predkemon-korge/src/commonMain/kotlin/model/Battle.kt

package model

import korlibs.datastructure.*
import korlibs.datastructure.iterators.*
import korlibs.io.lang.*
import korlibs.time.*
import kotlinx.serialization.Serializable

class Battle(val initializer: HistoryEntry.Load = HistoryEntry.Load.ZERO) {
    private val _battlers: MutableList<Battler> =
        initializer.battlers.map { Battler(it, initializer.timestamp) }.toMutableList()
    private val _pendingEffects: PriorityQueue<BattleEffect> =
        PriorityQueue<BattleEffect>().apply { addAll(initializer.pendingEffects) }
    var currentTime: TimeSpan = initializer.timestamp
        private set

    /** Full history entries needed for rewinding. Stored from oldest to newest. */
    private val _history: Deque<HistoryEntry> = Deque<HistoryEntry>().also { it.add(initializer) }
    /** Actions which will be executed at a later timestamp. */
    private val _pendingActions: PriorityQueue<BattleAction> = PriorityQueue()
    /** Abbreviated history entries used only for saving replay data. Stored from oldest to newest. */
    private val _pastHistory: Queue<BattleAction> = Queue()

    val battlers: List<Battler.Readonly> get() = _battlers.map { it.asReadonly }
    val pendingEffects: List<BattleEffect> get() = _pendingEffects.toList()
    val history: List<HistoryEntry> get() = _history.toList()
    val pendingActions: List<BattleAction> get() = _pendingActions.toList()
    val pastHistory: List<BattleAction> get() = _pastHistory.toList()

    private val eventAPI: EventAPI by lazy { EventAPI(this) }

    constructor(initializer: HistoryEntry.Load, actions: List<BattleAction>, timestamp: TimeSpan? = null):
        this(initializer) {
        injectActions(actions)
        if (timestamp != null) {
            setTimeTo(timestamp)
        }
    }

    class EventAPI(private val battle: Battle) {
        val battlers: List<Battler.Readonly> get() = battle.battlers

        fun addBattler(battler: Battler.Saved) {
            if (battle._battlers.any { it.id == battler.id }) {
                throw IllegalArgumentException("Can't add a battler who's already in the fight!")
            }
            battle._battlers.add(Battler(saved = battler, at = battle.currentTime))
        }

        fun removeBattler(id: Battler.Id) {
            battle._battlers.fastIterateRemove { it.id == id }
        }

        fun battlers(block: Battler.EventAPI.() -> Unit) {
            battle._battlers.forEach { it.updateAt(battle.currentTime, block) }
        }

        fun battler(id: Battler.Id): Battler.Readonly? = battle._battlers.find { it.id == id }?.asReadonly

        fun battler(id: Battler.Id, block: Battler.EventAPI.() -> Unit) {
            battle._battlers.find { it.id == id }?.updateAt(battle.currentTime, block)
        }

        fun Battler.Readonly.update(block: Battler.EventAPI.() -> Unit) {
            battler(id, block)
        }

        fun Battler.Readonly.remove() {
            removeBattler(id)
        }

        fun injectEffect(effect: BattleEffect) {
            when {
                effect.timestamp > battle.currentTime -> battle._pendingEffects.add(effect)
                else -> throw InvalidArgumentException(
                    "can't inject an effect that would take place now or in the past: $effect")
            }
        }

        fun injectEffects(effects: Iterable<BattleEffect>) {
            effects.forEach { injectEffect(it) }
        }
    }

    fun injectAction(action: BattleAction) {
        when {
            action.timestamp > currentTime -> _pendingActions.add(action)
            action.timestamp == currentTime -> applyEvent(action)
            action.timestamp < currentTime -> {
                val present = currentTime
                rewindTo(action.timestamp)
                applyEvent(action)
                advanceTo(present)
            }
        }
    }

    fun injectActions(actions: Iterable<BattleAction>) {
        actions.forEach { injectAction(it) }
    }

