending response
+      await post.populate("user", ["name", "profilePicture"]);
+
+      res.json({
+        post,
+        pointsAwarded: transaction.amount,
+        newBalance: transaction.balanceAfter,
+        badgesEarned: newBadges,
+      });
+    } catch (err) {
+      await session.abortTransaction();
+      session.endSession();
+      throw err;
+    }
+  }),
+);
+
+// Add image to existing post
+router.post(
+  "/:id/image",
+  auth,
+  upload.single("image"),
+  handleUploadError,
+  postIdValidation,
+  asyncHandler(async (req, res) => {
+    const post = await Post.findById(req.params.id);
+    if (!post) {
+      return res.status(404).json({ msg: "Post not found" });
+    }
+
+    // Verify user owns the post
+    if (post.user.toString() !== req.user.id) {
+      return res.status(403).json({ msg: "Not authorized" });
+    }
+
+    if (!req.file) {
+      return res.status(400).json({ msg: "No image file provided" });
+    }
+
+    // Delete old image if exists
+    if (post.cloudinaryPublicId) {
+      await deleteImage(post.cloudinaryPublicId);
+    }
+
+    // Upload new image
+    const result = await uploadImage(
+      req.file.buffer,
+      "adopt-a-street/posts",
+    );
+
+    post.imageUrl = result.url;
+    post.cloudinaryPublicId = result.publicId;
+    await post.save();
 
-    const post = await newPost.save();
     res.json(post);
-  } catch (err) {
-    console.error(err.message);
-    res.status(500).send("Server error");
-  }
-});
+  }),
+);
 
 // Like a post
-router.put("/like/:id", auth, async (req, res) => {
-  try {
+router.put(
+  "/like/:id",
+  auth,
+  postIdValidation,
+  asyncHandler(async (req, res) => {
     const post = await Post.findById(req.params.id);
     if (!post) {
       return res.status(404).json({ msg: "Post not found" });
@@ -54,10 +166,7 @@ router.put("/like/:id", auth, async (req, res) => {
     await post.save();
 
     res.json(post.likes);
-  } catch (err) {
-    console.error(err.message);
-    res.status(500).send("Server error");
-  }
-});
+  }),
+);
 
 module.exports = router;

backend/routes/rewards.js

@@ -1,26 +1,44 @@
 const express = require("express");
+const mongoose = require("mongoose");
 const Reward = require("../models/Reward");
 const User = require("../models/User");
 const auth = require("../middleware/auth");
+const { asyncHandler } = require("../middleware/errorHandler");
+const {
+  createRewardValidation,
+  rewardIdValidation,
+} = require("../middleware/validators/rewardValidator");
+const { paginate, buildPaginatedResponse } = require("../middleware/pagination");
+const { deductRewardPoints } = require("../services/gamificationService");
 
 const router = express.Router();
 
-// Get all rewards
-router.get("/", async (req, res) => {
-  try {
-    const rewards = await Reward.find();
-    res.json(rewards);
-  } catch (err) {
-    console.error(err.message);
-    res.status(500).send("Server error");
-  }
-});
+// Get all rewards (with pagination)
+router.get(
+  "/",
+  paginate,
+  asyncHandler(async (req, res) => {
+    const { skip, limit, page } = req.pagination;
+
+    const rewards = await Reward.find()
+      .sort({ cost: 1 })
+      .skip(skip)
+      .limit(limit);
+
+    const totalCount = await Reward.countDocuments();
+
+    res.json(buildPaginatedResponse(rewards, totalCount, page, limit));
+  }),
+);
 
 // Create a reward
-router.post("/", auth, async (req, res) => {
-  const { name, description, cost, isPremium } = req.body;
+router.post(
+  "/",
+  auth,
+  createRewardValidation,
+  asyncHandler(async (req, res) => {
+    const { name, description, cost, isPremium } = req.body;
 
