// Code generated by running "go generate" in golang.org/x/text. DO NOT EDIT.

// Copyright 2016 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 idna

// This file implements the Punycode algorithm from RFC 3492.

import (

	"math"

	"strings"

	"unicode/utf8"

)

// These parameter values are specified in section 5.

//

// All computation is done with int32s, so that overflow behavior is identical

// regardless of whether int is 32-bit or 64-bit.

const (

	base        int32 = 36

	damp        int32 = 700

	initialBias int32 = 72

	initialN    int32 = 128

	skew        int32 = 38

	tmax        int32 = 26

	tmin        int32 = 1

)

func punyError(s string) error { return &labelError{s, "A3"} }

// decode decodes a string as specified in section 6.2.

func decode(encoded string) (string, error) {

	if encoded == "" {

		return "", nil

	}

	pos := 1 + strings.LastIndex(encoded, "-")

	if pos == 1 {

		return "", punyError(encoded)

	}

	if pos == len(encoded) {

		return encoded[:len(encoded)-1], nil

	}

	output := make([]rune, 0, len(encoded))

	if pos != 0 {

		for _, r := range encoded[:pos-1] {

			output = append(output, r)

		}

	}

	i, n, bias := int32(0), initialN, initialBias

	for pos < len(encoded) {

		oldI, w := i, int32(1)

		for k := base; ; k += base {

			if pos == len(encoded) {

				return "", punyError(encoded)

			}

			digit, ok := decodeDigit(encoded[pos])

			if !ok {

				return "", punyError(encoded)

			}

			pos++

			i += digit * w

			if i < 0 {

				return "", punyError(encoded)

			}

			t := k - bias

			if t < tmin {

				t = tmin

			} else if t > tmax {

				t = tmax

			}

			if digit < t {

				break

			}

			w *= base - t

			if w >= math.MaxInt32/base {

				return "", punyError(encoded)

			}

		}

		x := int32(len(output) + 1)

		bias = adapt(i-oldI, x, oldI == 0)

		n += i / x

		i %= x

		if n > utf8.MaxRune || len(output) >= 1024 {

			return "", punyError(encoded)

		}

		output = append(output, 0)

		copy(output[i+1:], output[i:])

		output[i] = n

		i++

	}

	return string(output), nil

}

// encode encodes a string as specified in section 6.3 and prepends prefix to

// the result.

//

// The "while h < length(input)" line in the specification becomes "for

// remaining != 0" in the Go code, because len(s) in Go is in bytes, not runes.

func encode(prefix, s string) (string, error) {

	output := make([]byte, len(prefix), len(prefix)+1+2*len(s))

	copy(output, prefix)

	delta, n, bias := int32(0), initialN, initialBias

	b, remaining := int32(0), int32(0)

	for _, r := range s {

		if r < 0x80 {

			b++

			output = append(output, byte(r))

		} else {

			remaining++

		}

	}

	h := b

	if b > 0 {

		output = append(output, '-')

	}

	for remaining != 0 {

		m := int32(0x7fffffff)

		for _, r := range s {

			if m > r && r >= n {

				m = r

			}

		}

		delta += (m - n) * (h + 1)

		if delta < 0 {

			return "", punyError(s)

		}

		n = m

		for _, r := range s {

			if r < n {

				delta++

				if delta < 0 {

					return "", punyError(s)

				}

				continue

			}

			if r > n {

				continue

			}

			q := delta

			for k := base; ; k += base {

				t := k - bias

				if t < tmin {

					t = tmin

				} else if t > tmax {

					t = tmax

				}

				if q < t {

					break

				}

				output = append(output, encodeDigit(t+(q-t)%(base-t)))

				q = (q - t) / (base - t)

			}

			output = append(output, encodeDigit(q))

			bias = adapt(delta, h+1, h == b)

			delta = 0

			h++

			remaining--

		}

		delta++

		n++

	}

	return string(output), nil

}

func decodeDigit(x byte) (digit int32, ok bool) {

	switch {

	case '0' <= x && x <= '9':

		return int32(x - ('0' - 26)), true

	case 'A' <= x && x <= 'Z':

		return int32(x - 'A'), true

	case 'a' <= x && x <= 'z':

		return int32(x - 'a'), true

	}

	return 0, false

}

func encodeDigit(digit int32) byte {

	switch {

	case 0 <= digit && digit < 26:

		return byte(digit + 'a')

	case 26 <= digit && digit < 36:

		return byte(digit + ('0' - 26))

	}

	panic("idna: internal error in punycode encoding")

}

// adapt is the bias adaptation function specified in section 6.1.

func adapt(delta, numPoints int32, firstTime bool) int32 {

	if firstTime {

		delta /= damp

	} else {

		delta /= 2

	}

	delta += delta / numPoints

	k := int32(0)

	for delta > ((base-tmin)*tmax)/2 {

		delta /= base - tmin

		k += base

	}

	return k + (base-tmin+1)*delta/(delta+skew)

}