Add validator lib

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

pkg/validator/validator_common.go

@@ -0,0 +1,71 @@
+// 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 (
+	"reflect"
+	"strings"
+)
+
+// Required validates that a field has a value.
+// For strings, it also checks that the value is not empty or just whitespace.
+// For slices, it checks that the slice is not empty.
+func Required() ValidatorFunc {
+	return func(value any) *ValidationError {
+		actualValue, isNil := dereferenceValue(value)
+		if isNil {
+			return newValidationError(ErrorCodeRequired, "field is required")
+		}
+
+		switch v := actualValue.(type) {
+		case string:
+			if strings.TrimSpace(v) == "" {
+				return newValidationError(ErrorCodeRequired, "field is required")
+			}
+		default:
+			rv := reflect.ValueOf(actualValue)
+			if rv.Kind() == reflect.Slice && rv.Len() == 0 {
+				return newValidationError(ErrorCodeRequired, "field is required")
+			}
+		}
+
+		return nil
+	}
+}
+
+// NotEmpty validates that a field is not empty.
+// Similar to Required, but can be used independently.
+func NotEmpty() ValidatorFunc {
+	return func(value any) *ValidationError {
+		actualValue, isNil := dereferenceValue(value)
+		if isNil {
+			return nil
+		}
+
+		switch v := actualValue.(type) {
+		case string:
+			if strings.TrimSpace(v) == "" {
+				return newValidationError(ErrorCodeRequired, "field cannot be empty")
+			}
+		default:
+			rv := reflect.ValueOf(actualValue)
+			if rv.Kind() == reflect.Slice && rv.Len() == 0 {
+				return newValidationError(ErrorCodeRequired, "field cannot be empty")
+			}
+		}
+
+		return nil
+	}
+}