using System.Collections.Generic;

namespace Salmon.Core.Depth;

public class StateMachine
{
    public Persistence? History { get; set; }
    public EventManager? Events { get; set; }

    class ImplValue
    {
        public object? Value { get; set; }
        public DateTime When { get; set; } = DateTime.Now;

        public ImplValue(object? value, DateTime? when = null)
        {
            Value = value;
            When = when ?? DateTime.Now;
        }
    }

    object Mutex = new object();
    Dictionary<string, Dictionary<string, ImplValue>> Implementation = new ();
    public bool Populated { get; private set; } = false;

    public async Task<long> PopulateWithHistory()
    {
        Populated = true;
        long count = 0;
        if (History is not null)
            await foreach (var i in History.GetState())
            {
                Push(i);
                count++;
            }
                        
        return count;
    }

    public void Push(Triplet triplet)
    {
        Push(triplet.key, triplet.predicate, triplet.value, triplet.LastFlush);
    }

    /// <summary>
    /// Update string value in dictionary
    /// Must be thread safe
    /// </summary>
    /// <param name="key">May not be null</param>
    /// <param name="value">May be null</param>
    public void Push(string key, string predicate, object? value, DateTime when)
    {
        if(key == null) throw new ArgumentNullException(nameof(key));


        if (Get(key, predicate) == value)
            return;

        var implVal = new ImplValue(value, when);

        lock (Mutex)
        {
            if(!Implementation.ContainsKey(key))
            {
                Dictionary<string, ImplValue> dic = new();
                dic.Add(predicate, implVal);
                Implementation.Add(key, dic);
            }

            var keyDic = Implementation[key];
            if(!keyDic.TryAdd(predicate, implVal))
            {
                var old = keyDic[predicate];
                if (old.When > when)
                    return;
                keyDic[predicate] = implVal;
            }
                         
        }
        
        if(History is not null)
            History.PushStateChange(key, predicate, value, when);

        if (Events is not null)
            Events.Push(Event.FromStateChange(key, value, when));
    }

    public IEnumerable<string> GetIds()
    {
        lock (Mutex)
        {
            if (!Populated)
                PopulateWithHistory().Wait();

            foreach (var kv in Implementation)
                yield return kv.Key;
        }

    }

    public IEnumerable<Triplet> Get()
    {
        lock (Mutex)
        {
            if (!Populated)
                PopulateWithHistory().Wait();

            foreach (var kv in Implementation)
                foreach (var kvv in kv.Value)
                    yield return new Triplet
                    {
                        key = kv.Key,
                        predicate = kvv.Key,
                        value = kvv.Value.Value,
                        LastFlush = kvv.Value.When
                    };
        }

    }

    public IEnumerable<Triplet> Get(string key)
    {
        Dictionary<string, ImplValue> dic;


        lock (Mutex)
        {
            if (!Populated)
                PopulateWithHistory().Wait();

            if (!Implementation.TryGetValue(key, out dic))
                yield break;
        }


        foreach(var kv in dic)
            yield return new Triplet
            {
                key = key,
                predicate = kv.Key,
                value = kv.Value.Value,
                LastFlush = kv.Value.When
            };
    }

    public DateTime? GetLastUpdate(string key)
    {
        Dictionary<string, ImplValue> dic;



        lock (Mutex)
        {
            if (!Populated)
                PopulateWithHistory().Wait();

            if (!Implementation.TryGetValue(key, out dic))
                return null;
        }


        DateTime mostrecent = DateTime.MinValue;
        foreach (var kv in dic)
            if(kv.Value.When >  mostrecent)
                mostrecent = kv.Value.When;

        if (mostrecent == DateTime.MinValue)
            return null;

        return mostrecent;
    }

    public object? Get(string key, string predicate)
    {
        lock (Mutex)
        {
            if (!Populated)
                PopulateWithHistory().Wait();

            if (Implementation.TryGetValue(key, out var value))
                if (value.TryGetValue(predicate, out var ret))
                    return ret;
        }


        return null;
    }

    public long CountTriplets()
    {
        lock(Mutex)
        {
            if (!Populated)
                PopulateWithHistory().Wait();

            long c = 0;
            foreach (var kv in Implementation)
                foreach (var i in kv.Key)
                    c++;

            return c;
        }
            
    }
}