// Copyright 2015 Tony Bai.
//
// 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,
// See the License for the specific language governing permissions and
// limitations under the License.

package cmpputils

import (
	"bytes"
	"errors"
	"fmt"
	"io/ioutil"
	"strings"
	"unicode/utf8"
	"unsafe"

	"golang.org/x/text/encoding/simplifiedchinese"
	"golang.org/x/text/encoding/unicode"
	"golang.org/x/text/transform"
)

var ErrInvalidUtf8Rune = errors.New("Not Invalid Utf8 runes")

func IsBigEndian() bool {
	var i uint16 = 0x1234
	var p *[2]byte = (*[2]byte)(unsafe.Pointer(&i))
	if (*p)[0] == 0x12 {
		return true
	}
	return false
}

// TimeStamp2Str converts a timestamp(MMDDHHMMSS) int to a string(10 bytes).
func TimeStamp2Str(t uint32) string {
	return fmt.Sprintf("%010d", t)
}

func Utf8ToUcs2(in string) (string, error) {
	if !utf8.ValidString(in) {
		return "", ErrInvalidUtf8Rune
	}

	r := bytes.NewReader([]byte(in))
	t := transform.NewReader(r, unicode.UTF16(unicode.BigEndian, unicode.IgnoreBOM).NewEncoder()) //UTF-16 bigendian, no-bom
	out, err := ioutil.ReadAll(t)
	if err != nil {
		return "", err
	}
	return string(out), nil
}

func Ucs2ToUtf8(in string) (string, error) {
	r := bytes.NewReader([]byte(in))
	t := transform.NewReader(r, unicode.UTF16(unicode.BigEndian, unicode.IgnoreBOM).NewDecoder()) //UTF-16 bigendian, no-bom
	out, err := ioutil.ReadAll(t)
	if err != nil {
		return "", err
	}
	return string(out), nil
}

func Utf8ToGB18030(in string) (string, error) {
	if !utf8.ValidString(in) {
		return "", ErrInvalidUtf8Rune
	}

	r := bytes.NewReader([]byte(in))
	t := transform.NewReader(r, simplifiedchinese.GB18030.NewEncoder())
	out, err := ioutil.ReadAll(t)
	if err != nil {
		return "", err
	}
	return string(out), nil
}

func GB18030ToUtf8(in string) (string, error) {
	r := bytes.NewReader([]byte(in))
	t := transform.NewReader(r, simplifiedchinese.GB18030.NewDecoder())
	out, err := ioutil.ReadAll(t)
	if err != nil {
		return "", err
	}
	return string(out), nil
}

func OctetString(s string, fixedLength int) string {
	length := len(s)
	if length == fixedLength {
		return s
	}

	if length > fixedLength {
		return s[length-fixedLength:]
	}

	return strings.Join([]string{s, string(make([]byte, fixedLength-length))}, "")
}