// Theme handling
const themeToggle = document.getElementById('themeToggle');
const themeIcon = document.getElementById('themeIcon');

function applyStoredTheme() {
  const stored = localStorage.getItem('theme');
  const prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
  const useDark = stored ? stored === 'dark' : prefersDark;
  document.documentElement.classList.toggle('dark', useDark);
  themeIcon.textContent = useDark ? '☀️' : '🌙';
}
applyStoredTheme();

themeToggle.addEventListener('click', () => {
  const isDark = document.documentElement.classList.toggle('dark');
  localStorage.setItem('theme', isDark ? 'dark' : 'light');
  themeIcon.textContent = isDark ? '☀️' : '🌙';
});

const editor = document.getElementById('editor');
const preview = document.getElementById('preview');
const renderBtn = document.getElementById('renderBtn');
const copyTexBtn = document.getElementById('copyTexBtn');
const clearBtn = document.getElementById('clearBtn');
const renderError = document.getElementById('renderError');
const autofixStatus = document.getElementById('autofixStatus');

function renderLatex(value) {
  renderError.classList.add('hidden');
  renderError.textContent = '';
  preview.innerHTML = '';

  try {
    // Reset content before rendering to ensure size recalculations
    katex.render(value || '', preview, {
      throwOnError: true,
      displayMode: true,
      trust: false,
      strict: 'warn',
      output: 'htmlAndMathml',
      macros: {
        '\\f': '#1f(#2)',
      },
    });
  } catch (err) {
    renderError.classList.remove('hidden');
    renderError.textContent = 'KaTeX error: ' + (err?.message || String(err));
    // Render with throwOnError=false to still show a best-effort preview
    try {
      katex.render(value || '', preview, {
        throwOnError: false,
        displayMode: true,
        trust: false,
        strict: 'warn',
        output: 'htmlAndMathml',
      });
    } catch (e2) {
      // ignore
    }
  }
}

function escapeRegExp(string) {
  return string.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
}

// Simple tokenizer to avoid replacing inside macro or environment names
function findLikelyCommandRanges(text) {
  // Return ranges [start,end) of sequences likely to be command names
  // (alphabetic sequences after a backslash)
  const ranges = [];
  const re = /\\([A-Za-z]+)/g;
  let m;
  while ((m = re.exec(text)) !== null) {
    ranges.push([m.index, m.index + m[0].length]);
  }
  return ranges;
}

function isIndexInRanges(index, ranges) {
  for (const [s, e] of ranges) {
    if (index >= s && index < e) return true;
  }
  return false;
}

// Auto syntax fixer
function autoFixLatex(input) {
  if (!input) return input;

  let text = input;

  // Normalize whitespace and dashes
  text = text
    .replace(/\r\n?/g, '\n')
    .replace(/[ \t]+/g, ' ')
    .replace(/–|—/g, '-')
    .replace(/−/g, '-');

  // Convert common ASCII relations to LaTeX
  const replacements = [
    { from: '>=', to: '\\geq' },
    { from: '<=', to: '\\leq' },
    { from: '!=', to: '\\neq' },
    { from: '~=', to: '\\approx' },
    { from: '+=+', to: '\\pm' },   // handle user typed "+=+"
    { from: '+/-', to: '\\pm' },
  ];
  for (const r of replacements) {
    const re = new RegExp(escapeRegExp(r.from), 'g');
    text = text.replace(re, r.to);
  }

  // Convert common words to functions
  const funcs = ['sin', 'cos', 'tan', 'cot', 'sec', 'csc', 'log', 'ln', 'exp', 'max', 'min', 'argmax', 'argmin'];
  const ranges = findLikelyCommandRanges(text);
  for (const fn of funcs) {
    const re = new RegExp(`\\b${escapeRegExp(fn)}\\b`, 'gi');
    text = text.replace(re, (m) => {
      const idx = m.index ?? 0;
      // If already preceded by backslash, leave it
      if (idx > 0 && text[idx - 1] === '\\') return m;
      // If inside an already detected command, leave it
      if (isIndexInRanges(idx, ranges)) return m;
      return `\\${m.toLowerCase()}`;
    });
  }

  // sqrt shortcuts: "sqrt(...)" or user typed "^/" to suggest root
  text = text.replace(/\bsqrt\s*\(\s*([^)]+?)\s*\)/gi, (_, inside) => `\\sqrt{${inside}}`);
  // If user typed "n√" like n√x, convert to \sqrt[n]{x} when braces after caret were intended
  text = text.replace(/(\d+)\s*\^\s*\/\s*([A-Za-z0-9\\]+)/g, (_, n, expr) => `\\sqrt[${n}]{${expr}}`);

  // Replace slash "a/b" with fraction if likely math context (alphanumeric on both sides)
  text = text.replace(/([A-Za-z0-9}\)])\s*\/\s*([A-Za-z0-9{($]|\^|_|\\\\)/g, (m, a, b) => {
    // Avoid http:// and similar
    if (/https?:\/\//.test(m)) return m;
    return `\\frac{${a}}{${b}}`;
  });

