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

Same unordered cursor-paginated Scan pattern as wo_repo (no GSIs; listing
serves reconciliation, not ranked queries). VendorReplies is deliberately
absent: the table is dead (its writer was deleted) and must not gain new
consumers.
"""

import os

import boto3

from pagination import decode_cursor, encode_cursor

dynamodb = boto3.resource("dynamodb")

PO_TABLE = os.environ.get("PO_TABLE", "purchase-orders")
VERIFIED_SITES_TABLE = os.environ.get("VERIFIED_SITES_TABLE", "verified-sites")

PO_KEY_ATTRS = frozenset({"po_number"})
SITE_KEY_ATTRS = frozenset({"siteCode"})


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


def get_purchase_order(po_number: str) -> dict | None:
    table = dynamodb.Table(PO_TABLE)
    return table.get_item(Key={"po_number": po_number}).get("Item")


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


def get_verified_site(site_code: str) -> dict | None:
    table = dynamodb.Table(VERIFIED_SITES_TABLE)
    return table.get_item(Key={"siteCode": site_code}).get("Item")