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// Copyright 2009 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 bytes implements functions for the manipulation of byte slices.
// It is analogous to the facilities of the strings package.
package bytes

import (
        "unicode"
        "unicode/utf8"
)

// Compare returns an integer comparing the two byte arrays lexicographically.
// The result will be 0 if a==b, -1 if a < b, and +1 if a > b
func Compare(a, b []byte) int {
        m := len(a)
        if m > len(b) {
                m = len(b)
        }
        for i, ac := range a[0:m] {
                bc := b[i]
                switch {
                case ac > bc:
                        return 1
                case ac < bc:
                        return -1
                }
        }
        switch {
        case len(a) < len(b):
                return -1
        case len(a) > len(b):
                return 1
        }
        return 0
}

// Equal returns a boolean reporting whether a == b.
func Equal(a, b []byte) bool

func equalPortable(a, b []byte) bool {
        if len(a) != len(b) {
                return false
        }
        for i, c := range a {
                if c != b[i] {
                        return false
                }
        }
        return true
}

// explode splits s into an array of UTF-8 sequences, one per Unicode character (still arrays of bytes),
// up to a maximum of n byte arrays. Invalid UTF-8 sequences are chopped into individual bytes.
func explode(s []byte, n int) [][]byte {
        if n <= 0 {
                n = len(s)
        }
        a := make([][]byte, n)
        var size int
        na := 0
        for len(s) > 0 {
                if na+1 >= n {
                        a[na] = s
                        na++
                        break
                }
                _, size = utf8.DecodeRune(s)
                a[na] = s[0:size]
                s = s[size:]
                na++
        }
        return a[0:na]
}

// Count counts the number of non-overlapping instances of sep in s.
func Count(s, sep []byte) int {
        n := len(sep)
        if n == 0 {
                return utf8.RuneCount(s) + 1
        }
        if n > len(s) {
                return 0
        }
        count := 0
        c := sep[0]
        i := 0
        t := s[:len(s)-n+1]
        for i < len(t) {
                if t[i] != c {
                        o := IndexByte(t[i:], c)
                        if o < 0 {
                                break
                        }
                        i += o
                }
                if n == 1 || Equal(s[i:i+n], sep) {
                        count++
                        i += n
                        continue
                }
                i++
        }
        return count
}

// Contains returns whether subslice is within b.
func Contains(b, subslice []byte) bool {
        return Index(b, subslice) != -1
}

// Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
func Index(s, sep []byte) int {
        n := len(sep)
        if n == 0 {
                return 0
        }
        if n > len(s) {
                return -1
        }
        c := sep[0]
        if n == 1 {
                return IndexByte(s, c)
        }
        i := 0
        t := s[:len(s)-n+1]
        for i < len(t) {
                if t[i] != c {
                        o := IndexByte(t[i:], c)
                        if o < 0 {
                                break
                        }
                        i += o
                }
                if Equal(s[i:i+n], sep) {
                        return i
                }
                i++
        }
        return -1
}

func indexBytePortable(s []byte, c byte) int {
        for i, b := range s {
                if b == c {
                        return i
                }
        }
        return -1
}

// LastIndex returns the index of the last instance of sep in s, or -1 if sep is not present in s.
func LastIndex(s, sep []byte) int {
        n := len(sep)
        if n == 0 {
                return len(s)
        }
        c := sep[0]
        for i := len(s) - n; i >= 0; i-- {
                if s[i] == c && (n == 1 || Equal(s[i:i+n], sep)) {
                        return i
                }
        }
        return -1
}

// IndexRune interprets s as a sequence of UTF-8-encoded Unicode code points.
// It returns the byte index of the first occurrence in s of the given rune.
// It returns -1 if rune is not present in s.
func IndexRune(s []byte, r rune) int {
        for i := 0; i < len(s); {
                r1, size := utf8.DecodeRune(s[i:])
                if r == r1 {
                        return i
                }
                i += size
        }
        return -1
}

