"""The IPython kernel spec for Jupyter"""

# Copyright (c) IPython Development Team.
# Distributed under the terms of the Modified BSD License.

import errno
import json
import os
import shutil
import stat
import sys
import tempfile

from jupyter_client.kernelspec import KernelSpecManager

pjoin = os.path.join

KERNEL_NAME = 'python%i' % sys.version_info[0]

# path to kernelspec resources
RESOURCES = pjoin(os.path.dirname(__file__), 'resources')


def make_ipkernel_cmd(mod="ipykernel_launcher", executable=None, extra_arguments=None):
    """Build Popen command list for launching an IPython kernel.

    Parameters
    ----------
    mod : str, optional (default 'ipykernel')
        A string of an IPython module whose __main__ starts an IPython kernel
    executable : str, optional (default sys.executable)
        The Python executable to use for the kernel process.
    extra_arguments : list, optional
        A list of extra arguments to pass when executing the launch code.

    Returns
    -------
    A Popen command list
    """
    if executable is None:
        executable = sys.executable
    extra_arguments = extra_arguments or []
    arguments = [executable, '-m', mod, '-f', '{connection_file}']
    arguments.extend(extra_arguments)

    return arguments


def get_kernel_dict(extra_arguments=None):
    """Construct dict for kernel.json"""
    return {
        'argv': make_ipkernel_cmd(extra_arguments=extra_arguments),
        'display_name': 'Python %i (ipykernel)' % sys.version_info[0],
        'language': 'python',
        'metadata': { 'debugger': True}
    }


def write_kernel_spec(path=None, overrides=None, extra_arguments=None):
    """Write a kernel spec directory to `path`

    If `path` is not specified, a temporary directory is created.
    If `overrides` is given, the kernelspec JSON is updated before writing.

    The path to the kernelspec is always returned.
    """
    if path is None:
        path = os.path.join(tempfile.mkdtemp(suffix='_kernels'), KERNEL_NAME)
    
    # stage resources
    shutil.copytree(RESOURCES, path)

    # ensure path is writable
    mask = os.stat(path).st_mode
    if not mask & stat.S_IWUSR:
        os.chmod(path, mask | stat.S_IWUSR)

    # write kernel.json
    kernel_dict = get_kernel_dict(extra_arguments)

    if overrides:
        kernel_dict.update(overrides)
    with open(pjoin(path, 'kernel.json'), 'w') as f:
        json.dump(kernel_dict, f, indent=1)
    
    return path


def install(kernel_spec_manager=None, user=False, kernel_name=KERNEL_NAME, display_name=None,
            prefix=None, profile=None, env=None):
    """Install the IPython kernelspec for Jupyter

    Parameters
    ----------
    kernel_spec_manager : KernelSpecManager [optional]
        A KernelSpecManager to use for installation.
        If none provided, a default instance will be created.
    user : bool [default: False]
        Whether to do a user-only install, or system-wide.
    kernel_name : str, optional
        Specify a name for the kernelspec.
        This is needed for having multiple IPython kernels for different environments.
    display_name : str, optional
        Specify the display name for the kernelspec
    profile : str, optional
        Specify a custom profile to be loaded by the kernel.
    prefix : str, optional
        Specify an install prefix for the kernelspec.
        This is needed to install into a non-default location, such as a conda/virtual-env.
    env : dict, optional
        A dictionary of extra environment variables for the kernel.
        These will be added to the current environment variables before the
        kernel is started

    Returns
    -------
    The path where the kernelspec was installed.
    """
    if kernel_spec_manager is None:
        kernel_spec_manager = KernelSpecManager()

    if (kernel_name != KERNEL_NAME) and (display_name is None):
        # kernel_name is specified and display_name is not
        # default display_name to kernel_name
        display_name = kernel_name
    overrides = {}
    if display_name:
        overrides["display_name"] = display_name
    if profile:
        extra_arguments = ["--profile", profile]
        if not display_name:
            # add the profile to the default display name
            overrides["display_name"] = 'Python %i [profile=%s]' % (sys.version_info[0], profile)
    else:
        extra_arguments = None
    if env:
        overrides['env'] = env
    path = write_kernel_spec(overrides=overrides, extra_arguments=extra_arguments)
    dest = kernel_spec_manager.install_kernel_spec(
        path, kernel_name=kernel_name, user=user, prefix=prefix)
    # cleanup afterward
    shutil.rmtree(path)
    return dest

# Entrypoint

from traitlets.config import Application


class InstallIPythonKernelSpecApp(Application):
    """Dummy app wrapping argparse"""
    name = 'ipython-kernel-install'
    
    def initialize(self, argv=None):
        if argv is None:
            argv = sys.argv[1:]
        self.argv = argv
    
    def start(self):
        import argparse
        parser = argparse.ArgumentParser(prog=self.name,
            description="Install the IPython kernel spec.")
        parser.add_argument('--user', action='store_true',
            help="Install for the current user instead of system-wide")
        parser.add_argument('--name', type=str, default=KERNEL_NAME,
            help="Specify a name for the kernelspec."
            " This is needed to have multiple IPython kernels at the same time.")
        parser.add_argument('--display-name', type=str,
            help="Specify the display name for the kernelspec."
            " This is helpful when you have multiple IPython kernels.")
        parser.add_argument('--profile', type=str,
            help="Specify an IPython profile to load. "
            "This can be used to create custom versions of the kernel.")
        parser.add_argument('--prefix', type=str,
            help="Specify an install prefix for the kernelspec."
            " This is needed to install into a non-default location, such as a conda/virtual-env.")
        parser.add_argument('--sys-prefix', action='store_const', const=sys.prefix, dest='prefix',
            help="Install to Python's sys.prefix."
            " Shorthand for --prefix='%s'. For use in conda/virtual-envs." % sys.prefix)
        parser.add_argument('--env', action='append', nargs=2, metavar=('ENV', 'VALUE'),
            help="Set environment variables for the kernel.")
        opts = parser.parse_args(self.argv)
        if opts.env:
            opts.env = {k:v for (k, v) in opts.env}
        try:
            dest = install(user=opts.user, kernel_name=opts.name, profile=opts.profile,
                           prefix=opts.prefix, display_name=opts.display_name, env=opts.env)
        except OSError as e:
            if e.errno == errno.EACCES:
                print(e, file=sys.stderr)
                if opts.user:
                    print("Perhaps you want `sudo` or `--user`?", file=sys.stderr)
                self.exit(1)
            raise
        print("Installed kernelspec %s in %s" % (opts.name, dest))


if __name__ == '__main__':
    InstallIPythonKernelSpecApp.launch_instance()
