/*
 * Copyright 2014-present Facebook, Inc.
 *
 * 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
 *
 *     http://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.
 */

package com.facebook.buck.python;

import com.facebook.buck.cli.BuckConfig;
import com.facebook.buck.io.MorePaths;
import com.facebook.buck.util.HumanReadableException;
import com.facebook.buck.util.ProcessExecutor;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.CharMatcher;
import com.google.common.base.Optional;
import com.google.common.collect.ImmutableList;

import java.io.File;
import java.io.IOException;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.EnumSet;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class PythonBuckConfig {

  private static final String SECTION = "python";

  private static final Pattern PYTHON_VERSION_REGEX =
      Pattern.compile(".*?(\\wython \\d+\\.\\d+).*");

  // Prefer "python2" where available (Linux), but fall back to "python" (Mac).
  private static final ImmutableList<String> PYTHON_INTERPRETER_NAMES =
      ImmutableList.of("python2", "python");

  private final BuckConfig delegate;

  public PythonBuckConfig(BuckConfig config) {
    this.delegate = config;
  }

  /**
   * @return true if file is executable and not a directory.
   */
  private boolean isExecutableFile(File file) {
    return file.canExecute() && !file.isDirectory();
  }

  /**
   * Returns the path to python interpreter. If python is specified in the tools section
   * that is used and an error reported if invalid.
   * @return The found python interpreter.
   */
  public String getPythonInterpreter() {
    Optional<String> configPath = delegate.getValue(SECTION, "interpreter");
    ImmutableList<String> pythonInterpreterNames = PYTHON_INTERPRETER_NAMES;
    if (configPath.isPresent()) {
      // Python path in config. Use it or report error if invalid.
      File python = new File(configPath.get());
      if (isExecutableFile(python)) {
        return python.getAbsolutePath();
      }
      if (python.isAbsolute()) {
        throw new HumanReadableException("Not a python executable: " + configPath.get());
      }
      pythonInterpreterNames = ImmutableList.of(configPath.get());
    }

    ImmutableList.Builder<Path> paths = ImmutableList.builder();
    for (String path : delegate.getEnv("PATH", File.pathSeparator)) {
      paths.add(Paths.get(path));
    }
    for (String interpreterName : pythonInterpreterNames) {
      Optional<Path> python = MorePaths.searchPathsForExecutable(
          Paths.get(interpreterName),
          paths.build(),
          ImmutableList.copyOf(delegate.getEnv("PATHEXT", File.pathSeparator)));
      if (python.isPresent()) {
        return python.get().toAbsolutePath().toString();
      }
    }

    if (configPath.isPresent()) {
      throw new HumanReadableException("Not a python executable: " + configPath.get());
    } else {
      throw new HumanReadableException("No python2 or python found.");
    }
  }

  public PythonEnvironment getPythonEnvironment(ProcessExecutor processExecutor)
      throws InterruptedException {
    Path pythonPath = Paths.get(getPythonInterpreter());
    PythonVersion pythonVersion = getPythonVersion(processExecutor, pythonPath);
    return new PythonEnvironment(pythonPath, pythonVersion);
  }

  public Optional<Path> getPathToTestMain() {
    Optional <Path> testMain = delegate.getPath(SECTION, "path_to_python_test_main");
     if (testMain.isPresent()) {
       return testMain;
    }

    // In some configs (particularly tests) it's possible that this variable will not be set.

    String rawPath = System.getProperty("buck.path_to_python_test_main");
    if (rawPath == null) {
      return Optional.absent();
    }

    return Optional.of(Paths.get(rawPath));
  }

  public Optional<Path> getPathToPex() {
    return delegate.getPath(SECTION, "path_to_pex");
  }


  private static PythonVersion getPythonVersion(ProcessExecutor processExecutor, Path pythonPath)
      throws InterruptedException {
    try {
      ProcessExecutor.Result versionResult = processExecutor.execute(
          Runtime.getRuntime().exec(new String[]{pythonPath.toString(), "--version"}),
          EnumSet.of(ProcessExecutor.Option.EXPECTING_STD_ERR),
          /* stdin */ Optional.<String>absent(),
          /* timeOutMs */ Optional.<Long>absent());
      return extractPythonVersion(pythonPath, versionResult);
    } catch (IOException e) {
      throw new HumanReadableException(
          e,
          "Could not run \"%s --version\": %s",
          pythonPath,
          e.getMessage());
    }
  }

  @VisibleForTesting
  static PythonVersion extractPythonVersion(
      Path pythonPath,
      ProcessExecutor.Result versionResult) {
    if (versionResult.getExitCode() == 0) {
      String versionString = CharMatcher.WHITESPACE.trimFrom(versionResult.getStderr().get());
      Matcher matcher = PYTHON_VERSION_REGEX.matcher(versionString);
      if (!matcher.matches()) {
        throw new HumanReadableException(
            "`%s --version` returned an invalid version string %s",
            pythonPath,
            versionString);
      }
      return ImmutablePythonVersion.of(matcher.group(1));
    } else {
      throw new HumanReadableException(versionResult.getStderr().get());
    }
  }
}