from __future__ import annotations


def summarize_rtcm_types(payload: bytes) -> dict[int, int]:
    counts: dict[int, int] = {}
    i = 0

    while i + 6 <= len(payload):
        if payload[i] != 0xD3:
            i += 1
            continue

        length = ((payload[i + 1] & 0x03) << 8) | payload[i + 2]
        frame_end = i + 3 + length + 3
        if frame_end > len(payload):
            break

        message_type = ((payload[i + 3] << 4) | (payload[i + 4] >> 4)) & 0x0FFF
        counts[message_type] = counts.get(message_type, 0) + 1
        i = frame_end

    return counts