// IndexAny interprets s as a sequence of UTF-8-encoded Unicode code points.
// It returns the byte index of the first occurrence in s of any of the Unicode
// code points in chars.  It returns -1 if chars is empty or if there is no code
// point in common.
func IndexAny(s []byte, chars string) int {
        if len(chars) > 0 {
                var r rune
                var width int
                for i := 0; i < len(s); i += width {
                        r = rune(s[i])
                        if r < utf8.RuneSelf {
                                width = 1
                        } else {
                                r, width = utf8.DecodeRune(s[i:])
                        }
                        for _, ch := range chars {
                                if r == ch {
                                        return i
                                }
                        }
                }
        }
        return -1
}

// LastIndexAny interprets s as a sequence of UTF-8-encoded Unicode code
// points.  It returns the byte index of the last occurrence in s of any of
// the Unicode code points in chars.  It returns -1 if chars is empty or if
// there is no code point in common.
func LastIndexAny(s []byte, chars string) int {
        if len(chars) > 0 {
                for i := len(s); i > 0; {
                        r, size := utf8.DecodeLastRune(s[0:i])
                        i -= size
                        for _, ch := range chars {
                                if r == ch {
                                        return i
                                }
                        }
                }
        }
        return -1
}

// Generic split: splits after each instance of sep,
// including sepSave bytes of sep in the subarrays.
func genSplit(s, sep []byte, sepSave, n int) [][]byte {
        if n == 0 {
                return nil
        }
        if len(sep) == 0 {
                return explode(s, n)
        }
        if n < 0 {
                n = Count(s, sep) + 1
        }
        c := sep[0]
        start := 0
        a := make([][]byte, n)
        na := 0
        for i := 0; i+len(sep) <= len(s) && na+1 < n; i++ {
                if s[i] == c && (len(sep) == 1 || Equal(s[i:i+len(sep)], sep)) {
                        a[na] = s[start : i+sepSave]
                        na++
                        start = i + len(sep)
                        i += len(sep) - 1
                }
        }
        a[na] = s[start:]
        return a[0 : na+1]
}

// SplitN slices s into subslices separated by sep and returns a slice of
// the subslices between those separators.
// If sep is empty, SplitN splits after each UTF-8 sequence.
// The count determines the number of subslices to return:
//   n > 0: at most n subslices; the last subslice will be the unsplit remainder.
//   n == 0: the result is nil (zero subslices)
//   n < 0: all subslices
func SplitN(s, sep []byte, n int) [][]byte { return genSplit(s, sep, 0, n) }

// SplitAfterN slices s into subslices after each instance of sep and
// returns a slice of those subslices.
// If sep is empty, SplitAfterN splits after each UTF-8 sequence.
// The count determines the number of subslices to return:
//   n > 0: at most n subslices; the last subslice will be the unsplit remainder.
//   n == 0: the result is nil (zero subslices)
//   n < 0: all subslices
func SplitAfterN(s, sep []byte, n int) [][]byte {
        return genSplit(s, sep, len(sep), n)
}

// Split slices s into all subslices separated by sep and returns a slice of
// the subslices between those separators.
// If sep is empty, Split splits after each UTF-8 sequence.
// It is equivalent to SplitN with a count of -1.
func Split(s, sep []byte) [][]byte { return genSplit(s, sep, 0, -1) }

// SplitAfter slices s into all subslices after each instance of sep and
// returns a slice of those subslices.
// If sep is empty, SplitAfter splits after each UTF-8 sequence.
// It is equivalent to SplitAfterN with a count of -1.
func SplitAfter(s, sep []byte) [][]byte {
        return genSplit(s, sep, len(sep), -1)
}

// Fields splits the array s around each instance of one or more consecutive white space
// characters, returning a slice of subarrays of s or an empty list if s contains only white space.
func Fields(s []byte) [][]byte {
        return FieldsFunc(s, unicode.IsSpace)
}