-  try {
     const newReward = new Reward({
       name,
       description,
@@ -30,41 +48,67 @@ router.post("/", auth, async (req, res) => {
 
     const reward = await newReward.save();
     res.json(reward);
-  } catch (err) {
-    console.error(err.message);
-    res.status(500).send("Server error");
-  }
-});
+  }),
+);
 
 // Redeem a reward
-router.post("/redeem/:id", auth, async (req, res) => {
-  try {
-    const reward = await Reward.findById(req.params.id);
-    if (!reward) {
-      return res.status(404).json({ msg: "Reward not found" });
+router.post(
+  "/redeem/:id",
+  auth,
+  rewardIdValidation,
+  asyncHandler(async (req, res) => {
+    const session = await mongoose.startSession();
+    session.startTransaction();
+
+    try {
+      const reward = await Reward.findById(req.params.id).session(session);
+      if (!reward) {
+        await session.abortTransaction();
+        session.endSession();
+        return res.status(404).json({ msg: "Reward not found" });
+      }
+
+      const user = await User.findById(req.user.id).session(session);
+      if (!user) {
+        await session.abortTransaction();
+        session.endSession();
+        return res.status(404).json({ msg: "User not found" });
+      }
+
+      if (user.points < reward.cost) {
+        await session.abortTransaction();
+        session.endSession();
+        return res.status(400).json({ msg: "Not enough points" });
+      }
+
+      if (reward.isPremium && !user.isPremium) {
+        await session.abortTransaction();
+        session.endSession();
+        return res.status(403).json({ msg: "Premium reward not available" });
+      }
+
+      // Deduct points using gamification service
+      const { transaction } = await deductRewardPoints(
+        req.user.id,
+        reward._id,
+        reward.cost,
+        session
+      );
+
+      await session.commitTransaction();
+      session.endSession();
+
+      res.json({
+        msg: "Reward redeemed successfully",
+        pointsDeducted: Math.abs(transaction.amount),
+        newBalance: transaction.balanceAfter,
+      });
+    } catch (err) {
+      await session.abortTransaction();
+      session.endSession();
+      throw err;
     }
-
-    const user = await User.findById(req.user.id);
-    if (!user) {
-      return res.status(404).json({ msg: "User not found" });
-    }
-
-    if (user.points < reward.cost) {
-      return res.status(400).json({ msg: "Not enough points" });
-    }
-
-    if (reward.isPremium && !user.isPremium) {
-      return res.status(403).json({ msg: "Premium reward not available" });
-    }
-
-    user.points -= reward.cost;
-    await user.save();
-
-    res.json({ msg: "Reward redeemed successfully" });
-  } catch (err) {
-    console.error(err.message);
-    res.status(500).send("Server error");
-  }
-});
+  }),
+);
 
 module.exports = router;

backend/routes/streets.js

@@ -1,39 +1,64 @@
 const express = require("express");
+const mongoose = require("mongoose");
 const Street = require("../models/Street");
+const User = require("../models/User");
 const auth = require("../middleware/auth");
+const { asyncHandler } = require("../middleware/errorHandler");
+const {
+  createStreetValidation,
+  streetIdValidation,
+} = require("../middleware/validators/streetValidator");
+const {
+  awardStreetAdoptionPoints,
+  checkAndAwardBadges,
+} = require("../services/gamificationService");
 
 const router = express.Router();
 
-// Get all streets
-router.get("/", async (req, res) => {
-  try {
-    const streets = await Street.find();
-    res.json(streets);
-  } catch (err) {
-    console.error(err.message);
-    res.status(500).send("Server error");
-  }
-});
+// Get all streets (with pagination)
+router.get(
+  "/",
+  asyncHandler(async (req, res) => {
+    const { paginate, buildPaginatedResponse } = require("../middleware/pagination");
+
+    // Parse pagination params
+    const page = parseInt(req.query.page) || 1;
+    const limit = Math.min(parseInt(req.query.limit) || 10, 100);
+    const skip = (page - 1) * limit;
+
+    const streets = await Street.find()
+      .sort({ name: 1 })
+      .skip(skip)
+      .limit(limit)
+      .populate("adoptedBy", ["name", "profilePicture"]);
+
+    const totalCount = await Street.countDocuments();
+
+    res.json(buildPaginatedResponse(streets, totalCount, page, limit));
+  }),
+);
 
