/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * 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.android.telecomm;

import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.content.pm.PackageManager;
import android.content.pm.ResolveInfo;
import android.content.pm.ServiceInfo;
import android.os.IBinder;
import android.telecomm.ICallService;
import android.telecomm.ICallServiceProvider;
import android.util.Log;

import com.google.common.base.Preconditions;
import com.google.common.collect.Lists;
import com.google.common.collect.Sets;

import java.util.List;
import java.util.Set;
import java.util.Timer;
import java.util.TimerTask;

/**
 * Finds {@link ICallService} and {@link ICallServiceProvider} implementations on the device.
 * Uses binder APIs to find ICallServiceProviders and calls method on ICallServiceProvider to
 * find ICallService implementations.
 * TODO(santoscordon): Add performance timing to async calls.
 */
final class CallServiceFinder {

    /**
     * Helper class to register/unregister call-service providers.
     */
    private class ProviderRegistrar {

        /**
         * The name of the call-service provider that is expected to register with this finder.
         */
        private ComponentName mProviderName;

        /**
         * A unique identifier for a given lookup cycle, see nextLookupId.
         * TODO(gilad): Potentially unnecessary, consider removing.
         */
        int mLookupId;

        /**
         * Persists the specified parameters.
         *
         * @param providerName The component name of the relevant provider.
         * @param lookupId The lookup-cycle ID.
         */
        ProviderRegistrar(ComponentName providerName, int lookupId) {
            this.mProviderName = providerName;
            this.mLookupId = lookupId;
        }

        ComponentName getProviderName() {
            return mProviderName;
        }

        /**
         * Registers the specified call-service provider.
         *
         * @param provider The provider object to register.
         */
        void register(ICallServiceProvider provider) {
            registerProvider(mLookupId, mProviderName, provider);
        }

        /** Unregisters this provider. */
        void unregister() {
            unregisterProvider(mProviderName);
        }
    }

    /**
     * Wrapper around ICallServiceProvider, mostly used for binding etc.
     *
     * TODO(gilad): Consider making this wrapper unnecessary.
     */
    private class ProviderWrapper {

        /**
         * Persists the specified parameters and attempts to bind the specified provider.
         *
         * TODO(gilad): Consider embedding ProviderRegistrar into this class and do away
         * with the former, or vice versa.
         *
         * @param context The relevant application context.
         * @param registrar The registrar with which to register and unregister this provider.
         */
        ProviderWrapper(Context context, final ProviderRegistrar registrar) {
          ComponentName name = registrar.getProviderName();
          Preconditions.checkNotNull(name);
          Preconditions.checkNotNull(context);

          Intent serviceIntent = new Intent(CALL_SERVICE_PROVIDER_CLASS_NAME).setComponent(name);
          Log.i(TAG, "Binding to ICallServiceProvider through " + serviceIntent);

          // Connection object for the service binding.
          ServiceConnection connection = new ServiceConnection() {
              @Override
              public void onServiceConnected(ComponentName className, IBinder service) {
                  registrar.register(ICallServiceProvider.Stub.asInterface(service));
              }

              @Override
              public void onServiceDisconnected(ComponentName className) {
                  registrar.unregister();
              }
          };

          if (!context.bindService(serviceIntent, connection, Context.BIND_AUTO_CREATE)) {
              // TODO(santoscordon): Handle error.
          }
        }
    }

    /**
     * A timer task to ensure each lookup cycle is time-bound, see LOOKUP_TIMEOUT.
     */
    private class LookupTerminator extends TimerTask {
        @Override
        public void run() {
          terminateLookup();
        }
    }

    /** Used to identify log entries by this class */
    private static final String TAG = CallServiceFinder.class.getSimpleName();

    /**
     * The longest period in milliseconds each lookup cycle is allowed to span over, see mTimer.
     * TODO(gilad): Likely requires tuning.
     */
    private static final int LOOKUP_TIMEOUT = 100;

    /**
     * Used to retrieve all known ICallServiceProvider implementations from the framework.
     * TODO(gilad): Move to a more logical place for this to be shared.
     */
    static final String CALL_SERVICE_PROVIDER_CLASS_NAME = ICallServiceProvider.class.getName();

    private final Switchboard mSwitchboard;

    /**
     * Determines whether or not a lookup cycle is already running.
     */
    private boolean mIsLookupInProgress = false;

    /**
     * Used to generate unique lookup-cycle identifiers. Incremented upon initiateLookup calls.
     */
    private int mNextLookupId = 0;

    /**
     * The set of bound call-service providers.  Only populated via initiateLookup scenarios.
     * Providers should only be removed upon unbinding.
     */
    private Set<ICallServiceProvider> mProviderRegistry = Sets.newHashSet();

