// HTTP as FILIUS writes and reads it (filius.software.www.HTTPNachricht):
// lines ended by "\n", a request line, a Host header, for POST an empty line
// and the form's data; a response line with Java's status text, a
// Content-type header, an empty line and the body. Paths go encoded as
// Spring's UriUtils.encodePath encodes them (UTF-8, every character a path
// segment may not hold) and are decoded by the server.
//
// Better than Java: a request Java cannot read (a first line without path,
// or an unknown method) gets 400 or 501 (HTTPNachricht throws, the server's
// thread closes the connection without a word); a request without a version
// is HTTP/1.1, the version HTTPNachricht starts with.

export const HTTP_GET = 'GET';
export const HTTP_POST = 'POST';

export type HttpContentType = 'text/html' | 'image/png' | 'image/bmp' | 'image/gif' | 'image/jpg' | 'text/plain';

export interface HttpRequest {
  readonly method: string;
  /** Decoded, with its query; `httpPath` gives it without. */
  readonly path: string;
  readonly protocolVersion: string;
  readonly host: string | undefined;
  /** POST only: what follows the empty line. */
  readonly data: string | undefined;
}

export interface HttpResponse {
  readonly protocolVersion: string;
  readonly statusCode: number;
  readonly contentType: string | undefined;
  readonly body: string | undefined;
}

/** A first line FILIUS' server cannot read: no method, or a method without path (400), or another method (501). */
export type HttpRequestParse = { readonly type: 'request'; readonly request: HttpRequest } | { readonly type: 'invalid'; readonly statusCode: 400 | 501 };

/** Java's StringTokenizer on spaces: the words, without empty ones. */
function words(line: string): string[] {
  return line.split(' ').filter((word) => word !== '');
}

/** Java's String.trim. */
function javaTrim(text: string): string {
  let start = 0;
  let end = text.length;
  while (start < end && text.charCodeAt(start) <= 0x20) start += 1;
  while (end > start && text.charCodeAt(end - 1) <= 0x20) end -= 1;
  return text.slice(start, end);
}

/** Java's String.split("\n"): trailing empty lines dropped. */
function javaLines(text: string): string[] {
  const lines = text.split('\n');
  while (lines.length > 1 && lines[lines.length - 1] === '') lines.pop();
  return lines;
}

/** HTTPNachricht(String) for a request, as the server reads it. */
export function parseHttpRequest(message: string): HttpRequestParse {
  const lines = javaLines(message);
  const [method, rawPath, version] = words(lines[0] ?? '').map(javaTrim);
  if (method === undefined) return { type: 'invalid', statusCode: 400 };
  const upper = method.toUpperCase();
  if (upper !== HTTP_GET && upper !== HTTP_POST) return { type: 'invalid', statusCode: 501 };
  if (rawPath === undefined) return { type: 'invalid', statusCode: 400 };
  const path = decodeUriPath(rawPath);
  if (path === undefined) return { type: 'invalid', statusCode: 400 };
  let host: string | undefined;
  let data: string | undefined;
  for (let index = 1; index < lines.length; index += 1) {
    const line = lines[index]!;
    if (line === '' && upper === HTTP_POST) {
      data = lines.slice(index).join('\n');
      break;
    }
    const [name, value] = words(line).map(javaTrim);
    if (name !== undefined && name.toLowerCase() === 'host:' && value !== undefined) host = value;
  }
  return { type: 'request', request: { method, path, protocolVersion: version ?? 'HTTP/1.1', host, data } };
}

/** HTTPNachricht.getPfad: "/" for none, else without the query. */
export function httpPath(path: string): string {
  if (javaTrim(path) === '') return '/';
  const query = path.indexOf('?');
  return query > 0 ? path.slice(0, query) : path;
}

/** HTTPNachricht.toString for a request (CLIENT): the path without its query, encoded. */
export function formatHttpRequest(request: { method: string; path: string; host: string | undefined; data?: string | undefined }): string {
  let text = `${request.method} ${encodeUriPath(httpPath(request.path))} HTTP/1.1\n`;
  if (request.host !== undefined) text += `Host: ${request.host}\n`;
  if (request.method === HTTP_POST && request.data !== undefined) text += `\n${request.data}`;
  return text;
}

