using System;
using System.Collections.Generic;
using UnityEngine;

namespace IdleSpectator;

/// <summary>World-session immutable observation store. Persistence is added in Phase 5.</summary>
public static class NarrativeEventStore
{
    private static readonly Dictionary<string, NarrativeEventRecord> Events =
        new Dictionary<string, NarrativeEventRecord>(StringComparer.Ordinal);
    private static readonly Dictionary<long, List<NarrativeEventRecord>> ChildEventsByParent =
        new Dictionary<long, List<NarrativeEventRecord>>();
    private static readonly Dictionary<long, List<NarrativeEventRecord>> ChildEventsByChild =
        new Dictionary<long, List<NarrativeEventRecord>>();

    public static int Count => Events.Count;

    public static void Clear()
    {
        Events.Clear();
        ChildEventsByParent.Clear();
        ChildEventsByChild.Clear();
    }

    public static NarrativeEventRecord Get(string id)
    {
        if (string.IsNullOrEmpty(id))
        {
            return null;
        }

        Events.TryGetValue(id, out NarrativeEventRecord record);
        return record;
    }

    public static bool Add(NarrativeEventRecord record)
    {
        if (record == null || string.IsNullOrEmpty(record.Id) || Events.ContainsKey(record.Id))
        {
            return false;
        }

        Events[record.Id] = record;
        Index(record);
        NarrativePersistence.MarkDirty();
        return true;
    }

    public static IEnumerable<NarrativeEventRecord> All() => Events.Values;

    internal static bool Import(NarrativeEventRecord record)
    {
        if (record == null || string.IsNullOrEmpty(record.Id) || Events.ContainsKey(record.Id))
        {
            return false;
        }

        Events[record.Id] = record;
        Index(record);
        return true;
    }

    public static IReadOnlyList<NarrativeEventRecord> ChildrenOf(long parentId)
    {
        return parentId != 0 && ChildEventsByParent.TryGetValue(parentId, out List<NarrativeEventRecord> records)
            ? records
            : Array.Empty<NarrativeEventRecord>();
    }

    public static IReadOnlyList<NarrativeEventRecord> ParentsOf(long childId)
    {
        return childId != 0 && ChildEventsByChild.TryGetValue(childId, out List<NarrativeEventRecord> records)
            ? records
            : Array.Empty<NarrativeEventRecord>();
    }

    /// <summary>
    /// Keep the event side of the runtime graph aligned with retained developments.
    /// Recent unprojected observations fill any remaining room so dedupe remains useful.
    /// </summary>
    internal static int Compact(HashSet<string> retainedDevelopmentIds, int max)
    {
        if (Events.Count <= max || max <= 0)
        {
            return 0;
        }

        var retained = new HashSet<string>(StringComparer.Ordinal);
        var ranked = new List<NarrativeEventRecord>(Events.Values);
        ranked.Sort((a, b) =>
        {
            bool aLinked = a != null
                           && retainedDevelopmentIds != null
                           && retainedDevelopmentIds.Contains(a.DevelopmentId ?? "");
            bool bLinked = b != null
                           && retainedDevelopmentIds != null
                           && retainedDevelopmentIds.Contains(b.DevelopmentId ?? "");
            if (aLinked != bLinked) return aLinked ? -1 : 1;
            float aAt = a?.ObservedAt ?? float.MinValue;
            float bAt = b?.ObservedAt ?? float.MinValue;
            int observed = bAt.CompareTo(aAt);
            if (observed != 0) return observed;
            return (b?.WorldTime ?? double.MinValue).CompareTo(
                a?.WorldTime ?? double.MinValue);
        });

        for (int i = 0; i < ranked.Count && retained.Count < max; i++)
        {
            NarrativeEventRecord record = ranked[i];
            if (record != null && !string.IsNullOrEmpty(record.Id))
            {
                retained.Add(record.Id);
            }
        }

        int before = Events.Count;
        var remove = new List<string>();
        foreach (string id in Events.Keys)
        {
            if (!retained.Contains(id)) remove.Add(id);
        }
        for (int i = 0; i < remove.Count; i++) Events.Remove(remove[i]);
        if (remove.Count > 0)
        {
            RebuildRelationIndexes();
        }
        return Mathf.Max(0, before - Events.Count);
    }

    private static void Index(NarrativeEventRecord record)
    {
        if (record == null || record.Kind != NarrativeEventKind.ChildBorn)
        {
            return;
        }

        AddIndexed(ChildEventsByParent, record.SubjectId, record);
        AddIndexed(ChildEventsByChild, record.OtherId, record);
    }

    private static void AddIndexed(
        Dictionary<long, List<NarrativeEventRecord>> index,
        long id,
        NarrativeEventRecord record)
    {
        if (id == 0)
        {
            return;
        }

        if (!index.TryGetValue(id, out List<NarrativeEventRecord> records))
        {
            records = new List<NarrativeEventRecord>(2);
            index[id] = records;
        }

        records.Add(record);
    }

    private static void RebuildRelationIndexes()
    {
        ChildEventsByParent.Clear();
        ChildEventsByChild.Clear();
        foreach (NarrativeEventRecord record in Events.Values)
        {
            Index(record);
        }
    }
}