from datetime import timedelta

import django.db.models.deletion
import django.utils.timezone
from django.db import migrations, models


def copy_group_boards_to_memberships(apps, schema_editor):
    group_model = apps.get_model("tasks", "TaskBoardGroup")
    membership_model = apps.get_model("tasks", "TaskBoardGroupMembership")
    old_through = group_model.boards.through
    base_time = django.utils.timezone.now()
    positions = {}
    memberships = []

    for link in old_through.objects.order_by(
        "taskboardgroup_id",
        "id",
    ).iterator():
        group_id = link.taskboardgroup_id
        positions[group_id] = positions.get(group_id, 0) + 1
        memberships.append(
            membership_model(
                group_id=group_id,
                board_id=link.taskboard_id,
                position=positions[group_id],
                added_at=base_time + timedelta(microseconds=link.id),
            )
        )

    membership_model.objects.bulk_create(memberships)


def restore_implicit_group_boards(apps, schema_editor):
    group_model = apps.get_model("tasks", "TaskBoardGroup")
    membership_model = apps.get_model("tasks", "TaskBoardGroupMembership")
    old_through = group_model.boards.through
    old_through.objects.bulk_create(
        [
            old_through(
                taskboardgroup_id=membership.group_id,
                taskboard_id=membership.board_id,
            )
            for membership in membership_model.objects.order_by(
                "group_id",
                "position",
                "id",
            ).iterator()
        ],
        ignore_conflicts=True,
    )


class Migration(migrations.Migration):
    dependencies = [
        ("tasks", "0037_shared_task_board_groups"),
    ]

    operations = [
        migrations.CreateModel(
            name="TaskBoardGroupMembership",
            fields=[
                (
                    "id",
                    models.BigAutoField(
                        auto_created=True,
                        primary_key=True,
                        serialize=False,
                        verbose_name="ID",
                    ),
                ),
                ("position", models.PositiveIntegerField(verbose_name="Позиция")),
                (
                    "added_at",
                    models.DateTimeField(
                        default=django.utils.timezone.now,
                        verbose_name="Добавлено",
                    ),
                ),
                (
                    "board",
                    models.ForeignKey(
                        on_delete=django.db.models.deletion.CASCADE,
                        related_name="group_memberships",
                        to="tasks.taskboard",
                        verbose_name="Доска",
                    ),
                ),
                (
                    "group",
                    models.ForeignKey(
                        on_delete=django.db.models.deletion.CASCADE,
                        related_name="board_memberships",
                        to="tasks.taskboardgroup",
                        verbose_name="Группа",
                    ),
                ),
            ],
            options={
                "verbose_name": "Доска в группе",
                "verbose_name_plural": "Доски в группах",
                "ordering": ["group_id", "position", "id"],
                "constraints": [
                    models.UniqueConstraint(
                        fields=("group", "board"),
                        name="uniq_task_board_group_membership",
                    ),
                    models.UniqueConstraint(
                        fields=("group", "position"),
                        name="uniq_task_board_group_position",
                    ),
                ],
            },
        ),
        migrations.RunPython(
            copy_group_boards_to_memberships,
            restore_implicit_group_boards,
        ),
        migrations.RemoveField(
            model_name="taskboardgroup",
            name="boards",
        ),
        migrations.AddField(
            model_name="taskboardgroup",
            name="boards",
            field=models.ManyToManyField(
                blank=True,
                related_name="board_groups",
                through="tasks.TaskBoardGroupMembership",
                to="tasks.taskboard",
                verbose_name="Доски",
            ),
        ),
        migrations.AlterField(
            model_name="taskboardgroupmembership",
            name="added_at",
            field=models.DateTimeField(auto_now_add=True, verbose_name="Добавлено"),
        ),
    ]