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.
///
/// StoreAndForward-008: every method opens a fresh <see cref="SqliteConnection"/> for
/// the duration of the call rather than holding a long-lived connection. This is a
/// deliberate trade-off, not an oversight: Microsoft.Data.Sqlite maintains an internal
/// connection pool keyed on the connection string, so <c>OpenAsync</c> on a previously
/// used connection string reuses a pooled handle instead of performing a real file
/// open. The retry sweep therefore relies on that pool for acceptable performance —
/// it calls <see cref="RemoveMessageAsync"/> / <see cref="UpdateMessageIfStatusAsync"/>
/// once per due message, and with no max buffer size (by design) the buffer can grow
/// large. The connection-per-call style keeps each method self-contained and
/// transaction-scoped; if profiling ever shows the pooled open to be a bottleneck on
/// the hot retry path, the remedy is a batched sweep API that opens one connection (and
/// one transaction) per sweep.
/// </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()
    {
        EnsureDatabaseDirectoryExists();

        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();

        // Audit Log #23 (ExecutionId Task 4): additively add the execution_id /
        // source_script columns. CREATE TABLE IF NOT EXISTS above does NOT add
        // columns to a table that already exists from before these fields, so a
        // databases created by an older build needs the columns ALTER-ed in.
        // SQLite has no "ADD COLUMN IF NOT EXISTS"; the column presence is
        // probed first and the ALTER skipped when already there. Both columns
        // are nullable with no default, so any row buffered before this
        // migration reads back ExecutionId/SourceScript = null (back-compat).
        await AddColumnIfMissingAsync(connection, "execution_id", "TEXT");
        await AddColumnIfMissingAsync(connection, "source_script", "TEXT");

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

    /// <summary>
    /// Audit Log #23 (ExecutionId Task 4): adds a column to <c>sf_messages</c>
    /// only when it is not already present. SQLite lacks <c>ADD COLUMN IF NOT
    /// EXISTS</c>, so the schema is probed via <c>PRAGMA table_info</c> first.
    /// Idempotent — safe to run on every <see cref="InitializeAsync"/>.
    /// </summary>
    private static async Task AddColumnIfMissingAsync(
        SqliteConnection connection, string columnName, string columnType)
    {
        await using var probe = connection.CreateCommand();
        probe.CommandText = "SELECT COUNT(*) FROM pragma_table_info('sf_messages') WHERE name = @name";
        probe.Parameters.AddWithValue("@name", columnName);
        var exists = Convert.ToInt32(await probe.ExecuteScalarAsync()) > 0;
        if (exists)
        {
            return;
        }

        await using var alter = connection.CreateCommand();
        // Column name + type are caller-controlled constants, never user input —
        // safe to interpolate (parameters are not permitted in DDL).
        alter.CommandText = $"ALTER TABLE sf_messages ADD COLUMN {columnName} {columnType}";
        await alter.ExecuteNonQueryAsync();
    }

    /// <summary>
    /// Ensures the directory for a file-backed SQLite database exists. SQLite creates
    /// the database file on demand but not its parent directory, so a configured path
    /// such as "./data/store-and-forward.db" fails to open ("unable to open database
    /// file") when the "data" directory does not yet exist. In-memory databases and
    /// bare filenames in the working directory have no directory to create and are
    /// skipped.
    /// </summary>
    private void EnsureDatabaseDirectoryExists()
    {
        var builder = new SqliteConnectionStringBuilder(_connectionString);
        if (builder.Mode == SqliteOpenMode.Memory)
            return;

        var dataSource = builder.DataSource;
        if (string.IsNullOrEmpty(dataSource) || dataSource == ":memory:")
            return;

        var directory = System.IO.Path.GetDirectoryName(System.IO.Path.GetFullPath(dataSource));
        if (!string.IsNullOrEmpty(directory) && !System.IO.Directory.Exists(directory))
        {
            System.IO.Directory.CreateDirectory(directory);
            _logger.LogInformation("Created store-and-forward database directory: {Directory}", directory);
        }
    }

    /// <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, execution_id, source_script)
            VALUES (@id, @category, @target, @payload, @retryCount, @maxRetries,
                    @retryIntervalMs, @createdAt, @lastAttempt, @status, @lastError,
                    @origin, @executionId, @sourceScript)";

