using System.Data.Common;
using System.Diagnostics;
using System.Globalization;
using System.Text;
using ZB.MOM.WW.Audit;
using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Services;
using ZB.MOM.WW.ScadaBridge.Commons.Types.Audit;
using ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;

namespace ZB.MOM.WW.ScadaBridge.InboundAPI;

/// <summary>
/// Scoped, parameterized database access exposed to inbound API scripts as
/// <c>InboundScriptContext.Database</c>. This is the dedicated, curated data-access
/// helper authorized by the design doc (Component-InboundAPI.md, "Database access") —
/// not a raw connection handed to the script. All ADO.NET stays internal here: scripts
/// call <see cref="QueryAsync"/> / <see cref="QuerySingleAsync{T}"/> / <see cref="ExecuteAsync"/>
/// by name and never reference <c>System.Data</c>.
///
/// <para>
/// <b>SQL-injection protection.</b> Statement text is authored by the
/// (design-time) method script, but every <em>value</em> is bound as a named SQL
/// parameter (anonymous-object properties become <c>@</c>-prefixed parameters via
/// <see cref="AddParameters"/>) and is NEVER string-concatenated into the command text.
/// Request-derived values therefore reach the database only through parameter binding,
/// closing the injection vector. Connection access is restricted to the named
/// connections configured on the central <see cref="IDatabaseGateway"/> — a script
/// cannot supply an arbitrary connection string.
/// </para>
///
/// <para>
/// <b>Reads and writes are both permitted</b>: the move-in
/// integration needs to record results, not just read them. Use <see cref="QueryAsync"/>
/// / <see cref="QuerySingleAsync{T}"/> for reads and <see cref="ExecuteAsync"/> for writes.
/// </para>
///
/// <para>
/// <b>Async + deadline-bound.</b> Every call uses the async ADO.NET path
/// end-to-end (no <c>.GetAwaiter().GetResult()</c> blocking a pool thread) and honours the
/// executing method's deadline token on the command itself, with a <see cref="DbCommand.CommandTimeout"/>
/// backstop derived from the method timeout — so a slow query is bounded by the method
/// timeout instead of running unbounded.
/// </para>
///
/// <para>
/// <b>Audited (Audit Log #23, outbound DB scope; Flow Debugger outbound-calls plan
/// 2026-09-06 D7).</b> Every call emits exactly ONE <c>DbOutbound</c>/<c>DbWrite</c> row
/// through the central <see cref="ICentralAuditWriter"/> using the site's
/// <c>AuditingDbCommand</c> vocabulary: <c>Extra = {"op":"write","rowsAffected":N}</c> for
/// <see cref="ExecuteAsync"/>, <c>{"op":"read","rowsReturned":N}</c> for the two query
/// methods; <c>RequestSummary</c> = <c>{"sql":…,"parameters":{"@name":"value"}}</c>. The
/// 8 KB payload cap and per-target SQL-parameter redaction are applied at write time by
/// the writer's <c>IAuditRedactor</c> — the same stage that caps the site's rows — so the
/// helper builds the raw summary only. Emission is best-effort: a build, write or sink
/// fault never reaches the script; the original result (or exception) always does. When
/// a flow-trace sink is present the same <see cref="AuditEvent"/> instance goes to the
/// sink first, then to the writer, so a Live Flow Debugger run renders the row without
/// a round-trip to the audit store. A helper built without a writer and without a sink
/// (the pre-existing three-argument shape) emits nothing.
/// </para>
/// </summary>
public sealed class InboundDatabaseHelper
{
    private readonly IDatabaseGateway? _gateway;
    private readonly CancellationToken _ct;
    private readonly int _commandTimeoutSeconds;
    private readonly ICentralAuditWriter? _auditWriter;
    private readonly INodeIdentityProvider? _nodeIdentity;
    private readonly Guid? _executionId;
    private readonly Guid? _parentExecutionId;
    private readonly string? _actor;
    private readonly Action<AuditEvent>? _traceSink;

