/* SPDX-License-Identifier: MIT
 *
 * jsonschema is licensed under MIT license.
 *
 * Copyright (C) 2012-2015 Tom de Grunt <tom@degrunt.nl>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
 * of the Software, and to permit persons to whom the Software is furnished to do
 * so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#IMPORT common/jsonschema/helpers.js

/** @type ValidatorResult */
var ValidatorResult = helpers.ValidatorResult;
/** @type SchemaError */
var SchemaError = helpers.SchemaError;

var attribute = {};

const ignoreProperties = {
  // informative properties
  'id': true,
  'default': true,
  'description': true,
  'title': true,
  // arguments to other properties
  'additionalItems': true,
  'then': true,
  'else': true,
  // special-handled properties
  '$schema': true,
  '$ref': true,
  'extends': true,
};
#EXPORT ignoreProperties

/**
 * @name validators
 */
const validators = {};

/**
 * Validates whether the instance if of a certain type
 * @param instance
 * @param schema
 * @param options
 * @param ctx
 * @return {ValidatorResult|null}
 */
validators.type = function validateType (instance, schema, options, ctx) {
  // Ignore undefined instances
  if (instance === undefined) {
    return null;
  }
  var result = new ValidatorResult(instance, schema, options, ctx);
  var types = Array.isArray(schema.type) ? schema.type : [schema.type];
  if (!types.some(this.testType.bind(this, instance, schema, options, ctx))) {
    var list = types.map(function (v) {
      if(!v) return;
      var id = v.$id || v.id;
      return id ? ('<' + id + '>') : (v+'');
    });
    result.addError({
      name: 'type',
      argument: list,
      message: "is not of a type(s) " + list,
    });
  }
  return result;
};

function testSchemaNoThrow(instance, options, ctx, callback, schema){
  var throwError = options.throwError;
  var throwAll = options.throwAll;
  options.throwError = false;
  options.throwAll = false;
  var res = this.validateSchema(instance, schema, options, ctx);
  options.throwError = throwError;
  options.throwAll = throwAll;

  if (!res.valid && callback instanceof Function) {
    callback(res);
  }
  return res.valid;
}

/**
 * Validates whether the instance matches some of the given schemas
 * @param instance
 * @param schema
 * @param options
 * @param ctx
 * @return {ValidatorResult|null}
 */
validators.anyOf = function validateAnyOf (instance, schema, options, ctx) {
  // Ignore undefined instances
  if (instance === undefined) {
    return null;
  }
  var result = new ValidatorResult(instance, schema, options, ctx);
  var inner = new ValidatorResult(instance, schema, options, ctx);
  if (!Array.isArray(schema.anyOf)){
    throw new SchemaError("anyOf must be an array");
  }
  if (!schema.anyOf.some(
    testSchemaNoThrow.bind(
      this, instance, options, ctx, function(res){inner.importErrors(res);}
    ))) {
    var list = schema.anyOf.map(function (v, i) {
      var id = v.$id || v.id;
      if(id) return '<' + id + '>';
      return(v.title && JSON.stringify(v.title)) || (v['$ref'] && ('<' + v['$ref'] + '>')) || '[subschema '+i+']';
    });
    if (options.nestedErrors) {
      result.importErrors(inner);
    }
    result.addError({
      name: 'anyOf',
      argument: list,
      message: "is not any of " + list.join(','),
    });
  }
  return result;
};

/**
 * Validates whether the instance matches every given schema
 * @param instance
 * @param schema
 * @param options
 * @param ctx
 * @return {String|null}
 */
validators.allOf = function validateAllOf (instance, schema, options, ctx) {
  // Ignore undefined instances
  if (instance === undefined) {
    return null;
  }
  if (!Array.isArray(schema.allOf)){
    throw new SchemaError("allOf must be an array");
  }
  var result = new ValidatorResult(instance, schema, options, ctx);
  var self = this;
  schema.allOf.forEach(function(v, i){
    var valid = self.validateSchema(instance, v, options, ctx);
    if(!valid.valid){
      var id = v.$id || v.id;
      var msg = id || (v.title && JSON.stringify(v.title)) || (v['$ref'] && ('<' + v['$ref'] + '>')) || '[subschema '+i+']';
      result.addError({
        name: 'allOf',
        argument: { id: msg, length: valid.errors.length, valid: valid },
        message: 'does not match allOf schema ' + msg + ' with ' + valid.errors.length + ' error[s]:',
      });
      result.importErrors(valid);
    }
  });
  return result;
};

