import csv
import io
import logging
import uuid

from django.db import transaction
from django.utils import timezone

from apps.account.models import User
from apps.banker.models import Contact
from apps.bizapps.models import (
    Customer,
    Invoice,
    InvoiceItem,
    LedgerEntry,
    LedgerInstallment,
    Product,
    StockMovement,
    Transaction,
)

logger = logging.getLogger(__name__)

# کدهای حساب — دفترکل ساده طبق سند فنی (بدون نیاز به جدول Chart of Accounts
# جدا، چون این اپ برای کسب‌وکارهای خرد است نه حسابداری شرکتی کامل).
ACCOUNT_CASH = "1000"  # صندوق
ACCOUNT_RECEIVABLE = "1100"  # مطالبات (فروش اعتباری — نسخه‌ی آتی)
ACCOUNT_SALES = "4000"  # فروش


class InvoiceService:
    @staticmethod
    def _next_sequenced_number(user: User, model, field_name: str, prefix: str) -> str:
        """فرمت PREFIX-YYMM-NNNN با سکانسِ ماهانه‌ی جداگانه برای هر کاربر —
        سطر آخرِ همان ماه را قفل می‌کند (select_for_update) تا دو درخواستِ
        هم‌زمان شماره‌ی تکراری نگیرند."""
        now = timezone.now()
        month_prefix = f"{prefix}-{now:%y%m}-"
        last = (
            model.objects.select_for_update()
            .filter(user=user, **{f"{field_name}__startswith": month_prefix})
            .order_by(f"-{field_name}")
            .first()
        )
        if last:
            last_seq = int(getattr(last, field_name).rsplit("-", 1)[-1])
        else:
            last_seq = 0
        return f"{month_prefix}{last_seq + 1:04d}"

    @staticmethod
    def _upsert_customer_contact(user: User, phone: str, name: str) -> Contact | None:
        phone = (phone or "").strip()
        if not phone:
            return None
        contact = Contact.objects.filter(user=user, phone=phone).first()
        if contact:
            return contact
        return Contact.objects.create(id=str(uuid.uuid4()), user=user, name=name or phone, phone=phone)

    @staticmethod
    @transaction.atomic
    def create_invoice(user: User, data: dict, send_sms: bool = False) -> Invoice:
        items_data = data["items"]

        invoice_number = InvoiceService._next_sequenced_number(user, Invoice, "invoice_number", "INV")
        customer: Customer | None = data.get("customer")
        payment_type = data.get("payment_type", Invoice.PaymentType.CASH)
        order_status = (
            Invoice.OrderStatus.PENDING_PAYMENT
            if payment_type == Invoice.PaymentType.CREDIT
            else Invoice.OrderStatus.READY_TO_SHIP
        )

        invoice = Invoice.objects.create(
            id=str(uuid.uuid4()),
            user=user,
            invoice_number=invoice_number,
            invoice_date=data.get("invoice_date") or timezone.now(),
            customer=customer,
            buyer_name=data.get("buyer_name", "") or (customer.name if customer else ""),
            buyer_phone=data.get("buyer_phone", "") or (customer.phone if customer else ""),
            buyer_address=data.get("buyer_address", "") or (customer.address if customer else ""),
            seller_name=data.get("seller_name", ""),
            seller_phone=data.get("seller_phone", ""),
            seller_address=data.get("seller_address", ""),
            discount_amount=data.get("discount_amount", 0),
            tax_lines=data.get("tax_lines", []),
            payment_type=payment_type,
            shipping_method=data.get("shipping_method", Invoice.ShippingMethod.PICKUP),
            order_status=order_status,
            tracking_code=data.get("tracking_code", ""),
            notes=data.get("notes", ""),
        )

        subtotal = 0.0
        for item_data in items_data:
            product: Product | None = item_data.get("product")
            quantity = item_data["quantity"]
            # طبق سند: قیمت واحد در زمان فروش از SellingPrice کالا کپی می‌شود
            # (سمت کلاینت قابل‌دستکاری نیست) — فقط برای ردیف‌های آزاد (بدون
            # کالا) قیمتِ ارسالی کلاینت به‌عنوان قیمت واحد پذیرفته می‌شود.
            unit_price = product.unit_price if product else item_data["unit_price"]
            description = item_data.get("description") or (product.name if product else "")