        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);
        // Audit Log #23 (ExecutionId Task 4): the execution id is stored as its
        // canonical string form ("D") so it round-trips cleanly through the
        // TEXT column; null when not a cached call / not threaded.
        cmd.Parameters.AddWithValue("@executionId",
            message.ExecutionId.HasValue ? message.ExecutionId.Value.ToString("D") : DBNull.Value);
        cmd.Parameters.AddWithValue("@sourceScript", (object?)message.SourceScript ?? 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,
                   execution_id, source_script
            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: Updates a message after a delivery attempt, but only if the row is still
    /// in the expected status. Returns true if the row was updated, false if it had
    /// already been changed (e.g. an operator retried or discarded the message) and so
    /// was skipped.
    ///
    /// StoreAndForward-005: the retry sweep uses this for its state-changing writes so
    /// it cannot clobber a concurrent operator action (RetryParkedMessageAsync /
    /// DiscardParkedMessageAsync). Those operator operations are themselves SQL-
    /// conditional on <c>status = Parked</c>; making the sweep's writes conditional on
    /// the status the sweep observed closes the sweep-vs-management race rather than
    /// relying only on the in-process overlapping-sweep guard.
    /// </summary>
    public async Task<bool> UpdateMessageIfStatusAsync(
        StoreAndForwardMessage message,
        StoreAndForwardMessageStatus expectedStatus)
    {
        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 AND status = @expectedStatus";

        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);
        cmd.Parameters.AddWithValue("@expectedStatus", (int)expectedStatus);

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

    /// <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.
    ///
    /// StoreAndForward-006: the COUNT(*) and the paged SELECT run inside a single
    /// transaction so they observe one consistent snapshot. Without it, a concurrent
    /// enqueue/park/discard arriving between the two statements yields a TotalCount
    /// inconsistent with the returned page (flickering totals / off-by-one page math
    /// in the paginated UI).
    /// </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();

        await using var transaction = (SqliteTransaction)await connection.BeginTransactionAsync();

        // Count
        await using var countCmd = connection.CreateCommand();
        countCmd.Transaction = transaction;
        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();
        pageCmd.Transaction = transaction;
        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,
                   execution_id, source_script
            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);

        await transaction.CommitAsync();
        return (messages, totalCount);
    }

    /// <summary>
    /// WP-12: Moves a parked message back to pending for retry.
    ///
    /// StoreAndForward-010: <c>last_attempt_at</c> is reset to NULL so the re-queued
    /// message is unambiguously due on the next retry sweep. An operator-initiated
    /// retry means "attempt this again now"; leaving the stale parked timestamp in
    /// place would make the message's retry timing depend on the configured retry
    /// interval relative to the original (pre-park) attempt — "try immediately" only
    /// by accident, and a long interval would instead delay the operator's 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, last_attempt_at = 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,
                   execution_id, source_script
            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),
                // Audit Log #23 (ExecutionId Task 4): rows persisted before the
                // additive migration have no execution_id / source_script value;
                // IsDBNull guards keep those reading back as null (back-compat).
                // Guid.TryParse (not Parse) guards the retry sweep: a corrupt
                // non-null execution_id is treated as "no execution id" rather
                // than throwing FormatException and aborting the whole sweep.
                ExecutionId = ParseExecutionId(reader, 12),
                SourceScript = reader.IsDBNull(13) ? null : reader.GetString(13)
            });
        }
        return results;
    }

    /// <summary>
    /// Audit Log #23 (ExecutionId Task 4): defensively reads the
    /// <c>execution_id</c> column. A <c>null</c> value (legacy pre-migration
    /// rows) and a malformed non-null value both yield <c>null</c> — a corrupt
    /// id must not throw and abort the retry sweep, which reads many rows.
    /// </summary>
    private static Guid? ParseExecutionId(System.Data.Common.DbDataReader reader, int ordinal)
    {
        if (reader.IsDBNull(ordinal))
        {
            return null;
        }

        return Guid.TryParse(reader.GetString(ordinal), out var executionId)
            ? executionId
            : null;
    }
}