package javaapplication;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.List;
import java.util.function.Consumer;
import java.util.function.Supplier;
import java.util.stream.Collectors;
import java.util.stream.Stream;

final public class Executor {

    Executor() {
    }

    Executor setOutputConsumer(Consumer<Stream<String>> v) {
        outputConsumer = v;
        return this;
    }

    Executor saveOutput(boolean v) {
        saveOutput = v;
        return this;
    }

    Executor setWaitBeforeOutput(boolean v) {
        waitBeforeOutput = v;
        return this;
    }

    Executor setProcessBuilder(ProcessBuilder v) {
        pb = v;
        return this;
    }

    Executor setCommandLine(String... cmdline) {
        return setProcessBuilder(new ProcessBuilder(cmdline));
    }

    List<String> getOutput() {
        return output;
    }

    Executor executeExpectSuccess() throws IOException {
        int ret = execute();
        if (0 != ret) {
            throw new IOException(
                    String.format("Command %s exited with %d code",
                            createLogMessage(pb), ret));
        }
        return this;
    }

    int execute() throws IOException {
        output = null;

        boolean needProcessOutput = true;
        if (needProcessOutput) {
            pb.redirectErrorStream(true);
        } else {
            // We are not going to read process output, so need to notify
            // ProcessBuilder about this. Otherwise some processes might just
            // hang up (`ldconfig -p`).
            pb.redirectError(ProcessBuilder.Redirect.DISCARD);
            pb.redirectOutput(ProcessBuilder.Redirect.DISCARD);
        }

        System.out.println(String.format("Running %s", createLogMessage(pb)));
        Process p = pb.start();

        int code = 0;
        if (waitBeforeOutput) {
            try {
                code = p.waitFor();
            } catch (InterruptedException ex) {
                System.err.println(ex);
                throw new RuntimeException(ex);
            }
        }

        if (needProcessOutput) {
            try (BufferedReader br = new BufferedReader(new InputStreamReader(
                    p.getInputStream()))) {
                final List<String> savedOutput;
                // Need to save output if explicitely requested (saveOutput=true) or
                // if will be used used by multiple consumers
                savedOutput = br.lines().collect(Collectors.toList());

                Supplier<Stream<String>> outputStream = () -> {
                    if (savedOutput != null) {
                        return savedOutput.stream();
                    }
                    return br.lines();
                };

                outputStream.get().forEach(System.out::println);

                if (outputConsumer != null) {
                    outputConsumer.accept(outputStream.get());
                }

                if (savedOutput == null) {
                    // For some processes on Linux if the output stream
                    // of the process is opened but not consumed, the process
                    // would exit with code 141.
                    // It turned out that reading just a single line of process
                    // output fixes the problem, but let's process
                    // all of the output, just in case.
                    br.lines().forEach(x -> {
                    });
                }
            }
        }

        try {
            if (!waitBeforeOutput) {
                code = p.waitFor();
            }
            return code;
        } catch (InterruptedException ex) {
            System.err.println(ex);
            throw new RuntimeException(ex);
        }
    }

    static Executor of(String... cmdline) {
        return new Executor().setCommandLine(cmdline);
    }

    static Executor of(ProcessBuilder pb) {
        return new Executor().setProcessBuilder(pb);
    }

    private static String createLogMessage(ProcessBuilder pb) {
        StringBuilder sb = new StringBuilder();
        sb.append(String.format("%s", pb.command()));
        if (pb.directory() != null) {
            sb.append(String.format("in %s", pb.directory().getAbsolutePath()));
        }
        return sb.toString();
    }

    private ProcessBuilder pb;
    private boolean saveOutput;
    private boolean waitBeforeOutput;
    private List<String> output;
    private Consumer<Stream<String>> outputConsumer;
}