Min length checker added. (#32)

Fixes #15

README.md

@@ -66,5 +66,6 @@ type Person struct {
 
 This package currently provides the following checkers:
 
+- [min-length](doc/checkers/minlength.md) checks if the length of the given value is greather than the given minimum length.
 - [required](doc/checkers/required.md) checks if the required value is provided.
 - [same](doc/checkers/same.md) checks if the given value is equal to the value of the field with the given name.

checker.go

@@ -31,8 +31,9 @@ const ResultValid Result = "VALID"
 
 // makers provides mapping to maker function for the checkers.
 var makers = map[string]MakeFunc{
-	"required": makeRequired,
-	"same":     makeSame,
+	CheckerMinLength: makeMinLength,
+	CheckerRequired:  makeRequired,
+	CheckerSame:      makeSame,
 }
 
 // Register registers the given checker name and the maker function.

doc/checkers/minlength.md

@@ -0,0 +1,32 @@
+# Min Length Checker
+
+The ```min-length``` checker checks if the length of the given value is greather than the given minimum length. If the length of the value is below the minimum length, the checker will return the ```NOT_MIN_LENGTH``` result. Here is an example:
+
+```golang
+type User struct {
+  Password string `checkers:"min-length:4"`
+}
+
+user := &User{
+  Password: "1234",
+}
+
+mistakes, valid := Check(user)
+if !valid {
+  // Send the mistakes back to the user
+}
+```
+
+The checker can be applied to all types that are supported by the [reflect.Value.Len()](https://pkg.go.dev/reflect#Value.Len) function.
+
+If you do not want to validate user input stored in a struct, you can individually call the ```min-length``` checker function ```IsMinLength``` to validate the user input. Here is an example:
+
+```golang
+s := "1234"
+
+result := IsMinLength(s, 4)
+
+if result != ResultValid {
+  // Send the mistakes back to the user
+}
+```

minlenght.go

@@ -0,0 +1,39 @@
+package checker
+
+import (
+	"reflect"
+	"strconv"
+)
+
+// CheckerMinLength is the name of the checker.
+const CheckerMinLength = "min-length"
+
+// ResultNotMinLength indicates that the length of the given value is below the defined number.
+const ResultNotMinLength = "NOT_MIN_LENGTH"
+
+// IsMinLength checks if the length of the given value is greather than the given minimum length.
+func IsMinLength(value interface{}, minLength int) Result {
+	return checkMinLength(reflect.Indirect(reflect.ValueOf(value)), reflect.ValueOf(nil), minLength)
+}
+
+// makeMinLength makes a checker function for the min length checker.
+func makeMinLength(config string) CheckFunc {
+	minLength, err := strconv.Atoi(config)
+	if err != nil {
+		panic("unable to parse min length value")
+	}
+
+	return func(value, parent reflect.Value) Result {
+		return checkMinLength(value, parent, minLength)
+	}
+}
+
+// checkMinLength checks if the length of the given value is greather than the given minimum length.
+// The function uses the reflect.Value.Len() function to determine the length of the value.
+func checkMinLength(value, _ reflect.Value, minLength int) Result {
+	if value.Len() < minLength {
+		return ResultNotMinLength
+	}
+
+	return ResultValid
+}

minlength_test.go

@@ -0,0 +1,57 @@
+package checker
+
+import "testing"
+
+func TestIsMinLengthValid(t *testing.T) {
+	s := "1234"
+
+	if IsMinLength(s, 4) != ResultValid {
+		t.Fail()
+	}
+}
+
+func TestCheckMinLengthInvalidConfig(t *testing.T) {
+	defer func() {
+		if r := recover(); r == nil {
+			t.Fail()
+		}
+	}()
+
+	type User struct {
+		Password string `checkers:"min-length:AB"`
+	}
+
+	user := &User{}
+
+	Check(user)
+}
+
+func TestCheckMinLengthValid(t *testing.T) {
+	type User struct {
+		Password string `checkers:"min-length:4"`
+	}
+
+	user := &User{
+		Password: "1234",
+	}
+
+	_, valid := Check(user)
+	if !valid {
+		t.Fail()
+	}
+}
+
+func TestCheckMinLengthInvalid(t *testing.T) {
+	type User struct {
+		Password string `checkers:"min-length:4"`
+	}
+
+	user := &User{
+		Password: "12",
+	}
+
+	_, valid := Check(user)
+	if valid {
+		t.Fail()
+	}
+}

required.go

@@ -2,6 +2,9 @@ package checker
 
 import "reflect"
 
+// CheckerRequired is the name of the checker.
+const CheckerRequired = "required"
+
 // ResultRequired indicates that the required value is missing.
 const ResultRequired Result = "REQUIRED"
 

same.go

@@ -4,6 +4,9 @@ import (
 	"reflect"
 )
 
+// CheckerSame is the name of the checker.
+const CheckerSame = "same"
+
 // ResultNotSame indicates that the given two values are not equal to each other.
 const ResultNotSame = "NOT_SAME"