import {
  DocumentNode,
  SelectionSetNode,
  FieldNode,
  FragmentDefinitionNode,
  InlineFragmentNode,
} from 'graphql';

import {
  getMainDefinition,
  getFragmentDefinitions,
  createFragmentMap,
  FragmentMap,
  DirectiveInfo,
  shouldInclude,
  getDirectiveInfoFromField,
  isField,
  isInlineFragment,
  resultKeyNameFromField,
  argumentsObjectFromField,
} from 'apollo-utilities';

export type Resolver = (
  fieldName: string,
  rootValue: any,
  args: any,
  context: any,
  info: ExecInfo,
) => any;

export type VariableMap = { [name: string]: any };

export type ResultMapper = (
  values: { [fieldName: string]: any },
  rootValue: any,
) => any;
export type FragmentMatcher = (
  rootValue: any,
  typeCondition: string,
  context: any,
) => boolean;

export type ExecContext = {
  fragmentMap: FragmentMap;
  contextValue: any;
  variableValues: VariableMap;
  resultMapper: ResultMapper;
  resolver: Resolver;
  fragmentMatcher: FragmentMatcher;
};

export type ExecInfo = {
  isLeaf: boolean;
  resultKey: string;
  directives: DirectiveInfo;
  field: FieldNode;
};

export type ExecOptions = {
  resultMapper?: ResultMapper;
  fragmentMatcher?: FragmentMatcher;
};

/* Based on graphql function from graphql-js:
 *
 * graphql(
 *   schema: GraphQLSchema,
 *   requestString: string,
 *   rootValue?: ?any,
 *   contextValue?: ?any,
 *   variableValues?: ?{[key: string]: any},
 *   operationName?: ?string
 * ): Promise<GraphQLResult>
 *
 * The default export as of graphql-anywhere is sync as of 4.0,
 * but below is an exported alternative that is async.
 * In the 5.0 version, this will be the only export again
 * and it will be async
 */
export function graphql(
  resolver: Resolver,
  document: DocumentNode,
  rootValue?: any,
  contextValue?: any,
  variableValues: VariableMap = {},
  execOptions: ExecOptions = {},
) {
  const mainDefinition = getMainDefinition(document);

  const fragments = getFragmentDefinitions(document);
  const fragmentMap = createFragmentMap(fragments);

  const resultMapper = execOptions.resultMapper;

  // Default matcher always matches all fragments
  const fragmentMatcher = execOptions.fragmentMatcher || (() => true);

  const execContext: ExecContext = {
    fragmentMap,
    contextValue,
    variableValues,
    resultMapper,
    resolver,
    fragmentMatcher,
  };

  return executeSelectionSet(
    mainDefinition.selectionSet,
    rootValue,
    execContext,
  );
}

function executeSelectionSet(
  selectionSet: SelectionSetNode,
  rootValue: any,
  execContext: ExecContext,
) {
  const { fragmentMap, contextValue, variableValues: variables } = execContext;

  const result = {};

  selectionSet.selections.forEach(selection => {
    if (variables && !shouldInclude(selection, variables)) {
      // Skip selection sets which we're able to determine should not be run
      return;
    }

    if (isField(selection)) {
      const fieldResult = executeField(selection, rootValue, execContext);

      const resultFieldKey = resultKeyNameFromField(selection);

      if (fieldResult !== undefined) {
        if (result[resultFieldKey] === undefined) {
          result[resultFieldKey] = fieldResult;
        } else {
          merge(result[resultFieldKey], fieldResult);
        }
      }
    } else {
      let fragment: InlineFragmentNode | FragmentDefinitionNode;

      if (isInlineFragment(selection)) {
        fragment = selection;
      } else {
        // This is a named fragment
        fragment = fragmentMap[selection.name.value];

        if (!fragment) {
          throw new Error(`No fragment named ${selection.name.value}`);
        }
      }

      const typeCondition = fragment.typeCondition.name.value;

      if (execContext.fragmentMatcher(rootValue, typeCondition, contextValue)) {
        const fragmentResult = executeSelectionSet(
          fragment.selectionSet,
          rootValue,
          execContext,
        );

        merge(result, fragmentResult);
      }
    }
  });

  if (execContext.resultMapper) {
    return execContext.resultMapper(result, rootValue);
  }

  return result;
}

function executeField(
  field: FieldNode,
  rootValue: any,
  execContext: ExecContext,
): any {
  const { variableValues: variables, contextValue, resolver } = execContext;

  const fieldName = field.name.value;
  const args = argumentsObjectFromField(field, variables);

  const info: ExecInfo = {
    isLeaf: !field.selectionSet,
    resultKey: resultKeyNameFromField(field),
    directives: getDirectiveInfoFromField(field, variables),
    field,
  };

  const result = resolver(fieldName, rootValue, args, contextValue, info);

  // Handle all scalar types here
  if (!field.selectionSet) {
    return result;
  }

  // From here down, the field has a selection set, which means it's trying to
  // query a GraphQLObjectType
  if (result == null) {
    // Basically any field in a GraphQL response can be null, or missing
    return result;
  }

  if (Array.isArray(result)) {
    return executeSubSelectedArray(field, result, execContext);
  }

  // Returned value is an object, and the query has a sub-selection. Recurse.
  return executeSelectionSet(field.selectionSet, result, execContext);
}

function executeSubSelectedArray(field, result, execContext) {
  return result.map(item => {
    // null value in array
    if (item === null) {
      return null;
    }

    // This is a nested array, recurse
    if (Array.isArray(item)) {
      return executeSubSelectedArray(field, item, execContext);
    }

    // This is an object, run the selection set on it
    return executeSelectionSet(field.selectionSet, item, execContext);
  });
}

const hasOwn = Object.prototype.hasOwnProperty;

export function merge(dest, src) {
  if (src !== null && typeof src === 'object') {
    Object.keys(src).forEach(key => {
      const srcVal = src[key];
      if (!hasOwn.call(dest, key)) {
        dest[key] = srcVal;
      } else {
        merge(dest[key], srcVal);
      }
    });
  }
}