// 文本比对算法
function textCompare(original, comparison) {
  // 将文本按字符分割为数组
  const originalChars = [...original];
  const comparisonChars = [...comparison];

  // 计算最长公共子序列(LCS)
  const lcsMatrix = computeLCSMatrix(originalChars, comparisonChars);

  // 获取差异结果
  const diffResult = getDiffResult(lcsMatrix, originalChars, comparisonChars);

  return diffResult;
}

// 计算LCS矩阵
function computeLCSMatrix(seq1, seq2) {
  const m = seq1.length;
  const n = seq2.length;
  const matrix = Array(m + 1).fill().map(() => Array(n + 1).fill(0));

  for (let i = 1; i <= m; i++) {
    for (let j = 1; j <= n; j++) {
      if (seq1[i - 1] === seq2[j - 1]) {
        matrix[i][j] = matrix[i - 1][j - 1] + 1;
      } else {
        matrix[i][j] = Math.max(matrix[i - 1][j], matrix[i][j - 1]);
      }
    }
  }

  return matrix;
}

// 获取差异结果
function getDiffResult(matrix, seq1, seq2) {
  let i = seq1.length;
  let j = seq2.length;
  const result1 = []; // 原文结果
  const result2 = []; // 对比文本结果

  while (i > 0 || j > 0) {
    if (i > 0 && j > 0 && seq1[i - 1] === seq2[j - 1]) {
      // 字符相同
      result1.unshift({ char: seq1[i - 1], type: 'same' });
      result2.unshift({ char: seq2[j - 1], type: 'same' });
      i--;
      j--;
    } else if (j > 0 && (i === 0 || matrix[i][j - 1] >= matrix[i - 1][j])) {
      // 对比文本有额外字符
      result2.unshift({ char: seq2[j - 1], type: 'added' });
      j--;
    } else if (i > 0 && (j === 0 || matrix[i][j - 1] < matrix[i - 1][j])) {
      // 原文有额外字符
      result1.unshift({ char: seq1[i - 1], type: 'deleted' });
      i--;
    }
  }

  return { original: result1, comparison: result2 };
}

// 渲染比对结果
function renderComparison(result) {
  const originalResult = document.getElementById('originalResult');
  const comparisonResult = document.getElementById('comparisonResult');

  // 渲染原文
  originalResult.innerHTML = '';
  let currentSpan = null;

  result.original.forEach(item => {
    if (item.type === 'same') {
      if (currentSpan && currentSpan.className === 'highlight-red') {
        originalResult.appendChild(currentSpan);
        currentSpan = null;
      }

      if (!currentSpan || currentSpan.className !== 'same-text') {
        if (currentSpan) originalResult.appendChild(currentSpan);
        currentSpan = document.createElement('span');
        currentSpan.className = 'same-text';
      }

      currentSpan.textContent += item.char;
    } else { // deleted
      if (currentSpan && currentSpan.className === 'same-text') {
        originalResult.appendChild(currentSpan);
        currentSpan = null;
      }

      if (!currentSpan || currentSpan.className !== 'highlight-red') {
        if (currentSpan) originalResult.appendChild(currentSpan);
        currentSpan = document.createElement('span');
        currentSpan.className = 'highlight-red';
      }

      currentSpan.textContent += item.char;
    }
  });

  if (currentSpan) originalResult.appendChild(currentSpan);

  // 渲染对比文本
  currentSpan = null;
  comparisonResult.innerHTML = '';

  result.comparison.forEach(item => {
    if (item.type === 'same') {
      if (currentSpan && currentSpan.className === 'highlight-green') {
        comparisonResult.appendChild(currentSpan);
        currentSpan = null;
      }

      if (!currentSpan || currentSpan.className !== 'same-text') {
        if (currentSpan) comparisonResult.appendChild(currentSpan);
        currentSpan = document.createElement('span');
        currentSpan.className = 'same-text';
      }

      currentSpan.textContent += item.char;
    } else { // added
      if (currentSpan && currentSpan.className === 'same-text') {
        comparisonResult.appendChild(currentSpan);
        currentSpan = null;
      }

      if (!currentSpan || currentSpan.className !== 'highlight-green') {
        if (currentSpan) comparisonResult.appendChild(currentSpan);
        currentSpan = document.createElement('span');
        currentSpan.className = 'highlight-green';
      }

      currentSpan.textContent += item.char;
    }
  });

  if (currentSpan) comparisonResult.appendChild(currentSpan);
}

// 执行比对
function compareTexts() {
  const originalText = document.getElementById('originalText').value;
  const comparisonText = document.getElementById('comparisonText').value;

  const result = textCompare(originalText, comparisonText);
  renderComparison(result);
}

// 页面加载时执行一次比对
window.onload = compareTexts;