/**
 * @license
 * Copyright 2025 Vybestack LLC
 * SPDX-License-Identifier: Apache-2.0
 */

import { StreamingState } from '../ui/types.js';

// Matches C0 control characters (U+0000–U+001F) and DEL (U+007F). Built via
// RegExp from a character-class string so the source contains no literal
// control bytes.
const CONTROL_CHAR_PATTERN = `[${String.fromCharCode(0)}-${String.fromCharCode(
  0x1f,
)}${String.fromCharCode(0x7f)}]`;
const CONTROL_CHAR_REGEX = new RegExp(CONTROL_CHAR_PATTERN, 'g');

export interface TerminalTitleOptions {
  streamingState: StreamingState;
  thoughtSubject?: string;
  isConfirming: boolean;
  folderName: string;
  showThoughts: boolean;
  useDynamicTitle: boolean;
}

function truncate(text: string, maxLen: number): string {
  if (text.length <= maxLen) {
    return text;
  }
  return text.substring(0, maxLen - 1) + '…';
}

/**
 * Computes the dynamic terminal window title based on the current CLI state.
 *
 * @param options - The current state of the CLI and environment context
 * @returns A formatted string padded to 80 characters for the terminal title
 */
export function computeTerminalTitle({
  streamingState,
  thoughtSubject,
  isConfirming,
  folderName,
  showThoughts,
  useDynamicTitle,
}: TerminalTitleOptions): string {
  const MAX_LEN = 80;

  // Use CLI_TITLE env var if set and non-empty, otherwise use the folder name.
  const cliTitle = process.env['CLI_TITLE'];
  let displayContext =
    cliTitle !== undefined && cliTitle.length > 0 ? cliTitle : folderName;

  if (!useDynamicTitle) {
    const base = 'LLxprt ';
    // Max context length is 80 - base.length - 2 (for brackets)
    const maxContextLen = MAX_LEN - base.length - 2;
    displayContext = truncate(displayContext, maxContextLen);
    return `${base}(${displayContext})`.padEnd(MAX_LEN, ' ');
  }

  // Pre-calculate suffix but keep it flexible
  const getSuffix = (context: string) => ` (${context})`;

  let title;
  if (
    isConfirming ||
    streamingState === StreamingState.WaitingForConfirmation
  ) {
    const base = '  Action Required';
    // Max context length is 80 - base.length - 3 (for ' (' and ')')
    const maxContextLen = MAX_LEN - base.length - 3;
    const context = truncate(displayContext, maxContextLen);
    title = `${base}${getSuffix(context)}`;
  } else if (streamingState === StreamingState.Idle) {
    const base = '◇  Ready';
    // Max context length is 80 - base.length - 3 (for ' (' and ')')
    const maxContextLen = MAX_LEN - base.length - 3;
    const context = truncate(displayContext, maxContextLen);
    title = `${base}${getSuffix(context)}`;
  } else {
    // Active/Working state
    const rawSubject =
      showThoughts === true
        ? thoughtSubject?.replace(/[\r\n]+/g, ' ').trim()
        : undefined;
    const cleanSubject =
      rawSubject !== undefined && rawSubject !== '' ? rawSubject : undefined;

    // If we have a thought subject and it's too long to fit with the suffix,
    // we drop the suffix to maximize space for the thought.
    // Otherwise, we keep the suffix.
    const suffix = getSuffix(displayContext);
    const suffixLen = suffix.length;
    const canFitThoughtWithSuffix =
      cleanSubject !== undefined
        ? cleanSubject.length + suffixLen + 3 <= MAX_LEN
        : true;

    let activeSuffix = '';
    let maxStatusLen = MAX_LEN - 3; // Subtract icon prefix "  " (3 chars)

    if (cleanSubject === undefined || canFitThoughtWithSuffix) {
      activeSuffix = suffix;
      maxStatusLen -= activeSuffix.length;
    }

    const displayStatus =
      cleanSubject !== undefined
        ? truncate(cleanSubject, maxStatusLen)
        : 'Working…';

    title = `  ${displayStatus}${activeSuffix}`;
  }

  // Remove control characters that could cause issues in terminal titles
  const safeTitle = title.replace(CONTROL_CHAR_REGEX, '');

  // Pad the title to a fixed width to prevent taskbar icon resizing/jitter.
  // We also slice it to ensure it NEVER exceeds MAX_LEN.
  return safeTitle.padEnd(MAX_LEN, ' ').substring(0, MAX_LEN);
}