define(['dojo/_base/lang'],function(lang){

    /** Note on dojox.json.schema
     * This implementation is not according to the version 03 of the json-schema
     * draft. Differences:
     * - doesn't support the 'required' property, but uses 'optional' (which is
     *   false by default).
     */

    ////////////////////////////////////////
    // Base schema types
    //

    var dateRe = "\\d{4}-\\d{2}-\\d{2}"; // YYYY-MM-DD
    var timeRe = "\\d{2}:\\d{2}:\\d{2}"; // hh:mm:ss 
    var datetimeRe = dateRe+"T"+timeRe+"Z"; // YYYY-MM-DDThh:mm:ssZ

    function mixin(obj1,obj2) {
        return lang.mixin({},obj1||{},obj2||{});
    }
    function mkType(base) {
        return function(props) {
            return mixin(base,props);
        };
    }

    var nestring = mkType({ type:'string', minLength:1 });
    var string = mkType({ type:'string' });
    var integer = mkType({ type: 'integer' });
    var bool = mkType({ type: 'boolean' });
    var pattern = function(p){
        return mixin({
            type: 'string',
            pattern: p
        });
    };
    var date = mkType(pattern(dateRe));
    var time = mkType(pattern(timeRe));
    var datetime = mkType(pattern(datetimeRe));
    var array = function(items,props) {
        return mixin({
            type: 'array',
            items: items
        },props);
    };
    var object = function(properties,props) {
        return mixin({
            type: 'object',
            properties: properties,
            additionalProperties: false
        },props);
    };
    var optional = mkType({ optional: true });

    ////////////////////////////////////////
    // Domain specific
    //

    var typedobject = function(type,properties,props) {
        return object(mixin(properties,{
            type: pattern(type)
        }),props);
    };

    var dbobject = function(type,properties,props) {
        return typedobject(type,mixin(properties,{
            _id: nestring(optional()),
            _rev: nestring(optional())
        }),props);
    };

    ////////////////////////////////////////
    // The QED schema
    //

    var Respondent = dbobject('Respondent',{
        secret: nestring()
    });

    var Question = dbobject('Question',{
        code:nestring(),
        title: nestring(),
        description: string(optional()),
        topic: string(optional()),
        categories: array(nestring(),optional()),
        content: array([
            typedobject('Header',{
                content:string(optional())
            }),
            typedobject('Text',{
                content:string(optional())
            }),
            typedobject('Divider'),
            typedobject('StringInput'),
            typedobject('TextInput',{
                maxLength:integer()
            }),
            typedobject('IntegerInput',{
                min:integer(),
                max:integer(),
                step:integer()
            }),
            typedobject('MultipleChoiceInput',{
                multiple:bool(),
                items:array(nestring())
            })
        ],optional()),
        publicationDate:datetime(optional())
    });

    var Survey = dbobject('Survey',{
        title: nestring(),
        description: string(optional()),
        questions: array(Question,optional()),
        publicationDate:datetime(optional())
    });

    var SurveyRun = dbobject('SurveyRun',{
        description: string(optional()),
        survey: Survey,
        publicationDate:datetime(optional()),
        startDate:datetime(optional()),
        endDate:datetime(optional()),
        mode:{type:'string','enum':['open','closed'],optional:true},
        metadata:string(optional())
    });

    var Response = dbobject('Response',{
        surveyRunId: nestring(),
        answers:{type:'object',optional:true},
        publicationDate:datetime(optional())
    });

    var Session = dbobject('Session',{
        title: nestring(),
        description: string(optional()),
        publicationDate: datetime(optional())
    });

    var SessionTemplate = dbobject('SessionTemplate',{
        title: nestring(),
        description: string(optional()),
        publicationDate: datetime(optional()),
        plannedDate: datetime(optional())
    });

    var schema = {type:[
        Question,
        Survey,
        SurveyRun,
        Response,
        Session,
        SessionTemplate
    ]};

    return schema;
});