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

namespace StellaOps.Doctor.Plugins.Database.Checks;

/// <summary>
/// Checks for schema version consistency across database objects.
/// </summary>
public sealed class SchemaVersionCheck : DatabaseCheckBase
{
    /// <inheritdoc />
    public override string CheckId => "check.db.schema.version";

    /// <inheritdoc />
    public override string Name => "Schema Version";

    /// <inheritdoc />
    public override string Description => "Verifies database schema version and consistency";

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

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

        // Get schema information
        await using var cmd = new NpgsqlCommand(@"
            SELECT
                n.nspname AS schema_name,
                COUNT(c.relname) AS table_count
            FROM pg_catalog.pg_namespace n
            LEFT JOIN pg_catalog.pg_class c ON c.relnamespace = n.oid AND c.relkind = 'r'
            WHERE n.nspname NOT IN ('pg_catalog', 'information_schema', 'pg_toast')
            GROUP BY n.nspname
            ORDER BY n.nspname",
            connection);

        var schemas = new List<(string Name, int TableCount)>();

        await using var reader = await cmd.ExecuteReaderAsync(ct);
        while (await reader.ReadAsync(ct))
        {
            schemas.Add((
                reader.GetString(0),
                reader.GetInt32(1)
            ));
        }
        await reader.CloseAsync();

        // Get latest migration info if available
        string? latestMigration = null;
        var migrationTableExists = await CheckMigrationTableExistsAsync(connection, ct);

        if (migrationTableExists)
        {
            await using var migrationCmd = new NpgsqlCommand(
                "SELECT \"MigrationId\" FROM \"__EFMigrationsHistory\" ORDER BY \"MigrationId\" DESC LIMIT 1",
                connection);
            latestMigration = await migrationCmd.ExecuteScalarAsync(ct) as string;
        }

        // Check for orphaned foreign keys
        var orphanedFks = await GetOrphanedForeignKeysCountAsync(connection, ct);

        if (orphanedFks > 0)
        {
            return result
                .Warn($"Schema has {orphanedFks} orphaned foreign key constraint(s)")
                .WithEvidence("Schema details", e =>
                {
                    e.Add("SchemaCount", schemas.Count.ToString(CultureInfo.InvariantCulture));
                    e.Add("OrphanedForeignKeys", orphanedFks.ToString(CultureInfo.InvariantCulture));
                    if (latestMigration != null)
                    {
                        e.Add("LatestMigration", latestMigration);
                    }
                    foreach (var schema in schemas)
                    {
                        e.Add($"Schema_{schema.Name}", $"{schema.TableCount} tables");
                    }
                })
                .WithCauses(
                    "Failed migration left orphaned constraints",
                    "Manual DDL changes")
                .WithRemediation(r => r
                    .AddShellStep(1, "List orphaned FKs", "psql -c \"SELECT conname FROM pg_constraint WHERE NOT convalidated\"")
                    .AddManualStep(2, "Review and clean up", "Drop or fix orphaned constraints"))
                .WithVerification("stella doctor --check check.db.schema.version")
                .Build();
        }

        var totalTables = schemas.Sum(s => s.TableCount);

        return result
            .Pass($"Schema healthy: {schemas.Count} schema(s), {totalTables} table(s)")
            .WithEvidence("Schema details", e =>
            {
                e.Add("SchemaCount", schemas.Count.ToString(CultureInfo.InvariantCulture));
                e.Add("TotalTables", totalTables.ToString(CultureInfo.InvariantCulture));
                e.Add("OrphanedForeignKeys", "0");
                if (latestMigration != null)
                {
                    e.Add("LatestMigration", latestMigration);
                }
                foreach (var schema in schemas)
                {
                    e.Add($"Schema_{schema.Name}", $"{schema.TableCount} tables");
                }
            })
            .Build();
    }

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

    private static async Task<int> GetOrphanedForeignKeysCountAsync(NpgsqlConnection connection, CancellationToken ct)
    {
        await using var cmd = new NpgsqlCommand(
            "SELECT COUNT(*) FROM pg_constraint WHERE NOT convalidated",
            connection);
        return Convert.ToInt32(await cmd.ExecuteScalarAsync(ct), CultureInfo.InvariantCulture);
    }
}