using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.IO;
using System.Linq;

namespace game.PlayerDataStorage
{
    /// <summary>
    /// Synchronous, fixed-identity cache state. No HTTP, gameplay initialization or timers.
    /// All transitions and disk writes share a gate. The phase-3B owner must drain its
    /// admitted network operations before disposing this state and its filesystem lease.
    /// </summary>
    public sealed class PlayerKVSyncState : IDisposable
    {
        readonly object gate = new object();
        readonly PlayerKVCacheStore store;
        KVSnapshot snapshot;
        PlayerKVSyncStatus status;
        public PlayerKVSyncStatus Status { get { lock (gate) return status; } }
        public string ApiBaseUri { get; }
        public string PlayerId { get; }

        PlayerKVSyncState(KVIdentity identity, PlayerKVCacheStore store, KVSnapshot snapshot)
        {
            ApiBaseUri = identity.Api; PlayerId = identity.PlayerId; this.store = store; this.snapshot = snapshot;
            // Authentication belongs to the old owner. A new owner must obtain a fresh
            // successful Get before Ready; this never clears a persisted unknown batch.
            snapshot.AuthenticationInvalid = false;
            // A recovered active batch might have reached the server. Never acknowledge it by guessing.
            if (snapshot.Active != null) { snapshot.Unknown = snapshot.Active; snapshot.Active = null; }
            status = snapshot.Unknown != null ? PlayerKVSyncStatus.UnknownOutcome : PlayerKVSyncStatus.NotLoaded;
        }

        public static PlayerKVOpenResult Open(string root, Uri api, string playerId) => Open(root, api, playerId, null);
        internal static PlayerKVOpenResult Open(string root, Uri api, string playerId, Action<KVCacheWriteStage> fault)
        {
            KVIdentity identity;
            try { identity = new KVIdentity(root, api, playerId); }
            catch (Exception ex) when (ex is ArgumentException || ex is NotSupportedException || ex is PathTooLongException)
            { return new PlayerKVOpenResult(PlayerKVOpenError.Validation); }
            var error = PlayerKVCacheStore.Open(identity, fault, out var store, out var snapshot);
            return error == PlayerKVOpenError.None ? new PlayerKVOpenResult(error, new PlayerKVSyncState(identity, store, snapshot)) : new PlayerKVOpenResult(error);
        }

        public PlayerKVDiagnosticSnapshot Inspect() { lock (gate) return new PlayerKVDiagnosticSnapshot(snapshot); }

        public IReadOnlyDictionary<string, string> ReadLocal()
        {
            lock (gate)
            {
                if (status != PlayerKVSyncStatus.Ready) throw new InvalidOperationException("KV data is not ready.");
                var result = new Dictionary<string, string>(snapshot.Baseline, StringComparer.Ordinal);
                foreach (var item in snapshot.Pending.Values) Apply(result, item.Key, item.Target);
                foreach (var pair in snapshot.LocalOnly) result[pair.Key] = pair.Value;
                return new ReadOnlyDictionary<string, string>(result);
            }
        }

        // The caller must supply a successful complete Get. Failed reads must use RecordReadFailure.
        public PlayerKVStateResult Reconcile(IReadOnlyDictionary<string, string> remote)
        {
            lock (gate)
            {
                if (Terminal || snapshot.Active != null || snapshot.AuthenticationInvalid) return Blocked();
                if (remote == null || remote.Any(p => !KVSnapshot.ValidKey(p.Key) || p.Value == null)) return Invalid();
                var copy = snapshot.Clone();
                copy.Conflicts.Clear();
                if (copy.Unknown != null)
                {
                    foreach (var item in copy.Pending.Values) copy.Conflicts[item.Key] = PlayerKVValue.At(remote, item.Key);
                    return Commit(copy, PlayerKVSyncStatus.UnknownOutcome);
                }
                foreach (var item in copy.Pending.Values.ToArray())
                {
                    var observed = PlayerKVValue.At(remote, item.Key);
                    if (observed.Equals(item.Target)) copy.Pending.Remove(item.Key);
                    else if (!observed.Equals(item.BaseValue)) copy.Conflicts[item.Key] = observed;
                }
                copy.Baseline = remote.ToDictionary(p => p.Key, p => p.Value, StringComparer.Ordinal);
                copy.HasBaseline = true;
                return Commit(copy, copy.Conflicts.Count == 0 ? PlayerKVSyncStatus.Ready : PlayerKVSyncStatus.Conflict);
            }
        }

        public PlayerKVStateResult RecordReadFailure(bool unauthorized = false)
        {
            lock (gate)
            {
                if (Terminal || snapshot.Active != null) return Blocked();
                if (unauthorized)
                {
                    var copy = snapshot.Clone(); copy.AuthenticationInvalid = true;
                    return Commit(copy, copy.Unknown == null ? PlayerKVSyncStatus.Unauthorized : PlayerKVSyncStatus.UnknownOutcome);
                }
                status = snapshot.Unknown != null ? PlayerKVSyncStatus.UnknownOutcome : PlayerKVSyncStatus.ReadFailed;
                return new PlayerKVStateResult(PlayerKVChangeError.None, revision: snapshot.Revision);
            }
        }

        public PlayerKVStateResult Update(string key, string value, bool remoteStore = true) =>
            Edit(key, value == null ? null : PlayerKVValue.Present(value), remoteStore);
        public PlayerKVStateResult Delete(string key) => Edit(key, PlayerKVValue.Missing, true);