/**
 * Validates whether the instance matches exactly one of the given schemas
 * @param instance
 * @param schema
 * @param options
 * @param ctx
 * @return {String|null}
 */
validators.oneOf = function validateOneOf (instance, schema, options, ctx) {
  // Ignore undefined instances
  if (instance === undefined) {
    return null;
  }
  if (!Array.isArray(schema.oneOf)){
    throw new SchemaError("oneOf must be an array");
  }
  var result = new ValidatorResult(instance, schema, options, ctx);
  var inner = new ValidatorResult(instance, schema, options, ctx);
  var count = schema.oneOf.filter(
    testSchemaNoThrow.bind(
      this, instance, options, ctx, function(res) {inner.importErrors(res);}
    ) ).length;
  var list = schema.oneOf.map(function (v, i) {
    var id = v.$id || v.id;
    return id || (v.title && JSON.stringify(v.title)) || (v['$ref'] && ('<' + v['$ref'] + '>')) || '[subschema '+i+']';
  });
  if (count!==1) {
    if (options.nestedErrors) {
      result.importErrors(inner);
    }
    result.addError({
      name: 'oneOf',
      argument: list,
      message: "is not exactly one from " + list.join(','),
    });
  }
  return result;
};

/**
 * Validates "then" or "else" depending on the result of validating "if"
 * @param instance
 * @param schema
 * @param options
 * @param ctx
 * @return {String|null}
 */
validators.if = function validateIf (instance, schema, options, ctx) {
  // Ignore undefined instances
  if (instance === undefined) return null;
  if (!helpers.isSchema(schema.if)) throw new Error('Expected "if" keyword to be a schema');
  var ifValid = testSchemaNoThrow.call(this, instance, options, ctx, null, schema.if);
  var result = new ValidatorResult(instance, schema, options, ctx);
  var res;
  if(ifValid){
    if (schema.then === undefined) return;
    if (!helpers.isSchema(schema.then)) throw new Error('Expected "then" keyword to be a schema');
    res = this.validateSchema(instance, schema.then, options, ctx.makeChild(schema.then));
    result.importErrors(res);
  }else{
    if (schema.else === undefined) return;
    if (!helpers.isSchema(schema.else)) throw new Error('Expected "else" keyword to be a schema');
    res = this.validateSchema(instance, schema.else, options, ctx.makeChild(schema.else));
    result.importErrors(res);
  }
  return result;
};

function getEnumerableProperty(object, key){
  // Determine if `key` shows up in `for(var key in object)`
  // First test Object.hasOwnProperty.call as an optimization: that guarantees it does
  if(Object.hasOwnProperty.call(object, key)) return object[key];
  // Test `key in object` as an optimization; false means it won't
  if(!(key in object)) return;
  while( (object = Object.getPrototypeOf(object)) ){
    if(Object.propertyIsEnumerable.call(object, key)) return object[key];
  }
}

/**
 * Validates propertyNames
 * @param instance
 * @param schema
 * @param options
 * @param ctx
 * @return {String|null|ValidatorResult}
 */
validators.propertyNames = function validatePropertyNames (instance, schema, options, ctx) {
  if(!this.types.object(instance)) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  var subschema = schema.propertyNames!==undefined ? schema.propertyNames : {};
  if(!helpers.isSchema(subschema)) throw new SchemaError('Expected "propertyNames" to be a schema (object or boolean)');

  for (var property in instance) {
    if(getEnumerableProperty(instance, property) !== undefined){
      var res = this.validateSchema(property, subschema, options, ctx.makeChild(subschema));
      result.importErrors(res);
    }
  }

  return result;
};

