Add validator lib

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

pkg/validator/validator_collection.go

@@ -0,0 +1,109 @@
+// 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"
+)
+
+// MinItems validates that a slice or array has at least the specified minimum number of items.
+func MinItems(min int) ValidatorFunc {
+	return func(value any) *ValidationError {
+		v := reflect.ValueOf(value)
+		if v.Kind() == reflect.Ptr {
+			if v.IsNil() {
+				return nil
+			}
+			v = v.Elem()
+		}
+
+		if v.Kind() != reflect.Slice && v.Kind() != reflect.Array {
+			return newValidationError(ErrorCodeInvalidFormat, "value must be a slice or array")
+		}
+
+		if v.Len() < min {
+			return newValidationError(
+				ErrorCodeOutOfRange,
+				fmt.Sprintf("must contain at least %d items", min),
+			)
+		}
+
+		return nil
+	}
+}
+
+// MaxItems validates that a slice or array does not exceed the specified maximum number of items.
+func MaxItems(max int) ValidatorFunc {
+	return func(value any) *ValidationError {
+		v := reflect.ValueOf(value)
+		if v.Kind() == reflect.Ptr {
+			if v.IsNil() {
+				return nil
+			}
+			v = v.Elem()
+		}
+
+		if v.Kind() != reflect.Slice && v.Kind() != reflect.Array {
+			return newValidationError(ErrorCodeInvalidFormat, "value must be a slice or array")
+		}
+
+		if v.Len() > max {
+			return newValidationError(
+				ErrorCodeOutOfRange,
+				fmt.Sprintf("must contain at most %d items", max),
+			)
+		}
+
+		return nil
+	}
+}
+
+// UniqueItems validates that all items in a slice or array are unique.
+func UniqueItems() ValidatorFunc {
+	return func(value any) *ValidationError {
+		v := reflect.ValueOf(value)
+		if v.Kind() == reflect.Ptr {
+			if v.IsNil() {
+				return nil
+			}
+			v = v.Elem()
+		}
+
+		if v.Kind() != reflect.Slice && v.Kind() != reflect.Array {
+			return newValidationError(ErrorCodeInvalidFormat, "value must be a slice or array")
+		}
+
+		if v.Len() == 0 {
+			return nil
+		}
+
+		elemType := v.Type().Elem()
+		if !elemType.Comparable() {
+			return newValidationError(ErrorCodeInvalidFormat, "cannot validate uniqueness for non-comparable types")
+		}
+
+		seen := make(map[any]bool)
+		for i := 0; i < v.Len(); i++ {
+			item := v.Index(i).Interface()
+			if seen[item] {
+				return newValidationError(ErrorCodeInvalidFormat, "items must be unique")
+			}
+			seen[item] = true
+		}
+
+		return nil
+	}
+}