// Copyright 2015 The TCell Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use 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 tcell

import (
	"sync"

	"golang.org/x/text/encoding"
)

var encodings map[string]encoding.Encoding
var encodingLk sync.Mutex

// RegisterEncoding may be called by the application to register an encoding.  The
// presence of additional encodings will facilitate application usage with terminal
// environments where the I/O subsystem does not support Unicode.  Please see the
// Go documentation for encodings -- most of the common ones exist already as stock
// variables.  For example, ISO8859-15 can be registered using the following code:
//
//   import "golang.org/x/text/encoding/charmap"
//
//     ...
//     RegisterEncoding("ISO8859-15", charmap.ISO8859_15)
//
// Aliases can be registered as well, for example "8859-15" could be an alias for
// "ISO8859-15".
//
// For POSIX systems, the tcell pacakge will check the environment variables LC_ALL, LC_CTYPE,
// and LANG (in that order) to determine the character set.  These are expected to have the
// following pattern:  $language[.$codeset[@$variant]  We extract only the $codeset part,
// which will usually be something like UTF-8 or ISO8859-15 or KOI8-R.  Note that if the
// locale is either "POSIX" or "C", then we assume US-ASCII (the POSIX 'portable character set'
// and assume all other characters are somehow invalid.)
//
// On Windows systems, the Console is assumed to be UTF-16LE.  As we communicate with the
// console subsystem using UTF-16LE, no conversions are necessary.  So none of this is required
// for Windows systems.
//
// Modern POSIX systems and terminal emulators may use UTF-8, and for those systems, this
// API is also unnecessary.  For example, Darwin (MacOS X) and modern Linux running modern
// xterm generally will out of the box without any of this.
//
// Note that some encodings are quite large (for example GB18030 which is a superset of
// Unicode) and so the application size can be expected ot increase quite a bit as each
// encoding is added.
//
func RegisterEncoding(name string, enc encoding.Encoding) {
	encodingLk.Lock()
	if encodings == nil {
		encodings = make(map[string]encoding.Encoding)
	}
	encodings[name] = enc
	encodingLk.Unlock()
}

func GetEncoding(name string) encoding.Encoding {
	encodingLk.Lock()
	defer encodingLk.Unlock()
	if enc, ok := encodings[name]; ok {
		return enc
	}
	return nil
}