/**
 * Validates properties
 * @param instance
 * @param schema
 * @param options
 * @param ctx
 * @return {String|null|ValidatorResult}
 */
validators.properties = function validateProperties (instance, schema, options, ctx) {
  if(!this.types.object(instance)) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  var properties = schema.properties || {};
  for (var property in properties) {
    var subschema = properties[property];
    if(subschema===undefined){
      continue;
    }else if(subschema===null){
      throw new SchemaError('Unexpected null, expected schema in "properties"');
    }
    if (typeof options.preValidateProperty == 'function') {
      options.preValidateProperty(instance, property, subschema, options, ctx);
    }
    var prop = getEnumerableProperty(instance, property);
    var res = this.validateSchema(prop, subschema, options, ctx.makeChild(subschema, property));
    if(res.instance !== result.instance[property]) result.instance[property] = res.instance;
    result.importErrors(res);
  }
  return result;
};

/**
 * Test a specific property within in instance against the additionalProperties schema attribute
 * This ignores properties with definitions in the properties schema attribute, but no other attributes.
 * If too many more types of property-existence tests pop up they may need their own class of tests (like `type` has)
 * @private
 * @return {boolean}
 */
function testAdditionalProperty (instance, schema, options, ctx, property, result) {
  if(!this.types.object(instance)) return;
  if (schema.properties && schema.properties[property] !== undefined) {
    return;
  }
  if (schema.additionalProperties === false) {
    result.addError({
      name: 'additionalProperties',
      argument: property,
      message: "is not allowed to have the additional property " + JSON.stringify(property),
    });
  } else {
    var additionalProperties = schema.additionalProperties || {};

    if (typeof options.preValidateProperty == 'function') {
      options.preValidateProperty(instance, property, additionalProperties, options, ctx);
    }

    var res = this.validateSchema(instance[property], additionalProperties, options, ctx.makeChild(additionalProperties, property));
    if(res.instance !== result.instance[property]) result.instance[property] = res.instance;
    result.importErrors(res);
  }
}

/**
 * Validates patternProperties
 * @param instance
 * @param schema
 * @param options
 * @param ctx
 * @return {String|null|ValidatorResult}
 */
validators.patternProperties = function validatePatternProperties (instance, schema, options, ctx) {
  if(!this.types.object(instance)) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  var patternProperties = schema.patternProperties || {};

  for (var property in instance) {
    var test = true;
    for (var pattern in patternProperties) {
      var subschema = patternProperties[pattern];
      if(subschema===undefined){
        continue;
      }else if(subschema===null){
        throw new SchemaError('Unexpected null, expected schema in "patternProperties"');
      }
      try {
        var regexp = new RegExp(pattern, 'u');
      } catch(_e) {
        // In the event the stricter handling causes an error, fall back on the forgiving handling
        // DEPRECATED
        regexp = new RegExp(pattern);
      }
      if (!regexp.test(property)) {
        continue;
      }
      test = false;

      if (typeof options.preValidateProperty == 'function') {
        options.preValidateProperty(instance, property, subschema, options, ctx);
      }

      var res = this.validateSchema(instance[property], subschema, options, ctx.makeChild(subschema, property));
      if(res.instance !== result.instance[property]) result.instance[property] = res.instance;
      result.importErrors(res);
    }
    if (test) {
      testAdditionalProperty.call(this, instance, schema, options, ctx, property, result);
    }
  }

  return result;
};

/**
 * Validates additionalProperties
 * @param instance
 * @param schema
 * @param options
 * @param ctx
 * @return {String|null|ValidatorResult}
 */
validators.additionalProperties = function validateAdditionalProperties (instance, schema, options, ctx) {
  if(!this.types.object(instance)) return;
  // if patternProperties is defined then we'll test when that one is called instead
  if (schema.patternProperties) {
    return null;
  }
  var result = new ValidatorResult(instance, schema, options, ctx);
  for (var property in instance) {
    testAdditionalProperty.call(this, instance, schema, options, ctx, property, result);
  }
  return result;
};

