# Copyright 2020 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.

#  List of libraries that are cleared for use with this template.

allowed_libraries = [
  "fuchsia.debugdata",
  "fuchsia.io",
  "fuchsia.io2",
  "fuchsia.mem",
  "zx",
]

# This template provides the minimum build support for generating C headers out
# of FIDL libraries.
#
# Parameters
#
#  sources
#    Required: List of `.fidl` source files.
#
#  deps
#    Optional: Other `fidl_c_header` targets this target depends on.

template("fidl_c_header") {
  assert(defined(invoker.sources), "Sources are mandatory")

  # Parameters used in every toolchain.
  fidlc_target = "$target_name.fidlc"
  fidl_name = string_replace(target_name, "-", ".")
  fidl_path = string_replace(fidl_name, ".", "/")
  default_gen_dir =
      get_label_info("//:bogus($default_toolchain)", "target_gen_dir")
  include_dir = "$default_gen_dir/$target_name.fidl/include"
  header_file = "$include_dir/$fidl_path/c/fidl.h"

  # Check that this is one of the authorized libraries.
  if (allowed_libraries + [ fidl_name ] - [ fidl_name ] == allowed_libraries) {
    assert(false,
           "fidl_c_header may only be used with the following " +
               "libraries: $allowed_libraries.")
  }

  # Pre-process the dependencies so that they all look like:
  #   //foo/bar:blah
  fidl_deps = []
  if (defined(invoker.deps)) {
    foreach(dep, invoker.deps) {
      assert(get_label_info(dep, "toolchain") == current_toolchain,
             "fidl_c_header() `deps` must be in the same toolchain")
      label = get_label_info(dep, "label_no_toolchain")
      fidl_deps += [ label ]
    }
  }

  if (current_toolchain == default_toolchain) {
    # fidlc is invoked once in the default toolchain; targets in other
    # toolchains simply defer to it.

    # Names of the various targets declared by this template.
    library_target = "$target_name.library"
    rsp_target = "$target_name.rsp"

    # Intermediate files needed by fidlc.
    rsp_file = "$target_gen_dir/$target_name.fidl.rsp"
    dep_file = "$target_gen_dir/$target_name.fidl.d"

    # Represents the FIDL library itself.
    # This lets dependent have access to the library's sources.
    group(library_target) {
      deps = []
      foreach(dep, fidl_deps) {
        deps += [ "$dep.library" ]
      }
      metadata = {
        # These inputs are needed both here and in every dependent library.
        # Each --files switch introduces a group of source files that make
        # up a single FIDL library (all have identical `library ...;` lines).
        fidl_rspfile =
            [ "--files" ] + rebase_path(invoker.sources, root_build_dir)
      }
    }

    # Generates a response file with every "--files" switch provided by
    # dependencies.
    generated_file(rsp_target) {
      deps = [ ":$library_target" ]
      outputs = [ rsp_file ]
      output_conversion = "list lines"
      data_keys = [ "fidl_rspfile" ]
    }

    # NOTE: The reason zx_host_tool_action() is not used with the Fuchsia build
    # is because it doesn't support a depfile generated by a dependency (see
    # above).
    #
    # Instead, we use a single script to run fidlc and generate the right
    # depfile at the same time. This achieves the same result while keeping
    # complexity in the build system low.
    #
    action(fidlc_target) {
      # Find the path to the fidlc binary.
      fidlc_target = "//tools/fidl/fidlc:fidlc($host_toolchain)"
      fidlc_path = get_label_info(fidlc_target, "root_out_dir") + "/fidlc"
      if (host_os == "win") {
        fidlc_path += ".exe"
      }

      script = "//build/zircon/create_fidl_header.py"
      outputs = [ header_file ]
      deps = [
        ":$library_target",
        ":$rsp_target",
        fidlc_target,
      ]
      inputs = [ fidlc_path ]
      sources = [ rsp_file ]
      depfile = dep_file
      args = [
        "--name",
        fidl_name,
        "--c-header",
        rebase_path(header_file, root_build_dir),
        "--rsp-file",
        rebase_path(rsp_file, root_build_dir),
        "--dep-file",
        rebase_path(dep_file, root_build_dir),
        "--fidlc",
        rebase_path(fidlc_path, root_build_dir),
      ]
    }
  } else {  # current_toolchain != default_toolchain
    config_target = "$target_name.config"
    header_target = "$target_name.c_header"

    not_needed(invoker, [ "sources" ])

    # Allows dependents to find the header in the output directory.
    config(config_target) {
      include_dirs = [ include_dir ]
    }

    # Presents the generated header as a classic C source.
    source_set(header_target) {
      sources = [ header_file ]
      public_configs = [ ":$config_target" ]
      deps = [ ":$fidlc_target($default_toolchain)" ]
      public_deps = []
      foreach(dep, fidl_deps) {
        public_deps += [ "$dep.c_header" ]
      }
    }
  }
}