room/compiler/src/main/kotlin/android/arch/persistence/room/solver/query/result/LiveDataQueryResultBinder.kt

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * 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 android.arch.persistence.room.solver.query.result

import android.arch.persistence.room.ext.L
import android.arch.persistence.room.ext.LifecyclesTypeNames
import android.arch.persistence.room.ext.N
import android.arch.persistence.room.ext.RoomTypeNames
import android.arch.persistence.room.ext.RoomTypeNames.INVALIDATION_OBSERVER
import android.arch.persistence.room.ext.typeName
import android.arch.persistence.room.solver.CodeGenScope
import android.support.annotation.NonNull
import com.squareup.javapoet.FieldSpec
import com.squareup.javapoet.MethodSpec
import com.squareup.javapoet.ParameterSpec
import com.squareup.javapoet.ParameterizedTypeName
import com.squareup.javapoet.TypeName
import com.squareup.javapoet.TypeSpec
import javax.lang.model.element.Modifier
import javax.lang.model.type.TypeMirror

/**
 * Converts the query into a LiveData and returns it. No query is run until necessary.
 */
class LiveDataQueryResultBinder(val typeArg: TypeMirror, val tableNames: Set<String>,
                                adapter: QueryResultAdapter?)
    : BaseObservableQueryResultBinder(adapter) {
    @Suppress("JoinDeclarationAndAssignment")
    override fun convertAndReturn(
            roomSQLiteQueryVar: String,
            canReleaseQuery: Boolean,
            dbField: FieldSpec,
            inTransaction: Boolean,
            scope: CodeGenScope
    ) {
        val typeName = typeArg.typeName()

        val liveDataImpl = TypeSpec.anonymousClassBuilder("").apply {
            superclass(ParameterizedTypeName.get(LifecyclesTypeNames.COMPUTABLE_LIVE_DATA,
                    typeName))
            val observerField = FieldSpec.builder(RoomTypeNames.INVALIDATION_OBSERVER,
                    scope.getTmpVar("_observer"), Modifier.PRIVATE).build()
            addField(observerField)
            addMethod(createComputeMethod(
                    observerField = observerField,
                    typeName = typeName,
                    roomSQLiteQueryVar = roomSQLiteQueryVar,
                    dbField = dbField,
                    inTransaction = inTransaction,
                    scope = scope
            ))
            if (canReleaseQuery) {
                addMethod(createFinalizeMethod(roomSQLiteQueryVar))
            }
        }.build()
        scope.builder().apply {
            addStatement("return $L.getLiveData()", liveDataImpl)
        }
    }

    private fun createComputeMethod(
            roomSQLiteQueryVar: String,
            typeName: TypeName,
            observerField: FieldSpec,
            dbField: FieldSpec,
            inTransaction: Boolean,
            scope: CodeGenScope
    ): MethodSpec {
        return MethodSpec.methodBuilder("compute").apply {
            addAnnotation(Override::class.java)
            addModifiers(Modifier.PROTECTED)
            returns(typeName)

            beginControlFlow("if ($N == null)", observerField).apply {
                addStatement("$N = $L", observerField, createAnonymousObserver())
                addStatement("$N.getInvalidationTracker().addWeakObserver($N)",
                        dbField, observerField)
            }
            endControlFlow()

            createRunQueryAndReturnStatements(builder = this,
                    roomSQLiteQueryVar = roomSQLiteQueryVar,
                    dbField = dbField,
                    inTransaction = inTransaction,
                    scope = scope)
        }.build()
    }

    private fun createAnonymousObserver(): TypeSpec {
        val tableNamesList = tableNames.joinToString(",") { "\"$it\"" }
        return TypeSpec.anonymousClassBuilder(tableNamesList).apply {
            superclass(INVALIDATION_OBSERVER)
            addMethod(MethodSpec.methodBuilder("onInvalidated").apply {
                returns(TypeName.VOID)
                addAnnotation(Override::class.java)
                addParameter(ParameterSpec.builder(
                        ParameterizedTypeName.get(Set::class.java, String::class.java), "tables")
                        .addAnnotation(NonNull::class.java)
                        .build())
                addModifiers(Modifier.PUBLIC)
                addStatement("invalidate()")
            }.build())
        }.build()
    }
}