using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;

namespace game.PlayerDataStorage
{
    public enum PlayerKVSyncStatus { NotLoaded, Ready, ReadFailed, Conflict, UnknownOutcome, Unauthorized, StorageError, Closed }
    public enum PlayerKVOpenError { None, Validation, Busy, StorageError, RecoveryRequired }
    public enum PlayerKVChangeError { None, Validation, Blocked, StorageError }

    public sealed class PlayerKVStateResult
    {
        public bool Success => Error == PlayerKVChangeError.None;
        public PlayerKVChangeError Error { get; }
        public long AttemptSequence { get; }
        public long Revision { get; }
        public bool LocalCommitMayHaveSucceeded { get; }
        internal PlayerKVStateResult(PlayerKVChangeError error, long sequence = 0, long revision = 0, bool uncertain = false)
        { Error = error; AttemptSequence = sequence; Revision = revision; LocalCommitMayHaveSucceeded = uncertain; }
    }

    public sealed class PlayerKVOpenResult
    {
        public bool Success => Error == PlayerKVOpenError.None;
        public PlayerKVOpenError Error { get; }
        public PlayerKVSyncState State { get; }
        internal PlayerKVOpenResult(PlayerKVOpenError error, PlayerKVSyncState state = null) { Error = error; State = state; }
    }

    // Existence is separate from value: an empty string is not a deletion.
    public sealed class PlayerKVValue : IEquatable<PlayerKVValue>
    {
        public static readonly PlayerKVValue Missing = new PlayerKVValue(false, null);
        public bool Exists { get; }
        public string Value { get; }
        PlayerKVValue(bool exists, string value) { Exists = exists; Value = value; }
        public static PlayerKVValue Present(string value) => new PlayerKVValue(true, value ?? throw new ArgumentNullException(nameof(value)));
        public bool Equals(PlayerKVValue other) => other != null && Exists == other.Exists && Value == other.Value;
        public override bool Equals(object obj) => Equals(obj as PlayerKVValue);
        public override int GetHashCode() => Exists ? (Value.GetHashCode() ^ 397) : 0;
        internal static PlayerKVValue At(IReadOnlyDictionary<string, string> data, string key) =>
            data.TryGetValue(key, out var value) ? Present(value) : Missing;
    }

    public sealed class PlayerKVChange
    {
        public string Key { get; }
        public long Sequence { get; }
        public PlayerKVValue BaseValue { get; }
        public PlayerKVValue Target { get; }
        internal PlayerKVChange(string key, long sequence, PlayerKVValue baseline, PlayerKVValue target)
        { Key = key; Sequence = sequence; BaseValue = baseline; Target = target; }
        internal PlayerKVChange WithBase(PlayerKVValue baseline) => new PlayerKVChange(Key, Sequence, baseline, Target);
    }

    public sealed class PlayerKVBatch
    {
        public string Id { get; }
        public IReadOnlyList<PlayerKVChange> Items { get; }
        public bool IsDelete => !Items[0].Target.Exists;
        internal PlayerKVBatch(string id, IEnumerable<PlayerKVChange> items)
        { Id = id; Items = Array.AsReadOnly(items.ToArray()); }
    }

    public sealed class PlayerKVDiagnosticSnapshot
    {
        public long Revision { get; }
        public long NextSequence { get; }
        public bool HasBaseline { get; }
        public bool AuthenticationInvalid { get; }
        public IReadOnlyDictionary<string, string> Baseline { get; }
        public IReadOnlyDictionary<string, string> LocalOnly { get; }
        public IReadOnlyDictionary<string, PlayerKVChange> Pending { get; }
        public IReadOnlyDictionary<string, PlayerKVValue> ConflictObservations { get; }
        public PlayerKVBatch ActiveBatch { get; }
        public PlayerKVBatch UnknownBatch { get; }
        internal PlayerKVDiagnosticSnapshot(KVSnapshot source)
        {
            Revision = source.Revision; NextSequence = source.NextSequence; HasBaseline = source.HasBaseline;
            AuthenticationInvalid = source.AuthenticationInvalid;
            Baseline = ReadOnly(source.Baseline); LocalOnly = ReadOnly(source.LocalOnly);
            Pending = ReadOnly(source.Pending); ConflictObservations = ReadOnly(source.Conflicts);
            ActiveBatch = source.Active; UnknownBatch = source.Unknown;
        }
        static IReadOnlyDictionary<string, T> ReadOnly<T>(Dictionary<string, T> source) =>
            new ReadOnlyDictionary<string, T>(new Dictionary<string, T>(source, StringComparer.Ordinal));
    }