    /// <summary>
    /// Initializes the helper.
    /// </summary>
    /// <param name="gateway">The central database gateway, or null when no gateway is registered (the helper then throws on first use).</param>
    /// <param name="ct">The executing method's deadline token; forwarded to every async DB call so a slow query is bounded by the method timeout.</param>
    /// <param name="commandTimeout">The method timeout; used to derive a <see cref="DbCommand.CommandTimeout"/> backstop. <see cref="TimeSpan.Zero"/> (the default) leaves the provider default.</param>
    /// <param name="auditWriter">Central-direct-write audit writer for the per-call <c>DbOutbound</c>/<c>DbWrite</c> row; null = no row is written.</param>
    /// <param name="nodeIdentity">Stamps <c>SourceNode</c> (central-a/central-b) on the row; null = NULL.</param>
    /// <param name="executionId">The executing inbound request's per-request execution id, stamped as the row's <c>ExecutionId</c>.</param>
    /// <param name="parentExecutionId">The spawning execution's id, if any (an inbound request is a root, so callers normally pass null).</param>
    /// <param name="methodName">The executing API method's name; the row's <c>Actor</c> becomes <c>api:{methodName}</c>. Null = NULL actor.</param>
    /// <param name="traceSink">Flow Debugger trace sink; receives the same event instance before the writer does. Null = none.</param>
    // Trailing optional parameters: the original (gateway, ct, commandTimeout) shape stays
    // source-compatible for every existing caller and test.
    public InboundDatabaseHelper(
        IDatabaseGateway? gateway,
        CancellationToken ct,
        TimeSpan commandTimeout = default,
        ICentralAuditWriter? auditWriter = null,
        INodeIdentityProvider? nodeIdentity = null,
        Guid? executionId = null,
        Guid? parentExecutionId = null,
        string? methodName = null,
        Action<AuditEvent>? traceSink = null)
    {
        _gateway = gateway;
        _ct = ct;
        _commandTimeoutSeconds = commandTimeout > TimeSpan.Zero
            ? (int)Math.Ceiling(commandTimeout.TotalSeconds)
            : 0;
        _auditWriter = auditWriter;
        _nodeIdentity = nodeIdentity;
        _executionId = executionId;
        _parentExecutionId = parentExecutionId;
        _actor = string.IsNullOrEmpty(methodName) ? null : "api:" + methodName;
        _traceSink = traceSink;
    }

    /// <summary>First column of the first row converted to <typeparamref name="T"/> (default if no rows).</summary>
    /// <typeparam name="T">The type to convert the scalar result to.</typeparam>
    /// <param name="connectionName">Name of a connection configured on the central database gateway.</param>
    /// <param name="sql">The SQL statement. Values MUST be supplied via <paramref name="parameters"/>, not concatenated.</param>
    /// <param name="parameters">Optional anonymous object whose properties become bound <c>@</c>-prefixed parameters.</param>
    /// <returns>The converted scalar, or <c>default</c> when there are no rows / a NULL value.</returns>
    public async Task<T?> QuerySingleAsync<T>(string connectionName, string sql, object? parameters = null)
    {
        var (result, _) = await RunAudited(connectionName, sql, parameters, op: "read", async () =>
        {
            await using var conn = await _gateway!.GetConnectionAsync(connectionName, _ct);
            await using var cmd = CreateCommand(conn, sql, parameters);
            var scalar = await cmd.ExecuteScalarAsync(_ct);
            if (scalar is null or DBNull) return (default(T), 0);
            if (scalar is T t) return (t, 1);
            return ((T)Convert.ChangeType(scalar, typeof(T), CultureInfo.InvariantCulture), 1);
        });
        return result;
    }

    /// <summary>All rows as column→value dictionaries (case-insensitive keys).</summary>
    /// <param name="connectionName">Name of a connection configured on the central database gateway.</param>
    /// <param name="sql">The SQL statement. Values MUST be supplied via <paramref name="parameters"/>, not concatenated.</param>
    /// <param name="parameters">Optional anonymous object whose properties become bound <c>@</c>-prefixed parameters.</param>
    /// <returns>The result rows; empty when nothing matches.</returns>
    public async Task<IReadOnlyList<IReadOnlyDictionary<string, object?>>> QueryAsync(
        string connectionName, string sql, object? parameters = null)
    {
        var (rows, _) = await RunAudited(connectionName, sql, parameters, op: "read", async () =>
        {
            await using var conn = await _gateway!.GetConnectionAsync(connectionName, _ct);
            await using var cmd = CreateCommand(conn, sql, parameters);
            await using var reader = await cmd.ExecuteReaderAsync(_ct);
            var list = new List<IReadOnlyDictionary<string, object?>>();
            while (await reader.ReadAsync(_ct))
            {
                var row = new Dictionary<string, object?>(StringComparer.OrdinalIgnoreCase);
                for (var i = 0; i < reader.FieldCount; i++)
                {
                    var v = reader.GetValue(i);
                    row[reader.GetName(i)] = v is DBNull ? null : v;
                }
                list.Add(row);
            }
            return ((IReadOnlyList<IReadOnlyDictionary<string, object?>>)list, list.Count);
        });
        return rows;
    }

