// Optimize does optimization and creates a Plan.
// The node must be prepared first.
func Optimize(ctx context.Context, node ast.Node) (plan.Plan, error) {
	// We have to infer type again because after parameter is set, the expression type may change.
	if err := InferType(node); err != nil {
		return nil, errors.Trace(err)
	}
	if err := logicOptimize(ctx, node); err != nil {
		return nil, errors.Trace(err)
	}
	p, err := plan.BuildPlan(node)
	if err != nil {
		return nil, errors.Trace(err)
	}
	alts, err := plan.Alternatives(p)
	if err != nil {
		return nil, errors.Trace(err)
	}
	err = plan.Refine(p)
	if err != nil {
		return nil, errors.Trace(err)
	}
	bestCost := plan.EstimateCost(p)
	bestPlan := p
	for _, alt := range alts {
		err = plan.Refine(alt)
		if err != nil {
			return nil, errors.Trace(err)
		}
		cost := plan.EstimateCost(alt)
		if cost < bestCost {
			bestCost = cost
			bestPlan = alt
		}
	}
	return bestPlan, nil
}

// Next implements Executor Next interface.
// The data in the returned row is not used by caller.
// If inner executor didn't get any row for an outer executor row,
// a row with 0 len Data indicates there is no inner row matched for
// an outer row.
func (e *JoinOuterExec) Next() (*Row, error) {
	for {
		if e.innerExec == nil {
			e.gotRow = false
			outerRow, err := e.OuterExec.Next()
			if err != nil {
				return nil, errors.Trace(err)
			}
			if outerRow == nil {
				return nil, nil
			}
			plan.Refine(e.InnerPlan)
			e.innerExec = e.builder.build(e.InnerPlan)
			if e.builder.err != nil {
				return nil, errors.Trace(e.builder.err)
			}
		}
		row, err := e.innerExec.Next()
		if err != nil {
			return nil, errors.Trace(err)
		}
		if row == nil {
			e.innerExec = nil
			if e.gotRow {
				continue
			}
			e.setInnerNull()
			return &Row{}, nil
		}
		if len(row.Data) != 0 {
			e.gotRow = true
			return row, nil
		}
	}
}

// Next implements Executor Next interface.
// The data in the returned row is not used by caller.
func (e *JoinInnerExec) Next() (*Row, error) {
	if e.done {
		return nil, nil
	}
	rowKeysSlice := make([][]*RowKeyEntry, len(e.InnerPlans))
	for {
		exec := e.innerExecs[e.cursor]
		if exec == nil {
			innerPlan := e.InnerPlans[e.cursor]
			plan.Refine(innerPlan)
			exec = e.builder.build(innerPlan)
			if e.builder.err != nil {
				return nil, errors.Trace(e.builder.err)
			}
			e.innerExecs[e.cursor] = exec
		}
		row, err := exec.Next()
		if err != nil {
			return nil, errors.Trace(err)
		}
		if row == nil {
			exec.Close()
			e.innerExecs[e.cursor] = nil
			if e.cursor == 0 {
				e.done = true
				return nil, nil
			}
			e.cursor--
			continue
		}
		rowKeysSlice[e.cursor] = row.RowKeys
		if e.cursor < len(e.innerExecs)-1 {
			e.cursor++
			continue
		}
		var match = true
		if e.Condition != nil {
			match, err = evaluator.EvalBool(e.ctx, e.Condition)
			if err != nil {
				return nil, errors.Trace(err)
			}
		}
		if match {
			row.RowKeys = joinRowKeys(rowKeysSlice)
			return row, nil
		}
	}
}

// Optimize does optimization and creates a Plan.
// The node must be prepared first.
func Optimize(ctx context.Context, node ast.Node, sb plan.SubQueryBuilder) (plan.Plan, error) {
	// We have to infer type again because after parameter is set, the expression type may change.
	if err := InferType(node); err != nil {
		return nil, errors.Trace(err)
	}
	if err := logicOptimize(ctx, node); err != nil {
		return nil, errors.Trace(err)
	}
	p, err := plan.BuildPlan(node, sb)
	if err != nil {
		return nil, errors.Trace(err)
	}
	err = plan.Refine(p)
	if err != nil {
		return nil, errors.Trace(err)
	}
	return p, nil
}

func (sq *subquery) EvalRows(ctx context.Context, rowCount int) ([]interface{}, error) {
	b := newExecutorBuilder(ctx, sq.is)
	plan.Refine(sq.plan)
	e := b.build(sq.plan)
	if b.err != nil {
		return nil, errors.Trace(b.err)
	}
	defer e.Close()
	if len(e.Fields()) == 0 {
		// No result fields means no Recordset.
		for {
			row, err := e.Next()
			if err != nil {
				return nil, errors.Trace(err)
			}
			if row == nil {
				return nil, nil
			}
		}
	}
	var (
		err  error
		row  *Row
		rows = []interface{}{}
	)
	for rowCount != 0 {
		row, err = e.Next()
		if err != nil {
			return rows, errors.Trace(err)
		}
		if row == nil {
			break
		}
		if len(row.Data) == 1 {
			rows = append(rows, row.Data[0])
		} else {
			rows = append(rows, row.Data)
		}
		if rowCount > 0 {
			rowCount--
		}
	}
	return rows, nil
}