import { digest } from "@chainsafe/as-sha256";
import { ATTESTATION_SUBNET_COUNT, ATTESTATION_SUBNET_PREFIX_BITS, NODE_ID_BITS } from "@lodestar/params";
import { computeShuffledIndex } from "@lodestar/state-transition";
import { ssz } from "@lodestar/types";
/**
 * Spec https://github.com/ethereum/consensus-specs/blob/v1.4.0-alpha.3/specs/phase0/p2p-interface.md
 */
export function computeSubscribedSubnet(config, nodeId, epoch) {
    const subnets = [];
    for (let index = 0; index < config.SUBNETS_PER_NODE; index++) {
        subnets.push(computeSubscribedSubnetByIndex(config, nodeId, epoch, index));
    }
    return subnets;
}
/**
 * Spec https://github.com/ethereum/consensus-specs/blob/v1.4.0-alpha.3/specs/phase0/p2p-interface.md
 */
export function computeSubscribedSubnetByIndex(config, nodeId, epoch, index) {
    const nodeIdPrefix = getNodeIdPrefix(nodeId);
    const nodeOffset = getNodeOffset(nodeId);
    const permutationSeed = digest(ssz.UintNum64.serialize(Math.floor((epoch + nodeOffset) / config.EPOCHS_PER_SUBNET_SUBSCRIPTION)));
    const permutatedPrefix = computeShuffledIndex(nodeIdPrefix, 1 << ATTESTATION_SUBNET_PREFIX_BITS, permutationSeed);
    return (permutatedPrefix + index) % ATTESTATION_SUBNET_COUNT;
}
/**
 * Should return node_id >> (NODE_ID_BITS - int(ATTESTATION_SUBNET_PREFIX_BITS))
 * Ideally we should use bigint here but since these constants are not likely to change we can use number
 */
export function getNodeIdPrefix(nodeId) {
    const totalShiftedBits = NODE_ID_BITS - ATTESTATION_SUBNET_PREFIX_BITS;
    const shiftedBytes = Math.floor(totalShiftedBits / 8);
    const shiftedBits = totalShiftedBits % 8;
    const prefixBytes = nodeId.slice(0, nodeId.length - shiftedBytes);
    const dataView = new DataView(prefixBytes.buffer, prefixBytes.byteOffset, prefixBytes.byteLength);
    // only 6 bits are used for prefix so getUint8() is safe
    const prefix = dataView.getUint8(0) >> shiftedBits;
    return prefix;
}
/**
 * Should return node_offset = node_id % EPOCHS_PER_SUBNET_SUBSCRIPTION
 * This function is safe to return number because EPOCHS_PER_SUBNET_SUBSCRIPTION is 256
 */
export function getNodeOffset(nodeId) {
    // Big endian means that the least significant byte comes last
    // The n % 256 is equivalent to the last byte of the node_id
    const lastByte = nodeId.at(-1);
    if (lastByte === undefined)
        throw new Error("Can not get node offset");
    return lastByte;
}
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