/* Borland Pascal dynamic-method-table resolution and dispatch. */

#include "tdkpin_dispatch.h"

enum {
    VMT_DYNAMIC_TABLE_OFFSET = 4,
    DYNAMIC_PARENT_OFFSET = 0,
    DYNAMIC_CACHE_ID_OFFSET = 2,
    DYNAMIC_CACHE_SLOT_OFFSET = 4,
    DYNAMIC_COUNT_OFFSET = 6,
    DYNAMIC_IDS_OFFSET = 8,
};

/*
 * 1020:16e6 — resolve AX in the dynamic table referenced by DS:[DI+4].
 *
 * Each near-DGROUP table node contains a parent pointer, a mutable one-entry
 * cache, a count, `count` method ids, then `count` far procedure pointers.
 * Search proceeds from the most-derived node through its parent chain. The
 * returned far pointer addresses the selected four-byte slot, not its target.
 */
Win16FarPtr borland_resolve_dynamic_method_slot(
    uint16_t vmt, uint16_t method_id)
{
    uint16_t table = win16_read_u16(
        win16_dgroup_pointer((uint16_t)(vmt + VMT_DYNAMIC_TABLE_OFFSET)));

    while (true) {
        Win16FarPtr node = win16_dgroup_pointer(table);
        if (method_id == win16_read_u16(win16_far_add_offset(
                             node, DYNAMIC_CACHE_ID_OFFSET))) {
            uint16_t cached_slot = win16_read_u16(win16_far_add_offset(
                node, DYNAMIC_CACHE_SLOT_OFFSET));
            return win16_dgroup_pointer(cached_slot);
        }

        uint16_t count = win16_read_u16(win16_far_add_offset(
            node, DYNAMIC_COUNT_OFFSET));
        for (uint16_t index = 0; index < count; index++) {
            uint16_t id = win16_read_u16(win16_far_add_offset(
                node,
                (uint16_t)(DYNAMIC_IDS_OFFSET + index * 2u)));
            if (id != method_id) {
                continue;
            }

            uint16_t slot = (uint16_t)(
                table + DYNAMIC_IDS_OFFSET + count * 2u + index * 4u);
            win16_write_u16(node, DYNAMIC_CACHE_ID_OFFSET, method_id);
            win16_write_u16(node, DYNAMIC_CACHE_SLOT_OFFSET, slot);
            return win16_dgroup_pointer(slot);
        }

        table = win16_read_u16(win16_far_add_offset(
            node, DYNAMIC_PARENT_OFFSET));
        if (table == 0) {
            borland_runtime_error(210);
        }
    }
}

/* 1020:16dd — public lookup entry; DI receives the selected far slot. */
Win16FarPtr borland_find_dynamic_method(uint16_t vmt, uint16_t method_id)
{
    return borland_resolve_dynamic_method_slot(vmt, method_id);
}

/* 1020:16e1 — resolve the slot and indirect through its far procedure. */
void borland_dispatch_dynamic_method(uint16_t vmt, uint16_t method_id)
{
    Win16FarPtr slot = borland_resolve_dynamic_method_slot(vmt, method_id);
    win16_call_dynamic_method(win16_read_far_pointer(slot, 0));
}

static void dispatch_two_far_arguments(
    Win16FarPtr receiver, Win16FarPtr argument, uint16_t method_id)
{
    uint16_t vmt = win16_read_u16(receiver);
    Win16FarPtr slot =
        borland_resolve_dynamic_method_slot(vmt, method_id);
    win16_call_dynamic_method_two_far(
        win16_read_far_pointer(slot, 0), receiver, argument);
}

/* 1008:2d66 — generated two-far-argument dispatch for dynamic id 0x8002. */
void borland_dispatch_method_8002(
    Win16FarPtr receiver, Win16FarPtr argument)
{
    dispatch_two_far_arguments(receiver, argument, 0x8002);
}

/* 1018:16eb — generated two-far-argument dispatch for dynamic id 0x0006. */
void borland_dispatch_method_0006(
    Win16FarPtr receiver, Win16FarPtr argument)
{
    dispatch_two_far_arguments(receiver, argument, 0x0006);
}