using Microsoft.Data.Sqlite;
using Microsoft.Extensions.Logging;
using ScadaLink.Commons.Types.Enums;

namespace ScadaLink.StoreAndForward;

/// <summary>
/// WP-9: SQLite persistence layer for store-and-forward messages.
/// Uses direct Microsoft.Data.Sqlite (not EF Core) for lightweight site-side storage.
/// No max buffer size per design decision.
/// </summary>
public class StoreAndForwardStorage
{
    private readonly string _connectionString;
    private readonly ILogger<StoreAndForwardStorage> _logger;

    public StoreAndForwardStorage(string connectionString, ILogger<StoreAndForwardStorage> logger)
    {
        _connectionString = connectionString;
        _logger = logger;
    }

    /// <summary>
    /// Creates the sf_messages table if it does not exist.
    /// </summary>
    public async Task InitializeAsync()
    {
        await using var connection = new SqliteConnection(_connectionString);
        await connection.OpenAsync();

        await using var command = connection.CreateCommand();
        command.CommandText = @"
            CREATE TABLE IF NOT EXISTS sf_messages (
                id                TEXT PRIMARY KEY,
                category          INTEGER NOT NULL,
                target            TEXT    NOT NULL,
                payload_json      TEXT    NOT NULL,
                retry_count       INTEGER NOT NULL DEFAULT 0,
                max_retries       INTEGER NOT NULL DEFAULT 50,
                retry_interval_ms INTEGER NOT NULL DEFAULT 30000,
                created_at        TEXT    NOT NULL,
                last_attempt_at   TEXT,
                status            INTEGER NOT NULL DEFAULT 0,
                last_error        TEXT,
                origin_instance   TEXT
            );

            CREATE INDEX IF NOT EXISTS idx_sf_messages_status ON sf_messages(status);
            CREATE INDEX IF NOT EXISTS idx_sf_messages_category ON sf_messages(category);
        ";
        await command.ExecuteNonQueryAsync();

        _logger.LogInformation("Store-and-forward SQLite storage initialized");
    }

    /// <summary>
    /// WP-9: Enqueues a new message with Pending status.
    /// </summary>
    public async Task EnqueueAsync(StoreAndForwardMessage message)
    {
        await using var connection = new SqliteConnection(_connectionString);
        await connection.OpenAsync();

        await using var cmd = connection.CreateCommand();
        cmd.CommandText = @"
            INSERT INTO sf_messages (id, category, target, payload_json, retry_count, max_retries,
                                     retry_interval_ms, created_at, last_attempt_at, status, last_error, origin_instance)
            VALUES (@id, @category, @target, @payload, @retryCount, @maxRetries,
                    @retryIntervalMs, @createdAt, @lastAttempt, @status, @lastError, @origin)";

        cmd.Parameters.AddWithValue("@id", message.Id);
        cmd.Parameters.AddWithValue("@category", (int)message.Category);
        cmd.Parameters.AddWithValue("@target", message.Target);
        cmd.Parameters.AddWithValue("@payload", message.PayloadJson);
        cmd.Parameters.AddWithValue("@retryCount", message.RetryCount);
        cmd.Parameters.AddWithValue("@maxRetries", message.MaxRetries);
        cmd.Parameters.AddWithValue("@retryIntervalMs", message.RetryIntervalMs);
        cmd.Parameters.AddWithValue("@createdAt", message.CreatedAt.ToString("O"));
        cmd.Parameters.AddWithValue("@lastAttempt", message.LastAttemptAt.HasValue
            ? message.LastAttemptAt.Value.ToString("O") : DBNull.Value);
        cmd.Parameters.AddWithValue("@status", (int)message.Status);
        cmd.Parameters.AddWithValue("@lastError", (object?)message.LastError ?? DBNull.Value);
        cmd.Parameters.AddWithValue("@origin", (object?)message.OriginInstanceName ?? DBNull.Value);

        await cmd.ExecuteNonQueryAsync();
    }

    /// <summary>
    /// WP-10: Gets all messages that are due for retry (Pending status, last attempt older than retry interval).
    /// </summary>
    public async Task<List<StoreAndForwardMessage>> GetMessagesForRetryAsync()
    {
        await using var connection = new SqliteConnection(_connectionString);
        await connection.OpenAsync();

        await using var cmd = connection.CreateCommand();
        cmd.CommandText = @"
            SELECT id, category, target, payload_json, retry_count, max_retries,
                   retry_interval_ms, created_at, last_attempt_at, status, last_error, origin_instance
            FROM sf_messages
            WHERE status = @pending
              AND (last_attempt_at IS NULL
                   OR retry_interval_ms = 0
                   OR (julianday('now') - julianday(last_attempt_at)) * 86400000 >= retry_interval_ms)
            ORDER BY created_at ASC";

        cmd.Parameters.AddWithValue("@pending", (int)StoreAndForwardMessageStatus.Pending);

