import io
import json
import os
import sys

pjoin = os.path.join

from IPython.utils.path import get_ipython_dir
from IPython.utils.py3compat import PY3
from IPython.utils.traitlets import HasTraits, List, Unicode

USER_KERNEL_DIR = pjoin(get_ipython_dir(), 'kernels')

if os.name == 'nt':
    programdata = os.environ.get('PROGRAMDATA', None)
    if programdata:
        SYSTEM_KERNEL_DIR = pjoin(programdata, 'ipython', 'kernels')
    else:  # PROGRAMDATA is not defined by default on XP.
        SYSTEM_KERNEL_DIR = None
else:
    SYSTEM_KERNEL_DIR = "/usr/share/ipython/kernels"
    
NATIVE_KERNEL_NAME = 'python3' if PY3 else 'python2'

class KernelSpec(HasTraits):
    argv = List()
    display_name = Unicode()
    language = Unicode()
    codemirror_mode = Unicode()
    
    resource_dir = Unicode()
    
    def __init__(self, resource_dir, argv, display_name, language,
                 codemirror_mode=None):
        super(KernelSpec, self).__init__(resource_dir=resource_dir, argv=argv,
                display_name=display_name, language=language,
                codemirror_mode=codemirror_mode)
        if not self.codemirror_mode:
            self.codemirror_mode = self.language
    
    @classmethod
    def from_resource_dir(cls, resource_dir):
        """Create a KernelSpec object by reading kernel.json
        
        Pass the path to the *directory* containing kernel.json.
        """
        kernel_file = pjoin(resource_dir, 'kernel.json')
        with io.open(kernel_file, 'r', encoding='utf-8') as f:
            kernel_dict = json.load(f)
        return cls(resource_dir=resource_dir, **kernel_dict)

def _is_kernel_dir(path):
    """Is ``path`` a kernel directory?"""
    return os.path.isdir(path) and os.path.isfile(pjoin(path, 'kernel.json'))

def _list_kernels_in(dir):
    """Ensure dir exists, and return a mapping of kernel names to resource
    directories from it.
    """
    if dir is None:
        return {}
    if not os.path.isdir(dir):
        os.makedirs(dir, mode=0o644)
    return {f.lower(): pjoin(dir, f) for f in os.listdir(dir)
                        if _is_kernel_dir(pjoin(dir, f))}

def _make_native_kernel_dir():
    """Makes a kernel directory for the native kernel.
    
    The native kernel is the kernel using the same Python runtime as this
    process. This will put its informatino in the user kernels directory.
    """
    path = pjoin(USER_KERNEL_DIR, NATIVE_KERNEL_NAME)
    os.mkdir(path)
    with io.open(pjoin(path, 'kernel.json'), 'w', encoding='utf-8') as f:
        json.dump({'argv':[NATIVE_KERNEL_NAME, '-c',
                           'from IPython.kernel.zmq.kernelapp import main; main()',
                            '-f', '{connection_file}'],
                   'display_name': 'Python 3' if PY3 else 'Python 2',
                   'language': 'python',
                   'codemirror_mode': {'name': 'python',
                                       'version': sys.version_info[0]},
                  },
                  f)
    # TODO: Copy icons into directory
    return path

def list_kernel_specs():
    """Returns a dict mapping kernel names to resource directories."""
    d = _list_kernels_in(SYSTEM_KERNEL_DIR)
    d.update(_list_kernels_in(USER_KERNEL_DIR))
    
    if NATIVE_KERNEL_NAME not in d:
        d[NATIVE_KERNEL_NAME] = _make_native_kernel_dir()
    return d
    # TODO: Caching?

def get_kernel_spec(kernel_name):
    """Returns a :class:`KernelSpec` instance for the given kernel_name.
    
    Raises KeyError if the given kernel name is not found.
    """
    if kernel_name == 'native':
        kernel_name = NATIVE_KERNEL_NAME
    d = list_kernel_specs()
    resource_dir = d[kernel_name.lower()]
    return KernelSpec.from_resource_dir(resource_dir)