Issue #12: Basic implementation of transformation service

src/main/kotlin/dev/dnpm/etl/processor/services/TransformationService.kt

@@ -0,0 +1,62 @@
+package dev.dnpm.etl.processor.services
+
+import com.fasterxml.jackson.databind.ObjectMapper
+import com.jayway.jsonpath.JsonPath
+import com.jayway.jsonpath.PathNotFoundException
+import de.ukw.ccc.bwhc.dto.MtbFile
+
+class TransformationService(private val objectMapper: ObjectMapper) {
+    fun transform(mtbFile: MtbFile, vararg transformations: Transformation): MtbFile {
+        var json = objectMapper.writeValueAsString(mtbFile)
+
+        transformations.forEach { transformation ->
+            val jsonPath = JsonPath.parse(json)
+
+            try {
+                val before = transformation.path.substringBeforeLast(".")
+                val last = transformation.path.substringAfterLast(".")
+
+                val existingValue = if (transformation.existingValue is Number) transformation.existingValue else transformation.existingValue.toString()
+                val newValue = if (transformation.newValue is Number) transformation.newValue else transformation.newValue.toString()
+
+                jsonPath.set("$.$before.[?]$last", newValue, {
+                    it.item(HashMap::class.java)[last] == existingValue
+                })
+            } catch (e: PathNotFoundException) {
+                // Ignore
+            }
+
+            json = jsonPath.jsonString()
+        }
+
+        return objectMapper.readValue(json, MtbFile::class.java)
+    }
+
+}
+
+class Transformation private constructor(internal val path: String) {
+
+    lateinit var existingValue: Any
+        private set
+    lateinit var newValue: Any
+        private set
+
+    infix fun from(value: Any): Transformation {
+        this.existingValue = value
+        return this
+    }
+
+    infix fun to(value: Any): Transformation {
+        this.newValue = value
+        return this
+    }
+
+    companion object {
+
+        fun of(path: String): Transformation {
+            return Transformation(path)
+        }
+
+    }
+
+}