Catalogger.NET/Catalogger.Backend/Database/DatabaseMigrator.cs

// Copyright (C) 2021-present sam (starshines.gay)
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published
// by the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

using System.Data.Common;
using Dapper;
using NodaTime;

namespace Catalogger.Backend.Database;

public class DatabaseMigrator(ILogger logger, IClock clock, DatabaseConnection conn)
    : IDisposable,
        IAsyncDisposable
{
    private const string RootPath = "Catalogger.Backend.Database";
    private static readonly int MigrationsPathLength = $"{RootPath}.Migrations.".Length;

    public async Task Migrate()
    {
        var migrations = GetMigrationNames().ToArray();
        logger.Debug("Getting current database migration");
        var currentMigration = await GetCurrentMigration();
        if (currentMigration != null)
            migrations = migrations
                .Where(s => string.CompareOrdinal(s, currentMigration.MigrationName) > 0)
                .ToArray();

        logger.Information(
            "Current migration: {Migration}. Applying {Count} migrations",
            currentMigration?.MigrationName,
            migrations.Length
        );
        if (migrations.Length == 0)
        {
            return;
        }

        // Wrap all migrations in a transaction
        await using var tx = await conn.BeginTransactionAsync();
        var totalStartTime = clock.GetCurrentInstant();
        foreach (var migration in migrations)
        {
            logger.Debug("Executing migration {Migration}", migration);
            var startTime = clock.GetCurrentInstant();
            await ExecuteMigration(tx, migration);
            var took = clock.GetCurrentInstant() - startTime;
            logger.Debug("Executed migration {Migration} in {Took}", migration, took);
        }

        var totalTook = clock.GetCurrentInstant() - totalStartTime;
        logger.Information("Executed {Count} migrations in {Took}", migrations.Length, totalTook);

        // Finally, commit the transaction
        await tx.CommitAsync();
    }

    private async Task ExecuteMigration(DbTransaction tx, string migrationName, bool up = true)
    {
        var query = await GetResource(
            $"{RootPath}.Migrations.{migrationName}.{(up ? "up" : "down")}.sql"
        );

        // Run the migration
        await conn.ExecuteAsync(query, transaction: tx);
        // Store that we ran the migration
        await conn.ExecuteAsync(
            "INSERT INTO migrations (migration_name, applied_at) VALUES (@MigrationName, @AppliedAt)",
            new { MigrationName = migrationName, AppliedAt = clock.GetCurrentInstant() }
        );
    }

    /// Returns the current migration. If no migrations have been applied, returns null
    private async Task<MigrationEntry?> GetCurrentMigration()
    {
        // Check if the migrations table exists
        var hasMigrationTable =
            await conn.QuerySingleOrDefaultAsync<int>(
                "SELECT COUNT(*) FROM information_schema.tables WHERE table_name = 'migrations'"
            ) == 1;
        // If so, return the current migration
        if (hasMigrationTable)
        {
            return await conn.QuerySingleOrDefaultAsync<MigrationEntry>(
                "SELECT * FROM migrations ORDER BY applied_at DESC LIMIT 1"
            );
        }

        logger.Debug("Migrations table does not exist, assuming this is a new database");

        // Else, create the migrations table then return null
        var migrationTableQuery = await GetResource($"{RootPath}.setup_migrations.sql");
        await conn.ExecuteAsync(migrationTableQuery);
        return null;
    }

    /// Returns a resource by name as a string.
    private static async Task<string> GetResource(string name)
    {
        await using var stream =
            typeof(DatabasePool).Assembly.GetManifestResourceStream(name)
            ?? throw new ArgumentException($"Invalid resource '{name}'");
        using var reader = new StreamReader(stream);
        return await reader.ReadToEndAsync();
    }

    public static IEnumerable<string> GetMigrationNames() =>
        typeof(DatabasePool)
            .Assembly.GetManifestResourceNames()
            .Where(s => s.StartsWith($"{RootPath}.Migrations"))
            .Where(s => s.EndsWith(".up.sql"))
            .Select(s =>
                s.Substring(
                    MigrationsPathLength,
                    s.Length - MigrationsPathLength - ".up.sql".Length
                )
            )
            .OrderBy(s => s);

    private record MigrationEntry
    {
        public string MigrationName { get; init; } = null!;
        public Instant AppliedAt { get; init; }
    }

    public void Dispose()
    {
        conn.Dispose();
        GC.SuppressFinalize(this);
    }

    public async ValueTask DisposeAsync()
    {
        await conn.DisposeAsync();
        GC.SuppressFinalize(this);
    }
}