"""Read access to the work-order tables for the procurement API.

Listing is a cursor-paginated Scan -- deliberately: the WO tables carry no
GSIs (removed 2026-06-03 for zero reads), and the API's list consumers
(SHOC reconciliation/backfill) walk the full table anyway, which is exactly
the access pattern SHOC's retired SyncController used. Listings are therefore
UNORDERED across pages; per-work-order comment listing is a cheap Query on
the partition key.
"""

import os

import boto3
from boto3.dynamodb.conditions import Key

from pagination import BadCursor, decode_cursor, encode_cursor

dynamodb = boto3.resource("dynamodb")

WORK_ORDERS_TABLE = os.environ.get("WORK_ORDERS_TABLE", "WorkOrders")
COMMENTS_TABLE = os.environ.get("COMMENTS_TABLE", "WorkOrderComments")

WO_KEY_ATTRS = frozenset({"work_order_id"})
COMMENT_KEY_ATTRS = frozenset({"work_order_id", "comment_id"})


def _page(response) -> tuple[list, str | None]:
    items = response.get("Items", [])
    lek = response.get("LastEvaluatedKey")
    return items, (encode_cursor(lek) if lek else None)


def list_work_orders(limit: int, cursor: str | None) -> tuple[list, str | None]:
    table = dynamodb.Table(WORK_ORDERS_TABLE)
    kwargs = {"Limit": limit}
    if cursor:
        kwargs["ExclusiveStartKey"] = decode_cursor(cursor, WO_KEY_ATTRS)
    return _page(table.scan(**kwargs))


def get_work_order(work_order_id: str) -> dict | None:
    table = dynamodb.Table(WORK_ORDERS_TABLE)
    return table.get_item(Key={"work_order_id": work_order_id}).get("Item")


def list_comments(
    work_order_id: str, limit: int, cursor: str | None
) -> tuple[list, str | None]:
    table = dynamodb.Table(COMMENTS_TABLE)
    kwargs = {
        "KeyConditionExpression": Key("work_order_id").eq(work_order_id),
        "Limit": limit,
    }
    if cursor:
        start_key = decode_cursor(cursor, COMMENT_KEY_ATTRS)
        # Pin the cursor's partition to the path entity: a cursor minted for
        # WO A must never resume WO B's Query (DynamoDB would reject the
        # partition mismatch as a 500; reject it as a 400 here instead).
        if start_key["work_order_id"] != work_order_id:
            raise BadCursor("cursor is not valid")
        kwargs["ExclusiveStartKey"] = start_key
    return _page(table.query(**kwargs))