add: database to reflection decoder

interfaces/11-reflection-decoder/database.go

@@ -0,0 +1,107 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+	"reflect"
+)
+
+type database struct {
+	list  *list
+	types map[string]item
+}
+
+func (db *database) save() error {
+	data, err := json.MarshalIndent(db, "", "\t")
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	return ioutil.WriteFile("database.json", data, os.ModePerm)
+}
+
+func (db *database) load() error {
+	data, err := ioutil.ReadFile("database.json")
+	if err != nil {
+		return err
+	}
+
+	if err = json.Unmarshal(data, db); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (db *database) MarshalJSON() ([]byte, error) {
+	type encodable struct {
+		Category string
+		Item     item
+	}
+
+	var e []encodable
+
+	for _, it := range *db.list {
+		// TypeOf -> finds the dynamic type of "it"
+		// Elem   -> returns the element type of the pointer
+		// Name   -> returns the type name as string
+		cat := reflect.TypeOf(it).Elem().Name()
+		e = append(e, encodable{cat, it})
+	}
+
+	return json.Marshal(e)
+}
+
+func (db *database) UnmarshalJSON(data []byte) error {
+	var decodables []struct {
+		Category string
+		Item     json.RawMessage
+	}
+
+	if err := json.Unmarshal(data, &decodables); err != nil {
+		return err
+	}
+
+	for _, d := range decodables {
+		it, err := db.newItem(d.Category)
+		if err != nil {
+			return err
+		}
+
+		if err := json.Unmarshal(d.Item, &it); err != nil {
+			return err
+		}
+
+		*db.list = append(*db.list, it)
+	}
+
+	return nil
+}
+
+func (db *database) register(category string, t item) {
+	if db.types == nil {
+		db.types = make(map[string]item)
+	}
+	db.types[category] = t
+}
+
+func (db *database) newItem(category string) (item, error) {
+	it, ok := db.types[category]
+	if !ok {
+		return nil, fmt.Errorf("register %q within database before decoding", category)
+	}
+
+	t := reflect.TypeOf(it).Elem()
+	v := reflect.New(t)
+	return v.Interface().(item), nil
+}