import {
  GraphQLExecutionResult,
  GraphQLRequestContext,
} from 'apollo-server-types';
import { Headers } from 'apollo-server-env';
import {
  execute,
  GraphQLError,
  Kind,
  TypeNameMetaFieldDef,
  GraphQLFieldResolver,
  GraphQLFormattedError,
  isAbstractType,
  GraphQLSchema,
} from 'graphql';
import { Trace, google } from 'apollo-reporting-protobuf';
import { defaultRootOperationNameLookup } from '@apollo/federation';
import { GraphQLDataSource, GraphQLDataSourceRequestKind } from './datasources/types';
import { OperationContext } from './operationContext';
import {
  FetchNode,
  PlanNode,
  QueryPlan,
  ResponsePath,
  QueryPlanSelectionNode,
  QueryPlanFieldNode,
  getResponseName,
  toAPISchema
} from '@apollo/query-planner';
import { deepMerge } from './utilities/deepMerge';
import { isNotNullOrUndefined } from './utilities/array';
import { SpanStatusCode } from "@opentelemetry/api";
import { OpenTelemetrySpanNames, tracer } from "./utilities/opentelemetry";

export type ServiceMap = {
  [serviceName: string]: GraphQLDataSource;
};

type ResultMap = Record<string, any>;

interface ExecutionContext<TContext> {
  queryPlan: QueryPlan;
  operationContext: OperationContext;
  serviceMap: ServiceMap;
  requestContext: GraphQLRequestContext<TContext>;
  errors: GraphQLError[];
}

export async function executeQueryPlan<TContext>(
  queryPlan: QueryPlan,
  serviceMap: ServiceMap,
  requestContext: GraphQLRequestContext<TContext>,
  operationContext: OperationContext,
): Promise<GraphQLExecutionResult> {

  const logger = requestContext.logger || console;

  return tracer.startActiveSpan(OpenTelemetrySpanNames.EXECUTE, async span => {
    try {
      const errors: GraphQLError[] = [];

      const context: ExecutionContext<TContext> = {
        queryPlan,
        operationContext,
        serviceMap,
        requestContext,
        errors,
      };

      let data: ResultMap | undefined | null = Object.create(null);

      const captureTraces = !!(
          requestContext.metrics && requestContext.metrics.captureTraces
      );

      if (queryPlan.node) {
        const traceNode = await executeNode(
          context,
          queryPlan.node,
          data!,
          [],
          captureTraces,
        );
        if (captureTraces) {
          requestContext.metrics!.queryPlanTrace = traceNode;
        }
      }

      let result = await tracer.startActiveSpan(OpenTelemetrySpanNames.POST_PROCESSING, async (span) => {

        // FIXME: Re-executing the query is a pretty heavy handed way of making sure
        // only explicitly requested fields are included and field ordering follows
        // the original query.
        // It is also used to allow execution of introspection queries though.
        try {
          const schema = toAPISchema(operationContext.schema);
          ({ data } = await execute({
            schema,
            document: {
              kind: Kind.DOCUMENT,
              definitions: [
                operationContext.operation,
                ...Object.values(operationContext.fragments),
              ],
            },
            rootValue: data,
            variableValues: requestContext.request.variables,
            // See also `wrapSchemaWithAliasResolver` in `gateway-js/src/index.ts`.
            fieldResolver: defaultFieldResolverWithAliasSupport,
          }));
        } catch (error) {
          span.setStatus({ code:SpanStatusCode.ERROR });
          if (error instanceof GraphQLError) {
            return { errors: [error] };
          } else if (error instanceof Error) {
            return {
              errors: [
                new GraphQLError(
                  error.message,
                  undefined,
                  undefined,
                  undefined,
                  undefined,
                  error as Error,
                )
              ]
            };
          } else {
            // The above cases should cover the known cases, but if we received
            // something else in the `catch` — like an object or something, we
            // may not want to merely return this to the client.
            logger.error(
              "Unexpected error during query plan execution: " + error);
            return {
              errors: [
                new GraphQLError(
                  "Unexpected error during query plan execution",
                )
              ]
            };
          }
        }
        finally {
          span.end()
        }
        if(errors.length > 0) {
          span.setStatus({ code:SpanStatusCode.ERROR });
        }
        return errors.length === 0 ? { data } : { errors, data };
      });

      if(result.errors) {
        span.setStatus({ code:SpanStatusCode.ERROR });
      }
      return result;
    }
    catch (err) {
      span.setStatus({ code:SpanStatusCode.ERROR });
      throw err;
    }
    finally {
      span.end();
    }
  });
}

