"""A contents manager that uses the local file system for storage."""

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

import base64
from contextlib import contextmanager
import errno
import io
import os
import shutil
import mimetypes

from tornado import web

from .manager import (
    CheckpointManager,
    ContentsManager,
)
from IPython import nbformat
from IPython.utils.io import atomic_writing
from IPython.utils.importstring import import_item
from IPython.utils.path import ensure_dir_exists
from IPython.utils.traitlets import Any, Unicode, Bool, TraitError
from IPython.utils.py3compat import getcwd, string_types, str_to_unicode
from IPython.utils import tz
from IPython.html.utils import (
    is_hidden,
    to_api_path,
    to_os_path,
)

_script_exporter = None

def _post_save_script(model, os_path, contents_manager, **kwargs):
    """convert notebooks to Python script after save with nbconvert

    replaces `ipython notebook --script`
    """
    from IPython.nbconvert.exporters.script import ScriptExporter

    if model['type'] != 'notebook':
        return

    global _script_exporter
    if _script_exporter is None:
        _script_exporter = ScriptExporter(parent=contents_manager)
    log = contents_manager.log

    base, ext = os.path.splitext(os_path)
    py_fname = base + '.py'
    script, resources = _script_exporter.from_filename(os_path)
    script_fname = base + resources.get('output_extension', '.txt')
    log.info("Saving script /%s", to_api_path(script_fname, contents_manager.root_dir))
    with io.open(script_fname, 'w', encoding='utf-8') as f:
        f.write(script)


class FileManagerMixin(object):
    """
    Mixin for ContentsAPI classes that interact with the filesystem.

    Provides facilities for reading, writing, and copying both notebooks and
    generic files.

    Shared by FileContentsManager and FileCheckpointManager.

    Note
    ----
    Classes using this mixin must provide the following attributes:

    root_dir : unicode
        A directory against against which API-style paths are to be resolved.

    log : logging.Logger
    """

    @contextmanager
    def open(self, os_path, *args, **kwargs):
        """wrapper around io.open that turns permission errors into 403"""
        with self.perm_to_403(os_path):
            with io.open(os_path, *args, **kwargs) as f:
                yield f

    @contextmanager
    def atomic_writing(self, os_path, *args, **kwargs):
        """wrapper around atomic_writing that turns permission errors into 403"""
        with self.perm_to_403(os_path):
            with atomic_writing(os_path, *args, **kwargs) as f:
                yield f

    @contextmanager
    def perm_to_403(self, os_path=''):
        """context manager for turning permission errors into 403."""
        try:
            yield
        except OSError as e:
            if e.errno in {errno.EPERM, errno.EACCES}:
                # make 403 error message without root prefix
                # this may not work perfectly on unicode paths on Python 2,
                # but nobody should be doing that anyway.
                if not os_path:
                    os_path = str_to_unicode(e.filename or 'unknown file')
                path = to_api_path(os_path, root=self.root_dir)
                raise web.HTTPError(403, u'Permission denied: %s' % path)
            else:
                raise

    def _copy(self, src, dest):
        """copy src to dest

        like shutil.copy2, but log errors in copystat
        """
        shutil.copyfile(src, dest)
        try:
            shutil.copystat(src, dest)
        except OSError:
            self.log.debug("copystat on %s failed", dest, exc_info=True)

    def _get_os_path(self, path):
        """Given an API path, return its file system path.

        Parameters
        ----------
        path : string
            The relative API path to the named file.