        return await ReadMessagesAsync(cmd);
    }

    /// <summary>
    /// WP-10: Updates a message after a delivery attempt.
    /// </summary>
    public async Task UpdateMessageAsync(StoreAndForwardMessage message)
    {
        await using var connection = new SqliteConnection(_connectionString);
        await connection.OpenAsync();

        await using var cmd = connection.CreateCommand();
        cmd.CommandText = @"
            UPDATE sf_messages
            SET retry_count = @retryCount,
                last_attempt_at = @lastAttempt,
                status = @status,
                last_error = @lastError
            WHERE id = @id";

        cmd.Parameters.AddWithValue("@id", message.Id);
        cmd.Parameters.AddWithValue("@retryCount", message.RetryCount);
        cmd.Parameters.AddWithValue("@lastAttempt", message.LastAttemptAt.HasValue
            ? message.LastAttemptAt.Value.ToString("O") : DBNull.Value);
        cmd.Parameters.AddWithValue("@status", (int)message.Status);
        cmd.Parameters.AddWithValue("@lastError", (object?)message.LastError ?? DBNull.Value);

        await cmd.ExecuteNonQueryAsync();
    }

    /// <summary>
    /// WP-10: Removes a successfully delivered message.
    /// </summary>
    public async Task RemoveMessageAsync(string messageId)
    {
        await using var connection = new SqliteConnection(_connectionString);
        await connection.OpenAsync();

        await using var cmd = connection.CreateCommand();
        cmd.CommandText = "DELETE FROM sf_messages WHERE id = @id";
        cmd.Parameters.AddWithValue("@id", messageId);

        await cmd.ExecuteNonQueryAsync();
    }

    /// <summary>
    /// WP-12: Gets all parked messages, optionally filtered by category, with pagination.
    /// </summary>
    public async Task<(List<StoreAndForwardMessage> Messages, int TotalCount)> GetParkedMessagesAsync(
        StoreAndForwardCategory? category = null,
        int pageNumber = 1,
        int pageSize = 50)
    {
        await using var connection = new SqliteConnection(_connectionString);
        await connection.OpenAsync();

        // Count
        await using var countCmd = connection.CreateCommand();
        countCmd.CommandText = category.HasValue
            ? "SELECT COUNT(*) FROM sf_messages WHERE status = @parked AND category = @category"
            : "SELECT COUNT(*) FROM sf_messages WHERE status = @parked";
        countCmd.Parameters.AddWithValue("@parked", (int)StoreAndForwardMessageStatus.Parked);
        if (category.HasValue) countCmd.Parameters.AddWithValue("@category", (int)category.Value);
        var totalCount = Convert.ToInt32(await countCmd.ExecuteScalarAsync());

        // Page
        await using var pageCmd = connection.CreateCommand();
        var categoryFilter = category.HasValue ? " AND category = @category" : "";
        pageCmd.CommandText = $@"
            SELECT id, category, target, payload_json, retry_count, max_retries,
                   retry_interval_ms, created_at, last_attempt_at, status, last_error, origin_instance
            FROM sf_messages
            WHERE status = @parked{categoryFilter}
            ORDER BY created_at ASC
            LIMIT @limit OFFSET @offset";

        pageCmd.Parameters.AddWithValue("@parked", (int)StoreAndForwardMessageStatus.Parked);
        if (category.HasValue) pageCmd.Parameters.AddWithValue("@category", (int)category.Value);
        pageCmd.Parameters.AddWithValue("@limit", pageSize);
        pageCmd.Parameters.AddWithValue("@offset", (pageNumber - 1) * pageSize);

        var messages = await ReadMessagesAsync(pageCmd);
        return (messages, totalCount);
    }

    /// <summary>
    /// WP-12: Moves a parked message back to pending for retry.
    /// </summary>
    public async Task<bool> RetryParkedMessageAsync(string messageId)
    {
        await using var connection = new SqliteConnection(_connectionString);
        await connection.OpenAsync();

        await using var cmd = connection.CreateCommand();
        cmd.CommandText = @"
            UPDATE sf_messages
            SET status = @pending, retry_count = 0, last_error = NULL
            WHERE id = @id AND status = @parked";

        cmd.Parameters.AddWithValue("@id", messageId);
        cmd.Parameters.AddWithValue("@pending", (int)StoreAndForwardMessageStatus.Pending);
        cmd.Parameters.AddWithValue("@parked", (int)StoreAndForwardMessageStatus.Parked);

        var rows = await cmd.ExecuteNonQueryAsync();
        return rows > 0;
    }

    /// <summary>
    /// WP-12: Permanently discards a parked message.
    /// </summary>
    public async Task<bool> DiscardParkedMessageAsync(string messageId)
    {
        await using var connection = new SqliteConnection(_connectionString);
        await connection.OpenAsync();

        await using var cmd = connection.CreateCommand();
        cmd.CommandText = "DELETE FROM sf_messages WHERE id = @id AND status = @parked";
        cmd.Parameters.AddWithValue("@id", messageId);
        cmd.Parameters.AddWithValue("@parked", (int)StoreAndForwardMessageStatus.Parked);