// Note: this function always returns a protobuf QueryPlanNode tree, even if
// we're going to ignore it, because it makes the code much simpler and more
// typesafe. However, it doesn't actually ask for traces from the backend
// service unless we are capturing traces for Studio.
async function executeNode<TContext>(
  context: ExecutionContext<TContext>,
  node: PlanNode,
  results: ResultMap | ResultMap[],
  path: ResponsePath,
  captureTraces: boolean,
): Promise<Trace.QueryPlanNode> {
  if (!results) {
    // XXX I don't understand `results` threading well enough to understand when this happens
    //     and if this corresponds to a real query plan node that should be reported or not.
    //
    // This may be if running something like `query { fooOrNullFromServiceA {
    // somethingFromServiceB } }` and the first field is null, then we don't bother to run the
    // inner field at all.
    return new Trace.QueryPlanNode();
  }

  switch (node.kind) {
    case 'Sequence': {
      const traceNode = new Trace.QueryPlanNode.SequenceNode();
      for (const childNode of node.nodes) {
        const childTraceNode = await executeNode(
          context,
          childNode,
          results,
          path,
          captureTraces,
        );
        traceNode.nodes.push(childTraceNode!);
      }
      return new Trace.QueryPlanNode({ sequence: traceNode });
    }
    case 'Parallel': {
      const childTraceNodes = await Promise.all(
        node.nodes.map(async childNode =>
          executeNode(context, childNode, results, path, captureTraces),
        ),
      );
      return new Trace.QueryPlanNode({
        parallel: new Trace.QueryPlanNode.ParallelNode({
          nodes: childTraceNodes,
        }),
      });
    }
    case 'Flatten': {
      return new Trace.QueryPlanNode({
        flatten: new Trace.QueryPlanNode.FlattenNode({
          responsePath: node.path.map(
            id =>
              new Trace.QueryPlanNode.ResponsePathElement(
                typeof id === 'string' ? { fieldName: id } : { index: id },
              ),
          ),
          node: await executeNode(
            context,
            node.node,
            flattenResultsAtPath(results, node.path),
            [...path, ...node.path],
            captureTraces,
          ),
        }),
      });
    }
    case 'Fetch': {
      const traceNode = new Trace.QueryPlanNode.FetchNode({
        serviceName: node.serviceName,
        // executeFetch will fill in the other fields if desired.
      });
      try {
        await executeFetch(
          context,
          node,
          results,
          path,
          captureTraces ? traceNode : null,
        );
      } catch (error) {
        context.errors.push(error);
      }
      return new Trace.QueryPlanNode({ fetch: traceNode });
    }
  }
}

async function executeFetch<TContext>(
  context: ExecutionContext<TContext>,
  fetch: FetchNode,
  results: ResultMap | (ResultMap | null | undefined)[],
  _path: ResponsePath,
  traceNode: Trace.QueryPlanNode.FetchNode | null,
): Promise<void> {

  const logger = context.requestContext.logger || console;
  const service = context.serviceMap[fetch.serviceName];

  return tracer.startActiveSpan(OpenTelemetrySpanNames.FETCH, {attributes:{service:fetch.serviceName}}, async span => {
    try {
      if (!service) {
        throw new Error(`Couldn't find service with name "${fetch.serviceName}"`);
      }

      let entities: ResultMap[];
      if (Array.isArray(results)) {
        // Remove null or undefined entities from the list
        entities = results.filter(isNotNullOrUndefined);
      } else {
        entities = [results];
      }

      if (entities.length < 1) return;

      let variables = Object.create(null);
      if (fetch.variableUsages) {
        for (const variableName of fetch.variableUsages) {
          const providedVariables = context.requestContext.request.variables;
          if (
              providedVariables &&
              typeof providedVariables[variableName] !== 'undefined'
          ) {
            variables[variableName] = providedVariables[variableName];
          }
        }
      }

      if (!fetch.requires) {
        const dataReceivedFromService = await sendOperation(
            context,
            fetch.operation,
            variables,
        );

        for (const entity of entities) {
          deepMerge(entity, dataReceivedFromService);
        }
      } else {
        const requires = fetch.requires;

        const representations: ResultMap[] = [];
        const representationToEntity: number[] = [];

        entities.forEach((entity, index) => {
          const representation = executeSelectionSet(
            context.operationContext,
            entity,
            requires,
          );
          if (representation && representation[TypeNameMetaFieldDef.name]) {
            representations.push(representation);
            representationToEntity.push(index);
          }
        });

