using Npgsql;
using StellaOps.Doctor.Models;
using StellaOps.Doctor.Plugins;
using StellaOps.Doctor.Plugins.Builders;

namespace StellaOps.Doctor.Plugins.Database.Checks;

/// <summary>
/// Checks for failed or incomplete database migrations.
/// </summary>
public sealed class FailedMigrationsCheck : DatabaseCheckBase
{
    /// <inheritdoc />
    public override string CheckId => "check.db.migrations.failed";

    /// <inheritdoc />
    public override string Name => "Failed Migrations";

    /// <inheritdoc />
    public override string Description => "Checks for failed or incomplete database migrations";

    /// <inheritdoc />
    public override IReadOnlyList<string> Tags => ["database", "migrations", "schema"];

    /// <inheritdoc />
    protected override async Task<DoctorCheckResult> ExecuteCheckAsync(
        DoctorPluginContext context,
        string connectionString,
        CheckResultBuilder result,
        CancellationToken ct)
    {
        await using var connection = await CreateConnectionAsync(connectionString, ct);

        // Check for Stella Ops migration tracking table
        var hasTrackingTable = await CheckTableExistsAsync(connection, "stella_migration_history", ct);

        if (!hasTrackingTable)
        {
            return result
                .Info("No migration tracking table found - using EF Core migrations only")
                .WithEvidence("Migration status", e => e
                    .Add("TrackingTableExists", "false"))
                .Build();
        }

        // Check for failed migrations in tracking table
        await using var cmd = new NpgsqlCommand(@"
            SELECT migration_id, status, error_message, applied_at
            FROM stella_migration_history
            WHERE status = 'failed' OR status = 'incomplete'
            ORDER BY applied_at DESC
            LIMIT 5",
            connection);

        var failedMigrations = new List<(string Id, string Status, string? Error)>();

        await using var reader = await cmd.ExecuteReaderAsync(ct);
        while (await reader.ReadAsync(ct))
        {
            failedMigrations.Add((
                reader.GetString(0),
                reader.GetString(1),
                reader.IsDBNull(2) ? null : reader.GetString(2)
            ));
        }

        if (failedMigrations.Count > 0)
        {
            return result
                .Fail($"{failedMigrations.Count} failed/incomplete migration(s) found")
                .WithEvidence("Failed migrations", e =>
                {
                    e.Add("FailedCount", failedMigrations.Count.ToString());
                    for (int i = 0; i < failedMigrations.Count; i++)
                    {
                        var m = failedMigrations[i];
                        e.Add($"Migration_{i + 1}", $"{m.Id} ({m.Status})");
                        if (m.Error != null)
                        {
                            e.Add($"Error_{i + 1}", m.Error);
                        }
                    }
                })
                .WithCauses(
                    "Migration script has errors",
                    "Database permission issues",
                    "Concurrent migration attempts")
                .WithRemediation(r => r
                    .AddManualStep(1, "Review migration logs", "Check application logs for migration error details")
                    .AddManualStep(2, "Fix migration issues", "Resolve the underlying issue and retry migration")
                    .AddShellStep(3, "Retry migrations", "dotnet ef database update"))
                .WithVerification("stella doctor --check check.db.migrations.failed")
                .Build();
        }

        return result
            .Pass("No failed migrations found")
            .WithEvidence("Migration status", e => e
                .Add("FailedMigrations", "0")
                .Add("TrackingTableExists", "true"))
            .Build();
    }

    private static async Task<bool> CheckTableExistsAsync(NpgsqlConnection connection, string tableName, CancellationToken ct)
    {
        await using var cmd = new NpgsqlCommand(
            $"SELECT EXISTS (SELECT FROM information_schema.tables WHERE table_name = '{tableName}')",
            connection);
        return Convert.ToBoolean(await cmd.ExecuteScalarAsync(ct));
    }
}