pubgrub/src/commonMain/kotlin/Term.kt

package net.cijber.pubgrub

import net.cijber.pubgrub.packages.PackageSelection
import net.cijber.pubgrub.stubs.PackageId
import net.cijber.pubgrub.stubs.Version
import net.cijber.pubgrub.version.VersionConstraint


open class Term<P : PackageId, V : Version<V>>(val pkgSelection: PackageSelection<P, V>, val exclusive: Boolean) {
    val constraint
        get() = pkgSelection.constraint

    val pkg
        get() = pkgSelection.pkg

    val inverse by lazy {
        Term(pkgSelection, !exclusive)
    }

    infix fun relation(rhs: Term<P, V>): SetRelation {
        if (rhs.pkg !== pkg) {
            throw RuntimeException("Relations between terms can only be compared if they have the same package id")
        }

        val rhsConstraint = rhs.constraint
        if (!rhs.exclusive) {
            if (exclusive) {
                if (rhsConstraint.allowsAll(constraint))
                    return SetRelation.Subset
            }
        }

        return SetRelation.Disjoint
    }

    fun intersect(rhs: Term<P, V>): Term<P, V>? {
        if (rhs.pkg !== pkg) {
            throw RuntimeException("Relations between terms can only be compared if they have the same package id")
        }

        return if (exclusive != rhs.exclusive) {
            val positive = if (!exclusive) this else rhs
            val negative = if (!exclusive) rhs else this

            nonEmptyTerm(positive.constraint.difference(negative.constraint), false)
        } else if (!exclusive) {
            nonEmptyTerm(constraint.intersect(rhs.constraint), false)
        } else {
            nonEmptyTerm(constraint.union(rhs.constraint), true)
        }
    }

    private fun nonEmptyTerm(constraint: VersionConstraint<V>, exclusive: Boolean): Term<P, V>? {
        if (constraint.isEmpty) return null

        return Term(PackageSelection(pkg, constraint), exclusive)
    }

    fun satisfies(term: Term<P, V>): Boolean = term.pkg == pkg &&
            (relation(term) == SetRelation.Subset || relation(term) == SetRelation.Equal)

    fun difference(rhs: Term<P, V>) = intersect(rhs.inverse)
}