        // If there are no representations, that means the type conditions in
        // the requires don't match any entities.
        if (representations.length < 1) return;

        if ('representations' in variables) {
          throw new Error(`Variables cannot contain key "representations"`);
        }

        const dataReceivedFromService = await sendOperation(
            context,
            fetch.operation,
            {...variables, representations},
        );

        if (!dataReceivedFromService) {
          return;
        }

        if (
            !(
                dataReceivedFromService._entities &&
                Array.isArray(dataReceivedFromService._entities)
            )
        ) {
          throw new Error(`Expected "data._entities" in response to be an array`);
        }

        const receivedEntities = dataReceivedFromService._entities;

        if (receivedEntities.length !== representations.length) {
          throw new Error(
              `Expected "data._entities" to contain ${representations.length} elements`,
          );
        }

        for (let i = 0; i < entities.length; i++) {
          deepMerge(entities[representationToEntity[i]], receivedEntities[i]);
        }
      }
    }
    catch (err) {
      span.setStatus({ code:SpanStatusCode.ERROR });
      throw err;
    }
    finally
    {
      span.end();
    }
  });
  async function sendOperation(
    context: ExecutionContext<TContext>,
    source: string,
    variables: Record<string, any>,
  ): Promise<ResultMap | void | null> {
    // We declare this as 'any' because it is missing url and method, which
    // GraphQLRequest.http is supposed to have if it exists.
    let http: any;

    // If we're capturing a trace for Studio, then save the operation text to
    // the node we're building and tell the federated service to include a trace
    // in its response.
    if (traceNode) {
      http = {
        headers: new Headers({ 'apollo-federation-include-trace': 'ftv1' }),
      };
      if (
        context.requestContext.metrics &&
        context.requestContext.metrics.startHrTime
      ) {
        traceNode.sentTimeOffset = durationHrTimeToNanos(
          process.hrtime(context.requestContext.metrics.startHrTime),
        );
      }
      traceNode.sentTime = dateToProtoTimestamp(new Date());
    }

    const response = await service.process({
      kind: GraphQLDataSourceRequestKind.INCOMING_OPERATION,
      request: {
        query: source,
        variables,
        http,
      },
      incomingRequestContext: context.requestContext,
      context: context.requestContext.context,
    });

    if (response.errors) {
      const errors = response.errors.map((error) =>
        downstreamServiceError(error, fetch.serviceName),
      );
      context.errors.push(...errors);
    }

    // If we're capturing a trace for Studio, save the received trace into the
    // query plan.
    if (traceNode) {
      traceNode.receivedTime = dateToProtoTimestamp(new Date());

      if (response.extensions && response.extensions.ftv1) {
        const traceBase64 = response.extensions.ftv1;

        let traceBuffer: Buffer | undefined;
        let traceParsingFailed = false;
        try {
          // XXX support non-Node implementations by using Uint8Array? protobufjs
          // supports that, but there's not a no-deps base64 implementation.
          traceBuffer = Buffer.from(traceBase64, 'base64');
        } catch (err) {
          logger.error(
            `error decoding base64 for federated trace from ${fetch.serviceName}: ${err}`,
          );
          traceParsingFailed = true;
        }

        if (traceBuffer) {
          try {
            const trace = Trace.decode(traceBuffer);
            traceNode.trace = trace;
          } catch (err) {
            logger.error(
              `error decoding protobuf for federated trace from ${fetch.serviceName}: ${err}`,
            );
            traceParsingFailed = true;
          }
        }
        if (traceNode.trace) {
          // Federation requires the root operations in the composed schema
          // to have the default names (Query, Mutation, Subscription) even
          // if the implementing services choose different names, so we override
          // whatever the implementing service reported here.
          const rootTypeName =
            defaultRootOperationNameLookup[
              context.operationContext.operation.operation
            ];
          traceNode.trace.root?.child?.forEach((child) => {
            child.parentType = rootTypeName;
          });
        }
        traceNode.traceParsingFailed = traceParsingFailed;
      }
    }

    return response.data;
  }
}

/**
 *
 * @param source Result of GraphQL execution.
 * @param selectionSet
 */
function executeSelectionSet(
  operationContext: OperationContext,
  source: Record<string, any> | null,
  selections: QueryPlanSelectionNode[],
): Record<string, any> | null {

