# DeleteCommandBuilder.java

    package org.codefilarete.stalactite.sql.order;

    import java.util.Collection;
    import java.util.HashMap;
    import java.util.HashSet;
    import java.util.Iterator;
    import java.util.LinkedHashSet;
    import java.util.Map;
    import java.util.Set;
    import java.util.stream.Collectors;
    import javax.annotation.Nullable;

    import org.codefilarete.stalactite.query.builder.ExpandableSQLAppender;
    import org.codefilarete.stalactite.query.builder.PreparableSQLBuilder;
    import org.codefilarete.stalactite.query.builder.PreparedSQLAppender;
    import org.codefilarete.stalactite.query.builder.SQLAppender;
    import org.codefilarete.stalactite.query.builder.SQLBuilder;
    import org.codefilarete.stalactite.query.builder.StringSQLAppender;
    import org.codefilarete.stalactite.query.builder.WhereSQLBuilderFactory.WhereSQLBuilder;
    import org.codefilarete.stalactite.query.model.ColumnCriterion;
    import org.codefilarete.stalactite.query.model.Placeholder;
    import org.codefilarete.stalactite.query.api.Selectable;
    import org.codefilarete.stalactite.query.model.UnitaryOperator;
    import org.codefilarete.stalactite.query.model.ValuedVariable;
    import org.codefilarete.stalactite.sql.Dialect;
    import org.codefilarete.stalactite.sql.ddl.structure.Column;
    import org.codefilarete.stalactite.sql.ddl.structure.Table;
    import org.codefilarete.stalactite.sql.statement.DMLGenerator;
    import org.codefilarete.stalactite.sql.statement.PreparedSQL;
    import org.codefilarete.stalactite.sql.statement.binder.ParameterBinder;
    import org.codefilarete.tool.collection.Iterables;
    import org.codefilarete.tool.trace.MutableInt;

    /**
     * A SQL builder for {@link Delete} objects
     * Can hardly be shared with {@link DMLGenerator} because the latter doesn't handle multi
     * tables update.
     *
     * @author Guillaume Mary
     */
    public class DeleteCommandBuilder<T extends Table<T>> implements SQLBuilder, PreparableSQLBuilder {

    	private final Delete<T> delete;
    	private final Dialect dialect;
    	private final MultiTableAwareDMLNameProvider dmlNameProvider;

    	public DeleteCommandBuilder(Delete<T> delete, Dialect dialect) {
    		this.delete = delete;
    		this.dialect = dialect;
    		this.dmlNameProvider = new MultiTableAwareDMLNameProvider(dialect.getDmlNameProviderFactory());
    	}

    	@Override
    	public String toSQL() {
    		StringSQLAppender result = new StringSQLAppender(dmlNameProvider);
    		appendDeleteStatement(result, dmlNameProvider);
    		return result.getSQL();
    	}

    	@Override
    	public ExpandableSQLAppender toPreparableSQL() {
    		// We ask for SQL generation through a ExpandableSQLAppender because we need SQL placeholders for where + update clause
    		ExpandableSQLAppender preparedSQLAppender = new ExpandableSQLAppender(dialect.getColumnBinderRegistry(), dmlNameProvider);
    		appendDeleteStatement(preparedSQLAppender, dmlNameProvider);

    		return preparedSQLAppender;
    	}

    	private void appendDeleteStatement(SQLAppender target, MultiTableAwareDMLNameProvider dmlNameProvider) {
    		target.cat("delete from ");

    		// looking for additional Tables : more than the updated one, can be found in conditions
    		Set<Column<Table<?>, Object>> whereColumns = new LinkedHashSet<>();
    		delete.getCriteria().forEach(c -> {
    			if (c instanceof ColumnCriterion && ((ColumnCriterion) c).getColumn() instanceof Column) {
    				whereColumns.add((Column<Table<?>, Object>) ((ColumnCriterion) c).getColumn());
    				Object condition = ((ColumnCriterion) c).getCondition();
    				if (condition instanceof UnitaryOperator
    						&& ((UnitaryOperator) condition).getValue() instanceof ValuedVariable
    						&& ((ValuedVariable) ((UnitaryOperator) condition).getValue()).getValue() instanceof Column) {
    					whereColumns.add((Column) ((ValuedVariable) ((UnitaryOperator) condition).getValue()).getValue());
    				}
    			}
    		});
    		Collection<? extends Table<?>> tablesInCondition = Iterables.collect(whereColumns, Column::getTable, HashSet::new);
    		tablesInCondition.remove(this.delete.getTargetTable());
    		Collection<? extends Table<?>> additionalTables = tablesInCondition;

    		// update of the single-table-marker
    		dmlNameProvider.setMultiTable(!additionalTables.isEmpty());

    		target.cat(this.delete.getTargetTable().getAbsoluteName())    // main table is always referenced with name (not alias)
    				.catIf(dmlNameProvider.isMultiTable(), ", ");
    		// additional tables (with optional alias)
    		Iterator<? extends Table<?>> iterator = additionalTables.iterator();
    		while (iterator.hasNext()) {
    			Table next = iterator.next();
    			target.cat(next.getAbsoluteName()).catIf(iterator.hasNext(), ", ");
    		}

