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// Copyright 2010 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 path

import (
        "errors"
        "strings"
        "unicode/utf8"
)

var ErrBadPattern = errors.New("syntax error in pattern")

// Match returns true if name matches the shell file name pattern.
// The pattern syntax is:
//
//      pattern:
//              { term }
//      term:
//              '*'         matches any sequence of non-/ characters
//              '?'         matches any single non-/ character
//              '[' [ '^' ] { character-range } ']'
//                          character class (must be non-empty)
//              c           matches character c (c != '*', '?', '\\', '[')
//              '\\' c      matches character c
//
//      character-range:
//              c           matches character c (c != '\\', '-', ']')
//              '\\' c      matches character c
//              lo '-' hi   matches character c for lo <= c <= hi
//
// Match requires pattern to match all of name, not just a substring.
// The only possible error return is when pattern is malformed.
//
func Match(pattern, name string) (matched bool, err error) {
Pattern:
        for len(pattern) > 0 {
                var star bool
                var chunk string
                star, chunk, pattern = scanChunk(pattern)
                if star && chunk == "" {
                        // Trailing * matches rest of string unless it has a /.
                        return strings.Index(name, "/") < 0, nil
                }
                // Look for match at current position.
                t, ok, err := matchChunk(chunk, name)
                // if we're the last chunk, make sure we've exhausted the name
                // otherwise we'll give a false result even if we could still match
                // using the star
                if ok && (len(t) == 0 || len(pattern) > 0) {
                        name = t
                        continue
                }
                if err != nil {
                        return false, err
                }
                if star {
                        // Look for match skipping i+1 bytes.
                        // Cannot skip /.
                        for i := 0; i < len(name) && name[i] != '/'; i++ {
                                t, ok, err := matchChunk(chunk, name[i+1:])
                                if ok {
                                        // if we're the last chunk, make sure we exhausted the name
                                        if len(pattern) == 0 && len(t) > 0 {
                                                continue
                                        }
                                        name = t
                                        continue Pattern
                                }
                                if err != nil {
                                        return false, err
                                }
                        }
                }
                return false, nil
        }
        return len(name) == 0, nil
}

// scanChunk gets the next segment of pattern, which is a non-star string
// possibly preceded by a star.
func scanChunk(pattern string) (star bool, chunk, rest string) {
        for len(pattern) > 0 && pattern[0] == '*' {
                pattern = pattern[1:]
                star = true
        }
        inrange := false
        var i int
Scan:
        for i = 0; i < len(pattern); i++ {
                switch pattern[i] {
                case '\\':
                        // error check handled in matchChunk: bad pattern.
                        if i+1 < len(pattern) {
                                i++
                        }
                case '[':
                        inrange = true
                case ']':
                        inrange = false
                case '*':
                        if !inrange {
                                break Scan
                        }
                }
        }
        return star, pattern[0:i], pattern[i:]
}

// matchChunk checks whether chunk matches the beginning of s.
// If so, it returns the remainder of s (after the match).
// Chunk is all single-character operators: literals, char classes, and ?.
func matchChunk(chunk, s string) (rest string, ok bool, err error) {
        for len(chunk) > 0 {
                if len(s) == 0 {
                        return
                }
                switch chunk[0] {
                case '[':
                        // character class
                        r, n := utf8.DecodeRuneInString(s)
                        s = s[n:]
                        chunk = chunk[1:]
                        // possibly negated
                        notNegated := true
                        if len(chunk) > 0 && chunk[0] == '^' {
                                notNegated = false
                                chunk = chunk[1:]
                        }
                        // parse all ranges
                        match := false
                        nrange := 0
                        for {
                                if len(chunk) > 0 && chunk[0] == ']' && nrange > 0 {
                                        chunk = chunk[1:]
                                        break
                                }
                                var lo, hi rune
                                if lo, chunk, err = getEsc(chunk); err != nil {
                                        return
                                }
                                hi = lo
                                if chunk[0] == '-' {
                                        if hi, chunk, err = getEsc(chunk[1:]); err != nil {
                                                return
                                        }
                                }
                                if lo <= r && r <= hi {
                                        match = true
                                }
                                nrange++
                        }
                        if match != notNegated {
                                return
                        }

                case '?':
                        if s[0] == '/' {
                                return
                        }
                        _, n := utf8.DecodeRuneInString(s)
                        s = s[n:]
                        chunk = chunk[1:]

                case '\\':
                        chunk = chunk[1:]
                        if len(chunk) == 0 {
                                err = ErrBadPattern
                                return
                        }
                        fallthrough

                default:
                        if chunk[0] != s[0] {
                                return
                        }
                        s = s[1:]
                        chunk = chunk[1:]
                }
        }
        return s, true, nil
}

// getEsc gets a possibly-escaped character from chunk, for a character class.
func getEsc(chunk string) (r rune, nchunk string, err error) {
        if len(chunk) == 0 || chunk[0] == '-' || chunk[0] == ']' {
                err = ErrBadPattern
                return
        }
        if chunk[0] == '\\' {
                chunk = chunk[1:]
                if len(chunk) == 0 {
                        err = ErrBadPattern
                        return
                }
        }
        r, n := utf8.DecodeRuneInString(chunk)
        if r == utf8.RuneError && n == 1 {
                err = ErrBadPattern
        }
        nchunk = chunk[n:]
        if len(nchunk) == 0 {
                err = ErrBadPattern
        }
        return
}