// Copyright 2016 The Vanadium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package examples.baku.io.permissions;

import com.google.common.collect.HashMultimap;
import com.google.common.collect.Multimap;
import com.google.firebase.database.ChildEventListener;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.ValueEventListener;

import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.Stack;


/**
 * Created by phamilton on 6/28/16.
 */
public class PermissionManager {

    DatabaseReference mDatabaseRef;
    DatabaseReference mBlessingsRef;
    DatabaseReference mRequestsRef;

    public static final int FLAG_DEFAULT = 0;
    public static final int FLAG_WRITE = 1 << 0;
    public static final int FLAG_READ = 1 << 1;
    public static final int FLAG_PUSH = 1 << 2;     //2-way
//    public static final int FLAG_REFER = 1 << 3;       //1-way

    static final String KEY_PERMISSIONS = "_permissions";
    static final String KEY_REQUESTS = "_requests";
    static final String KEY_BLESSINGS = "_blessings";

    private String mId;

    final Map<String, PermissionRequest> mRequests = new HashMap<>();

    //    final Map<String, Set<OnRequestListener>> requestListeners = new HashMap<>();
    final Set<OnRequestListener> requestListeners = new HashSet<>();
    final Multimap<String, OnReferralListener> referralListeners = HashMultimap.create();

    final Map<String, Blessing> mBlessings = new HashMap<>();
    //<targetId, blessingId>
    //TODO: allow for multiple granted blessings per target
    final Map<String, Blessing> mGrantedBlessings = new HashMap<>();

    final Map<String, Integer> mCachedPermissions = new HashMap<>();
    final Multimap<String, OnPermissionChangeListener> mPermissionValueEventListeners = HashMultimap.create();
    final Multimap<String, String> mNearestAncestors = HashMultimap.create();


    //TODO: replace string ownerId with Auth
    public PermissionManager(final DatabaseReference databaseReference, String owner) {
        this.mDatabaseRef = databaseReference;
        this.mId = owner;

        mRequestsRef = databaseReference.child(KEY_REQUESTS);
        //TODO: only consider requests from sources within the constelattion
        mRequestsRef.addChildEventListener(requestListener);

        mBlessingsRef = mDatabaseRef.child(KEY_BLESSINGS);
        mBlessingsRef.orderByChild("target").equalTo(mId).addChildEventListener(blessingListener);
        mBlessingsRef.orderByChild("source").equalTo(mId).addListenerForSingleValueEvent(grantedBlessingListener);
    }

    void onBlessingUpdated(DataSnapshot snapshot) {
        if (!snapshot.exists()) {
            throw new IllegalArgumentException("snapshot value doesn't exist");
        }
        String key = snapshot.getKey();
        Blessing blessing = mBlessings.get(key);
        if (blessing == null) {
            blessing = new Blessing(snapshot);
            mBlessings.put(key, blessing);
        } else {
            blessing.setSnapshot(snapshot);
        }

        refreshPermissions();
    }

    //TODO: optimize this mess. Currently, recalculating entire permission tree.
    void refreshPermissions() {
        Map<String, Integer> updatedPermissions = new HashMap<>();
        for (Blessing blessing : mBlessings.values()) {
            if (blessing.isSynched()) {
                for (Blessing.Rule rule : blessing) {
                    String path = rule.getPath();
                    if (updatedPermissions.containsKey(path)) {
                        updatedPermissions.put(path, updatedPermissions.get(path) | rule.getPermissions());
                    } else {
                        updatedPermissions.put(path, rule.getPermissions());
                    }
                }
            }
        }

        mNearestAncestors.clear();
        for (String path : mPermissionValueEventListeners.keySet()) {
            String nearestAncestor = getNearestCommonAncestor(path, updatedPermissions.keySet());
            if (nearestAncestor != null) {
                mNearestAncestors.put(nearestAncestor, path);
            }
        }

        Set<String> changedPermissions = new HashSet<>();

        Set<String> removedPermissions = new HashSet<>(mCachedPermissions.keySet());
        removedPermissions.removeAll(updatedPermissions.keySet());
        for (String path : removedPermissions) {
            mCachedPermissions.remove(path);
            String newPath = getNearestCommonAncestor(path, updatedPermissions.keySet());
            changedPermissions.add(newPath);   //reset to default
        }

        for (String path : updatedPermissions.keySet()) {
            int current = updatedPermissions.get(path);
            if (!mCachedPermissions.containsKey(path)) {
                mCachedPermissions.put(path, current);
                changedPermissions.add(path);
            } else {
                int previous = mCachedPermissions.get(path);
                if (previous != current) {
                    mCachedPermissions.put(path, current);
                    changedPermissions.add(path);
                }
            }
        }

        for (String path : changedPermissions) {
            onPermissionsChange(path);
        }


