// Based on the code in the `express-graphql` package.
// https://github.com/graphql/express-graphql/blob/main/src/index.ts

import {
  Source,
  parse,
  execute,
  validateSchema,
  validate,
  specifiedRules,
  getOperationAST,
  GraphQLError,
} from "https://cdn.skypack.dev/graphql@16.5.0?dts";

import type {
  GraphQLSchema,
  DocumentNode,
  ValidationRule,
  FormattedExecutionResult,
  GraphQLFormattedError,
} from "https://cdn.skypack.dev/graphql@16.5.0?dts";

import type { Context } from "https://raw.githubusercontent.com/honojs/hono/v2.0.2/deno_dist/mod.ts";
import type { Next } from "https://raw.githubusercontent.com/honojs/hono/v2.0.2/deno_dist/mod.ts";
import { parseBody } from "./parse-body.ts";

type Options = {
  schema: GraphQLSchema;
  rootValue?: unknown;
  pretty?: boolean;
  validationRules?: ReadonlyArray<ValidationRule>;
  // graphiql?: boolean
};

export const graphqlServer = (options: Options) => {
  const schema = options.schema;
  const rootValue = options.rootValue;
  const pretty = options.pretty ?? false;
  const validationRules = options.validationRules ?? [];
  // const showGraphiQL = options.graphiql ?? false

  return async (c: Context, next: Next) => {
    // GraphQL HTTP only supports GET and POST methods.
    if (c.req.method !== "GET" && c.req.method !== "POST") {
      return c.json(
        errorMessages(["GraphQL only supports GET and POST requests."]),
        405,
        {
          Allow: "GET, POST",
        }
      );
    }

    let params: GraphQLParams;
    try {
      params = await getGraphQLParams(c.req);
    } catch (e) {
      if (e instanceof Error) {
        console.error(`${e.stack || e.message}`);
        return c.json(errorMessages([e.message], [e]), 400);
      }
      throw e;
    }

    const { query, variables, operationName } = params;

    if (query == null) {
      return c.json(errorMessages(["Must provide query string."]), 400);
    }

    const schemaValidationErrors = validateSchema(schema);
    if (schemaValidationErrors.length > 0) {
      // Return 500: Internal Server Error if invalid schema.
      return c.json(
        errorMessages(
          ["GraphQL schema validation error."],
          schemaValidationErrors
        ),
        500
      );
    }

    let documentAST: DocumentNode;
    try {
      documentAST = parse(new Source(query, "GraphQL request"));
    } catch (syntaxError: unknown) {
      // Return 400: Bad Request if any syntax errors errors exist.
      if (syntaxError instanceof Error) {
        console.error(`${syntaxError.stack || syntaxError.message}`);
        const e = new GraphQLError(syntaxError.message, {
          originalError: syntaxError,
        });
        return c.json(errorMessages(["GraphQL syntax error."], [e]), 400);
      }
      throw syntaxError;
    }

    // Validate AST, reporting any errors.
    const validationErrors = validate(schema, documentAST, [
      ...specifiedRules,
      ...validationRules,
    ]);

    if (validationErrors.length > 0) {
      // Return 400: Bad Request if any validation errors exist.
      return c.json(
        errorMessages(["GraphQL validation error."], validationErrors),
        400
      );
    }

    if (c.req.method === "GET") {
      // Determine if this GET request will perform a non-query.
      const operationAST = getOperationAST(documentAST, operationName);
      if (operationAST && operationAST.operation !== "query") {
        /*
        Now , does not support GraphiQL
        if (showGraphiQL) {
          //return respondWithGraphiQL(response, graphiqlOptions, params)
        }
        */

        // Otherwise, report a 405: Method Not Allowed error.
        return c.json(
          errorMessages([
            `Can only perform a ${operationAST.operation} operation from a POST request.`,
          ]),
          405,
          { Allow: "POST" }
        );
      }
    }

    let result: FormattedExecutionResult;

    try {
      result = await execute({
        schema,
        document: documentAST,
        rootValue,
        variableValues: variables,
        operationName: operationName,
      });
    } catch (contextError: unknown) {
      if (contextError instanceof Error) {
        console.error(`${contextError.stack || contextError.message}`);
        const e = new GraphQLError(contextError.message, {
          originalError: contextError,
          nodes: documentAST,
        });
        // Return 400: Bad Request if any execution context errors exist.
        return c.json(
          errorMessages(["GraphQL execution context error."], [e]),
          400
        );
      }
      throw contextError;
    }

    if (!result.data) {
      if (result.errors) {
        return c.json(
          errorMessages([result.errors.toString()], result.errors),
          500
        );
      }
    }

    /*
    Now, does not support GraphiQL
    if (showGraphiQL) {
    }
    */

    if (pretty) {
      const payload = JSON.stringify(result, null, pretty ? 2 : 0);
      return c.text(payload, 200, {
        "Content-Type": "application/json",
      });
    } else {
      return c.json(result);
    }

    await next(); // XXX
  };
};

export interface GraphQLParams {
  query: string | null;
  variables: { readonly [name: string]: unknown } | null;
  operationName: string | null;
  raw: boolean;
}

export const getGraphQLParams = async (
  request: Request
): Promise<GraphQLParams> => {
  const urlData = new URLSearchParams(request.url.split("?")[1]);
  const bodyData = await parseBody(request);

  // GraphQL Query string.
  let query = urlData.get("query") ?? (bodyData.query as string | null);

  if (typeof query !== "string") {
    query = null;
  }

  // Parse the variables if needed.
  let variables = (urlData.get("variables") ?? bodyData.variables) as {
    readonly [name: string]: unknown;
  } | null;
  if (typeof variables === "string") {
    try {
      variables = JSON.parse(variables);
    } catch {
      throw Error("Variables are invalid JSON.");
    }
  } else if (typeof variables !== "object") {
    variables = null;
  }

  // Name of GraphQL operation to execute.
  let operationName =
    urlData.get("operationName") ?? (bodyData.operationName as string | null);
  if (typeof operationName !== "string") {
    operationName = null;
  }

  const raw = urlData.get("raw") != null || bodyData.raw !== undefined;

  const params: GraphQLParams = {
    query: query,
    variables: variables,
    operationName: operationName,
    raw: raw,
  };

  return params;
};

export const errorMessages = (
  messages: string[],
  graphqlErrors?: readonly GraphQLError[] | readonly GraphQLFormattedError[]
) => {
  if (graphqlErrors) {
    return {
      errors: graphqlErrors,
    };
  }

  return {
    errors: messages.map((message) => {
      return {
        message: message,
      };
    }),
  };
};

// export const graphiQLResponse = () => {}