using System;
using System.Collections.Generic;
using System.Data.Common;
using System.Text.Json;
using System.Threading;
using System.Threading.Tasks;
using Dapper;
using Junction.Domain;
using Junction.Domain.Models;
using Junction.Domain.Persistence;

namespace Junction.Persistence
{
    /// <summary>
    /// Dapper + SQLite adapter for <see cref="IMachineRepository"/>.
    /// </summary>
    /// <remarks>
    /// Provider-swap seam: all SQLite/Dapper/ADO.NET types stay inside this class. Only
    /// <see cref="Junction.Domain"/> types and BCL primitives cross the boundary.
    ///
    /// Column mapping (see <see cref="SqliteSchema"/> DDL):
    /// <list type="bullet">
    ///   <item><description><see cref="Guid"/> &lt;-&gt; TEXT via <c>ToString("D")</c> (canonical 8-4-4-4-12).</description></item>
    ///   <item><description><see cref="Machine.PollInterval"/> &lt;-&gt; INTEGER ticks (<see cref="TimeSpan.Ticks"/>).</description></item>
    ///   <item><description><see cref="Machine.ConnectionConfig"/> &lt;-&gt; TEXT JSON of a Dictionary&lt;string,string&gt; (System.Text.Json). Null/blank JSON rehydrates to an empty dictionary.</description></item>
    ///   <item><description><see cref="DateTimeOffset"/> &lt;-&gt; TEXT ISO 8601 round-trip ("O").</description></item>
    ///   <item><description><see cref="ConnectionState"/> &lt;-&gt; INTEGER (enum cast).</description></item>
    /// </list>
    ///
    /// Not-found policy: <see cref="GetByIdAsync"/> and <see cref="GetLatestSnapshotAsync"/> return
    /// <c>Result.Fail</c> carrying an <see cref="OperationError"/> with code <c>"not_found"</c> — never throw,
    /// never a success with a null value.
    ///
    /// Errors: expected failures are reported via <see cref="Result"/>/<see cref="Result{T}"/>. Store
    /// exceptions are caught and mapped to <c>Result.Fail</c>; cancellation is mapped to <c>Result.Cancelled</c>.
    /// </remarks>
    public sealed class SqliteMachineRepository : IMachineRepository
    {
        private const string Source = "SqliteMachineRepository";
        private const string NotFoundCode = "not_found";

        private static readonly JsonSerializerOptions JsonOptions = new JsonSerializerOptions();

        private readonly IConnectionFactory _connectionFactory;

        public SqliteMachineRepository(IConnectionFactory connectionFactory)
        {
            _connectionFactory = connectionFactory ?? throw new ArgumentNullException(nameof(connectionFactory));
        }

        public async Task<Result<IReadOnlyList<Machine>>> GetAllAsync(CancellationToken cancellationToken)
        {
            if (cancellationToken.IsCancellationRequested)
            {
                return Result<IReadOnlyList<Machine>>.Cancelled();
            }

            try
            {
                using (var connection = OpenConnection())
                {
                    var command = new CommandDefinition(
                        "SELECT Id, Name, ProtocolId, PollIntervalTicks, ConnectionConfigJson FROM machines;",
                        cancellationToken: cancellationToken);

                    var rows = await connection.QueryAsync<MachineRow>(command).ConfigureAwait(false);

                    var machines = new List<Machine>();
                    foreach (var row in rows)
                    {
                        machines.Add(MapMachine(row));
                    }

                    return Result<IReadOnlyList<Machine>>.Ok(machines);
                }
            }
            catch (OperationCanceledException)
            {
                return Result<IReadOnlyList<Machine>>.Cancelled();
            }
            catch (Exception ex)
            {
                return Result<IReadOnlyList<Machine>>.Fail(
                    OperationError.Of(Source, "GetAll failed: " + ex.Message));
            }
        }