// FieldsFunc interprets s as a sequence of UTF-8-encoded Unicode code points.
// It splits the array s at each run of code points c satisfying f(c) and
// returns a slice of subarrays of s.  If no code points in s satisfy f(c), an
// empty slice is returned.
func FieldsFunc(s []byte, f func(rune) bool) [][]byte {
        n := 0
        inField := false
        for i := 0; i < len(s); {
                r, size := utf8.DecodeRune(s[i:])
                wasInField := inField
                inField = !f(r)
                if inField && !wasInField {
                        n++
                }
                i += size
        }

        a := make([][]byte, n)
        na := 0
        fieldStart := -1
        for i := 0; i <= len(s) && na < n; {
                r, size := utf8.DecodeRune(s[i:])
                if fieldStart < 0 && size > 0 && !f(r) {
                        fieldStart = i
                        i += size
                        continue
                }
                if fieldStart >= 0 && (size == 0 || f(r)) {
                        a[na] = s[fieldStart:i]
                        na++
                        fieldStart = -1
                }
                if size == 0 {
                        break
                }
                i += size
        }
        return a[0:na]
}

// Join concatenates the elements of a to create a single byte array.   The separator
// sep is placed between elements in the resulting array.
func Join(a [][]byte, sep []byte) []byte {
        if len(a) == 0 {
                return []byte{}
        }
        if len(a) == 1 {
                return a[0]
        }
        n := len(sep) * (len(a) - 1)
        for i := 0; i < len(a); i++ {
                n += len(a[i])
        }

        b := make([]byte, n)
        bp := copy(b, a[0])
        for _, s := range a[1:] {
                bp += copy(b[bp:], sep)
                bp += copy(b[bp:], s)
        }
        return b
}

// HasPrefix tests whether the byte array s begins with prefix.
func HasPrefix(s, prefix []byte) bool {
        return len(s) >= len(prefix) && Equal(s[0:len(prefix)], prefix)
}

// HasSuffix tests whether the byte array s ends with suffix.
func HasSuffix(s, suffix []byte) bool {
        return len(s) >= len(suffix) && Equal(s[len(s)-len(suffix):], suffix)
}

// Map returns a copy of the byte array s with all its characters modified
// according to the mapping function. If mapping returns a negative value, the character is
// dropped from the string with no replacement.  The characters in s and the
// output are interpreted as UTF-8-encoded Unicode code points.
func Map(mapping func(r rune) rune, s []byte) []byte {
        // In the worst case, the array can grow when mapped, making
        // things unpleasant.  But it's so rare we barge in assuming it's
        // fine.  It could also shrink but that falls out naturally.
        maxbytes := len(s) // length of b
        nbytes := 0        // number of bytes encoded in b
        b := make([]byte, maxbytes)
        for i := 0; i < len(s); {
                wid := 1
                r := rune(s[i])
                if r >= utf8.RuneSelf {
                        r, wid = utf8.DecodeRune(s[i:])
                }
                r = mapping(r)
                if r >= 0 {
                        if nbytes+utf8.RuneLen(r) > maxbytes {
                                // Grow the buffer.
                                maxbytes = maxbytes*2 + utf8.UTFMax
                                nb := make([]byte, maxbytes)
                                copy(nb, b[0:nbytes])
                                b = nb
                        }
                        nbytes += utf8.EncodeRune(b[nbytes:maxbytes], r)
                }
                i += wid
        }
        return b[0:nbytes]
}

// Repeat returns a new byte slice consisting of count copies of b.
func Repeat(b []byte, count int) []byte {
        nb := make([]byte, len(b)*count)
        bp := 0
        for i := 0; i < count; i++ {
                for j := 0; j < len(b); j++ {
                        nb[bp] = b[j]
                        bp++
                }
        }
        return nb
}

// ToUpper returns a copy of the byte array s with all Unicode letters mapped to their upper case.
func ToUpper(s []byte) []byte { return Map(unicode.ToUpper, s) }

// ToUpper returns a copy of the byte array s with all Unicode letters mapped to their lower case.
func ToLower(s []byte) []byte { return Map(unicode.ToLower, s) }

// ToTitle returns a copy of the byte array s with all Unicode letters mapped to their title case.
func ToTitle(s []byte) []byte { return Map(unicode.ToTitle, s) }

// ToUpperSpecial returns a copy of the byte array s with all Unicode letters mapped to their
// upper case, giving priority to the special casing rules.
func ToUpperSpecial(_case unicode.SpecialCase, s []byte) []byte {
        return Map(func(r rune) rune { return _case.ToUpper(r) }, s)
}

