/*   SHS: Syntactically Homogeneous Shell
 *   Copyright (C) 2019  Aidan Hahn
 *
 *   This program is free software: you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, either version 3 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

package ast

func (t *Token) Eval(funcs FuncTable, vars VarTable) *Token {
    if t == nil {
        return nil
    }

    var iter *Token
    eligibleForSystemCall := true

    var reduce func(*Token) *Token
    reduce = func(t_ *Token) *Token {
        if t_.Next != nil {
            t_.Next = reduce(t_.Next)
        }

        switch (t_.Tag) {
        case SYMBOL:
            maybeToken := GetVar(t_.Inner.(string), vars)
            if maybeToken != nil {
                tok := maybeToken.Eval(funcs, vars)
                if tok == LIST {
                    eligibleForSystemCall = false
                }
            }

        case LIST:
            eligibleForSystemCall = false
            t.Inner = Eval(t_.Inner)
        }

        return t_
    }

    ret := reduce(t)
    if ret.Tag == SYMBOL {
        f := funcs.GetFunction(ret.Inner)
        if f == nil {
            if !eligibleForSystemCall {
                // TODO: log error
                return nil
            }

            // hook into stdlib exec
            return
        }

        return (*f).CallFunction(ret.Next)
    }

    return ret
}