implement SMS sending feature with user balance validation and MySQL integration

Author: Armin

app/app.go

@@ -1,17 +1,71 @@
 package app
 
 import (
+	"fmt"
+	"log/slog"
+	"os"
+
+	_ "github.com/go-sql-driver/mysql"
+	"github.com/jmoiron/sqlx"
 	"github.com/labstack/echo/v4"
 )
 
 var (
-	Echo *echo.Echo
+	Echo   *echo.Echo
+	Logger *slog.Logger
+	DB     *sqlx.DB
 )
 
 func Init() {
-	InitEcho()
+	initLogger()
+	initDB()
+	initEcho()
+}
+
+func initLogger() {
+	handler := slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{})
+	Logger = slog.New(handler)
+}
+
+type dbConfig struct {
+	Username string
+	Password string
+	Host     string
+	Port     int
+	DBName   string
+}
+
+func ConnectionString(dbConfig dbConfig) string {
+	url := fmt.Sprintf("%s:%s@tcp(%s:%d)/%s",
+		dbConfig.Username,
+		dbConfig.Password,
+		dbConfig.Host,
+		dbConfig.Port,
+		dbConfig.DBName)
+	return url
+}
+
+func initDB() {
+	var err error
+	DB, err = sqlx.Open("mysql", ConnectionString(dbConfig{
+		Username: "sms_user",
+		Password: "sms_pass",
+		Host:     "localhost",
+		Port:     3306,
+		DBName:   "sms_gateway",
+	}))
+	if err != nil {
+		panic(err)
+	}
+
+	if err := DB.Ping(); err != nil {
+		panic(err)
+	}
+
+	// migrate
+
 }
 
-func InitEcho() {
+func initEcho() {
 	Echo = echo.New()
 }

cmd/api/main.go

@@ -4,11 +4,14 @@ import (
 	"fmt"
 	"sms-gateway/app"
 	"sms-gateway/config"
+	"sms-gateway/internal/sms"
 )
 
 func main() {
 	app.Init()
 
+	app.Echo.POST("/sms/send", sms.SendHandler)
+
 	fmt.Printf("Starting server on %s ...\n", config.AppListenAddr)
 	if err := app.Echo.Start(config.AppListenAddr); err != nil {
 		panic(err)

docker-compose.yml

@@ -0,0 +1,25 @@
+version: "3.9"
+
+services:
+  mysql:
+    image: mysql:8.4
+    container_name: sms_gateway_mysql
+    restart: unless-stopped
+    environment:
+      MYSQL_DATABASE: sms_gateway
+      MYSQL_USER: sms_user
+      MYSQL_PASSWORD: sms_pass
+      MYSQL_ROOT_PASSWORD: root_pass
+    ports:
+      - "3306:3306"
+    volumes:
+      - mysql_data:/var/lib/mysql
+    healthcheck:
+      test: ["CMD", "mysqladmin", "ping", "-h", "localhost"]
+      interval: 10s
+      timeout: 5s
+      retries: 5
+
+volumes:
+  mysql_data:
+

go.mod

@@ -3,11 +3,14 @@ module sms-gateway
 go 1.25
 
 require (
+	github.com/jmoiron/sqlx v1.4.0
 	github.com/joho/godotenv v1.5.1
 	github.com/labstack/echo/v4 v4.14.0
 )
 
 require (
+	filippo.io/edwards25519 v1.1.0 // indirect
+	github.com/go-sql-driver/mysql v1.9.3 // indirect
 	github.com/labstack/gommon v0.4.2 // indirect
 	github.com/mattn/go-colorable v0.1.14 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect

go.sum

@@ -1,15 +1,27 @@
+filippo.io/edwards25519 v1.1.0 h1:FNf4tywRC1HmFuKW5xopWpigGjJKiJSV0Cqo0cJWDaA=
+filippo.io/edwards25519 v1.1.0/go.mod h1:BxyFTGdWcka3PhytdK4V28tE5sGfRvvvRV7EaN4VDT4=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/go-sql-driver/mysql v1.8.1 h1:LedoTUt/eveggdHS9qUFC1EFSa8bU2+1pZjSRpvNJ1Y=
+github.com/go-sql-driver/mysql v1.8.1/go.mod h1:wEBSXgmK//2ZFJyE+qWnIsVGmvmEKlqwuVSjsCm7DZg=
+github.com/go-sql-driver/mysql v1.9.3 h1:U/N249h2WzJ3Ukj8SowVFjdtZKfu9vlLZxjPXV1aweo=
+github.com/go-sql-driver/mysql v1.9.3/go.mod h1:qn46aNg1333BRMNU69Lq93t8du/dwxI64Gl8i5p1WMU=
+github.com/jmoiron/sqlx v1.4.0 h1:1PLqN7S1UYp5t4SrVVnt4nUVNemrDAtxlulVe+Qgm3o=
+github.com/jmoiron/sqlx v1.4.0/go.mod h1:ZrZ7UsYB/weZdl2Bxg6jCRO9c3YHl8r3ahlKmRT4JLY=
 github.com/joho/godotenv v1.5.1 h1:7eLL/+HRGLY0ldzfGMeQkb7vMd0as4CfYvUVzLqw0N0=
 github.com/joho/godotenv v1.5.1/go.mod h1:f4LDr5Voq0i2e/R5DDNOoa2zzDfwtkZa6DnEwAbqwq4=
 github.com/labstack/echo/v4 v4.14.0 h1:+tiMrDLxwv6u0oKtD03mv+V1vXXB3wCqPHJqPuIe+7M=
 github.com/labstack/echo/v4 v4.14.0/go.mod h1:xmw1clThob0BSVRX1CRQkGQ/vjwcpOMjQZSZa9fKA/c=
 github.com/labstack/gommon v0.4.2 h1:F8qTUNXgG1+6WQmqoUWnz8WiEU60mXVVw0P4ht1WRA0=
 github.com/labstack/gommon v0.4.2/go.mod h1:QlUFxVM+SNXhDL/Z7YhocGIBYOiwB0mXm1+1bAPHPyU=
+github.com/lib/pq v1.10.9 h1:YXG7RB+JIjhP29X+OtkiDnYaXQwpS4JEWq7dtCCRUEw=
+github.com/lib/pq v1.10.9/go.mod h1:AlVN5x4E4T544tWzH6hKfbfQvm3HdbOxrmggDNAPY9o=
 github.com/mattn/go-colorable v0.1.14 h1:9A9LHSqF/7dyVVX6g0U9cwm9pG3kP9gSzcuIPHPsaIE=
 github.com/mattn/go-colorable v0.1.14/go.mod h1:6LmQG8QLFO4G5z1gPvYEzlUgJ2wF+stgPZH1UqBm1s8=
 github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWEY=
 github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
+github.com/mattn/go-sqlite3 v1.14.22 h1:2gZY6PC6kBnID23Tichd1K+Z0oS6nE/XwU+Vz/5o4kU=
+github.com/mattn/go-sqlite3 v1.14.22/go.mod h1:Uh1q+B4BYcTPb+yiD3kU8Ct7aC0hY9fxUwlHK0RXw+Y=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=

internal/balance/db/db.sql

@@ -0,0 +1,25 @@
+CREATE TABLE user_balances (
+    user_id BIGINT PRIMARY KEY,
+    balance BIGINT NOT NULL DEFAULT 0,
+    last_updated TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    version BIGINT NOT NULL DEFAULT 0
+);
+
+-- seed
+insert into user_balances (user_id, balance)
+values (1,100);
+
+
+CREATE TABLE user_transactions (
+                                   transaction_id BIGINT AUTO_INCREMENT PRIMARY KEY,
+                                   user_id BIGINT NOT NULL,
+                                   amount BIGINT NOT NULL,  -- Positive for deposit, negative for withdrawal
+                                   new_balance BIGINT NOT NULL,  -- Balance after this transaction
+                                   transaction_type VARCHAR(50) NOT NULL,  -- e.g., 'deposit', 'withdrawal', 'transfer'
+                                   description TEXT,
+                                   created_at DATETIME(6) NOT NULL DEFAULT CURRENT_TIMESTAMP(6),
+
+                                   INDEX idx_user_id_created_at (user_id, created_at DESC),
+                                   INDEX idx_transaction_type (transaction_type),
+                                   FOREIGN KEY (user_id) REFERENCES user_balances(user_id) ON DELETE CASCADE
+) ENGINE=InnoDB;