// ToLowerSpecial returns a copy of the byte array s with all Unicode letters mapped to their
// lower case, giving priority to the special casing rules.
func ToLowerSpecial(_case unicode.SpecialCase, s []byte) []byte {
        return Map(func(r rune) rune { return _case.ToLower(r) }, s)
}

// ToTitleSpecial returns a copy of the byte array s with all Unicode letters mapped to their
// title case, giving priority to the special casing rules.
func ToTitleSpecial(_case unicode.SpecialCase, s []byte) []byte {
        return Map(func(r rune) rune { return _case.ToTitle(r) }, s)
}

// isSeparator reports whether the rune could mark a word boundary.
// TODO: update when package unicode captures more of the properties.
func isSeparator(r rune) bool {
        // ASCII alphanumerics and underscore are not separators
        if r <= 0x7F {
                switch {
                case '0' <= r && r <= '9':
                        return false
                case 'a' <= r && r <= 'z':
                        return false
                case 'A' <= r && r <= 'Z':
                        return false
                case r == '_':
                        return false
                }
                return true
        }
        // Letters and digits are not separators
        if unicode.IsLetter(r) || unicode.IsDigit(r) {
                return false
        }
        // Otherwise, all we can do for now is treat spaces as separators.
        return unicode.IsSpace(r)
}

// BUG(r): The rule Title uses for word boundaries does not handle Unicode punctuation properly.

// Title returns a copy of s with all Unicode letters that begin words
// mapped to their title case.
func Title(s []byte) []byte {
        // Use a closure here to remember state.
        // Hackish but effective. Depends on Map scanning in order and calling
        // the closure once per rune.
        prev := ' '
        return Map(
                func(r rune) rune {
                        if isSeparator(prev) {
                                prev = r
                                return unicode.ToTitle(r)
                        }
                        prev = r
                        return r
                },
                s)
}

// TrimLeftFunc returns a subslice of s by slicing off all leading UTF-8-encoded
// Unicode code points c that satisfy f(c).
func TrimLeftFunc(s []byte, f func(r rune) bool) []byte {
        i := indexFunc(s, f, false)
        if i == -1 {
                return nil
        }
        return s[i:]
}

// TrimRightFunc returns a subslice of s by slicing off all trailing UTF-8
// encoded Unicode code points c that satisfy f(c).
func TrimRightFunc(s []byte, f func(r rune) bool) []byte {
        i := lastIndexFunc(s, f, false)
        if i >= 0 && s[i] >= utf8.RuneSelf {
                _, wid := utf8.DecodeRune(s[i:])
                i += wid
        } else {
                i++
        }
        return s[0:i]
}

// TrimFunc returns a subslice of s by slicing off all leading and trailing
// UTF-8-encoded Unicode code points c that satisfy f(c).
func TrimFunc(s []byte, f func(r rune) bool) []byte {
        return TrimRightFunc(TrimLeftFunc(s, f), f)
}

// IndexFunc interprets s as a sequence of UTF-8-encoded Unicode code points.
// It returns the byte index in s of the first Unicode
// code point satisfying f(c), or -1 if none do.
func IndexFunc(s []byte, f func(r rune) bool) int {
        return indexFunc(s, f, true)
}

// LastIndexFunc interprets s as a sequence of UTF-8-encoded Unicode code points.
// It returns the byte index in s of the last Unicode
// code point satisfying f(c), or -1 if none do.
func LastIndexFunc(s []byte, f func(r rune) bool) int {
        return lastIndexFunc(s, f, true)
}

// indexFunc is the same as IndexFunc except that if
// truth==false, the sense of the predicate function is
// inverted.
func indexFunc(s []byte, f func(r rune) bool, truth bool) int {
        start := 0
        for start < len(s) {
                wid := 1
                r := rune(s[start])
                if r >= utf8.RuneSelf {
                        r, wid = utf8.DecodeRune(s[start:])
                }
                if f(r) == truth {
                        return start
                }
                start += wid
        }
        return -1
}

// lastIndexFunc is the same as LastIndexFunc except that if
// truth==false, the sense of the predicate function is
// inverted.
func lastIndexFunc(s []byte, f func(r rune) bool, truth bool) int {
        for i := len(s); i > 0; {
                r, size := utf8.DecodeLastRune(s[0:i])
                i -= size
                if f(r) == truth {
                        return i
                }
        }
        return -1
}

func makeCutsetFunc(cutset string) func(r rune) bool {
        return func(r rune) bool {
                for _, c := range cutset {
                        if c == r {
                                return true
                        }
                }
                return false
        }
}