    /** Abbreviates [_history] up to and including the given [timestamp], moving it to [_pastHistory]. */
    fun abbreviateHistoryUpTo(timestamp: TimeSpan) {
        while (_history.isNotEmpty() && _history.first.timestamp <= timestamp) {
            val previous = _history.removeFirst()
            if (previous is HistoryEntry.Action) {
                _pastHistory.enqueue(previous.action)
            }
        }
    }

    fun setTimeTo(timestamp: TimeSpan) {
        if (timestamp == currentTime) {
            // then we're done already!
        } else if (timestamp > currentTime){
            advanceTo(timestamp)
        } else {
            rewindTo(timestamp)
        }
    }

    private fun rewindTo(timestamp: TimeSpan) {
        if (_history.isEmpty()) {
            throw IllegalStateException(
                "tried to rewind to ${timestamp.inWholeMilliseconds}ms, but have no full history at all")
        }

        if (_history.first.timestamp > timestamp) {
            throw IllegalStateException(
                "tried to rewind to ${timestamp.inWholeMilliseconds}ms, " +
                    "but only have full history back to ${_history.first.timestamp.inWholeMilliseconds}")
        }

        while (_history.isNotEmpty() && _history.last.timestamp > timestamp) {
            val previous = _history.removeLast()
            if (previous is HistoryEntry.Action) {
                _pendingActions.add(previous.action)
            }
        }

        applyHistoryEntry(_history.last)
        if (timestamp > currentTime) {
            advanceTo(timestamp)
        }
    }

    private fun advanceTo(timestamp: TimeSpan) {
        while (nextEventAt < timestamp) {
            val nextEvent = if (nextActionAt < nextEffectAt) {
                _pendingActions.removeHead()
            } else {
                _pendingEffects.removeHead()
            }
            applyEvent(nextEvent)
        }
        advanceTimeTo(timestamp)
    }

    val nextActionAt: TimeSpan get() = nextAction?.timestamp ?: TimeSpan.INFINITE
    val nextEffectAt: TimeSpan get() = nextEffect?.timestamp ?: TimeSpan.INFINITE
    val nextEventAt: TimeSpan get() = nextEvent?.timestamp ?: TimeSpan.INFINITE

    val nextAction: BattleAction? get() = when {
        _pendingActions.isNotEmpty() -> _pendingActions.head
        else -> null
    }

    val nextEffect: BattleEffect? get() = when {
        _pendingEffects.isNotEmpty() -> _pendingEffects.head
        else -> null
    }

    val nextEvent: TimedEvent? get() {
        val action = nextAction
        val effect = nextEffect
        return when {
            action == null || (effect != null && effect < action) -> effect
            else -> action
        }
    }

    private fun advanceTimeTo(timestamp: TimeSpan) {
        if (currentTime == timestamp) {
            return
        }
        currentTime = timestamp
        _battlers.forEach { it.advanceTo(currentTime) }
    }

    private fun applyEvent(event: TimedEvent) {
        advanceTimeTo(event.timestamp)
        with(event) { with(eventAPI) {
            execute()
        } }
        saveHistoryEntry(event)
    }

    private fun saveHistoryEntry(entry: TimedEvent) {
        val archivedBattlers = _battlers.map { it.asSaved }
        val archivedEffects = _pendingEffects.toList()
        _history.add(when (entry) {
            is BattleAction -> HistoryEntry.Action(
                action = entry,
                battlers = archivedBattlers,
                pendingEffects = archivedEffects,
            )
            is BattleEffect -> HistoryEntry.Effect(
                effect = entry,
                battlers = archivedBattlers,
                pendingEffects = archivedEffects,
            )
        })
    }

    private fun applyHistoryEntry(entry: HistoryEntry) {
        currentTime = entry.timestamp
        _pendingEffects.clear()
        _pendingEffects.addAll(entry.pendingEffects)
        _battlers.retainAll { live -> entry.battlers.any { saved -> saved.id == live.id } }
        _battlers.fastForEach {
            live -> live.revertTo(entry.battlers.find { saved -> saved.id == live.id }!!, entry.timestamp) }
        if (_battlers.size < entry.battlers.size) {
            entry.battlers.forEach { saved ->
                if (!_battlers.any { live -> live.id == saved.id }) {
                    _battlers.add(Battler(saved, entry.timestamp))
                }
            }
        }
    }

    val asSaved: Saved get() = Saved(
        currentTime = currentTime,
        initializer = initializer,
        history = buildList {
            addAll(pastHistory)
            _history.forEach {
                if (it is HistoryEntry.Action) {
                    add(it.action)
                }
            }
            addAll(pendingActions)
        }
    )

    constructor(saved: Saved):
        this(initializer = saved.initializer, actions = saved.history, timestamp = saved.currentTime)

    @Serializable
    data class Saved(
        val currentTime: TimeSpan,
        val initializer: HistoryEntry.Load,
        val history: List<BattleAction>,
    )
}