programA-3/handler.go

package main

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"net/http"
	"strconv"
	"strings"
	"time"
)

func healthHandler(w http.ResponseWriter, r *http.Request) {
	now := time.Now().Format(time.RFC3339)
	ok(w, &map[string]string{"status": "UP", "time": now})
}

func studentsHandler(w http.ResponseWriter, r *http.Request) {
	switch r.Method {
	case http.MethodGet:
		listStudents(w, r)
	case http.MethodPost:
		createStudent(w, r)
	default:
		w.Header().Set("Allow", "GET, POST")
		fail(w, http.StatusMethodNotAllowed, "method not allowed")
	}
}

func studentByIDHandler(w http.ResponseWriter, r *http.Request) {
	idStr := strings.TrimPrefix(r.URL.Path, "/students/")
	id, err := strconv.ParseInt(idStr, 10, 64)
	if err != nil {
		fail(w, http.StatusBadRequest, "invalid student id")
		return
	}

	switch r.Method {
	case http.MethodGet:
		getStudent(w, r, id)
	case http.MethodPut:
		updateStudent(w, r, id)
	case http.MethodDelete:
		deleteStudent(w, r, id)
	default:
		w.Header().Set("Allow", "GET, PUT, DELETE")
		fail(w, http.StatusMethodNotAllowed, "method not allowed")
	}

}

func getStudent(w http.ResponseWriter, r *http.Request, id int64) {
	ctx, cancel := context.WithTimeout(r.Context(), 3*time.Second)
	defer cancel()

	var s Student

	err := db.QueryRowContext(ctx,
		`SELECT id,name,age,email,created_at,updated_at FROM students WHERE id=?`, id,
	).Scan(&s.ID, &s.Name, &s.Age, &s.Email, &s.CreatedAt, &s.UpdatedAt)
	if errors.Is(err, sql.ErrNoRows) {
		fail(w, http.StatusNotFound, "student not found")
		return
	} else if err != nil {
		fail(w, http.StatusInternalServerError, "db query error: "+err.Error())
		return
	}
	ok(w, &s)
}

func updateStudent(w http.ResponseWriter, r *http.Request, id int64) {
	if ct := r.Header.Get("Content-Type"); !strings.HasPrefix(strings.ToLower(ct), "application/json") {
		fail(w, http.StatusUnsupportedMediaType, "Content-Type must be application/json")
		return
	}

	var in struct {
		Name  string `json:"name"`
		Age   int    `json:"age"`
		Email string `json:"email"`
	}
	if err := json.NewDecoder(r.Body).Decode(&in); err != nil {
		fail(w, http.StatusBadRequest, "invalid json: "+err.Error())
		return
	}

	ctx, cancel := context.WithTimeout(r.Context(), 3*time.Second)
	defer cancel()

	res, err := db.ExecContext(ctx,
		`UPDATE students SET name=?, age=?, email=? WHERE id=?`,
		in.Name, in.Age, in.Email, id)
	if err != nil {
		if strings.Contains(strings.ToLower(err.Error()), "duplicate") {
			fail(w, http.StatusConflict, "email already exists")
			return
		}
		fail(w, http.StatusInternalServerError, "update error: "+err.Error())
		return
	}
	n, _ := res.RowsAffected()
	if n == 0 {
		fail(w, http.StatusNotFound, "student not found")
		return
	}

	getStudent(w, r, id)
}

func deleteStudent(w http.ResponseWriter, r *http.Request, id int64) {
	ctx, cancel := context.WithTimeout(r.Context(), 3*time.Second)
	defer cancel()

	res, err := db.ExecContext(ctx, `DELETE FROM students WHERE id=?`, id)
	if err != nil {
		fail(w, http.StatusInternalServerError, "delete error: "+err.Error())
		return
	}
	n, _ := res.RowsAffected()
	if n == 0 {
		fail(w, http.StatusNotFound, "student not found")
		return
	}

	ok(w, &map[string]any{"deleted": id})
}

func createStudent(w http.ResponseWriter, r *http.Request) {
	if ct := r.Header.Get("Content-Type"); !strings.HasPrefix(strings.ToLower(ct), "application/json") {
		fail(w, http.StatusUnsupportedMediaType, "Context-Type must be application/json")
		return
	}
	var in struct {
		Name  string `json:"name"`
		Age   int    `json:"age"`
		Email string `json:"email"`
	}
	if err := json.NewDecoder(r.Body).Decode(&in); err != nil {
		fail(w, http.StatusBadRequest, "invalid json: "+err.Error())
		return
	}
	if strings.TrimSpace(in.Name) == "" || in.Age <= 0 || strings.TrimSpace(in.Email) == "" {
		fail(w, http.StatusBadRequest, "name/age/email required")
		return
	}

	ctx, cancel := context.WithTimeout(r.Context(), 3*time.Second)
	defer cancel()

	res, err := db.ExecContext(ctx,
		`INSERT INTO students(name, age, email) VALUES(?,?,?)`,
		in.Name, in.Age, in.Email)
	if err != nil {
		fail(w, http.StatusInternalServerError, "insert error: "+err.Error())
		return
	}
	id, _ := res.LastInsertId()

	var out Student
	err = db.QueryRowContext(ctx,
		`SELECT id,name,age,email,created_at,updated_at FROM students WHERE id=?`, id,
	).Scan(&out.ID, &out.Name, &out.Age, &out.Email, &out.CreatedAt, &out.UpdatedAt)
	if err != nil {
		fail(w, http.StatusInternalServerError, "fetch created row error: "+err.Error())
		return
	}

	created(w, "/students/"+strconv.FormatInt(out.ID, 10), &out)
}

func listStudents(w http.ResponseWriter, r *http.Request) {
	ctx, cancel := context.WithTimeout(r.Context(), 3*time.Second)
	defer cancel()
	rows, err := db.QueryContext(ctx,
		`SELECT id,name,age,email,created_at,updated_at FROM students ORDER BY id`)
	if err != nil {
		fail(w, http.StatusInternalServerError, "db query error: "+err.Error())
		return
	}
	defer rows.Close()

	var items []Student
	for rows.Next() {
		var s Student
		if err := rows.Scan(&s.ID, &s.Name, &s.Age, &s.Email, &s.CreatedAt, &s.UpdatedAt); err != nil {
			fail(w, http.StatusInternalServerError, "scan error: "+err.Error())
			return
		}
		items = append(items, s)
	}
	if err := rows.Err(); err != nil {
		fail(w, http.StatusInternalServerError, "rows error: "+err.Error())
		return
	}
	ok(w, &items)
}