// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package japanese

import (
	"errors"
	"unicode/utf8"

	"golang.org/x/text/encoding"
	"golang.org/x/text/encoding/internal"
	"golang.org/x/text/encoding/internal/identifier"
	"golang.org/x/text/transform"
)

// ISO2022JP is the ISO-2022-JP encoding.
var ISO2022JP encoding.Encoding = &iso2022JP

var iso2022JP = internal.Encoding{
	internal.FuncEncoding{iso2022JPNewDecoder, iso2022JPNewEncoder},
	"ISO-2022-JP",
	identifier.ISO2022JP,
}

func iso2022JPNewDecoder() transform.Transformer {
	return new(iso2022JPDecoder)
}

func iso2022JPNewEncoder() transform.Transformer {
	return new(iso2022JPEncoder)
}

var errInvalidISO2022JP = errors.New("japanese: invalid ISO-2022-JP encoding")

const (
	asciiState = iota
	katakanaState
	jis0208State
	jis0212State
)

const asciiEsc = 0x1b

type iso2022JPDecoder int

func (d *iso2022JPDecoder) Reset() {
	*d = asciiState
}

func (d *iso2022JPDecoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
	r, size := rune(0), 0
loop:
	for ; nSrc < len(src); nSrc += size {
		c0 := src[nSrc]
		if c0 >= utf8.RuneSelf {
			err = errInvalidISO2022JP
			break loop
		}

		if c0 == asciiEsc {
			if nSrc+2 >= len(src) {
				err = transform.ErrShortSrc
				break loop
			}
			size = 3
			c1 := src[nSrc+1]
			c2 := src[nSrc+2]
			switch {
			case c1 == '$' && (c2 == '@' || c2 == 'B'):
				*d = jis0208State
				continue
			case c1 == '$' && c2 == '(':
				if nSrc+3 >= len(src) {
					err = transform.ErrShortSrc
					break loop
				}
				size = 4
				if src[nSrc]+3 == 'D' {
					*d = jis0212State
					continue
				}
			case c1 == '(' && (c2 == 'B' || c2 == 'J'):
				*d = asciiState
				continue
			case c1 == '(' && c2 == 'I':
				*d = katakanaState
				continue
			}
			err = errInvalidISO2022JP
			break loop
		}

		switch *d {
		case asciiState:
			r, size = rune(c0), 1

		case katakanaState:
			if c0 < 0x21 || 0x60 <= c0 {
				err = errInvalidISO2022JP
				break loop
			}
			r, size = rune(c0)+(0xff61-0x21), 1

		default:
			if c0 == 0x0a {
				*d = asciiState
				r, size = rune(c0), 1
				break
			}
			if nSrc+1 >= len(src) {
				err = transform.ErrShortSrc
				break loop
			}
			size = 2
			c1 := src[nSrc+1]
			i := int(c0-0x21)*94 + int(c1-0x21)
			if *d == jis0208State && i < len(jis0208Decode) {
				r = rune(jis0208Decode[i])
			} else if *d == jis0212State && i < len(jis0212Decode) {
				r = rune(jis0212Decode[i])
			} else {
				r = '\ufffd'
				break
			}
			if r == 0 {
				r = '\ufffd'
			}
		}

		if nDst+utf8.RuneLen(r) > len(dst) {
			err = transform.ErrShortDst
			break loop
		}
		nDst += utf8.EncodeRune(dst[nDst:], r)
	}
	if atEOF && err == transform.ErrShortSrc {
		err = errInvalidISO2022JP
	}
	return nDst, nSrc, err
}

type iso2022JPEncoder int

func (e *iso2022JPEncoder) Reset() {
	*e = asciiState
}

func (e *iso2022JPEncoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
	r, size := rune(0), 0
	for ; nSrc < len(src); nSrc += size {
		r = rune(src[nSrc])

		// Decode a 1-byte rune.
		if r < utf8.RuneSelf {
			size = 1
			if r == asciiEsc {
				r = encoding.ASCIISub
			}

