Implement issue #1 Add builtin flag: -config

README.md

@@ -10,6 +10,8 @@ Arguments are parsed from command line with the standard `flag` library.
 - [How to use](#how-to-use)
 - [Supported types](#supported-types)
 - [Builtin configuration keys](#builtin-configuration-keys)
+  - [-help](#-help)
+  - [-config](#-config)
 - [Contribute](#contribute)
 - [Testing](#testing)
 - [Example project](#example-project)
@@ -100,9 +102,32 @@ Type `slice` or `array` is also being considered.
 
 # Builtin configuration keys
 
+## -help
+
 Since `flag` library is using the key `-help` to show usage, Goconf is behaving
 in the same way.
 
+## -config
+
+Builtin flag `-config` allow read configuration from a file. For the example
+configuration above, this is a sample config.json file:
+
+```json
+{
+  "name": "Fulanito",
+  "usersdb": {
+    "host": "localhost",
+    "user": "admin",
+    "pass": "123"
+  }
+}
+```
+
+Configuration precedence is as follows (higher to lower):
+* Arg command line
+* Json config file
+* Default value
+
 
 # Contribute
 

goconfig.go

@@ -1,19 +1,45 @@
 package goconfig
 
 import (
+	"encoding/json"
 	"flag"
+	"fmt"
+	"io/ioutil"
+	"os"
 	"reflect"
 	"strings"
 )
 
+var values = map[string]interface{}{}
+
 func Read(c interface{}) {
 
 	path := []string{}
 
-	parse_struct(c, path)
+	// Add builtin -config flag
+	filename := ""
+	flag.StringVar(&filename, "config", filename, "Configuration JSON file")
 
+	parse_struct(c, path)
 	flag.Parse()
 
+	// Put default values
+	flag.VisitAll(func(f *flag.Flag) {
+		if v, e := values[f.Name]; e {
+			Set(v, f.Value)
+		}
+	})
+
+	// Read from file JSON
+	read_json(c, filename)
+
+	// Overwrite configuration with command line args:
+	flag.Visit(func(f *flag.Flag) {
+		if v, e := values[f.Name]; e {
+			Set(v, f.Value)
+		}
+	})
+
 }
 
 func parse_struct(c interface{}, p []string) {
@@ -40,39 +66,74 @@ func parse_struct(c interface{}, p []string) {
 			// Do nothing
 
 		} else if reflect.Bool == kind {
-			flag.BoolVar(ptr.(*bool), name_path, value.Interface().(bool), usage)
+			flag.Bool(name_path, value.Interface().(bool), usage)
 
 		} else if reflect.Float64 == kind {
-			flag.Float64Var(ptr.(*float64), name_path, value.Interface().(float64), usage)
+			flag.Float64(name_path, value.Interface().(float64), usage)
 
 		} else if reflect.Int64 == kind {
-			flag.Int64Var(ptr.(*int64), name_path, value.Interface().(int64), usage)
+			flag.Int64(name_path, value.Interface().(int64), usage)
 
 		} else if reflect.Int == kind {
-			flag.IntVar(ptr.(*int), name_path, value.Interface().(int), usage)
+			flag.Int(name_path, value.Interface().(int), usage)
 
 		} else if reflect.String == kind {
-			flag.StringVar(ptr.(*string), name_path, value.Interface().(string), usage)
+			flag.String(name_path, value.Interface().(string), usage)
 
 		} else if reflect.Uint64 == kind {
-			flag.Uint64Var(ptr.(*uint64), name_path, value.Interface().(uint64), usage)
+			flag.Uint64(name_path, value.Interface().(uint64), usage)
 
 		} else if reflect.Uint == kind {
-			flag.UintVar(ptr.(*uint), name_path, value.Interface().(uint), usage)
+			flag.Uint(name_path, value.Interface().(uint), usage)
 
 		} else if reflect.Struct == kind {
-			// fmt.Println("TODO: Struct")
 			parse_struct(ptr, p)
 
 		} else if reflect.Slice == kind {
 			panic("Slice is not supported by goconfig at this moment.")
 
 		} else {
-			panic("Kind `" + kind.String() + "` is not supported by goconfig (field `" + name + "`)")
+			panic("Kind `" + kind.String() +
+				"` is not supported by goconfig (field `" + name + "`)")
 		}
 
+		values[name_path] = ptr
+
 		p = p[0 : len(p)-1]
 
 	}
 
 }
+
+func read_json(c interface{}, filename string) {
+	if "" == filename {
+		return
+	}
+
+	data, err := ioutil.ReadFile(filename)
+	if nil != err {
+		fmt.Println("Unable to read config file `" + filename + "`!")
+		os.Exit(1)
+	}
+
+	err = json.Unmarshal(data, &c)
+	if nil != err {
+		fmt.Println("Config file should be a valid JSON")
+		os.Exit(1)
+	}
+
+	// f, err := os.Open(filename)
+	// if nil != err {
+	// 	fmt.Println("Unable to read config file `" + filename + "`!")
+	// 	os.Exit(1)
+	// }
+	// json.NewDecoder(f).Decode(&c)
+}
+
+func Set(dest, value interface{}) {
+	dest_v := reflect.ValueOf(dest)
+	dest_t := reflect.TypeOf(dest)
+	value_v := reflect.ValueOf(value)
+
+	dest_v.Elem().Set(value_v.Convert(dest_t).Elem())
+}