# -*- coding: utf-8 -*-
# leap_backend.py
# Copyright (C) 2013 LEAP
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.


"""
A U1DB backend for encrypting data before sending to server and decrypting
after receiving.
"""

import uuid
try:
    import simplejson as json
except ImportError:
    import json  # noqa


from u1db import Document
from u1db.remote import utils
from u1db.errors import BrokenSyncStream
from u1db.remote.http_target import HTTPSyncTarget


from leap.common.keymanager import KeyManager
from leap.common.check import leap_assert
from leap.soledad.auth import (
    set_token_credentials,
    _sign_request,
)


#
# Exceptions
#

class DocumentNotEncrypted(Exception):
    """
    Raised for failures in document encryption.
    """
    pass


class UnknownEncryptionSchemes(Exception):
    """
    Raised when trying to decrypt from unknown encryption schemes.
    """


#
# Encryption schemes used for encryption.
#

class EncryptionSchemes(object):
    """
    Representation of encryption schemes used to encrypt documents.
    """

    NONE = 'none'
    SYMKEY = 'symkey'
    PUBKEY = 'pubkey'


#
# Crypto utilities for a LeapDocument.
#

ENC_JSON_KEY = '_enc_json'
ENC_SCHEME_KEY = '_enc_scheme'
MAC_KEY = '_mac'


def encrypt_doc_json(crypto, doc_id, doc_json):
    """
    Return a valid JSON string containing the C{doc} content encrypted to
    a symmetric key and the encryption scheme.

    The returned JSON string is the serialization of the following dictionary:

        {
            ENC_JSON_KEY: encrypt_sym(doc_content),
            '_encryption_scheme: 'symkey',
        }

    @param crypto: A SoledadCryto instance to perform the encryption.
    @type crypto: leap.soledad.crypto.SoledadCrypto
    @param doc_id: The unique id of the document.
    @type doc_id: str
    @param doc_json: The JSON serialization of the document's contents.
    @type doc_json: str

    @return: The JSON serialization representing the encrypted content.
    @rtype: str
    """
    ciphertext = crypto.encrypt_sym(
        doc_json,
        crypto.passphrase_hash(doc_id))
    if not crypto.is_encrypted_sym(ciphertext):
        raise DocumentNotEncrypted('Failed encrypting document.')
    return json.dumps({
        ENC_JSON_KEY: ciphertext,
        ENC_SCHEME_KEY: EncryptionSchemes.SYMKEY,
    })


def decrypt_doc_json(crypto, doc_id, doc_json):
    """
    Return a JSON serialization of the decrypted content contained in
    C{encrypted_json}.

    The C{encrypted_json} parameter is the JSON serialization of the
    following dictionary:

        {
            ENC_JSON_KEY: enc_blob,
            ENC_SCHEME_KEY: enc_scheme,
        }

    C{enc_blob} is the encryption of the JSON serialization of the document's
    content. For now Soledad just deals with documents whose C{enc_scheme} is
    EncryptionSchemes.SYMKEY.

    @param crypto: A SoledadCryto instance to perform the encryption.
    @type crypto: leap.soledad.crypto.SoledadCrypto
    @param doc_id: The unique id of the document.
    @type doc_id: str
    @param doc_json: The JSON serialization representation of the encrypted
        document's contents.
    @type doc_json: str

    @return: The JSON serialization of the decrypted content.
    @rtype: str
    """
    leap_assert(isinstance(doc_id, str))
    leap_assert(doc_id != '')
    leap_assert(isinstance(doc_json, str))
    leap_assert(doc_json != '')
    content = json.loads(doc_json)
    ciphertext = content[ENC_JSON_KEY]
    enc_scheme = content[ENC_SCHEME_KEY]
    plainjson = None
    if enc_scheme == EncryptionSchemes.SYMKEY:
        if not crypto.is_encrypted_sym(ciphertext):
            raise DocumentNotEncrypted(
                'Unable to identify document encryption for incoming '
                'document, although it is marked as being encrypted with a '
                'symmetric key.')
        plainjson = crypto.decrypt_sym(
            ciphertext,
            crypto.passphrase_hash(doc_id))
    else:
        raise UnknownEncryptionScheme(enc_scheme)
    return plainjson


class LeapDocument(Document):
    """
    Encryptable and syncable document.

    LEAP Documents can be flagged as syncable or not, so the replicas
    might not sync every document.
    """

    def __init__(self, doc_id=None, rev=None, json='{}', has_conflicts=False,
                 syncable=True):
        """
        Container for handling an encryptable document.

        @param doc_id: The unique document identifier.
        @type doc_id: str
        @param rev: The revision identifier of the document.
        @type rev: str
        @param json: The JSON string for this document.
        @type json: str
        @param has_conflicts: Boolean indicating if this document has conflicts
        @type has_conflicts: bool
        @param syncable: Should this document be synced with remote replicas?
        @type syncable: bool
        """
        Document.__init__(self, doc_id, rev, json, has_conflicts)
        self._syncable = syncable

    def _get_syncable(self):
        """
        Return whether this document is syncable.

        @return: Is this document syncable?
        @rtype: bool
        """
        return self._syncable

    def _set_syncable(self, syncable=True):
        """
        Determine if this document should be synced with remote replicas.

        @param syncable: Should this document be synced with remote replicas?
        @type syncable: bool
        """
        self._syncable = syncable

    syncable = property(
        _get_syncable,
        _set_syncable,
        doc="Determine if document should be synced with server."
    )

    def _get_rev(self):
        """
        Get the document revision.

