KotlinJsonAdapter.kt

/*
 * Copyright (C) 2017 Square, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.squareup.moshi.kotlin.reflect

import com.squareup.moshi.Json
import com.squareup.moshi.JsonAdapter
import com.squareup.moshi.JsonDataException
import com.squareup.moshi.JsonReader
import com.squareup.moshi.JsonWriter
import com.squareup.moshi.Moshi
import com.squareup.moshi.Types
import com.squareup.moshi.internal.Util
import com.squareup.moshi.internal.Util.generatedAdapter
import com.squareup.moshi.internal.Util.resolve
import java.lang.reflect.Modifier
import java.lang.reflect.Type
import java.util.AbstractMap.SimpleEntry
import kotlin.collections.Map.Entry
import kotlin.reflect.KFunction
import kotlin.reflect.KMutableProperty1
import kotlin.reflect.KParameter
import kotlin.reflect.KProperty1
import kotlin.reflect.full.findAnnotation
import kotlin.reflect.full.memberProperties
import kotlin.reflect.full.primaryConstructor
import kotlin.reflect.jvm.isAccessible
import kotlin.reflect.jvm.javaField
import kotlin.reflect.jvm.javaType

/** Classes annotated with this are eligible for this adapter. */
private val KOTLIN_METADATA = Metadata::class.java

/**
 * Placeholder value used when a field is absent from the JSON. Note that this code
 * distinguishes between absent values and present-but-null values.
 */
private val ABSENT_VALUE = Any()

/**
 * This class encodes Kotlin classes using their properties. It decodes them by first invoking the
 * constructor, and then by setting any additional properties that exist, if any.
 */
internal class KotlinJsonAdapter<T>(
  val constructor: KFunction<T>,
  val allBindings: List<Binding<T, Any?>?>,
  val nonTransientBindings: List<Binding<T, Any?>>,
  val options: JsonReader.Options
) : JsonAdapter<T>() {

  override fun fromJson(reader: JsonReader): T {
    val constructorSize = constructor.parameters.size

    // Read each value into its slot in the array.
    val values = Array<Any?>(allBindings.size) { ABSENT_VALUE }
    reader.beginObject()
    while (reader.hasNext()) {
      val index = reader.selectName(options)
      if (index == -1) {
        reader.skipName()
        reader.skipValue()
        continue
      }
      val binding = nonTransientBindings[index]

      val propertyIndex = binding.propertyIndex
      if (values[propertyIndex] !== ABSENT_VALUE) {
        throw JsonDataException(
            "Multiple values for '${binding.property.name}' at ${reader.path}")
      }

      values[propertyIndex] = binding.adapter.fromJson(reader)

      if (values[propertyIndex] == null && !binding.property.returnType.isMarkedNullable) {
        throw Util.unexpectedNull(
            binding.property.name,
            binding.jsonName,
            reader
        )
      }
    }
    reader.endObject()

    // Confirm all parameters are present, optional, or nullable.
    for (i in 0 until constructorSize) {
      if (values[i] === ABSENT_VALUE && !constructor.parameters[i].isOptional) {
        if (!constructor.parameters[i].type.isMarkedNullable) {
          throw Util.missingProperty(
              constructor.parameters[i].name,
              allBindings[i]?.jsonName,
              reader
          )
        }
        values[i] = null // Replace absent with null.
      }
    }

    // Call the constructor using a Map so that absent optionals get defaults.
    val result = constructor.callBy(IndexedParameterMap(constructor.parameters, values))

    // Set remaining properties.
    for (i in constructorSize until allBindings.size) {
      val binding = allBindings[i]!!
      val value = values[i]
      binding.set(result, value)
    }

    return result
  }

  override fun toJson(writer: JsonWriter, value: T?) {
    if (value == null) throw NullPointerException("value == null")

    writer.beginObject()
    for (binding in allBindings) {
      if (binding == null) continue // Skip constructor parameters that aren't properties.

      writer.name(binding.name)
      binding.adapter.toJson(writer, binding.get(value))
    }
    writer.endObject()
  }

  override fun toString() = "KotlinJsonAdapter(${constructor.returnType})"

  data class Binding<K, P>(
    val name: String,
    val jsonName: String?,
    val adapter: JsonAdapter<P>,
    val property: KProperty1<K, P>,
    val parameter: KParameter?,
    val propertyIndex: Int
  ) {
    fun get(value: K) = property.get(value)

    fun set(result: K, value: P) {
      if (value !== ABSENT_VALUE) {
        (property as KMutableProperty1<K, P>).set(result, value)
      }
    }
  }

