#
#  Copyright (C) 2018 Codethink Limited
#
#  This program is free software; you can redistribute it and/or
#  modify it under the terms of the GNU Lesser General Public
#  License as published by the Free Software Foundation; either
#  version 2 of the License, or (at your option) any later version.
#
#  This library 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
#  Lesser General Public License for more details.
#
#  You should have received a copy of the GNU Lesser General Public
#  License along with this library. If not, see <http://www.gnu.org/licenses/>.
#
#  Authors:
#        Jürg Billeter <juerg.billeter@codethink.co.uk>

from concurrent import futures
import logging
import os
import signal
import sys
import tempfile

import click
import grpc

from .._protos.build.bazel.remote.execution.v2 import remote_execution_pb2, remote_execution_pb2_grpc
from .._protos.google.bytestream import bytestream_pb2, bytestream_pb2_grpc
from .._protos.buildstream.v2 import buildstream_pb2, buildstream_pb2_grpc

from .._exceptions import ArtifactError
from .._context import Context

from .cascache import CASCache


# Trying to push an artifact that is too large
class ArtifactTooLargeException(Exception):
    pass


# create_server():
#
# Create gRPC CAS artifact server as specified in the Remote Execution API.
#
# Args:
#     repo (str): Path to CAS repository
#     enable_push (bool): Whether to allow blob uploads and artifact updates
#
def create_server(repo, *, enable_push):
    context = Context()
    context.artifactdir = os.path.abspath(repo)

    artifactcache = CASCache(context)

    # Use max_workers default from Python 3.5+
    max_workers = (os.cpu_count() or 1) * 5
    server = grpc.server(futures.ThreadPoolExecutor(max_workers))

    bytestream_pb2_grpc.add_ByteStreamServicer_to_server(
        _ByteStreamServicer(artifactcache, enable_push=enable_push), server)

    remote_execution_pb2_grpc.add_ContentAddressableStorageServicer_to_server(
        _ContentAddressableStorageServicer(artifactcache), server)

    buildstream_pb2_grpc.add_ReferenceStorageServicer_to_server(
        _ReferenceStorageServicer(artifactcache, enable_push=enable_push), server)

    return server


@click.command(short_help="CAS Artifact Server")
@click.option('--port', '-p', type=click.INT, required=True, help="Port number")
@click.option('--server-key', help="Private server key for TLS (PEM-encoded)")
@click.option('--server-cert', help="Public server certificate for TLS (PEM-encoded)")
@click.option('--client-certs', help="Public client certificates for TLS (PEM-encoded)")
@click.option('--enable-push', default=False, is_flag=True,
              help="Allow clients to upload blobs and update artifact cache")
@click.argument('repo')
def server_main(repo, port, server_key, server_cert, client_certs, enable_push):
    server = create_server(repo, enable_push=enable_push)

    use_tls = bool(server_key)

    if bool(server_cert) != use_tls:
        click.echo("ERROR: --server-key and --server-cert are both required for TLS", err=True)
        sys.exit(-1)

    if client_certs and not use_tls:
        click.echo("ERROR: --client-certs can only be used with --server-key", err=True)
        sys.exit(-1)

    if use_tls:
        # Read public/private key pair
        with open(server_key, 'rb') as f:
            server_key_bytes = f.read()
        with open(server_cert, 'rb') as f:
            server_cert_bytes = f.read()

        if client_certs:
            with open(client_certs, 'rb') as f:
                client_certs_bytes = f.read()
        else:
            client_certs_bytes = None

        credentials = grpc.ssl_server_credentials([(server_key_bytes, server_cert_bytes)],
                                                  root_certificates=client_certs_bytes,
                                                  require_client_auth=bool(client_certs))
        server.add_secure_port('[::]:{}'.format(port), credentials)
    else:
        server.add_insecure_port('[::]:{}'.format(port))

    # Run artifact server
    server.start()
    try:
        while True:
            signal.pause()
    except KeyboardInterrupt:
        server.stop(0)


class _ByteStreamServicer(bytestream_pb2_grpc.ByteStreamServicer):
    def __init__(self, cas, *, enable_push):
        super().__init__()
        self.cas = cas
        self.enable_push = enable_push

    def Read(self, request, context):
        resource_name = request.resource_name
        client_digest = _digest_from_resource_name(resource_name)
        assert request.read_offset <= client_digest.size_bytes

        try:
            with open(self.cas.objpath(client_digest), 'rb') as f:
                assert os.fstat(f.fileno()).st_size == client_digest.size_bytes
                if request.read_offset > 0:
                    f.seek(request.read_offset)

                remaining = client_digest.size_bytes - request.read_offset
                while remaining > 0:
                    chunk_size = min(remaining, 64 * 1024)
                    remaining -= chunk_size

                    response = bytestream_pb2.ReadResponse()
                    # max. 64 kB chunks
                    response.data = f.read(chunk_size)
                    yield response
        except FileNotFoundError:
            context.set_code(grpc.StatusCode.NOT_FOUND)