  // If the underlying service has returned null for the parent (source)
  // then there is no need to iterate through the parent's selection set
  if (source === null) {
    return null;
  }

  const result: Record<string, any> = Object.create(null);

  for (const selection of selections) {
    switch (selection.kind) {
      case Kind.FIELD:
        const responseName = getResponseName(selection as QueryPlanFieldNode);
        const selections = (selection as QueryPlanFieldNode).selections;

        if (typeof source[responseName] === 'undefined') {
          throw new Error(`Field "${responseName}" was not found in response.`);
        }
        if (Array.isArray(source[responseName])) {
          result[responseName] = source[responseName].map((value: any) =>
            selections
              ? executeSelectionSet(operationContext, value, selections)
              : value,
          );
        } else if (selections) {
          result[responseName] = executeSelectionSet(
            operationContext,
            source[responseName],
            selections,
          );
        } else {
          result[responseName] = source[responseName];
        }
        break;
      case Kind.INLINE_FRAGMENT:
        if (!selection.typeCondition) continue;

        const typename = source && source['__typename'];
        if (!typename) continue;

        if (doesTypeConditionMatch(operationContext.schema, selection.typeCondition, typename)) {
          deepMerge(
            result,
            executeSelectionSet(operationContext, source, selection.selections),
          );
        }
        break;
    }
  }

  return result;
}

function doesTypeConditionMatch(
  schema: GraphQLSchema,
  typeCondition: string,
  typename: string,
): boolean {
  if (typeCondition === typename) {
    return true;
  }

  const type = schema.getType(typename);
  if (!type) {
    return false;
  }

  const conditionalType = schema.getType(typeCondition);
  if (!conditionalType) {
    return false;
  }

  if (isAbstractType(conditionalType)) {
    return schema.isSubType(conditionalType, type);
  }

  return false;
}

function flattenResultsAtPath(value: any, path: ResponsePath): any {
  if (path.length === 0) return value;
  if (value === undefined || value === null) return value;

  const [current, ...rest] = path;
  if (current === '@') {
    return value.flatMap((element: any) => flattenResultsAtPath(element, rest));
  } else {
    return flattenResultsAtPath(value[current], rest);
  }
}

function downstreamServiceError(
  originalError: GraphQLFormattedError,
  serviceName: string,
) {
  let { message, extensions } = originalError;

  if (!message) {
    message = `Error while fetching subquery from service "${serviceName}"`;
  }
  extensions = {
    code: 'DOWNSTREAM_SERVICE_ERROR',
    // XXX The presence of a serviceName in extensions is used to
    // determine if this error should be captured for metrics reporting.
    serviceName,
    ...extensions,
  };
  return new GraphQLError(
    message,
    undefined,
    undefined,
    undefined,
    undefined,
    originalError as Error,
    extensions,
  );
}

export const defaultFieldResolverWithAliasSupport: GraphQLFieldResolver<
  any,
  any
> = function(source, args, contextValue, info) {
  // ensure source is a value for which property access is acceptable.
  if (typeof source === 'object' || typeof source === 'function') {
    // if this is an alias, check it first because a downstream service
    // would have returned the data *already cast* to an alias responseName
    const property = source[info.path.key];
    if (typeof property === 'function') {
      return source[info.fieldName](args, contextValue, info);
    }
    return property;
  }
};

// Converts an hrtime array (as returned from process.hrtime) to nanoseconds.
//
// ONLY CALL THIS ON VALUES REPRESENTING DELTAS, NOT ON THE RAW RETURN VALUE
// FROM process.hrtime() WITH NO ARGUMENTS.
//
// The entire point of the hrtime data structure is that the JavaScript Number
// type can't represent all int64 values without loss of precision:
// Number.MAX_SAFE_INTEGER nanoseconds is about 104 days. Calling this function
// on a duration that represents a value less than 104 days is fine. Calling
// this function on an absolute time (which is generally roughly time since
// system boot) is not a good idea.
//
// XXX We should probably use google.protobuf.Duration on the wire instead of
// ever trying to store durations in a single number.
function durationHrTimeToNanos(hrtime: [number, number]) {
  return hrtime[0] * 1e9 + hrtime[1];
}

// Converts a JS Date into a Timestamp.
function dateToProtoTimestamp(date: Date): google.protobuf.Timestamp {
  const totalMillis = +date;
  const millis = totalMillis % 1000;
  return new google.protobuf.Timestamp({
    seconds: (totalMillis - millis) / 1000,
    nanos: millis * 1e6,
  });
}