  // Ensure some common operators are LaTeX
  text = text.replace(/\[/g, '\\left[').replace(/\]/g, '\\right]');
  text = text.replace(/\(/g, '\\left(').replace(/\)/g, '\\right)');
  text = text.replace(/\|/g, '\\left|\\,\\right|'); // moderate auto-grouping

  // Normalize percentages and degrees
  text = text.replace(/([A-Za-z0-9\)])\s*%\s*/g, '$1\\%');

  // Fix double backslashes and missing backslash in common commands
  text = text.replace(/\\+/g, (m) => (m.length % 2 === 0 ? '\\' : m)); // keep single backslash

  // Replace plain asterisks with \cdot in likely math contexts
  text = text.replace(/([A-Za-z0-9])\s*\*\s*([A-Za-z0-9])/g, '$1\\cdot$2');

  return text;
}

// Insert snippet helpers
function insertSnippet(value) {
  const start = editor.selectionStart;
  const end = editor.selectionEnd;
  const before = editor.value.slice(0, start);
  const after = editor.value.slice(end);

  // If snippet contains ■, select the first placeholder region (including braces) so user can type over it
  let newValue = before + value + after;
  let cursorPos = newValue.length;

  const placeholderIdx = value.indexOf('■');
  if (placeholderIdx !== -1) {
    // Replace only the first ■ with empty string; we'll select a region around it to ease typing
    const cleaned = value.replace('■', '');
    const insertPos = before.length + placeholderIdx;

    // Try to find the nearest pair of braces after the placeholder to select content inside
    let selectStart = insertPos;
    let selectEnd = insertPos;

    // Naive: select a short word after placeholder if exists; else just place cursor
    const rest = value.slice(placeholderIdx + 1);
    const matchWord = rest.match(/^[A-Za-z0-9\\^_]+/);
    if (matchWord) {
      selectEnd = insertPos + matchWord[0].length;
    } else {
      selectStart = insertPos;
      selectEnd = insertPos;
    }

    newValue = before + cleaned + after;
    editor.value = newValue;

    // Put cursor or select content
    requestAnimationFrame(() => {
      editor.focus();
      if (selectEnd > selectStart) {
        editor.setSelectionRange(selectStart, selectEnd);
      } else {
        editor.setSelectionRange(insertPos, insertPos);
      }
      // Trigger rendering and fixing
      triggerUpdate();
    });
    return;
  }

  // No placeholder: just insert
  editor.value = newValue;
  requestAnimationFrame(() => {
    const caret = before.length + value.length;
    editor.setSelectionRange(caret, caret);
    editor.focus();
    triggerUpdate();
  });
}

// Command board click handling
document.querySelectorAll('.cmd').forEach(btn => {
  btn.addEventListener('click', () => {
    const snippet = btn.getAttribute('data-insert') || '';
    insertSnippet(snippet);
  });
});

// Keyboard navigation within command board (Tab/Shift+Tab)
document.addEventListener('keydown', (e) => {
  const isCommandRegion = e.target.closest('.cmd') !== null;
  if (!isCommandRegion) return;
  const cmds = Array.from(document.querySelectorAll('.cmd'));
  const idx = cmds.indexOf(e.target);
  if (e.key === 'Tab') {
    e.preventDefault();
    const dir = e.shiftKey ? -1 : 1;
    const next = (idx + dir + cmds.length) % cmds.length;
    cmds[next].focus();
  }
});

// Update pipeline
let lastRendered = '';
let lastFixed = '';
let lastUserInput = '';

function triggerUpdate() {
  const current = editor.value;
  if (current === lastUserInput) {
    // If nothing changed (e.g., selection change only), still try to render
    renderLatex(lastFixed || current);
    return;
  }

  const fixed = autoFixLatex(current);
  lastUserInput = current;
  lastFixed = fixed;

  // Only render if changed to reduce churn
  if (fixed !== lastRendered) {
    lastRendered = fixed;
    renderLatex(fixed);
  } else {
    renderLatex(fixed);
  }
}

editor.addEventListener('input', triggerUpdate);
renderBtn.addEventListener('click', triggerUpdate);

copyTexBtn.addEventListener('click', async () => {
  try {
    const text = lastFixed || editor.value || '';
    await navigator.clipboard.writeText(text);
    copyTexBtn.textContent = 'Copied!';
    setTimeout(() => (copyTexBtn.textContent = 'Copy LaTeX'), 1200);
  } catch {
    alert('Copy failed. Please select and copy manually.');
  }
});

clearBtn.addEventListener('click', () => {
  editor.value = '';
  lastUserInput = '';
  lastFixed = '';
  lastRendered = '';
  renderLatex('');
  editor.focus();
});

// Initial render with sample
editor.value = String.raw`\int_{0}^{\infty} e^{-x^2} \, dx = \frac{\sqrt{\pi}}{2}`;
triggerUpdate();