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CDS QL Execution Engine

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/************************************************************************
 * © 2021-2024 SAP SE or an SAP affiliate company. All rights reserved. *
 ************************************************************************/
package com.sap.cds.impl.docstore;

import static com.sap.cds.impl.sql.SQLStatementBuilder.commaSeparated;
import static com.sap.cds.impl.sql.SpaceSeparatedCollector.joining;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Stream;

import com.sap.cds.impl.Context;
import com.sap.cds.impl.PreparedCqnStmt;
import com.sap.cds.impl.sql.SQLStatementBuilder;
import com.sap.cds.impl.sql.TokenToSQLTransformer;
import com.sap.cds.jdbc.spi.SqlMapping;
import com.sap.cds.ql.cqn.CqnSelect;
import com.sap.cds.ql.cqn.CqnSortSpecification;
import com.sap.cds.reflect.CdsEntity;

public class DocStoreSelectStatementBuilder implements DocStoreStatementBuilder {
	private final CqnSelect select;
	private final TokenToSQLTransformer toSql;
	private final SqlMapping sqlMapping;
	private final String tableName;
	private final CdsEntity entity;
	private final List params = new ArrayList<>();

	public DocStoreSelectStatementBuilder(Context context, CqnSelect select) {
		this.entity = context.getCdsModel().getEntity(select.ref().firstSegment());
		this.select = select;
		this.sqlMapping = context.getDbContext().getSqlMapping(entity);
		this.tableName = this.sqlMapping.tableName();
		this.toSql = TokenToSQLTransformer.notCollating(context, sqlMapping::columnName, entity, this.tableName, params,
				DocStoreUtils::valueToParamCastExpression);
	}

	@Override
	public SQLStatementBuilder.SQLStatement build() {

		Stream.Builder builder = Stream.builder();
		builder.add("SELECT * FROM");
		builder.add(tableName);

		select.where().map(toSql::toSQL).ifPresent(whereSql -> {
			builder.add("WHERE");
			builder.add(whereSql);
		});

		List orderBy = select.orderBy();
		if (!orderBy.isEmpty()) {
			builder.add("ORDER BY");
			commaSeparated(orderBy.stream(), this::sort).forEach(builder);
		}

		String sql = builder.build().collect(joining());

		return new SQLStatementBuilder.SQLStatement(sql, params);
	}

	private String sort(CqnSortSpecification o) {
		StringBuilder sort = new StringBuilder(toSql.apply(o.value()));
		switch (o.order()) {
			case DESC:
			case DESC_NULLS_FIRST:
				sort.append(" DESC");
				break;
			case ASC_NULLS_LAST:
			default: // ASC
		}
		return sort.toString();
	}

}