migrate additional dependencies to ergochat

vendor/github.com/ergochat/confusables/confusables.go

@@ -0,0 +1,82 @@
+//go:generate go run maketables.go > tables.go
+
+package confusables
+
+import (
+	"bytes"
+
+	"golang.org/x/text/unicode/norm"
+)
+
+// TODO: document casefolding approaches
+// (suggest to force casefold strings; explain how to catch paypal - pAypal)
+// TODO: DOC you might want to store the Skeleton and check against it later
+// TODO: implement xidmodifications.txt restricted characters
+
+type lookupFunc func(rune) (string)
+
+func lookupReplacement(r rune) string {
+	return confusablesMap[r]
+}
+
+func lookupReplacementTweaked(r rune) string {
+	if replacement, ok := tweaksMap[r]; ok {
+		return replacement
+	}
+	return confusablesMap[r]
+}
+
+func skeletonBase(s string, lookup lookupFunc) string {
+
+	// 1. Converting X to NFD format
+	s = norm.NFD.String(s)
+
+	// 2. Successively mapping each source character in X to the target string
+	// according to the specified data table
+	var buf bytes.Buffer
+	changed := false // fast path: if this remains false, keep s intact
+	prevPos := 0
+	var replacement string
+	for i, r := range s {
+		if changed && replacement == "" {
+			buf.WriteString(s[prevPos:i])
+		}
+		prevPos = i
+		replacement = lookup(r)
+		if replacement != "" {
+			if !changed {
+				changed = true
+				// first replacement: copy over the previously unmodified text
+				buf.WriteString(s[:i])
+			}
+			buf.WriteString(replacement)
+		}
+	}
+	if changed && replacement == "" {
+		buf.WriteString(s[prevPos:]) // loop-and-a-half
+	}
+	if changed {
+		s = buf.String()
+	}
+
+	// 3. Reapplying NFD
+	s = norm.NFD.String(s)
+
+	return s
+}
+
+// Skeleton converts a string to its "skeleton" form
+// as described in http://www.unicode.org/reports/tr39/#Confusable_Detection
+func Skeleton(s string) string {
+	return skeletonBase(s, lookupReplacement)
+}
+
+// SkeletonTweaked is like Skeleton, but it implements some custom overrides
+// to the confusables table (currently it removes the m -> rn mapping):
+func SkeletonTweaked(s string) string {
+	return skeletonBase(s, lookupReplacementTweaked)
+}
+
+func Confusable(x, y string) bool {
+	return Skeleton(x) == Skeleton(y)
+}