Add proper support for unicode characters

src/commonMain/kotlin/io/github/optimumcode/json/schema/internal/factories/string/LengthAssertion.kt

@@ -5,6 +5,7 @@ import io.github.optimumcode.json.schema.ErrorCollector
 import io.github.optimumcode.json.schema.ValidationError
 import io.github.optimumcode.json.schema.internal.AssertionContext
 import io.github.optimumcode.json.schema.internal.JsonSchemaAssertion
+import io.github.optimumcode.json.schema.internal.factories.string.util.codePointCount
 import kotlinx.serialization.json.JsonElement
 import kotlinx.serialization.json.JsonPrimitive
 import kotlinx.serialization.json.contentOrNull
@@ -20,14 +21,15 @@ internal class LengthAssertion(
       return true
     }
     val content = element.contentOrNull ?: return true
-    if (check(content.length, lengthValue)) {
+    val codePointCount = content.codePointCount()
+    if (check(codePointCount, lengthValue)) {
       return true
     }
     errorCollector.onError(
       ValidationError(
         schemaPath = path,
         objectPath = context.objectPath,
-        message = "string length (${content.length}) $errorMessage $lengthValue",
+        message = "string length ($codePointCount) $errorMessage $lengthValue",
       ),
     )
     return false

src/commonMain/kotlin/io/github/optimumcode/json/schema/internal/factories/string/util/UnicodeUtil.kt

@@ -0,0 +1,21 @@
+package io.github.optimumcode.json.schema.internal.factories.string.util
+
+internal fun CharSequence.codePointCount(): Int {
+  val endIndex = length
+  var index = 0
+  var count = 0
+  while (index < endIndex) {
+    val firstChar = this[index]
+    index++
+    if (firstChar.isHighSurrogate() && index < endIndex) {
+      val nextChar = this[index]
+      if (nextChar.isLowSurrogate()) {
+        index++
+      }
+    }
+
+    count++
+  }
+
+  return count
+}

src/commonTest/kotlin/io/github/optimumcode/json/schema/assertions/string/JsonSchemaMaxLengthValidationTest.kt

@@ -4,6 +4,7 @@ import io.github.optimumcode.json.pointer.JsonPointer
 import io.github.optimumcode.json.schema.JsonSchema
 import io.github.optimumcode.json.schema.ValidationError
 import io.github.optimumcode.json.schema.base.KEY
+import io.github.optimumcode.json.schema.internal.factories.string.util.codePointCount
 import io.kotest.core.spec.style.FunSpec
 import io.kotest.matchers.collections.shouldContainExactly
 import io.kotest.matchers.collections.shouldHaveSize
@@ -32,6 +33,8 @@ class JsonSchemaMaxLengthValidationTest : FunSpec() {
       "╒",
       "V",
       "",
+      "💩".repeat(20),
+      "💩",
     )
     for (str in validStrings) {
       test("'$str' passes validation") {
@@ -46,6 +49,7 @@ class JsonSchemaMaxLengthValidationTest : FunSpec() {
       "EFDzZMRawYGD9eNfknAUB",
       "⌻ⲝ⣞ℤ⸍⠗⠜ↈ✋☧⾛✩ⓥ⇩⡽⚘\u20FC◭┐⥸⒗",
       "⠺⪒⑸⋶⥠⇀⨑⨋ⅸ⥼\u245F⏇Ⓙⴷ⻘⢢≧\u20C8⬫⡜⸁",
+      "💩".repeat(21),
     )
     for (str in invalidStrings) {
       test("'$str' does not pass validation") {
@@ -56,7 +60,7 @@ class JsonSchemaMaxLengthValidationTest : FunSpec() {
           ValidationError(
             schemaPath = JsonPointer("/maxLength"),
             objectPath = JsonPointer.ROOT,
-            message = "string length (${str.length}) must be less or equal to 20",
+            message = "string length (${str.codePointCount()}) must be less or equal to 20",
           ),
         )
       }

src/commonTest/kotlin/io/github/optimumcode/json/schema/assertions/string/JsonSchemaMinLengthValidationTest.kt

@@ -4,6 +4,7 @@ import io.github.optimumcode.json.pointer.JsonPointer
 import io.github.optimumcode.json.schema.JsonSchema
 import io.github.optimumcode.json.schema.ValidationError
 import io.github.optimumcode.json.schema.base.KEY
+import io.github.optimumcode.json.schema.internal.factories.string.util.codePointCount
 import io.kotest.core.spec.style.FunSpec
 import io.kotest.matchers.collections.shouldContainExactly
 import io.kotest.matchers.collections.shouldHaveSize
@@ -31,6 +32,8 @@ class JsonSchemaMinLengthValidationTest : FunSpec() {
       "JpEblYiJE57H70qGNXs",
       "ⅵ┡\u243A⢻␀⁾⡪∛⫑⏽",
       "Si1kaAhdpS",
+      "💩".repeat(11),
+      "💩".repeat(10),
     )
     for (str in validStrings) {
       test("'$str' passes validation") {
@@ -47,6 +50,7 @@ class JsonSchemaMinLengthValidationTest : FunSpec() {
       " ⍘↽♔⚪➕ⷰ➖",
       "⧦",
       "",
+      "💩".repeat(9),
     )
     for (str in invalidStrings) {
       test("'$str' does not pass validation") {
@@ -57,7 +61,7 @@ class JsonSchemaMinLengthValidationTest : FunSpec() {
           ValidationError(
             schemaPath = JsonPointer("/minLength"),
             objectPath = JsonPointer.ROOT,
-            message = "string length (${str.length}) must be greater or equal to 10",
+            message = "string length (${str.codePointCount()}) must be greater or equal to 10",
           ),
         )
       }