package com.sptmobile.endpoint

import com.sptmobile.browse.BrowsedInstance
import com.sptmobile.browse.EndpointDirectory
import com.sptmobile.browse.WireSubnet

// [impl->REQ-DIGEST-DIRECT-ROUTE]
/**
 * Most-direct-route digest choice (DESIGN.md ruling 4): a digest is served
 * only by a paired host CO-LOCATED with the target endpoint — the host's
 * endpoint listing names its co-located ids in the `local` section. Listings
 * arrive in dial order, so the first co-located host is the one we dial; no
 * co-located host means the caller renders the registry card + "pending
 * cross-node" instead of a digest. Pure (no Android/JNI) so the routing rule
 * is JVM-unit-testable.
 */
object DigestRouter {
    /** One linked host's parsed listing — [choose] input, in dial order. */
    data class HostListing(
        val hostNode: String,
        val localIds: Set<String>,
        val subnets: List<WireSubnet>,
    )

    /** Node key of the first co-located linked host, or null (pending). */
    fun choose(endpointId: String, listings: List<HostListing>): String? =
        listings.firstOrNull { endpointId in it.localIds }?.hostNode

    // [impl->REQ-ENDPOINT-INSTANCES]
    /**
     * The registry-card fallback: the endpoint's Instance rows (ruling 9 —
     * one row per node presence) unioned across every linked host's listing,
     * same merge the browser uses.
     */
    fun registryCard(endpointId: String, listings: List<HostListing>): List<BrowsedInstance> =
        EndpointDirectory.merge(listings.map { it.hostNode to it.subnets })
            .flatMap { subnet -> subnet.endpoints.filter { it.id == endpointId } }
            .flatMap { it.instances }
}