    def Write(self, request_iterator, context):
        response = bytestream_pb2.WriteResponse()

        if not self.enable_push:
            context.set_code(grpc.StatusCode.PERMISSION_DENIED)
            return response

        offset = 0
        finished = False
        resource_name = None
        with tempfile.NamedTemporaryFile(dir=os.path.join(self.cas.casdir, 'tmp')) as out:
            for request in request_iterator:
                assert not finished
                assert request.write_offset == offset
                if resource_name is None:
                    # First request
                    resource_name = request.resource_name
                    client_digest = _digest_from_resource_name(resource_name)
                    try:
                        _clean_up_cache(self.cas, client_digest.size_bytes)
                    except ArtifactTooLargeException as e:
                        context.set_code(grpc.StatusCode.RESOURCE_EXHAUSTED)
                        context.set_details(str(e))
                        return response
                elif request.resource_name:
                    # If it is set on subsequent calls, it **must** match the value of the first request.
                    assert request.resource_name == resource_name
                out.write(request.data)
                offset += len(request.data)
                if request.finish_write:
                    assert client_digest.size_bytes == offset
                    out.flush()
                    digest = self.cas.add_object(path=out.name)
                    assert digest.hash == client_digest.hash
                    finished = True

        assert finished

        response.committed_size = offset
        return response


class _ContentAddressableStorageServicer(remote_execution_pb2_grpc.ContentAddressableStorageServicer):
    def __init__(self, cas):
        super().__init__()
        self.cas = cas

    def FindMissingBlobs(self, request, context):
        response = remote_execution_pb2.FindMissingBlobsResponse()
        for digest in request.blob_digests:
            if not _has_object(self.cas, digest):
                d = response.missing_blob_digests.add()
                d.hash = digest.hash
                d.size_bytes = digest.size_bytes
        return response


class _ReferenceStorageServicer(buildstream_pb2_grpc.ReferenceStorageServicer):
    def __init__(self, cas, *, enable_push):
        super().__init__()
        self.cas = cas
        self.enable_push = enable_push

    def GetReference(self, request, context):
        response = buildstream_pb2.GetReferenceResponse()

        try:
            tree = self.cas.resolve_ref(request.key, update_mtime=True)

            response.digest.hash = tree.hash
            response.digest.size_bytes = tree.size_bytes
        except ArtifactError:
            context.set_code(grpc.StatusCode.NOT_FOUND)

        return response

    def UpdateReference(self, request, context):
        response = buildstream_pb2.UpdateReferenceResponse()

        if not self.enable_push:
            context.set_code(grpc.StatusCode.PERMISSION_DENIED)
            return response

        for key in request.keys:
            self.cas.set_ref(key, request.digest)

        return response

    def Status(self, request, context):
        response = buildstream_pb2.StatusResponse()

        response.allow_updates = self.enable_push

        return response


def _digest_from_resource_name(resource_name):
    parts = resource_name.split('/')
    assert len(parts) == 2
    digest = remote_execution_pb2.Digest()
    digest.hash = parts[0]
    digest.size_bytes = int(parts[1])
    return digest


def _has_object(cas, digest):
    objpath = cas.objpath(digest)
    return os.path.exists(objpath)


# _clean_up_cache()
#
# Keep removing Least Recently Pushed (LRP) artifacts in a cache until there
# is enough space for the incoming artifact
#
# Args:
#   cas: CASCache object
#   object_size: The size of the object being received in bytes
#
# Returns:
#   int: The total bytes removed on the filesystem
#
def _clean_up_cache(cas, object_size):
    # Determine the available disk space, in bytes, of the file system
    # which mounts the repo
    stats = os.statvfs(cas.casdir)
    buffer_ = int(2e9)                # Add a 2 GB buffer
    free_disk_space = (stats.f_bfree * stats.f_bsize) - buffer_
    total_disk_space = (stats.f_blocks * stats.f_bsize) - buffer_

    if object_size > total_disk_space:
        raise ArtifactTooLargeException("Artifact of size: {} is too large for "
                                        "the filesystem which mounts the remote "
                                        "cache".format(object_size))

    if object_size <= free_disk_space:
        # No need to clean up
        return 0

    # obtain a list of LRP artifacts
    LRP_artifacts = cas.list_artifacts()

    removed_size = 0  # in bytes
    while object_size - removed_size > free_disk_space:
        try:
            to_remove = LRP_artifacts.pop(0)  # The first element in the list is the LRP artifact
        except IndexError:
            # This exception is caught if there are no more artifacts in the list
            # LRP_artifacts. This means the the artifact is too large for the filesystem
            # so we abort the process
            raise ArtifactTooLargeException("Artifact of size {} is too large for "
                                            "the filesystem which mounts the remote "
                                            "cache".format(object_size))

        removed_size += cas.remove(to_remove, defer_prune=False)

    if removed_size > 0:
        logging.info("Successfully removed {} bytes from the cache".format(removed_size))
    else:
        logging.info("No artifacts were removed from the cache.")

    return removed_size