        Returns
        -------
        path : string
            Native, absolute OS path to for a file.
        """
        return to_os_path(path, self.root_dir)

    def _read_notebook(self, os_path, as_version=4):
        """Read a notebook from an os path."""
        with self.open(os_path, 'r', encoding='utf-8') as f:
            try:
                return nbformat.read(f, as_version=as_version)
            except Exception as e:
                raise web.HTTPError(
                    400,
                    u"Unreadable Notebook: %s %r" % (os_path, e),
                )

    def _save_notebook(self, os_path, nb):
        """Save a notebook to an os_path."""
        with self.atomic_writing(os_path, encoding='utf-8') as f:
            nbformat.write(nb, f, version=nbformat.NO_CONVERT)

    def _read_file(self, os_path, format):
        """Read a non-notebook file.

        os_path: The path to be read.
        format:
          If 'text', the contents will be decoded as UTF-8.
          If 'base64', the raw bytes contents will be encoded as base64.
          If not specified, try to decode as UTF-8, and fall back to base64
        """
        if not os.path.isfile(os_path):
            raise web.HTTPError(400, "Cannot read non-file %s" % os_path)

        with self.open(os_path, 'rb') as f:
            bcontent = f.read()

        if format is None or format == 'text':
            # Try to interpret as unicode if format is unknown or if unicode
            # was explicitly requested.
            try:
                return bcontent.decode('utf8'), 'text'
            except UnicodeError as e:
                if format == 'text':
                    raise web.HTTPError(
                        400,
                        "%s is not UTF-8 encoded" % os_path,
                        reason='bad format',
                    )
        return base64.encodestring(bcontent).decode('ascii'), 'base64'

    def _save_file(self, os_path, content, format):
        """Save content of a generic file."""
        if format not in {'text', 'base64'}:
            raise web.HTTPError(
                400,
                "Must specify format of file contents as 'text' or 'base64'",
            )
        try:
            if format == 'text':
                bcontent = content.encode('utf8')
            else:
                b64_bytes = content.encode('ascii')
                bcontent = base64.decodestring(b64_bytes)
        except Exception as e:
            raise web.HTTPError(400, u'Encoding error saving %s: %s' % (os_path, e))

        with self.atomic_writing(os_path, text=False) as f:
            f.write(bcontent)


class FileCheckpointManager(FileManagerMixin, CheckpointManager):
    """
    A CheckpointManager that caches checkpoints for files in adjacent
    directories.
    """

    checkpoint_dir = Unicode(
        '.ipynb_checkpoints',
        config=True,
        help="""The directory name in which to keep file checkpoints

        This is a path relative to the file's own directory.

        By default, it is .ipynb_checkpoints
        """,
    )

    root_dir = Unicode(config=True)

    def _root_dir_default(self):
        try:
            return self.parent.root_dir
        except AttributeError:
            return getcwd()

    # public checkpoint API
    def create_file_checkpoint(self, content, format, path):
        """Create a checkpoint from the current content of a notebook."""
        path = path.strip('/')
        # only the one checkpoint ID:
        checkpoint_id = u"checkpoint"
        os_checkpoint_path = self.checkpoint_path(checkpoint_id, path)
        self.log.debug("creating checkpoint for %s", path)
        with self.perm_to_403():
            self._save_file(os_checkpoint_path, content, format=format)

        # return the checkpoint info
        return self.checkpoint_model(checkpoint_id, os_checkpoint_path)

    def create_notebook_checkpoint(self, nb, path):
        """Create a checkpoint from the current content of a notebook."""
        path = path.strip('/')
        # only the one checkpoint ID:
        checkpoint_id = u"checkpoint"
        os_checkpoint_path = self.checkpoint_path(checkpoint_id, path)
        self.log.debug("creating checkpoint for %s", path)
        with self.perm_to_403():
            self._save_notebook(os_checkpoint_path, nb)

        # return the checkpoint info
        return self.checkpoint_model(checkpoint_id, os_checkpoint_path)

    def get_checkpoint(self, checkpoint_id, path, type):
        """Get the content of a checkpoint.

