from __future__ import annotations

import argparse
from typing import Any

from django.conf import settings
from django.core.cache import InvalidCacheBackendError
from django.core.cache import caches
from django.core.management import BaseCommand
from django.core.management import CommandError

from django_mysql.cache import MySQLCache
from django_mysql.utils import collapse_spaces


class Command(BaseCommand):
    args = "<app_name>"

    help = collapse_spaces(
        """
        Outputs a migration that will create a table.
    """
    )

    def add_arguments(self, parser: argparse.ArgumentParser) -> None:
        parser.add_argument(
            "aliases",
            metavar="aliases",
            nargs="*",
            help="Specify the cache alias(es) to create migrations for.",
        )

    def handle(self, *args: Any, aliases: list[str], **options: Any) -> None:
        if not aliases:
            aliases = list(settings.CACHES)

        tables = set()
        for alias in aliases:
            try:
                cache = caches[alias]
            except InvalidCacheBackendError:
                raise CommandError(f"Cache {alias!r} does not exist")

            if not isinstance(cache, MySQLCache):  # pragma: no cover
                continue

            tables.add(cache._table)

        if not tables:
            self.stderr.write("No MySQLCache instances in CACHES")
            return

        migration = self.render_migration(tables)
        self.stdout.write(migration)

    def render_migration(self, tables: set[str]) -> str:
        # This used to use a Django template, but we can't instantiate them
        # direct now, as the user may not have the django template engine
        # defined in TEMPLATES
        out = [header]
        for table in tables:
            out.append(table_operation.replace("{{ table }}", table))
        out.append(footer)
        return "".join(out)


header = """
from django.db import migrations


class Migration(migrations.Migration):

    dependencies = [
        # Add a dependency in here on an existing migration in the app you
        # put this migration in, for example:
        # ('myapp', '0001_initial'),
    ]

    operations = [
""".strip()

create_table_sql = "\n".join(
    "    " * 3 + line for line in MySQLCache.create_table_sql.splitlines()
).format(table_name="{{ table }}")


table_operation = (
    '''
        migrations.RunSQL(
            """
'''
    + create_table_sql
    + '''
            """,
            "DROP TABLE `{{ table }}`",
        ),
'''.rstrip()
)


footer = """
    ]
"""