def reverse_apply_diff()

in jobs/webcompat-kb/webcompat_kb/metric_changes.py [0:0]

• 37 lines of code
• 12 McCabe index (conditional complexity)

def reverse_apply_diff(input_str: str, diff: str) -> str:
    """Apply a diff in reverse to get the original string"""

    input_lines = input_str.splitlines(True)
    input_idx = 0
    diff_lines = diff.splitlines(True)
    diff_idx = 0
    output_lines = []
    while diff_idx < len(diff_lines):
        m = header_pattern.match(diff_lines[diff_idx])
        if m is None:
            raise ValueError(f"Bad user story diff (missing header line):\n{diff}")
        start_line_number = int(m.group(3))
        end_line_number = int(m.group(4)) if m.group(4) else None
        start_idx = max(start_line_number - 1, 0)
        if start_idx < input_idx or (
            end_line_number is not None and end_line_number > len(input_lines)
        ):
            raise ValueError(f"Bad user story diff (index out of bounds):\n{diff}")
        output_lines.extend(input_lines[input_idx:start_idx])
        diff_idx += 1
        input_idx = start_idx
        while diff_idx < len(diff_lines) and diff_lines[diff_idx][0] != "@":
            change_char = diff_lines[diff_idx][0]
            data = diff_lines[diff_idx][1:]
            if change_char == "+":
                input_idx += 1
            elif change_char == " ":
                if input_lines[input_idx].strip() != data.strip():
                    raise ValueError(
                        f"Bad user story diff (patch doesn't match):\n{diff}\nInput line {input_idx} expected {data} got {input_lines[input_idx]}"
                    )
                output_lines.append(data)
                input_idx += 1
            else:
                output_lines.append(data)
            diff_idx += 1

    output_lines.extend(input_lines[input_idx:])
    return "".join(output_lines)