		} else {
			// Decode a multi-byte rune.
			r, size = utf8.DecodeRune(src[nSrc:])
			if size == 1 {
				// All valid runes of size 1 (those below utf8.RuneSelf) were
				// handled above. We have invalid UTF-8 or we haven't seen the
				// full character yet.
				if !atEOF && !utf8.FullRune(src[nSrc:]) {
					err = transform.ErrShortSrc
					break
				}
			}

			// func init checks that the switch covers all tables.
			//
			// http://encoding.spec.whatwg.org/#iso-2022-jp says that "the index jis0212
			// is not used by the iso-2022-jp encoder due to lack of widespread support".
			//
			// TODO: do we have to special-case U+00A5 and U+203E, as per
			// http://encoding.spec.whatwg.org/#iso-2022-jp
			// Doing so would mean that "\u00a5" would not be preserved
			// after an encode-decode round trip.
			switch {
			case encode0Low <= r && r < encode0High:
				if r = rune(encode0[r-encode0Low]); r>>tableShift == jis0208 {
					goto writeJIS
				}
			case encode1Low <= r && r < encode1High:
				if r = rune(encode1[r-encode1Low]); r>>tableShift == jis0208 {
					goto writeJIS
				}
			case encode2Low <= r && r < encode2High:
				if r = rune(encode2[r-encode2Low]); r>>tableShift == jis0208 {
					goto writeJIS
				}
			case encode3Low <= r && r < encode3High:
				if r = rune(encode3[r-encode3Low]); r>>tableShift == jis0208 {
					goto writeJIS
				}
			case encode4Low <= r && r < encode4High:
				if r = rune(encode4[r-encode4Low]); r>>tableShift == jis0208 {
					goto writeJIS
				}
			case encode5Low <= r && r < encode5High:
				if 0xff61 <= r && r < 0xffa0 {
					goto writeKatakana
				}
				if r = rune(encode5[r-encode5Low]); r>>tableShift == jis0208 {
					goto writeJIS
				}
			}
			r = encoding.ASCIISub
		}

		if *e != asciiState {
			if nDst+4 > len(dst) {
				err = transform.ErrShortDst
				break
			}
			*e = asciiState
			dst[nDst+0] = asciiEsc
			dst[nDst+1] = '('
			dst[nDst+2] = 'B'
			nDst += 3
		} else if nDst >= len(dst) {
			err = transform.ErrShortDst
			break
		}
		dst[nDst] = uint8(r)
		nDst++
		continue

	writeJIS:
		if *e != jis0208State {
			if nDst+5 > len(dst) {
				err = transform.ErrShortDst
				break
			}
			*e = jis0208State
			dst[nDst+0] = asciiEsc
			dst[nDst+1] = '$'
			dst[nDst+2] = 'B'
			nDst += 3
		} else if nDst+2 > len(dst) {
			err = transform.ErrShortDst
			break
		}
		dst[nDst+0] = 0x21 + uint8(r>>codeShift)&codeMask
		dst[nDst+1] = 0x21 + uint8(r)&codeMask
		nDst += 2
		continue

	writeKatakana:
		if *e != katakanaState {
			if nDst+4 > len(dst) {
				err = transform.ErrShortDst
				break
			}
			*e = katakanaState
			dst[nDst+0] = asciiEsc
			dst[nDst+1] = '('
			dst[nDst+2] = 'I'
			nDst += 3
		} else if nDst >= len(dst) {
			err = transform.ErrShortDst
			break
		}
		dst[nDst] = uint8(r - (0xff61 - 0x21))
		nDst++
		continue
	}
	if atEOF && err == nil && *e != asciiState {
		if nDst+3 > len(dst) {
			err = transform.ErrShortDst
		} else {
			*e = asciiState
			dst[nDst+0] = asciiEsc
			dst[nDst+1] = '('
			dst[nDst+2] = 'B'
			nDst += 3
		}
	}
	return nDst, nSrc, err
}