"""Pack a Modelling Run's resolved properties into SQS-message-sized batches.

Batches stay postcode-grouped — properties sharing a postcode ride the same
message so the workers' prediction cohort cache keeps paying (ADR-0055), the
same packing the trigger script has been running.
"""

from backend.app.modelling.property_filters import FilteredProperty

BATCH_SIZE = 50


def pack_postcode_batches(
    properties: list[FilteredProperty], batch_size: int = BATCH_SIZE
) -> list[list[FilteredProperty]]:
    """Pack *properties* into batches of ~*batch_size*, never splitting a
    postcode across batches. A single postcode larger than *batch_size*
    becomes its own oversized batch."""
    groups: dict[str, list[FilteredProperty]] = {}
    for prop in properties:
        groups.setdefault(prop.postcode or "", []).append(prop)

    batches: list[list[FilteredProperty]] = []
    current: list[FilteredProperty] = []
    for group in groups.values():
        if current and len(current) + len(group) > batch_size:
            batches.append(current)
            current = list(group)
        else:
            current.extend(group)
    if current:
        batches.append(current)
    return batches