package graphql.execution;

import graphql.ExecutionResult;
import graphql.ExecutionResultImpl;
import graphql.execution.incremental.DeferredExecutionSupport;
import graphql.execution.instrumentation.ExecuteObjectInstrumentationContext;
import graphql.execution.instrumentation.Instrumentation;
import graphql.execution.instrumentation.parameters.InstrumentationExecutionStrategyParameters;

import java.util.List;
import java.util.Map;
import java.util.concurrent.CompletableFuture;
import java.util.function.BiConsumer;

/**
 * Base class to control how the map is build. Must be in this graphql.execution package because it used
 * package-private methods.
 */
public abstract class CustomizableExecutionStrategy extends AsyncExecutionStrategy {

    // copy-pasted code
    protected Object /* CompletableFuture<Map<String, Object>> | Map<String, Object> */
    executeObject(ExecutionContext executionContext, ExecutionStrategyParameters parameters) throws NonNullableFieldWasNullException {
        DataLoaderDispatchStrategy dataLoaderDispatcherStrategy = executionContext.getDataLoaderDispatcherStrategy();
        dataLoaderDispatcherStrategy.executeObject(executionContext, parameters);
        Instrumentation instrumentation = executionContext.getInstrumentation();
        InstrumentationExecutionStrategyParameters instrumentationParameters = new InstrumentationExecutionStrategyParameters(executionContext, parameters);

        ExecuteObjectInstrumentationContext resolveObjectCtx = ExecuteObjectInstrumentationContext.nonNullCtx(
                instrumentation.beginExecuteObject(instrumentationParameters, executionContext.getInstrumentationState())
        );

        List<String> fieldNames = parameters.getFields().getKeys();

        DeferredExecutionSupport deferredExecutionSupport = createDeferredExecutionSupport(executionContext, parameters);
        Async.CombinedBuilder<FieldValueInfo> resolvedFieldFutures = super.getAsyncFieldValueInfo(executionContext, parameters, deferredExecutionSupport);

        CompletableFuture<Map<String, Object>> overallResult = new CompletableFuture<>();
        List<String> fieldsExecutedOnInitialResult = deferredExecutionSupport.getNonDeferredFieldNames(fieldNames);
        BiConsumer<List<Object>, Throwable> handleResultsConsumer = buildFieldValueMap(fieldsExecutedOnInitialResult, overallResult, executionContext);

        resolveObjectCtx.onDispatched();

        Object fieldValueInfosResult = resolvedFieldFutures.awaitPolymorphic();
        if (fieldValueInfosResult instanceof CompletableFuture) {
            CompletableFuture<List<FieldValueInfo>> fieldValueInfos = (CompletableFuture<List<FieldValueInfo>>) fieldValueInfosResult;
            fieldValueInfos.whenComplete((completeValueInfos, throwable) -> {
                if (throwable != null) {
                    handleResultsConsumer.accept(null, throwable);
                    return;
                }

                Async.CombinedBuilder<Object> resultFutures = fieldValuesCombinedBuilder(completeValueInfos);
                dataLoaderDispatcherStrategy.executeObjectOnFieldValuesInfo(completeValueInfos, parameters);
                resolveObjectCtx.onFieldValuesInfo(completeValueInfos);
                resultFutures.await().whenComplete(handleResultsConsumer);
            }).exceptionally((ex) -> {
                // if there are any issues with combining/handling the field results,
                // complete the future at all costs and bubble up any thrown exception so
                // the execution does not hang.
                dataLoaderDispatcherStrategy.executeObjectOnFieldValuesException(ex, parameters);
                resolveObjectCtx.onFieldValuesException();
                overallResult.completeExceptionally(ex);
                return null;
            });
            overallResult.whenComplete(resolveObjectCtx::onCompleted);
            return overallResult;
        } else {
            List<FieldValueInfo> completeValueInfos = (List<FieldValueInfo>) fieldValueInfosResult;

            Async.CombinedBuilder<Object> resultFutures = fieldValuesCombinedBuilder(completeValueInfos);
            dataLoaderDispatcherStrategy.executeObjectOnFieldValuesInfo(completeValueInfos, parameters);
            resolveObjectCtx.onFieldValuesInfo(completeValueInfos);

            Object completedValuesObject = resultFutures.awaitPolymorphic();
            if (completedValuesObject instanceof CompletableFuture) {
                CompletableFuture<List<Object>> completedValues = (CompletableFuture<List<Object>>) completedValuesObject;
                completedValues.whenComplete(handleResultsConsumer);
                overallResult.whenComplete(resolveObjectCtx::onCompleted);
                return overallResult;
            } else {
                Map<String, Object> fieldValueMap = buildFieldValueMap(fieldsExecutedOnInitialResult, (List<Object>) completedValuesObject);
                resolveObjectCtx.onCompleted(fieldValueMap, null);
                return fieldValueMap;
            }
        }
    }

    private static Async.CombinedBuilder<Object> fieldValuesCombinedBuilder(List<FieldValueInfo> completeValueInfos) {
        Async.CombinedBuilder<Object> resultFutures = Async.ofExpectedSize(completeValueInfos.size());
        for (FieldValueInfo completeValueInfo : completeValueInfos) {
            resultFutures.addObject(completeValueInfo.getFieldValueObject());
        }
        return resultFutures;
    }

    private BiConsumer<List<Object>, Throwable> buildFieldValueMap(List<String> fieldNames, CompletableFuture<Map<String, Object>> overallResult, ExecutionContext executionContext) {
        return (List<Object> results, Throwable exception) -> {
            if (exception != null) {
                handleValueException(overallResult, exception, executionContext);
                return;
            }
            final Map<String, Object> resolvedValuesByField = buildFieldValueMap(fieldNames, results);
            overallResult.complete(resolvedValuesByField);
        };
    }

    @Override
    protected BiConsumer<List<Object>, Throwable> handleResults(ExecutionContext executionContext, List<String> fieldNames, CompletableFuture<ExecutionResult> overallResult) {
        return (List<Object> results, Throwable exception) -> {
            if (exception != null) {
                handleNonNullException(executionContext, overallResult, exception);
                return;
            }
            final var map = buildFieldValueMap(fieldNames, results);
            overallResult.complete(new ExecutionResultImpl(map, executionContext.getErrors()));
        };
    }

    /**
     * This is the idea of class: concrete classes can override it to provide custom implementation of the resulting Map.
     */
    protected abstract Map<String, Object> buildFieldValueMap(List<String> fieldNames, List<Object> results);

}