from decimal import Decimal

from rest_framework import serializers

from api.models.data.currency import CURRENCY_CHOICES, currency_details as _currency_details_fn
from api.models.data.customers import Customer
from api.models.data.loan import Loan, LoanPayment
from api.models.data.vendors import Vendor
from api.serializers.data.base import DataRootSerializer
from api.mixins.base_currency import BaseCurrencySerializerMixin




class LoanPaymentSerializer(DataRootSerializer):
    class Meta:
        model = LoanPayment
        fields = '__all__'


class LoanSerializer(BaseCurrencySerializerMixin, DataRootSerializer):
    base_currency_amount_fields = ('amount', 'amount_paid')
    base_currency_date_field = 'loan_date'

    currency = serializers.IntegerField()
    customer_details = serializers.SerializerMethodField()
    vendor_details = serializers.SerializerMethodField()
    loaner_name = serializers.CharField(source='get_loaner_name', read_only=True)
    currency_details = serializers.SerializerMethodField()
    loan_type_display = serializers.CharField(source='get_loan_type_display', read_only=True)
    loaner_type_display = serializers.CharField(source='get_loaner_type_display', read_only=True)
    balance_due = serializers.DecimalField(max_digits=15, decimal_places=2, read_only=True)
    payments = LoanPaymentSerializer(many=True, read_only=True)
    loan_scenario = serializers.SerializerMethodField()
    amount_paid = serializers.DecimalField(
        max_digits=15,
        decimal_places=2,
        read_only=True,
    )

    class Meta:
        model = Loan
        fields = '__all__'
        read_only_fields = (
        )

    def get_customer_details(self, obj):
        if obj.customer:
            return {
                'id': obj.customer.id,
                'name': obj.customer.name,
                'phone': obj.customer.phone,
                'email': obj.customer.email,
            }
        return None

    def get_vendor_details(self, obj):
        if obj.vendor:
            return {
                'id': obj.vendor.id,
                'name': obj.vendor.name,
                'phone': obj.vendor.phone,
                'email': obj.vendor.email,
            }
        return None

    def get_currency_details(self, obj):
        return _currency_details_fn(obj.currency)

    def get_loan_scenario(self, obj):
        if obj.loaner_type == 'customer' and obj.loan_type == 'loan_out':
            return 'customer_receivable'
        if obj.loaner_type == 'customer' and obj.loan_type == 'loan_in':
            return 'customer_payable'
        if obj.loaner_type == 'vendor' and obj.loan_type == 'loan_out':
            return 'vendor_receivable'
        if obj.loaner_type == 'vendor' and obj.loan_type == 'loan_in':
            return 'vendor_payable'
        return None

    def validate(self, data):
        loaner_type = data.get('loaner_type', getattr(self.instance, 'loaner_type', 'customer'))
        customer = data.get('customer', getattr(self.instance, 'customer', None))
        vendor = data.get('vendor', getattr(self.instance, 'vendor', None))

        if loaner_type == 'customer':
            if not customer:
                raise serializers.ValidationError({'customer': 'Customer is required for customer loans'})
            data['vendor'] = None
        elif loaner_type == 'vendor':
            if not vendor:
                raise serializers.ValidationError({'vendor': 'Vendor is required for vendor loans'})
            data['customer'] = None



        if self.instance is None:
            data['amount_paid'] = Decimal('0')

        if self.instance is not None and 'is_opening_balance' in data:
            if data['is_opening_balance'] != self.instance.is_opening_balance:
                if self.instance.payments.exists():
                    raise serializers.ValidationError({
                        'is_opening_balance': 'Cannot change opening balance flag after payments exist.',
                    })

        return super().validate(data)