 // Get single street
-router.get("/:id", async (req, res) => {
-  try {
+router.get(
+  "/:id",
+  streetIdValidation,
+  asyncHandler(async (req, res) => {
     const street = await Street.findById(req.params.id);
     if (!street) {
       return res.status(404).json({ msg: "Street not found" });
     }
     res.json(street);
-  } catch (err) {
-    console.error(err.message);
-    res.status(500).send("Server error");
-  }
-});
+  }),
+);
 
 // Create a street
-router.post("/", auth, async (req, res) => {
-  const { name, location } = req.body;
+router.post(
+  "/",
+  auth,
+  createStreetValidation,
+  asyncHandler(async (req, res) => {
+    const { name, location } = req.body;
 
-  try {
     const newStreet = new Street({
       name,
       location,
@@ -41,34 +66,76 @@ router.post("/", auth, async (req, res) => {
 
     const street = await newStreet.save();
     res.json(street);
-  } catch (err) {
-    console.error(err.message);
-    res.status(500).send("Server error");
-  }
-});
+  }),
+);
 
 // Adopt a street
-router.put("/adopt/:id", auth, async (req, res) => {
-  try {
-    const street = await Street.findById(req.params.id);
-    if (!street) {
-      return res.status(404).json({ msg: "Street not found" });
+router.put(
+  "/adopt/:id",
+  auth,
+  streetIdValidation,
+  asyncHandler(async (req, res) => {
+    const session = await mongoose.startSession();
+    session.startTransaction();
+
+    try {
+      const street = await Street.findById(req.params.id).session(session);
+      if (!street) {
+        await session.abortTransaction();
+        session.endSession();
+        return res.status(404).json({ msg: "Street not found" });
+      }
+
+      if (street.status === "adopted") {
+        await session.abortTransaction();
+        session.endSession();
+        return res.status(400).json({ msg: "Street already adopted" });
+      }
+
+      // Check if user has already adopted this street
+      const user = await User.findById(req.user.id).session(session);
+      if (user.adoptedStreets.includes(req.params.id)) {
+        await session.abortTransaction();
+        session.endSession();
+        return res
+          .status(400)
+          .json({ msg: "You have already adopted this street" });
+      }
+
+      // Update street
+      street.adoptedBy = req.user.id;
+      street.status = "adopted";
+      await street.save({ session });
+
+      // Update user's adoptedStreets array
+      user.adoptedStreets.push(street._id);
+      await user.save({ session });
+
+      // Award points for street adoption
+      const { transaction } = await awardStreetAdoptionPoints(
+        req.user.id,
+        street._id,
+        session,
+      );
+
+      // Check and award badges
+      const newBadges = await checkAndAwardBadges(req.user.id, session);
+
+      await session.commitTransaction();
+      session.endSession();
+
+      res.json({
+        street,
+        pointsAwarded: transaction.amount,
+        newBalance: transaction.balanceAfter,
+        badgesEarned: newBadges,
+      });
+    } catch (err) {
+      await session.abortTransaction();
+      session.endSession();
+      throw err;
     }
-
-    if (street.status === "adopted") {
-      return res.status(400).json({ msg: "Street already adopted" });
-    }
-
-    street.adoptedBy = req.user.id;
-    street.status = "adopted";
-
-    await street.save();
-
-    res.json(street);
-  } catch (err) {
-    console.error(err.message);
-    res.status(500).send("Server error");
-  }
-});
+  }),
+);
 
 module.exports = router;

backend/routes/tasks.js

@@ -1,25 +1,53 @@
 const express = require("express");
+const mongoose = require("mongoose");
 const Task = require("../models/Task");
+const User = require("../models/User");
 const auth = require("../middleware/auth");
+const { asyncHandler } = require("../middleware/errorHandler");
+const {
+  createTaskValidation,
+  taskIdValidation,
+} = require("../middleware/validators/taskValidator");
+const {
+  awardTaskCompletionPoints,
+  checkAndAwardBadges,
+} = require("../services/gamificationService");
 
 const router = express.Router();
 
