from django.core.management.base import BaseCommand
from django.contrib.auth import get_user_model

from finance.models import Account, Budget, FinancialYear, YearlyIncome, YearlyBudgetItem

User = get_user_model()
TARGET_YEAR = 2026


class Command(BaseCommand):
    help = 'Migrate existing revenue accounts and budgets into FinancialYear 2026. Idempotent — safe to run multiple times.'

    def add_arguments(self, parser):
        parser.add_argument(
            '--dry-run',
            action='store_true',
            help='Preview what would be created without writing to the database.',
        )

    def handle(self, *args, **options):
        dry_run = options['dry_run']
        if dry_run:
            self.stdout.write(self.style.WARNING('DRY RUN — no changes will be saved.\n'))

        total_incomes = 0
        total_budgets = 0

        for user in User.objects.all():
            revenue_accounts = Account.objects.filter(user=user, account_type='revenue', active=True)
            budgets = Budget.objects.filter(account__user=user, active=True)

            if not revenue_accounts.exists() and not budgets.exists():
                continue

            self.stdout.write(f'\nUser: {user.email}')

            if dry_run:
                fy = FinancialYear.objects.filter(user=user, year=TARGET_YEAR).first()
                if fy:
                    self.stdout.write(f'  FinancialYear {TARGET_YEAR} already exists (id={fy.pk})')
                else:
                    self.stdout.write(f'  Would create FinancialYear {TARGET_YEAR}')
            else:
                fy, fy_created = FinancialYear.objects.get_or_create(user=user, year=TARGET_YEAR)
                if fy_created:
                    self.stdout.write(f'  Created FinancialYear {TARGET_YEAR} (id={fy.pk})')
                else:
                    self.stdout.write(f'  FinancialYear {TARGET_YEAR} exists (id={fy.pk})')

            for account in revenue_accounts:
                label = f'YearlyIncome "{account.name}" CHF {account.balance}'
                if dry_run:
                    exists = fy and YearlyIncome.objects.filter(financial_year=fy, name=account.name).exists()
                    self.stdout.write(f'  {"SKIP (exists)" if exists else "Would create"}: {label}')
                else:
                    _, created = YearlyIncome.objects.get_or_create(
                        financial_year=fy,
                        name=account.name,
                        defaults={'amount': account.balance, 'member': user, 'active': True},
                    )
                    self.stdout.write(f'  {"Created" if created else "Skipped (exists)"}: {label}')
                    if created:
                        total_incomes += 1

            for budget in budgets:
                label = f'YearlyBudgetItem "{budget.name}" CHF {budget.amount}'
                if dry_run:
                    exists = fy and YearlyBudgetItem.objects.filter(financial_year=fy, name=budget.name).exists()
                    self.stdout.write(f'  {"SKIP (exists)" if exists else "Would create"}: {label}')
                else:
                    _, created = YearlyBudgetItem.objects.get_or_create(
                        financial_year=fy,
                        name=budget.name,
                        defaults={'amount': budget.amount, 'active': budget.active},
                    )
                    self.stdout.write(f'  {"Created" if created else "Skipped (exists)"}: {label}')
                    if created:
                        total_budgets += 1

        if not dry_run:
            self.stdout.write(self.style.SUCCESS(
                f'\nDone. Created {total_incomes} income(s) and {total_budgets} budget item(s).'
            ))
        else:
            self.stdout.write(self.style.WARNING('\nDry run complete. Re-run without --dry-run to apply.'))