using System.Data.Common;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Diagnostics;

namespace TenantRls;

// One instance per request scope. Null means nothing resolved a tenant.
public sealed class TenantContext
{
    public Guid? TenantId { get; set; }
}

public sealed class Tenant
{
    public Guid Id { get; set; }
    public string Name { get; set; } = "";
}

public sealed class Invoice
{
    public Guid Id { get; set; }
    public Guid TenantId { get; set; }
    public string Number { get; set; } = "";
    public decimal Amount { get; set; }
    public string Status { get; set; } = "";
    public DateTimeOffset CreatedAt { get; set; }
}

public sealed class AppDbContext(DbContextOptions<AppDbContext> options, TenantContext tenant)
    : DbContext(options)
{
    public DbSet<Tenant> Tenants => Set<Tenant>();
    public DbSet<Invoice> Invoices => Set<Invoice>();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Tenant>(b =>
        {
            b.ToTable("tenants");
            b.Property(t => t.Id).HasColumnName("id");
            b.Property(t => t.Name).HasColumnName("name");
        });

        modelBuilder.Entity<Invoice>(b =>
        {
            b.ToTable("invoices");
            b.Property(i => i.Id).HasColumnName("id");
            b.Property(i => i.TenantId).HasColumnName("tenant_id");
            b.Property(i => i.Number).HasColumnName("number");
            b.Property(i => i.Amount).HasColumnName("amount");
            b.Property(i => i.Status).HasColumnName("status");
            b.Property(i => i.CreatedAt).HasColumnName("created_at");

            // The application layer. Row-level security is the database layer underneath it.
            b.HasQueryFilter(i => i.TenantId == tenant.TenantId);
        });
    }
}

// Runs on every connection open, so the setting is in place before EF sends the first command,
// no matter which pooled physical connection EF got.
public sealed class TenantConnectionInterceptor(TenantContext tenant) : DbConnectionInterceptor
{
    private const string Sql = "SELECT set_config('app.tenant_id', @tenant, false)";

    public override void ConnectionOpened(DbConnection connection, ConnectionEndEventData eventData)
    {
        using var command = Build(connection);
        command.ExecuteNonQuery();
    }

    public override async Task ConnectionOpenedAsync(
        DbConnection connection, ConnectionEndEventData eventData, CancellationToken cancellationToken = default)
    {
        await using var command = Build(connection);
        await command.ExecuteNonQueryAsync(cancellationToken);
    }

    private DbCommand Build(DbConnection connection)
    {
        var command = connection.CreateCommand();
        command.CommandText = Sql;
        var parameter = command.CreateParameter();
        parameter.ParameterName = "tenant";
        parameter.Value = tenant.TenantId?.ToString() ?? "";
        command.Parameters.Add(parameter);
        return command;
    }
}