1 files changed, 96 insertions, 0 deletions
diff --git a/internal/norm/norm.go b/internal/norm/norm.go
new file mode 100644
index 0000000..e7933ec
--- /dev/null
+++ b/internal/norm/norm.go
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// Package norm puts text into the form krino compares it in: optionally
+// without diacritics, optionally lower case, with white space collapsed.
+package norm
+
+import (
+	"strings"
+	"unicode"
+
+	unorm "golang.org/x/text/unicode/norm"
+)
+
+// special holds the letters that do not decompose under Unicode NFD, so
+// Fold maps them explicitly.
+var special = map[rune]string{
+	'ł': "l", 'Ł': "L",
+	'ø': "o", 'Ø': "O",
+	'đ': "d", 'Đ': "D",
+	'ħ': "h", 'Ħ': "H",
+	'ß': "ss",
+	'æ': "ae", 'Æ': "AE",
+	'œ': "oe", 'Œ': "OE",
+	'ı': "i",
+}
+
+// Fold strips diacritics: Unicode NFD, drop combining marks (category Mn),
+// then map the letters that do not decompose. ASCII input is returned
+// unchanged without allocating.
+func Fold(s string) string {
+	ascii := true
+	for i := 0; i < len(s); i++ {
+		if s[i] >= 0x80 {
+			ascii = false
+			break
+		}
+	}
+	if ascii {
+		return s
+	}
+
+	var b strings.Builder
+	b.Grow(len(s))
+	for _, r := range unorm.NFD.String(s) {
+		if unicode.Is(unicode.Mn, r) {
+			continue
+		}
+		if rep, ok := special[r]; ok {
+			b.WriteString(rep)
+			continue
+		}
+		b.WriteRune(r)
+	}
+	return b.String()
+}
+
+// Text puts s into the form content and keywords are compared in: Fold if
+// fold, strings.ToLower if ignoreCase, then every run of Unicode white
+// space becomes one ASCII space and both ends are trimmed.
+func Text(s string, ignoreCase, fold bool) string {
+	if fold {
+		s = Fold(s)
+	}
+	if ignoreCase {
+		s = strings.ToLower(s)
+	}
+
+	var b strings.Builder
+	b.Grow(len(s))
+	inSpace := false
+	started := false
+	for _, r := range s {
+		if unicode.IsSpace(r) {
+			if started {
+				inSpace = true
+			}
+			continue
+		}
+		if inSpace {
+			b.WriteByte(' ')
+			inSpace = false
+		}
+		b.WriteRune(r)
+		started = true
+	}
+	return b.String()
+}
+
+// Name puts a file name into the form it is matched against: Fold(s) if
+// fold, else s. Case is handled by the regex flag, not here.
+func Name(s string, fold bool) string {
+	if fold {
+		return Fold(s)
+	}
+	return s
+}