/**
 * Validates whether the instance value is at least of a certain length, when the instance value is a string.
 * @param instance
 * @param schema
 * @return {String|null}
 */
validators.minProperties = function validateMinProperties (instance, schema, options, ctx) {
  if (!this.types.object(instance)) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  var keys = Object.keys(instance);
  if (!(keys.length >= schema.minProperties)) {
    result.addError({
      name: 'minProperties',
      argument: schema.minProperties,
      message: "does not meet minimum property length of " + schema.minProperties,
    });
  }
  return result;
};

/**
 * Validates whether the instance value is at most of a certain length, when the instance value is a string.
 * @param instance
 * @param schema
 * @return {String|null}
 */
validators.maxProperties = function validateMaxProperties (instance, schema, options, ctx) {
  if (!this.types.object(instance)) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  var keys = Object.keys(instance);
  if (!(keys.length <= schema.maxProperties)) {
    result.addError({
      name: 'maxProperties',
      argument: schema.maxProperties,
      message: "does not meet maximum property length of " + schema.maxProperties,
    });
  }
  return result;
};

/**
 * Validates items when instance is an array
 * @param instance
 * @param schema
 * @param options
 * @param ctx
 * @return {String|null|ValidatorResult}
 */
validators.items = function validateItems (instance, schema, options, ctx) {
  var self = this;
  if (!this.types.array(instance)) return;
  if (schema.items===undefined) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  instance.every(function (value, i) {
    if(Array.isArray(schema.items)){
      var items =  schema.items[i]===undefined ? schema.additionalItems : schema.items[i];
    }else{
      var items = schema.items;
    }
    if (items === undefined) {
      return true;
    }
    if (items === false) {
      result.addError({
        name: 'items',
        message: "additionalItems not permitted",
      });
      return false;
    }
    var res = self.validateSchema(value, items, options, ctx.makeChild(items, i));
    if(res.instance !== result.instance[i]) result.instance[i] = res.instance;
    result.importErrors(res);
    return true;
  });
  return result;
};

/**
 * Validates the "contains" keyword
 * @param instance
 * @param schema
 * @param options
 * @param ctx
 * @return {String|null|ValidatorResult}
 */
validators.contains = function validateContains (instance, schema, options, ctx) {
  var self = this;
  if (!this.types.array(instance)) return;
  if (schema.contains===undefined) return;
  if (!helpers.isSchema(schema.contains)) throw new Error('Expected "contains" keyword to be a schema');
  var result = new ValidatorResult(instance, schema, options, ctx);
  var count = instance.some(function (value, i) {
    var res = self.validateSchema(value, schema.contains, options, ctx.makeChild(schema.contains, i));
    return res.errors.length===0;
  });
  if(count===false){
    result.addError({
      name: 'contains',
      argument: schema.contains,
      message: "must contain an item matching given schema",
    });
  }
  return result;
};

/**
 * Validates minimum and exclusiveMinimum when the type of the instance value is a number.
 * @param instance
 * @param schema
 * @return {String|null}
 */
validators.minimum = function validateMinimum (instance, schema, options, ctx) {
  if (!this.types.number(instance)) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  if (schema.exclusiveMinimum && schema.exclusiveMinimum === true) {
    if(!(instance > schema.minimum)){
      result.addError({
        name: 'minimum',
        argument: schema.minimum,
        message: "must be greater than " + schema.minimum,
      });
    }
  } else {
    if(!(instance >= schema.minimum)){
      result.addError({
        name: 'minimum',
        argument: schema.minimum,
        message: "must be greater than or equal to " + schema.minimum,
      });
    }
  }
  return result;
};

/**
 * Validates maximum and exclusiveMaximum when the type of the instance value is a number.
 * @param instance
 * @param schema
 * @return {String|null}
 */
validators.maximum = function validateMaximum (instance, schema, options, ctx) {
  if (!this.types.number(instance)) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  if (schema.exclusiveMaximum && schema.exclusiveMaximum === true) {
    if(!(instance < schema.maximum)){
      result.addError({
        name: 'maximum',
        argument: schema.maximum,
        message: "must be less than " + schema.maximum,
      });
    }
  } else {
    if(!(instance <= schema.maximum)){
      result.addError({
        name: 'maximum',
        argument: schema.maximum,
        message: "must be less than or equal to " + schema.maximum,
      });
    }
  }
  return result;
};

