fix(discord): cap lines per message

src/discord/chunk.ts

@@ -0,0 +1,191 @@
+export type ChunkDiscordTextOpts = {
+  /** Max characters per Discord message. Default: 2000. */
+  maxChars?: number;
+  /**
+   * Soft max line count per message. Default: 17.
+   *
+   * Discord clients can clip/collapse very tall messages in the UI; splitting
+   * by lines keeps long multi-paragraph replies readable.
+   */
+  maxLines?: number;
+};
+
+type OpenFence = {
+  indent: string;
+  markerChar: string;
+  markerLen: number;
+  openLine: string;
+};
+
+const DEFAULT_MAX_CHARS = 2000;
+const DEFAULT_MAX_LINES = 17;
+const FENCE_RE = /^( {0,3})(`{3,}|~{3,})(.*)$/;
+
+function countLines(text: string) {
+  if (!text) return 0;
+  return text.split("\n").length;
+}
+
+function parseFenceLine(line: string): OpenFence | null {
+  const match = line.match(FENCE_RE);
+  if (!match) return null;
+  const indent = match[1] ?? "";
+  const marker = match[2] ?? "";
+  return {
+    indent,
+    markerChar: marker[0] ?? "`",
+    markerLen: marker.length,
+    openLine: line,
+  };
+}
+
+function closeFenceLine(openFence: OpenFence) {
+  return `${openFence.indent}${openFence.markerChar.repeat(
+    openFence.markerLen,
+  )}`;
+}
+
+function closeFenceIfNeeded(text: string, openFence: OpenFence | null) {
+  if (!openFence) return text;
+  const closeLine = closeFenceLine(openFence);
+  if (!text) return closeLine;
+  if (!text.endsWith("\n")) return `${text}\n${closeLine}`;
+  return `${text}${closeLine}`;
+}
+
+function splitLongLine(
+  line: string,
+  maxChars: number,
+  opts: { preserveWhitespace: boolean },
+): string[] {
+  const limit = Math.max(1, Math.floor(maxChars));
+  if (line.length <= limit) return [line];
+  const out: string[] = [];
+  let remaining = line;
+  while (remaining.length > limit) {
+    if (opts.preserveWhitespace) {
+      out.push(remaining.slice(0, limit));
+      remaining = remaining.slice(limit);
+      continue;
+    }
+    const window = remaining.slice(0, limit);
+    let breakIdx = -1;
+    for (let i = window.length - 1; i >= 0; i--) {
+      if (/\s/.test(window[i])) {
+        breakIdx = i;
+        break;
+      }
+    }
+    if (breakIdx <= 0) breakIdx = limit;
+    out.push(remaining.slice(0, breakIdx));
+    const brokeOnSeparator =
+      breakIdx < remaining.length && /\s/.test(remaining[breakIdx]);
+    remaining = remaining.slice(breakIdx + (brokeOnSeparator ? 1 : 0));
+  }
+  if (remaining.length) out.push(remaining);
+  return out;
+}
+
+/**
+ * Chunks outbound Discord text by both character count and (soft) line count,
+ * while keeping fenced code blocks balanced across chunks.
+ */
+export function chunkDiscordText(
+  text: string,
+  opts: ChunkDiscordTextOpts = {},
+): string[] {
+  const maxChars = Math.max(1, Math.floor(opts.maxChars ?? DEFAULT_MAX_CHARS));
+  const maxLines = Math.max(1, Math.floor(opts.maxLines ?? DEFAULT_MAX_LINES));
+
+  const body = text ?? "";
+  if (!body) return [];
+
+  const alreadyOk = body.length <= maxChars && countLines(body) <= maxLines;
+  if (alreadyOk) return [body];
+
+  const lines = body.split("\n");
+  const chunks: string[] = [];
+
+  let current = "";
+  let currentLines = 0;
+  let openFence: OpenFence | null = null;
+
+  const flush = () => {
+    if (!current) return;
+    const payload = closeFenceIfNeeded(current, openFence);
+    if (payload.trim().length) chunks.push(payload);
+    current = "";
+    currentLines = 0;
+    if (openFence) {
+      current = openFence.openLine;
+      currentLines = 1;
+    }
+  };
+
+  for (const originalLine of lines) {
+    const fenceInfo = parseFenceLine(originalLine);
+    const wasInsideFence = openFence !== null;
+    let nextOpenFence: OpenFence | null = openFence;
+    if (fenceInfo) {
+      if (!openFence) {
+        nextOpenFence = fenceInfo;
+      } else if (
+        openFence.markerChar === fenceInfo.markerChar &&
+        fenceInfo.markerLen >= openFence.markerLen
+      ) {
+        nextOpenFence = null;
+      }
+    }
+
+    const reserveChars = nextOpenFence
+      ? closeFenceLine(nextOpenFence).length + 1
+      : 0;
+    const reserveLines = nextOpenFence ? 1 : 0;
+    const effectiveMaxChars = maxChars - reserveChars;
+    const effectiveMaxLines = maxLines - reserveLines;
+    const charLimit = effectiveMaxChars > 0 ? effectiveMaxChars : maxChars;
+    const lineLimit = effectiveMaxLines > 0 ? effectiveMaxLines : maxLines;
+    const prefixLen = current.length > 0 ? current.length + 1 : 0;
+    const segmentLimit = Math.max(1, charLimit - prefixLen);
+    const segments = splitLongLine(originalLine, segmentLimit, {
+      preserveWhitespace: wasInsideFence,
+    });
+
+    for (let segIndex = 0; segIndex < segments.length; segIndex++) {
+      const segment = segments[segIndex];
+      const isLineContinuation = segIndex > 0;
+      const delimiter = isLineContinuation
+        ? ""
+        : current.length > 0
+          ? "\n"
+          : "";
+      const addition = `${delimiter}${segment}`;
+      const nextLen = current.length + addition.length;
+      const nextLines = currentLines + (isLineContinuation ? 0 : 1);
+
+      const wouldExceedChars = nextLen > charLimit;
+      const wouldExceedLines = nextLines > lineLimit;
+
+      if ((wouldExceedChars || wouldExceedLines) && current.length > 0) {
+        flush();
+      }
+
+      if (current.length > 0) {
+        current += addition;
+        if (!isLineContinuation) currentLines += 1;
+      } else {
+        current = segment;
+        currentLines = 1;
+      }
+    }
+
+    openFence = nextOpenFence;
+  }
+
+  if (current.length) {
+    const payload = closeFenceIfNeeded(current, openFence);
+    if (payload.trim().length) chunks.push(payload);
+  }
+
+  return chunks;
+}