# Copyright 2019 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 file provides GN build integration for Go. These templates are limited,
# supporting only legacy GOPATH-based builds.

import("exec.gni")
import("input_group.gni")

# Defines a Go package.
#
# A Go package consists of one or more Go files in a single directory. The
# package can depend on other Go packages or generated Go code.
#
# Args:
#   sources: List of Go source files.
#   deps: Optional list of target dependencies.
#   external_deps: Optional list of Go package dependencies outside of Pigweed.
#   gopath: Root of the GOPATH in which the package is located.
#
# Example:
#
#   # In //my_module/go/src/example.com/foo/BUILD.gn
#   pw_go_package("foo_package") {
#     sources = [ "main.go" ]
#     deps = [
#       "//my_module:foo_proto_go"
#     ]
#     external_deps = [
#       "github.com/golang/glog"
#     ]
#     gopath = "//my_module/go"
#   }
#
template("pw_go_package") {
  assert(defined(invoker.sources), "pw_go_source_set requires sources")
  assert(defined(invoker.gopath), "pw_go_source_set requires a GOPATH root")

  _gopath = rebase_path(invoker.gopath)

  # List the sources in an input group with GOPATH environment metadata.
  pw_input_group(target_name) {
    inputs = invoker.sources
    forward_variables_from(invoker,
                           [
                             "deps",
                             "metadata",
                           ])
    if (!defined(metadata)) {
      metadata = {
      }
    }
    metadata.gopath = [ "GOPATH+=${_gopath}" ]

    if (defined(invoker.external_deps)) {
      metadata.external_deps = invoker.external_deps
    }
  }
}

# Builds a Go executable from a Go package.
#
# The package must include only a main.go file labelled "package main". It may
# depend on other Go packages defined in the build.
#
# Args:
#   deps: List of size one specifying the GN path to the Go package target.
#   package: Name of the Go package as resolved by the Go compiler.
#
# Example:
#
#   # In //my_module/go
#   pw_go_executable("foo") {
#     deps = [ "//my_module/go/src/example.com/foo:foo_package" ]
#     package = "example.com/foo"
#   }
#
template("pw_go_executable") {
  assert(defined(invoker.deps),
         "pw_go_executable requires at least one Go package as a dependency")
  assert(defined(invoker.package),
         "pw_go_executable requires the name of the package to build")

  _metadata_target_name = "${target_name}_pw_go_metadata"
  _metadata_file = "$target_gen_dir/${target_name}_pw_go_env.env"

  # Collect all the GOPATH metadata from pw_go_package and _pw_go_proto_library
  # targets into a plaintext file of environment variable definitions.
  generated_file(_metadata_target_name) {
    deps = invoker.deps
    data_keys = [ "gopath" ]
    outputs = [
      _metadata_file,
    ]
  }

  # Collect all of the external dependencies of the executable and its packages.
  _deps_metadata_target_name = "${target_name}_pw_go_deps"
  _deps_metadata_file = "$target_gen_dir/${target_name}_pw_go_deps.txt"
  generated_file(_deps_metadata_target_name) {
    deps = invoker.deps
    data_keys = [ "external_deps" ]
    outputs = [
      _deps_metadata_file,
    ]
  }

  _default_gopath = rebase_path("$root_gen_dir/go")

  # Create a target to download all external dependencies into the default
  # GOPATH in the out directory. This is only run once; "go get" does not
  # re-download existing packages.
  _download_target_name = "${target_name}_pw_go_get"
  pw_exec(_download_target_name) {
    program = "go"
    args = [ "get" ]
    deps = [ ":$_deps_metadata_target_name" ] + invoker.deps
    env = [ "GOPATH=$_default_gopath" ]
    args_file = _deps_metadata_file

    # If the args file is empty, don't run the "go get" command.
    skip_empty_args = true

    # Limit download parallelization to 1.
    pool = "$dir_pw_build:go_download_pool"
  }

  # Run a "go build" command with the environment configured from metadata.
  pw_exec(target_name) {
    program = "go"
    args = [
      "build",
      "-o",
      target_out_dir,
      invoker.package,
    ]
    deps = [
      ":$_download_target_name",
      ":$_metadata_target_name",
    ]
    env = [ "GOPATH+=$_default_gopath" ]
    env_file = _metadata_file
  }
}