        Returns a model suitable for passing to ContentsManager.save.
        """
        path = path.strip('/')
        self.log.info("restoring %s from checkpoint %s", path, checkpoint_id)
        os_checkpoint_path = self.checkpoint_path(checkpoint_id, path)
        if not os.path.isfile(os_checkpoint_path):
            self.no_such_checkpoint(path, checkpoint_id)
        if type == 'notebook':
            return {
                'type': type,
                'content': self._read_notebook(
                    os_checkpoint_path,
                    as_version=4,
                ),
            }
        else:
            content, format = self._read_file(os_checkpoint_path, format=None)
            return {
                'type': type,
                'content': content,
                'format': format,
            }

    def rename_checkpoint(self, checkpoint_id, old_path, new_path):
        """Rename a checkpoint from old_path to new_path."""
        old_cp_path = self.checkpoint_path(checkpoint_id, old_path)
        new_cp_path = self.checkpoint_path(checkpoint_id, new_path)
        if os.path.isfile(old_cp_path):
            self.log.debug(
                "Renaming checkpoint %s -> %s",
                old_cp_path,
                new_cp_path,
            )
            with self.perm_to_403():
                shutil.move(old_cp_path, new_cp_path)

    def delete_checkpoint(self, checkpoint_id, path):
        """delete a file's checkpoint"""
        path = path.strip('/')
        cp_path = self.checkpoint_path(checkpoint_id, path)
        if not os.path.isfile(cp_path):
            self.no_such_checkpoint(path, checkpoint_id)

        self.log.debug("unlinking %s", cp_path)
        with self.perm_to_403():
            os.unlink(cp_path)

    def list_checkpoints(self, path):
        """list the checkpoints for a given file

        This contents manager currently only supports one checkpoint per file.
        """
        path = path.strip('/')
        checkpoint_id = "checkpoint"
        os_path = self.checkpoint_path(checkpoint_id, path)
        if not os.path.isfile(os_path):
            return []
        else:
            return [self.checkpoint_model(checkpoint_id, os_path)]

    # Checkpoint-related utilities
    def checkpoint_path(self, checkpoint_id, path):
        """find the path to a checkpoint"""
        path = path.strip('/')
        parent, name = ('/' + path).rsplit('/', 1)
        parent = parent.strip('/')
        basename, ext = os.path.splitext(name)
        filename = u"{name}-{checkpoint_id}{ext}".format(
            name=basename,
            checkpoint_id=checkpoint_id,
            ext=ext,
        )
        os_path = self._get_os_path(path=parent)
        cp_dir = os.path.join(os_path, self.checkpoint_dir)
        with self.perm_to_403():
            ensure_dir_exists(cp_dir)
        cp_path = os.path.join(cp_dir, filename)
        return cp_path

    def checkpoint_model(self, checkpoint_id, os_path):
        """construct the info dict for a given checkpoint"""
        stats = os.stat(os_path)
        last_modified = tz.utcfromtimestamp(stats.st_mtime)
        info = dict(
            id=checkpoint_id,
            last_modified=last_modified,
        )
        return info

    # Error Handling
    def no_such_checkpoint(self, path, checkpoint_id):
        raise web.HTTPError(
            404,
            u'Checkpoint does not exist: %s@%s' % (path, checkpoint_id)
        )


class FileContentsManager(FileManagerMixin, ContentsManager):

    root_dir = Unicode(config=True)

    def _root_dir_default(self):
        try:
            return self.parent.notebook_dir
        except AttributeError:
            return getcwd()

    save_script = Bool(False, config=True, help='DEPRECATED, use post_save_hook')
    def _save_script_changed(self):
        self.log.warn("""
        `--script` is deprecated. You can trigger nbconvert via pre- or post-save hooks:

            ContentsManager.pre_save_hook
            FileContentsManager.post_save_hook

        A post-save hook has been registered that calls:

            ipython nbconvert --to script [notebook]

        which behaves similarly to `--script`.
        """)

        self.post_save_hook = _post_save_script

    post_save_hook = Any(None, config=True,
        help="""Python callable or importstring thereof

        to be called on the path of a file just saved.

