/**
 * Scope
 * A scope stores functions.
 *
 * @constructor mathnotepad.Scope
 * @param {Scope} [parentScope]
 */
function Scope(parentScope) {
    this.parentScope = parentScope;
    this.nestedScopes = undefined;

    this.symbols = {}; // the actual symbols

    // the following objects are just used to test existence.
    this.defs = {};    // definitions by name (for example "a = [1, 2; 3, 4]")
    this.updates = {}; // updates by name     (for example "a(2, 1) = 5.2")
    this.links = {};   // links by name       (for example "2 * a")
}

math.parser.node.Scope = Scope;

// TODO: rethink the whole scoping solution again. Try to simplify

/**
 * Create a nested scope
 * The variables in a nested scope are not accessible from the parent scope
 * @return {Scope} nestedScope
 */
Scope.prototype.createNestedScope = function () {
    var nestedScope = new Scope(this);
    if (!this.nestedScopes) {
        this.nestedScopes = [];
    }
    this.nestedScopes.push(nestedScope);
    return nestedScope;
};

/**
 * Clear all symbols in this scope and its nested scopes
 * (parent scope will not be cleared)
 */
Scope.prototype.clear = function () {
    this.symbols = {};
    this.defs = {};
    this.links = {};
    this.updates = {};

    if (this.nestedScopes) {
        var nestedScopes = this.nestedScopes;
        for (var i = 0, iMax = nestedScopes.length; i < iMax; i++) {
            nestedScopes[i].clear();
        }
    }
};

/**
 * create a symbol
 * @param {String} name
 * @return {function} symbol
 * @private
 */
Scope.prototype.createSymbol = function (name) {
    var symbol = this.symbols[name];
    if (!symbol) {
        // get a link to the last definition
        var lastDef = this.findDef(name);

        // create a new symbol
        symbol = this.newSymbol(name, lastDef);
        this.symbols[name] = symbol;

    }
    return symbol;
};

/**
 * Create a new symbol
 * @param {String} name
 * @param {*} [value]
 * @return {function} symbol
 * @private
 */
Scope.prototype.newSymbol = function (name, value) {
    // create a new symbol
    var scope = this;
    var symbol = function () {
        if (!symbol.value) {
            // try to resolve again
            symbol.value = scope.findDef(name);

            if (!symbol.value) {
                throw new Error('Undefined symbol ' + name);
            }
        }
        if (typeof symbol.value == 'function') {
            return symbol.value.apply(null, arguments);
        }
        else {
            // TODO: implement subset for all types
            return symbol.value;
        }
    };

    symbol.value = value;

    symbol.toString = function () {
        return symbol.value ? symbol.value.toString() : '';
    };

    return symbol;
};

/**
 * create a link to a value.
 * @param {String} name
 * @return {function} symbol
 */
Scope.prototype.createLink = function (name) {
    var symbol = this.links[name];
    if (!symbol) {
        symbol = this.createSymbol(name);
        this.links[name] = symbol;
    }
    return symbol;
};

/**
 * Create a variable definition
 * Returns the created symbol
 * @param {String} name
 * @param {*} [value]
 * @return {function} symbol
 */
Scope.prototype.createDef = function (name, value) {
    var symbol = this.defs[name];
    if (!symbol) {
        symbol = this.createSymbol(name);
        this.defs[name] = symbol;
    }
    if (symbol && value != undefined) {
        symbol.value = value;
    }
    return symbol;
};

/**
 * Create a variable update definition
 * Returns the created symbol
 * @param {String} name
 * @return {function} symbol
 */
Scope.prototype.createUpdate = function (name) {
    var symbol = this.updates[name];
    if (!symbol) {
        symbol = this.createLink(name);
        this.updates[name] = symbol;
    }
    return symbol;
};

/**
 * get the link to a symbol definition or update.
 * If the symbol is not found in this scope, it will be looked up in its parent
 * scope.
 * @param {String} name
 * @return {function | undefined} symbol, or undefined when not found
 */
Scope.prototype.findDef = function (name) {
    var symbol;

    // check scope
    symbol = this.defs[name];
    if (symbol) {
        return symbol;
    }
    symbol = this.updates[name];
    if (symbol) {
        return symbol;
    }

