using System.Text;

namespace Connected.Data.Schema.Sql
{
	internal class DefaultDrop : ColumnTransaction
	{
		public DefaultDrop(ISchemaColumn column) : base(column)
		{
		}

		protected override async Task OnExecute()
		{
			if (string.IsNullOrWhiteSpace(DefaultName))
				return;

			await Context.Execute(CommandText);
		}

		private string CommandText
		{
			get
			{
				var text = new StringBuilder();

				text.AppendLine($"ALTER TABLE {Escape(Context.Schema.SchemaName(), Context.Schema.Name)}");
				text.AppendLine($"DROP CONSTRAINT {DefaultName};");

				return text.ToString();
			}
		}

		private string? DefaultName
		{
			get
			{
				if (Context.ExistingSchema is null)
					return null;

				foreach (var constraint in Context.ExistingSchema.Descriptor.Constraints)
				{
					if (constraint.ConstraintType == ConstraintType.Default)
					{
						if (constraint.Columns.Count == 1 && string.Equals(constraint.Columns[0], Column.Name, StringComparison.OrdinalIgnoreCase))
							return constraint.Name;
					}
				}

				return null;
			}
		}
	}
}