/*
 * Copyright 2012-2019 the original author or 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.
 */

package org.springframework.boot.system;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.lang.management.ManagementFactory;
import java.nio.file.Files;
import java.nio.file.attribute.PosixFilePermission;
import java.util.Set;

import org.springframework.util.Assert;
import org.springframework.util.ObjectUtils;

/**
 * An application process ID.
 *
 * @author Phillip Webb
 * @since 2.0.0
 */
public class ApplicationPid {

    private static final PosixFilePermission[] WRITE_PERMISSIONS = { PosixFilePermission.OWNER_WRITE,
            PosixFilePermission.GROUP_WRITE, PosixFilePermission.OTHERS_WRITE };

    private final String pid;

    public ApplicationPid() {
        this.pid = getPid();
    }

    protected ApplicationPid(String pid) {
        this.pid = pid;
    }

    private String getPid() {
        try {
            String jvmName = ManagementFactory.getRuntimeMXBean().getName();
            return jvmName.split("@")[0];
        }
        catch (Throwable ex) {
            return null;
        }
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == this) {
            return true;
        }
        if (obj instanceof ApplicationPid) {
            return ObjectUtils.nullSafeEquals(this.pid, ((ApplicationPid) obj).pid);
        }
        return false;
    }

    @Override
    public int hashCode() {
        return ObjectUtils.nullSafeHashCode(this.pid);
    }

    @Override
    public String toString() {
        return (this.pid != null) ? this.pid : "???";
    }

    /**
     * Write the PID to the specified file.
     * @param file the PID file
     * @throws IllegalStateException if no PID is available.
     * @throws IOException if the file cannot be written
     */
    public void write(File file) throws IOException {
        Assert.state(this.pid != null, "No PID available");
        createParentFolder(file);
        if (file.exists()) {
            assertCanOverwrite(file);
        }
        try (FileWriter writer = new FileWriter(file)) {
            writer.append(this.pid);
        }
    }

    private void createParentFolder(File file) {
        File parent = file.getParentFile();
        if (parent != null) {
            parent.mkdirs();
        }
    }

    private void assertCanOverwrite(File file) throws IOException {
        if (!file.canWrite() || !canWritePosixFile(file)) {
            throw new FileNotFoundException(file.toString() + " (permission denied)");
        }
    }

    private boolean canWritePosixFile(File file) throws IOException {
        try {
            Set<PosixFilePermission> permissions = Files.getPosixFilePermissions(file.toPath());
            for (PosixFilePermission permission : WRITE_PERMISSIONS) {
                if (permissions.contains(permission)) {
                    return true;
                }
            }
            return false;
        }
        catch (UnsupportedOperationException ex) {
            // Assume that we can
            return true;
        }
    }

}