Make ReplaceAll re-useable

tools/utils/regexp.go

@@ -0,0 +1,51 @@
+// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package utils
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+	"sync"
+)
+
+var _ = fmt.Print
+
+var pat_cache = map[string]*regexp.Regexp{}
+var pat_cache_lock = sync.RWMutex{}
+
+func ReplaceAll(pat, str string, repl func(full_match string, groupdict map[string]string) string) string {
+	pat_cache_lock.RLock()
+	cpat := pat_cache[pat]
+	pat_cache_lock.RUnlock()
+	if cpat == nil {
+		cpat = regexp.MustCompile(pat)
+		pat_cache_lock.Lock()
+		pat_cache[pat] = cpat
+		pat_cache_lock.Unlock()
+	}
+	result := strings.Builder{}
+	result.Grow(len(str) + 256)
+	last_index := 0
+	matches := cpat.FindAllStringSubmatchIndex(str, -1)
+	names := cpat.SubexpNames()
+	for _, v := range matches {
+		match_start, match_end := v[0], v[1]
+		full_match := str[match_start:match_end]
+		groupdict := make(map[string]string, len(names))
+		for i, name := range names {
+			if i == 0 {
+				continue
+			}
+			idx := 2 * i
+			if v[idx] > -1 && v[idx+1] > -1 {
+				groupdict[name] = str[v[idx]:v[idx+1]]
+			}
+		}
+		result.WriteString(str[last_index:match_start])
+		result.WriteString(repl(full_match, groupdict))
+		last_index = match_end
+	}
+	result.WriteString(str[last_index:])
+	return result.String()
+}