erc-c/src/option.c

/*
 * option.c
 * 
 * This file contains the functions which support our CLI options; you
 * are both able to parse options and retrieve information from that
 * option parsing.
 */

#include <errno.h>
#include <getopt.h>
#include <string.h>
#include <unistd.h>

#include "option.h"
#include "log.h"
#include "vm_di.h"

/*
 * These are the file inputs we may have to the system. What their
 * contents are will vary based on emulation context, and these values
 * may change through the course of the program's execution.
 */
static FILE *input1 = NULL;
static FILE *input2 = NULL;

static FILE *disasm_log = NULL;

/*
 * The size of our error buffer for anything we want to record while our
 * option parsing goes on.
 */
#define ERRBUF_SIZE 2048

/*
 * The alluded-to error buffer.
 */
static char error_buffer[ERRBUF_SIZE] = "";

/*
 * The default width and height of the window. This is "roughly"
 * 640x480, but because the Apple II has a 4.375:3 aspect ratio, we had
 * to bump up the width to a number that respects that ratio.
 */
static int width = 840;
static int height = 576;

/*
 * These are all of the options we allow in our long-form options. It's
 * a bit faster to identify them by integer symbols than to do string
 * comparisons.
 */
enum options {
    DISK1,
    DISK2,
    HELP,
    DISASSEMBLE,
};

/*
 * Here are the options we support for program execution.
 */
static struct option long_options[] = {
    { "disassemble", 1, NULL, DISASSEMBLE },
    { "disk1", 1, NULL, DISK1 },
    { "disk2", 1, NULL, DISK2 },
    { "help", 0, NULL, HELP },
};

/*
 * This simply returns the pointer of our error buffer, with the
 * qualification that the caller cannot modify the error buffer once
 * they get the pointer back.
 */
const char *
option_get_error()
{
    return error_buffer;
}

/*
 * Directly set the error buffer with something (that has to be less
 * than ERRBUF_SIZE). This function is not itself hugely useful, but
 * does allow for some better testing on option_error().
 */
void
option_set_error(const char *str)
{
    // Use `- 1` so that we can ensure error_buffer is NUL-terminated.
    // Otherwise, strncpy will copy all of src but leave the dst
    // unterminated. Not that we're _likely_ to so self-injure
    // ourselves, but, ya know.
    strncpy(error_buffer, str, ERRBUF_SIZE - 1);
}

/*
 * Parse our command-line arguments from the given argc and argv. This
 * may or may not be what the kernel passes into the main() function!
 * We return 1 if we can continue beyond the option parse phase, and 0
 * if something came up to cause us to exit early. But whether you
 * actually exit early is left up to the caller.
 */
int
option_parse(int argc, char **argv)
{
    int index;
    int opt = -1;

    // To begin with, let's (effectively) NUL-out the error buffer.
    error_buffer[0] = '\0';

    vm_di_set(VM_WIDTH, &width);
    vm_di_set(VM_HEIGHT, &height);

    do {
        opt = getopt_long_only(argc, argv, "", long_options, &index);

        switch (opt) {
            case DISASSEMBLE:
                if (!option_open_file(&disasm_log, optarg, "w")) {
                    return 0;
                }

                vm_di_set(VM_DISASM_LOG, disasm_log);
                break;

            case DISK1:
                if (!option_open_file(&input1, optarg, "r+")) {
                    return 0;
                }

                vm_di_set(VM_DISK1, input1);
                break;

            case DISK2:
                if (!option_open_file(&input2, optarg, "r+")) {
                    return 0;
                }

                vm_di_set(VM_DISK2, input2);
                break;

            case HELP:
                option_print_help();
                
                // The help option should terminate normal execution
                return 0;
        }
    } while (opt != -1);

    return 1;
}

/*
 * Given a file path, we open a FILE stream and set our given input
 * source to that stream. If we cannot do so, we will set an error
 * string in the buffer. Assuming all goes well, we will return 1, and
 * 0 if not.
 */
int
option_open_file(FILE **stream, const char *file, const char *opts)
{
    if (!file) {
        snprintf(error_buffer,
                 ERRBUF_SIZE, 
                 "No file given\n");
        return 0;
    }

    *stream = fopen(file, opts);
    if (*stream == NULL) {
        snprintf(error_buffer,
                 ERRBUF_SIZE,
                 "open file for %s: %s", 
                 file, strerror(errno));
        return 0;
    }

    return 1;
}

/*
 * Print out a help message. You'll note this is not automatically
 * generated; it must be manually updated as we add other options.
 */
void
option_print_help()
{
    fprintf(stderr, "Usage: erc [options...]\n");
    fprintf(stderr, "Options:\n");
    fprintf(stderr, "\
  --disassemble=FILE          Write assembly notation into FILE\n\
  --disk1=FILE                Load FILE into disk drive 1\n\
  --disk2=FILE                Load FILE into disk drive 2\n\
  --help                      Print this help message\n\
  --size=WIDTHxHEIGHT         Use WIDTH and HEIGHT for window size\n\
                              (only 700x480 and 875x600 are supported)\n");
}