using System;
using System.Data;
using Junction.Domain;

namespace Junction.Persistence
{
    /// <summary>
    /// Owns the SQLite schema (DDL). Idempotent: safe to run on every startup.
    /// Only-latest policy — one snapshot row and one item-set per machine — but the
    /// shape leaves room to add history tables later without breaking these tables.
    /// </summary>
    public static class SqliteSchema
    {
        // machines: one row per configured machine. ConnectionConfig bag stored as JSON text.
        private const string CreateMachines =
            @"CREATE TABLE IF NOT EXISTS machines (
                Id                    TEXT    NOT NULL PRIMARY KEY,
                Name                  TEXT    NOT NULL,
                ProtocolId            TEXT    NOT NULL,
                PollIntervalTicks     INTEGER NOT NULL,
                ConnectionConfigJson  TEXT    NOT NULL
            );";

        // latest_snapshots: exactly one row per machine (PK = MachineId). Upsert overwrites.
        private const string CreateLatestSnapshots =
            @"CREATE TABLE IF NOT EXISTS latest_snapshots (
                MachineId       TEXT    NOT NULL PRIMARY KEY,
                CapturedAt      TEXT    NOT NULL,
                ConnectionState INTEGER NOT NULL
            );";

        // snapshot_items: datums of the latest snapshot. Replaced on each SaveSnapshot.
        private const string CreateSnapshotItems =
            @"CREATE TABLE IF NOT EXISTS snapshot_items (
                MachineId TEXT NOT NULL,
                ItemId    TEXT NOT NULL,
                Name      TEXT NOT NULL,
                Value     TEXT NOT NULL,
                Category  TEXT NOT NULL,
                Timestamp TEXT NOT NULL,
                PRIMARY KEY (MachineId, ItemId)
            );";

        /// <summary>
        /// Creates all tables if they do not already exist. Idempotent.
        /// Returns a failed <see cref="Result"/> instead of throwing on store errors.
        /// </summary>
        public static Result EnsureCreated(IDbConnection connection)
        {
            if (connection == null)
            {
                return Result.Fail(OperationError.Of("SqliteSchema", "Connection is null."));
            }

            try
            {
                if (connection.State != ConnectionState.Open)
                {
                    connection.Open();
                }

                Execute(connection, CreateMachines);
                Execute(connection, CreateLatestSnapshots);
                Execute(connection, CreateSnapshotItems);

                return Result.Ok();
            }
            catch (Exception ex)
            {
                return Result.Fail(OperationError.Of("SqliteSchema", "Schema init failed: " + ex.Message));
            }
        }

        /// <summary>Convenience overload: opens a connection from the factory and runs <see cref="EnsureCreated(IDbConnection)"/>.</summary>
        public static Result EnsureCreated(IConnectionFactory connectionFactory)
        {
            if (connectionFactory == null)
            {
                return Result.Fail(OperationError.Of("SqliteSchema", "Connection factory is null."));
            }

            try
            {
                using (var connection = connectionFactory.CreateOpenConnection())
                {
                    return EnsureCreated(connection);
                }
            }
            catch (Exception ex)
            {
                return Result.Fail(OperationError.Of("SqliteSchema", "Schema init failed: " + ex.Message));
            }
        }

        private static void Execute(IDbConnection connection, string sql)
        {
            using (var command = connection.CreateCommand())
            {
                command.CommandText = sql;
                command.ExecuteNonQuery();
            }
        }
    }
}