    internal sealed class KVIdentity
    {
        internal readonly string Api, PlayerId, DirectoryPath;
        internal KVIdentity(string root, Uri api, string playerId)
        {
            if (string.IsNullOrWhiteSpace(root) || !Path.IsPathFullyQualified(root) || api == null || !api.IsAbsoluteUri ||
                (api.Scheme != "http" && api.Scheme != "https") || api.UserInfo.Length != 0 || api.Query.Length != 0 || api.Fragment.Length != 0 ||
                !long.TryParse(playerId, NumberStyles.None, CultureInfo.InvariantCulture, out var id) || id <= 0)
                throw new ArgumentException("Invalid KV cache identity.");
            Api = api.AbsoluteUri.TrimEnd('/') + "/";
            PlayerId = id.ToString(CultureInfo.InvariantCulture);
            using (var hash = SHA256.Create())
            {
                var bytes = hash.ComputeHash(Encoding.UTF8.GetBytes(Api));
                var fingerprint = string.Concat(bytes.Select(b => b.ToString("x2", CultureInfo.InvariantCulture)));
                DirectoryPath = Path.Combine(Path.GetFullPath(root), "player-kv", "v1", fingerprint, PlayerId);
            }
        }
    }

    internal sealed class KVSnapshot
    {
        internal long Revision, NextSequence = 1;
        internal bool HasBaseline, AuthenticationInvalid;
        internal Dictionary<string, string> Baseline = new Dictionary<string, string>(StringComparer.Ordinal);
        internal Dictionary<string, string> LocalOnly = new Dictionary<string, string>(StringComparer.Ordinal);
        internal Dictionary<string, PlayerKVChange> Pending = new Dictionary<string, PlayerKVChange>(StringComparer.Ordinal);
        internal Dictionary<string, PlayerKVValue> Conflicts = new Dictionary<string, PlayerKVValue>(StringComparer.Ordinal);
        internal PlayerKVBatch Active, Unknown;
        internal KVSnapshot Clone() => new KVSnapshot {
            Revision = Revision, NextSequence = NextSequence, HasBaseline = HasBaseline, AuthenticationInvalid = AuthenticationInvalid,
            Baseline = new Dictionary<string, string>(Baseline, StringComparer.Ordinal), LocalOnly = new Dictionary<string, string>(LocalOnly, StringComparer.Ordinal),
            Pending = new Dictionary<string, PlayerKVChange>(Pending, StringComparer.Ordinal), Conflicts = new Dictionary<string, PlayerKVValue>(Conflicts, StringComparer.Ordinal),
            Active = Active, Unknown = Unknown
        };
        internal static bool ValidKey(string key) => !string.IsNullOrEmpty(key) && key.Length <= 128;

        internal string Encode(KVIdentity identity)
        {
            var pending = new JArray(Pending.Values.OrderBy(p => p.Sequence).Select(ChangeJson));
            var conflicts = new JObject();
            foreach (var pair in Conflicts) conflicts.Add(pair.Key, ValueJson(pair.Value));
            return new JObject {
                ["formatVersion"] = 1, ["apiBaseUri"] = identity.Api, ["playerId"] = identity.PlayerId,
                ["revision"] = Revision, ["nextSequence"] = NextSequence, ["hasBaseline"] = HasBaseline,
                ["authenticationInvalid"] = AuthenticationInvalid, ["baseline"] = JObject.FromObject(Baseline),
                ["localOnly"] = JObject.FromObject(LocalOnly), ["pending"] = pending, ["conflictObservations"] = conflicts,
                ["activeBatch"] = BatchJson(Active), ["unknownBatch"] = BatchJson(Unknown)
            }.ToString(Formatting.None);
        }
        static JObject ValueJson(PlayerKVValue value) => new JObject { ["exists"] = value.Exists, ["value"] = value.Value };
        static JObject ChangeJson(PlayerKVChange item) => new JObject {
            ["key"] = item.Key, ["sequence"] = item.Sequence, ["base"] = ValueJson(item.BaseValue), ["target"] = ValueJson(item.Target)
        };
        static JToken BatchJson(PlayerKVBatch batch) => batch == null ? JValue.CreateNull() : (JToken)new JObject {
            ["id"] = batch.Id, ["items"] = new JArray(batch.Items.Select(ChangeJson))
        };

