optimize edit-tool rendering (#463)

Co-authored-by: opencode <noreply@opencode.ai>
Co-authored-by: Adam <2363879+adamdotdevin@users.noreply.github.com>

packages/tui/internal/util/concurrency.go

@@ -0,0 +1,50 @@
+package util
+
+import (
+	"strings"
+	"sync"
+)
+
+// MapReducePar performs a parallel map-reduce operation on a slice of items.
+// It applies a function to each item in the slice concurrently,
+// and combines the results serially using a reducer returned from
+// each one of the functions, allowing the use of closures.
+func MapReducePar[a, b any](items []a, init b, fn func(a) func(b) b) b {
+	itemCount := len(items)
+	locks := make([]*sync.Mutex, itemCount)
+	mapped := make([]func(b) b, itemCount)
+
+	for i, value := range items {
+		lock := &sync.Mutex{}
+		lock.Lock()
+		locks[i] = lock
+		go func() {
+			defer lock.Unlock()
+			mapped[i] = fn(value)
+		}()
+	}
+
+	result := init
+	for i := range itemCount {
+		locks[i].Lock()
+		defer locks[i].Unlock()
+		f := mapped[i]
+		if f != nil {
+			result = f(result)
+		}
+	}
+
+	return result
+}
+
+// WriteStringsPar allows to iterate over a list and compute strings in parallel,
+// yet write them in order.
+func WriteStringsPar[a any](sb *strings.Builder, items []a, fn func(a) string) {
+	MapReducePar(items, sb, func(item a) func(*strings.Builder) *strings.Builder {
+		str := fn(item)
+		return func(sbdr *strings.Builder) *strings.Builder {
+			sbdr.WriteString(str)
+			return sbdr
+		}
+	})
+}