refactor(app): extract terminal runtime out of react lifecycle

packages/app/src/utils/terminal-output-buffer.ts

@@ -0,0 +1,95 @@
+export interface TerminalOutputBuffer {
+  segments: string[];
+  startIndex: number;
+  totalChars: number;
+}
+
+const COMPACT_SEGMENT_THRESHOLD = 256;
+
+export function createTerminalOutputBuffer(): TerminalOutputBuffer {
+  return {
+    segments: [],
+    startIndex: 0,
+    totalChars: 0,
+  };
+}
+
+function normalizeMaxChars(input: { maxChars: number }): number {
+  if (!Number.isFinite(input.maxChars)) {
+    return 0;
+  }
+  return Math.max(0, Math.floor(input.maxChars));
+}
+
+function compactTerminalOutputBuffer(input: { buffer: TerminalOutputBuffer }): void {
+  const { buffer } = input;
+  if (buffer.startIndex <= COMPACT_SEGMENT_THRESHOLD) {
+    return;
+  }
+
+  buffer.segments = buffer.segments.slice(buffer.startIndex);
+  buffer.startIndex = 0;
+}
+
+function trimTerminalOutputBufferToMax(input: {
+  buffer: TerminalOutputBuffer;
+  maxChars: number;
+}): void {
+  const { buffer } = input;
+  const maxChars = normalizeMaxChars({ maxChars: input.maxChars });
+
+  while (buffer.totalChars > maxChars) {
+    const leadingSegment = buffer.segments[buffer.startIndex];
+    if (!leadingSegment) {
+      buffer.segments = [];
+      buffer.startIndex = 0;
+      buffer.totalChars = 0;
+      return;
+    }
+
+    const overflowChars = buffer.totalChars - maxChars;
+    if (leadingSegment.length <= overflowChars) {
+      buffer.startIndex += 1;
+      buffer.totalChars -= leadingSegment.length;
+      continue;
+    }
+
+    buffer.segments[buffer.startIndex] = leadingSegment.slice(overflowChars);
+    buffer.totalChars -= overflowChars;
+    break;
+  }
+
+  compactTerminalOutputBuffer({ buffer });
+}
+
+export function appendTerminalOutputBuffer(input: {
+  buffer: TerminalOutputBuffer;
+  text: string;
+  maxChars: number;
+}): void {
+  if (!input.text) {
+    return;
+  }
+
+  input.buffer.segments.push(input.text);
+  input.buffer.totalChars += input.text.length;
+  trimTerminalOutputBufferToMax({
+    buffer: input.buffer,
+    maxChars: input.maxChars,
+  });
+}
+
+export function readTerminalOutputBuffer(input: {
+  buffer: TerminalOutputBuffer;
+}): string {
+  const { buffer } = input;
+  if (buffer.totalChars <= 0) {
+    return "";
+  }
+
+  if (buffer.startIndex === 0) {
+    return buffer.segments.join("");
+  }
+
+  return buffer.segments.slice(buffer.startIndex).join("");
+}