#!/usr/bin/env python
#
# __init__.py - Miscellaneous functions used throughout fsl_ci.
#
# Author: Paul McCarthy <pauldmccarthy@gmail.com>
#


import os.path    as op
import               os
import               errno
import               shlex
import               string
import               time
import               tempfile
import contextlib as ctxlib
import subprocess as sp


__version__ = '0.1.0'
"""Current version of the fsl-ci-rules."""


USERNAME = 'fsl-ci-rules'
"""Username to be used for all git interactions which require one. """


EMAIL = 'fsl-ci-rules@git.fmrib.ox.ac.uk'
"""Password to be used for all git interactions which require one. """


def fprint(*args, **kwargs):
    """Print with flush=True. """
    print(*args, **kwargs, flush=True)


@ctxlib.contextmanager
def tempdir():
    """Context manager to create, and change into, a temporary directory, and
    then afterwards delete it and change back to the original working
    directory.
    """
    with tempfile.TemporaryDirectory() as td:
        prevdir = os.getcwd()
        os.chdir(td)
        try:
            yield td
        finally:
            os.chdir(prevdir)


@ctxlib.contextmanager
def indir(dirname):
    """Context manager to change into a directory, and then afterwards
    change back to the original working directory.
    """
    prevdir = os.getcwd()
    os.chdir(dirname)
    try:
        yield
    finally:
        os.chdir(prevdir)


def sprun(cmd, **kwargs):
    """Runs the given command with subprocess.run. """
    fprint(f'Running {cmd}')
    cmd = shlex.split(cmd)
    return sp.run(cmd, check=True, **kwargs)


def is_valid_project_version(version):
    """Return True if the given version/tag is "valid" - it must
    be a sequence of integers, separated by periods, with an optional
    leading 'v'.
    """
    if version.lower().startswith('v'):
        version = version[1:]

    for part in version.split('.'):
        if not all([c in string.digits for c in part]):
            return False
    return True


@ctxlib.contextmanager
def lockdir(dirname):
    """Primitive mechanism by which concurrent access to a directory can be
    prevented. Attempts to create a semaphore file in the directory, but waits
    if that file already exists. Removes the file when finished.
    """

    delay    = 10
    lockfile = op.join(dirname, '.fsl_ci.lockdir')

    while True:
        try:
            fprint(f'Attempting to lock {dirname} for exclusive access.')
            fd = os.open(os.O_CREAT | os.O_EXCL | os.O_RDWR)
            break
        except OSError as e:
            if e.errno != errno.EEXIST:
                raise e
            fprint(f'{dirname} is already locked - '
                   f'trying again in {delay} seconds ...')
        time.sleep(10)

    fprint(f'Exclusive access acquired for {dirname} ...')
    try:
        yield

    finally:
        fprint(f'Relinquishing lock on {dirname}')
        os.close( fd)
        os.unlink(lockfile)