// Copyright 2016 The Cockroach Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
// implied. See the License for the specific language governing
// permissions and limitations under the License.

package sqlbase

import (
	"github.com/cockroachdb/cockroach/pkg/sql/parser"
)

// MakeDefaultExprs returns a slice of the default expressions for the slice
// of input column descriptors, or nil if none of the input column descriptors
// have default expressions.
func MakeDefaultExprs(
	cols []ColumnDescriptor, parse *parser.Parser, evalCtx *parser.EvalContext,
) ([]parser.TypedExpr, error) {
	// Check to see if any of the columns have DEFAULT expressions. If there
	// are no DEFAULT expressions, we don't bother with constructing the
	// defaults map as the defaults are all NULL.
	haveDefaults := false
	for _, col := range cols {
		if col.DefaultExpr != nil {
			haveDefaults = true
			break
		}
	}
	if !haveDefaults {
		return nil, nil
	}

	// Build the default expressions map from the parsed SELECT statement.
	defaultExprs := make([]parser.TypedExpr, 0, len(cols))
	exprStrings := make([]string, 0, len(cols))
	for _, col := range cols {
		if col.DefaultExpr != nil {
			exprStrings = append(exprStrings, *col.DefaultExpr)
		}
	}
	exprs, err := parser.ParseExprs(exprStrings)
	if err != nil {
		return nil, err
	}

	defExprIdx := 0
	for _, col := range cols {
		if col.DefaultExpr == nil {
			defaultExprs = append(defaultExprs, parser.DNull)
			continue
		}
		expr := exprs[defExprIdx]
		typedExpr, err := parser.TypeCheck(expr, nil, col.Type.ToDatumType())
		if err != nil {
			return nil, err
		}
		if typedExpr, err = parse.NormalizeExpr(evalCtx, typedExpr); err != nil {
			return nil, err
		}
		defaultExprs = append(defaultExprs, typedExpr)
		defExprIdx++
	}
	return defaultExprs, nil
}