        PlayerKVStateResult Edit(string key, PlayerKVValue target, bool remote)
        {
            lock (gate)
            {
                if (status != PlayerKVSyncStatus.Ready || snapshot.AuthenticationInvalid) return Blocked();
                if (!KVSnapshot.ValidKey(key) || target == null || snapshot.NextSequence == long.MaxValue) return Invalid();
                var copy = snapshot.Clone();
                var sequence = copy.NextSequence++;
                if (remote)
                {
                    var baseline = copy.Pending.TryGetValue(key, out var previous) ? previous.BaseValue : PlayerKVValue.At(copy.Baseline, key);
                    copy.Pending[key] = new PlayerKVChange(key, sequence, baseline, target);
                    copy.LocalOnly.Remove(key);
                }
                else copy.LocalOnly[key] = target.Value;
                return Commit(copy, PlayerKVSyncStatus.Ready, sequence);
            }
        }

        public PlayerKVStateResult BeginBatch(long throughSequence, out PlayerKVBatch batch)
        {
            lock (gate)
            {
                batch = null;
                if (status != PlayerKVSyncStatus.Ready || snapshot.Active != null || snapshot.Unknown != null || snapshot.AuthenticationInvalid) return Blocked();
                if (throughSequence < 0) return Invalid();
                var ordered = snapshot.Pending.Values.Where(p => p.Sequence <= throughSequence).OrderBy(p => p.Sequence).ToArray();
                if (ordered.Length == 0) return new PlayerKVStateResult(PlayerKVChangeError.None, revision: snapshot.Revision);
                var copy = snapshot.Clone();
                copy.Active = new PlayerKVBatch(Guid.NewGuid().ToString("N"), ordered.TakeWhile(p => p.Target.Exists == ordered[0].Target.Exists).Take(10));
                var result = Commit(copy, PlayerKVSyncStatus.Ready);
                if (result.Success) batch = snapshot.Active; // Never expose a batch until its write-ahead record is durable.
                return result;
            }
        }

        public PlayerKVStateResult ConfirmBatch(string batchId)
        {
            lock (gate)
            {
                if (status != PlayerKVSyncStatus.Ready || snapshot.Active == null || snapshot.Active.Id != batchId) return Blocked();
                var copy = snapshot.Clone();
                foreach (var item in copy.Active.Items)
                {
                    Apply(copy.Baseline, item.Key, item.Target);
                    var current = copy.Pending[item.Key];
                    if (current.Sequence == item.Sequence) copy.Pending.Remove(item.Key);
                    else copy.Pending[item.Key] = current.WithBase(item.Target);
                }
                copy.Active = null;
                return Commit(copy, PlayerKVSyncStatus.Ready);
            }
        }

        // mayHaveCommitted=false is only valid with positive evidence of no dispatch.
        public PlayerKVStateResult FailBatch(string batchId, bool mayHaveCommitted, bool unauthorized = false)
        {
            lock (gate)
            {
                if (Terminal || snapshot.Active == null || snapshot.Active.Id != batchId) return Blocked();
                var copy = snapshot.Clone();
                copy.AuthenticationInvalid |= unauthorized;
                if (mayHaveCommitted) copy.Unknown = copy.Active;
                copy.Active = null;
                return Commit(copy, mayHaveCommitted ? PlayerKVSyncStatus.UnknownOutcome :
                    copy.AuthenticationInvalid ? PlayerKVSyncStatus.Unauthorized : PlayerKVSyncStatus.ReadFailed);
            }
        }

        bool Terminal => status == PlayerKVSyncStatus.Closed || status == PlayerKVSyncStatus.StorageError;
        PlayerKVStateResult Commit(KVSnapshot copy, PlayerKVSyncStatus nextStatus, long sequence = 0)
        {
            if (snapshot.Revision == long.MaxValue)
            { status = PlayerKVSyncStatus.StorageError; return new PlayerKVStateResult(PlayerKVChangeError.StorageError, sequence, snapshot.Revision); }
            copy.Revision = snapshot.Revision + 1;
            if (!store.Save(copy, out var uncertain))
            {
                status = PlayerKVSyncStatus.StorageError;
                return new PlayerKVStateResult(PlayerKVChangeError.StorageError, sequence, copy.Revision, uncertain);
            }
            snapshot = copy; status = nextStatus;
            return new PlayerKVStateResult(PlayerKVChangeError.None, sequence, copy.Revision);
        }
        static void Apply(Dictionary<string, string> data, string key, PlayerKVValue value)
        { if (value.Exists) data[key] = value.Value; else data.Remove(key); }
        PlayerKVStateResult Blocked() => new PlayerKVStateResult(PlayerKVChangeError.Blocked, revision: snapshot.Revision);
        PlayerKVStateResult Invalid() => new PlayerKVStateResult(PlayerKVChangeError.Validation, revision: snapshot.Revision);

        public void Dispose()
        {
            lock (gate)
            {
                if (status == PlayerKVSyncStatus.Closed) return;
                status = PlayerKVSyncStatus.Closed;
                store.Dispose();
            }
        }
    }
}