        Returning the revision as string solves the following exception in
        Twisted web:
            exceptions.TypeError: Can only pass-through bytes on Python 2

        @return: The document revision.
        @rtype: str
        """
        if self._rev is None:
            return None
        return str(self._rev)

    def _set_rev(self, rev):
        """
        Set document revision.

        @param rev: The new document revision.
        @type rev: bytes
        """
        self._rev = rev

    rev = property(
        _get_rev,
        _set_rev,
        doc="Wrapper to ensure `doc.rev` is always returned as bytes.")


#
# LeapSyncTarget
#

class LeapSyncTarget(HTTPSyncTarget):
    """
    A SyncTarget that encrypts data before sending and decrypts data after
    receiving.
    """

    #
    # Token auth methods.
    #

    set_token_credentials = set_token_credentials

    _sign_request = _sign_request

    #
    # Modified HTTPSyncTarget methods.
    #

    @staticmethod
    def connect(url, crypto=None):
        return LeapSyncTarget(url, crypto=crypto)

    def __init__(self, url, creds=None, crypto=None):
        """
        Initialize the LeapSyncTarget.

        @param url: The url of the target replica to sync with.
        @type url: str
        @param creds: optional dictionary giving credentials.
            to authorize the operation with the server.
        @type creds: dict
        @param soledad: An instance of Soledad so we can encrypt/decrypt
            document contents when syncing.
        @type soledad: soledad.Soledad
        """
        HTTPSyncTarget.__init__(self, url, creds)
        self._crypto = crypto

    def _parse_sync_stream(self, data, return_doc_cb, ensure_callback=None):
        """
        Does the same as parent's method but ensures incoming content will be
        decrypted.

        @param data: The body of the HTTP response.
        @type data: str
        @param return_doc_cb: A callback to insert docs from target.
        @type return_doc_cb: function
        @param ensure_callback: A callback to ensure we have the correct
            target_replica_uid, if it was just created.
        @type ensure_callback: function

        @return: The parsed sync stream.
        @rtype: list of str
        """
        parts = data.splitlines()  # one at a time
        if not parts or parts[0] != '[':
            raise BrokenSyncStream
        data = parts[1:-1]
        comma = False
        if data:
            line, comma = utils.check_and_strip_comma(data[0])
            res = json.loads(line)
            if ensure_callback and 'replica_uid' in res:
                ensure_callback(res['replica_uid'])
            for entry in data[1:]:
                if not comma:  # missing in between comma
                    raise BrokenSyncStream
                line, comma = utils.check_and_strip_comma(entry)
                entry = json.loads(line)
                #-------------------------------------------------------------
                # symmetric decryption of document's contents
                #-------------------------------------------------------------
                # if arriving content was symmetrically encrypted, we decrypt
                # it.
                doc = LeapDocument(entry['id'], entry['rev'], entry['content'])
                if doc.content and ENC_SCHEME_KEY in doc.content:
                    if doc.content[ENC_SCHEME_KEY] == \
                            EncryptionSchemes.SYMKEY:
                        doc.set_json(
                            decrypt_doc_json(
                                self._crypto, doc.doc_id, entry['content']))
                #-------------------------------------------------------------
                # end of symmetric decryption
                #-------------------------------------------------------------
                return_doc_cb(doc, entry['gen'], entry['trans_id'])
        if parts[-1] != ']':
            try:
                partdic = json.loads(parts[-1])
            except ValueError:
                pass
            else:
                if isinstance(partdic, dict):
                    self._error(partdic)
            raise BrokenSyncStream
        if not data or comma:  # no entries or bad extra comma
            raise BrokenSyncStream
        return res

    def sync_exchange(self, docs_by_generations, source_replica_uid,
                      last_known_generation, last_known_trans_id,
                      return_doc_cb, ensure_callback=None):
        """
        Does the same as parent's method but encrypts content before syncing.
        """
        self._ensure_connection()
        if self._trace_hook:  # for tests
            self._trace_hook('sync_exchange')
        url = '%s/sync-from/%s' % (self._url.path, source_replica_uid)
        self._conn.putrequest('POST', url)
        self._conn.putheader('content-type', 'application/x-u1db-sync-stream')
        for header_name, header_value in self._sign_request('POST', url, {}):
            self._conn.putheader(header_name, header_value)
        entries = ['[']
        size = 1

        def prepare(**dic):
            entry = comma + '\r\n' + json.dumps(dic)
            entries.append(entry)
            return len(entry)

        comma = ''
        size += prepare(
            last_known_generation=last_known_generation,
            last_known_trans_id=last_known_trans_id,
            ensure=ensure_callback is not None)
        comma = ','
        for doc, gen, trans_id in docs_by_generations:
            # skip non-syncable docs
            if isinstance(doc, LeapDocument) and not doc.syncable:
                continue
            #-------------------------------------------------------------
            # symmetric encryption of document's contents
            #-------------------------------------------------------------
            enc_json = doc.get_json()
            if not doc.is_tombstone():
                enc_json = encrypt_doc_json(
                    self._crypto, doc.doc_id, doc.get_json())
            #-------------------------------------------------------------
            # end of symmetric encryption
            #-------------------------------------------------------------
            size += prepare(id=doc.doc_id, rev=doc.rev,
                            content=enc_json,
                            gen=gen, trans_id=trans_id)
        entries.append('\r\n]')
        size += len(entries[-1])
        self._conn.putheader('content-length', str(size))
        self._conn.endheaders()
        for entry in entries:
            self._conn.send(entry)
        entries = None
        data, _ = self._response()
        res = self._parse_sync_stream(data, return_doc_cb, ensure_callback)
        data = None
        return res['new_generation'], res['new_transaction_id']