    // check parent scope
    if (this.parentScope) {
        return this.parentScope.findDef(name);
    }
    else {
        // this is the root scope (has no parent)

        var newSymbol = this.newSymbol,
            symbols = this.symbols,
            defs = this.defs;

        /**
         * Store a symbol in the root scope
         * @param {String} name
         * @param {*} value
         * @return {function} symbol
         */
        function put(name, value) {
            var symbol = newSymbol(name, value);
            symbols[name] = symbol;
            defs[name] = symbol;
            return symbol;
        }

        // check constant (and load the constant)
        if (name == 'pi') {
            return put(name, math.PI);
        }
        if (name == 'e') {
            return put(name, math.E);
        }
        if (name == 'i') {
            return put(name, new Complex(0, 1));
        }

        // check function (and load the function), for example "sin" or "sqrt"
        // search in the mathnotepad.math namespace for this symbol
        var fn = math[name];
        if (fn) {
            return put(name, fn);
        }

        // Check if token is a unit
        // Note: we do not check the upper case name, units are case sensitive!
        if (Unit.isUnit(name)) {
            var unit = new Unit(null, name);
            return put(name, unit);
        }
    }

    return undefined;
};

/**
 * Remove a link to a symbol
 * @param {String} name
 */
Scope.prototype.removeLink = function (name) {
    delete this.links[name];
};

/**
 * Remove a definition of a symbol
 * @param {String} name
 */
Scope.prototype.removeDef = function (name) {
    delete this.defs[name];
};

/**
 * Remove an update definition of a symbol
 * @param {String} name
 */
Scope.prototype.removeUpdate = function (name) {
    delete this.updates[name];
};

/**
 * initialize the scope and its nested scopes
 *
 * All functions are linked to their previous definition
 * If there is no parentScope, or no definition of the func in the parent scope,
 * the link will be set undefined
 */
Scope.prototype.init = function () {
    var symbols = this.symbols;
    var parentScope = this.parentScope;

    for (var name in symbols) {
        if (symbols.hasOwnProperty(name)) {
            var symbol = symbols[name];
            symbol.value = (parentScope ? parentScope.findDef(name) : undefined);
        }
    }

    if (this.nestedScopes) {
        this.nestedScopes.forEach(function (nestedScope) {
            nestedScope.init();
        });
    }
};

/**
 * Check whether this scope or any of its nested scopes contain a link to a
 * symbol with given name
 * @param {String} name
 * @return {boolean} hasLink   True if a link with given name is found
 */
Scope.prototype.hasLink = function (name) {
    if (this.links[name]) {
        return true;
    }

    if (this.nestedScopes) {
        var nestedScopes = this.nestedScopes;
        for (var i = 0, iMax = nestedScopes.length; i < iMax; i++) {
            if (nestedScopes[i].hasLink(name)) {
                return true;
            }
        }
    }

    return false;
};

/**
 * Check whether this scope contains a definition of a symbol with given name
 * @param {String} name
 * @return {boolean} hasDef   True if a definition with given name is found
 */
Scope.prototype.hasDef = function (name) {
    return (this.defs[name] != undefined);
};

/**
 * Check whether this scope contains an update definition of a symbol with
 * given name
 * @param {String} name
 * @return {boolean} hasUpdate   True if an update definition with given name is found
 */
Scope.prototype.hasUpdate = function (name) {
    return (this.updates[name] != undefined);
};

/**
 * Retrieve all undefined symbols
 * @return {function[]} undefinedSymbols   All symbols which are undefined
 */
Scope.prototype.getUndefinedSymbols = function () {
    var symbols = this.symbols;
    var undefinedSymbols = [];
    for (var i in symbols) {
        if (symbols.hasOwnProperty(i)) {
            var symbol = symbols[i];
            if (symbol.value == undefined) {
                undefinedSymbols.push(symbol);
            }
        }
    }

    if (this.nestedScopes) {
        this.nestedScopes.forEach(function (nestedScope) {
            undefinedSymbols =
                undefinedSymbols.concat(nestedScope.getUndefinedSymbols());
        });
    }

    return undefinedSymbols;
};