merge_pdf.py

#!/usr/bin/env python3
"""
PDF Merger
Usage: ./merge_pdf.py /path/to/output.pdf /path/to/1.pdf /path/to/2.pdf ...

Behavior:
- Merge input PDFs in the exact order provided into a single output PDF
- Inputs are untouched; output must not already exist
- All-or-nothing: on any error, prints an error and exits with code 1 (no partial output)
"""

from pathlib import Path

import sys
import time
import shutil

try:
    import fitz  # PyMuPDF
except ImportError as e:
    print(f"Error: Missing dependency - {e}")
    sys.exit(1)


def run_pdf_merge(output_path: str, input_paths: list[str]) -> None:
    try:
        out = Path(output_path)
        if out.suffix.lower() != ".pdf":
            print("Error: Output must be a .pdf file")
            sys.exit(1)
        if out.exists():
            print("Error: Output file already exists")
            sys.exit(1)
        if not out.parent.is_dir():
            print("Error: Output directory does not exist")
            sys.exit(1)

        if len(input_paths) < 2:
            print("Error: Provide at least two input PDF files to merge")
            sys.exit(1)

        inputs: list[Path] = []
        for p_str in input_paths:
            p = Path(p_str)
            if not p.is_file() or p.suffix.lower() != ".pdf":
                print(f"Error: Invalid input PDF - {p}")
                sys.exit(1)
            inputs.append(p)

        temp_output = out.parent / f".{out.stem}.tmp-{int(time.time())}.pdf"

        merged = fitz.open()
        try:
            for src in inputs:
                try:
                    doc = fitz.open(str(src))
                except Exception as e:
                    raise RuntimeError(f"Failed to open '{src}': {e}")
                try:
                    # Reject encrypted PDFs that require a password
                    if getattr(doc, "needs_pass", False):
                        raise RuntimeError(f"Encrypted PDF not supported: {src}")
                    # Insert all pages
                    merged.insert_pdf(doc, from_page=0, to_page=doc.page_count - 1)
                finally:
                    doc.close()

            # Save to temporary file first
            merged.save(str(temp_output), garbage=4, deflate=True)
        finally:
            merged.close()

        # Atomic move into place
        try:
            shutil.move(str(temp_output), str(out))
        except Exception as e:
            # Cleanup temp and fail
            try:
                if temp_output.exists():
                    temp_output.unlink()
            except Exception:
                pass
            print(f"Error: {e}")
            sys.exit(1)

        print("Success: merge_pdf completed")
    except Exception as e:
        # Best-effort cleanup
        try:
            temp_output  # type: ignore[name-defined]
            if isinstance(temp_output, Path) and temp_output.exists():
                temp_output.unlink()
        except Exception:
            pass
        print(f"Error: {e}")
        sys.exit(1)


def main():
    if len(sys.argv) < 4:
        print("Usage: merge_pdf.py /path/to/output.pdf /path/to/1.pdf /path/to/2.pdf ...")
        sys.exit(1)
    output = sys.argv[1]
    inputs = sys.argv[2:]
    run_pdf_merge(output, inputs)


if __name__ == "__main__":
    main()