            item = InvoiceItem(
                id=str(uuid.uuid4()),
                invoice=invoice,
                product=product,
                description=description,
                quantity=quantity,
                unit_price=unit_price,
                discount_percent=item_data.get("discount_percent", 0),
            )
            item.compute_total()
            item.save()
            subtotal += item.total_price

            if product is not None:
                product = Product.objects.select_for_update().get(pk=product.pk)
                product.quantity -= quantity
                product.recompute_purchase_value()
                product.save(update_fields=["quantity", "total_purchase_value", "updated_at"])
                StockMovement.objects.create(
                    product=product,
                    delta=-quantity,
                    quantity_after=product.quantity,
                    note=f"فروش فاکتور {invoice_number}",
                )

        tax_amount = sum(subtotal * float(line.get("percent", 0)) / 100 for line in invoice.tax_lines)
        invoice.total_amount = subtotal
        invoice.final_amount = subtotal - invoice.discount_amount + tax_amount
        invoice.save(update_fields=["total_amount", "final_amount"])

        transaction_number = InvoiceService._next_sequenced_number(user, Transaction, "transaction_number", "TRX")
        is_credit = payment_type == Invoice.PaymentType.CREDIT
        Transaction.objects.create(
            id=str(uuid.uuid4()),
            user=user,
            transaction_number=transaction_number,
            transaction_date=invoice.invoice_date,
            reference_invoice=invoice,
            transaction_type=(
                Transaction.TransactionType.CREDIT_SALE if is_credit else Transaction.TransactionType.CASH_SALE
            ),
            debit_account=ACCOUNT_RECEIVABLE if is_credit else ACCOUNT_CASH,
            credit_account=ACCOUNT_SALES,
            amount=invoice.final_amount,
            description=f"فروش فاکتور {invoice_number}",
        )

        if customer is not None:
            customer = Customer.objects.select_for_update().get(pk=customer.pk)
            customer.total_purchases_count += 1
            customer.total_purchase_amount += invoice.final_amount
            customer.last_purchase_date = invoice.invoice_date
            customer.save(
                update_fields=["total_purchases_count", "total_purchase_amount", "last_purchase_date", "updated_at"]
            )

        # طبق درخواست: فروشِ قسطی/نسیه باید خودکار به دفتر درآمد/هزینه به‌عنوان
        # یک ردیفِ بدهی‌دار (نه صرفا یک عدد در لیست فاکتورها) وصل شود — همان
        # مثالِ «۱۰۰ تومن فروش قسطی از نظر عادی درآمد، از نظر حرفه‌ای بدهکاریه».
        if is_credit:
            LedgerEntry.objects.create(
                id=str(uuid.uuid4()),
                user=user,
                entry_type=LedgerEntry.EntryType.INCOME,
                title=f"فاکتور {invoice_number}",
                amount=invoice.final_amount,
                category=LedgerEntry.Category.SALE_CREDIT,
                entry_date=invoice.invoice_date.date(),
                total_amount=invoice.final_amount,
                counterparty_name=invoice.buyer_name,
                counterparty_phone=invoice.buyer_phone,
                linked_invoice=invoice,
            )
            if invoice.buyer_phone:
                LedgerService.recompute_customer_balance(user, invoice.buyer_phone)

        if send_sms and invoice.buyer_phone:
            InvoiceService._send_invoice_sms(user, invoice)

        logger.info(
            "invoice created: user=%s invoice=%s final_amount=%s transaction=%s",
            user.phone,
            invoice_number,
            invoice.final_amount,
            transaction_number,
        )
        return invoice

    @staticmethod
    def _send_invoice_sms(user: User, invoice: Invoice) -> None:
        # ایمپورت دیرهنگام برای جلوگیری از وابستگی چرخه‌ای در import-time
        # بین اپ‌های bizapps و messaging.
        from apps.messaging.api.services import BulkMessageService
        from apps.messaging.models import Channel

        contact = InvoiceService._upsert_customer_contact(user, invoice.buyer_phone, invoice.buyer_name)
        if contact is None:
            return
        body = f"فاکتور {invoice.invoice_number} به مبلغ {invoice.final_amount:,.0f} تومان ثبت شد."
        BulkMessageService.create_and_dispatch(
            user=user,
            channels=[Channel.SMS],
            contact_ids=[contact.id],
            body_override=body,
        )

