"""
In-memory data store using Pydantic models.

This module is NOT thread-safe and is intended for demos and scaffolds only.
This module provides a minimal, process-local data store for the
model-based CRUD example application. It stores and returns domain
objects defined using Pydantic models and is intended solely for
demonstration and scaffolding purposes.

The implementation intentionally avoids:
- persistence
- concurrency guarantees
- transactional semantics
- validation beyond what Pydantic provides

It is not part of the ``openapi_first`` library API surface.
"""

from typing import Dict

from models import Item, ItemCreate


# In-memory storage keyed by item ID.
_items: Dict[int, Item] = {
    1: Item(id=1, name="Apple", price=0.5),
    2: Item(id=2, name="Banana", price=0.3),
}

# Auto-incrementing identifier.
_next_id = 3


def list_items() -> list[Item]:
    """
    Return all items in the data store.

    Returns
    -------
    list[Item]
        A list of item domain objects.
    """
    return list(_items.values())


def get_item(item_id: int) -> Item:
    """
    Retrieve a single item by ID.

    Parameters
    ----------
    item_id : int
        Identifier of the item to retrieve.

    Returns
    -------
    Item
        The requested item.

    Raises
    ------
    KeyError
        If the item does not exist.
    """
    return _items[item_id]


def create_item(payload: ItemCreate) -> Item:
    """
    Create a new item in the data store.

    A new identifier is assigned automatically. No additional validation
    is performed beyond Pydantic model validation.

    Parameters
    ----------
    payload : ItemCreate
        Data required to create a new item.

    Returns
    -------
    Item
        The newly created item.
    """
    global _next_id
    item = Item(id=_next_id, **payload.model_dump())
    _items[_next_id] = item
    _next_id += 1
    return item


def update_item(item_id: int, payload: ItemCreate) -> Item:
    """
    Replace an existing item in the data store.

    This function performs a full replacement of the stored item.
    Partial updates are not supported.

    Parameters
    ----------
    item_id : int
        Identifier of the item to update.
    payload : ItemCreate
        New item data.

    Returns
    -------
    Item
        The updated item.

    Raises
    ------
    KeyError
        If the item does not exist.
    """
    if item_id not in _items:
        raise KeyError(item_id)
    item = Item(id=item_id, **payload.model_dump())
    _items[item_id] = item
    return item


def delete_item(item_id: int) -> None:
    """
    Remove an item from the data store.

    Parameters
    ----------
    item_id : int
        Identifier of the item to delete.

    Raises
    ------
    KeyError
        If the item does not exist.
    """
    del _items[item_id]