/**
 * Log levels.
 * 
 * Note: Currently, this acts like a bit set, where the upper 4 bits of an
 * unsigned 16 bit value are the log level flags.
 */
export enum LogLevel {
  CERR_FATAL = 0x8000,
  CERR_ERROR = 0x4000,
  CERR_WARNING = 0x2000,
  // Note: 0x01000 is a memory error, but that is never raised in TypeScript
  CERR_INFO = 0x0000,  // N.B., not in widespread use
};

/**
 * Error codes. Use these when logging messages.
 * 
 * Extends https://github.com/keymanapp/keyman/blob/99db3c0d2448f448242e6397f9d72e9a7ccee4b9/windows/src/global/inc/Comperr.h
 */
export enum KeymanCompilerError {
  CERR_LEXICAL_MODEL_MIN = 0x0800,
  CERR_LEXICAL_MODEL_MAX = 0x08FF,


  CERR_FATAL_LM = LogLevel.CERR_FATAL | CERR_LEXICAL_MODEL_MIN,
  /* Place all fatal LM compiler errors here! */

  CERR_ERROR_LM = LogLevel.CERR_ERROR | CERR_LEXICAL_MODEL_MIN,
  /* Place all recoverable LM compiler errors here! */

  CERR_WARN_LM = LogLevel.CERR_WARNING | CERR_LEXICAL_MODEL_MIN,
  /* Place all LM compiler warnings here! */
  CWARN_MixedNormalizationForms = 0x2801,
  CWARN_DuplicateWordInSameFile = 0x2802,

  /* Errors that are not specific to the lexical model compiler: */
  CWARN_TooManyErrorsOrWarnings = 0x20A7,
}

/**
 * Human-readable titles for the various log levels.
 * 
 * Taken from https://github.com/keymanapp/keyman/blob/d83cfffe511ce65b781f919e89e3693146844849/windows/src/developer/TIKE/project/Keyman.Developer.System.Project.ProjectLog.pas#L39-L46
 */
const LOG_LEVEL_TITLE: {[level in LogLevel]: string} = {
  [LogLevel.CERR_INFO]: '',
  [LogLevel.CERR_WARNING]: 'Warning',
  [LogLevel.CERR_ERROR]: 'Error',
  [LogLevel.CERR_FATAL]: 'Fatal Error',
};

/**
 * How many errors or warnings are too many!
 */
export const MAX_MESSAGES = 100;

/**
 * Direct where log messages go.
 */
let _logHandler: (log: LogMessage) => void = printLogs;

/**
 * How many logs or warnings have been witnessed so far.
 */
let _messagesSeen = 0;

/**
 * Logs compiler messages (warnings, errors, logs).
 * 
 * @param code Error code
 * @param message A helpful message!
 * @param source [optional] the filename/line number in the source that induced this error
 * 
 * @see https://github.com/keymanapp/keyman/blob/99db3c0d2448f448242e6397f9d72e9a7ccee4b9/windows/src/developer/TIKE/project/Keyman.Developer.System.Project.ProjectLog.pas#L60-L77
 */
export function log(code: KeymanCompilerError, message: string, source?: FilenameAndLineNo) {
  // Ignore the request if there are too many messages
  if (_messagesSeen > MAX_MESSAGES)
    return;

  let logMessage = source
    ? new LogMessageFromSource(code, message, source)
    : new OrdinaryLogMessage(code, message);

  _logHandler(logMessage)
  _messagesSeen++;

  if (_messagesSeen > MAX_MESSAGES) {
      _logHandler(new OrdinaryLogMessage(
        KeymanCompilerError.CWARN_TooManyErrorsOrWarnings,
        `More than ${MAX_MESSAGES} warnings or errors received; suppressing further messages`
      ));
  }
}

/**
 * Override where log messages go.
 * 
 * @param fn The desired log message handler.
 */
export function redirectLogMessagesTo(fn: (log: LogMessage) => void) {
  _logHandler = fn;
}

/**
 * Reset the log message handler to the default.
 */
export function resetLogMessageHandler() {
  _logHandler = printLogs;
  _messagesSeen = 0;
}

/**
 * Prints log messages to stdout. The default log action.
 */
export function printLogs(log: LogMessage): void {
  console.log(log.format());
}

/**
 * Duct tapes together a filename and a line number of a log.
 */
interface FilenameAndLineNo {
  readonly filename: string;
  readonly lineno: number;
}

/**
 * A log message that knows how to format itself.
 */
export interface LogMessage {
  readonly code: KeymanCompilerError;
  readonly level: LogLevel;
  readonly message: string;

  format(): string;
}

/**
 * Concrete implementation of the log message.
 */
class OrdinaryLogMessage implements LogMessage {
  readonly code: KeymanCompilerError;
  readonly message: string;

  constructor(code: KeymanCompilerError, message: string) {
    this.code = code;
    this.message = message;
  }

  get level(): LogLevel {
    return this.code & 0xF000;
  }

  determineLogLevelTitle(): string {
    return LOG_LEVEL_TITLE[this.level] || '';
  }

  format(): string {
    let prefix = this.determineLogLevelTitle();
    if (prefix)
      prefix = `${prefix}: `;

    return `${prefix}${h(this.code)} ${this.message}`   
  }
}

/**
 * A log message with a filename and line number.
 */
class LogMessageFromSource extends OrdinaryLogMessage {
  readonly filename: string;
  readonly lineno: number;

  constructor(code: KeymanCompilerError, message: string, source: FilenameAndLineNo) {
    super(code, message);
    this.filename = source.filename;
    this.lineno = source.lineno;
  }

  format(): string {
    let originalMessage = super.format();
    return `${this.filename} (${this.lineno}): ${originalMessage}`;
  }
}

/**
 * Format a number as a zero-padded 4 digit hexadecimal.
 */
function h(n: number) {
  let formatted = n.toString(16).toUpperCase();
  if (formatted.length < 4) {
    formatted = '0'.repeat(4 - formatted.length);
  }

  return formatted; 
}