commit 40c37b58806199fe17bcec83bf8fdcd47ba9ce68
Author: Matthew-js <matthewjsetiawan@gmail.com>
Date:   Fri Oct 3 14:32:45 2025 +0700

    first commit

diff --git a/config/db.go b/config/db.go
new file mode 100644
index 0000000..8b8b819
--- /dev/null
+++ b/config/db.go
@@ -0,0 +1,51 @@
+package config
+
+import (
+	"database/sql"
+	"fmt"
+	"time"
+
+	_ "github.com/lib/pq"
+)
+
+// DB global var (may be nil if connection fails)
+var DB *sql.DB
+
+// Use the credentials you provided
+const (
+	host     = "202.46.28.160"
+	port     = 45432
+	user     = "5803024022"
+	password = "PW5803024022"
+	dbname   = "tgs03_5803024022"
+)
+
+// InitDB attempts to open a connection pool to Postgres.
+// It returns error if ping fails.
+func InitDB() (*sql.DB, error) {
+	dsn := fmt.Sprintf("host=%s port=%d user=%s password=%s dbname=%s sslmode=disable",
+		host, port, user, password, dbname)
+	db, err := sql.Open("postgres", dsn)
+	if err != nil {
+		return nil, err
+	}
+	// reasonable settings
+	db.SetMaxOpenConns(10)
+	db.SetMaxIdleConns(5)
+	db.SetConnMaxLifetime(time.Minute * 5)
+
+	// Ping with timeout
+	done := make(chan error, 1)
+	go func() {
+		done <- db.Ping()
+	}()
+	select {
+	case err := <-done:
+		if err != nil {
+			return nil, err
+		}
+	case <-time.After(2 * time.Second):
+		return nil, fmt.Errorf("db ping timeout")
+	}
+	return db, nil
+}
diff --git a/context_handler/context_handler.go b/context_handler/context_handler.go
new file mode 100644
index 0000000..3b537aa
--- /dev/null
+++ b/context_handler/context_handler.go
@@ -0,0 +1,43 @@
+package context_handler
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"time"
+)
+
+type keyType string
+
+const userKey keyType = "userID"
+
+// WithUserID stores user id in context
+func WithUserID(ctx context.Context, userID string) context.Context {
+	return context.WithValue(ctx, userKey, userID)
+}
+
+// FetchRiwayatKursus simulates fetching course history but respects context deadlines/cancel.
+func FetchRiwayatKursus(ctx context.Context) (string, error) {
+	// try to read user ID
+	uid, _ := ctx.Value(userKey).(string)
+	if uid == "" {
+		uid = "unknown"
+	}
+
+	// simulate work that may take up to 2 seconds
+	work := make(chan string, 1)
+
+	go func() {
+		// simulate slower work 1.5s
+		time.Sleep(1500 * time.Millisecond)
+		work <- fmt.Sprintf("history for user %s: [Course-A, Course-B]", uid)
+	}()
+
+	select {
+	case <-ctx.Done():
+		// context timed out or cancelled
+		return "", errors.New("fetch cancelled or timed out: " + ctx.Err().Error())
+	case res := <-work:
+		return res, nil
+	}
+}
diff --git a/enrollment/enrollment.go b/enrollment/enrollment.go
new file mode 100644
index 0000000..73d6084
--- /dev/null
+++ b/enrollment/enrollment.go
@@ -0,0 +1,79 @@
+package enrollment
+
+import (
+	"fmt"
+	"sync"
+	"time"
+)
+
+// IdempotencyStore stores results keyed by idempotency key.
+var (
+	store      map[string]string
+	storeMutex sync.RWMutex
+)
+
+// InitStore initializes the in-memory store.
+func InitStore() {
+	store = make(map[string]string)
+}
+
+// EnrollCourseIdempotent processes an enrollment with idempotency key.
+// If key exists, returns existing result immediately. If not, simulates
+// 1.5s work, stores and returns result.
+func EnrollCourseIdempotent(key string) string {
+	// check read lock first
+	storeMutex.RLock()
+	if res, ok := store[key]; ok {
+		storeMutex.RUnlock()
+		return res
+	}
+	storeMutex.RUnlock()
+
+	// Acquire write lock to ensure only one goroutine does the processing
+	storeMutex.Lock()
+	// double-check after acquiring write lock
+	if res, ok := store[key]; ok {
+		storeMutex.Unlock()
+		return res
+	}
+
+	// Simulate processing (1.5s)
+	time.Sleep(1500 * time.Millisecond)
+	res := fmt.Sprintf("enrolled-successful-for-key-%s", key)
+
+	// Save and release lock
+	store[key] = res
+	storeMutex.Unlock()
+	return res
+}
+
+// RunConcurrentEnrollments runs n goroutines that call EnrollCourseIdempotent with same key.
+// Returns map: which goroutine got what result and runtime info.
