define([
    '/bower_components/proxy-polyfill/proxy.min.js', // https://github.com/GoogleChrome/proxy-polyfill
], function () {
    // linter complains if this isn't defined
    var Proxy = window.Proxy;

    var deepProxy = {};

    // for passing messages while recursing. use powers of two in case we ever
    // need to pass multiple message types (via bitpacking)
    var Messages = deepProxy.Messages = {
        CHANGE: 1,
        REMOVE: 2
    };

    var isArray = deepProxy.isArray = function (obj) {
        return Object.prototype.toString.call(obj)==='[object Array]';
    };

    /*  Arrays and nulls both register as 'object' when using native typeof
        we need to distinguish them as their own types, so use this instead. */
    var type = deepProxy.type = function (dat) {
        return dat === null?  'null': isArray(dat)?'array': typeof(dat);
    };

    var isProxyable = deepProxy.isProxyable = function (obj) {
        return ['object', 'array'].indexOf(type(obj)) !== -1;
    };

    /*  Any time you set a value, check its type.
        If that type is proxyable, make a new proxy. */
    var setter = deepProxy.set = function (cb) {
        return function (obj, prop, value) {
            if (prop === 'on') {
                throw new Error("'on' is a reserved attribute name for realtime lists and maps");
            }

            if (isProxyable(value)) {
                var proxy = obj[prop] = deepProxy.create(value, cb);
            } else {
                obj[prop] = value;
            }

            cb();
            return obj[prop] || true; // always return truthey or you have problems
        };
    };

    var pathMatches = deepProxy.pathMatches = function (path, pattern) {
        return !pattern.some(function (x, i) {
            return x !== path[i];
        });
    };

    var lengthDescending = function (a, b) { return b.pattern.length - a.pattern.length; };

    var getter = deepProxy.get = function (cb) {
        var events = {
            disconnect: [],
            change: [],
            ready: [],
            remove: [],
            create: [],
        };

        var on = function (evt, pattern, f) {
            switch (evt) {
                case 'change':
                    // pattern needs to be an array
                    pattern = type(pattern) === 'array'? pattern: [pattern];

                    events.change.push({
                        cb: function (oldval, newval, path, root) {
                            if (pathMatches(path, pattern)) {
                                return f(oldval, newval, path, root);
                            }
                        },
                        pattern: pattern,
                    });
                    // sort into descending order so we evaluate in order of specificity
                    events.change.sort(lengthDescending);

                    break;
                case 'remove':
                    pattern = type(pattern) === 'array'? pattern: [pattern];

                    events.remove.push({
                        cb: function (oldval, path, root) {
                            if (pathMatches(path, pattern)) { return f(oldval, path, root); }
                        },
                        pattern: pattern,
                    });

                    events.remove.sort(lengthDescending);

                    break;
                case 'ready':
                    events.ready.push({
                        // on('ready' has a different signature than 
                        // change and delete, so use 'pattern', not 'f'

                        cb: function (info) {
                            pattern(info);
                        }
                    });
                    break;
                case 'disconnect':
                    events.disconnect.push({
                        cb: function (info) {
                            // as above
                            pattern(info);
                        }
                    });
                    break;
                case 'create':
                    events.create.push({
                        cb: function (info) {
                            pattern(info);
                        }
                    });
                    break;
                default:
                    break;
            }
            return this;
        };

        return function (obj, prop) {
            if (prop === 'on') {
                return on;
            } else if (prop === '_events') {
                return events;
            }
            return obj[prop];
        };
    };

    var handlers = deepProxy.handlers = function (cb) {
        return {
            set: setter(cb),
            get: getter(cb),
        };
    };

    var create = deepProxy.create = function (obj, opt) {
        /*  recursively create proxies in case users do:
            `x.a = {b: {c: 5}};

            otherwise the inner object is not a proxy, which leads to incorrect
            behaviour on the client that initiated the object (but not for
            clients that receive the objects) */

        // if the user supplied a callback, use it to create handlers
        // this saves a bit of work in recursion
        var methods = type(opt) === 'function'? handlers(opt) : opt;
        switch (type(obj)) {
            case 'object':
                var keys = Object.keys(obj);
                keys.forEach(function (k) {
                    if (isProxyable(obj[k])) {
                        obj[k] = create(obj[k], opt);
                    }
                });
                break;
            case 'array':
                obj.forEach(function (o, i) {
                    if (isProxyable(o)) {
                        obj[i] = create(obj[i], opt);
                    }
                });
                break;
            default:
                // if it's not an array or object, you don't need to proxy it
                throw new Error('attempted to make a proxy of an unproxyable object');
        }

        return new Proxy(obj, methods);
    };

