add daemon config

cmd/server/core/config/config.go

@@ -0,0 +1,71 @@
+package config
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+type (
+	DaemonConfiguration struct {
+		Server   ServerConfiguration   `json:"server"`
+		Database DatabaseConfiguration `json:"database"`
+	}
+
+	ServerConfiguration struct {
+		Address string `json:"addr"`
+		Port    uint16 `json:"port"`
+	}
+
+	DatabaseConfiguration struct {
+		Path string `json:"path"`
+	}
+)
+
+func Load(path string) (DaemonConfiguration, error) {
+	path = filepath.Join(path, "config.json")
+
+	f, err := os.OpenFile(path, os.O_RDONLY, 0)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return Default(), nil
+		}
+		return DaemonConfiguration{}, fmt.Errorf("failed to load configuration file (%s): %s", path, err)
+	}
+	defer f.Close()
+
+	var c DaemonConfiguration
+	d := json.NewDecoder(f)
+	if err := d.Decode(&c); err != nil {
+		return DaemonConfiguration{}, fmt.Errorf("failed to read configuration file (%s): %s", path, err)
+	}
+
+	return fillDefault(c), nil
+}
+
+func Default() DaemonConfiguration {
+	return DaemonConfiguration{
+		Server: ServerConfiguration{
+			Address: "127.0.0.1",
+			Port:    25697,
+		},
+		Database: DatabaseConfiguration{
+			Path: "/var/lib/mirror-sync/data.db",
+		},
+	}
+}
+
+func fillDefault(c DaemonConfiguration) DaemonConfiguration {
+	if len(c.Database.Path) == 0 {
+		c.Database.Path = Default().Database.Path
+	}
+	if len(c.Server.Address) == 0 {
+		c.Server.Address = Default().Server.Address
+	}
+	if c.Server.Port == 0 {
+		c.Server.Port = Default().Server.Port
+	}
+	return c
+}