# Copyright 2022 The Fuchsia Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

import("//build/compiled_action.gni")
import("//build/rust/rustc_library.gni")

# Generate a rust library based on the provided protobufs.
#
#   sources (required)
#     The paths to the .proto sources
#
#   packages (required)
#     The protobuf packages represented by the specified sources and
#     their dependencies
#
#   include_dirs (optional, default = [])
#     Directories in which to search for imported proto files.
#
#   deps (optional, default = [])
#     Additional rust crates for the generated library to depend on. It is not
#     necessary to include the prost runtime, it is included implicitly.
#
# Ex:
#    rust_proto_library("vm_guest_proto") {
#      sources = [
#        "vm_guest.proto",
#      ]
#      packages = [
#        "vm_tools", "google.protobuf",
#      ]
#      include_dirs = [
#        "//third_party/protobuf/src"
#      ]
#    }
#
#    rustc_binary("bin") {
#      edition = "2021"
#      output_name = "example"
#      deps = [
#        ":vm_guest_proto",
#      ]
#      sources = [
#        "src/main.rs",
#      ]
#    }

template("rust_proto_library") {
  assert(defined(invoker.sources), "Need protobuf sources for $target_name")
  proto_sources = rebase_path(invoker.sources, root_build_dir)
  assert(defined(invoker.packages),
         "The protobuf packages that are being generated should be specified.")
  proto_packages = invoker.packages

  if (!defined(invoker.include_dirs)) {
    proto_include_dirs = []
  } else {
    proto_include_dirs = rebase_path(invoker.include_dirs, root_build_dir)
  }

  crate_deps = [ "//third_party/rust_crates:prost" ]
  if (defined(invoker.deps)) {
    crate_deps += invoker.deps
  }

  target_crate_root = "${target_gen_dir}/${target_name}"

  # The rust code we expect to be generated by our compiled action
  expected_outputs = []
  foreach(package, proto_packages) {
    expected_outputs += [ "${target_crate_root}/${package}.rs" ]
  }

  rebased_out_dir = rebase_path(target_crate_root, root_build_dir)

  protoc_label = "//third_party/protobuf:protoc($host_toolchain)"
  protoc_path = get_label_info(protoc_label, "root_out_dir") + "/protoc"

  prost_build_label =
      "//tools/protobuf/rust_proto:prost_build_standalone($host_toolchain)"
  prost_build_path = get_label_info(prost_build_label, "root_out_dir") +
                     "/prost_build_standalone"

  include_args = []
  foreach(dir, proto_include_dirs) {
    include_args += [
      "--include-dirs",
      dir,
    ]
  }

  proto_args = []
  foreach(proto, proto_sources) {
    proto_args += [
      "--protos",
      proto,
    ]
  }

  _main_target_label = get_label_info(":$target_name", "label_with_toolchain")

  action("gen_${target_name}") {
    script = "//tools/protobuf/rust_proto/prost_build_wrapper.py"
    inputs = [
      prost_build_path,
      protoc_path,
    ]
    deps = [
      prost_build_label,
      protoc_label,
    ]
    sources = invoker.sources
    outputs = [ "${target_crate_root}/lib.rs" ] + expected_outputs
    depfile = "$target_gen_dir/$target_name.d"
    args =
        [
          "--protoc",
          rebase_path(protoc_path, root_build_dir),
          "--prost_build",
          rebase_path(prost_build_path, root_build_dir),
          "--out-dir",
          rebased_out_dir,
          "--gn-target",
          _main_target_label,
          "--depfile",
          rebase_path(depfile, root_build_dir),
          "--expected-outputs",
        ] + rebase_path(outputs, root_build_dir) + [ "--expected-packages" ] +
        proto_packages + include_args + proto_args
  }

  rustc_library(target_name) {
    edition = "2021"
    deps = [ ":gen_${target_name}" ] + crate_deps
    source_root = "${target_crate_root}/lib.rs"
    sources = get_target_outputs(":gen_${target_name}")
  }
}