        var rows = await cmd.ExecuteNonQueryAsync();
        return rows > 0;
    }

    /// <summary>
    /// WP-14: Gets buffer depth by category (count of pending messages per category).
    /// </summary>
    public async Task<Dictionary<StoreAndForwardCategory, int>> GetBufferDepthByCategoryAsync()
    {
        await using var connection = new SqliteConnection(_connectionString);
        await connection.OpenAsync();

        await using var cmd = connection.CreateCommand();
        cmd.CommandText = @"
            SELECT category, COUNT(*) as cnt
            FROM sf_messages
            WHERE status = @pending
            GROUP BY category";
        cmd.Parameters.AddWithValue("@pending", (int)StoreAndForwardMessageStatus.Pending);

        var result = new Dictionary<StoreAndForwardCategory, int>();
        await using var reader = await cmd.ExecuteReaderAsync();
        while (await reader.ReadAsync())
        {
            var category = (StoreAndForwardCategory)reader.GetInt32(0);
            var count = reader.GetInt32(1);
            result[category] = count;
        }

        return result;
    }

    /// <summary>
    /// WP-13: Verifies messages are NOT deleted when an instance is deleted.
    /// Returns the count of messages for a given origin instance.
    /// </summary>
    public async Task<int> GetMessageCountByOriginInstanceAsync(string instanceName)
    {
        await using var connection = new SqliteConnection(_connectionString);
        await connection.OpenAsync();

        await using var cmd = connection.CreateCommand();
        cmd.CommandText = @"
            SELECT COUNT(*)
            FROM sf_messages
            WHERE origin_instance = @origin";
        cmd.Parameters.AddWithValue("@origin", instanceName);

        return Convert.ToInt32(await cmd.ExecuteScalarAsync());
    }

    /// <summary>
    /// Gets a message by ID.
    /// </summary>
    public async Task<StoreAndForwardMessage?> GetMessageByIdAsync(string messageId)
    {
        await using var connection = new SqliteConnection(_connectionString);
        await connection.OpenAsync();

        await using var cmd = connection.CreateCommand();
        cmd.CommandText = @"
            SELECT id, category, target, payload_json, retry_count, max_retries,
                   retry_interval_ms, created_at, last_attempt_at, status, last_error, origin_instance
            FROM sf_messages
            WHERE id = @id";
        cmd.Parameters.AddWithValue("@id", messageId);

        var messages = await ReadMessagesAsync(cmd);
        return messages.FirstOrDefault();
    }

    /// <summary>
    /// Gets the count of parked messages (for health reporting).
    /// </summary>
    public async Task<int> GetParkedMessageCountAsync()
    {
        await using var conn = new SqliteConnection(_connectionString);
        await conn.OpenAsync();
        await using var cmd = conn.CreateCommand();
        cmd.CommandText = "SELECT COUNT(*) FROM sf_messages WHERE status = @parked";
        cmd.Parameters.AddWithValue("@parked", (int)StoreAndForwardMessageStatus.Parked);
        var result = await cmd.ExecuteScalarAsync();
        return Convert.ToInt32(result);
    }

    /// <summary>
    /// Gets total message count by status.
    /// </summary>
    public async Task<int> GetMessageCountByStatusAsync(StoreAndForwardMessageStatus status)
    {
        await using var connection = new SqliteConnection(_connectionString);
        await connection.OpenAsync();

        await using var cmd = connection.CreateCommand();
        cmd.CommandText = "SELECT COUNT(*) FROM sf_messages WHERE status = @status";
        cmd.Parameters.AddWithValue("@status", (int)status);

        return Convert.ToInt32(await cmd.ExecuteScalarAsync());
    }

    private static async Task<List<StoreAndForwardMessage>> ReadMessagesAsync(SqliteCommand cmd)
    {
        var results = new List<StoreAndForwardMessage>();
        await using var reader = await cmd.ExecuteReaderAsync();
        while (await reader.ReadAsync())
        {
            results.Add(new StoreAndForwardMessage
            {
                Id = reader.GetString(0),
                Category = (StoreAndForwardCategory)reader.GetInt32(1),
                Target = reader.GetString(2),
                PayloadJson = reader.GetString(3),
                RetryCount = reader.GetInt32(4),
                MaxRetries = reader.GetInt32(5),
                RetryIntervalMs = reader.GetInt64(6),
                CreatedAt = DateTimeOffset.Parse(reader.GetString(7)),
                LastAttemptAt = reader.IsDBNull(8) ? null : DateTimeOffset.Parse(reader.GetString(8)),
                Status = (StoreAndForwardMessageStatus)reader.GetInt32(9),
                LastError = reader.IsDBNull(10) ? null : reader.GetString(10),
                OriginInstanceName = reader.IsDBNull(11) ? null : reader.GetString(11)
            });
        }
        return results;
    }
}