// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
const { listen, copy, toAsyncIterator } = Deno;
type Listener = Deno.Listener;
type Conn = Deno.Conn;
type Reader = Deno.Reader;
type Writer = Deno.Writer;
import { BufReader, BufState, BufWriter } from "../io/bufio.ts";
import { TextProtoReader } from "../textproto/mod.ts";
import { STATUS_TEXT } from "./http_status.ts";
import { assert, fail } from "../testing/asserts.ts";
import {
  collectUint8Arrays,
  deferred,
  Deferred,
  MuxAsyncIterator
} from "../util/async.ts";

function bufWriter(w: Writer): BufWriter {
  if (w instanceof BufWriter) {
    return w;
  } else {
    return new BufWriter(w);
  }
}

export function setContentLength(r: Response): void {
  if (!r.headers) {
    r.headers = new Headers();
  }

  if (r.body) {
    if (!r.headers.has("content-length")) {
      if (r.body instanceof Uint8Array) {
        const bodyLength = r.body.byteLength;
        r.headers.append("Content-Length", bodyLength.toString());
      } else {
        r.headers.append("Transfer-Encoding", "chunked");
      }
    }
  }
}

async function writeChunkedBody(w: Writer, r: Reader): Promise<void> {
  const writer = bufWriter(w);
  const encoder = new TextEncoder();

  for await (const chunk of toAsyncIterator(r)) {
    if (chunk.byteLength <= 0) continue;
    const start = encoder.encode(`${chunk.byteLength.toString(16)}\r\n`);
    const end = encoder.encode("\r\n");
    await writer.write(start);
    await writer.write(chunk);
    await writer.write(end);
  }

  const endChunk = encoder.encode("0\r\n\r\n");
  await writer.write(endChunk);
}

export async function writeResponse(w: Writer, r: Response): Promise<void> {
  const protoMajor = 1;
  const protoMinor = 1;
  const statusCode = r.status || 200;
  const statusText = STATUS_TEXT.get(statusCode);
  const writer = bufWriter(w);
  if (!statusText) {
    throw Error("bad status code");
  }

  let out = `HTTP/${protoMajor}.${protoMinor} ${statusCode} ${statusText}\r\n`;

  setContentLength(r);

  if (r.headers) {
    for (const [key, value] of r.headers) {
      out += `${key}: ${value}\r\n`;
    }
  }
  out += "\r\n";

  const header = new TextEncoder().encode(out);
  let n = await writer.write(header);
  assert(header.byteLength == n);

  if (r.body) {
    if (r.body instanceof Uint8Array) {
      n = await writer.write(r.body);
      assert(r.body.byteLength == n);
    } else {
      if (r.headers.has("content-length")) {
        const bodyLength = parseInt(r.headers.get("content-length"));
        const n = await copy(writer, r.body);
        assert(n == bodyLength);
      } else {
        await writeChunkedBody(writer, r.body);
      }
    }
  }
  await writer.flush();
}

export class ServerRequest {
  url: string;
  method: string;
  proto: string;
  headers: Headers;
  conn: Conn;
  r: BufReader;
  w: BufWriter;
  done: Deferred<void> = deferred();

  public async *bodyStream(): AsyncIterableIterator<Uint8Array> {
    if (this.headers.has("content-length")) {
      const len = +this.headers.get("content-length");
      if (Number.isNaN(len)) {
        return new Uint8Array(0);
      }
      let buf = new Uint8Array(1024);
      let rr = await this.r.read(buf);
      let nread = rr.nread;
      while (!rr.eof && nread < len) {
        yield buf.subarray(0, rr.nread);
        buf = new Uint8Array(1024);
        rr = await this.r.read(buf);
        nread += rr.nread;
      }
      yield buf.subarray(0, rr.nread);
    } else {
      if (this.headers.has("transfer-encoding")) {
        const transferEncodings = this.headers
          .get("transfer-encoding")
          .split(",")
          .map((e): string => e.trim().toLowerCase());
        if (transferEncodings.includes("chunked")) {
          // Based on https://tools.ietf.org/html/rfc2616#section-19.4.6
          const tp = new TextProtoReader(this.r);
          let [line] = await tp.readLine();
          // TODO: handle chunk extension
          let [chunkSizeString] = line.split(";");
          let chunkSize = parseInt(chunkSizeString, 16);
          if (Number.isNaN(chunkSize) || chunkSize < 0) {
            throw new Error("Invalid chunk size");
          }
          while (chunkSize > 0) {
            let data = new Uint8Array(chunkSize);
            let [nread] = await this.r.readFull(data);
            if (nread !== chunkSize) {
              throw new Error("Chunk data does not match size");
            }
            yield data;
            await this.r.readLine(); // Consume \r\n
            [line] = await tp.readLine();
            chunkSize = parseInt(line, 16);
          }
          const [entityHeaders, err] = await tp.readMIMEHeader();
          if (!err) {
            for (let [k, v] of entityHeaders) {
              this.headers.set(k, v);
            }
          }
          /* Pseudo code from https://tools.ietf.org/html/rfc2616#section-19.4.6
          length := 0
          read chunk-size, chunk-extension (if any) and CRLF
          while (chunk-size > 0) {
            read chunk-data and CRLF
            append chunk-data to entity-body
            length := length + chunk-size
            read chunk-size and CRLF
          }
          read entity-header
          while (entity-header not empty) {
            append entity-header to existing header fields
            read entity-header
          }
          Content-Length := length
          Remove "chunked" from Transfer-Encoding
          */
          return; // Must return here to avoid fall through
        }
        // TODO: handle other transfer-encoding types
      }
      // Otherwise...
      yield new Uint8Array(0);
    }
  }