    /// <summary>
    /// Executes a write statement (INSERT/UPDATE/DELETE/DDL) and returns the number of
    /// rows affected. Writes are authorized for inbound API scripts;
    /// values are still bound as parameters, never concatenated.
    /// </summary>
    /// <param name="connectionName">Name of a connection configured on the central database gateway.</param>
    /// <param name="sql">The SQL statement. Values MUST be supplied via <paramref name="parameters"/>, not concatenated.</param>
    /// <param name="parameters">Optional anonymous object whose properties become bound <c>@</c>-prefixed parameters.</param>
    /// <returns>The number of rows affected.</returns>
    public async Task<int> ExecuteAsync(string connectionName, string sql, object? parameters = null)
    {
        var (affected, _) = await RunAudited(connectionName, sql, parameters, op: "write", async () =>
        {
            await using var conn = await _gateway!.GetConnectionAsync(connectionName, _ct);
            await using var cmd = CreateCommand(conn, sql, parameters);
            var n = await cmd.ExecuteNonQueryAsync(_ct);
            return (n, n);
        });
        return affected;
    }

    /// <summary>
    /// Runs <paramref name="body"/> and emits the one <c>DbOutbound</c>/<c>DbWrite</c> row for
    /// it — <c>Delivered</c> with the body's row count, or <c>Failed</c> with the thrown
    /// exception's message, which is then rethrown untouched to the script. The gateway
    /// null-check is inside the audited span deliberately so "Database is not available"
    /// is itself recorded as a failed outbound DB call.
    /// </summary>
    private async Task<(T Result, int Rows)> RunAudited<T>(
        string connectionName, string sql, object? parameters, string op,
        Func<Task<(T Result, int Rows)>> body)
    {
        var startedUtc = DateTime.UtcNow;
        var sw = Stopwatch.StartNew();
        (T Result, int Rows) outcome;
        try
        {
            if (_gateway is null) throw new InvalidOperationException("Database is not available for this inbound method");
            outcome = await body();
        }
        catch (Exception ex)
        {
            EmitAudit(connectionName, sql, parameters, op, startedUtc, sw.ElapsedMilliseconds, rows: 0, thrown: ex);
            throw;
        }

        EmitAudit(connectionName, sql, parameters, op, startedUtc, sw.ElapsedMilliseconds, outcome.Rows, thrown: null);
        return outcome;
    }

    /// <summary>
    /// Best-effort emission (mirrors <c>RouteTarget.EmitRouteCall</c> and the site's
    /// <c>AuditingDbCommand.EmitAudit</c>): build, sink, write — every layer swallows its
    /// own faults so nothing reaches the script.
    /// </summary>
    private void EmitAudit(
        string connectionName, string sql, object? parameters, string op,
        DateTime startedUtc, long elapsedMs, int rows, Exception? thrown)
    {
        if (_auditWriter is null && _traceSink is null) return;

        AuditEvent evt;
        try
        {
            // Vocabulary lock with the site's AuditingDbCommand: both reads and writes are
            // DbWrite rows on the DbOutbound channel; Extra carries the discriminator.
            var extra = op == "write"
                ? $"{{\"op\":\"write\",\"rowsAffected\":{rows}}}"
                : $"{{\"op\":\"read\",\"rowsReturned\":{rows}}}";

            evt = ScadaBridgeAuditEventFactory.Create(
                channel: AuditChannel.DbOutbound,
                kind: AuditKind.DbWrite,
                status: thrown is null ? AuditStatus.Delivered : AuditStatus.Failed,
                occurredAtUtc: DateTime.SpecifyKind(startedUtc, DateTimeKind.Utc),
                actor: _actor,
                target: connectionName,
                sourceNode: _nodeIdentity?.NodeName,
                // A sync one-shot DB call has no operation lifecycle, so CorrelationId stays
                // null; ExecutionId ties the row to the inbound request's other rows.
                correlationId: null,
                executionId: _executionId,
                parentExecutionId: _parentExecutionId,
                durationMs: (int)Math.Min(elapsedMs, int.MaxValue),
                errorMessage: thrown?.Message,
                errorDetail: thrown?.ToString(),
                requestSummary: BuildRequestSummary(sql, parameters),
                responseSummary: null,
                payloadTruncated: false,
                extra: extra);
        }
        catch (Exception)
        {
            return;
        }

