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

// operand-var.go
package expr

import (
	"fmt"

	"git.portale-stac.it/go-pkg/expr/kern"
	"git.portale-stac.it/go-pkg/expr/scan"
)

// -------- variable term
func newVarTerm(tk *scan.Token) *scan.Term {
	t := &scan.Term{
		Tk:       *tk,
		Parent:   nil,
		Children: nil,
		Position: scan.PosLeaf,
		Priority: scan.PriValue,
		EvalFunc: evalVar,
	}
	t.Tk.Sym = scan.SymVariable
	return t
}

// -------- eval func
func evalVar(ctx kern.ExprContext, opTerm *scan.Term) (v any, err error) {
	var exists bool
	name := opTerm.Source()
	if v, exists = ctx.GetVar(name); !exists {
		if info, exists := ctx.GetFuncInfo(name); exists {
			v = info.Functor()
		} else {
			err = fmt.Errorf("undefined variable or function %q", name)
		}
	}
	return
}

// init
func init() {
	scan.RegisterTermConstructor(scan.SymIdentifier, newVarTerm)
}