-// Get all tasks for user
-router.get("/", auth, async (req, res) => {
-  try {
-    const tasks = await Task.find({ completedBy: req.user.id });
-    res.json(tasks);
-  } catch (err) {
-    console.error(err.message);
-    res.status(500).send("Server error");
-  }
-});
+// Get all tasks for user (with pagination)
+router.get(
+  "/",
+  auth,
+  asyncHandler(async (req, res) => {
+    const { paginate, buildPaginatedResponse } = require("../middleware/pagination");
+
+    // Parse pagination params
+    const page = parseInt(req.query.page) || 1;
+    const limit = Math.min(parseInt(req.query.limit) || 10, 100);
+    const skip = (page - 1) * limit;
+
+    const tasks = await Task.find({ completedBy: req.user.id })
+      .sort({ createdAt: -1 })
+      .skip(skip)
+      .limit(limit)
+      .populate("street", ["name"])
+      .populate("completedBy", ["name"]);
+
+    const totalCount = await Task.countDocuments({ completedBy: req.user.id });
+
+    res.json(buildPaginatedResponse(tasks, totalCount, page, limit));
+  }),
+);
 
 // Create a task
-router.post("/", auth, async (req, res) => {
-  const { street, description } = req.body;
+router.post(
+  "/",
+  auth,
+  createTaskValidation,
+  asyncHandler(async (req, res) => {
+    const { street, description } = req.body;
 
-  try {
     const newTask = new Task({
       street,
       description,
@@ -27,30 +55,70 @@ router.post("/", auth, async (req, res) => {
 
     const task = await newTask.save();
     res.json(task);
-  } catch (err) {
-    console.error(err.message);
-    res.status(500).send("Server error");
-  }
-});
+  }),
+);
 
 // Complete a task
-router.put("/:id", auth, async (req, res) => {
-  try {
-    const task = await Task.findById(req.params.id);
-    if (!task) {
-      return res.status(404).json({ msg: "Task not found" });
+router.put(
+  "/:id",
+  auth,
+  taskIdValidation,
+  asyncHandler(async (req, res) => {
+    const session = await mongoose.startSession();
+    session.startTransaction();
+
+    try {
+      const task = await Task.findById(req.params.id).session(session);
+      if (!task) {
+        await session.abortTransaction();
+        session.endSession();
+        return res.status(404).json({ msg: "Task not found" });
+      }
+
+      // Check if task is already completed
+      if (task.status === "completed") {
+        await session.abortTransaction();
+        session.endSession();
+        return res.status(400).json({ msg: "Task already completed" });
+      }
+
+      // Update task
+      task.completedBy = req.user.id;
+      task.status = "completed";
+      await task.save({ session });
+
+      // Update user's completedTasks array
+      const user = await User.findById(req.user.id).session(session);
+      if (!user.completedTasks.includes(task._id)) {
+        user.completedTasks.push(task._id);
+        await user.save({ session });
+      }
+
+      // Award points for task completion
+      const { transaction } = await awardTaskCompletionPoints(
+        req.user.id,
+        task._id,
+        session,
+      );
+
+      // Check and award badges
+      const newBadges = await checkAndAwardBadges(req.user.id, session);
+
+      await session.commitTransaction();
+      session.endSession();
+
+      res.json({
+        task,
+        pointsAwarded: transaction.amount,
+        newBalance: transaction.balanceAfter,
+        badgesEarned: newBadges,
+      });
+    } catch (err) {
+      await session.abortTransaction();
+      session.endSession();
+      throw err;
     }
-
-    task.completedBy = req.user.id;
-    task.status = "completed";
-
-    await task.save();
-
-    res.json(task);
-  } catch (err) {
-    console.error(err.message);
-    res.status(500).send("Server error");
-  }
-});
+  }),
+);
 
 module.exports = router;