// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/files/file_enumerator.h"
#include "base/files/file_path.h"
#include "base/files/file_util.h"
#include "base/strings/string_split.h"
#include "base/strings/string_util.h"
#include "base/strings/stringprintf.h"
#include "gn/commands.h"
#include "gn/err.h"
#include "gn/filesystem_utils.h"
#include "gn/setup.h"

namespace {

// Extracts from a build.ninja the commands to run GN.
//
// The commands to run GN are the gn rule and build.ninja build step at the top
// of the build.ninja file. We want to keep these when deleting GN builds since
// we want to preserve the command-line flags to GN.
//
// On error, returns the empty string.
std::string ExtractGNBuildCommands(const base::FilePath& build_ninja_file) {
  std::string file_contents;
  if (!base::ReadFileToString(build_ninja_file, &file_contents))
    return std::string();

  std::vector<std::string_view> lines = base::SplitStringPiece(
      file_contents, "\n", base::KEEP_WHITESPACE, base::SPLIT_WANT_ALL);

  std::string result;
  int num_blank_lines = 0;
  for (const auto& line : lines) {
    result.append(line);
    result.push_back('\n');
    if (line.empty())
      ++num_blank_lines;
    if (num_blank_lines == 3)
      break;
  }

  return result;
}

bool CleanOneDir(const std::string& dir) {
  // Deliberately leaked to avoid expensive process teardown.
  Setup* setup = new Setup;
  if (!setup->DoSetup(dir, false))
    return false;

  base::FilePath build_dir(setup->build_settings().GetFullPath(
      SourceDir(setup->build_settings().build_dir().value())));

  // NOTE: Not all GN builds have args.gn file hence we check here
  // if a build.ninja.d files exists instead.
  base::FilePath build_ninja_d_file = build_dir.AppendASCII("build.ninja.d");
  if (!base::PathExists(build_ninja_d_file)) {
    Err(Location(),
        base::StringPrintf(
            "%s does not look like a build directory.\n",
            FilePathToUTF8(build_ninja_d_file.DirName().value()).c_str()))
        .PrintToStdout();
    return false;
  }

  // Erase everything but the args file, and write a dummy build.ninja file that
  // will automatically rerun GN the next time Ninja is run.
  base::FilePath build_ninja_file = build_dir.AppendASCII("build.ninja");
  std::string build_commands = ExtractGNBuildCommands(build_ninja_file);
  if (build_commands.empty()) {
    // Couldn't parse the build.ninja file.
    Err(Location(), "Couldn't read build.ninja in this directory.",
        "Try running \"gn gen\" on it and then re-running \"gn clean\".")
        .PrintToStdout();
    return false;
  }

  base::FileEnumerator traversal(
      build_dir, false,
      base::FileEnumerator::FILES | base::FileEnumerator::DIRECTORIES);
  for (base::FilePath current = traversal.Next(); !current.empty();
       current = traversal.Next()) {
    if (base::ToLowerASCII(current.BaseName().value()) !=
        FILE_PATH_LITERAL("args.gn")) {
      base::DeleteFile(current, true);
    }
  }

  // Write the build.ninja file sufficiently to regenerate itself.
  if (base::WriteFile(build_ninja_file, build_commands.data(),
                      static_cast<int>(build_commands.size())) == -1) {
    Err(Location(), std::string("Failed to write build.ninja."))
        .PrintToStdout();
    return false;
  }

  // Write a .d file for the build which references a nonexistent file.
  // This will make Ninja always mark the build as dirty.
  std::string dummy_content("build.ninja: nonexistant_file.gn\n");
  if (base::WriteFile(build_ninja_d_file, dummy_content.data(),
                      static_cast<int>(dummy_content.size())) == -1) {
    Err(Location(), std::string("Failed to write build.ninja.d."))
        .PrintToStdout();
    return false;
  }

  return true;
}

}  // namespace

namespace commands {

const char kClean[] = "clean";
const char kClean_HelpShort[] = "clean: Cleans the output directory.";
const char kClean_Help[] =
    "gn clean <out_dir>...\n"
    "\n"
    "  Deletes the contents of the output directory except for args.gn and\n"
    "  creates a Ninja build environment sufficient to regenerate the build.\n";

int RunClean(const std::vector<std::string>& args) {
  if (args.empty()) {
    Err(Location(), "Missing argument.", "Usage: \"gn clean <out_dir>...\"")
        .PrintToStdout();
    return 1;
  }

  for (const auto& dir : args) {
    if (!CleanOneDir(dir))
      return 1;
  }

  return 0;
}

}  // namespace commands
