feat: enhance filter options handling in request parameters

Author: jwilkinson87

src/main/kotlin/com/ctrlhub/core/router/request/RequestParameters.kt

@@ -1,7 +1,7 @@
 package com.ctrlhub.core.router.request
 
 data class FilterOption(
-    val field: String,
+    val field: String?,
     val value: String
 )
 
@@ -15,7 +15,17 @@ abstract class AbstractRequestParameters(
         offset?.let { queryParams["offset"] = it.toString() }
         limit?.let { queryParams["limit"] = it.toString() }
 
-        filterOptions.forEach { queryParams["filter"] = "${it.field}('${it.value}')" }
+        filterOptions.forEach {
+            // compute key once; if field is null use plain "filter", otherwise use "filter[field]"
+            val key = it.field?.let { f -> "filter[$f]" } ?: "filter"
+            val existing = queryParams[key]
+            queryParams[key] = if (existing.isNullOrEmpty()) {
+                it.value
+            } else {
+                // append multiple filter values with a comma
+                "$existing,${it.value}"
+            }
+        }
 
         return queryParams
     }
@@ -27,6 +37,7 @@ class RequestParameters(
     filterOptions: List<FilterOption> = emptyList()
 ) : AbstractRequestParameters(offset, limit, filterOptions)
 
+
 open class RequestParametersWithIncludes<TIncludes>(
     offset: Int? = null,
     limit: Int? = null,

src/test/kotlin/com/ctrlhub/core/router/request/RequestParametersTest.kt

@@ -0,0 +1,69 @@
+package com.ctrlhub.core.router.request
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNotNull
+
+private enum class TestIncludes(private val v: String) : JsonApiIncludes {
+    AUTHOR("author"), FORM("form");
+    override fun value() = v
+}
+
+class RequestParametersTest {
+
+    @Test
+    fun `toMap includes offset and limit`() {
+        val request = RequestParameters(offset = 5, limit = 25)
+        val map = request.toMap()
+
+        assertEquals("5", map["offset"])
+        assertEquals("25", map["limit"])
+    }
+
+    @Test
+    fun `single filter option produces filter key`() {
+        val request = RequestParameters(
+            filterOptions = listOf(FilterOption("status", "open"))
+        )
+
+        val map = request.toMap()
+        assertEquals("open", map["filter[status]"])
+    }
+
+    @Test
+    fun `multiple filter options for same field are appended with comma`() {
+        val request = RequestParameters(
+            filterOptions = listOf(
+                FilterOption("status", "open"),
+                FilterOption("status", "closed"),
+            )
+        )
+
+        val map = request.toMap()
+        assertEquals("open,closed", map["filter[status]"])
+    }
+
+    @Test
+    fun `anonymous filter options append to filter key`() {
+        val request = RequestParameters(
+            filterOptions = listOf(
+                FilterOption(null, "a"),
+                FilterOption(null, "b")
+            )
+        )
+
+        val map = request.toMap()
+        assertEquals("a,b", map["filter"])
+    }
+
+    @Test
+    fun `includes are serialized when using RequestParametersWithIncludes`() {
+        val request = RequestParametersWithIncludes<TestIncludes>(
+            includes = listOf(TestIncludes.AUTHOR, TestIncludes.FORM)
+        )
+
+        val map = request.toMap()
+        assertNotNull(map["include"]) // something present
+        assertEquals("author,form", map["include"])
+    }
+}