/*
Copyright 2022.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package luamanager

import (
	"encoding/json"
	"errors"

	lua "github.com/yuin/gopher-lua"
)

const JsonLibName = "json"

// OpenJson is the module loader function.
func OpenJson(L *lua.LState) int {
	mod := L.RegisterModule(JsonLibName, jsonFuncs)
	L.Push(mod)
	return 1
}

var jsonFuncs = map[string]lua.LGFunction{
	"decode": jsonDecode,
	"encode": jsonEncode,
}

func jsonDecode(L *lua.LState) int {
	str := L.CheckString(1)

	value, err := Decode(L, []byte(str))
	if err != nil {
		L.Push(lua.LNil)
		L.Push(lua.LString(err.Error()))
		return 2
	}
	L.Push(value)
	return 1
}

func jsonEncode(L *lua.LState) int {
	value := L.CheckAny(1)

	data, err := Encode(value)
	if err != nil {
		L.Push(lua.LNil)
		L.Push(lua.LString(err.Error()))
		return 2
	}
	L.Push(lua.LString(string(data)))
	return 1
}

var (
	errNested      = errors.New("cannot encode recursively nested tables to JSON")
	errSparseArray = errors.New("cannot encode sparse array")
	errInvalidKeys = errors.New("cannot encode mixed or invalid key types")
)

type invalidTypeError lua.LValueType

func (i invalidTypeError) Error() string {
	return `cannot encode ` + lua.LValueType(i).String() + ` to JSON`
}

// Encode returns the JSON encoding of value.
func Encode(value lua.LValue) ([]byte, error) {
	return json.Marshal(jsonValue{
		LValue:  value,
		visited: make(map[*lua.LTable]bool),
	})
}

type jsonValue struct {
	lua.LValue
	visited map[*lua.LTable]bool
}

func (j jsonValue) MarshalJSON() (data []byte, err error) {
	switch converted := j.LValue.(type) {
	case lua.LBool:
		data, err = json.Marshal(bool(converted))
	case lua.LNumber:
		data, err = json.Marshal(float64(converted))
	case *lua.LNilType:
		data = []byte(`null`)
	case lua.LString:
		data, err = json.Marshal(string(converted))
	case *lua.LTable:
		if j.visited[converted] {
			return nil, errNested
		}
		j.visited[converted] = true

		key, value := converted.Next(lua.LNil)

		switch key.Type() {
		case lua.LTNil: // empty table
			data = []byte(`null`)
		case lua.LTNumber:
			arr := make([]jsonValue, 0, converted.Len())
			expectedKey := lua.LNumber(1)
			for key != lua.LNil {
				if key.Type() != lua.LTNumber {
					err = errInvalidKeys
					return
				}
				if expectedKey != key {
					err = errSparseArray
					return
				}
				arr = append(arr, jsonValue{value, j.visited})
				expectedKey++
				key, value = converted.Next(key)
			}
			data, err = json.Marshal(arr)
		case lua.LTString:
			obj := make(map[string]jsonValue)
			for key != lua.LNil {
				if key.Type() != lua.LTString {
					err = errInvalidKeys
					return
				}
				obj[key.String()] = jsonValue{value, j.visited}
				key, value = converted.Next(key)
			}
			data, err = json.Marshal(obj)
		default:
			err = errInvalidKeys
		}
	default:
		err = invalidTypeError(j.LValue.Type())
	}
	return
}

// Decode converts the JSON encoded data to Lua values.
func Decode(L *lua.LState, data []byte) (lua.LValue, error) {
	var value interface{}
	err := json.Unmarshal(data, &value)
	if err != nil {
		return nil, err
	}
	return DecodeValue(L, value), nil
}

// DecodeValue converts the value to a Lua value.
//
// This function only converts values that the encoding/json package decodes to.
// All other values will return lua.LNil.
func DecodeValue(L *lua.LState, value interface{}) lua.LValue {
	switch converted := value.(type) {
	case bool:
		return lua.LBool(converted)
	case float64:
		return lua.LNumber(converted)
	case string:
		return lua.LString(converted)
	case json.Number:
		return lua.LString(converted)
	case []interface{}:
		arr := L.CreateTable(len(converted), 0)
		for _, item := range converted {
			arr.Append(DecodeValue(L, item))
		}
		return arr
	case map[string]interface{}:
		tbl := L.CreateTable(0, len(converted))
		for key, item := range converted {
			tbl.RawSetH(lua.LString(key), DecodeValue(L, item))
		}
		return tbl
	case nil:
		return lua.LNil
	}

	return lua.LNil
}