ai-app/app/androidApp/src/main/kotlin/com/example/aiapp/BenchFixture.kt

package com.example.aiapp

import android.content.Context
import java.util.concurrent.CopyOnWriteArrayList

/**
 * P0's benchmark gate (see docs/RUST.md and the 2026-09-05 decision): an in-process fake of the
 * backend, so the `bench` build type can drive a real session screen -- the real
 * [TranscriptSource], the real fold, the real paging -- with no server and no network permission.
 *
 * Only ever installed when [BuildConfig.FIXTURE_MODE] is true (see [MainActivity]); everything else
 * in this build compiles it in but never calls it, since Kotlin has no per-build-type source set
 * that both [MainActivity] (which every variant compiles) and this can share without one.
 *
 * The design: [requestFromServer] and [Sse] talk to `https://$FIXTURE_HOST:$FIXTURE_PORT` through
 * ordinary `java.net.URL`, exactly as they would talk to a real server. A
 * [java.net.URLStreamHandlerFactory] registered once for the whole process intercepts every
 * `https://` connection to that host and answers from this object's in-memory event log instead of
 * opening a socket -- see BenchNetwork.kt. Everything above that (TranscriptSource, SessionScreen,
 * the fold, uniqueItems) never learns the difference.
 */
object BenchFixture {
    const val FIXTURE_HOST = "bench.fixture.invalid"
    const val FIXTURE_PORT = 1

    /** How many of the fixture's events are the opening backlog; see bench-fixture/README.md. */
    private const val BACKLOG_COUNT = 3202

    val settings = ServerSettings(FIXTURE_HOST, FIXTURE_PORT, "bench")

    /** The session id every bench run opens; nothing else in this build ever mints one. */
    const val SESSION_ID = "bench-fixture-session"

    /**
     * The whole transcript, seq order, growing as [pushLive] is called during the streaming phase.
     * Read by both the REST page handler and the SSE handler, so a page requested mid- stream and a
     * live frame agree on what has "already happened" -- the same thing a real server's own
     * transcript file guarantees.
     */
    private val log = CopyOnWriteArrayList<Pair<String, SeqEvent>>()

    /** The events not yet appended to [log] -- the streaming phase's own source. */
    private var streamTail: List<Pair<String, SeqEvent>> = emptyList()

    private val images = mutableMapOf<String, ByteArray>()

    @Volatile private var loaded = false

    /**
     * Parses the bundled fixture once. Safe to call more than once; only the first does anything.
     */
    @Synchronized
    fun ensureLoaded(context: Context) {
        if (loaded) return
        val lines =
            context.assets.open("transcript.jsonl").bufferedReader().readLines().filter {
                it.isNotBlank()
            }
        val parsed = lines.map { it to parseSeqEvent(it) }
        log.addAll(parsed.take(BACKLOG_COUNT))
        streamTail = parsed.drop(BACKLOG_COUNT)
        for (name in listOf("bench1.png", "bench2.png")) {
            images[name] = context.assets.open(name).readBytes()
        }
        loaded = true
    }

    /** The events the streaming phase has left to send. */
    fun remainingStreamEvents(): Int = streamTail.size

    /** Sends the next fixture event onto the live log, as a real SSE frame would arrive. */
    fun pushNextLiveEvent(): Boolean {
        val next = streamTail.firstOrNull() ?: return false
        streamTail = streamTail.drop(1)
        log.add(next)
        return true
    }

    /** Undoes [pushNextLiveEvent] and reloads the opening backlog, for running the bench twice. */
    @Synchronized
    fun resetToBacklog(context: Context) {
        loaded = false
        log.clear()
        ensureLoaded(context)
    }

    fun fileBytes(name: String): ByteArray? = images[name]

    /**
     * Raw JSON lines with seq > [after], in order -- what an `/events?after=` connection replays.
     */
    fun linesAfter(after: Long): List<String> =
        log.filter { it.second.seq > after }.map { it.first }

    /**
     * One REST page: [fetchTranscript]'s `before`/`limit`/`after`, against the growing log. Ignores
     * `coalesce` -- the fixture's own deltas are already split the way a real reply streams, and
     * what the benchmark exercises is the fold and the paging, not the server's row-joining, which
     * client-core's own port tracks separately (CLIENT_CORE.md).
     */
    fun page(before: Long?, limit: Int, after: Long?): List<String> {
        val upper = before ?: (log.lastOrNull()?.second?.seq?.plus(1) ?: 1L)
        val candidates = log.filter {
            it.second.seq < upper && (after == null || it.second.seq > after)
        }
        return candidates.takeLast(limit).map { it.first }
    }
}