using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace PLib.Infrastructure.Persistence;

/// <summary>
/// Brings the local database up to date before the first window is shown.
/// </summary>
public sealed class DatabaseInitializer(
    IServiceScopeFactory scopeFactory,
    ILogger<DatabaseInitializer> logger) : IHostedService
{
    public async Task StartAsync(CancellationToken cancellationToken)
    {
        await using var scope = scopeFactory.CreateAsyncScope();
        var dbContext = scope.ServiceProvider.GetRequiredService<LibraryDbContext>();

        if (await IsPreMigrationDatabaseAsync(dbContext, cancellationToken))
        {
            // Earlier builds created the schema straight from the model, so there is no
            // migration history to continue from and no honest way to baseline one — the
            // columns a baseline would claim exist do not. The database is a cache over the
            // file system, so throwing it away costs one rescan; poster frames are keyed by
            // file and survive untouched.
            logger.LogWarning("Replacing a database created before migrations were introduced");
            await dbContext.Database.EnsureDeletedAsync(cancellationToken);
        }

        var pending = await dbContext.Database.GetPendingMigrationsAsync(cancellationToken);
        var pendingCount = pending.Count();

        if (pendingCount > 0)
        {
            logger.LogInformation("Applying {Count} database migration(s)", pendingCount);
        }

        await dbContext.Database.MigrateAsync(cancellationToken);
        logger.LogInformation("Library database ready");
    }

    public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;

    /// <summary>
    /// True when the file holds a schema but no migration history — the shape earlier
    /// versions left behind.
    /// </summary>
    private static async Task<bool> IsPreMigrationDatabaseAsync(
        LibraryDbContext dbContext,
        CancellationToken cancellationToken)
    {
        if (!await dbContext.Database.CanConnectAsync(cancellationToken))
        {
            return false;
        }

        var applied = await dbContext.Database.GetAppliedMigrationsAsync(cancellationToken);

        if (applied.Any())
        {
            return false;
        }

        var tables = await dbContext.Database
            .SqlQuery<string>($"SELECT name FROM sqlite_master WHERE type = 'table' AND name = 'Videos'")
            .ToListAsync(cancellationToken);

        return tables.Count > 0;
    }
}