(function (tree) {

//
// A number with a unit
//
tree.Dimension = function (value, unit) {
    this.value = parseFloat(value);
    this.unit = (unit && unit instanceof tree.Unit) ? unit :
      new(tree.Unit)(unit ? [unit] : undefined);
};

tree.Dimension.prototype = {
    type: "Dimension",
    accept: function (visitor) {
        this.unit = visitor.visit(this.unit);
    },
    eval: function (env) {
        return this;
    },
    toColor: function () {
        return new(tree.Color)([this.value, this.value, this.value]);
    },
    genCSS: function (env, output) {
        if ((env && env.strictUnits) && !this.unit.isSingular()) {
            throw new Error("Multiple units in dimension. Correct the units or use the unit function. Bad unit: "+this.unit.toString());
        }

        var value = tree.fround(env, this.value),
            strValue = String(value);

        if (value !== 0 && value < 0.000001 && value > -0.000001) {
            // would be output 1e-6 etc.
            strValue = value.toFixed(20).replace(/0+$/, "");
        }

        if (env && env.compress) {
            // Zero values doesn't need a unit
            if (value === 0 && this.unit.isLength()) {
                output.add(strValue);
                return;
            }

            // Float values doesn't need a leading zero
            if (value > 0 && value < 1) {
                strValue = (strValue).substr(1);
            }
        }

        output.add(strValue);
        this.unit.genCSS(env, output);
    },
    toCSS: tree.toCSS,

    // In an operation between two Dimensions,
    // we default to the first Dimension's unit,
    // so `1px + 2` will yield `3px`.
    operate: function (env, op, other) {
        /*jshint noempty:false */
        var value = tree.operate(env, op, this.value, other.value),
            unit = this.unit.clone();

        if (op === '+' || op === '-') {
            if (unit.numerator.length === 0 && unit.denominator.length === 0) {
                unit.numerator = other.unit.numerator.slice(0);
                unit.denominator = other.unit.denominator.slice(0);
            } else if (other.unit.numerator.length === 0 && unit.denominator.length === 0) {
                // do nothing
            } else {
                other = other.convertTo(this.unit.usedUnits());

                if(env.strictUnits && other.unit.toString() !== unit.toString()) {
                  throw new Error("Incompatible units. Change the units or use the unit function. Bad units: '" + unit.toString() +
                    "' and '" + other.unit.toString() + "'.");
                }

                value = tree.operate(env, op, this.value, other.value);
            }
        } else if (op === '*') {
            unit.numerator = unit.numerator.concat(other.unit.numerator).sort();
            unit.denominator = unit.denominator.concat(other.unit.denominator).sort();
            unit.cancel();
        } else if (op === '/') {
            unit.numerator = unit.numerator.concat(other.unit.denominator).sort();
            unit.denominator = unit.denominator.concat(other.unit.numerator).sort();
            unit.cancel();
        }
        return new(tree.Dimension)(value, unit);
    },

    compare: function (other) {
        if (other instanceof tree.Dimension) {
            var a = this.unify(), b = other.unify(),
                aValue = a.value, bValue = b.value;

            if (bValue > aValue) {
                return -1;
            } else if (bValue < aValue) {
                return 1;
            } else {
                if (!b.unit.isEmpty() && a.unit.compare(b.unit) !== 0) {
                    return -1;
                }
                return 0;
            }
        } else {
            return -1;
        }
    },

    unify: function () {
        return this.convertTo({ length: 'm', duration: 's', angle: 'rad' });
    },

    convertTo: function (conversions) {
        var value = this.value, unit = this.unit.clone(),
            i, groupName, group, targetUnit, derivedConversions = {}, applyUnit;

        if (typeof conversions === 'string') {
            for(i in tree.UnitConversions) {
                if (tree.UnitConversions[i].hasOwnProperty(conversions)) {
                    derivedConversions = {};
                    derivedConversions[i] = conversions;
                }
            }
            conversions = derivedConversions;
        }
        applyUnit = function (atomicUnit, denominator) {
          /*jshint loopfunc:true */
            if (group.hasOwnProperty(atomicUnit)) {
                if (denominator) {
                    value = value / (group[atomicUnit] / group[targetUnit]);
                } else {
                    value = value * (group[atomicUnit] / group[targetUnit]);
                }

                return targetUnit;
            }

            return atomicUnit;
        };

        for (groupName in conversions) {
            if (conversions.hasOwnProperty(groupName)) {
                targetUnit = conversions[groupName];
                group = tree.UnitConversions[groupName];

                unit.map(applyUnit);
            }
        }

        unit.cancel();

        return new(tree.Dimension)(value, unit);
    }
};