    		// append where clause
    		if (delete.getCriteria().iterator().hasNext()) {
    			target.cat(" where ");
    			WhereSQLBuilder whereSqlBuilder = dialect.getQuerySQLBuilderFactory().getWhereBuilderFactory().whereBuilder(this.delete.getCriteria(), dmlNameProvider, dialect.getQuerySQLBuilderFactory());
    			whereSqlBuilder.appendTo(target);
    		}
    	}

    	public DeleteStatement<T> toStatement() {
    		// We ask for SQL generation through a PreparedSQLWrapper because we need SQL placeholders for where + update clause
    		MutableInt variableCounter = new MutableInt();
    		Map<String, Set<Integer>> placeholderIndexes = new HashMap<>();

    		PreparedSQLAppender statementAppender = new PreparedSQLAppender(new StringSQLAppender(dmlNameProvider), dialect.getColumnBinderRegistry()) {

    			@Override
    			public <V> PreparedSQLAppender catValue(@Nullable Selectable<V> column, Object value) {
    				PreparedSQLAppender result = super.catValue(column, value);
    				if (value instanceof Placeholder) {
    					placeholderIndexes.computeIfAbsent(((Placeholder) value).getName(), name -> new HashSet<>())
    							.add(variableCounter.increment());
    				}
    				return result;
    			}
    		};
    		appendDeleteStatement(statementAppender, dmlNameProvider);

    		// final assembly
    		Map<Integer, Object> values = new HashMap<>(statementAppender.getValues());
    		Map<Integer, ParameterBinder<?>> parameterBinders = statementAppender.getParameterBinders();

    		Iterator<PlaceholderVariable<?, T>> placeholderIterator = delete.getRow().iterator();
    		while (placeholderIterator.hasNext()) {
    			PlaceholderVariable<?, T> c = placeholderIterator.next();
    			Set<Integer> indexes = placeholderIndexes.get(c.getName());
    			if (indexes == null) {
    				throw new IllegalArgumentException("No placeholder named \"" + c.getName() + "\" found in statement, available are "
    						+ placeholderIndexes.keySet());
    			}
    			indexes.forEach(index -> values.put(index, c.getValue()));
    		}

    		DeleteStatement<T> result = new DeleteStatement<>(
    				statementAppender.getSQL(),
    				parameterBinders,
    				placeholderIndexes);
    		result.setValues(values);
    		return result;
    	}

    	/**
    	 * A specialized version of {@link PreparedSQL} dedicated to {@link Delete} so one can set column values of the where clause
    	 * through {@link #setValue(String, Object)} and make it {@link Delete} "reusable".
    	 * Here is a usage example:
    	 * <pre>{@code
    	 * UpdateStatement updateStatement = new UpdateCommandBuilder(this).toStatement(dialect.getColumnBinderRegistry());
    	 * try (WriteOperation<Integer> writeOperation = dialect.getWriteOperationFactory().createInstance(updateStatement, connectionProvider)) {
    	 *     writeOperation.setValues(updateStatement.getValues());
    	 *     writeOperation.execute();
    	 * }
    	 * // eventually change some values and re-execute it
    	 * updateStatement.setValue(..);
    	 * }</pre>
    	 */
    	public static class DeleteStatement<T extends Table<T>> extends PreparedSQL implements WherableStatement {

    		private final Map<String, Set<Integer>> placeholderIndexes;

    		/**
    		 * Single constructor, not expected to be used elsewhere than {@link DeleteCommandBuilder}.
    		 *
    		 * @param sql the update sql order as a prepared statement
    		 * @param parameterBinders binder for prepared statement values
    		 * @param placeholderIndexes indexes of variables of criteria clause
    		 */
    		public DeleteStatement(String sql,
    							   Map<Integer, ? extends ParameterBinder<?>> parameterBinders,
    							   Map<String, Set<Integer>> placeholderIndexes) {
    			super(sql, parameterBinders);
    			this.placeholderIndexes = placeholderIndexes;
    		}

    		@Override
    		public void assertValuesAreApplyable() {
    			super.assertValuesAreApplyable();
    			Set<Placeholder> presentPlaceholders = getValues().values().stream()
    					.filter(Placeholder.class::isInstance)
    					.map(Placeholder.class::cast)
    					.collect(Collectors.toSet());
    			if (!presentPlaceholders.isEmpty()) {
    				throw new IllegalStateException("Statement expect values for placeholders: " + presentPlaceholders.stream()
    						.map(Placeholder::getName)
    						.collect(Collectors.joining(", ")));
    			}
    		}

    		@Override
    		public <C> void setValue(String placeholderName, C value) {
    			Set<Integer> placeholderIndex = placeholderIndexes.get(placeholderName);
    			if (placeholderIndex == null) {
    				throw new IllegalArgumentException("Placeholder '" + placeholderName + "' is not declared as a criteria in the where clause");
    			}
    			placeholderIndex.forEach(index -> setValue(index, value));
    		}
    	}
    }