from __future__ import annotations

import re
from dataclasses import dataclass
from datetime import date
from typing import Dict, List, Optional, Tuple

# Month maps (EN + RU)
MONTHS = {
    "jan": 1, "january": 1, "янв": 1, "январ": 1,
    "feb": 2, "february": 2, "фев": 2, "феврал": 2,
    "mar": 3, "march": 3, "мар": 3, "март": 3,
    "apr": 4, "april": 4, "апр": 4, "апрел": 4,
    "may": 5, "май": 5,
    "jun": 6, "june": 6, "июн": 6, "июнь": 6,
    "jul": 7, "july": 7, "июл": 7, "июль": 7,
    "aug": 8, "august": 8, "авг": 8, "август": 8,
    "sep": 9, "september": 9, "сен": 9, "сент": 9,
    "oct": 10, "october": 10, "окт": 10, "октя": 10,
    "nov": 11, "november": 11, "ноя": 11, "ноябр": 11,
    "dec": 12, "december": 12, "дек": 12, "дека": 12,
}

PRESENT_RE = re.compile(r"\b(present|now|current|настоящее время|по н\.в\.|по настоящее)\b", re.I)

# Direct "X years" patterns
DIRECT_YEARS_RE = re.compile(r"(\d+(?:[.,]\d+)?)\s*(?:\+?\s*)?(?:years?|yrs?|лет|года|год)\b", re.I)

# Dates like 03.2019, 2019, Jan 2020, янв 2020
MMYYYY_RE = re.compile(r"\b(0?[1-9]|1[0-2])[./-](\d{4})\b")
YYYY_RE = re.compile(r"\b(19\d{2}|20\d{2})\b")
MON_YYYY_RE = re.compile(r"\b([A-Za-z]{3,9}|[А-Яа-я]{3,9})\.?\s*(\d{4})\b")

# Range separators
RANGE_RE = re.compile(r"(?P<a>.+?)\s*(?:—|–|-|to|по)\s*(?P<b>.+?)$", re.I)

@dataclass
class ExpResult:
    years: Optional[float]
    confidence: float
    debug: Dict

def _clamp_years(y: float) -> Optional[float]:
    if 0.0 <= y <= 45.0:
        return y
    return None

def _parse_mon(mon: str) -> Optional[int]:
    m = mon.strip().lower()
    m = re.sub(r"[^\wа-я]+", "", m, flags=re.I)
    # allow prefixes: "январ", "феврал"
    for k, v in MONTHS.items():
        if m.startswith(k):
            return v
    return None

def _as_ymd(y: int, m: int) -> date:
    return date(y, m, 1)

def _parse_one_date(s: str) -> Optional[date]:
    s = s.strip()
    if PRESENT_RE.search(s):
        today = date.today()
        return date(today.year, today.month, 1)

    m1 = MMYYYY_RE.search(s)
    if m1:
        mm = int(m1.group(1))
        yy = int(m1.group(2))
        return _as_ymd(yy, mm)

    m2 = MON_YYYY_RE.search(s)
    if m2:
        mon = _parse_mon(m2.group(1))
        yy = int(m2.group(2))
        if mon:
            return _as_ymd(yy, mon)

    m3 = YYYY_RE.search(s)
    if m3:
        yy = int(m3.group(1))
        return _as_ymd(yy, 1)

    return None

def _merge_intervals(intervals: List[Tuple[date, date]]) -> List[Tuple[date, date]]:
    if not intervals:
        return []
    intervals = sorted(intervals, key=lambda x: (x[0], x[1]))
    merged = [intervals[0]]
    for s, e in intervals[1:]:
        ls, le = merged[-1]
        if s <= le:
            merged[-1] = (ls, max(le, e))
        else:
            merged.append((s, e))
    return merged

def _months_between(a: date, b: date) -> int:
    # month-level difference (inclusive-ish): b >= a
    return (b.year - a.year) * 12 + (b.month - a.month)

def extract_experience(text: str) -> ExpResult:
    debug: Dict = {"direct_matches": [], "ranges": [], "intervals": []}

    # 1) Direct years
    directs = []
    for m in DIRECT_YEARS_RE.finditer(text):
        try:
            v = float(m.group(1).replace(",", "."))
            if 0 <= v <= 45:
                directs.append(v)
                debug["direct_matches"].append({"match": m.group(0), "value": v})
        except Exception:
            pass
    if directs:
        years = _clamp_years(max(directs))
        return ExpResult(years=years, confidence=0.90, debug=debug)

    # 2) Ranges in lines: try to detect "start - end"
    intervals: List[Tuple[date, date]] = []
    for line in text.splitlines():
        ln = line.strip()
        if len(ln) < 7:
            continue
        # require range separator
        if not any(x in ln for x in ("—", "–", "-", " to ", " по ")):
            continue
        rr = RANGE_RE.match(ln)
        if not rr:
            continue
        a = rr.group("a")
        b = rr.group("b")
        da = _parse_one_date(a)
        db = _parse_one_date(b)
        if da and db:
            if db < da:
                da, db = db, da
            # cap extremely old
            if da.year < 1990:
                continue
            intervals.append((da, db))
            debug["ranges"].append({"line": ln, "start": da.isoformat(), "end": db.isoformat()})

    intervals = _merge_intervals(intervals)
    debug["intervals"] = [{"start": s.isoformat(), "end": e.isoformat()} for s, e in intervals]

    if not intervals:
        return ExpResult(years=None, confidence=0.0, debug=debug)

    total_months = 0
    for s, e in intervals:
        total_months += max(0, _months_between(s, e))
    years = round(total_months / 12.0, 2)
    years = _clamp_years(years) if years is not None else None

    # confidence depends on amount of evidence
    conf = 0.70 if total_months >= 12 else 0.55
    return ExpResult(years=years, confidence=conf, debug=debug)