// http://www.w3.org/TR/css3-values/#absolute-lengths
tree.UnitConversions = {
    length: {
         'm': 1,
        'cm': 0.01,
        'mm': 0.001,
        'in': 0.0254,
        'pt': 0.0254 / 72,
        'pc': 0.0254 / 72 * 12
    },
    duration: {
        's': 1,
        'ms': 0.001
    },
    angle: {
        'rad': 1/(2*Math.PI),
        'deg': 1/360,
        'grad': 1/400,
        'turn': 1
    }
};

tree.Unit = function (numerator, denominator, backupUnit) {
    this.numerator = numerator ? numerator.slice(0).sort() : [];
    this.denominator = denominator ? denominator.slice(0).sort() : [];
    this.backupUnit = backupUnit;
};

tree.Unit.prototype = {
    type: "Unit",
    clone: function () {
        return new tree.Unit(this.numerator.slice(0), this.denominator.slice(0), this.backupUnit);
    },
    genCSS: function (env, output) {
        if (this.numerator.length >= 1) {
            output.add(this.numerator[0]);
        } else
        if (this.denominator.length >= 1) {
            output.add(this.denominator[0]);
        } else
        if ((!env || !env.strictUnits) && this.backupUnit) {
            output.add(this.backupUnit);
        }
    },
    toCSS: tree.toCSS,

    toString: function () {
      var i, returnStr = this.numerator.join("*");
      for (i = 0; i < this.denominator.length; i++) {
          returnStr += "/" + this.denominator[i];
      }
      return returnStr;
    },

    compare: function (other) {
        return this.is(other.toString()) ? 0 : -1;
    },

    is: function (unitString) {
        return this.toString() === unitString;
    },

    isLength: function () {
        return Boolean(this.toCSS().match(/px|em|%|in|cm|mm|pc|pt|ex/));
    },

    isEmpty: function () {
        return this.numerator.length === 0 && this.denominator.length === 0;
    },

    isSingular: function() {
        return this.numerator.length <= 1 && this.denominator.length === 0;
    },

    map: function(callback) {
        var i;

        for (i = 0; i < this.numerator.length; i++) {
            this.numerator[i] = callback(this.numerator[i], false);
        }

        for (i = 0; i < this.denominator.length; i++) {
            this.denominator[i] = callback(this.denominator[i], true);
        }
    },

    usedUnits: function() {
        var group, result = {}, mapUnit;

        mapUnit = function (atomicUnit) {
        /*jshint loopfunc:true */
            if (group.hasOwnProperty(atomicUnit) && !result[groupName]) {
                result[groupName] = atomicUnit;
            }

            return atomicUnit;
        };

        for (var groupName in tree.UnitConversions) {
            if (tree.UnitConversions.hasOwnProperty(groupName)) {
                group = tree.UnitConversions[groupName];

                this.map(mapUnit);
            }
        }

        return result;
    },

    cancel: function () {
        var counter = {}, atomicUnit, i, backup;

        for (i = 0; i < this.numerator.length; i++) {
            atomicUnit = this.numerator[i];
            if (!backup) {
                backup = atomicUnit;
            }
            counter[atomicUnit] = (counter[atomicUnit] || 0) + 1;
        }

        for (i = 0; i < this.denominator.length; i++) {
            atomicUnit = this.denominator[i];
            if (!backup) {
                backup = atomicUnit;
            }
            counter[atomicUnit] = (counter[atomicUnit] || 0) - 1;
        }

        this.numerator = [];
        this.denominator = [];

        for (atomicUnit in counter) {
            if (counter.hasOwnProperty(atomicUnit)) {
                var count = counter[atomicUnit];

                if (count > 0) {
                    for (i = 0; i < count; i++) {
                        this.numerator.push(atomicUnit);
                    }
                } else if (count < 0) {
                    for (i = 0; i < -count; i++) {
                        this.denominator.push(atomicUnit);
                    }
                }
            }
        }

        if (this.numerator.length === 0 && this.denominator.length === 0 && backup) {
            this.backupUnit = backup;
        }

        this.numerator.sort();
        this.denominator.sort();
    }
};

})(require('../tree'));