openthebox/src/OpenTheBox/Simulation/InteractionEngine.cs

using OpenTheBox.Core;
using OpenTheBox.Core.Enums;
using OpenTheBox.Core.Interactions;
using OpenTheBox.Core.Items;
using OpenTheBox.Data;
using OpenTheBox.Simulation.Events;

namespace OpenTheBox.Simulation;

/// <summary>
/// Evaluates interaction rules against newly received items and the current game state,
/// triggering automatic chain reactions that can cascade recursively.
/// </summary>
public class InteractionEngine(ContentRegistry registry)
{
    private const int MaxChainDepth = 10;

    /// <summary>
    /// Runs the full chain reaction loop: checks new items for interactions,
    /// executes them, and re-checks any produced items until no more reactions fire.
    /// Returns all events produced across the entire chain.
    /// </summary>
    public List<GameEvent> RunChainReactions(List<ItemInstance> newItems, GameState state, Random rng)
    {
        var allEvents = new List<GameEvent>();
        var itemsToCheck = new List<ItemInstance>(newItems);
        int chainStep = 0;

        while (itemsToCheck.Count > 0 && chainStep < MaxChainDepth)
        {
            var producedItems = new List<ItemInstance>();

            foreach (var newItem in itemsToCheck)
            {
                var itemDef = registry.GetItem(newItem.DefinitionId);
                if (itemDef is null)
                    continue;

                var matchingRules = FindMatchingRules(itemDef, state);

                if (matchingRules.Count == 0)
                {
                    // Special case: key without a matching openable item
                    if (itemDef.Tags.Contains("Key"))
                    {
                        var hasMatchingOpenable = state.Inventory.Any(i =>
                        {
                            var def = registry.GetItem(i.DefinitionId);
                            return def is not null && def.Tags.Contains("Openable");
                        });

                        if (!hasMatchingOpenable)
                        {
                            allEvents.Add(new MessageEvent("interaction.key_no_match"));
                        }
                    }

                    continue;
                }

                var automaticRules = matchingRules
                    .Where(r => r.IsAutomatic)
                    .OrderByDescending(r => r.Priority)
                    .ToList();

                if (automaticRules.Count >= 1)
                {
                    var rule = automaticRules[0];
                    var ruleEvents = ExecuteRule(rule, newItem, state, chainStep);
                    allEvents.AddRange(ruleEvents);

                    // Collect items produced by this reaction for the next chain iteration
                    foreach (var evt in ruleEvents)
                    {
                        if (evt is ItemReceivedEvent received)
                            producedItems.Add(received.Item);
                    }
                }
            }

            if (producedItems.Count == 0)
                break;

            itemsToCheck = producedItems;
            chainStep++;
        }

        // Award chain bonus if chain was 2+ steps
        if (chainStep >= 2)
        {
            string bonusItemId = chainStep >= 4 ? "box_legendary"
                               : chainStep >= 3 ? "box_cool"
                               : "box_ok_tier";

            var bonusInstance = ItemInstance.Create(bonusItemId);
            state.AddItem(bonusInstance);
            allEvents.Add(new ItemReceivedEvent(bonusInstance));
            allEvents.Add(new ChainBonusEvent(chainStep, bonusItemId));
        }

        return allEvents;
    }

    /// <summary>
    /// Finds all interaction rules that match the given item definition and game state.
    /// </summary>
    private List<InteractionRule> FindMatchingRules(ItemDefinition itemDef, GameState state)
    {
        var matching = new List<InteractionRule>();

        foreach (var rule in registry.InteractionRules)
        {
            // Check required tags
            var tagsMatch = rule.RequiredItemTags.All(tag => itemDef.Tags.Contains(tag));
            if (!tagsMatch)
                continue;

            // Check required item ids (if specified, all must be in inventory)
            if (rule.RequiredItemIds is not null && rule.RequiredItemIds.Count > 0)
            {
                var hasRequiredItem = rule.RequiredItemIds.All(id => state.HasItem(id));
                if (!hasRequiredItem)
                    continue;
            }

            matching.Add(rule);
        }

        return matching;
    }

    /// <summary>
    /// Executes a single interaction rule, consuming items and producing results.
    /// </summary>
    private List<GameEvent> ExecuteRule(InteractionRule rule, ItemInstance triggerItem, GameState state, int chainStep)
    {
        var events = new List<GameEvent>();

        // Find the partner item (first matching required item id) for the interaction message
        string? partnerItemId = null;
        if (rule.RequiredItemIds is not null && rule.RequiredItemIds.Count > 0)
        {
            partnerItemId = rule.RequiredItemIds[0];
        }

        // Consume the trigger item (unless it's a catalyst)
        if (rule.ConsumeTrigger)
        {
            state.RemoveItem(triggerItem.Id);
            events.Add(new ItemConsumedEvent(triggerItem.Id));
        }

        // Consume required inventory items (the partner items)
        if (rule.RequiredItemIds is not null)
        {
            foreach (var requiredId in rule.RequiredItemIds)
            {
                var invItem = state.Inventory.FirstOrDefault(i => i.DefinitionId == requiredId);
                if (invItem is not null)
                {
                    state.RemoveItem(invItem.Id);
                    events.Add(new ItemConsumedEvent(invItem.Id));
                }
            }
        }

        // Emit the interaction event with context
        events.Add(new InteractionTriggeredEvent(rule.Id, rule.DescriptionKey, triggerItem.DefinitionId, partnerItemId, chainStep));

        // Handle result based on ResultData
        if (rule.ResultData is not null)
        {
            if (rule.ResultData.StartsWith("adventure:") || rule.ResultData.StartsWith("adventure_unlock:"))
            {
                var themeName = rule.ResultData.Contains("adventure_unlock:")
                    ? rule.ResultData["adventure_unlock:".Length..]
                    : rule.ResultData["adventure:".Length..];
                if (Enum.TryParse<AdventureTheme>(themeName, out var theme)
                    && state.UnlockedAdventures.Add(theme))
                {
                    events.Add(new AdventureUnlockedEvent(theme));
                }
            }
            else
            {
                // Produce result items
                var resultItemIds = rule.ResultData.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
                foreach (var resultItemId in resultItemIds)
                {
                    var resultInstance = ItemInstance.Create(resultItemId);
                    state.AddItem(resultInstance);
                    events.Add(new ItemReceivedEvent(resultInstance));
                }
            }
        }

        return events;
    }
}