chore: add simple JSON builder

core/support/src/main/kotlin/au/com/dius/pact/core/support/json/JsonBuilder.kt

@@ -0,0 +1,47 @@
+package au.com.dius.pact.core.support.json
+
+import au.com.dius.pact.core.support.Json
+
+sealed class JsonBuilder(open val root: JsonValue) {
+  class JsonObjectBuilder(override val root: JsonValue.Object = JsonValue.Object()): JsonBuilder(root) {
+    operator fun set(name: String, value: Any?) {
+      root[name] = Json.toJson(value)
+    }
+
+    fun `object`(function: (JsonObjectBuilder) -> Unit): JsonValue.Object {
+      return build(function)
+    }
+
+    fun array(function: (JsonArrayBuilder) -> Unit): JsonValue.Array {
+      val builder = JsonArrayBuilder()
+      function(builder)
+      return builder.root
+    }
+  }
+
+  class JsonArrayBuilder(override val root: JsonValue.Array = JsonValue.Array()): JsonBuilder(root) {
+    operator fun set(i: Int, value: Any?) {
+      root[i] = Json.toJson(value)
+    }
+
+    fun push(value: Any?) {
+      root.append(Json.toJson(value))
+    }
+
+    operator fun plusAssign(value: Any?) {
+      push(value)
+    }
+
+    fun `object`(function: (JsonObjectBuilder) -> Unit): JsonValue.Object {
+      return build(function)
+    }
+  }
+
+  companion object {
+    fun build(function: (JsonObjectBuilder) -> Unit): JsonValue.Object {
+      val builder = JsonObjectBuilder()
+      function(builder)
+      return builder.root
+    }
+  }
+}

core/support/src/test/kotlin/au/com/dius/pact/core/support/json/JsonBuilderTest.kt

@@ -0,0 +1,102 @@
+package au.com.dius.pact.core.support.json
+
+import org.hamcrest.MatcherAssert.assertThat
+import org.hamcrest.Matchers.equalTo
+import org.hamcrest.Matchers.`is`
+import org.junit.jupiter.api.Test
+
+class JsonBuilderTest {
+  @Test
+  fun testEmptyBuilder() {
+    val json = JsonBuilder.build {
+      it
+    }
+
+    val expected = JsonValue.Object()
+
+    assertThat(json, `is`(equalTo(expected)))
+  }
+
+  @Test
+  fun testBasicJson() {
+    val json = JsonBuilder.build {
+      it["integer"] = 100
+      it["decimal"] = 100.22
+      it["string"] = "100.22"
+      it["bool"] = true
+      it["null"] = null
+    }
+
+    val expected = JsonValue.Object(mutableMapOf(
+      "bool" to JsonValue.True,
+      "decimal" to JsonValue.Decimal(100.22),
+      "integer" to JsonValue.Integer(100),
+      "null" to JsonValue.Null,
+      "string" to JsonValue.StringValue("100.22")
+    ))
+
+    assertThat(json, `is`(equalTo(expected)))
+  }
+
+  @Test
+  fun testChildObjectJson() {
+    val json = JsonBuilder.build {
+      it["child"] = it.`object` { child ->
+        child["integer"] = 100
+        child["decimal"] = 100.22
+        child["string"] = "100.22"
+        child["bool"] = true
+        child["null"] = null
+      }
+    }
+
+    val expected = JsonValue.Object(mutableMapOf("child" to JsonValue.Object(mutableMapOf(
+      "bool" to JsonValue.True,
+      "decimal" to JsonValue.Decimal(100.22),
+      "integer" to JsonValue.Integer(100),
+      "null" to JsonValue.Null,
+      "string" to JsonValue.StringValue("100.22")
+    ))))
+
+    assertThat(json, `is`(equalTo(expected)))
+  }
+
+  @Test
+  fun testChildArrayJson() {
+    val json = JsonBuilder.build {
+      it["child"] = it.array { child ->
+        child.push(100.22)
+        child += "100.22"
+        child.push(null)
+        child[2] = 100
+      }
+    }
+
+    val expected = JsonValue.Object(mutableMapOf("child" to JsonValue.Array(
+      mutableListOf(
+        JsonValue.Decimal(100.22),
+        JsonValue.StringValue("100.22"),
+        JsonValue.Integer(100),
+      )
+    )))
+
+    assertThat(json, `is`(equalTo(expected)))
+  }
+
+  @Test
+  fun testChildMultiLevel() {
+    val json = JsonBuilder.build {
+      it["child"] = it.array { child ->
+        child.push(child.`object` { child2 ->
+          child2["term"] = true
+        })
+      }
+    }
+
+    val expected = JsonValue.Object(mutableMapOf("child" to JsonValue.Array(
+      mutableListOf(JsonValue.Object("term" to JsonValue.True))
+    )))
+
+    assertThat(json, `is`(equalTo(expected)))
+  }
+}