# Copyright 2020 The Pigweed Authors
#
# 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
#
#     https://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.
"""This module generates the code for nanopb-based pw_rpc services."""

from datetime import datetime
import os
from typing import Iterable

from pw_protobuf.output_file import OutputFile
from pw_protobuf.proto_tree import ProtoNode, ProtoServiceMethod
from pw_protobuf.proto_tree import build_node_tree
import pw_rpc.ids

PLUGIN_NAME = 'pw_rpc_codegen'
PLUGIN_VERSION = '0.1.0'

PROTO_H_EXTENSION = '.pb.h'
PROTO_CC_EXTENSION = '.pb.cc'
NANOPB_H_EXTENSION = '.pb.h'

RPC_NAMESPACE = '::pw::rpc'


def _proto_filename_to_nanopb_header(proto_file: str) -> str:
    """Returns the generated nanopb header name for a .proto file."""
    return os.path.splitext(proto_file)[0] + NANOPB_H_EXTENSION


def _proto_filename_to_generated_header(proto_file: str) -> str:
    """Returns the generated C++ RPC header name for a .proto file."""
    filename = os.path.splitext(proto_file)[0]
    return f'{filename}_rpc{PROTO_H_EXTENSION}'


def _generate_method_descriptor(method: ProtoServiceMethod,
                                output: OutputFile) -> None:
    """Generates a nanopb method descriptor for an RPC method."""

    method_class = f'{RPC_NAMESPACE}::internal::Method'

    if method.type() == ProtoServiceMethod.Type.UNARY:
        func = f'{method_class}::Unary<{method.name()}>'
    elif method.type() == ProtoServiceMethod.Type.SERVER_STREAMING:
        func = f'{method_class}::ServerStreaming<{method.name()}>'
    else:
        raise NotImplementedError(
            'Only unary and server streaming RPCs are currently supported')

    method_id = pw_rpc.ids.calculate(method.name())
    req_fields = f'{method.request_type().nanopb_name()}_fields'
    res_fields = f'{method.response_type().nanopb_name()}_fields'

    output.write_line(f'{func}(')
    with output.indent(4):
        output.write_line(
            f'{hex(method_id)},  // 65599 hash of "{method.name()}"')
        output.write_line(f'{req_fields},')
        output.write_line(f'{res_fields}),')


def _generate_code_for_method(method: ProtoServiceMethod,
                              output: OutputFile) -> None:
    """Generates the function singature of a nanopb RPC method."""

    req_type = method.request_type().nanopb_name()
    res_type = method.response_type().nanopb_name()
    signature = f'static ::pw::Status {method.name()}'

    output.write_line()

    if method.type() == ProtoServiceMethod.Type.UNARY:
        output.write_line(f'{signature}(')
        with output.indent(4):
            output.write_line('ServerContext& ctx,')
            output.write_line(f'const {req_type}& request,')
            output.write_line(f'{res_type}& response);')
    elif method.type() == ProtoServiceMethod.Type.SERVER_STREAMING:
        output.write_line(f'{signature}(')
        with output.indent(4):
            output.write_line('ServerContext& ctx,')
            output.write_line(f'const {req_type}& request,')
            output.write_line(f'ServerWriter<{res_type}>& writer);')
    else:
        raise NotImplementedError(
            'Only unary and server streaming RPCs are currently supported')


def _generate_code_for_service(service: ProtoNode, root: ProtoNode,
                               output: OutputFile) -> None:
    """Generates a C++ derived class for a nanopb RPC service."""

    base_class = f'{RPC_NAMESPACE}::internal::Service'
    output.write_line(
        f'\nclass {service.cpp_namespace(root)} : public {base_class} {{')
    output.write_line(' public:')

    with output.indent():
        output.write_line(
            f'using ServerContext = {RPC_NAMESPACE}::ServerContext;')
        output.write_line('template <typename T> using ServerWriter = '
                          f'{RPC_NAMESPACE}::ServerWriter<T>;')
        output.write_line()

        output.write_line(f'constexpr {service.name()}()'
                          f' : {base_class}(kServiceId, kMethods) {{}}')

        output.write_line()
        output.write_line(
            f'{service.name()}(const {service.name()}&) = delete;')
        output.write_line(f'{service.name()}& operator='
                          f'(const {service.name()}&) = delete;')

        for method in service.methods():
            _generate_code_for_method(method, output)

    service_name_hash = pw_rpc.ids.calculate(service.name())
    output.write_line('\n private:')

    with output.indent():
        output.write_line(f'// 65599 hash of "{service.name()}".')
        output.write_line(
            f'static constexpr uint32_t kServiceId = {hex(service_name_hash)};'
        )
        output.write_line(
            f'static constexpr char* kServiceName = "{service.name()}";')
        output.write_line()

        output.write_line(
            f'static constexpr std::array<{RPC_NAMESPACE}::internal::Method,'
            f' {len(service.methods())}> kMethods = {{')

        with output.indent(4):
            for method in service.methods():
                _generate_method_descriptor(method, output)

        output.write_line('};')

    output.write_line('};')


def generate_code_for_package(file_descriptor_proto, package: ProtoNode,
                              output: OutputFile) -> None:
    """Generates code for a header file corresponding to a .proto file."""

    assert package.type() == ProtoNode.Type.PACKAGE

    output.write_line(f'// {os.path.basename(output.name())} automatically '
                      f'generated by {PLUGIN_NAME} {PLUGIN_VERSION}')
    output.write_line(f'// on {datetime.now()}')
    output.write_line('// clang-format off')
    output.write_line('#pragma once\n')
    output.write_line('#include <cstddef>')
    output.write_line('#include <cstdint>\n')
    output.write_line('#include "pw_rpc/internal/service.h"')

    # Include the corresponding nanopb header file for this proto file, in which
    # the file's messages and enums are generated.
    nanopb_header = _proto_filename_to_nanopb_header(
        file_descriptor_proto.name)
    output.write_line(f'#include "{nanopb_header}"\n')

    for imported_file in file_descriptor_proto.dependency:
        generated_header = _proto_filename_to_nanopb_header(imported_file)
        output.write_line(f'#include "{generated_header}"')

    if package.cpp_namespace():
        file_namespace = package.cpp_namespace()
        if file_namespace.startswith('::'):
            file_namespace = file_namespace[2:]

        output.write_line(f'\nnamespace {file_namespace} {{')

    for node in package:
        if node.type() == ProtoNode.Type.SERVICE:
            _generate_code_for_service(node, package, output)

    if package.cpp_namespace():
        output.write_line(f'\n}}  // namespace {file_namespace}')


def process_proto_file(proto_file) -> Iterable[OutputFile]:
    """Generates code for a single .proto file."""

    _, package_root = build_node_tree(proto_file)
    output_filename = _proto_filename_to_generated_header(proto_file.name)
    output_file = OutputFile(output_filename)
    generate_code_for_package(proto_file, package_root, output_file)

    return [output_file]