    // onChange(path, key, root, oldval, newval)
    var onChange = function (path, key, root, oldval, newval) {
        var P = path.slice(0);
        P.push(key);

        /*  returning false in your callback terminates 'bubbling up'
            we can accomplish this with Array.some because we've presorted
            listeners by the specificity of their path
        */
        root._events.change.some(function (handler, i) {
            return handler.cb(oldval, newval, P, root) === false;
        });
    };

    var find = deepProxy.find = function (map, path) {
        /* safely search for nested values in an object via a path */
        return (map && path.reduce(function (p, n) {
            return typeof p[n] !== 'undefined' && p[n];
        }, map)) || undefined;
    };

    var onRemove = function (path, key, root, old, top) {
        var newpath = path.concat(key);
        var X = find(root, newpath);

        var t_X = type(X);

        /*  TODO 'find' is correct but unnecessarily expensive.
            optimize it. */

        switch (t_X) {
            case 'array':

                if (top) {
                    // the top of an onremove should emit an onchange instead
                    onChange(path, key, root, old, undefined);// no newval since it's a deletion
                } else {
                    root._events.remove.forEach(function (handler, i) {
                        return handler.cb(X, newpath, root);
                    });
                }
                // remove all of the array's children
                X.forEach(function (x, i) {
                    onRemove(newpath, i, root);
                });

                break;
            case 'object':
                if (top) {
                    onChange(path, key, root, old, undefined);// no newval since it's a deletion
                } else {
                    root._events.remove.forEach(function (handler, i) {
                        return handler.cb(X, newpath, root, old, false);
                    });
                }
                // remove all of the object's children
                Object.keys(X).forEach(function (key, i) {
                    onRemove(newpath, key, root, X[key], false);
                });

                break;
            default:
                root._events.remove.forEach(function (handler, i) {
                    return handler.cb(X, newpath, root);
                });
                break;
        }
    };

    /*  compare a new object 'B' against an existing proxy object 'A'
        provide a unary function 'f' for the purpose of constructing new
        deep proxies from regular objects and arrays.

        Supply the path as you recurse, for the purpose of emitting events
        attached to particular paths within the complete structure.

        Operates entirely via side effects on 'A'
    */
    var objects = deepProxy.objects = function (A, B, f, path, root) {
        var Akeys = Object.keys(A);
        var Bkeys = Object.keys(B);

        /*  iterating over the keys in B will tell you if a new key exists
            it will not tell you if a key has been removed.
            to accomplish that you will need to iterate over A's keys
        */

        /*  TODO return a truthy or falsey value (in 'objects' and 'arrays')
            so that we have some measure of whether an object or array changed
            (from the higher level in the tree, rather than doing everything
            at the leaf level).

            bonus points if you can defer events until the complete diff has
            finished (collect them into an array or something, and simplify
            the event if possible)
        */

        Bkeys.forEach(function (b) {
            var t_b = type(B[b]);
            var old = A[b];

            if (Akeys.indexOf(b) === -1) {
                // there was an insertion

                // mind the fallthrough behaviour
                switch (t_b) {
                    case 'undefined':
                        // umm. this should never happen?
                        throw new Error("undefined type has key. this shouldn't happen?");
                    case 'array':
                    case 'object':
                        A[b] = f(B[b]);
                        break;
                    default:
                        A[b] = B[b];
                }

                // insertions are a change

                // onChange(path, key, root, oldval, newval)
                onChange(path, b, root, old, B[b]);
                return;
            }

            // else the key already existed
            var t_a = type(A[b]);
            if (t_a !== t_b) {
                // its type changed!
                console.log("type changed from [%s] to [%s]", t_a, t_b);
                switch (t_b) {
                    case 'undefined':
                        throw new Error("first pass should never reveal undefined keys");
                    case 'array':
                        A[b] = f(B[b]);
                        // make a new proxy
                        break;
                    case 'object':
                        A[b] = f(B[b]);
                        // make a new proxy
                        break;
                    default:
                        // all other datatypes just require assignment.
                        A[b] = B[b];
                        break;
                }

                // type changes always mean a change happened
                onChange(path, b, root, old, B[b]);
                return;
            }

            // values might have changed, if not types
            if (['array', 'object'].indexOf(t_a) === -1) {
                // it's not an array or object, so we can do deep equality
                if (A[b] !== B[b]) {
                    // not equal, so assign
                    A[b] = B[b];

                    onChange(path, b, root, old, B[b]);
                }
                return;
            }

