"""Capture and restore board layouts without copying tasks or access grants."""

from django.db import transaction

from .models import (
    TaskBoard,
    TaskBoardAccessScope,
    TaskColumn,
    TaskColumnRow,
)


def snapshot_board_structure(board: TaskBoard) -> dict:
    """Capture visible columns, nested columns and swimlanes in stable order."""
    columns = list(
        TaskColumn.objects.filter(board=board, is_archived=False).order_by(
            "position", "id"
        )
    )
    rows = list(
        TaskColumnRow.objects.filter(
            column__board=board, column__is_archived=False
        ).order_by("position", "id")
    )
    children_by_parent: dict[int | None, list[TaskColumn]] = {}
    for column in columns:
        children_by_parent.setdefault(column.parent_id, []).append(column)
    rows_by_column: dict[int, list[TaskColumnRow]] = {}
    for row in rows:
        rows_by_column.setdefault(row.column_id, []).append(row)

    seen: set[int] = set()

    def serialize(column: TaskColumn) -> dict:
        if column.id in seen:
            return {}
        seen.add(column.id)
        return {
            "name": column.name,
            "position": column.position,
            "color": column.color,
            "is_done": column.is_done,
            "rows": [
                {"name": row.name, "position": row.position, "color": row.color}
                for row in rows_by_column.get(column.id, [])
            ],
            "subcolumns": [
                value
                for child in children_by_parent.get(column.id, [])
                if (value := serialize(child))
            ],
        }

    return {
        "columns": [serialize(column) for column in children_by_parent.get(None, [])]
    }


@transaction.atomic
def create_board_from_template(template, *, owner, name: str) -> TaskBoard:
    """Instantiate a private board so a shared template cannot leak user data."""
    board = TaskBoard.objects.create(
        name=name,
        description=template.description,
        created_by=owner,
        access_scope=TaskBoardAccessScope.PRIVATE,
    )

    def create_column(spec: dict, parent: TaskColumn | None = None) -> None:
        column = TaskColumn.objects.create(
            board=board,
            parent=parent,
            name=spec["name"],
            position=spec.get("position", 0),
            color=spec.get("color", ""),
            is_done=bool(spec.get("is_done", False)),
        )
        for row in spec.get("rows", []):
            TaskColumnRow.objects.create(
                column=column,
                name=row["name"],
                position=row.get("position", 0),
                color=row.get("color", ""),
            )
        for child in spec.get("subcolumns", []):
            create_column(child, column)

    for column_spec in template.layout.get("columns", []):
        create_column(column_spec)
    return board