#==============================================================================
# Copyright 2011 Amazon.com, Inc. or its affiliates. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#==============================================================================
from cfnbootstrap import security, util
from cfnbootstrap.construction_errors import ToolError
from contextlib import contextmanager
import base64
import logging
import os
import requests
import stat

_templates_supported = True
try:
    from pystache.renderer import Renderer
except ImportError:
    _templates_supported = False

try:
    import simplejson as json
except ImportError:
    import json

log = logging.getLogger("cfn.init")


class FileTool(object):
    """
    Writes files to disk

    """

    _compare_buffer = 8 * 1024

    @classmethod
    def is_same_file(cls, f1, f2):
        if hasattr(os.path, "samefile"):
            return os.path.samefile(f1, f2)
        else:
            #Crude workaround for os.path.samefile only existing on Unix
            return os.path.normcase(os.path.abspath(f1)) == os.path.normcase(os.path.abspath(f2))

    @classmethod
    def compare_file_contents(cls, f1, f2):
        """
        Return true if f1 and f2 have the same content.
        """
        if os.path.getsize(f1) != os.path.getsize(f2):
            return False

        if cls.is_same_file(f1, f2):
            return True

        # Borrowed from filecmp
        with file(f1, 'rb') as fp1:
            with file(f2, 'rb') as fp2:
                bufsize = 8 * 1024
                while True:
                    b1 = fp1.read(bufsize)
                    b2 = fp2.read(bufsize)
                    if b1 != b2:
                        return False
                    if not b1:
                        return True

    def apply(self, action, auth_config):
        """
        Write a set of files to disk, returning a list of the files that have changed.

        Arguments:
        action -- a dict of pathname to attributes, such as owner, group, mode, content, and encoding
        auth_config -- an AuthenticationConfig object for managing authenticated downloads

        Exceptions:
        ToolError -- on expected failures
        """

        files_changed = []

        if not action.keys():
            log.debug("No files specified")
            return files_changed

        for (filename, attribs) in sorted(action.iteritems(), key=lambda pair: pair[0]):
            if not os.path.isabs(filename):
                raise ToolError('File specified with non-absolute path: %s' % filename)


            # The only difference between a file and a symlink is hidden in the mode
            file_is_link = "mode" in attribs and stat.S_ISLNK(int(attribs["mode"], 8))

            if file_is_link:
                if "content" not in attribs:
                    raise ToolError("Symbolic link specified without a destination")
                elif os.path.exists(filename) and FileTool.is_same_file(os.path.realpath(filename), attribs["content"]):
                    log.info("Symbolic link %s already exists", filename)
                    continue

            parent = os.path.dirname(filename)
            if not os.path.isdir(parent):
                if not os.path.exists(parent):
                    log.debug("Parent directory %s does not exist, creating", parent)
                    os.makedirs(parent)
                else:
                    raise ToolError("Parent directory %s exists and is a file" % parent)

            with self.backup(filename, files_changed):
                if file_is_link:
                    log.debug("%s is specified as a symbolic link to %s", filename, attribs['content'])
                    os.symlink(attribs["content"], filename)
                else:
                    file_is_text = 'content' in attribs and not self._is_base64(attribs)
                    with file(filename, 'w' + ('' if file_is_text else 'b')) as f:
                        log.debug("Writing content to %s", filename)
                        self._write_file(f, attribs, auth_config)

                if "mode" in attribs:
                    log.debug("Setting mode for %s to %s", filename, attribs["mode"])
                    os.chmod(filename, stat.S_IMODE(int(attribs["mode"], 8)))
                else:
                    log.debug("No mode specified for %s", filename)

                security.set_owner_and_group(filename, attribs.get("owner"), attribs.get("group"))

        return files_changed

    @contextmanager
    def backup(self, filename, files_changed):
        backup_file = None
        backup_backup_file = None
        if os.path.exists(filename):
            log.debug("%s already exists", filename)
            backup_file = filename + '.bak'
            if os.path.exists(backup_file):
                backup_backup_file = backup_file + "2"
                if os.path.exists(backup_backup_file):
                    os.remove(backup_backup_file)
                self._backup_file(backup_file, backup_backup_file)
            self._backup_file(filename, backup_file)

        try:
            yield backup_file
        except Exception:
            if backup_file:
                try:
                    if os.path.exists(filename):
                        os.remove(filename)
                    self._backup_file(backup_file, filename)
                    if backup_backup_file:
                        self._backup_file(backup_backup_file, backup_file)
                except ToolError, t:
                    log.warn("Error restoring %s from backup", filename)
            raise
        else:
            linkmode = backup_file and os.path.islink(backup_file) or os.path.islink(filename)
            # we assume any symbolic links changed because we short-circuit links to the same files early on
            if not backup_file or linkmode or not FileTool.compare_file_contents(backup_file, filename):
                files_changed.append(filename)
                if backup_backup_file:
                    os.remove(backup_backup_file)
            elif backup_file and backup_backup_file:
                try:
                    self._backup_file(backup_backup_file, backup_file)
                except ToolError, t:
                    log.warn("Error restoring backup file %s: %s", backup_file, str(t))

    def _backup_file(self, source, dest):
        try:
            log.debug("Moving %s to %s", source, dest)
            os.rename(source, dest)
        except OSError, e:
            log.error("Could not move %s to %s", source, dest)
            raise ToolError("Could not rename %s: %s" % (source, str(e)))

    def _is_base64(self, attribs):
        return attribs.get("encoding", "plain") == "base64"

    def _write_file(self, dest_fileobj, attribs, auth_config):
        content = attribs.get("content", "")
        if content:
            self._write_inline_content(dest_fileobj, content, self._is_base64(attribs),
                                       attribs.get('context'))
        else:
            source = attribs.get("source", "")
            if not source:
                raise ToolError("File specified without source or content")
            log.debug("Retrieving contents from %s", source)

            try:
                self._write_remote_file(source, auth_config.get_auth(attribs.get('authentication', None)), dest_fileobj,
                                      attribs.get('context'))
            except IOError, e:
                raise ToolError("Failed to retrieve %s: %s" % (source, e.strerror))

    def _render_template(self, content, context):
        if not _templates_supported:
            raise ToolError("Pystache must be installed in order to render files as Mustache templates")

        log.debug('Rendering as Mustache template')
        try:
            return Renderer(string_encoding='utf-8', file_encoding='utf-8').render(content, context)
        except Exception, e:
            raise ToolError("Failed to render content as a Mustache template: %s" % e.message)

    @util.retry_on_failure()
    def _write_remote_file(self, source, auth, dest, context):
        opts = util.req_opts({'auth': auth})
        remote_contents = util.EtagCheckedResponse(requests.get(source, **opts))

        if context is None:
            remote_contents.write_to(dest)
        else:
            dest.write(self._render_template(remote_contents.contents(), context))

    def _write_inline_content(self, dest, content, is_base64, context):
        if not isinstance(content, basestring):
            log.debug('Content will be serialized as a JSON structure')
            json.dump(content, dest)
            return

        if is_base64:
            try:
                log.debug("Decoding base64 content")
                dest.write(base64.b64decode(content.strip()))
            except TypeError:
                raise ToolError("Malformed base64: %s" % content)
        elif context is None:
            dest.write(content)
        else:
            dest.write(self._render_template(content, context))