/**
 * Validates the number form of exclusiveMinimum when the type of the instance value is a number.
 * @param instance
 * @param schema
 * @return {String|null}
 */
validators.exclusiveMinimum = function validateExclusiveMinimum (instance, schema, options, ctx) {
  // Support the boolean form of exclusiveMinimum, which is handled by the "minimum" keyword.
  if(typeof schema.exclusiveMinimum === 'boolean') return;
  if (!this.types.number(instance)) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  var valid = instance > schema.exclusiveMinimum;
  if (!valid) {
    result.addError({
      name: 'exclusiveMinimum',
      argument: schema.exclusiveMinimum,
      message: "must be strictly greater than " + schema.exclusiveMinimum,
    });
  }
  return result;
};

/**
 * Validates the number form of exclusiveMaximum when the type of the instance value is a number.
 * @param instance
 * @param schema
 * @return {String|null}
 */
validators.exclusiveMaximum = function validateExclusiveMaximum (instance, schema, options, ctx) {
  // Support the boolean form of exclusiveMaximum, which is handled by the "maximum" keyword.
  if(typeof schema.exclusiveMaximum === 'boolean') return;
  if (!this.types.number(instance)) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  var valid = instance < schema.exclusiveMaximum;
  if (!valid) {
    result.addError({
      name: 'exclusiveMaximum',
      argument: schema.exclusiveMaximum,
      message: "must be strictly less than " + schema.exclusiveMaximum,
    });
  }
  return result;
};

/**
 * Perform validation for multipleOf and divisibleBy, which are essentially the same.
 * @param instance
 * @param schema
 * @param validationType
 * @param errorMessage
 * @returns {String|null}
 */
var validateMultipleOfOrDivisbleBy = function validateMultipleOfOrDivisbleBy (instance, schema, options, ctx, validationType, errorMessage) {
  if (!this.types.number(instance)) return;

  var validationArgument = schema[validationType];
  if (validationArgument == 0) {
    throw new SchemaError(validationType + " cannot be zero");
  }

  var result = new ValidatorResult(instance, schema, options, ctx);

  var instanceDecimals = helpers.getDecimalPlaces(instance);
  var divisorDecimals = helpers.getDecimalPlaces(validationArgument);

  var maxDecimals = Math.max(instanceDecimals , divisorDecimals);
  var multiplier = Math.pow(10, maxDecimals);

  if (Math.round(instance * multiplier) % Math.round(validationArgument * multiplier) !== 0) {
    result.addError({
      name: validationType,
      argument:  validationArgument,
      message: errorMessage + JSON.stringify(validationArgument),
    });
  }

  return result;
};

/**
 * Validates divisibleBy when the type of the instance value is a number.
 * @param instance
 * @param schema
 * @return {String|null}
 */
validators.multipleOf = function validateMultipleOf (instance, schema, options, ctx) {
  return validateMultipleOfOrDivisbleBy.call(this, instance, schema, options, ctx, "multipleOf", "is not a multiple of (divisible by) ");
};

/**
 * Validates multipleOf when the type of the instance value is a number.
 * @param instance
 * @param schema
 * @return {String|null}
 */
validators.divisibleBy = function validateDivisibleBy (instance, schema, options, ctx) {
  return validateMultipleOfOrDivisbleBy.call(this, instance, schema, options, ctx, "divisibleBy", "is not divisible by (multiple of) ");
};

/**
 * Validates whether the instance value is present.
 * @param instance
 * @param schema
 * @return {String|null}
 */
validators.required = function validateRequired (instance, schema, options, ctx) {
  var result = new ValidatorResult(instance, schema, options, ctx);
  if (instance === undefined && schema.required === true) {
    // A boolean form is implemented for reverse-compatibility with schemas written against older drafts
    result.addError({
      name: 'required',
      message: "is required",
    });
  } else if (this.types.object(instance) && Array.isArray(schema.required)) {
    schema.required.forEach(function(n){
      if(getEnumerableProperty(instance, n)===undefined){
        result.addError({
          name: 'required',
          argument: n,
          message: "requires property " + JSON.stringify(n),
        });
      }
    });
  }
  return result;
};