        This can be used to process the file on disk,
        such as converting the notebook to a script or HTML via nbconvert.

        It will be called as (all arguments passed by keyword):

            hook(os_path=os_path, model=model, contents_manager=instance)

        path: the filesystem path to the file just written
        model: the model representing the file
        contents_manager: this ContentsManager instance
        """
    )
    def _post_save_hook_changed(self, name, old, new):
        if new and isinstance(new, string_types):
            self.post_save_hook = import_item(self.post_save_hook)
        elif new:
            if not callable(new):
                raise TraitError("post_save_hook must be callable")

    def run_post_save_hook(self, model, os_path):
        """Run the post-save hook if defined, and log errors"""
        if self.post_save_hook:
            try:
                self.log.debug("Running post-save hook on %s", os_path)
                self.post_save_hook(os_path=os_path, model=model, contents_manager=self)
            except Exception:
                self.log.error("Post-save hook failed on %s", os_path, exc_info=True)

    def _root_dir_changed(self, name, old, new):
        """Do a bit of validation of the root_dir."""
        if not os.path.isabs(new):
            # If we receive a non-absolute path, make it absolute.
            self.root_dir = os.path.abspath(new)
            return
        if not os.path.isdir(new):
            raise TraitError("%r is not a directory" % new)

    def _checkpoint_manager_class_default(self):
        return FileCheckpointManager

    def is_hidden(self, path):
        """Does the API style path correspond to a hidden directory or file?

        Parameters
        ----------
        path : string
            The path to check. This is an API path (`/` separated,
            relative to root_dir).

        Returns
        -------
        hidden : bool
            Whether the path exists and is hidden.
        """
        path = path.strip('/')
        os_path = self._get_os_path(path=path)
        return is_hidden(os_path, self.root_dir)

    def file_exists(self, path):
        """Returns True if the file exists, else returns False.

        API-style wrapper for os.path.isfile

        Parameters
        ----------
        path : string
            The relative path to the file (with '/' as separator)

        Returns
        -------
        exists : bool
            Whether the file exists.
        """
        path = path.strip('/')
        os_path = self._get_os_path(path)
        return os.path.isfile(os_path)

    def dir_exists(self, path):
        """Does the API-style path refer to an extant directory?

        API-style wrapper for os.path.isdir

        Parameters
        ----------
        path : string
            The path to check. This is an API path (`/` separated,
            relative to root_dir).

        Returns
        -------
        exists : bool
            Whether the path is indeed a directory.
        """
        path = path.strip('/')
        os_path = self._get_os_path(path=path)
        return os.path.isdir(os_path)

    def exists(self, path):
        """Returns True if the path exists, else returns False.

        API-style wrapper for os.path.exists

        Parameters
        ----------
        path : string
            The API path to the file (with '/' as separator)

        Returns
        -------
        exists : bool
            Whether the target exists.
        """
        path = path.strip('/')
        os_path = self._get_os_path(path=path)
        return os.path.exists(os_path)

    def _base_model(self, path):
        """Build the common base of a contents model"""
        os_path = self._get_os_path(path)
        info = os.stat(os_path)
        last_modified = tz.utcfromtimestamp(info.st_mtime)
        created = tz.utcfromtimestamp(info.st_ctime)
        # Create the base model.
        model = {}
        model['name'] = path.rsplit('/', 1)[-1]
        model['path'] = path
        model['last_modified'] = last_modified
        model['created'] = created
        model['content'] = None
        model['format'] = None
        model['mimetype'] = None
        try:
            model['writable'] = os.access(os_path, os.W_OK)
        except OSError:
            self.log.error("Failed to check write permissions on %s", os_path)
            model['writable'] = False
        return model

    def _dir_model(self, path, content=True):
        """Build a model for a directory

        if content is requested, will include a listing of the directory
        """
        os_path = self._get_os_path(path)

