const LAST_HOUR = 10;

// -------------------------------
// Helpers
// -------------------------------
export const cleanInput = (input) => (input ?? "").trim().replace(/\s+/g, " ");
export const isTeacherToken = (t) => /^[A-Za-z]+$/.test(t);

export const parseSpec = (spec) => {
  if (!spec) return null;
  let m;
  if ((m = spec.match(/^(\d+)\+$/))) {
    const from = Number(m[1]);
    return from >= 1 && from <= LAST_HOUR
      ? { kind: "range", value: { from, to: LAST_HOUR } }
      : null;
  }
  if ((m = spec.match(/^(\d+)-(\d+)$/))) {
    const from = Number(m[1]);
    const to = Number(m[2]);
    return from >= 1 && to >= from && to <= LAST_HOUR
      ? { kind: "range", value: { from, to } }
      : null;
  }
  if ((m = spec.match(/^(\d+)$/))) {
    const hour = Number(m[1]);
    return hour >= 1 && hour <= LAST_HOUR
      ? { kind: "single", value: hour }
      : null;
  }
  return null;
};

export const resolveTeacher = (teacherCode, teacherMap = {}) => ({
  code: teacherCode,
  name: teacherMap?.[teacherCode.toLowerCase()] ?? null,
});

const makeResult = (teacherCode, spec, teacherMap) => {
  const { name } = resolveTeacher(teacherCode, teacherMap);
  const type = spec ? (spec.kind === "range" ? "range" : "single") : "wholeDay";
  const hours = spec ? spec.value : null;
  return { teacher: name, teacherCode, type, hours };
};

// -------------------------------
// Teacher list processing (modular)
// -------------------------------
const processTeacherList = (teacherListStr, spec, teacherMap) => {
  let results = [];

  if (teacherListStr.includes(",")) {
    // Comma = spec applies to all
    const teachers = teacherListStr.split(/\s*,\s*/).filter(Boolean);
    results = teachers.map((t) => makeResult(t, spec, teacherMap));
  } else if (teacherListStr.includes(";")) {
    // Semicolon = spec applies only to last, others = whole day
    const teachers = teacherListStr.split(/\s*;\s*/).filter(Boolean);
    teachers.forEach((t, i) => {
      const resSpec = i === teachers.length - 1 ? spec : null;
      results.push(makeResult(t, resSpec, teacherMap));
    });
  } else {
    // Single teacher
    results.push(makeResult(teacherListStr, spec, teacherMap));
  }

  return results;
};

// -------------------------------
// Main parser
// -------------------------------
export default function parseAbsence(input, teacherMap = {}) {
  const s = cleanInput(input);
  if (!s) return [];

  const results = [];
  const consumed = [];
  const markConsumed = (start, end) => consumed.push([start, end]);
  const isConsumed = (i) => consumed.some(([a, b]) => i >= a && i < b);

  // Regex: teacher-list [+ optional spec]
  const teacherListThenSpecRe = /([A-Za-z]+(?:[,;]\s?[A-Za-z]+)*)(?:\s*)?(\d+(?:\+|-\d+)?)/g;
  let m;
  while ((m = teacherListThenSpecRe.exec(s)) !== null) {
    const matchStart = m.index;
    const matchEnd = teacherListThenSpecRe.lastIndex;
    if (isConsumed(matchStart)) continue;

    const [_, teacherListStr, specStr] = m;
    const spec = parseSpec(specStr);
    if (!spec) continue;

    results.push(...processTeacherList(teacherListStr, spec, teacherMap));
    markConsumed(matchStart, matchEnd);
  }

  // Standalone teachers → whole day
  const teacherOnlyRe = /([A-Za-z]+(?:[,;]\s?[A-Za-z]+)*)/g;
  while ((m = teacherOnlyRe.exec(s)) !== null) {
    const matchStart = m.index;
    const matchEnd = teacherOnlyRe.lastIndex;
    if (isConsumed(matchStart)) continue;

    const tList = m[1].split(/[,;]\s*/).filter(Boolean);
    tList.forEach((t) => {
      if (isTeacherToken(t)) results.push(makeResult(t, null, teacherMap));
      else
        results.push({
          type: "invalid",
          teacher: null,
          teacherCode: null,
          hours: null,
          original: t,
        });
    });
    markConsumed(matchStart, matchEnd);
  }

  // Bare specs without teacher → invalid
  const specOnlyRe = /\b(\d+(?:\+|-\d+)?)\b/g;
  while ((m = specOnlyRe.exec(s)) !== null) {
    const matchStart = m.index;
    if (isConsumed(matchStart)) continue;

    results.push({
      type: "invalid",
      teacher: null,
      teacherCode: null,
      hours: null,
      original: m[1],
    });
  }

  return results;
}