        public async Task<Result<Machine>> GetByIdAsync(Guid id, CancellationToken cancellationToken)
        {
            if (cancellationToken.IsCancellationRequested)
            {
                return Result<Machine>.Cancelled();
            }

            try
            {
                using (var connection = OpenConnection())
                {
                    var command = new CommandDefinition(
                        "SELECT Id, Name, ProtocolId, PollIntervalTicks, ConnectionConfigJson " +
                        "FROM machines WHERE Id = @Id;",
                        new { Id = GuidText(id) },
                        cancellationToken: cancellationToken);

                    var row = await connection.QuerySingleOrDefaultAsync<MachineRow>(command).ConfigureAwait(false);

                    if (row == null)
                    {
                        return Result<Machine>.Fail(new OperationError(
                            NotFoundCode, Source, "Machine not found: " + GuidText(id)));
                    }

                    return Result<Machine>.Ok(MapMachine(row));
                }
            }
            catch (OperationCanceledException)
            {
                return Result<Machine>.Cancelled();
            }
            catch (Exception ex)
            {
                return Result<Machine>.Fail(
                    OperationError.Of(Source, "GetById failed: " + ex.Message));
            }
        }

        public async Task<Result> UpsertAsync(Machine machine, CancellationToken cancellationToken)
        {
            if (machine == null)
            {
                return Result.Fail(OperationError.Of(Source, "Machine is null."));
            }

            if (cancellationToken.IsCancellationRequested)
            {
                return Result.Cancelled();
            }

            try
            {
                using (var connection = OpenConnection())
                {
                    var command = new CommandDefinition(
                        "INSERT INTO machines (Id, Name, ProtocolId, PollIntervalTicks, ConnectionConfigJson) " +
                        "VALUES (@Id, @Name, @ProtocolId, @PollIntervalTicks, @ConnectionConfigJson) " +
                        "ON CONFLICT(Id) DO UPDATE SET " +
                        "Name = excluded.Name, " +
                        "ProtocolId = excluded.ProtocolId, " +
                        "PollIntervalTicks = excluded.PollIntervalTicks, " +
                        "ConnectionConfigJson = excluded.ConnectionConfigJson;",
                        new
                        {
                            Id = GuidText(machine.Id),
                            machine.Name,
                            machine.ProtocolId,
                            PollIntervalTicks = machine.PollInterval.Ticks,
                            ConnectionConfigJson = SerializeConfig(machine.ConnectionConfig)
                        },
                        cancellationToken: cancellationToken);

                    await connection.ExecuteAsync(command).ConfigureAwait(false);

                    return Result.Ok();
                }
            }
            catch (OperationCanceledException)
            {
                return Result.Cancelled();
            }
            catch (Exception ex)
            {
                return Result.Fail(OperationError.Of(Source, "Upsert failed: " + ex.Message));
            }
        }

        public async Task<Result> DeleteAsync(Guid id, CancellationToken cancellationToken)
        {
            if (cancellationToken.IsCancellationRequested)
            {
                return Result.Cancelled();
            }

            try
            {
                using (var connection = OpenConnection())
                using (var transaction = connection.BeginTransaction())
                {
                    var idParam = new { Id = GuidText(id) };

                    await connection.ExecuteAsync(new CommandDefinition(
                        "DELETE FROM snapshot_items WHERE MachineId = @Id;",
                        idParam, transaction, cancellationToken: cancellationToken)).ConfigureAwait(false);

                    await connection.ExecuteAsync(new CommandDefinition(
                        "DELETE FROM latest_snapshots WHERE MachineId = @Id;",
                        idParam, transaction, cancellationToken: cancellationToken)).ConfigureAwait(false);

                    await connection.ExecuteAsync(new CommandDefinition(
                        "DELETE FROM machines WHERE Id = @Id;",
                        idParam, transaction, cancellationToken: cancellationToken)).ConfigureAwait(false);

                    transaction.Commit();

