// Copyright 2026 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

/**
 * Truncates a string to a target length, attempting to cut at the nearest word boundary (space).
 * If the string is truncated, it returns the truncated string and the number of characters removed.
 *
 * @param text The string to truncate.
 * @param targetLength The desired length of the string.
 * @returns An object containing the potentially truncated text and the number of characters removed.
 */
function smartTruncate(text: string, targetLength: number): {truncatedText: string, moreCharacters: number} {
  if (text.length <= targetLength) {
    return {truncatedText: text, moreCharacters: 0};
  }

  const lastSpaceBefore = text.lastIndexOf(' ', targetLength);
  const firstSpaceAfter = text.indexOf(' ', targetLength);

  let cutIndex = targetLength;
  if (lastSpaceBefore === -1 && firstSpaceAfter === -1) {
    cutIndex = targetLength;
  } else if (lastSpaceBefore === -1) {
    cutIndex = firstSpaceAfter;
  } else if (firstSpaceAfter === -1) {
    cutIndex = lastSpaceBefore;
  } else {
    // Both lastSpaceBefore and firstSpaceAfter exist.
    // Choose the one that is closer to the targetLength.
    const distanceToSpaceBefore = targetLength - lastSpaceBefore;
    const distanceToSpaceAfter = firstSpaceAfter - targetLength;
    cutIndex = distanceToSpaceBefore <= distanceToSpaceAfter ? lastSpaceBefore : firstSpaceAfter;
  }

  let truncatedText = text;
  let moreCharacters = 0;
  if (cutIndex < text.length) {
    truncatedText = text.slice(0, cutIndex);
    moreCharacters = text.length - cutIndex;
  }

  return {truncatedText, moreCharacters};
}

/**
 * Returns a label for the walkthrough toggle button.
 * The label includes the current action (Show/Hide) and a smart-truncated version of the prompt.
 */
export function getButtonLabel(input: {
  isExpanded: boolean,
  isLoading: boolean,
  hasWidgets: boolean,
  prompt: string,
  stepTitle?: string,
}): string {
  let labelBase = '';
  if (input.isLoading && !input.isExpanded && input.stepTitle) {
    labelBase = input.stepTitle;
  } else {
    const action = input.isExpanded ? 'Hide' : 'Show';
    const type = input.hasWidgets ? 'AI walkthrough' : 'thinking';
    labelBase = `${action} ${type}`;
  }

  if (input.isLoading) {
    return `Loading: ${labelBase}`;
  }

  const TARGET_LENGTH = 50;
  const {truncatedText, moreCharacters} = smartTruncate(input.prompt, TARGET_LENGTH);
  const promptSuffix = moreCharacters > 0 ? ` (and ${moreCharacters} more characters)` : '';
  return `${labelBase} for prompt ${truncatedText}${promptSuffix}`;
}