        four_o_four = u'directory does not exist: %r' % path

        if not os.path.isdir(os_path):
            raise web.HTTPError(404, four_o_four)
        elif is_hidden(os_path, self.root_dir):
            self.log.info("Refusing to serve hidden directory %r, via 404 Error",
                os_path
            )
            raise web.HTTPError(404, four_o_four)

        model = self._base_model(path)
        model['type'] = 'directory'
        if content:
            model['content'] = contents = []
            os_dir = self._get_os_path(path)
            for name in os.listdir(os_dir):
                os_path = os.path.join(os_dir, name)
                # skip over broken symlinks in listing
                if not os.path.exists(os_path):
                    self.log.warn("%s doesn't exist", os_path)
                    continue
                elif not os.path.isfile(os_path) and not os.path.isdir(os_path):
                    self.log.debug("%s not a regular file", os_path)
                    continue
                if self.should_list(name) and not is_hidden(os_path, self.root_dir):
                    contents.append(self.get(
                        path='%s/%s' % (path, name),
                        content=False)
                    )

            model['format'] = 'json'

        return model

    def _file_model(self, path, content=True, format=None):
        """Build a model for a file

        if content is requested, include the file contents.

        format:
          If 'text', the contents will be decoded as UTF-8.
          If 'base64', the raw bytes contents will be encoded as base64.
          If not specified, try to decode as UTF-8, and fall back to base64
        """
        model = self._base_model(path)
        model['type'] = 'file'

        os_path = self._get_os_path(path)

        if content:
            content, format = self._read_file(os_path, format)
            default_mime = {
                'text': 'text/plain',
                'base64': 'application/octet-stream'
            }[format]

            model.update(
                content=content,
                format=format,
                mimetype=mimetypes.guess_type(os_path)[0] or default_mime,
            )

        return model

    def _notebook_model(self, path, content=True):
        """Build a notebook model

        if content is requested, the notebook content will be populated
        as a JSON structure (not double-serialized)
        """
        model = self._base_model(path)
        model['type'] = 'notebook'
        if content:
            os_path = self._get_os_path(path)
            nb = self._read_notebook(os_path, as_version=4)
            self.mark_trusted_cells(nb, path)
            model['content'] = nb
            model['format'] = 'json'
            self.validate_notebook_model(model)
        return model

    def get(self, path, content=True, type=None, format=None):
        """ Takes a path for an entity and returns its model

        Parameters
        ----------
        path : str
            the API path that describes the relative path for the target
        content : bool
            Whether to include the contents in the reply
        type : str, optional
            The requested type - 'file', 'notebook', or 'directory'.
            Will raise HTTPError 400 if the content doesn't match.
        format : str, optional
            The requested format for file contents. 'text' or 'base64'.
            Ignored if this returns a notebook or directory model.

        Returns
        -------
        model : dict
            the contents model. If content=True, returns the contents
            of the file or directory as well.
        """
        path = path.strip('/')

        if not self.exists(path):
            raise web.HTTPError(404, u'No such file or directory: %s' % path)

        os_path = self._get_os_path(path)
        if os.path.isdir(os_path):
            if type not in (None, 'directory'):
                raise web.HTTPError(400,
                                u'%s is a directory, not a %s' % (path, type), reason='bad type')
            model = self._dir_model(path, content=content)
        elif type == 'notebook' or (type is None and path.endswith('.ipynb')):
            model = self._notebook_model(path, content=content)
        else:
            if type == 'directory':
                raise web.HTTPError(400,
                                u'%s is not a directory', reason='bad type')
            model = self._file_model(path, content=content, format=format)
        return model

    def _save_directory(self, os_path, model, path=''):
        """create a directory"""
        if is_hidden(os_path, self.root_dir):
            raise web.HTTPError(400, u'Cannot create hidden directory %r' % os_path)
        if not os.path.exists(os_path):
            with self.perm_to_403():
                os.mkdir(os_path)
        elif not os.path.isdir(os_path):
            raise web.HTTPError(400, u'Not a directory: %s' % (os_path))
        else:
            self.log.debug("Directory %r already exists", os_path)