                    return Result.Ok();
                }
            }
            catch (OperationCanceledException)
            {
                return Result.Cancelled();
            }
            catch (Exception ex)
            {
                return Result.Fail(OperationError.Of(Source, "Delete failed: " + ex.Message));
            }
        }

        public async Task<Result> SaveSnapshotAsync(MachineSnapshot snapshot, CancellationToken cancellationToken)
        {
            if (snapshot == null)
            {
                return Result.Fail(OperationError.Of(Source, "Snapshot is null."));
            }

            if (cancellationToken.IsCancellationRequested)
            {
                return Result.Cancelled();
            }

            try
            {
                using (var connection = OpenConnection())
                using (var transaction = connection.BeginTransaction())
                {
                    var machineIdText = GuidText(snapshot.MachineId);

                    // Upsert the single latest-snapshot header row.
                    await connection.ExecuteAsync(new CommandDefinition(
                        "INSERT INTO latest_snapshots (MachineId, CapturedAt, ConnectionState) " +
                        "VALUES (@MachineId, @CapturedAt, @ConnectionState) " +
                        "ON CONFLICT(MachineId) DO UPDATE SET " +
                        "CapturedAt = excluded.CapturedAt, " +
                        "ConnectionState = excluded.ConnectionState;",
                        new
                        {
                            MachineId = machineIdText,
                            CapturedAt = IsoText(snapshot.CapturedAt),
                            ConnectionState = (int)snapshot.ConnectionState
                        },
                        transaction, cancellationToken: cancellationToken)).ConfigureAwait(false);

                    // Only-latest policy: drop previous items, insert current set.
                    await connection.ExecuteAsync(new CommandDefinition(
                        "DELETE FROM snapshot_items WHERE MachineId = @MachineId;",
                        new { MachineId = machineIdText },
                        transaction, cancellationToken: cancellationToken)).ConfigureAwait(false);

                    if (snapshot.Items.Count > 0)
                    {
                        var itemParams = new List<object>(snapshot.Items.Count);
                        foreach (var item in snapshot.Items)
                        {
                            itemParams.Add(new
                            {
                                MachineId = machineIdText,
                                ItemId = item.Id,
                                item.Name,
                                item.Value,
                                item.Category,
                                Timestamp = IsoText(item.Timestamp)
                            });
                        }

                        await connection.ExecuteAsync(new CommandDefinition(
                            "INSERT INTO snapshot_items (MachineId, ItemId, Name, Value, Category, Timestamp) " +
                            "VALUES (@MachineId, @ItemId, @Name, @Value, @Category, @Timestamp);",
                            itemParams,
                            transaction, cancellationToken: cancellationToken)).ConfigureAwait(false);
                    }

                    transaction.Commit();

                    return Result.Ok();
                }
            }
            catch (OperationCanceledException)
            {
                return Result.Cancelled();
            }
            catch (Exception ex)
            {
                return Result.Fail(OperationError.Of(Source, "SaveSnapshot failed: " + ex.Message));
            }
        }

        public async Task<Result<MachineSnapshot>> GetLatestSnapshotAsync(Guid machineId, CancellationToken cancellationToken)
        {
            if (cancellationToken.IsCancellationRequested)
            {
                return Result<MachineSnapshot>.Cancelled();
            }

            try
            {
                using (var connection = OpenConnection())
                {
                    var machineIdText = GuidText(machineId);

                    var header = await connection.QuerySingleOrDefaultAsync<SnapshotRow>(new CommandDefinition(
                        "SELECT MachineId, CapturedAt, ConnectionState FROM latest_snapshots WHERE MachineId = @MachineId;",
                        new { MachineId = machineIdText },
                        cancellationToken: cancellationToken)).ConfigureAwait(false);

                    if (header == null)
                    {
                        return Result<MachineSnapshot>.Fail(new OperationError(
                            NotFoundCode, Source, "Snapshot not found for machine: " + machineIdText));
                    }

