package gs.predicate.v0.api

/** A _Predicate_ is some function that accepts any input and emits some
  * [[Predicate.Result]] (whether the predicate matched).
  *
  * Predicates evaluate input to see if the logic matches that input.
  */
trait Predicate:
  /** @return
    *   The serializable predicate type.
    */
  def predicateType: String

  /** Evaluate this predicate against the given input.
    *
    * @return
    *   Some [[Predicate.Result]] that describes whether the input matched the
    *   predicate.
    */
  def eval(input: Any): Predicate.Result

end Predicate

object Predicate:

  def alwaysTrue: Predicate = True

  def alwaysFalse: Predicate = False

  /** The result of evaluating a [[Predicate]] is a Boolean value where:
    *
    *   - `true`: The predicate matched the given input.
    *   - `false`: The predicate missed (did not match) the given input.
    */
  opaque type Result = Boolean

  object Result:

    /** @return
      *   A result indicating a predicate matched (`true`).
      */
    def matched(): Result = true

    /** @return
      *   A result indicating a predicate missed (`false`).
      */
    def missed(): Result = false

    /** Instantiate a new [[Predicate.Result]] from the given value.
      *
      * @param value
      *   The underlying `Boolean` value.
      * @return
      *   The new predicate result.
      */
    def apply(value: Boolean): Result = value

    given CanEqual[Result, Result] = CanEqual.derived

    extension (results: List[Result])
      /** @return
        *   True if all results are true. False if no results are given.
        */
      def allMatch(): Result = results.nonEmpty && results.forall(x => x)

      /** @return
        *   True if any results match. False if no results are given.
        */
      def anyMatch(): Result =
        results.nonEmpty && results.find(x => x).isDefined

    extension (result: Result)
      /** @return
        *   The underlying value.
        */
      def unwrap(): Boolean = result

      /** Logical AND operation.
        *
        * @param other
        *   The other result.
        * @return
        *   True if both results match. False otherwise.
        */
      def and(other: Result): Result = result && other

      /** Logical OR operation.
        *
        * @param other
        *   The other result.
        * @return
        *   True if either result matches. False otherwise.
        */
      def or(other: Result): Result = result || other

      /** @return
        *   True if this result is a match. False otherwise.
        */
      def isMatch: Boolean = result

      /** @return
        *   True if this result is a miss. False otherwise.
        */
      def isMiss: Boolean = !result

  end Result

end Predicate