using Microsoft.Data.Sqlite;

namespace ytLive.Services;

public partial class LayoutStore : IDisposable
{
    private static readonly string[] SnapshotTables =
    {
        "Scene", "Source", "Webcam", "WebcamSceneConfig", "Socials", "SocialEntry", "Music",
    };

    private const string DefaultsInitializedKey = "DefaultsInitialized";
    private const string CurrentBuildIdKey = "CurrentBuildId";

    private void EnsureLayoutSnapshotSchema()
    {
        using (var cmd = _connection.CreateCommand())
        {
            cmd.CommandText = """
                CREATE TABLE IF NOT EXISTS LayoutSnapshotState (
                    Key TEXT PRIMARY KEY,
                    Value TEXT NOT NULL
                );
                CREATE TABLE IF NOT EXISTS DefaultLayoutSetting (
                    Key TEXT PRIMARY KEY,
                    Value TEXT NOT NULL
                );
                """;
            cmd.ExecuteNonQuery();
        }

        foreach (var table in SnapshotTables)
        {
            var snapshotTable = "Default" + table;
            using (var create = _connection.CreateCommand())
            {
                create.CommandText = $"CREATE TABLE IF NOT EXISTS {snapshotTable} AS SELECT * FROM {table} WHERE 0;";
                create.ExecuteNonQuery();
            }

            var snapshotColumns = ReadColumnNames(snapshotTable);
            foreach (var (name, type, defaultValue) in ReadColumnDefinitions(table))
            {
                if (snapshotColumns.Contains(name, StringComparer.OrdinalIgnoreCase)) continue;
                var definition = string.IsNullOrWhiteSpace(type) ? "BLOB" : type;
                if (defaultValue != null) definition += " DEFAULT " + defaultValue;
                using var add = _connection.CreateCommand();
                add.CommandText = $"ALTER TABLE {snapshotTable} ADD COLUMN {QuoteIdentifier(name)} {definition};";
                add.ExecuteNonQuery();
            }
        }
    }

    /// <summary>Captures the installed layout once as the immutable branded default. Existing databases
    /// are snapshotted before MainViewModel loads them; a fresh database calls
    /// <see cref="CaptureDefaultsIfMissing"/> after its factory scenes have been seeded.</summary>
    public void PrepareLayoutSnapshots(string buildId)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(buildId);
        var defaultsInitialized = GetSnapshotState(DefaultsInitializedKey) == "1";
        if (!defaultsInitialized && HasStoredScenes())
        {
            CaptureDefaults();
            defaultsInitialized = true;
        }

        var currentBuildId = GetSnapshotState(CurrentBuildIdKey);
        if (defaultsInitialized && !string.Equals(currentBuildId, buildId, StringComparison.Ordinal))
            RestoreDefaults(buildId);
        else if (!defaultsInitialized && string.IsNullOrWhiteSpace(currentBuildId))
            SetSnapshotState(CurrentBuildIdKey, buildId);
    }

    /// <summary>Seeds the default snapshot after the first-run factory layout has been persisted.</summary>
    public void CaptureDefaultsIfMissing()
    {
        if (GetSnapshotState(DefaultsInitializedKey) != "1")
            CaptureDefaults();
    }

    private void CaptureDefaults()
    {
        var columnsByTable = SnapshotTables.ToDictionary(table => table, ReadColumnNames);
        using var tx = _connection.BeginTransaction();
        foreach (var table in SnapshotTables.Reverse())
        {
            using var delete = _connection.CreateCommand();
            delete.Transaction = tx;
            delete.CommandText = $"DELETE FROM Default{table};";
            delete.ExecuteNonQuery();
        }

        foreach (var table in SnapshotTables)
        {
            var columns = string.Join(", ", columnsByTable[table].Select(QuoteIdentifier));
            using var copy = _connection.CreateCommand();
            copy.Transaction = tx;
            copy.CommandText = $"INSERT INTO Default{table} ({columns}) SELECT {columns} FROM {table};";
            copy.ExecuteNonQuery();
        }