                    var itemRows = await connection.QueryAsync<SnapshotItemRow>(new CommandDefinition(
                        "SELECT ItemId, Name, Value, Category, Timestamp FROM snapshot_items WHERE MachineId = @MachineId;",
                        new { MachineId = machineIdText },
                        cancellationToken: cancellationToken)).ConfigureAwait(false);

                    var items = new List<DataItem>();
                    foreach (var itemRow in itemRows)
                    {
                        items.Add(new DataItem(
                            itemRow.ItemId,
                            itemRow.Name,
                            itemRow.Value,
                            itemRow.Category,
                            ParseIso(itemRow.Timestamp)));
                    }

                    var snapshot = new MachineSnapshot(
                        machineId,
                        ParseIso(header.CapturedAt),
                        (ConnectionState)header.ConnectionState,
                        items);

                    return Result<MachineSnapshot>.Ok(snapshot);
                }
            }
            catch (OperationCanceledException)
            {
                return Result<MachineSnapshot>.Cancelled();
            }
            catch (Exception ex)
            {
                return Result<MachineSnapshot>.Fail(
                    OperationError.Of(Source, "GetLatestSnapshot failed: " + ex.Message));
            }
        }

        // -- helpers -------------------------------------------------------------------------

        private DbConnection OpenConnection()
        {
            // SqliteConnectionFactory yields a SqliteConnection (a DbConnection); Dapper's *Async
            // needs the DbConnection surface. The concrete Sqlite type never escapes this class.
            var connection = _connectionFactory.CreateOpenConnection();
            if (connection is DbConnection dbConnection)
            {
                return dbConnection;
            }

            connection?.Dispose();
            throw new InvalidOperationException(
                "IConnectionFactory must return a DbConnection for async Dapper operations.");
        }

        private static Machine MapMachine(MachineRow row)
        {
            return new Machine(
                Guid.Parse(row.Id),
                row.Name,
                row.ProtocolId,
                DeserializeConfig(row.ConnectionConfigJson),
                TimeSpan.FromTicks(row.PollIntervalTicks));
        }

        private static string GuidText(Guid id) => id.ToString("D");

        private static string IsoText(DateTimeOffset value) => value.ToString("O");

        private static DateTimeOffset ParseIso(string value) =>
            DateTimeOffset.Parse(value, null, System.Globalization.DateTimeStyles.RoundtripKind);

        private static string SerializeConfig(IReadOnlyDictionary<string, string> config)
        {
            Dictionary<string, string> dict;
            if (config is Dictionary<string, string> concrete)
            {
                dict = concrete;
            }
            else
            {
                dict = new Dictionary<string, string>(config.Count);
                foreach (var pair in config)
                {
                    dict[pair.Key] = pair.Value;
                }
            }

            return JsonSerializer.Serialize(dict, JsonOptions);
        }

        private static IReadOnlyDictionary<string, string> DeserializeConfig(string? json)
        {
            if (string.IsNullOrWhiteSpace(json))
            {
                return new Dictionary<string, string>(0);
            }

            var dict = JsonSerializer.Deserialize<Dictionary<string, string>>(json!, JsonOptions);
            return dict ?? new Dictionary<string, string>(0);
        }

        // -- row DTOs (private; never cross the boundary) -----------------------------------

        private sealed class MachineRow
        {
            public string Id { get; set; } = "";
            public string Name { get; set; } = "";
            public string ProtocolId { get; set; } = "";
            public long PollIntervalTicks { get; set; }
            public string? ConnectionConfigJson { get; set; }
        }

        private sealed class SnapshotRow
        {
            public string MachineId { get; set; } = "";
            public string CapturedAt { get; set; } = "";
            public int ConnectionState { get; set; }
        }

        private sealed class SnapshotItemRow
        {
            public string ItemId { get; set; } = "";
            public string Name { get; set; } = "";
            public string Value { get; set; } = "";
            public string Category { get; set; } = "";
            public string Timestamp { get; set; } = "";
        }
    }
}