        // Sink FIRST (task contract): a Live Flow Debugger run reads the row from the
        // sink, and the writer's redaction stage must not be the thing gating it.
        if (_traceSink is not null)
        {
            try { _traceSink(evt); }
            catch (Exception) { /* a misbehaving sink must not fail the script */ }
        }

        if (_auditWriter is null) return;
        try
        {
            var t = _auditWriter.WriteAsync(evt, CancellationToken.None);
            if (!t.IsCompletedSuccessfully)
            {
                _ = t.ContinueWith(static _ => { }, TaskContinuationOptions.OnlyOnFaulted);
            }
        }
        catch (Exception)
        {
            // Best-effort: an audit failure never fails the DB call.
        }
    }

    /// <summary>
    /// Same JSON shape as the site's <c>AuditingDbCommand.BuildRequestSummary</c>:
    /// <c>{"sql":"…","parameters":{"@name":"value",…}}</c>, values stringified, NULL as
    /// JSON null. Built from the script's arguments rather than a <see cref="DbCommand"/>
    /// so a failure before the command exists (gateway/open) still carries the statement.
    /// Capping and per-target parameter redaction happen at write time in the redactor.
    /// </summary>
    private static string? BuildRequestSummary(string sql, object? parameters)
    {
        if (string.IsNullOrEmpty(sql)) return null;

        var sb = new StringBuilder(sql.Length + 64);
        sb.Append("{\"sql\":");
        AppendJsonString(sb, sql);

        var props = parameters?.GetType().GetProperties();
        if (props is { Length: > 0 })
        {
            sb.Append(",\"parameters\":{");
            var first = true;
            foreach (var prop in props)
            {
                if (!first) sb.Append(',');
                first = false;
                AppendJsonString(sb, "@" + prop.Name);
                sb.Append(':');
                var value = prop.GetValue(parameters);
                if (value is null || value is DBNull)
                {
                    sb.Append("null");
                }
                else
                {
                    AppendJsonString(sb, Convert.ToString(value, CultureInfo.InvariantCulture) ?? string.Empty);
                }
            }
            sb.Append('}');
        }

        sb.Append('}');
        return sb.ToString();
    }

    private static void AppendJsonString(StringBuilder sb, string value)
    {
        sb.Append('"');
        foreach (var ch in value)
        {
            switch (ch)
            {
                case '"': sb.Append("\\\""); break;
                case '\\': sb.Append("\\\\"); break;
                case '\b': sb.Append("\\b"); break;
                case '\f': sb.Append("\\f"); break;
                case '\n': sb.Append("\\n"); break;
                case '\r': sb.Append("\\r"); break;
                case '\t': sb.Append("\\t"); break;
                default:
                    if (ch < 0x20) sb.Append("\\u").Append(((int)ch).ToString("x4"));
                    else sb.Append(ch);
                    break;
            }
        }
        sb.Append('"');
    }

    private DbCommand CreateCommand(DbConnection conn, string sql, object? parameters)
    {
        var cmd = conn.CreateCommand();
        cmd.CommandText = sql;
        // A CommandTimeout backstop derived from the method timeout so a
        // slow query cannot outrun the method deadline even if the provider does not
        // honour token cancellation mid-statement.
        if (_commandTimeoutSeconds > 0) cmd.CommandTimeout = _commandTimeoutSeconds;
        AddParameters(cmd, parameters);
        return cmd;
    }

    private static void AddParameters(DbCommand cmd, object? parameters)
    {
        if (parameters is null) return;
        foreach (var prop in parameters.GetType().GetProperties())
        {
            var p = cmd.CreateParameter();
            p.ParameterName = "@" + prop.Name;
            p.Value = prop.GetValue(parameters) ?? DBNull.Value;
            cmd.Parameters.Add(p);
        }
    }
}