internal/balance/service.go

@@ -0,0 +1,42 @@
+package balance
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"sms-gateway/app"
+	"sms-gateway/internal/model"
+)
+
+type UserHasEnoughBalanceRequest struct {
+	CustomerID int64
+	Quantity   int
+	Type       model.Type
+}
+
+func UserHasEnoughBalance(ctx context.Context, req UserHasEnoughBalanceRequest) (bool, error) {
+
+	const query = `SELECT balance FROM user_balances WHERE user_id = ?`
+	var balance int64
+	if err := app.DB.QueryRowxContext(ctx, query, req.CustomerID).Scan(&balance); err != nil {
+		if errors.Is(err, sql.ErrNoRows) {
+			return false, nil
+		}
+		return false, err
+	}
+
+	price := calculatePrice(req.Type, req.Quantity)
+	return balance >= price, nil
+}
+
+func calculatePrice(Type model.Type, Quantity int) int64 {
+	return int64(getPricePerType(Type) * Quantity)
+}
+
+// could read from DB
+func getPricePerType(t model.Type) int {
+	if t == model.EXPRESS {
+		return 3
+	}
+	return 1
+}

internal/model/model.go

@@ -0,0 +1,15 @@
+package model
+
+type Type string
+
+const (
+	NORMAL  Type = "normal"
+	EXPRESS Type = "express"
+)
+
+type SMS struct {
+	CustomerID int64    `json:"customer_id"`
+	Text       string   `json:"text"`
+	Recipients []string `json:"recipients"`
+	Type       Type     `json:"type"`
+}

internal/sms/handler.go

@@ -0,0 +1,49 @@
+package sms
+
+import (
+	"encoding/json"
+	"net/http"
+	"sms-gateway/app"
+	"sms-gateway/internal/balance"
+	"sms-gateway/internal/model"
+
+	"github.com/labstack/echo/v4"
+)
+
+func SendHandler(c echo.Context) error {
+	var s model.SMS
+	if err := json.NewDecoder(c.Request().Body).Decode(&s); err != nil {
+		app.Logger.Error("invalid input ", "err", err)
+		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid input"})
+	}
+
+	if len(s.Recipients) == 0 {
+		app.Logger.Error("zero recipients")
+		return c.JSON(http.StatusBadRequest, map[string]string{"error": "zero recipients"})
+	}
+
+	app.Logger.Info("", "s", s)
+
+	// check user balance
+	hasBalance, err := balance.UserHasEnoughBalance(c.Request().Context(), balance.UserHasEnoughBalanceRequest{
+		CustomerID: s.CustomerID,
+		Quantity:   len(s.Recipients),
+		Type:       s.Type,
+	})
+	if err != nil {
+		app.Logger.Error("UserHasEnoughBalance ", "err", err)
+		return c.JSON(http.StatusInternalServerError, map[string]string{"error": "internal error"})
+	}
+	if !hasBalance {
+		app.Logger.Info("User Has Not Enough Balance ", "user id ", s.CustomerID)
+		return c.JSON(http.StatusPaymentRequired, map[string]string{"error": "dont have "})
+	}
+
+	app.Logger.Info("user has Enough Balance", "s", s)
+
+	// if not ok return err
+	//else cut down the balance
+	//then send it in quew
+
+	return c.JSON(http.StatusOK, nil)
+}

pkg/env/env.go

@@ -46,14 +46,3 @@ func RequiredNotEmpty(key string) string {
 	}
 	return value
 }
-
-func Required(key string) string {
-	_, osSet := os.LookupEnv(key)
-	_, dotEnvSet := dotEnvMap[key]
-	if !osSet && !dotEnvSet {
-		if !testing.Testing() {
-			panic(fmt.Sprintf("`%s` is not set", key))
-		}
-	}
-	return getEnv(key)
-}