feat: implements decoder and payload validator (#8)

* feat(helpers): adds Filter helper

* feat(parser): implements new struct methods

- `GetTag(reflect.StructField, string) map[string]string`
- `SetValuesFromMap(any, map[string]any)`
- `SetValuesFromBytes(any, []byte)`
- `RemoveValuesFromTag(string, []string, reflect.StructField) string`

* feat(structs): implements Decode() function

- adds `Decode([]byte, any, DecoderOptions) map[string][]string`

* feat(validators): implements ValidatePayload() function

- adds `ValidatePayload([]byte, any, ValidationOptions) map[string][]string`

go.mod

@@ -4,5 +4,13 @@ go 1.18
 
 require (
 	github.com/google/uuid v1.3.0
+	github.com/invopop/jsonschema v0.7.0
+	github.com/xeipuuv/gojsonschema v1.2.0
 	golang.org/x/text v0.4.0
 )
+
+require (
+	github.com/iancoleman/orderedmap v0.0.0-20190318233801-ac98e3ecb4b0 // indirect
+	github.com/xeipuuv/gojsonpointer v0.0.0-20180127040702-4e3ac2762d5f // indirect
+	github.com/xeipuuv/gojsonreference v0.0.0-20180127040603-bd5ef7bd5415 // indirect
+)

go.sum

@@ -1,4 +1,22 @@
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/google/uuid v1.3.0 h1:t6JiXgmwXMjEs8VusXIJk2BXHsn+wx8BZdTaoZ5fu7I=
 github.com/google/uuid v1.3.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/iancoleman/orderedmap v0.0.0-20190318233801-ac98e3ecb4b0 h1:i462o439ZjprVSFSZLZxcsoAe592sZB1rci2Z8j4wdk=
+github.com/iancoleman/orderedmap v0.0.0-20190318233801-ac98e3ecb4b0/go.mod h1:N0Wam8K1arqPXNWjMo21EXnBPOPp36vB07FNRdD2geA=
+github.com/invopop/jsonschema v0.7.0 h1:2vgQcBz1n256N+FpX3Jq7Y17AjYt46Ig3zIWyy770So=
+github.com/invopop/jsonschema v0.7.0/go.mod h1:O9uiLokuu0+MGFlyiaqtWxwqJm41/+8Nj0lD7A36YH0=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
+github.com/stretchr/testify v1.3.1-0.20190311161405-34c6fa2dc709 h1:Ko2LQMrRU+Oy/+EDBwX7eZ2jp3C47eDBB8EIhKTun+I=
+github.com/stretchr/testify v1.3.1-0.20190311161405-34c6fa2dc709/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
+github.com/xeipuuv/gojsonpointer v0.0.0-20180127040702-4e3ac2762d5f h1:J9EGpcZtP0E/raorCMxlFGSTBrsSlaDGf3jU/qvAE2c=
+github.com/xeipuuv/gojsonpointer v0.0.0-20180127040702-4e3ac2762d5f/go.mod h1:N2zxlSyiKSe5eX1tZViRH5QA0qijqEDrYZiPEAiq3wU=
+github.com/xeipuuv/gojsonreference v0.0.0-20180127040603-bd5ef7bd5415 h1:EzJWgHovont7NscjpAxXsDA8S8BMYve8Y5+7cuRE7R0=
+github.com/xeipuuv/gojsonreference v0.0.0-20180127040603-bd5ef7bd5415/go.mod h1:GwrjFmJcFw6At/Gs6z4yjiIwzuJ1/+UwLxMQDVQXShQ=
+github.com/xeipuuv/gojsonschema v1.2.0 h1:LhYJRs+L4fBtjZUfuSZIKGeVu0QRy8e5Xi7D17UxZ74=
+github.com/xeipuuv/gojsonschema v1.2.0/go.mod h1:anYRn/JVcOK2ZgGU+IjEV4nwlhoK5sQluxsYJ78Id3Y=
 golang.org/x/text v0.4.0 h1:BrVqGRd7+k1DiOgtnFvAkoQEWQvBc25ouMJM6429SFg=
 golang.org/x/text v0.4.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=

