const XLSX = require('xlsx');

const SUBJECT_NAMES = [
  'Русский язык', 'Математика', 'Обществознание', 'Физика',
  'Химия', 'Информатика', 'Биология', 'Английский язык',
  'География', 'Литература', 'История', 'Немецкий язык',
  'Французский язык', 'Испанский язык'
];

const HEADER_MAP = {
  'фамилия': 'last_name',
  'имя': 'first_name',
  'отчество': 'patronymic',
  'класс': 'class',
  'код оо': 'school_code',
  'серия': 'passport_series',
  'номер': 'passport_number',
  'первичный балл': 'primary_score',
  'оценка': 'grade'
};

function normalize(s) {
  return String(s || '').trim().toLowerCase();
}

function parseXls(filePath) {
  const workbook = XLSX.readFile(filePath);
  const sheetName = workbook.SheetNames[0];
  const sheet = workbook.Sheets[sheetName];
  const rows = XLSX.utils.sheet_to_json(sheet, { header: 1, defval: '' });

  const parsedSubjects = [];
  const studentsMap = new Map();
  const results = [];

  let currentSubject = null;
  let colIdx = null;

  for (let i = 0; i < rows.length; i++) {
    const row = rows[i];
    if (!row || row.every(c => c === '' || c === null || c === undefined)) continue;

    const firstCell = String(row[0] || '').trim();

    if (isSummaryRowText(firstCell)) {
      currentSubject = null;
      colIdx = null;
      continue;
    }

    const subjectInfo = detectSubject(firstCell);
    if (subjectInfo) {
      currentSubject = subjectInfo;
      parsedSubjects.push(subjectInfo);
      colIdx = null;
      continue;
    }

    if (currentSubject && !colIdx) {
      colIdx = findColumnHeaders(row);
      if (colIdx) continue;
    }

    if (currentSubject && colIdx) {
      const sd = extractStudentData(row, colIdx);
      if (sd && sd.last_name) {
        const key = `${normalize(sd.last_name)}|${normalize(sd.first_name)}|${normalize(sd.patronymic)}|${normalize(sd.class)}`;
        if (!studentsMap.has(key)) {
          studentsMap.set(key, {
            last_name: sd.last_name,
            first_name: sd.first_name,
            patronymic: sd.patronymic,
            class: sd.class,
            school_code: sd.school_code || '',
            passport_series: sd.passport_series || '',
            passport_number: sd.passport_number || ''
          });
        }
        results.push({
          student_key: key,
          subject_code: currentSubject.code,
          subject_name: currentSubject.name,
          exam_date: currentSubject.date || '',
          primary_score: sd.primary_score,
          grade: sd.grade
        });
      }
    }
  }

  return {
    subjects: uniqSubjects(parsedSubjects),
    students: [...studentsMap.values()],
    results
  };
}

function uniqSubjects(subjects) {
  const seen = new Set();
  return subjects.filter(s => {
    if (seen.has(s.code)) return false;
    seen.add(s.code);
    return true;
  });
}

function detectSubject(firstCell) {
  if (!firstCell) return null;
  const match = firstCell.match(/^(\d{2})\s*-\s*(.+?)\s+(\d{4}\.\d{2}\.\d{2})$/);
  if (!match) return null;
  const code = match[1];
  const name = match[2];
  const date = match[3];
  if (SUBJECT_NAMES.some(sn => sn.toLowerCase() === name.toLowerCase())) {
    return { code, name, date };
  }
  return null;
}

function isSummaryRowText(firstCell) {
  return /^(средни|всего|итого)/i.test(firstCell);
}

function findColumnHeaders(row) {
  const map = {};
  for (let i = 0; i < row.length; i++) {
    const s = normalize(String(row[i]));
    for (const [pattern, field] of Object.entries(HEADER_MAP)) {
      if (s === pattern || s.includes(pattern)) {
        map[field] = i;
        break;
      }
    }
  }
  if (map.last_name && (map.primary_score || map.grade)) return map;
  return null;
}

function extractStudentData(row, colIdx) {
  const get = (field) => {
    const idx = colIdx[field];
    if (idx === undefined || idx >= row.length) return '';
    return String(row[idx]).trim();
  };

  const firstCol = String(row[0] || '').trim();
  if (!firstCol || !/^\d+$/.test(firstCol)) return null;

  const last_name = get('last_name');
  if (!last_name || last_name.length < 2) return null;

  const toInt = (v) => {
    const n = parseInt(v, 10);
    return isNaN(n) ? null : n;
  };

  return {
    last_name,
    first_name: get('first_name'),
    patronymic: get('patronymic'),
    class: get('class'),
    school_code: get('school_code'),
    passport_series: get('passport_series'),
    passport_number: get('passport_number'),
    primary_score: toInt(get('primary_score')),
    grade: toInt(get('grade'))
  };
}

module.exports = { parseXls };