/**
 * 答案推導工具 - 從例句和挖空例句中動態推導正確答案
 */

export interface AnswerExtractionResult {
  answers: string[];
  isValid: boolean;
  error?: string;
}

/**
 * 從例句和挖空題目中提取答案
 * @param example 原始例句
 * @param filledQuestion 挖空後的題目
 * @returns 提取的答案陣列
 */
export function extractAnswerFromBlanks(example: string, filledQuestion: string): AnswerExtractionResult {
  try {
    // 輸入驗證
    if (!example || !filledQuestion) {
      return {
        answers: [],
        isValid: false,
        error: "例句或挖空題目為空"
      };
    }

    if (!filledQuestion.includes('____')) {
      return {
        answers: [],
        isValid: false,
        error: "挖空題目中沒有找到 ____"
      };
    }

    // 方法1: 正則匹配法 (推薦用於單個空格)
    if (filledQuestion.split('____').length === 2) {
      return extractSingleBlankAnswer(example, filledQuestion);
    }

    // 方法2: 差異比對法 (用於多個空格)
    return extractMultipleBlanksAnswers(example, filledQuestion);

  } catch (error) {
    return {
      answers: [],
      isValid: false,
      error: `答案提取失敗: ${error instanceof Error ? error.message : '未知錯誤'}`
    };
  }
}

/**
 * 提取單個空格的答案 (正則匹配法)
 */
function extractSingleBlankAnswer(example: string, filledQuestion: string): AnswerExtractionResult {
  try {
    // 轉義特殊字符並替換 ____ 為捕獲群組
    const escapedPattern = filledQuestion
      .replace(/[.*+?^${}()|[\]\\]/g, '\\$&')  // 轉義正則特殊字符
      .replace(/____/g, '(.+?)');               // 替換為非貪婪捕獲群組

    const regex = new RegExp(`^${escapedPattern}$`, 'i');
    const match = example.match(regex);

    if (match && match[1]) {
      const answer = match[1].trim();
      return {
        answers: [answer],
        isValid: true
      };
    }

    // 如果完全匹配失敗，嘗試部分匹配
    const partialRegex = new RegExp(escapedPattern, 'i');
    const partialMatch = example.match(partialRegex);

    if (partialMatch && partialMatch[1]) {
      const answer = partialMatch[1].trim();
      return {
        answers: [answer],
        isValid: true
      };
    }

    return {
      answers: [],
      isValid: false,
      error: "無法匹配例句和挖空題目"
    };

  } catch (error) {
    return {
      answers: [],
      isValid: false,
      error: `正則匹配失敗: ${error instanceof Error ? error.message : '未知錯誤'}`
    };
  }
}

/**
 * 提取多個空格的答案 (差異比對法)
 */
function extractMultipleBlanksAnswers(example: string, filledQuestion: string): AnswerExtractionResult {
  try {
    const parts = filledQuestion.split('____');
    const answers: string[] = [];

    let currentPos = 0;

    for (let i = 0; i < parts.length - 1; i++) {
      const beforePart = parts[i];
      const afterPart = parts[i + 1];

      // 找到前半部分的結束位置
      const startPos = currentPos + beforePart.length;

      // 找到後半部分的開始位置
      let endPos: number;
      if (afterPart === '') {
        // 如果是最後一個空格，到句子結尾
        endPos = example.length;
      } else {
        endPos = example.indexOf(afterPart, startPos);
        if (endPos === -1) {
          return {
            answers: [],
            isValid: false,
            error: `無法找到後半部分: "${afterPart}"`
          };
        }
      }

      // 提取中間的詞作為答案
      const answer = example.substring(startPos, endPos).trim();
      answers.push(answer);

      currentPos = endPos;
    }

    return {
      answers,
      isValid: answers.length > 0 && answers.every(ans => ans.length > 0)
    };

  } catch (error) {
    return {
      answers: [],
      isValid: false,
      error: `多空格提取失敗: ${error instanceof Error ? error.message : '未知錯誤'}`
    };
  }
}

/**
 * 獲取填空題的第一個答案 (最常用)
 * @param example 原始例句
 * @param filledQuestion 挖空後的題目
 * @param fallbackAnswer 降級答案 (通常是 word 屬性)
 * @returns 正確答案字串
 */
export function getCorrectAnswer(
  example: string,
  filledQuestion: string | undefined,
  fallbackAnswer: string
): string {
  if (!filledQuestion) {
    return fallbackAnswer;
  }

  const result = extractAnswerFromBlanks(example, filledQuestion);

  if (result.isValid && result.answers.length > 0) {
    return result.answers[0];
  }

  // 推導失敗時使用降級答案
  console.warn('答案推導失敗，使用降級答案:', result.error);
  return fallbackAnswer;
}

/**
 * 驗證用戶答案是否正確
 * @param userAnswer 用戶輸入的答案
 * @param example 原始例句
 * @param filledQuestion 挖空後的題目
 * @param fallbackAnswer 降級答案
 * @returns 是否正確
 */
export function validateAnswer(
  userAnswer: string,
  example: string,
  filledQuestion: string | undefined,
  fallbackAnswer: string
): boolean {
  const correctAnswer = getCorrectAnswer(example, filledQuestion, fallbackAnswer);
  return userAnswer.toLowerCase().trim() === correctAnswer.toLowerCase().trim();
}