+func RunConcurrentEnrollments(key string, n int) map[string]interface{} {
+	var wg sync.WaitGroup
+	wg.Add(n)
+	resCh := make(chan string, n)
+	start := time.Now()
+
+	for i := 0; i < n; i++ {
+		go func(id int) {
+			defer wg.Done()
+			r := EnrollCourseIdempotent(key)
+			resCh <- fmt.Sprintf("goroutine-%d: %s", id+1, r)
+		}(i)
+	}
+
+	wg.Wait()
+	close(resCh)
+	out := make([]string, 0, n)
+	for r := range resCh {
+		out = append(out, r)
+	}
+	duration := time.Since(start)
+	return map[string]interface{}{
+		"key":      key,
+		"count":    n,
+		"duration": duration.String(),
+		"results":  out,
+	}
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..2222d24
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,5 @@
+module elearning-backend
+
+go 1.25.0
+
+require github.com/lib/pq v1.10.9
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..aeddeae
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,2 @@
+github.com/lib/pq v1.10.9 h1:YXG7RB+JIjhP29X+OtkiDnYaXQwpS4JEWq7dtCCRUEw=
+github.com/lib/pq v1.10.9/go.mod h1:AlVN5x4E4T544tWzH6hKfbfQvm3HdbOxrmggDNAPY9o=
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..8420fe0
--- /dev/null
+++ b/main.go
@@ -0,0 +1,119 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"time"
+
+	_ "github.com/lib/pq"
+
+	"tgs03-backend/config"
+	"tgs03-backend/context_handler"
+	"tgs03-backend/enrollment"
+	"tgs03-backend/poll"
+	"tgs03-backend/pool"
+	"tgs03-backend/worker"
+)
+
+func writeJSON(w http.ResponseWriter, v interface{}) {
+	w.Header().Set("Content-Type", "application/json")
+	_ = json.NewEncoder(w).Encode(v)
+}
+
+func main() {
+	// initialize DB (attempt). If DB not reachable, still continue (some features simulate).
+	db, err := config.InitDB()
+	if err != nil {
+		log.Printf("Warning: failed connect DB: %v (continuing in simulation mode)", err)
+	} else {
+		// keep db on global package
+		defer db.Close()
+		config.DB = db
+	}
+
+	// Initialize pool manager (simulated connections)
+	pm := pool.NewDBManager(5) // capacity 5
+
+	// Initialize idempotency store
+	enrollment.InitStore()
+
+	mux := http.NewServeMux()
+
+	// Endpoint: /sertifikasi -> run 50 goroutines with WaitGroup (Tugas 1.1)
+	mux.HandleFunc("/sertifikasi", func(w http.ResponseWriter, r *http.Request) {
+		n := 50
+		start := time.Now()
+		results := worker.RunSertifikasi(n)
+		duration := time.Since(start)
+		writeJSON(w, map[string]interface{}{
+			"count":    n,
+			"duration": duration.String(),
+			"results":  results,
+		})
+	})
+
+	// Endpoint: /pool -> run 20 goroutines that call EksekusiQuery (Tugas 1.2)
+	mux.HandleFunc("/pool", func(w http.ResponseWriter, r *http.Request) {
+		n := 20
+		// run queries concurrently
+		res := pm.RunQueries(n)
+		writeJSON(w, map[string]interface{}{
+			"requested": n,
+			"results":   res,
+		})
+	})
+
+	// Endpoint: /poll -> worker pool 5 workers, send 100 jobs (Tugas 1.3)
+	mux.HandleFunc("/poll", func(w http.ResponseWriter, r *http.Request) {
+		jobCount := 100
+		workers := 5
+		results := poll.RunPollSimulation(workers, jobCount)
+		writeJSON(w, map[string]interface{}{
+			"workers":   workers,
+			"job_count": jobCount,
+			"results":   results,
+		})
+	})
+
+	// Endpoint: /context -> call FetchRiwayatKursus with 1s timeout (Tugas 2.1 & 2.2)
+	mux.HandleFunc("/context", func(w http.ResponseWriter, r *http.Request) {
+		ctx, cancel := context.WithTimeout(context.Background(), time.Second*1)
+		defer cancel()
+		// attach user id
+		ctx = context_handler.WithUserID(ctx, "REQ-456")
+
+		start := time.Now()
+		res, err := context_handler.FetchRiwayatKursus(ctx)
+		duration := time.Since(start)
+		if err != nil {
+			writeJSON(w, map[string]interface{}{
+				"error":    err.Error(),
+				"duration": duration.String(),
+			})
+			return
+		}
+		writeJSON(w, map[string]interface{}{
+			"duration": duration.String(),
+			"data":     res,
+		})
+	})
+
+	// Endpoint: /enroll -> demonstrates idempotent enrollment (Tugas 2.3)
+	// Query params: key (idempotency key). If omitted uses "idem-key-sample".