        using (var clearSettings = _connection.CreateCommand())
        {
            clearSettings.Transaction = tx;
            clearSettings.CommandText = "DELETE FROM DefaultLayoutSetting;";
            clearSettings.ExecuteNonQuery();
        }
        using (var copySettings = _connection.CreateCommand())
        {
            copySettings.Transaction = tx;
            copySettings.CommandText = """
                INSERT INTO DefaultLayoutSetting (Key, Value)
                SELECT Key, Value FROM Settings
                WHERE Key LIKE 'BackgroundPath_%' OR Key LIKE 'BackgroundUseDefault_%';
                """;
            copySettings.ExecuteNonQuery();
        }

        using (var state = _connection.CreateCommand())
        {
            state.Transaction = tx;
            state.CommandText = """
                INSERT INTO LayoutSnapshotState (Key, Value) VALUES ($key, '1')
                ON CONFLICT(Key) DO UPDATE SET Value = excluded.Value;
                """;
            state.Parameters.AddWithValue("$key", DefaultsInitializedKey);
            state.ExecuteNonQuery();
        }
        tx.Commit();
    }

    private void RestoreDefaults(string buildId)
    {
        var columnsByTable = SnapshotTables.ToDictionary(table => table, ReadColumnNames);
        using var tx = _connection.BeginTransaction();

        foreach (var table in SnapshotTables.Reverse())
        {
            using var delete = _connection.CreateCommand();
            delete.Transaction = tx;
            delete.CommandText = $"DELETE FROM {table};";
            delete.ExecuteNonQuery();
        }

        foreach (var table in SnapshotTables)
        {
            var columns = string.Join(", ", columnsByTable[table].Select(QuoteIdentifier));
            using var copy = _connection.CreateCommand();
            copy.Transaction = tx;
            copy.CommandText = $"INSERT INTO {table} ({columns}) SELECT {columns} FROM Default{table};";
            copy.ExecuteNonQuery();
        }

        using (var clearSettings = _connection.CreateCommand())
        {
            clearSettings.Transaction = tx;
            clearSettings.CommandText = "DELETE FROM Settings WHERE Key LIKE 'BackgroundPath_%' OR Key LIKE 'BackgroundUseDefault_%';";
            clearSettings.ExecuteNonQuery();
        }
        using (var copySettings = _connection.CreateCommand())
        {
            copySettings.Transaction = tx;
            copySettings.CommandText = "INSERT INTO Settings (Key, Value) SELECT Key, Value FROM DefaultLayoutSetting;";
            copySettings.ExecuteNonQuery();
        }

        SetSnapshotState(CurrentBuildIdKey, buildId, tx);
        tx.Commit();
    }

    private bool HasStoredScenes()
    {
        using var cmd = _connection.CreateCommand();
        cmd.CommandText = "SELECT EXISTS(SELECT 1 FROM Scene LIMIT 1);";
        return Convert.ToInt32(cmd.ExecuteScalar()) != 0;
    }

    private string? GetSnapshotState(string key)
    {
        using var cmd = _connection.CreateCommand();
        cmd.CommandText = "SELECT Value FROM LayoutSnapshotState WHERE Key = $key;";
        cmd.Parameters.AddWithValue("$key", key);
        return cmd.ExecuteScalar() as string;
    }

    private void SetSnapshotState(string key, string value, SqliteTransaction? transaction = null)
    {
        using var cmd = _connection.CreateCommand();
        cmd.Transaction = transaction;
        cmd.CommandText = """
            INSERT INTO LayoutSnapshotState (Key, Value) VALUES ($key, $value)
            ON CONFLICT(Key) DO UPDATE SET Value = excluded.Value;
            """;
        cmd.Parameters.AddWithValue("$key", key);
        cmd.Parameters.AddWithValue("$value", value);
        cmd.ExecuteNonQuery();
    }

    private List<string> ReadColumnNames(string table)
        => ReadColumnDefinitions(table).Select(column => column.Name).ToList();

    private List<(string Name, string Type, string? DefaultValue)> ReadColumnDefinitions(string table)
    {
        var columns = new List<(string, string, string?)>();
        using var cmd = _connection.CreateCommand();
        cmd.CommandText = $"PRAGMA table_info({table});";
        using var reader = cmd.ExecuteReader();
        while (reader.Read())
            columns.Add((reader.GetString(1), reader.IsDBNull(2) ? string.Empty : reader.GetString(2),
                reader.IsDBNull(4) ? null : reader.GetString(4)));
        return columns;
    }

    private static string QuoteIdentifier(string identifier)
        => "\"" + identifier.Replace("\"", "\"\"") + "\"";
}