  // Read the body of the request into a single Uint8Array
  public async body(): Promise<Uint8Array> {
    return collectUint8Arrays(this.bodyStream());
  }

  async respond(r: Response): Promise<void> {
    // Write our response!
    await writeResponse(this.w, r);
    // Signal that this request has been processed and the next pipelined
    // request on the same connection can be accepted.
    this.done.resolve();
  }
}

async function readRequest(
  conn: Conn,
  bufr: BufReader
): Promise<[ServerRequest, BufState]> {
  const req = new ServerRequest();
  req.conn = conn;
  req.r = bufr;
  req.w = new BufWriter(conn);
  const tp = new TextProtoReader(bufr);
  let err: BufState;
  // First line: GET /index.html HTTP/1.0
  let firstLine: string;
  [firstLine, err] = await tp.readLine();
  if (err) {
    return [null, err];
  }
  [req.method, req.url, req.proto] = firstLine.split(" ", 3);
  [req.headers, err] = await tp.readMIMEHeader();
  return [req, err];
}

export class Server implements AsyncIterable<ServerRequest> {
  private closing = false;

  constructor(public listener: Listener) {}

  close(): void {
    this.closing = true;
    this.listener.close();
  }

  // Yields all HTTP requests on a single TCP connection.
  private async *iterateHttpRequests(
    conn: Conn
  ): AsyncIterableIterator<ServerRequest> {
    const bufr = new BufReader(conn);
    let bufStateErr: BufState;
    let req: ServerRequest;

    while (!this.closing) {
      [req, bufStateErr] = await readRequest(conn, bufr);
      if (bufStateErr) break;
      yield req;
      // Wait for the request to be processed before we accept a new request on
      // this connection.
      await req.done;
    }

    if (bufStateErr === "EOF") {
      // The connection was gracefully closed.
    } else if (bufStateErr instanceof Error) {
      // TODO(ry): send something back like a HTTP 500 status.
    } else if (this.closing) {
      // There are more requests incoming but the server is closing.
      // TODO(ry): send a back a HTTP 503 Service Unavailable status.
    } else {
      fail(`unexpected BufState: ${bufStateErr}`);
    }

    conn.close();
  }

  // Accepts a new TCP connection and yields all HTTP requests that arrive on
  // it. When a connection is accepted, it also creates a new iterator of the
  // same kind and adds it to the request multiplexer so that another TCP
  // connection can be accepted.
  private async *acceptConnAndIterateHttpRequests(
    mux: MuxAsyncIterator<ServerRequest>
  ): AsyncIterableIterator<ServerRequest> {
    if (this.closing) return;
    // Wait for a new connection.
    const conn = await this.listener.accept();
    // Try to accept another connection and add it to the multiplexer.
    mux.add(this.acceptConnAndIterateHttpRequests(mux));
    // Yield the requests that arrive on the just-accepted connection.
    yield* this.iterateHttpRequests(conn);
  }

  [Symbol.asyncIterator](): AsyncIterableIterator<ServerRequest> {
    const mux: MuxAsyncIterator<ServerRequest> = new MuxAsyncIterator();
    mux.add(this.acceptConnAndIterateHttpRequests(mux));
    return mux.iterate();
  }
}

export function serve(addr: string): Server {
  const listener = listen("tcp", addr);
  return new Server(listener);
}

export async function listenAndServe(
  addr: string,
  handler: (req: ServerRequest) => void
): Promise<void> {
  const server = serve(addr);

  for await (const request of server) {
    handler(request);
  }
}

export interface Response {
  status?: number;
  headers?: Headers;
  body?: Uint8Array | Reader;
}