feat(/v0.1/countries/count): implement.

Fix #1

Author: php-coder

go.mod

@@ -0,0 +1,5 @@
+module github.com/php-coder/mystamps-country
+
+go 1.13
+
+require github.com/go-sql-driver/mysql v1.4.1

go.sum

@@ -0,0 +1,2 @@
+github.com/go-sql-driver/mysql v1.4.1 h1:g24URVg0OFbNUTx9qqY1IRZ9D9z3iPyi5zKhQZpNwpA=
+github.com/go-sql-driver/mysql v1.4.1/go.mod h1:zAC/RDZ24gD3HViQzih4MyKcchzm+sOG5ZlKdlhCg5w=

main.go

@@ -1,15 +1,79 @@
 package main
 
+import "database/sql"
+import "fmt"
 import "log"
 import "net/http"
+import "os"
+import _ "github.com/go-sql-driver/mysql"
 
+// @todo #1 /countries/count: add tests
 func main() {
 	log.SetFlags(log.Ldate | log.Ltime | log.Lshortfile)
 
+	// @todo #1 Load configuration from a file
+	user := os.Getenv("MYSQL_USER")
+	if user == "" {
+		log.Printf("MYSQL_USER env variable is not set. Defaults to 'mystamps'")
+		user = "mystamps"
+	}
+
+	pass := os.Getenv("MYSQL_PASSWORD")
+	if pass == "" {
+		log.Fatalf("MYSQL_PASSWORD env variable is not set")
+	}
+
+	dbName := os.Getenv("MYSQL_DB")
+	if dbName == "" {
+		log.Printf("MYSQL_DB env variable is not set. Defaults to 'mystamps'")
+		dbName = "mystamps"
+	}
+
+	// @todo #1 Consider passing params to db driver
+	dsn := fmt.Sprintf("%s:%s@tcp(localhost:3306)/%s", user, pass, dbName)
+
+	db, err := sql.Open("mysql", dsn)
+	if err != nil {
+		log.Fatalf("Open() has failed: %v", err)
+	}
+
+	err = db.Ping()
+	if err != nil {
+		log.Fatalf("Ping() has failed: %v", err)
+	}
+
 	http.HandleFunc("/", func(w http.ResponseWriter, _ *http.Request) {
 		w.Write([]byte("ok"))
 	})
 
+	// @todo #1 /countries/count: extract handler
+	// @todo #1 /countries/count: extract SQL query
+	// @todo #1 /countries/count: return JSON response
+	http.HandleFunc("/v0.1/countries/count", func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != "GET" {
+			http.Error(w, http.StatusText(405), 405)
+			return
+		}
+
+		// There is no check for ErrNoRows because COUNT(*) always returns a single row
+		row := db.QueryRow("SELECT COUNT(*) FROM countries")
+		if err != nil {
+			log.Printf("QueryRow() has failed: %v", err)
+			http.Error(w, http.StatusText(500), 500)
+			return
+		}
+
+		var count int
+		err := row.Scan(&count)
+		if err != nil {
+			log.Printf("Scan() has failed: %v", err)
+			http.Error(w, http.StatusText(500), 500)
+			return
+		}
+
+		fmt.Fprintf(w, "%d", count)
+	})
+
 	log.Println("Running the server on port 8080")
 
 	if err := http.ListenAndServe(":8080", nil); err != nil {