(function() {
"use strict";
angular.module('shared')
    .filter('duration', [ function() {
        return function (units, unitType, atomType) {

            var conversionChain = [
                { label: 'milliseconds', display: 'Millisecond',  degree: 1000 },
                { label: 'seconds', display: 'Second', degree: 60 },
                { label: 'minutes', display: 'Minute', degree: 60 },
                { label: 'hours', display: 'Hour', degree: 24 },
                { label: 'days', display: 'Day' }
            ];
            var unitConversionIndex = findIndexByLabel(unitType || 'seconds');
            var atomIndex = atomType ? findIndexByLabel(atomType) : unitConversionIndex;
            if(unitConversionIndex === -1 || atomIndex === -1) {
                throw new Error('type not recognized');
            }
            return buildDurationText(units, unitConversionIndex, atomIndex);

            function findIndexByLabel(unitType){
                for(var i = 0; i < conversionChain.length; ++i){
                    if(conversionChain[i].label === unitType){
                        return i;
                    }
                }
                return -1;
            }

            function buildDurationText(units, unitConversionIndex, atomIndex){
                var atoms = reduceToAtoms(units, unitConversionIndex, atomIndex);
                var highestUnitIndex = Math.max(findHighestUnitIndex(atoms, atomIndex), 0);
                var durationParts = [];
                for(var i = highestUnitIndex, atomsRemaining = atoms; i >= atomIndex; --i){
                    var target = toTarget(atomsRemaining, i, atomIndex);
                    durationParts.push(displayUnits(target.units, conversionChain[i].display));
                    atomsRemaining = target.remainder;
                }
                return durationParts.join(' ');
            }

            function reduceToAtoms(units, unitConversionIndex, atomIndex){
                var i = 0;
                if(unitConversionIndex < atomIndex){
                    for(i = unitConversionIndex; i < atomIndex; ++i){
                        units /= conversionChain[i].degree;
                    }
                }
                if(unitConversionIndex > atomIndex){
                    for(i = unitConversionIndex - 1; i >= atomIndex; --i){
                        units *= conversionChain[i].degree;
                    }
                }
                return Math.floor(units);
            }

            function findHighestUnitIndex(atoms, atomIndex){
                for(var i = atomIndex, units = atoms; i < conversionChain.length; ++i){
                    var conversion = conversionChain[i];
                    if(!conversion.degree){
                        return i;
                    }
                    units /= conversion.degree;
                    if(Math.floor(units) === 0){
                        return i;
                    }
                }
                return i;
            }

            function toTarget(atoms, targetIndex, atomIndex){
                var multiplicity = 1;
                for(var i = atomIndex; i < targetIndex; ++i){
                    multiplicity *= conversionChain[i].degree;
                }
                return { units: Math.floor(atoms / multiplicity), remainder:  atoms % multiplicity };
            }

            function displayUnits(quantity, displayLabel){
                displayLabel = quantity !== 1 ? displayLabel + 's' : displayLabel;
                return quantity + ' ' + displayLabel;
            }

        }
    }])
})();