/*
 * Copyright (C) 2013 Dominik Schürmann <dominik@dominikschuermann.de>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package org.sufficientlysecure.keychain.service.remote;

import java.util.ArrayList;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.TimeUnit;

import org.sufficientlysecure.keychain.Constants;
import org.sufficientlysecure.keychain.provider.KeychainContract;
import org.sufficientlysecure.keychain.provider.ProviderHelper;
import org.sufficientlysecure.keychain.util.Log;
import org.sufficientlysecure.keychain.util.PausableThreadPoolExecutor;

import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.net.Uri;
import android.os.Binder;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.os.Messenger;

/**
 * Abstract service for remote APIs that handle app registration and user input.
 */
public abstract class RemoteApiService extends Service {
    Context mContext;

    final ArrayBlockingQueue<Runnable> mPoolQueue = new ArrayBlockingQueue<Runnable>(100);
    // TODO: Are these parameters okay?
    PausableThreadPoolExecutor mThreadPool = new PausableThreadPoolExecutor(2, 4, 10,
            TimeUnit.SECONDS, mPoolQueue);

    private final Object userInputLock = new Object();

    /**
     * Override handleUserInput() to handle OKAY (1) and CANCEL (0). After handling the waiting
     * threads will be notified and the queue resumed
     */
    protected class UserInputCallback extends BaseCallback {

        public void handleUserInput(Message msg) {
        }

        @Override
        public boolean handleMessage(Message msg) {
            handleUserInput(msg);

            // resume
            synchronized (userInputLock) {
                userInputLock.notifyAll();
            }
            mThreadPool.resume();
            return true;
        }

    }

    /**
     * Extends Handler.Callback with OKAY (1), CANCEL (0) variables
     */
    private class BaseCallback implements Handler.Callback {
        public static final int OKAY = 1;
        public static final int CANCEL = 0;

        @Override
        public boolean handleMessage(Message msg) {
            return false;
        }

    }

    /**
     * Should be used from Stub implementations of AIDL interfaces to enqueue a runnable for
     * execution
     * 
     * @param r
     */
    protected void checkAndEnqueue(Runnable r) {
        if (isCallerAllowed(false)) {
            mThreadPool.execute(r);

            Log.d(Constants.TAG, "Enqueued runnable…");
        } else {
            String[] callingPackages = getPackageManager()
                    .getPackagesForUid(Binder.getCallingUid());

            Log.e(Constants.TAG, "Not allowed to use service! Starting activity for registration!");
            Bundle extras = new Bundle();
            // TODO: currently simply uses first entry
            extras.putString(OpenPgpServiceActivity.EXTRA_PACKAGE_NAME, callingPackages[0]);

            RegisterActivityCallback callback = new RegisterActivityCallback();
            Messenger messenger = new Messenger(new Handler(getMainLooper(), callback));

            pauseQueueAndStartServiceActivity(OpenPgpServiceActivity.ACTION_REGISTER, messenger,
                    extras);

            if (callback.isAllowed()) {
                mThreadPool.execute(r);
                Log.d(Constants.TAG, "Enqueued runnable…");
            } else {
                Log.d(Constants.TAG, "User disallowed app!");
            }
        }
    }

    /**
     * Locks current thread and pauses execution of runnables and starts activity for user input
     * 
     * @param action
     * @param messenger
     * @param extras
     */
    protected void pauseQueueAndStartServiceActivity(String action, Messenger messenger,
            Bundle extras) {
        synchronized (userInputLock) {
            mThreadPool.pause();

            Log.d(Constants.TAG, "starting activity...");
            Intent intent = new Intent(getBaseContext(), OpenPgpServiceActivity.class);
            intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
            intent.setAction(action);

            extras.putParcelable(OpenPgpServiceActivity.EXTRA_MESSENGER, messenger);
            intent.putExtras(extras);

            startActivity(intent);

            // lock current thread for user input
            try {
                userInputLock.wait();
            } catch (InterruptedException e) {
                Log.e(Constants.TAG, "CryptoService", e);
            }
        }
    }

    /**
     * Retrieves AppSettings from database for the application calling this remote service
     * 
     * @return
     */
    protected AppSettings getAppSettings() {
        String[] callingPackages = getPackageManager().getPackagesForUid(Binder.getCallingUid());

        // get app settings for this package
        for (int i = 0; i < callingPackages.length; i++) {
            String currentPkg = callingPackages[i];

            Uri uri = KeychainContract.ApiApps.buildByPackageNameUri(currentPkg);

            AppSettings settings = ProviderHelper.getApiAppSettings(this, uri);

            if (settings != null)
                return settings;
        }

        return null;
    }

    class RegisterActivityCallback extends BaseCallback {
        public static final String PACKAGE_NAME = "package_name";

        private boolean allowed = false;
        private String packageName;

        public boolean isAllowed() {
            return allowed;
        }

        public String getPackageName() {
            return packageName;
        }

        @Override
        public boolean handleMessage(Message msg) {
            if (msg.arg1 == OKAY) {
                allowed = true;
                packageName = msg.getData().getString(PACKAGE_NAME);

                // resume threads
                if (isPackageAllowed(packageName, false)) {
                    synchronized (userInputLock) {
                        userInputLock.notifyAll();
                    }
                    mThreadPool.resume();
                } else {
                    // Should not happen!
                    Log.e(Constants.TAG, "Should not happen! Emergency shutdown!");
                    mThreadPool.shutdownNow();
                }
            } else {
                allowed = false;

                synchronized (userInputLock) {
                    userInputLock.notifyAll();
                }
                mThreadPool.resume();
            }
            return true;
        }

    }

    /**
     * Checks if process that binds to this service (i.e. the package name corresponding to the
     * process) is in the list of allowed package names.
     * 
     * @param allowOnlySelf
     *            allow only Keychain app itself
     * @return true if process is allowed to use this service
     */
    private boolean isCallerAllowed(boolean allowOnlySelf) {
        String[] callingPackages = getPackageManager().getPackagesForUid(Binder.getCallingUid());

        // is calling package allowed to use this service?
        for (int i = 0; i < callingPackages.length; i++) {
            String currentPkg = callingPackages[i];

            if (isPackageAllowed(currentPkg, allowOnlySelf)) {
                return true;
            }
        }

        Log.d(Constants.TAG, "Caller is NOT allowed!");
        return false;
    }

    /**
     * Checks if packageName is a registered app for the API.
     * 
     * @param packageName
     * @param allowOnlySelf
     *            allow only Keychain app itself
     * @return
     */
    private boolean isPackageAllowed(String packageName, boolean allowOnlySelf) {
        Log.d(Constants.TAG, "packageName: " + packageName);

        ArrayList<String> allowedPkgs = ProviderHelper.getRegisteredApiApps(mContext);
        Log.d(Constants.TAG, "allowed: " + allowedPkgs);

        // check if package is allowed to use our service
        if (allowedPkgs.contains(packageName) && (!allowOnlySelf)) {
            Log.d(Constants.TAG, "Package is allowed! packageName: " + packageName);

            return true;
        } else if (Constants.PACKAGE_NAME.equals(packageName)) {
            Log.d(Constants.TAG, "Package is OpenPGP Keychain! -> allowed!");

            return true;
        }

        return false;
    }

    @Override
    public void onCreate() {
        super.onCreate();
        mContext = this;
    }

}