using System.Text;

namespace Connected.Data.Schema.Sql
{
    internal class ColumnAlter : ColumnTransaction
	{
		public ColumnAlter(ISchemaColumn column, ExistingSchema existing, ISchemaColumn existingColumn) : base(column)
		{
			Existing = existing;
			ExistingColumn = existingColumn;
		}

		private ExistingSchema Existing { get; }
		private ISchemaColumn ExistingColumn { get; }

		protected override async Task OnExecute()
		{
			if (ExistingColumn.Equals(Column))
				return;

			if (!string.IsNullOrWhiteSpace(ExistingColumn.DefaultValue))
			{
				var existingDefault = SchemaExtensions.ParseDefaultValue(ExistingColumn.DefaultValue);
				var def = SchemaExtensions.ParseDefaultValue(Column.DefaultValue);

				if (!string.Equals(existingDefault, def, StringComparison.Ordinal))
					await new DefaultDrop(Column).Execute(Context);
			}
			if (Column.DataType != ExistingColumn.DataType
				|| Column.IsNullable != ExistingColumn.IsNullable
				|| Column.MaxLength != ExistingColumn.MaxLength
				|| Column.IsVersion != ExistingColumn.IsVersion)
				await Context.Execute(CommandText);

			var ed = SchemaExtensions.ParseDefaultValue(ExistingColumn.DefaultValue);
			var nd = SchemaExtensions.ParseDefaultValue(Column.DefaultValue);

			if (!string.Equals(ed, nd, StringComparison.Ordinal) && nd is not null)
				await new DefaultAdd(Column, Context.Schema.Name).Execute(Context);

			if (!ExistingColumn.IsPrimaryKey && Column.IsPrimaryKey)
				await new PrimaryKeyAdd(Column).Execute(Context);
			else if (ExistingColumn.IsPrimaryKey && !Column.IsPrimaryKey)
				await new PrimaryKeyRemove(Existing, ExistingColumn).Execute(Context);
		}

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

				text.AppendLine($"ALTER TABLE {Escape(Context.Schema.SchemaName(), Context.Schema.Name)}");
				text.AppendLine($"ALTER COLUMN {CreateColumnCommandText(Column)}");

				return text.ToString();
			}
		}
	}
}