package prolog.components.terms

import java.util.Optional

data class Variable(val name: String) : Term {
    private var alias: Optional<Term> = Optional.empty()

    fun alias(): Optional<Term> {
        return alias
    }

    fun bind(term: Term): Optional<Term> {
        if (alias.isEmpty) {
            alias = Optional.of(term)
        }

        return alias
    }

    fun unbind() {
        alias = Optional.empty()
    }

    override fun toString(): String {
        return when {
            alias.isPresent -> "$name = ${alias.get()}"
            else -> name
        }
    }

    override fun equals(other: Any?): Boolean {
        return if (alias.isPresent) {
            alias.get() == other
        } else {
            name == other.toString()
        }
    }
}