/**
 * Validates whether the instance value matches the regular expression, when the instance value is a string.
 * @param instance
 * @param schema
 * @return {String|null}
 */
validators.pattern = function validatePattern (instance, schema, options, ctx) {
  if (!this.types.string(instance)) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  var pattern = schema.pattern;
  try {
    var regexp = new RegExp(pattern, 'u');
  } catch(_e) {
    // In the event the stricter handling causes an error, fall back on the forgiving handling
    // DEPRECATED
    regexp = new RegExp(pattern);
  }
  if (!instance.match(regexp)) {
    result.addError({
      name: 'pattern',
      argument: schema.pattern,
      message: "does not match pattern " + JSON.stringify(schema.pattern.toString()),
    });
  }
  return result;
};

/**
 * Validates whether the instance value is of a certain defined format or a custom
 * format.
 * The following formats are supported for string types:
 *   - date-time
 *   - date
 *   - time
 *   - ip-address
 *   - ipv6
 *   - uri
 *   - color
 *   - host-name
 *   - alpha
 *   - alpha-numeric
 *   - utc-millisec
 * @param instance
 * @param schema
 * @param [options]
 * @param [ctx]
 * @return {String|null}
 */
validators.format = function validateFormat (instance, schema, options, ctx) {
  if (instance===undefined) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  if (!result.disableFormat && !helpers.isFormat(instance, schema.format, this)) {
    result.addError({
      name: 'format',
      argument: schema.format,
      message: "does not conform to the " + JSON.stringify(schema.format) + " format",
    });
  }
  return result;
};

/**
 * Validates whether the instance value is at least of a certain length, when the instance value is a string.
 * @param instance
 * @param schema
 * @return {String|null}
 */
validators.minLength = function validateMinLength (instance, schema, options, ctx) {
  if (!this.types.string(instance)) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  var hsp = instance.match(/[\uDC00-\uDFFF]/g);
  var length = instance.length - (hsp ? hsp.length : 0);
  if (!(length >= schema.minLength)) {
    result.addError({
      name: 'minLength',
      argument: schema.minLength,
      message: "does not meet minimum length of " + schema.minLength,
    });
  }
  return result;
};

/**
 * Validates whether the instance value is at most of a certain length, when the instance value is a string.
 * @param instance
 * @param schema
 * @return {String|null}
 */
validators.maxLength = function validateMaxLength (instance, schema, options, ctx) {
  if (!this.types.string(instance)) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  // TODO if this was already computed in "minLength", use that value instead of re-computing
  var hsp = instance.match(/[\uDC00-\uDFFF]/g);
  var length = instance.length - (hsp ? hsp.length : 0);
  if (!(length <= schema.maxLength)) {
    result.addError({
      name: 'maxLength',
      argument: schema.maxLength,
      message: "does not meet maximum length of " + schema.maxLength,
    });
  }
  return result;
};

/**
 * Validates whether instance contains at least a minimum number of items, when the instance is an Array.
 * @param instance
 * @param schema
 * @return {String|null}
 */
validators.minItems = function validateMinItems (instance, schema, options, ctx) {
  if (!this.types.array(instance)) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  if (!(instance.length >= schema.minItems)) {
    result.addError({
      name: 'minItems',
      argument: schema.minItems,
      message: "does not meet minimum length of " + schema.minItems,
    });
  }
  return result;
};

/**
 * Validates whether instance contains no more than a maximum number of items, when the instance is an Array.
 * @param instance
 * @param schema
 * @return {String|null}
 */
validators.maxItems = function validateMaxItems (instance, schema, options, ctx) {
  if (!this.types.array(instance)) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  if (!(instance.length <= schema.maxItems)) {
    result.addError({
      name: 'maxItems',
      argument: schema.maxItems,
      message: "does not meet maximum length of " + schema.maxItems,
    });
  }
  return result;
};

/**
 * Deep compares arrays for duplicates
 * @param v
 * @param i
 * @param a
 * @private
 * @return {boolean}
 */
function testArrays (v, i, a) {
  var j, len = a.length;
  for (j = i + 1, len; j < len; j++) {
    if (helpers.deepCompareStrict(v, a[j])) {
      return false;
    }
  }
  return true;
}