    @staticmethod
    @transaction.atomic
    def cancel_invoice(user: User, invoice_id: str) -> Invoice:
        invoice = Invoice.objects.select_for_update().get(pk=invoice_id, user=user)
        if invoice.order_status == Invoice.OrderStatus.CANCELLED:
            raise ValueError("این فاکتور قبلا لغو شده است.")

        for item in invoice.items.select_related("product"):
            if item.product is None:
                continue
            product = Product.objects.select_for_update().get(pk=item.product_id)
            product.quantity += item.quantity
            product.recompute_purchase_value()
            product.save(update_fields=["quantity", "total_purchase_value", "updated_at"])
            StockMovement.objects.create(
                product=product,
                delta=item.quantity,
                quantity_after=product.quantity,
                note=f"لغو فاکتور {invoice.invoice_number}",
            )

        # ردیفِ دفترِ بدهی‌دارِ متصل به این فاکتور: اگر هنوز هیچ قسطی روی آن
        # ثبت نشده، با لغوِ فاکتور آن بدهی هم دیگر معنی ندارد — حذفش می‌کنیم.
        # اگر قسطی ثبت شده (یعنی پولی واقعا رد و بدل شده)، تاریخچه‌ی مالی را
        # پاک نمی‌کنیم؛ همان‌جا برای رسیدگیِ دستیِ کاربر می‌ماند.
        linked_entry = invoice.ledger_entries.first()
        if linked_entry is not None and not linked_entry.installments.exists():
            phone = linked_entry.counterparty_phone
            linked_entry.delete()
            if phone:
                LedgerService.recompute_customer_balance(user, phone)

        original = invoice.transactions.order_by("created_at").first()
        transaction_number = InvoiceService._next_sequenced_number(user, Transaction, "transaction_number", "TRX")
        Transaction.objects.create(
            id=str(uuid.uuid4()),
            user=user,
            transaction_number=transaction_number,
            transaction_date=timezone.now(),
            reference_invoice=invoice,
            transaction_type=original.transaction_type if original else Transaction.TransactionType.CASH_SALE,
            debit_account=original.credit_account if original else ACCOUNT_SALES,
            credit_account=original.debit_account if original else ACCOUNT_CASH,
            amount=-(original.amount if original else invoice.final_amount),
            description=f"لغو فاکتور {invoice.invoice_number}",
        )

        invoice.order_status = Invoice.OrderStatus.CANCELLED
        invoice.save(update_fields=["order_status", "updated_at"])
        logger.info(
            "invoice cancelled: user=%s invoice=%s reversal_transaction=%s",
            user.phone,
            invoice.invoice_number,
            transaction_number,
        )
        return invoice

    @staticmethod
    @transaction.atomic
    def update_status(
        user: User,
        invoice_id: str,
        order_status: str | None = None,
        payment_status: str | None = None,
        tracking_code: str | None = None,
    ) -> Invoice:
        invoice = Invoice.objects.select_for_update().get(pk=invoice_id, user=user)
        update_fields = ["updated_at"]

        status_changed = order_status is not None and order_status != invoice.order_status
        if order_status is not None:
            invoice.order_status = order_status
            update_fields.append("order_status")
        if payment_status is not None:
            invoice.payment_status = payment_status
            if payment_status == Invoice.PaymentStatus.PAID and invoice.paid_at is None:
                invoice.paid_at = timezone.now()
                update_fields.append("paid_at")
            update_fields.append("payment_status")
        if tracking_code is not None:
            invoice.tracking_code = tracking_code
            update_fields.append("tracking_code")

        invoice.save(update_fields=update_fields)
        logger.info(
            "invoice status updated: user=%s invoice=%s order_status=%s payment_status=%s",
            user.phone,
            invoice.invoice_number,
            invoice.order_status,
            invoice.payment_status,
        )

