export default function parseAbsence(str, teacherMap) {
  const LAST_HOUR = 10;

  const s = (str ?? "").trim().replace(/\s+/g, " ");
  const result = {
    teacher: null,        // String or null
    teacherCode: null,    // String or null
    type: null,           // "wholeDay" | "range" | "single" | "invalid"
    hours: null           // { from, to } or number
  };

  if (!s) {
    result.type = "invalid";
    result.original = s;
    return result;
  }

  const isTeacher = (t) => /^[A-Za-z]+$/.test(t);

  const parseSpec = (spec) => {
    let m;
    // "5+"  -> range 5..LAST_HOUR
    if ((m = spec.match(/^(\d+)\+$/))) {
      const from = parseInt(m[1], 10);
      if (from >= 1 && from <= LAST_HOUR) {
        return { kind: "range", value: { from, to: LAST_HOUR } };
      }
      return null;
    }
    // "5-7" -> range 5..7
    if ((m = spec.match(/^(\d+)-(\d+)$/))) {
      const from = parseInt(m[1], 10);
      const to = parseInt(m[2], 10);
      if (from >= 1 && to >= 1 && from <= to && to <= LAST_HOUR) {
        return { kind: "range", value: { from, to } };
      }
      return null;
    }
    // "5"   -> single 5
    if ((m = spec.match(/^(\d+)$/))) {
      const hour = parseInt(m[1], 10);
      if (hour >= 1 && hour <= LAST_HOUR) {
        return { kind: "single", value: hour };
      }
      return null;
    }
    return null;
  };

  const parts = s.split(" ");
  if (parts.length === 1) {
    const t = parts[0];
    if (isTeacher(t)) {
      result.teacherCode = t;
      result.teacher = teacherMap?.[t.toLowerCase()] ?? null;
      result.type = "wholeDay";
      return result;
    }
    result.type = "invalid";
    result.original = s;
    return result;
  }

  if (parts.length === 2) {
    const [a, b] = parts;

    // Teacher first: "Nm 5", "Nm 5-7", "Nm 5+"
    if (isTeacher(a)) {
      const spec = parseSpec(b);
      if (!spec) {
        result.type = "invalid";
        result.original = s;
        return result;
      }
      result.teacherCode = a;
      result.teacher = teacherMap?.[a.toLowerCase()] ?? null;
      result.type = spec.kind === "range" ? "range" : "single";
      result.hours = spec.value;
      return result;
    }

    // Teacher last: "5 Nm", "5-7 Nm", "5+ Nm"
    if (isTeacher(b)) {
      const spec = parseSpec(a);
      if (!spec) {
        result.type = "invalid";
        result.original = s;
        return result;
      }
      result.teacherCode = b;
      result.teacher = teacherMap?.[b.toLowerCase()] ?? null;
      result.type = spec.kind === "range" ? "range" : "single";
      result.hours = spec.value;
      return result;
    }

    result.type = "invalid";
    result.original = s;
    return result;
  }

  // Anything else is invalid
  result.type = "invalid";
  result.original = s;
  return result;
}