Export template source from 488f7e229afed8f03fc3bfa4abe707da0c613460:examples/local-first/packages/language-reader-presentation

src/canvas/line-breaks.ts

@@ -0,0 +1,36 @@
+import { PASS, Rules } from "@cto.af/linebreak";
+import type { Range } from "./types.js";
+import { graphemes } from "./text.js";
+
+const normal = new Rules();
+// Emergency wrapping may split an oversized word or number, but still obeys
+// the punctuation, bracket, combining-mark and nonbreaking-space rules. This
+// is UAX #14 tailoring, not a list of special cases for a particular language.
+const emergency = new Rules();
+for (const rule of ["LB23", "LB25", "LB28", "LB29"]) emergency.replaceRule(rule, () => PASS);
+const cached = new Map<string, { normal: Range[]; emergency: Range[] }>();
+
+/** Legal UTF-16 source spans for line wrapping. Intl.Segmenter still owns word
+ * targeting; line breaking is a separate Unicode operation. */
+export function lineSpans(text: string, emergencyWrap = false): Range[] {
+  let entry = cached.get(text);
+  if (!entry) {
+    const spans = (rules: Rules): Range[] => {
+      let start = 0;
+      const boundaries = new Set(graphemes(text).map((unit) => unit.end));
+      return Array.from(rules.breaks(text))
+        .filter(({ position }) => boundaries.has(position))
+        .map(({ position }) => {
+          const range = { start, end: position };
+          start = position;
+          return range;
+        });
+    };
+    entry = { normal: spans(normal), emergency: spans(emergency) };
+    if (text.length >= 256 && text.length <= 120000) {
+      if (cached.size >= 4) cached.delete(cached.keys().next().value!);
+      cached.set(text, entry);
+    }
+  }
+  return entry[emergencyWrap ? "emergency" : "normal"];
+}