function peek_next_section()

in codex-cli/src/utils/agent/apply-patch.ts [453:537]

• 77 lines of code
• 18 McCabe index (conditional complexity)

function peek_next_section(
  lines: Array<string>,
  initialIndex: number,
): [Array<string>, Array<Chunk>, number, boolean] {
  let index = initialIndex;
  const old: Array<string> = [];
  let delLines: Array<string> = [];
  let insLines: Array<string> = [];
  const chunks: Array<Chunk> = [];
  let mode: "keep" | "add" | "delete" = "keep";

  while (index < lines.length) {
    const s = lines[index]!;
    if (
      [
        "@@",
        PATCH_SUFFIX,
        UPDATE_FILE_PREFIX,
        DELETE_FILE_PREFIX,
        ADD_FILE_PREFIX,
        END_OF_FILE_PREFIX,
      ].some((p) => s.startsWith(p.trim()))
    ) {
      break;
    }
    if (s === "***") {
      break;
    }
    if (s.startsWith("***")) {
      throw new DiffError(`Invalid Line: ${s}`);
    }
    index += 1;
    const lastMode: "keep" | "add" | "delete" = mode;
    let line = s;
    if (line[0] === HUNK_ADD_LINE_PREFIX) {
      mode = "add";
    } else if (line[0] === "-") {
      mode = "delete";
    } else if (line[0] === " ") {
      mode = "keep";
    } else {
      // Tolerate invalid lines where the leading whitespace is missing. This is necessary as
      // the model sometimes doesn't fully adhere to the spec and returns lines without leading
      // whitespace for context lines.
      mode = "keep";
      line = " " + line;

      // TODO: Re-enable strict mode.
      // throw new DiffError(`Invalid Line: ${line}`)
    }

    line = line.slice(1);
    if (mode === "keep" && lastMode !== mode) {
      if (insLines.length || delLines.length) {
        chunks.push({
          orig_index: old.length - delLines.length,
          del_lines: delLines,
          ins_lines: insLines,
        });
      }
      delLines = [];
      insLines = [];
    }
    if (mode === "delete") {
      delLines.push(line);
      old.push(line);
    } else if (mode === "add") {
      insLines.push(line);
    } else {
      old.push(line);
    }
  }
  if (insLines.length || delLines.length) {
    chunks.push({
      orig_index: old.length - delLines.length,
      del_lines: delLines,
      ins_lines: insLines,
    });
  }
  if (index < lines.length && lines[index] === END_OF_FILE_PREFIX) {
    index += 1;
    return [old, chunks, index, true];
  }
  return [old, chunks, index, false];
}