/* Edge-triggered left/right flipper dispatcher at 1000:99f0. */

#include "tdkpin_flippers.h"

static Win16FarPtr caller_receiver(uint16_t caller_bp)
{
    uint16_t offset = win16_read_stack_u16((uint16_t)(caller_bp + 6));
    uint16_t selector = win16_read_stack_u16((uint16_t)(caller_bp + 8));
    return win16_make_far_pointer(selector, offset);
}

static void update_one_flipper(
    uint16_t caller_bp,
    Win16FarPtr receiver,
    uint16_t key_offset,
    uint16_t position_offset,
    uint16_t flipper)
{
    bool pressed = win16_read_u8(
        win16_far_add_offset(receiver, key_offset)) != 0;
    uint16_t position = win16_read_u16(
        win16_far_add_offset(receiver, position_offset));
    int32_t delta;
    if (pressed && position < 1) {
        win16_write_u16(receiver, position_offset, (uint16_t)(position + 1u));
        delta = -1;
    } else if (!pressed && position > 0) {
        win16_write_u16(receiver, position_offset, (uint16_t)(position - 1u));
        delta = 1;
    } else {
        return;
    }
    tdkpin_move_flipper_collision_geometry(
        caller_bp, delta, flipper, 0);
    tdkpin_move_flipper_bitmap_geometry_for_receiver(
        receiver, delta, flipper);
}

void tdkpin_update_flippers(uint16_t caller_bp)
{
    Win16FarPtr receiver = caller_receiver(caller_bp);
    update_one_flipper(caller_bp, receiver, 0x0bda, 0x0bd4, 1);
    update_one_flipper(caller_bp, receiver, 0x0bdb, 0x0bd6, 2);
}