// Trim returns a subslice of s by slicing off all leading and
// trailing UTF-8-encoded Unicode code points contained in cutset.
func Trim(s []byte, cutset string) []byte {
        return TrimFunc(s, makeCutsetFunc(cutset))
}

// TrimLeft returns a subslice of s by slicing off all leading
// UTF-8-encoded Unicode code points contained in cutset.
func TrimLeft(s []byte, cutset string) []byte {
        return TrimLeftFunc(s, makeCutsetFunc(cutset))
}

// TrimRight returns a subslice of s by slicing off all trailing
// UTF-8-encoded Unicode code points that are contained in cutset.
func TrimRight(s []byte, cutset string) []byte {
        return TrimRightFunc(s, makeCutsetFunc(cutset))
}

// TrimSpace returns a subslice of s by slicing off all leading and
// trailing white space, as defined by Unicode.
func TrimSpace(s []byte) []byte {
        return TrimFunc(s, unicode.IsSpace)
}

// Runes returns a slice of runes (Unicode code points) equivalent to s.
func Runes(s []byte) []rune {
        t := make([]rune, utf8.RuneCount(s))
        i := 0
        for len(s) > 0 {
                r, l := utf8.DecodeRune(s)
                t[i] = r
                i++
                s = s[l:]
        }
        return t
}

// Replace returns a copy of the slice s with the first n
// non-overlapping instances of old replaced by new.
// If n < 0, there is no limit on the number of replacements.
func Replace(s, old, new []byte, n int) []byte {
        m := 0
        if n != 0 {
                // Compute number of replacements.
                m = Count(s, old)
        }
        if m == 0 {
                // Nothing to do. Just copy.
                t := make([]byte, len(s))
                copy(t, s)
                return t
        }
        if n < 0 || m < n {
                n = m
        }

        // Apply replacements to buffer.
        t := make([]byte, len(s)+n*(len(new)-len(old)))
        w := 0
        start := 0
        for i := 0; i < n; i++ {
                j := start
                if len(old) == 0 {
                        if i > 0 {
                                _, wid := utf8.DecodeRune(s[start:])
                                j += wid
                        }
                } else {
                        j += Index(s[start:], old)
                }
                w += copy(t[w:], s[start:j])
                w += copy(t[w:], new)
                start = j + len(old)
        }
        w += copy(t[w:], s[start:])
        return t[0:w]
}

// EqualFold reports whether s and t, interpreted as UTF-8 strings,
// are equal under Unicode case-folding.
func EqualFold(s, t []byte) bool {
        for len(s) != 0 && len(t) != 0 {
                // Extract first rune from each.
                var sr, tr rune
                if s[0] < utf8.RuneSelf {
                        sr, s = rune(s[0]), s[1:]
                } else {
                        r, size := utf8.DecodeRune(s)
                        sr, s = r, s[size:]
                }
                if t[0] < utf8.RuneSelf {
                        tr, t = rune(t[0]), t[1:]
                } else {
                        r, size := utf8.DecodeRune(t)
                        tr, t = r, t[size:]
                }

                // If they match, keep going; if not, return false.

                // Easy case.
                if tr == sr {
                        continue
                }

                // Make sr < tr to simplify what follows.
                if tr < sr {
                        tr, sr = sr, tr
                }
                // Fast check for ASCII.
                if tr < utf8.RuneSelf && 'A' <= sr && sr <= 'Z' {
                        // ASCII, and sr is upper case.  tr must be lower case.
                        if tr == sr+'a'-'A' {
                                continue
                        }
                        return false
                }

                // General case.  SimpleFold(x) returns the next equivalent rune > x
                // or wraps around to smaller values.
                r := unicode.SimpleFold(sr)
                for r != sr && r < tr {
                        r = unicode.SimpleFold(r)
                }
                if r == tr {
                        continue
                }
                return false
        }

        // One string is empty.  Are both?
        return len(s) == len(t)
}