add validators

+package revel
+
+import (
+	"fmt"
+	"reflect"
+	"regexp"
+	"time"
+)
+
+type Validator interface {
+	IsSatisfied(interface{}) bool
+	DefaultMessage() string
+}
+
+type Required struct{}
+
+func (r Required) IsSatisfied(obj interface{}) bool {
+	if obj == nil {
+		return false
+	}
+
+	if str, ok := obj.(string); ok {
+		return len(str) > 0
+	}
+	if b, ok := obj.(bool); ok {
+		return b
+	}
+	if i, ok := obj.(int); ok {
+		return i != 0
+	}
+	if t, ok := obj.(time.Time); ok {
+		return !t.IsZero()
+	}
+	v := reflect.ValueOf(obj)
+	if v.Kind() == reflect.Slice {
+		return v.Len() > 0
+	}
+	return true
+}
+
+func (r Required) DefaultMessage() string {
+	return "Required"
+}
+
+// TODO
+// type Unique struct {}
+
+type Min struct {
+	Min int
+}
+
+func (m Min) IsSatisfied(obj interface{}) bool {
+	num, ok := obj.(int)
+	if ok {
+		return num >= m.Min
+	}
+	return false
+}
+
+func (m Min) DefaultMessage() string {
+	return fmt.Sprintln("Minimum is", m.Min)
+}
+
+type Max struct {
+	Max int
+}
+
+func (m Max) IsSatisfied(obj interface{}) bool {
+	num, ok := obj.(int)
+	if ok {
+		return num <= m.Max
+	}
+	return false
+}
+
+func (m Max) DefaultMessage() string {
+	return fmt.Sprintln("Maximum is", m.Max)
+}
+
+// Requires an integer to be within Min, Max inclusive.
+type Range struct {
+	Min
+	Max
+}
+
+func (r Range) IsSatisfied(obj interface{}) bool {
+	return r.Min.IsSatisfied(obj) && r.Max.IsSatisfied(obj)
+}
+
+func (r Range) DefaultMessage() string {
+	return fmt.Sprintln("Range is", r.Min.Min, "to", r.Max.Max)
+}
+
+// Requires an array or string to be at least a given length.
+type MinSize struct {
+	Min int
+}
+
+func (m MinSize) IsSatisfied(obj interface{}) bool {
+	if str, ok := obj.(string); ok {
+		return len(str) >= m.Min
+	}
+	v := reflect.ValueOf(obj)
+	if v.Kind() == reflect.Slice {
+		return v.Len() >= m.Min
+	}
+	return false
+}
+
+func (m MinSize) DefaultMessage() string {
+	return fmt.Sprintln("Minimum size is", m.Min)
+}
+
+// Requires an array or string to be at most a given length.
+type MaxSize struct {
+	Max int
+}
+
+func (m MaxSize) IsSatisfied(obj interface{}) bool {
+	if str, ok := obj.(string); ok {
+		return len(str) <= m.Max
+	}
+	v := reflect.ValueOf(obj)
+	if v.Kind() == reflect.Slice {
+		return v.Len() <= m.Max
+	}
+	return false
+}
+
+func (m MaxSize) DefaultMessage() string {
+	return fmt.Sprintln("Maximum size is", m.Max)
+}
+
+// Requires an array or string to be exactly a given length.
+type Length struct {
+	N int
+}
+
+func (s Length) IsSatisfied(obj interface{}) bool {
+	if str, ok := obj.(string); ok {
+		return len(str) == s.N
+	}
+	v := reflect.ValueOf(obj)
+	if v.Kind() == reflect.Slice {
+		return v.Len() == s.N
+	}
+	return false
+}
+
+func (s Length) DefaultMessage() string {
+	return fmt.Sprintln("Required length is", s.N)
+}
+
+type Alpha struct{}
+
+func (a Alpha) IsSatisfied(obj interface{}) bool {
+	if str, ok := obj.(string); ok {
+		for _, v := range str {
+			if ('Z' < v || v < 'A') && ('z' < v || v < 'a') {
+				return false
+			}
+		}
+	}
+	return false
+}
+
+func (a Alpha) DefaultMessage() string {
+	return fmt.Sprintln("Must be valid alpha characters")
+}
+
+type Numeric struct{}
+
+func (n Numeric) IsSatisfied(obj interface{}) bool {
+	if str, ok := obj.(string); ok {
+		for _, v := range str {
+			if '9' < v || v < '0' {
+				return false
+			}
+		}
+	}
+	return false
+}
+
+func (n Numeric) DefaultMessage() string {
+	return fmt.Sprintln("Must be valid numeric characters")
+}
+
+type AlphaNumeric struct{}
+
+func (a AlphaNumeric) IsSatisfied(obj interface{}) bool {
+	if str, ok := obj.(string); ok {
+		for _, v := range str {
+			if ('Z' < v || v < 'A') && ('z' < v || v < 'a') && ('9' < v || v < '0') {
+				return false
+			}
+		}
+	}
+	return false
+}
+
+func (a AlphaNumeric) DefaultMessage() string {
+	return fmt.Sprintln("Must be valid alpha or numeric characters")
+}
+
+// Requires a string to match a given regex.
+type Match struct {
+	Regexp *regexp.Regexp
+}
+
+func (m Match) IsSatisfied(obj interface{}) bool {
+	str := obj.(string)
+	return m.Regexp.MatchString(str)
+}
+
+func (m Match) DefaultMessage() string {
+	return fmt.Sprintln("Must match", m.Regexp)
+}
+
+// Requires a string to not match a given regex.
+type NoMatch struct {
+	Match
+}
+
+func (m NoMatch) IsSatisfied(obj interface{}) bool {
+	return !m.Match.IsSatisfied(obj)
+}
+
+func (m NoMatch) DefaultMessage() string {
+	return fmt.Sprintln("Must no match", m.Regexp)
+}
+
+var alphaDashPattern = regexp.MustCompile("[^\\d\\w-_]")
+
+type AlphaDash struct {
+	NoMatch
+}
+
+func (a AlphaDash) DefaultMessage() string {
+	return fmt.Sprintln("Must be valid characters")
+}
+
+var emailPattern = regexp.MustCompile("[\\w!#$%&'*+/=?^_`{|}~-]+(?:\\.[\\w!#$%&'*+/=?^_`{|}~-]+)*@(?:[\\w](?:[\\w-]*[\\w])?\\.)+[a-zA-Z0-9](?:[\\w-]*[\\w])?")
+
+type Email struct {
+	Match
+}
+
+func (e Email) DefaultMessage() string {
+	return fmt.Sprintln("Must be a valid email address")
+}
+
+var ipPattern = regexp.MustCompile("((2[0-4]\\d|25[0-5]|[01]?\\d\\d?)\\.){3}(2[0-4]\\d|25[0-5]|[01]?\\d\\d?)")
+
+type IP struct {
+	Match
+}
+
+func (i IP) DefaultMessage() string {
+	return fmt.Sprintln("Must be a valid ip address")
+}
+
+var base64Pattern = regexp.MustCompile("^(?:[A-Za-z0-99+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=)?$")
+
+type Base64 struct {
+	Match
+}
+
+func (b Base64) DefaultMessage() string {
+	return fmt.Sprintln("Must be valid base64 characters")
+}