        internal static KVSnapshot Decode(string text, KVIdentity identity)
        {
            JObject root;
            using (var reader = new JsonTextReader(new StringReader(text)) { DateParseHandling = DateParseHandling.None })
            {
                root = JObject.Load(reader, new JsonLoadSettings { DuplicatePropertyNameHandling = DuplicatePropertyNameHandling.Error });
                if (reader.Read()) throw Invalid();
            }
            if (Integer(root, "formatVersion") != 1 || String(root, "apiBaseUri") != identity.Api || String(root, "playerId") != identity.PlayerId) throw Invalid();
            var result = new KVSnapshot {
                Revision = Integer(root, "revision"), NextSequence = Integer(root, "nextSequence"),
                HasBaseline = Boolean(root, "hasBaseline"), AuthenticationInvalid = Boolean(root, "authenticationInvalid"),
                Baseline = Strings(Field(root, "baseline", JTokenType.Object)), LocalOnly = Strings(Field(root, "localOnly", JTokenType.Object)),
                Active = Batch(root, "activeBatch"), Unknown = Batch(root, "unknownBatch")
            };
            foreach (var item in Field(root, "pending", JTokenType.Array))
            {
                var change = Change(item);
                if (result.Pending.ContainsKey(change.Key)) throw Invalid();
                result.Pending.Add(change.Key, change);
            }
            foreach (var property in ((JObject)Field(root, "conflictObservations", JTokenType.Object)).Properties())
            {
                if (!ValidKey(property.Name)) throw Invalid();
                result.Conflicts.Add(property.Name, Value(property.Value));
            }
            result.Validate();
            return result;
        }
        internal void Validate()
        {
            if (Revision < 1 || NextSequence < 1 || (Active != null && Unknown != null) ||
                (!HasBaseline && (Baseline.Count != 0 || LocalOnly.Count != 0 || Pending.Count != 0 || Active != null || Unknown != null))) throw Invalid();
            var sequences = new Dictionary<long, string>();
            foreach (var item in Pending.Values)
            {
                if (item.Sequence < 1 || item.Sequence >= NextSequence || sequences.ContainsKey(item.Sequence)) throw Invalid();
                sequences.Add(item.Sequence, item.Key);
            }
            foreach (var key in Conflicts.Keys) if (!Pending.ContainsKey(key)) throw Invalid();
            var batch = Active ?? Unknown;
            if (batch == null) return;
            foreach (var item in batch.Items)
            {
                if (item.Sequence < 1 || item.Sequence >= NextSequence || !Pending.TryGetValue(item.Key, out var latest) || latest.Sequence < item.Sequence ||
                    (sequences.TryGetValue(item.Sequence, out var key) && key != item.Key) ||
                    !latest.BaseValue.Equals(item.BaseValue) ||
                    (latest.Sequence == item.Sequence && !latest.Target.Equals(item.Target))) throw Invalid();
            }
        }
        static Dictionary<string, string> Strings(JToken value)
        {
            var result = new Dictionary<string, string>(StringComparer.Ordinal);
            foreach (var property in ((JObject)value).Properties())
            {
                if (!ValidKey(property.Name) || property.Value.Type != JTokenType.String) throw Invalid();
                result.Add(property.Name, (string)property.Value);
            }
            return result;
        }
        static PlayerKVChange Change(JToken item)
        {
            var key = String(item, "key");
            if (!ValidKey(key)) throw Invalid();
            return new PlayerKVChange(key, Integer(item, "sequence"), Value(Field(item, "base", JTokenType.Object)), Value(Field(item, "target", JTokenType.Object)));
        }
        static PlayerKVValue Value(JToken item)
        {
            var exists = Boolean(item, "exists");
            var value = Field(item, "value", exists ? JTokenType.String : JTokenType.Null);
            return exists ? PlayerKVValue.Present((string)value) : PlayerKVValue.Missing;
        }
        static PlayerKVBatch Batch(JToken parent, string name)
        {
            var node = parent[name];
            if (node == null) throw Invalid();
            if (node.Type == JTokenType.Null) return null;
            var id = String(node, "id");
            if (!Guid.TryParseExact(id, "N", out _)) throw Invalid();
            var items = Field(node, "items", JTokenType.Array).Select(Change).ToArray();
            if (items.Length == 0 || items.Length > 10 || items.Select(i => i.Key).Distinct(StringComparer.Ordinal).Count() != items.Length ||
                items.Select(i => i.Sequence).Distinct().Count() != items.Length || items.Any(i => i.Target.Exists != items[0].Target.Exists) ||
                !items.Select(i => i.Sequence).SequenceEqual(items.Select(i => i.Sequence).OrderBy(s => s))) throw Invalid();
            return new PlayerKVBatch(id, items);
        }
        static JToken Field(JToken parent, string name, JTokenType type)
        {
            if (!(parent is JObject obj) || obj[name] == null || obj[name].Type != type) throw Invalid();
            return obj[name];
        }
        static string String(JToken parent, string name) => (string)Field(parent, name, JTokenType.String);
        static long Integer(JToken parent, string name) => (long)Field(parent, name, JTokenType.Integer);
        static bool Boolean(JToken parent, string name) => (bool)Field(parent, name, JTokenType.Boolean);
        internal static JsonException Invalid() => new JsonException("Invalid KV cache snapshot.");
    }
}