1 files changed, 150 insertions, 0 deletions
diff --git a/plumbing/format/gitignore/pattern.go b/plumbing/format/gitignore/pattern.go
new file mode 100644
index 0000000..bd0825b
--- /dev/null
+++ b/plumbing/format/gitignore/pattern.go
@@ -0,0 +1,150 @@
+package gitignore
+
+import (
+	"path/filepath"
+	"strings"
+)
+
+// MatchResult defines outcomes of a match, no match, exclusion or inclusion.
+type MatchResult int
+
+const (
+	// NoMatch defines the no match outcome of a match check
+	NoMatch MatchResult = iota
+	// Exclude defines an exclusion of a file as a result of a match check
+	Exclude
+	// Exclude defines an explicit inclusion of a file as a result of a match check
+	Include
+)
+
+const (
+	inclusionPrefix = "!"
+	zeroToManyDirs  = "**"
+	patternDirSep   = "/"
+)
+
+// Pattern defines a single gitignore pattern.
+type Pattern interface {
+	// Match matches the given path to the pattern.
+	Match(path []string, isDir bool) MatchResult
+}
+
+type pattern struct {
+	domain    []string
+	pattern   []string
+	inclusion bool
+	dirOnly   bool
+	isGlob    bool
+}
+
+// ParsePattern parses a gitignore pattern string into the Pattern structure.
+func ParsePattern(p string, domain []string) Pattern {
+	res := pattern{domain: domain}
+
+	if strings.HasPrefix(p, inclusionPrefix) {
+		res.inclusion = true
+		p = p[1:]
+	}
+
+	if !strings.HasSuffix(p, "\\ ") {
+		p = strings.TrimRight(p, " ")
+	}
+
+	if strings.HasSuffix(p, patternDirSep) {
+		res.dirOnly = true
+		p = p[:len(p)-1]
+	}
+
+	if strings.Contains(p, patternDirSep) {
+		res.isGlob = true
+	}
+
+	res.pattern = strings.Split(p, patternDirSep)
+	return &res
+}
+
+func (p *pattern) Match(path []string, isDir bool) MatchResult {
+	if len(path) <= len(p.domain) {
+		return NoMatch
+	}
+	for i, e := range p.domain {
+		if path[i] != e {
+			return NoMatch
+		}
+	}
+
+	path = path[len(p.domain):]
+	if p.isGlob && !p.globMatch(path, isDir) {
+		return NoMatch
+	} else if !p.isGlob && !p.simpleNameMatch(path, isDir) {
+		return NoMatch
+	}
+
+	if p.inclusion {
+		return Include
+	} else {
+		return Exclude
+	}
+}
+
+func (p *pattern) simpleNameMatch(path []string, isDir bool) bool {
+	for i, name := range path {
+		if match, err := filepath.Match(p.pattern[0], name); err != nil {
+			return false
+		} else if !match {
+			continue
+		}
+		if p.dirOnly && !isDir && i == len(path)-1 {
+			return false
+		}
+		return true
+	}
+	return false
+}
+
+func (p *pattern) globMatch(path []string, isDir bool) bool {
+	matched := false
+	canTraverse := false
+	for i, pattern := range p.pattern {
+		if pattern == "" {
+			canTraverse = false
+			continue
+		}
+		if pattern == zeroToManyDirs {
+			if i == len(p.pattern)-1 {
+				break
+			}
+			canTraverse = true
+			continue
+		}
+		if strings.Contains(pattern, zeroToManyDirs) {
+			return false
+		}
+		if len(path) == 0 {
+			return false
+		}
+		if canTraverse {
+			canTraverse = false
+			for len(path) > 0 {
+				e := path[0]
+				path = path[1:]
+				if match, err := filepath.Match(pattern, e); err != nil {
+					return false
+				} else if match {
+					matched = true
+					break
+				}
+			}
+		} else {
+			if match, err := filepath.Match(pattern, path[0]); err != nil || !match {
+				return false
+			}
+			matched = true
+			path = path[1:]
+		}
+	}
+	if matched && p.dirOnly && !isDir && len(path) == 0 {
+		matched = false
+	}
+	return matched
+}