expr/operator-selector.go

// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
// All rights reserved.

// operator-selector.go
package expr

//-------- selector term

func newSelectorTerm(tk *Token) (inst *term) {
	return &term{
		tk:       *tk,
		children: make([]*term, 0, 3),
		position: posInfix,
		priority: priSelector,
		evalFunc: evalSelector,
	}
}

func trySelectorCase(ctx ExprContext, exprValue, caseSel any, caseIndex int) (match bool, selectedValue any, err error) {
	caseData, _ := caseSel.(*selectorCase)
	if caseData.filterList == nil {
		selectedValue, err = caseData.caseExpr.Eval(ctx)
		match = true
	} else if filterList, ok := caseData.filterList.value().([]*term); ok {
		if len(filterList) == 0 && exprValue == int64(caseIndex) {
			selectedValue, err = caseData.caseExpr.Eval(ctx)
			match = true
		} else {
			var caseValue any
			for _, caseTerm := range filterList {
				if caseValue, err = caseTerm.compute(ctx); err != nil || caseValue == exprValue {
					selectedValue, err = caseData.caseExpr.Eval(ctx)
					match = true
					break
				}
			}
		}
	}
	return
}

func evalSelector(ctx ExprContext, self *term) (v any, err error) {
	var exprValue any
	var match bool

	if err = self.checkOperands(); err != nil {
		return
	}
	exprTerm := self.children[0]
	if exprValue, err = exprTerm.compute(ctx); err != nil {
		return
	}

	caseListTerm := self.children[1]
	caseList, _ := caseListTerm.value().([]*term)
	for i, caseTerm := range caseList {
		caseSel := caseTerm.value()
		if match, v, err = trySelectorCase(ctx, exprValue, caseSel, i); err != nil || match {
			break
		}
	}
	if err == nil && !match {
		err = exprTerm.tk.Errorf("no case catches the value (%v) of the selection expression", exprValue)
	}
	return
}

// init
func init() {
	registerTermConstructor(SymSelector, newSelectorTerm)
}