/**
 *  ops/truth.c
 *
 *  Post Scarcity Software Environment: nil? true? not.
 *
 *  Functions associated with truthiness.
 *
 *  (c) 2026 Simon Brooke <simon@journeyman.cc>
 *  Licensed under GPL version 2.0, or, at your option, any later version.
 */

#include <stdbool.h>

#include "memory/node.h"
#include "memory/pointer.h"
#include "memory/pso4.h"
#include "ops/stack_ops.h"

/**
 * @brief true if `p` points to `nil`, else false.
 *
 * Note that every node has its own copy of `t` and `nil`, and each instance of 
 * each is considered equivalent. So we don't check the node when considering
 * whether `nil` really is `nil`, or `t` really is `t`.
 * 
 * @param p a pointer
 * @return true if `p` points to `nil`.
 * @return false otherwise.
 */
bool c_nilp( struct pso_pointer p ) {
    return ( p.page == 0 && p.offset == 0 );
}

/**
 * @brief `true` if `p` points to `t`, else `false`.
 *
 * Note that every node has its own copy of `t` and `nil`, and each instance of 
 * each is considered equivalent. So we don't check the node when considering
 * whether `nil` really is `nil`, or `t` really is `t`.
 * 
 * Note that the offset is 4 because `t` should be the second pso2 allocated,
 * the offset is given in words, and the size of a pso2 should be four words
 *
 * @param p a pointer
 * @return true if `p` points to `t`.
 * @return false otherwise.
 */
bool c_truep( struct pso_pointer p ) {
    return ( p.page == 0 && p.offset == 4 );
}

/**
 * @brief return `t` if the first argument in this frame is `nil`, else `t`.
 * 
 * @param frame_pointer A pointer to the current stack frame;
 * @return `t` if the first argument in this frame is `nil`, else `t`
 */
struct pso_pointer nilp( struct pso_pointer frame_pointer ) {
    struct pso4 *frame = pointer_to_pso4( frame_pointer );

    return ( c_nilp( fetch_arg( frame, 0 ) ) ? t : nil );
}

/**
 * @brief return `t` if the first argument in this frame is `t`, else `nil`.
 * 
 * @param frame_pointer A pointer to the current stack frame;
 * @return `t` if the first argument in this frame is `t`, else `nil`.
 */
struct pso_pointer truep( struct pso_pointer frame_pointer ) {
    struct pso4 *frame = pointer_to_pso4( frame_pointer );

    return ( c_truep( fetch_arg( frame, 0 ) ) ? t : nil );
}

/**
 * @brief return `t` if the first argument in this frame is not `nil`, else 
 * `t`.
 * 
 * @param frame_pointer A pointer to the current stack frame;
 * @return `t` if the first argument in this frame is not `nil`, else `t`.
 */
struct pso_pointer not( struct pso_pointer frame_pointer ) {
    struct pso4 *frame = pointer_to_pso4( frame_pointer );

    return ( !c_nilp( fetch_arg( frame, 0 ) ) ? t : nil );
}

/**
 * @brief (and args...)
 *
 * @return `nil` if any `arg` is `nil`, else `t`.
 */
struct pso_pointer and( struct pso_pointer frame_pointer ) {
    struct pso4 *frame = pointer_to_pso4( frame_pointer );
    struct pso_pointer result = t;

    for ( int arg = 0;
          c_truep( result ) && arg < frame->payload.stack_frame.args; arg++ ) {
        if ( c_nilp( fetch_arg( frame, arg ) ) ) {
            result = nil;
            break;
        }
    }

    return result;
}


/**
 * @brief (or args...)
 *
 * @return `t` if any `arg` is non-nil, else `nil`.
 */
struct pso_pointer or( struct pso_pointer frame_pointer ) {
    struct pso4 *frame = pointer_to_pso4( frame_pointer );
    struct pso_pointer result = nil;

    for ( int arg = 0;
          c_truep( result ) && arg < frame->payload.stack_frame.args; arg++ ) {
        if ( !c_nilp( fetch_arg( frame, arg ) ) ) {
            result = t;
            break;
        }
    }

    return result;
}