"""shutil-like functionality while compressing blendfiles on the fly."""

import gzip
import logging
import pathlib
import shutil

log = logging.getLogger(__name__)

# Arbitrarily chosen block size, in bytes.
BLOCK_SIZE = 256 * 2 ** 10


def move(src: pathlib.Path, dest: pathlib.Path):
    """Move a file from src to dest, gzip-compressing if not compressed yet.

    Only compresses files ending in .blend; others are moved as-is.
    """
    my_log = log.getChild('move')
    my_log.debug('Moving %s to %s', src, dest)

    if src.suffix.lower() == '.blend':
        _move_or_copy(src, dest, my_log, source_must_remain=False)
    else:
        shutil.move(str(src), str(dest))


def copy(src: pathlib.Path, dest: pathlib.Path):
    """Copy a file from src to dest, gzip-compressing if not compressed yet.

    Only compresses files ending in .blend; others are copied as-is.
    """
    my_log = log.getChild('copy')
    my_log.debug('Copying %s to %s', src, dest)

    if src.suffix.lower() == '.blend':
        _move_or_copy(src, dest, my_log, source_must_remain=True)
    else:
        shutil.copy2(str(src), str(dest))


def _move_or_copy(src: pathlib.Path, dest: pathlib.Path,
                  my_log: logging.Logger,
                  *,
                  source_must_remain: bool):
    """Either move or copy a file, gzip-compressing if not compressed yet.

    :param src: File to copy/move.
    :param dest: Path to copy/move to.
    :source_must_remain: True to copy, False to move.
    :my_log: Logger to use for logging.
    """
    srcfile = src.open('rb')
    try:
        first_bytes = srcfile.read(2)
        if first_bytes == b'\x1f\x8b':
            # Already a gzipped file.
            srcfile.close()
            my_log.debug('Source file %s is GZipped already', src)
            if source_must_remain:
                shutil.copy2(str(src), str(dest))
            else:
                shutil.move(str(src), str(dest))
            return

        my_log.debug('Compressing %s on the fly while copying to %s', src, dest)
        with gzip.open(str(dest), mode='wb') as destfile:
            destfile.write(first_bytes)
            shutil.copyfileobj(srcfile, destfile, BLOCK_SIZE)

        srcfile.close()
        if not source_must_remain:
            my_log.debug('Deleting source file %s', src)
            src.unlink()
    finally:
        if not srcfile.closed:
            srcfile.close()