structs/decoder.go

@@ -0,0 +1,162 @@
+package structs
+
+import (
+	"regexp"
+	"strings"
+
+	"github.com/invopop/jsonschema"
+	"github.com/xeipuuv/gojsonschema"
+)
+
+type SchemaValidationRule string
+
+type DecoderOptions struct {
+	// Set of rules that should be checked when validation the provided data against the Go struct.
+	Rules []SchemaValidationRule
+
+	// A function that runs before the decoder starts processing the data.
+	// This could be used for setting/unsetting values in the provided bytes array.
+	BeforeHook func(data []byte, model any) []byte
+
+	// A function that runs after the decoder is done processing the data.
+	// This could be used for ignoring certain errors or providing custom error messages.
+	AfterHook func(validations map[string][]string) map[string][]string
+}
+
+const (
+	ADDITIONAL_PROPERTY SchemaValidationRule = "additional_property_not_allowed"
+	REQUIRED_ATTRIBUTE  SchemaValidationRule = "required"
+	INVALID_TYPE        SchemaValidationRule = "invalid_type"
+)
+
+var DecodingErrors = map[string]string{
+	"required":                        "REQUIRED_ATTRIBUTE_MISSING",
+	"invalid_payload":                 "INVALID_PAYLOAD",
+	"invalid_type":                    "INVALID_TYPE",
+	"additional_property_not_allowed": "ADDITIONAL_PROPERTY",
+}
+
+// Replacement for the standard `json.Unmarshal` implementation.
+// It deserializes a JSON object into a Go struct. This function does not
+// Panic when the value for a JSON field is incompatible with the type set in the struct.
+//
+// You're allowed to pass a list of `SchemaValidationType` to use while deserializing the JSON payload
+// into your struct. They are:
+// 	- `ATTRIBUTE_MUST_BE_PRESENT`:
+// checks if a required field is absent from the JSON payload.
+// 	- `ADDITIONAL_PROPERTY`:
+// checks if an unknown field was passed in the JSON payload.
+// 	- `INVALID_TYPE`:
+// checks if the type of a JSON attribute in the payload is compatible with the underlying type of the Go struct field.
+//
+//
+// Usage:
+//
+// 	type User struct {
+//		Id 	   int 		`json:"id"`
+//		Name   string 	`json:"name" validate:"is_present"`
+//		Emails []string	`json:"emails,omitempty"`
+//	}
+//
+//	payload := []byte(`{"name": 42, "emails": ["[email protected]", 0]}`)
+// 	parsedValues, errs := Decode(payload, User{}, options)
+//	/*
+//	expected errors:
+// 	[
+//		"id - REQUIRED_ATTRIBUTE_MISSING",
+// 		"name - INVALID_DATA_TYPE",
+// 		"emails[1] - INVALID_DATA_TYPE"
+// 	]
+//	*/
+func Decode(data []byte, model any, options DecoderOptions) map[string][]string {
+	validations := make(map[string][]string, 0)
+
+	if options.BeforeHook != nil {
+		data = options.BeforeHook(data, model)
+	}
+
+	SetValuesFromBytes(model, data)
+
+	afterFunc := func(validations map[string][]string) map[string][]string {
+		return validations
+	}
+
+	if options.AfterHook != nil {
+		afterFunc = options.AfterHook
+	}
+
+	if len(data) == 0 || len(options.Rules) == 0 {
+		return afterFunc(validations)
+	}
+
+	reflector := new(jsonschema.Reflector)
+	reflector.RequiredFromJSONSchemaTags = true
+	reflector.AllowAdditionalProperties = !Contains(options.Rules, ADDITIONAL_PROPERTY)
+
+	schema := reflector.Reflect(model)
+	decoded, _ := schema.MarshalJSON()
+
+	result, verr := gojsonschema.Validate(
+		gojsonschema.NewBytesLoader(decoded),
+		gojsonschema.NewBytesLoader(data),
+	)
+
+	if verr != nil {
+		validations["_"] = []string{DecodingErrors["invalid_payload"]}
+		return afterFunc(validations)
+	}
+
+	res := Filter(result.Errors(), func(index int, err gojsonschema.ResultError) bool {
+		return Contains(options.Rules, SchemaValidationRule(err.Type()))
+	})
+
+	for _, err := range res {
+		name := jsonAttributeName(err.String())
+		normalizedName := regexp.MustCompile(`\[\d+\]`).ReplaceAllString(name, "")
+		validations[normalizedName] = []string{DecodingErrors[err.Type()]}
+	}
+
+	return afterFunc(validations)
+}
+
+func jsonAttributeName(str string) string {
+	pattern := regexp.MustCompile(`\.([0-9]+)`)
+	scope := strings.Split(str, ": ")[0]
+	scope = pattern.ReplaceAllString(scope, "[$1]")
+
+	if scope == "(root)" {
+		scope = ""
+	}
+
+	if strings.Contains(str, "Additional property") {
+		/*
+			format:
+			- (root): Additional property extra is not allowed
+		*/
+		p := regexp.MustCompile(`Additional property (.*) is not allowed`)
+		name := p.FindStringSubmatch(str)[1]
+		return name
+	}
+
+	if strings.Contains(str, "required") {
+		/*
+			format:
+				- (root): field_name is required
+				- parent.0: field_name is required
+		*/
+		str = pattern.ReplaceAllString(str, "[$1]")
+		name := strings.Split(strings.Trim(strings.SplitAfter(str, ":")[1], " "), " ")
+		return strings.TrimPrefix(strings.Join([]string{scope, name[0]}, "."), ".")
+	}
+
+	if strings.Contains(str, "Invalid type") {
+		/*
+			for format:
+				- field_name. Expected: typeA, given: typeB
+				- field_name.0. Expected: typeA, given: typeB
+		*/
+		return scope
+	}
+
+	return str
+}