    }

    //call all the listeners effected by a permission change at this path
    void onPermissionsChange(String path) {
        int permission = getPermission(path);
        if (mNearestAncestors.containsKey(path)) {
            for (String listenerPath : mNearestAncestors.get(path)) {
                if (mPermissionValueEventListeners.containsKey(listenerPath)) {
                    for (OnPermissionChangeListener listener : mPermissionValueEventListeners.get(listenerPath)) {
                        listener.onPermissionChange(permission);
                    }
                }
            }
        }
    }

    private ValueEventListener grantedBlessingListener = new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            if (dataSnapshot.exists()) {
                for (DataSnapshot blessingSnap : dataSnapshot.getChildren()) {
                    Blessing blessing = new Blessing(blessingSnap);
                    mGrantedBlessings.put(blessing.getId(), blessing);
                }
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    };

    void onBlessingRemoved(DataSnapshot snapshot) {
        Blessing removedBlessing = mBlessings.remove(snapshot.getKey());
        refreshPermissions();
    }

    public Blessing getGrantedBlessing(String target) {
        return mGrantedBlessings.get(target);
    }

    static String getNearestCommonAncestor(String path, Set<String> ancestors) {
        if (path.startsWith("/")) {
            throw new IllegalArgumentException("Path can't start with /");
        }
        if (ancestors.contains(path)) {
            return path;
        }
        String subpath = path;
        int index;
        while ((index = subpath.lastIndexOf("/")) != -1) {
            subpath = subpath.substring(0, index);
            if (ancestors.contains(subpath)) {
                return subpath;
            }
        }

        return null;
    }

    //return a blessing interface for granting/revoking permissions
    public Blessing bless(String target) {
        Blessing result = getGrantedBlessing(target);
        if (result == null) {
            result = new Blessing(target, this.mId, mBlessingsRef.push());
            mGrantedBlessings.put(target, result);
        }
        return result;
    }

    private ChildEventListener requestListener = new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
            onBlessingUpdated(dataSnapshot);
        }

        @Override
        public void onChildChanged(DataSnapshot dataSnapshot, String s) {
            onBlessingUpdated(dataSnapshot);
        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {
            onBlessingRemoved(dataSnapshot);
        }

        @Override
        public void onChildMoved(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    };

    private void onRequestUpdated(DataSnapshot snapshot) {
        if (!snapshot.exists()) return;

        PermissionRequest request = snapshot.getValue(PermissionRequest.class);
        if (request != null) {
            mRequests.put(request.getId(), request);
            //TODO: filter relevant requests
            for (OnRequestListener listener : requestListeners) {
                listener.onRequest(request);
            }
        }
    }

    //TODO: only notify listeners that returned true when the request was added
    private void onRequestRemoved(DataSnapshot snapshot) {
        mRequests.remove(snapshot.getKey());
        PermissionRequest request = snapshot.getValue(PermissionRequest.class);
        if (request != null) {
            for (OnRequestListener listener : requestListeners) {
                listener.onRequestRemoved(request);
            }
        }
    }


    private ChildEventListener blessingListener = new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
            onBlessingUpdated(dataSnapshot);
        }

        @Override
        public void onChildChanged(DataSnapshot dataSnapshot, String s) {
            onBlessingUpdated(dataSnapshot);
        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {
            onBlessingRemoved(dataSnapshot);
        }

        @Override
        public void onChildMoved(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    };

    public int getPermission(String path) {
        if (mCachedPermissions.containsKey(path))
            return mCachedPermissions.get(path);
        int result = getCombinedPermission(path);
        mCachedPermissions.put(path, result);
        return result;
    }

    private int getCombinedPermission(String path) {
        int current = 0;
        for (Blessing blessing : mBlessings.values()) {
            current = blessing.getPermissionAt(path, current);
        }
        return current;
    }

    public OnPermissionChangeListener addPermissionEventListener(String path, OnPermissionChangeListener listener) {
        int current = FLAG_DEFAULT;
        mPermissionValueEventListeners.put(path, listener);

        String nearestAncestor = getNearestCommonAncestor(path, mCachedPermissions.keySet());
        if (nearestAncestor != null) {
            current = getPermission(nearestAncestor);
            mNearestAncestors.put(nearestAncestor, path);
        }
        listener.onPermissionChange(current);
        return listener;
    }

    public void removePermissionEventListener(String path, OnPermissionChangeListener listener) {
        mPermissionValueEventListeners.remove(path, listener);

        String nca = getNearestCommonAncestor(path, mCachedPermissions.keySet());
        mNearestAncestors.remove(nca, path);

    }

    public void removeOnRequestListener(PermissionManager.OnRequestListener requestListener) {
        requestListeners.remove(requestListener);
    }

    public PermissionManager.OnRequestListener addOnRequestListener(PermissionManager.OnRequestListener requestListener) {
        requestListeners.add(requestListener);
        return requestListener;
    }

    public void removeOnReferralListener(String path, OnReferralListener referralListener) {
        referralListeners.remove(path, referralListener);
    }

    public OnReferralListener addOnReferralListener(String path, OnReferralListener referralListener) {
        referralListeners.put(path, referralListener);
        return referralListener;
    }

    public void refer(PermissionReferral referral) {
    }

    public void request(PermissionRequest request) {
        if (request == null)
            throw new IllegalArgumentException("null request");

        DatabaseReference requestRef = mRequestsRef.push();
        request.setId(requestRef.getKey());
        requestRef.setValue(request);
    }

    public interface OnRequestListener {
        boolean onRequest(PermissionRequest request);

        void onRequestRemoved(PermissionRequest request);
    }

    public interface OnReferralListener {
        void onReferral();
    }

    public interface OnPermissionChangeListener {
        void onPermissionChange(int current);

        void onCancelled(DatabaseError databaseError);
    }
}