    def save(self, model, path=''):
        """Save the file model and return the model with no content."""
        path = path.strip('/')

        if 'type' not in model:
            raise web.HTTPError(400, u'No file type provided')
        if 'content' not in model and model['type'] != 'directory':
            raise web.HTTPError(400, u'No file content provided')

        self.run_pre_save_hook(model=model, path=path)

        os_path = self._get_os_path(path)
        self.log.debug("Saving %s", os_path)
        try:
            if model['type'] == 'notebook':
                nb = nbformat.from_dict(model['content'])
                self.check_and_sign(nb, path)
                self._save_notebook(os_path, nb)
                # One checkpoint should always exist for notebooks.
                if not self.checkpoint_manager.list_checkpoints(path):
                    self.checkpoint_manager.create_notebook_checkpoint(
                        nb,
                        path,
                    )
            elif model['type'] == 'file':
                # Missing format will be handled internally by _save_file.
                self._save_file(os_path, model['content'], model.get('format'))
            elif model['type'] == 'directory':
                self._save_directory(os_path, model, path)
            else:
                raise web.HTTPError(400, "Unhandled contents type: %s" % model['type'])
        except web.HTTPError:
            raise
        except Exception as e:
            self.log.error(u'Error while saving file: %s %s', path, e, exc_info=True)
            raise web.HTTPError(500, u'Unexpected error while saving file: %s %s' % (path, e))

        validation_message = None
        if model['type'] == 'notebook':
            self.validate_notebook_model(model)
            validation_message = model.get('message', None)

        model = self.get(path, content=False)
        if validation_message:
            model['message'] = validation_message

        self.run_post_save_hook(model=model, os_path=os_path)

        return model

    def delete_file(self, path):
        """Delete file at path."""
        path = path.strip('/')
        os_path = self._get_os_path(path)
        rm = os.unlink
        if os.path.isdir(os_path):
            listing = os.listdir(os_path)
            # Don't delete non-empty directories.
            # A directory containing only leftover checkpoints is
            # considered empty.
            cp_dir = getattr(self.checkpoint_manager, 'checkpoint_dir', None)
            for entry in listing:
                if entry != cp_dir:
                    raise web.HTTPError(400, u'Directory %s not empty' % os_path)
        elif not os.path.isfile(os_path):
            raise web.HTTPError(404, u'File does not exist: %s' % os_path)

        if os.path.isdir(os_path):
            self.log.debug("Removing directory %s", os_path)
            with self.perm_to_403():
                shutil.rmtree(os_path)
        else:
            self.log.debug("Unlinking file %s", os_path)
            with self.perm_to_403():
                rm(os_path)

    def rename_file(self, old_path, new_path):
        """Rename a file."""
        old_path = old_path.strip('/')
        new_path = new_path.strip('/')
        if new_path == old_path:
            return

        new_os_path = self._get_os_path(new_path)
        old_os_path = self._get_os_path(old_path)

        # Should we proceed with the move?
        if os.path.exists(new_os_path):
            raise web.HTTPError(409, u'File already exists: %s' % new_path)

        # Move the file
        try:
            with self.perm_to_403():
                shutil.move(old_os_path, new_os_path)
        except web.HTTPError:
            raise
        except Exception as e:
            raise web.HTTPError(500, u'Unknown error renaming file: %s %s' % (old_path, e))

    def info_string(self):
        return "Serving notebooks from local directory: %s" % self.root_dir

    def get_kernel_path(self, path, model=None):
        """Return the initial API path of  a kernel associated with a given notebook"""
        if '/' in path:
            parent_dir = path.rsplit('/', 1)[0]
        else:
            parent_dir = ''
        return parent_dir