            // else it's an array or object
            var nextPath = path.slice(0).concat(b);
            if (t_a === 'object') {
                // it's an object
                objects.call(root, A[b], B[b], f, nextPath, root);
            } else {
                // it's an array
                deepProxy.arrays.call(root, A[b], B[b], f, nextPath, root);
            }
        });
        Akeys.forEach(function (a) {
            var old = A[a];

            // the key was deleted
            if (Bkeys.indexOf(a) === -1 || type(B[a]) === 'undefined') {
                onRemove(path, a, root, old, true);
                delete A[a];
            }
        });

        return;
    };

    var arrays = deepProxy.arrays = function (A, B, f, path, root) {
        var l_A = A.length;
        var l_B = B.length;

        if (l_A !== l_B) {
            // B is longer than Aj
            // there has been an insertion

            // OR

            // A is longer than B
            // there has been a deletion

            B.forEach(function (b, i) {
                var t_a = type(A[i]);
                var t_b = type(b);

                var old = A[i];

                if (t_a !== t_b) {
                    // type changes are always destructive
                    // that's good news because destructive is easy
                    switch (t_b) {
                        case 'undefined':
                            throw new Error('this should never happen');
                        case 'object':
                            A[i] = f(b);
                            break;
                        case 'array':
                            A[i] = f(b);
                            break;
                        default:
                            A[i] = b;
                            break;
                    }

                    // path, key, root object, oldvalue, newvalue
                    onChange(path, i, root, old, b);
                } else {
                    // same type
                    var nextPath = path.slice(0).concat(i);

                    switch (t_b) {
                        case 'object':
                            objects.call(root, A[i], b, f, nextPath, root);
                            break;
                        case 'array':
                            if (arrays.call(root, A[i], b, f, nextPath, root)) {
                                onChange(path, i, root, old, b);
                            }
                            break;
                        default:
                            if (b !== A[i]) {
                                A[i] = b;
                                onChange(path, i, root, old, b);
                            }
                            break;
                    }
                }
            });

            if (l_A > l_B) {
                // A was longer than B, so there have been deletions
                var i = l_B;
                var t_a;
                var old;

                for (; i <= l_B; i++) {
                    // recursively delete
                    old = A[i];

                    onRemove(path, i, root, old, true);
                }
                // cool
            }

            A.length = l_B;
            return;
        }

        // else they are the same length, iterate over their values
        A.forEach(function (a, i) {
            var t_a = type(a);
            var t_b = type(B[i]);

            var old = a;

            // they have different types
            if (t_a !== t_b) {
                switch (t_b) {
                    case 'undefined':
                        onRemove(path, i, root, old, true);
                        break;

                // watch out for fallthrough behaviour
                    // if it's an object or array, create a proxy
                    case 'object':
                    case 'array':
                        A[i] = f(B[i]);
                        break;
                    default:
                        A[i] = B[i];
                        break;
                }

                onChange(path, i, root, old, B[i]);
                return;
            }

            // they are the same type, clone the paths array and push to it
            var nextPath = path.slice(0).concat(i);

            // same type
            switch (t_b) {
                case 'undefined':
                    throw new Error('existing key had type `undefined`. this should never happen');
                case 'object':
                    if (objects.call(root, A[i], B[i], f, nextPath, root)) {
                        onChange(path, i, root, old, B[i]);
                    }
                    break;
                case 'array':
                    if (arrays.call(root, A[i], B[i], f, nextPath, root)) {
                        onChange(path, i, root, old, B[i]);
                    }
                    break;
                default:
                    if (A[i] !== B[i]) {
                        A[i] = B[i];
                        onChange(path, i, root, old, B[i]);
                    }
                    break;
            }
        });
        return;
    };

    var update = deepProxy.update = function (A, B, cb) {
        var t_A = type(A);
        var t_B = type(B);

        if (t_A !== t_B) {
            throw new Error("Proxy updates can't result in type changes");
        }

        switch (t_B) {
            /* use .call so you can supply a different `this` value */
            case 'array':
                arrays.call(A, A, B, function (obj) {
                    return create(obj, cb);
                }, [], A);
                break;
            case 'object':
            //   arrays.call(this, A   , B   , f, path    , root)
                objects.call(A, A, B, function (obj) {
                    return create(obj, cb);
                }, [], A);
                break;
            default:
                throw new Error("unsupported realtime datatype:" + t_B);
        }
    };

    return deepProxy;
});