using System.Data.Common;
using SQLInsight.Core.DynamicsAx;
using SQLInsight.Core.Instances;

namespace SQLInsight.Collectors.DynamicsAx;

/// <summary>
/// Finds the Dynamics AX databases on one instance with the central detection (<see cref="AxDetection"/>) and keeps
/// the answer for <see cref="Refresh"/>, so new and removed AX databases are noticed within the hour. Shared by
/// everything AX-specific on the instance (the AX collectors and the AX community rules). Only databases chosen for
/// monitoring are looked at; reads metadata, plus the company list when the agent may read DATAAREA. Not thread-safe:
/// one instance's collectors run one at a time.
/// </summary>
public sealed class AxDatabaseDetector
{
    public static readonly TimeSpan Refresh = TimeSpan.FromHours(1);

    private readonly Dictionary<string, (DateTimeOffset At, AxDatabase? Database, string? Problem)> _cache = new(StringComparer.OrdinalIgnoreCase);
    private string? _login;

    /// <summary>Online user databases the login can enter, with their snapshot settings.</summary>
    internal const string DatabasesSql = """
        SELECT name, snapshot_isolation_state, is_read_committed_snapshot_on
        FROM sys.databases
        WHERE database_id > 4 AND state = 0 AND source_database_id IS NULL AND HAS_DBACCESS(name) = 1
        ORDER BY name
        """;

    /// <summary>The monitored AX databases, from the cache when younger than <see cref="Refresh"/> (unless <paramref name="force"/>).</summary>
    public async Task<AxDatabaseSnapshot> GetAsync(CollectorContext context, bool force = false)
    {
        ArgumentNullException.ThrowIfNull(context);
        var connection = context.Connection;
        var ct = context.CancellationToken;
        var databases = await Db.QueryAsync(connection, DatabasesSql, r => (Name: r.String(0), Snapshot: r.Int(1), Rcsi: r.Bool(2)), ct).ConfigureAwait(false);
        _login ??= (await Db.QueryAsync(connection, "SELECT SUSER_SNAME()", r => r.NullableString(0), ct).ConfigureAwait(false)).FirstOrDefault();
        var names = databases.Select(d => d.Name).ToList();
        var found = new List<AxDatabase>();
        var problems = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
        foreach (var (name, snapshot, rcsi) in databases)
        {
            if (!context.IncludesDatabase(name) || name.EndsWith("_model", StringComparison.OrdinalIgnoreCase))
            {
                continue;
            }

            if (force || !_cache.TryGetValue(name, out var cached) || context.Now - cached.At >= Refresh)
            {
                cached = await DetectAsync(context, name, names).ConfigureAwait(false);
                _cache[name] = cached;
            }

            if (cached.Problem is { } problem)
            {
                problems[name] = problem;
            }

            if (cached.Database is { } ax)
            {
                found.Add(ax with
                {
                    AgentLogin = _login,
                    Isolation = rcsi ? AxReadIsolation.ReadCommittedSnapshot : snapshot == 1 ? AxReadIsolation.Snapshot : AxReadIsolation.ReadCommitted,
                });
            }
        }

        foreach (var gone in _cache.Keys.Where(k => !names.Contains(k, StringComparer.OrdinalIgnoreCase)).ToList())
        {
            _cache.Remove(gone);
        }

        return new AxDatabaseSnapshot { CapturedAt = context.Now, Databases = found, AgentLogin = _login, Problems = problems };
    }

    private async Task<(DateTimeOffset, AxDatabase?, string?)> DetectAsync(CollectorContext context, string database, IReadOnlyList<string> names)
    {
        try
        {
            var rows = await Db.QueryAsync(context.Connection, AxSql.InDatabase(database, AxDetection.MetadataSql),
                r => new AxDetectionRow(r.String(0), r.String(1), r.String(2), r.NullableString(3) ?? "?", r.NullableInt(4) ?? 0, r.NullableInt(5) ?? 0, r.Bool(6), r.NullableString(7)),
                AxSql.CommandTimeoutSeconds, context.CancellationToken).ConfigureAwait(false);
            if (AxDetection.Recognise(database, rows, names) is not { } ax)
            {
                return (context.Now, null, null);
            }

            ax = ax with { AgentLogin = _login };
            if (AxSchemaAdapter.For(ax.Version) is not null)
            {
                var (companies, reason) = await AxReader.ReadAsync(context, ax, AxSchemaAdapter.Companies(ax),
                    r => new AxCompany(r.String(0), r.NullableString(1), r.Bool(2))).ConfigureAwait(false);
                ax = ax with { Companies = companies, CompaniesReason = reason };
            }

            return (context.Now, ax, null);
        }
        catch (DbException ex)
        {
            // No access to its metadata (e.g. no database user before 2014): it cannot be told apart, and nothing AX-specific runs there.
            return (context.Now, null, "AX-genkendelsen kunne ikke læse databasens metadata: " + ex.Message);
        }
    }
}

/// <summary>Reads an AX query: the rows, or why not (Danish). A lock timeout or a missing permission is a reason, never an exception.</summary>
internal static class AxReader
{
    public const string LockTimeoutText = "Ikke målt denne gang: AX-tabellen var låst i mere end 2 sekunder, og SQLInsight venter ikke på AX' låse. Prøves igen ved næste indsamling.";

    public static async Task<(List<T>? Rows, string? Problem)> ReadAsync<T>(CollectorContext context, AxDatabase database, AxQuery? query, Func<Row, T> map)
    {
        if (query is null)
        {
            return (null, null);
        }

        if (query.Sql is not { } sql)
        {
            return (null, query.NotMeasurable);
        }

        try
        {
            return (await Db.QueryAsync(context.Connection, AxSql.InDatabase(database.Database, sql, database.Isolation), map, AxSql.CommandTimeoutSeconds,
                context.CancellationToken).ConfigureAwait(false), null);
        }
        catch (DbException ex)
        {
            return (null, Db.ErrorNumber(ex) switch
            {
                AxSql.LockTimeoutError => LockTimeoutText,
                229 or 230 or 297 or 916 => "Ikke målbar: adgang nægtet. " + AxReadAccess.NotMeasurable(database, AxReadAccess.Tables(database)),
                _ => "Ikke målbar: læsningen fejlede (" + ex.Message + ").",
            });
        }
    }

    public static bool IsTransient(string? problem) => problem == LockTimeoutText;
}