/**
 * Validates whether there are no duplicates, when the instance is an Array.
 * @param instance
 * @return {String|null}
 */
validators.uniqueItems = function validateUniqueItems (instance, schema, options, ctx) {
  if (schema.uniqueItems!==true) return;
  if (!this.types.array(instance)) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  if (!instance.every(testArrays)) {
    result.addError({
      name: 'uniqueItems',
      message: "contains duplicate item",
    });
  }
  return result;
};

/**
 * Validate for the presence of dependency properties, if the instance is an object.
 * @param instance
 * @param schema
 * @param options
 * @param ctx
 * @return {null|ValidatorResult}
 */
validators.dependencies = function validateDependencies (instance, schema, options, ctx) {
  if (!this.types.object(instance)) return;
  var result = new ValidatorResult(instance, schema, options, ctx);
  for (var property in schema.dependencies) {
    if (instance[property] === undefined) {
      continue;
    }
    var dep = schema.dependencies[property];
    var childContext = ctx.makeChild(dep, property);
    if (typeof dep == 'string') {
      dep = [dep];
    }
    if (Array.isArray(dep)) {
      dep.forEach(function (prop) {
        if (instance[prop] === undefined) {
          result.addError({
            // FIXME there's two different "dependencies" errors here with slightly different outputs
            // Can we make these the same? Or should we create different error types?
            name: 'dependencies',
            argument: childContext.propertyPath,
            message: "property " + prop + " not found, required by " + childContext.propertyPath,
          });
        }
      });
    } else {
      var res = this.validateSchema(instance, dep, options, childContext);
      if(result.instance !== res.instance) result.instance = res.instance;
      if (res && res.errors.length) {
        result.addError({
          name: 'dependencies',
          argument: childContext.propertyPath,
          message: "does not meet dependency required by " + childContext.propertyPath,
        });
        result.importErrors(res);
      }
    }
  }
  return result;
};

/**
 * Validates whether the instance value is one of the enumerated values.
 *
 * @param instance
 * @param schema
 * @return {ValidatorResult|null}
 */
validators['enum'] = function validateEnum (instance, schema, options, ctx) {
  if (instance === undefined) {
    return null;
  }
  if (!Array.isArray(schema['enum'])) {
    throw new SchemaError("enum expects an array", schema);
  }
  var result = new ValidatorResult(instance, schema, options, ctx);
  if (!schema['enum'].some(helpers.deepCompareStrict.bind(null, instance))) {
    result.addError({
      name: 'enum',
      argument: schema['enum'],
      message: "is not one of enum values: " + schema['enum'].map(String).join(','),
    });
  }
  return result;
};

/**
 * Validates whether the instance exactly matches a given value
 *
 * @param instance
 * @param schema
 * @return {ValidatorResult|null}
 */
validators['const'] = function validateEnum (instance, schema, options, ctx) {
  if (instance === undefined) {
    return null;
  }
  var result = new ValidatorResult(instance, schema, options, ctx);
  if (!helpers.deepCompareStrict(schema['const'], instance)) {
    result.addError({
      name: 'const',
      argument: schema['const'],
      message: "does not exactly match expected constant: " + schema['const'],
    });
  }
  return result;
};

/**
 * Validates whether the instance if of a prohibited type.
 * @param instance
 * @param schema
 * @param options
 * @param ctx
 * @return {null|ValidatorResult}
 */
validators.not = validators.disallow = function validateNot (instance, schema, options, ctx) {
  var self = this;
  if(instance===undefined) return null;
  var result = new ValidatorResult(instance, schema, options, ctx);
  var notTypes = schema.not || schema.disallow;
  if(!notTypes) return null;
  if(!Array.isArray(notTypes)) notTypes=[notTypes];
  notTypes.forEach(function (type) {
    if (self.testType(instance, schema, options, ctx, type)) {
      var id = type && (type.$id || type.id);
      var schemaId = id || type;
      result.addError({
        name: 'not',
        argument: schemaId,
        message: "is of prohibited type " + schemaId,
      });
    }
  });
  return result;
};

#EXPORT validators