Coverage Summary for Class: FirstArgumentIndex (it.unibo.tuprolog.argumentation.core.engine.fsm)

 package it.unibo.tuprolog.argumentation.core.engine.fsm
 
 import it.unibo.tuprolog.argumentation.core.engine.ClauseSource
 import it.unibo.tuprolog.core.Clause
 import it.unibo.tuprolog.core.Struct
 import it.unibo.tuprolog.core.Term
 import it.unibo.tuprolog.core.Var
 import it.unibo.tuprolog.solve.Signature
 import it.unibo.tuprolog.solve.library.Runtime
 import it.unibo.tuprolog.theory.Theory
 import it.unibo.tuprolog.unify.Unificator
 
 /**
  * The clauses of an immutable theory, indexed once (arg2p): by the functor and the arity of their heads, then by the
  * first argument of their heads (see [FirstArgumentIndex]); those matching a goal are collected in a list. Theories
  * index their clauses in RETE trees, whose lookups merge lazy sequences (of each index) at every step.
  */
 internal class IndexedTheoryClauses(
     theory: Theory,
 ) : ClauseSource {
     // By functor, then by arity: looked up without building the signature (or the indicator) of the goal
     private val byFunctor: Map<String, Map<Int, FirstArgumentIndex>> =
         theory.clauses
             .filter { it.head != null }
             .groupBy { it.head!!.functor }
             .mapValues { (_, clauses) ->
                 clauses.groupBy { it.head!!.arity }.mapValues { (_, sameArity) -> FirstArgumentIndex(sameArity) }
             }
 
     // A single candidate is left to the resolution of the goal with it, which unifies them anyway: matching it first
     // would unify them twice. Among several, those not matching are left out, so that none is left to backtrack to.
     override fun clausesFor(
         goal: Struct,
         unificator: Unificator,
     ): List<Clause> {
         val candidates = byFunctor[goal.functor]?.get(goal.arity)?.candidates(goal) ?: return emptyList()
         return if (candidates.size == 1) candidates else candidates.filter { unificator.match(goal, it.head!!) }
     }
 }
 
 /**
  * The indexes of the immutable theories a solver resolves with (arg2p): the libraries of each module and the static
  * theory, the last ones met, by identity. A solver keeps them for all its resolutions, and shares them with the
  * solvers its resolutions create (for sub-goals, modules), which run in the same thread: the indexes need no
  * synchronization, and the resolutions of solvers in other threads have indexes of their own.
  */
 class TheoryIndexes {
     // Allocated when first needed: the root contexts of sub-solvers get indexes of their own before sharing others
     private val theories by lazy(LazyThreadSafetyMode.NONE) { arrayOfNulls<Theory>(CACHED) }
     private val indexes by lazy(LazyThreadSafetyMode.NONE) { arrayOfNulls<IndexedTheoryClauses>(CACHED) }
     private var last = 0
 
     /** The index of [theory], built the first time it is met */
     internal fun of(theory: Theory): IndexedTheoryClauses {
         for (i in 0 until CACHED) {
             if (theories[i] === theory) return indexes[i]!!
         }
         val index = IndexedTheoryClauses(theory)
         last = (last + 1) % CACHED
         theories[last] = theory
         indexes[last] = index
         return index
     }
 
     // The clauses of the programs met last (see [program]): libraries, static and dynamic theory, by identity
     private val programs = ArrayDeque<Pair<Triple<Any, Any, Any>, ProgramClauses>>()
 
     /**
      * The clauses of the program made of [libraries], [staticKb] and [dynamicKb], built by [build] the first time
      * they are met together (the libraries change with the modules called, the theories with the solvers)
      */
     internal fun program(
         libraries: Runtime,
         staticKb: Theory,
         dynamicKb: Theory,
         build: () -> ProgramClauses,
     ): ProgramClauses {
         for ((key, program) in programs) {
             if (key.first === libraries && key.second === staticKb && key.third === dynamicKb) return program
         }
         return build().also {
             if (programs.size == PROGRAMS) programs.removeLast()
             programs.addFirst(Triple(libraries, staticKb, dynamicKb) to it)
         }
     }
 
     private companion object {
         const val CACHED = 64
         const val PROGRAMS = 16
     }
 }
 
 /**
  * The clauses of a predicate indexed by the principal symbol of the first argument of their heads (a constant, or
  * the functor and arity of a compound term): the clauses for a goal whose first argument is bound are those with
  * the same symbol and those whose first argument is a variable, in their order.
  */
 internal class FirstArgumentIndex(
     private val clauses: List<Clause>,
 ) {
     // The clauses whose first argument is a variable, which any goal may match
     private val open = ArrayList<Clause>()
 
     // For each symbol, the clauses with that symbol or a variable as first argument, in order
     private val bySymbol = HashMap<Any, MutableList<Clause>>()
 
     init {
         for (clause in clauses) {
             val symbol = clause.head!!.firstArgumentSymbol()
             if (symbol == null) {
                 open.add(clause)
                 bySymbol.values.forEach { it.add(clause) }
             } else {
                 bySymbol.getOrPut(symbol) { ArrayList(open) }.add(clause)
             }
         }
     }
 
     /** The clauses whose heads may unify with [goal], in their order */
     fun candidates(goal: Struct): List<Clause> {
         val symbol = goal.firstArgumentSymbol() ?: return clauses
         return bySymbol[symbol] ?: open
     }
 
     private companion object {
         // The principal symbol of the first argument of a head, null if there is none or it is a variable
         fun Struct.firstArgumentSymbol(): Any? = if (arity == 0) null else symbol(this[0])
 
         fun symbol(term: Term): Any? =
             when {
                 term is Var -> null
                 term is Struct && term.arity > 0 -> Signature(term.functor, term.arity)
                 else -> term
             }
     }
 }