/*
 * Copyright (c) 2025 Ian Marco Moffett and the Osmora Team.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of Hyra nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <stdio.h>
#include <errno.h>
#include "rom.h"
#include "cpu/cpu.h"

/*
 * Fetch an instruction byte from memory
 *
 * @core: Core to fetch for
 * @byte_res: Result is written here
 *
 * XXX: Caller is to increment `core->pc'
 *
 * Returns zero on success
 */
static int
cpu_fetch(struct osmx_core *core, uint8_t *byte_res)
{
    uint8_t *rom;
    size_t rom_len;

    if (core == NULL || byte_res == NULL) {
        printf("fatal: bad arg in %s()\n", __func__);
        return -1;
    }

    if ((rom = g_firmware.buf) == NULL) {
        printf("fatal: ROM is uninitialized\n");
        return -1;
    }

    rom_len = g_firmware.length;
    if (core->pc >= (CPU_BUA_PBASE + rom_len)) {
        printf("fatal: PC outside of ROM\n");
        return -1;
    }

    if (core->pc >= CPU_BUA_PBASE) {
        *byte_res = rom[core->pc - CPU_BUA_PBASE];
    }

    return 0;
}

int
cpu_run(struct osmx_core *core)
{
    uint8_t opcode;
    int error;

    if (core == NULL) {
        return -EINVAL;
    }

    core->run = 1;
    while (core->run) {
        error = cpu_fetch(core, &opcode);
        if (error < 0) {
            core->run = 0;
            break;
        }

        /* Test opcode cases */
        switch (opcode) {
        case OP_HLT:
            printf("** HALTED **\n");
            core->run = false;
            continue;
        }

        ++core->pc;
    }
}