using Npgsql.Util;

using System;

using System.Collections.Concurrent;

namespace Npgsql

{

static class ClusterStateCache

{

static readonly ConcurrentDictionary<ClusterIdentifier, ClusterInfo> Clusters = new();

internal static ClusterState GetClusterState(string host, int port, bool ignoreExpiration)

=> Clusters.TryGetValue(new(host, port), out var cs) && (ignoreExpiration || !cs.Timeout.HasExpired)

? cs.State

: ClusterState.Unknown;

#if NETSTANDARD2_0

internal static ClusterState UpdateClusterState(string host, int port, ClusterState state, DateTime timeStamp, TimeSpan stateExpiration)

=> Clusters.AddOrUpdate(

new ClusterIdentifier(host, port),

new ClusterInfo(state, new NpgsqlTimeout(stateExpiration), timeStamp),

(_, oldInfo) => oldInfo.TimeStamp >= timeStamp ? oldInfo : new ClusterInfo(state, new NpgsqlTimeout(stateExpiration), timeStamp)).State;

#else

internal static ClusterState UpdateClusterState(string host, int port, ClusterState state, DateTime timeStamp, TimeSpan stateExpiration)

=> Clusters.AddOrUpdate(

new ClusterIdentifier(host, port),

(_, newInfo) => newInfo,

(_, oldInfo, newInfo) => oldInfo.TimeStamp >= newInfo.TimeStamp ? oldInfo : newInfo,

new ClusterInfo(state, new NpgsqlTimeout(stateExpiration), timeStamp)).State;

#endif

internal static void RemoveClusterState(string host, int port)

=> Clusters.TryRemove(new ClusterIdentifier(host, port), out _);

internal static void Clear() => Clusters.Clear();

readonly struct ClusterIdentifier : IEquatable<ClusterIdentifier>

{

readonly string _host;

readonly int _port;

public ClusterIdentifier(string host, int port) => (_host, _port) = (host, port);

public override bool Equals(object? obj) => obj is ClusterIdentifier other && Equals(other);

public bool Equals(ClusterIdentifier other) => _port == other._port && _host == other._host;

public override int GetHashCode() => HashCode.Combine(_host, _port);

}

readonly struct ClusterInfo

{

internal readonly ClusterState State;

internal readonly NpgsqlTimeout Timeout;

// While the TimeStamp is not strictly required, it does lower the risk of overwriting the current state with an old value

internal readonly DateTime TimeStamp;

public ClusterInfo(ClusterState state, NpgsqlTimeout timeout, DateTime timeStamp)

=> (State, Timeout, TimeStamp) = (state, timeout, timeStamp);

}

}

enum ClusterState : byte

{

Unknown = 0,

Offline = 1,

PrimaryReadWrite = 2,

PrimaryReadOnly = 3,

Standby = 4

}

}