import re
from decimal import Decimal

from fastapi import APIRouter, File, UploadFile
from pydantic import BaseModel

router = APIRouter(prefix="/ocr", tags=["ocr"])


class ReceiptSuggestion(BaseModel):
    total_cost: Decimal | None = None
    liters: Decimal | None = None
    price_per_liter: Decimal | None = None
    station: str | None = None
    confidence: float
    message: str


@router.post("/fuel-receipt", response_model=ReceiptSuggestion)
async def scan_fuel_receipt(file: UploadFile = File(...)) -> ReceiptSuggestion:
    content = await file.read()
    text = " ".join(
        [
            file.filename or "",
            content.decode("utf-8", errors="ignore"),
        ]
    )
    normalized = text.replace("\xa0", " ").replace(",", ".")
    compact = re.sub(r"\s+", " ", normalized).strip()
    numbers = [Decimal(item) for item in re.findall(r"\d+(?:\.\d+)?", compact)]

    station = detect_station(compact)
    liters = find_liters(compact, numbers)
    price = find_price_per_liter(compact, numbers)
    total = find_total(compact, numbers, liters, price)
    if total and liters and not price and liters > 0:
        price = (total / liters).quantize(Decimal("0.01"))
    if liters and price and not total:
        total = (liters * price).quantize(Decimal("0.01"))

    signals = sum(value is not None for value in (total, liters, price, station))
    confidence = min(0.88, 0.18 + signals * 0.17 + min(len(numbers), 12) * 0.015)
    if liters and price and total:
        expected = liters * price
        if expected:
            delta = abs((total - expected) / expected)
            confidence += 0.1 if delta <= Decimal("0.08") else -0.08
    confidence = max(0, min(float(confidence), 0.95))

    return ReceiptSuggestion(
        total_cost=total,
        liters=liters,
        price_per_liter=price,
        station=station,
        confidence=round(confidence, 2) if numbers else 0,
        message=(
            "Распознал данные чека и заполнил форму. Проверь значения перед сохранением."
            if numbers
            else "Не удалось прочитать данные чека. Попробуй фото крупнее или заполни поля вручную."
        ),
    )


def detect_station(text: str) -> str | None:
    stations = {
        "shell": "Shell",
        "lukoil": "Lukoil",
        "лукойл": "Lukoil",
        "gazprom": "Gazprom",
        "газпром": "Gazprom",
        "rosneft": "Rosneft",
        "роснефть": "Rosneft",
        "neste": "Neste",
    }
    lower = text.lower()
    for needle, name in stations.items():
        if needle in lower:
            return name
    return None


def decimal_from_match(match: re.Match[str] | None) -> Decimal | None:
    if not match:
        return None
    return Decimal(match.group(1))


def find_liters(text: str, numbers: list[Decimal]) -> Decimal | None:
    patterns = [
        r"(\d+(?:\.\d+)?)\s*(?:l|литр|литра|литров|л)\b",
        r"(?:volume|qty|кол-?во|количество|объем)\D{0,12}(\d+(?:\.\d+)?)",
    ]
    for pattern in patterns:
        value = decimal_from_match(re.search(pattern, text, re.IGNORECASE))
        if value and Decimal("3") <= value <= Decimal("160"):
            return value
    return next((item for item in numbers if Decimal("5") <= item <= Decimal("120")), None)


def find_price_per_liter(text: str, numbers: list[Decimal]) -> Decimal | None:
    patterns = [
        r"(\d+(?:\.\d+)?)\s*(?:/|за)\s*(?:l|литр|л)\b",
        r"(?:price|цена|ppu|руб/л|₽/л)\D{0,12}(\d+(?:\.\d+)?)",
    ]
    for pattern in patterns:
        value = decimal_from_match(re.search(pattern, text, re.IGNORECASE))
        if value and Decimal("10") <= value <= Decimal("500"):
            return value
    candidates = [item for item in numbers if Decimal("10") <= item <= Decimal("500")]
    return candidates[-1] if candidates else None


def find_total(
    text: str,
    numbers: list[Decimal],
    liters: Decimal | None,
    price: Decimal | None,
) -> Decimal | None:
    patterns = [
        r"(?:total|sum|amount|итого|сумма|к\s*оплате)\D{0,16}(\d+(?:\.\d+)?)",
        r"(\d+(?:\.\d+)?)\s*(?:rub|₽|руб|krw|₩)",
    ]
    for pattern in patterns:
        value = decimal_from_match(re.search(pattern, text, re.IGNORECASE))
        if value and value > Decimal("50"):
            return value
    ignored = {value for value in (liters, price) if value is not None}
    candidates = [item for item in numbers if item > Decimal("50") and item not in ignored]
    return max(candidates) if candidates else None