+	mux.HandleFunc("/enroll", func(w http.ResponseWriter, r *http.Request) {
+		key := r.URL.Query().Get("key")
+		if key == "" {
+			key = "idem-key-sample"
+		}
+		// run 5 goroutines concurrently with same key to demonstrate idempotency
+		results := enrollment.RunConcurrentEnrollments(key, 5)
+		writeJSON(w, results)
+	})
+
+	addr := ":8080"
+	fmt.Printf("Server running at %s\n", addr)
+	log.Fatal(http.ListenAndServe(addr, mux))
+}
diff --git a/poll/poll_worker.go b/poll/poll_worker.go
new file mode 100644
index 0000000..557c11c
--- /dev/null
+++ b/poll/poll_worker.go
@@ -0,0 +1,49 @@
+package poll
+
+import (
+	"fmt"
+	"sync"
+	"time"
+)
+
+// PollJobWorker is a worker that processes jobs from channel.
+func PollJobWorker(id int, jobs <-chan int, results chan<- string, wg *sync.WaitGroup) {
+	defer wg.Done()
+	for job := range jobs {
+		// simulate processing time
+		time.Sleep(time.Millisecond * 20)
+		res := fmt.Sprintf("worker-%d processed job-%d", id, job)
+		results <- res
+	}
+}
+
+// RunPollSimulation launches `workers` workers and sends `jobCount` jobs.
+func RunPollSimulation(workers, jobCount int) []string {
+	jobs := make(chan int, 10) // capacity 10 as requested
+	results := make(chan string, jobCount)
+	var wg sync.WaitGroup
+
+	// start workers
+	wg.Add(workers)
+	for w := 1; w <= workers; w++ {
+		go PollJobWorker(w, jobs, results, &wg)
+	}
+
+	// send jobs
+	for j := 1; j <= jobCount; j++ {
+		jobs <- j
+	}
+	close(jobs) // close after sending all jobs
+
+	// wait for workers to finish then close results
+	go func() {
+		wg.Wait()
+		close(results)
+	}()
+
+	out := make([]string, 0, jobCount)
+	for r := range results {
+		out = append(out, r)
+	}
+	return out
+}
diff --git a/pool/pool_manager.go b/pool/pool_manager.go
new file mode 100644
index 0000000..983b68b
--- /dev/null
+++ b/pool/pool_manager.go
@@ -0,0 +1,64 @@
+package pool
+
+import (
+	"fmt"
+	"sync"
+	"time"
+)
+
+// DBManager simulates a connection pool using a channel of "connections".
+type DBManager struct {
+	pool chan int
+}
+
+// NewDBManager creates a pool manager with capacity `cap`.
+func NewDBManager(cap int) *DBManager {
+	p := make(chan int, cap)
+	// initialize simulated connections IDs 1..cap
+	for i := 1; i <= cap; i++ {
+		p <- i
+	}
+	return &DBManager{pool: p}
+}
+
+// getConn pulls a connection id from pool (blocking if none available)
+func (m *DBManager) getConn() int {
+	return <-m.pool
+}
+
+// releaseConn returns a connection id to the pool
+func (m *DBManager) releaseConn(id int) {
+	m.pool <- id
+}
+
+// EksekusiQuery simulates executing a query: take connection, wait 1s, release.
+func (m *DBManager) EksekusiQuery(query string) string {
+	conn := m.getConn()
+	// Simulate query execution
+	time.Sleep(time.Second * 1)
+	m.releaseConn(conn)
+	return fmt.Sprintf("conn-%d executed: %s", conn, query)
+}
+
+// RunQueries launches n goroutines that call EksekusiQuery.
+// Returns list of responses in the order goroutines finished.
+func (m *DBManager) RunQueries(n int) []string {
+	var wg sync.WaitGroup
+	wg.Add(n)
+	resCh := make(chan string, n)
+	for i := 0; i < n; i++ {
+		q := fmt.Sprintf("SELECT %d", i+1)
+		go func(query string) {
+			defer wg.Done()
+			res := m.EksekusiQuery(query)
+			resCh <- res
+		}(q)
+	}
+	wg.Wait()
+	close(resCh)
+	out := make([]string, 0, n)
+	for s := range resCh {
+		out = append(out, s)
+	}
+	return out
+}
diff --git a/worker/worker.go b/worker/worker.go
new file mode 100644
index 0000000..51d1111
--- /dev/null
+++ b/worker/worker.go
@@ -0,0 +1,32 @@
+package worker
+
+import (
+	"fmt"
+	"sync"
+	"time"
+)
+
+// ProsesSertifikasi simulates certification processing for a single user.
+func ProsesSertifikasi(userID int) string {
+	// simulate variable work (sleep)
+	time.Sleep(time.Millisecond * time.Duration(50+userID%10*20))
+	return fmt.Sprintf("user-%d: done", userID)
+}
+
+// RunSertifikasi starts n goroutines and waits for all to finish.
+// Returns results in a slice.
+func RunSertifikasi(n int) []string {
+	var wg sync.WaitGroup
+	wg.Add(n)
+
+	results := make([]string, n)
+	for i := 0; i < n; i++ {
+		i := i // capture
+		go func() {
+			defer wg.Done()
+			results[i] = ProsesSertifikasi(i + 1)
+		}()
+	}
+	wg.Wait()
+	return results
+}