// iigsStart -- a GS/OS boot launcher for the headless IIgs harnesses.
//
// Installed as /System/Start on a copy of the GS/OS system disk, this runs
// at boot INSTEAD of the Finder and hands off to one JoeyLib example. The
// point is that the Finder cannot be driven from a script: measured under
// gssquared, injected keystrokes reach the $C000 latch but never reach the
// Finder -- Open-Apple-A, Tab, arrows and bare letters all left the desktop
// untouched. (The one redraw seen after the first key of a run is the
// Finder's own settling: byte-identical for three different keys.) Reaching
// the desktop also costs ~61s of boot that a probe must sit through; this
// route has the example on screen in ~52s.
//
// Two GS/OS calls, in this order:
//   SetPrefixGS -- point prefix 0 at the example's DIRECTORY. GS/OS does
//     NOT do this for a QuitGS launch; prefix 0 was measured still pointing
//     at the boot volume. That is not cosmetic: JoeyLib opens its NTP
//     replayer as bare "ntpplayer", and when that read fails jlpAudioInit
//     returns before ntpArm(), so the sound interrupt vector stays at its
//     ROM default ($E1002C = 5C xxxx FF) and the example is SILENT. The
//     Finder sets prefix 0 itself, which is why this only bites here.
//   QuitGS with pCount = 2 and a pathname -- "quit, and launch this".
//
// Build: clang-build.sh -DJOEY_START_PATH='"/JOEYLIB/STAXI"' \
//                       -o START iigsStart.c iigsStartQuit.s

#include <stdint.h>

// The program to launch. Overridden per-disk from the build.
#ifndef JOEY_START_PATH
#define JOEY_START_PATH    "/JOEYLIB/STAXI"
#endif

// Fixed scratch in bank $E1: the $E1:9DC8-$9DFD window that survives a
// present (SCB proper ends at $9DC7). The asm stubs hard-code the two
// parameter-block addresses, so these must agree with iigsStartQuit.s.
//   9DC8  mailbox            9DCC  QuitGS parm (8)
//   9DD4  pathname string    9DE4  SetPrefix parm (8)
//   9DEC  prefix string
#define QUIT_MAILBOX       ((volatile uint8_t *)0xE19DC8L)
#define QUIT_PARM          ((volatile uint8_t *)0xE19DCCL)
#define QUIT_PATH          ((volatile uint8_t *)0xE19DD4L)
#define PREFIX_PARM        ((volatile uint8_t *)0xE19DE4L)
#define PREFIX_PATH        ((volatile uint8_t *)0xE19DECL)
#define QUIT_PATH_ADDR     0x00E19DD4UL
#define PREFIX_PATH_ADDR   0x00E19DECUL

// A GS/OS class-1 input string is a length WORD followed by the characters.
#define GSOS_STRING_HEADER 2u

// Markers for the harness.
#define QUIT_REACHED       0xAAu
#define QUIT_RETURNED      0xEEu


void iigsStartQuit(void);
void iigsStartSetPrefix(void);


// Write a GS/OS input string (length word + characters) and return its length.
static uint16_t gsosString(volatile uint8_t *dst, const char *src, uint16_t len) {
    uint16_t i;

    dst[0] = (uint8_t)(len & 0xFFu);
    dst[1] = (uint8_t)((len >> 8) & 0xFFu);
    for (i = 0; i < len; i++) {
        dst[GSOS_STRING_HEADER + i] = (uint8_t)src[i];
    }
    return len;
}


static void putLong(volatile uint8_t *dst, uint32_t v) {
    dst[0] = (uint8_t)(v & 0xFFu);
    dst[1] = (uint8_t)((v >> 8) & 0xFFu);
    dst[2] = (uint8_t)((v >> 16) & 0xFFu);
    dst[3] = (uint8_t)((v >> 24) & 0xFFu);
}


int main(void) {
    const char *path = JOEY_START_PATH;
    uint16_t    len  = 0;
    uint16_t    dir  = 0;
    uint16_t    i;

    while (path[len] != '\0') {
        len++;
    }
    // Directory part, including the trailing '/': everything up to the last
    // separator. "/JOEYLIB/STAXI" -> "/JOEYLIB/".
    for (i = 0; i < len; i++) {
        if (path[i] == '/') {
            dir = (uint16_t)(i + 1u);
        }
    }

    gsosString(PREFIX_PATH, path, dir);
    PREFIX_PARM[0] = 2u;                    // pCount
    PREFIX_PARM[1] = 0u;
    PREFIX_PARM[2] = 0u;                    // prefixNum 0 = current directory
    PREFIX_PARM[3] = 0u;
    putLong(PREFIX_PARM + 4, PREFIX_PATH_ADDR);
    iigsStartSetPrefix();

    gsosString(QUIT_PATH, path, len);
    QUIT_PARM[0] = 2u;                      // pCount
    QUIT_PARM[1] = 0u;
    putLong(QUIT_PARM + 2, QUIT_PATH_ADDR); // pathname
    QUIT_PARM[6] = 0u;                      // flags
    QUIT_PARM[7] = 0u;

    *QUIT_MAILBOX = QUIT_REACHED;
    iigsStartQuit();
    *QUIT_MAILBOX = QUIT_RETURNED;

    // QuitGS only returns on failure. Nothing useful is left to do and the
    // llvm-mos post-main exit path is broken on GS/OS, so spin rather than
    // crash: the harness reads the mailbox to see what happened.
    for (;;) {
    }
}