  /** A simple [Map] that uses parameter indexes instead of sorting or hashing. */
  class IndexedParameterMap(
    private val parameterKeys: List<KParameter>,
    private val parameterValues: Array<Any?>
  ) : AbstractMap<KParameter, Any?>() {

    override val entries: Set<Entry<KParameter, Any?>>
      get() {
        val allPossibleEntries = parameterKeys.mapIndexed { index, value ->
          SimpleEntry<KParameter, Any?>(value, parameterValues[index])
        }
        return allPossibleEntries.filterTo(LinkedHashSet<Entry<KParameter, Any?>>()) {
          it.value !== ABSENT_VALUE
        }
      }

    override fun containsKey(key: KParameter) = parameterValues[key.index] !== ABSENT_VALUE

    override fun get(key: KParameter): Any? {
      val value = parameterValues[key.index]
      return if (value !== ABSENT_VALUE) value else null
    }
  }
}

class KotlinJsonAdapterFactory : JsonAdapter.Factory {
  override fun create(type: Type, annotations: MutableSet<out Annotation>, moshi: Moshi)
      : JsonAdapter<*>? {
    if (annotations.isNotEmpty()) return null

    val rawType = Types.getRawType(type)
    if (rawType.isInterface) return null
    if (rawType.isEnum) return null
    if (!rawType.isAnnotationPresent(KOTLIN_METADATA)) return null
    if (Util.isPlatformType(rawType)) return null
    try {
      val generatedAdapter = generatedAdapter(moshi, type, rawType)
      if (generatedAdapter != null) {
        return generatedAdapter
      }
    } catch (e: RuntimeException) {
      if (e.cause !is ClassNotFoundException) {
        throw e
      }
      // Fall back to a reflective adapter when the generated adapter is not found.
    }

    require(!rawType.isLocalClass) {
      "Cannot serialize local class or object expression ${rawType.name}"
    }
    val rawTypeKotlin = rawType.kotlin
    require(!rawTypeKotlin.isAbstract) {
      "Cannot serialize abstract class ${rawType.name}"
    }
    require(!rawTypeKotlin.isInner) {
      "Cannot serialize inner class ${rawType.name}"
    }
    require(rawTypeKotlin.objectInstance == null) {
      "Cannot serialize object declaration ${rawType.name}"
    }
    require(!rawTypeKotlin.isSealed) {
      "Cannot reflectively serialize sealed class ${rawType.name}. Please register an adapter."
    }

    val constructor = rawTypeKotlin.primaryConstructor ?: return null
    val parametersByName = constructor.parameters.associateBy { it.name }
    constructor.isAccessible = true

    val bindingsByName = LinkedHashMap<String, KotlinJsonAdapter.Binding<Any, Any?>>()

    for (property in rawTypeKotlin.memberProperties) {
      val parameter = parametersByName[property.name]

      if (Modifier.isTransient(property.javaField?.modifiers ?: 0)) {
        require(parameter == null || parameter.isOptional) {
          "No default value for transient constructor $parameter"
        }
        continue
      }

      require(parameter == null || parameter.type == property.returnType) {
        "'${property.name}' has a constructor parameter of type ${parameter!!.type} but a property of type ${property.returnType}."
      }

      if (property !is KMutableProperty1 && parameter == null) continue

      property.isAccessible = true
      val allAnnotations = property.annotations.toMutableList()
      var jsonAnnotation = property.findAnnotation<Json>()

      if (parameter != null) {
        allAnnotations += parameter.annotations
        if (jsonAnnotation == null) {
          jsonAnnotation = parameter.findAnnotation()
        }
      }

      val name = jsonAnnotation?.name ?: property.name
      val resolvedPropertyType = resolve(type, rawType, property.returnType.javaType)
      val adapter = moshi.adapter<Any>(
          resolvedPropertyType, Util.jsonAnnotations(allAnnotations.toTypedArray()), property.name)

      @Suppress("UNCHECKED_CAST")
      bindingsByName[property.name] = KotlinJsonAdapter.Binding(
          name,
          jsonAnnotation?.name ?: name,
          adapter,
          property as KProperty1<Any, Any?>,
          parameter,
          parameter?.index ?: -1
      )
    }

    val bindings = ArrayList<KotlinJsonAdapter.Binding<Any, Any?>?>()

    for (parameter in constructor.parameters) {
      val binding = bindingsByName.remove(parameter.name)
      require(binding != null || parameter.isOptional) {
        "No property for required constructor $parameter"
      }
      bindings += binding
    }

    var index = bindings.size
    for (bindingByName in bindingsByName) {
      bindings += bindingByName.value.copy(propertyIndex = index++)
    }

    val nonTransientBindings = bindings.filterNotNull()
    val options = JsonReader.Options.of(*nonTransientBindings.map { it.name }.toTypedArray())
    return KotlinJsonAdapter(constructor, bindings, nonTransientBindings, options).nullSafe()
  }
}