/** HTTPNachricht.toString for a response (SERVER). */
export function formatHttpResponse(response: HttpResponse): string {
  let text = `${response.protocolVersion} ${response.statusCode} ${httpStatusText(response.statusCode)}\n`;
  if (response.contentType !== undefined) text += `Content-type: ${response.contentType}\n`;
  if (response.body !== undefined) text += `\n${response.body}`;
  return text;
}

/** HTTPNachricht(String) for a response, as the browser reads it; undefined when its status is no number. */
export function parseHttpResponse(message: string): HttpResponse | undefined {
  const lines = javaLines(message);
  const [version, status] = words(lines[0] ?? '').map(javaTrim);
  if (version === undefined || status === undefined || !/^[+-]?\d+$/.test(status)) return undefined;
  let contentType: string | undefined;
  let body: string | undefined;
  for (let index = 1; index < lines.length; index += 1) {
    const line = lines[index]!;
    if (line === '') {
      body = lines.slice(index + 1).join('\n');
      break;
    }
    const [name, value] = words(line).map(javaTrim);
    if (name !== undefined && name.toLowerCase() === 'content-type:' && value !== undefined) contentType = value;
  }
  return { protocolVersion: version, statusCode: Number(status), contentType, body };
}

const STATUS_TEXTS: Record<number, string> = {
  100: 'Continue',
  101: 'Switching Protocols',
  102: 'Processing',
  200: 'OK',
  201: 'Created',
  202: 'Accepted',
  203: 'Non-Authoritative Information',
  204: 'No Content',
  205: 'Reset Content',
  206: 'Partial Content',
  207: 'Multi-Status',
  300: 'Multiple Choice',
  301: 'Moved Permanently',
  302: 'Found',
  303: 'See Other',
  304: 'Not Modified',
  305: 'Use Proxy',
  307: 'Temporary Redirect',
  400: 'Bad Request',
  401: 'Unauthorized',
  402: 'Payment Required',
  403: 'Forbidden',
  404: 'Not Found',
  405: 'Method Not Allowed',
  406: 'Not Acceptable',
  407: 'Proxy Authentication Required',
  408: 'Request Time-out',
  409: 'Conflict',
  410: 'Gone',
  411: 'Length Required',
  412: 'Precondition Failed',
  413: 'Request Entity Too Large',
  414: 'Request-URI Too Long',
  415: 'Unsupported Media Type',
  416: 'Requested range not satisfiable',
  417: 'Expectation Failed',
  422: 'Unprocessable Entity',
  423: 'Locked',
  424: 'Failed Dependency',
  500: 'Internal Server Error',
  501: 'Not Implemented',
  502: 'Bad Gateway',
  503: 'Service Unavailable',
  504: 'Gateway Time-out',
  505: 'HTTP Version not supported',
  507: 'Insufficient Storage',
  509: 'Bandwidth Limit Exceeded',
};

/** HTTPNachricht.holeStatusNachricht for the codes FILIUS' server sends (Java's texts for others are its message bundle's). */
export function httpStatusText(code: number): string {
  return STATUS_TEXTS[code] ?? '';
}

/** Characters a path may hold as they are (RFC 3986 pchar and "/"), as Spring's UriUtils.encodePath keeps them. */
const PATH_CHARACTERS = /[A-Za-z0-9\-._~!$&'()*+,;=:@/]/;

/** UriUtils.encodePath(path, "utf8"). */
export function encodeUriPath(path: string): string {
  let text = '';
  for (const character of path) {
    if (PATH_CHARACTERS.test(character)) {
      text += character;
      continue;
    }
    for (const byte of new TextEncoder().encode(character)) text += `%${byte.toString(16).toUpperCase().padStart(2, '0')}`;
  }
  return text;
}

/** UriUtils.decode(path, "utf8"): undefined where Java throws (a "%" without two hex digits). */
export function decodeUriPath(path: string): string | undefined {
  const bytes: number[] = [];
  const encoder = new TextEncoder();
  for (let index = 0; index < path.length; index += 1) {
    if (path[index] === '%') {
      const hex = path.slice(index + 1, index + 3);
      if (!/^[0-9A-Fa-f]{2}$/.test(hex)) return undefined;
      bytes.push(Number.parseInt(hex, 16));
      index += 2;
    } else {
      const code = path.codePointAt(index)!;
      if (code > 0xffff) index += 1;
      bytes.push(...encoder.encode(String.fromCodePoint(code)));
    }
  }
  return new TextDecoder().decode(new Uint8Array(bytes));
}