    /**
     * Stores the names of the providers to bind to in one lookup cycle.  The set size represents
     * the number of call-service providers this finder expects to hear back from upon initiating
     * call-service lookups, see initiateLookup. Whenever all providers respond before the lookup
     * timeout occurs, the complete set of (available) call services is passed to the switchboard
     * for further processing of outgoing calls etc.  When the timeout occurs before all responds
     * are received, the partial (potentially empty) set gets passed (to the switchboard) instead.
     * Note that cached providers do not require finding and hence are excluded from this count.
     * Also noteworthy is that providers are dynamically removed from this set as they register.
     */
    private Set<ComponentName> mUnregisteredProviders;

    /**
     * Used to interrupt lookup cycles that didn't terminate naturally within the allowed
     * period, see LOOKUP_TIMEOUT.
     */
    private Timer mTimer;

    /**
     * Persists the specified parameters.
     *
     * @param switchboard The switchboard for this finer to work against.
     */
    CallServiceFinder(Switchboard switchboard) {
        mSwitchboard = switchboard;
    }

    /**
     * Initiates a lookup cycle for call-service providers.
     * TODO(gilad): Expand this comment to describe the lookup flow in more detail.
     *
     * @param context The relevant application context.
     */
    synchronized void initiateLookup(Context context) {
        if (mIsLookupInProgress) {
            // At most one active lookup is allowed at any given time, bail out.
            return;
        }

        List<ComponentName> providerNames = getProviderNames(context);
        if (providerNames.isEmpty()) {
            Log.i(TAG, "No ICallServiceProvider implementations found.");
            updateSwitchboard();
            return;
        }

        mIsLookupInProgress = true;
        mUnregisteredProviders = Sets.newHashSet();

        int lookupId = mNextLookupId++;
        for (ComponentName name : providerNames) {
            if (!mProviderRegistry.contains(name)) {
                // The provider is either not yet registered or has been unregistered
                // due to unbinding etc.
                ProviderRegistrar registrar = new ProviderRegistrar(name, lookupId);
                new ProviderWrapper(context, registrar);
                mUnregisteredProviders.add(name);
            }
        }

        int providerCount = providerNames.size();
        int unregisteredProviderCount = mUnregisteredProviders.size();

        Log.i(TAG, "Found " + providerCount + " implementations for ICallServiceProvider, "
                + unregisteredProviderCount + " of which are not currently registered.");

        if (unregisteredProviderCount == 0) {
            // All known (provider) implementations are already registered, pass control
            // back to the switchboard.
            updateSwitchboard();
        } else {
            // Start the timeout for this lookup cycle.
            // TODO(gilad): Consider reusing the same timer instead of creating new ones.
            if (mTimer != null) {
                // Shouldn't be running but better safe than sorry.
                mTimer.cancel();
            }
            mTimer = new Timer();
            mTimer.schedule(new LookupTerminator(), LOOKUP_TIMEOUT);
        }
    }

    /**
     * Returns the all-inclusive list of call-service-provider names.
     *
     * @param context The relevant/application context to query against.
     * @return The list containing the (component) names of all known ICallServiceProvider
     *     implementations or the empty list upon no available providers.
     */
    private List<ComponentName> getProviderNames(Context context) {
        // The list of provider names to return to the caller, may be populated below.
        List<ComponentName> providerNames = Lists.newArrayList();

        PackageManager packageManager = context.getPackageManager();
        Intent intent = new Intent(CALL_SERVICE_PROVIDER_CLASS_NAME);
        for (ResolveInfo entry : packageManager.queryIntentServices(intent, 0)) {
            ServiceInfo serviceInfo = entry.serviceInfo;
            if (serviceInfo != null) {
                // The entry resolves to a proper service, add it to the list of provider names.
                providerNames.add(
                        new ComponentName(serviceInfo.packageName, serviceInfo.name));
            }
        }

        return providerNames;
    }

    /**
     * Registers the specified provider and performs the necessary bookkeeping to potentially
     * return control to the switchboard before the timeout for the current lookup cycle.
     *
     * @param lookupId The lookup-cycle ID.
     * @param providerName The component name of the relevant provider.
     * @param provider The provider object to register.
     */
    private void registerProvider(
            int lookupId, ComponentName providerName, ICallServiceProvider provider) {

      if (mUnregisteredProviders.remove(providerName)) {
          mProviderRegistry.add(provider);
          if (mUnregisteredProviders.size() < 1) {
              terminateLookup();  // No other providers to wait for.
          }
      }
    }

    /**
     * Unregisters the specified provider.
     *
     * @param providerName The component name of the relevant provider.
     */
    private void unregisterProvider(ComponentName providerName) {
        mProviderRegistry.remove(providerName);
    }

    /**
     * Timeouts the current lookup cycle, see LookupTerminator.
     */
    private void terminateLookup() {
        if (mTimer != null) {
            mTimer.cancel();  // Terminate the timer thread.
        }

        updateSwitchboard();
        mIsLookupInProgress = false;
    }

    /**
     * Updates the switchboard passing the relevant call services (as opposed
     * to call-service providers).
     */
    private void updateSwitchboard() {
        synchronized (mProviderRegistry) {
            // TODO(gilad): More here.
            mSwitchboard.setCallServices(null);
        }
    }
}