        # اگر فاکتور به «پرداخت‌شده» رفت و به یک ردیفِ بدهی‌دار وصل بود، همان
        # مانده را به‌عنوان یک قسطِ تسویه‌ی کامل ثبت می‌کنیم — کاربر مجبور
        # نیست دستی برود توی دفتر و قسط بزند.
        if payment_status == Invoice.PaymentStatus.PAID:
            linked_entry = invoice.ledger_entries.first()
            if linked_entry is not None and linked_entry.remaining_amount > 0:
                LedgerInstallment.objects.create(
                    id=str(uuid.uuid4()),
                    ledger_entry=linked_entry,
                    amount=linked_entry.remaining_amount,
                    paid_date=timezone.now().date(),
                    reference=f"تسویه‌ی کامل فاکتور {invoice.invoice_number}",
                )
                if linked_entry.counterparty_phone:
                    LedgerService.recompute_customer_balance(user, linked_entry.counterparty_phone)

        # طبق سند: «پس از هر تغییر وضعیت سفارش، یک پیامک ارسال شود» — برخلاف
        # پیامکِ ثبت فاکتور (که opt-in است)، این یکی خودکار است، چون همان
        # رفتاری‌ست که apps.orders از قبل برای مراحل پیگیری سفارش دارد و
        # کاربر با آن آشناست.
        if status_changed and invoice.buyer_phone:
            InvoiceService._send_status_sms(user, invoice)

        return invoice

    @staticmethod
    def _send_status_sms(user: User, invoice: Invoice) -> None:
        from apps.messaging.api.services import BulkMessageService
        from apps.messaging.models import Channel

        contact = InvoiceService._upsert_customer_contact(user, invoice.buyer_phone, invoice.buyer_name)
        if contact is None:
            return
        status_label = Invoice.OrderStatus(invoice.order_status).label
        body = f"وضعیت سفارش فاکتور {invoice.invoice_number}: {status_label}"
        BulkMessageService.create_and_dispatch(
            user=user,
            channels=[Channel.SMS],
            contact_ids=[contact.id],
            body_override=body,
        )


class LedgerService:
    """هماهنگیِ لایه‌ی «عادی» (دسته‌بندی ساده) با لایه‌ی «حرفه‌ای» (بدهکاری/
    بستانکاری واقعی) — طبق درخواست: کاربرِ معمولی فقط دسته را انتخاب می‌کند،
    این سرویس تضمین می‌کند مانده‌ی بدهیِ هر مشتری (Customer.outstanding_balance)
    همیشه با جمعِ واقعیِ ردیف‌های «فروش قسطی»ِ همان شماره‌تماس هم‌خوان بماند."""

    @staticmethod
    def recompute_customer_balance(user: User, phone: str) -> None:
        phone = (phone or "").strip()
        if not phone:
            return
        customer = Customer.objects.filter(user=user, phone=phone).first()
        if customer is None:
            return
        receivables = LedgerEntry.objects.filter(
            user=user, category=LedgerEntry.Category.SALE_CREDIT, counterparty_phone=phone
        ).prefetch_related("installments")
        balance = sum(e.remaining_amount for e in receivables)
        if customer.outstanding_balance != balance:
            customer.outstanding_balance = balance
            customer.save(update_fields=["outstanding_balance", "updated_at"])

    @staticmethod
    def export_csv(user: User, start=None, end=None) -> str:
        """خروجیِ CSV حرفه‌ای — UTF-8 BOM برای بازشدنِ درستِ فارسی در اکسل."""
        qs = LedgerEntry.objects.filter(user=user).order_by("entry_date").prefetch_related("installments")
        if start:
            qs = qs.filter(entry_date__gte=start)
        if end:
            qs = qs.filter(entry_date__lte=end)

        buf = io.StringIO()
        buf.write("")  # BOM
        writer = csv.writer(buf)
        writer.writerow(
            [
                "تاریخ",
                "نوع",
                "دسته",
                "عنوان",
                "مبلغ",
                "طرف حساب",
                "شماره طرف حساب",
                "مبلغ کل تعهد",
                "پرداخت‌شده",
                "مانده",
                "یادداشت",
            ]
        )
        for e in qs:
            writer.writerow(
                [
                    e.entry_date.isoformat(),
                    e.get_entry_type_display(),
                    e.get_category_display() if e.category else "",
                    e.title,
                    f"{e.amount:.0f}",
                    e.counterparty_name,
                    e.counterparty_phone,
                    f"{e.total_amount:.0f}" if e.is_debt else "",
                    f"{e.paid_amount:.0f}" if e.is_debt else "",
                    f"{e.remaining_amount:.0f}" if e.is_debt else "",
                    e.note,
                ]
            )
        return buf.getvalue()