Add validator lib

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

pkg/validator/validation.go

@@ -0,0 +1,149 @@
+// Copyright (c) 2025 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package validator
+
+import (
+	"fmt"
+	"reflect"
+)
+
+type Validator struct {
+	errors ValidationErrors
+}
+
+func New() *Validator {
+	return &Validator{
+		errors: ValidationErrors{},
+	}
+}
+
+func (v *Validator) Check(value any, field string, validators ...ValidatorFunc) {
+	if len(validators) == 0 {
+		return
+	}
+
+	// Dereference pointer values to get the actual value for validation
+	actualValue := value
+	if value != nil {
+		val := reflect.ValueOf(value)
+		// Dereference all pointer levels
+		for val.Kind() == reflect.Ptr && !val.IsNil() {
+			val = val.Elem()
+			actualValue = val.Interface()
+		}
+		// If we ended up with a nil pointer at any level, set actualValue to nil
+		if val.Kind() == reflect.Ptr && val.IsNil() {
+			actualValue = nil
+		}
+	}
+
+	for _, validator := range validators {
+		if err := validator(actualValue); err != nil {
+			v.errors = append(v.errors, &ValidationError{
+				Field:   field,
+				Code:    err.Code,
+				Message: err.Message,
+				Value:   value,
+			})
+		}
+	}
+}
+
+func (v *Validator) CheckEach(items any, field string, fn func(index int, item any)) {
+	if items == nil {
+		return
+	}
+
+	if slice, ok := items.([]any); ok {
+		for i, item := range slice {
+			fn(i, item)
+		}
+		return
+	}
+
+	val := reflect.ValueOf(items)
+	// Dereference pointer levels to get to the actual slice
+	for val.Kind() == reflect.Ptr {
+		if val.IsNil() {
+			return
+		}
+		val = val.Elem()
+	}
+
+	if val.Kind() != reflect.Slice {
+		v.errors = append(v.errors, &ValidationError{
+			Field:   field,
+			Code:    ErrorCodeInvalidFormat,
+			Message: "expected a slice",
+			Value:   items,
+		})
+		return
+	}
+
+	for i := 0; i < val.Len(); i++ {
+		fn(i, val.Index(i).Interface())
+	}
+}
+
+func (v *Validator) CheckNested(field string, fn func(v *Validator)) {
+	nestedValidator := New()
+	fn(nestedValidator)
+
+	for _, err := range nestedValidator.errors {
+		prefixedErr := &ValidationError{
+			Field:   fmt.Sprintf("%s.%s", field, err.Field),
+			Code:    err.Code,
+			Message: err.Message,
+			Value:   err.Value,
+		}
+		v.errors = append(v.errors, prefixedErr)
+	}
+}
+
+func (v *Validator) HasErrors() bool {
+	return len(v.errors) > 0
+}
+
+func (v *Validator) Errors() ValidationErrors {
+	return v.errors
+}
+
+func (v *Validator) Error() error {
+	if len(v.errors) == 0 {
+		return nil
+	}
+	return v.errors
+}
+
+type ValidatorFunc func(value any) *ValidationError
+
+// dereferenceValue recursively dereferences all pointer levels.
+// Returns the final dereferenced value and a boolean indicating if any pointer in the chain was nil.
+func dereferenceValue(value any) (any, bool) {
+	if value == nil {
+		return nil, true
+	}
+
+	val := reflect.ValueOf(value)
+	// Dereference all pointer levels
+	for val.Kind() == reflect.Ptr {
+		if val.IsNil() {
+			return nil, true
+		}
+		val = val.Elem()
+	}
+
+	return val.Interface(), false
+}