#include "config.h"
#define MINIRV32_IMPLEMENTATION
#include "uvm32.h"

#ifndef UVM32_MEMORY_SIZE
#error Define UVM32_MEMORY_SIZE
#endif

#define UVM32_NULL (void *)0

// On an invalid operation, an error is set in uvm32_state_t, but a valid pointer still needs to be temporarily used
static uint32_t garbage;

#ifndef UVM32_MEMCPY
#define UVM32_MEMCPY uvm32_memcpy
void uvm32_memcpy(void *dst, const void *src, int len) {
    uint8_t *d = (uint8_t *)dst;
    const uint8_t *s = (const uint8_t *)src;
    while(len--) {
        *(d++) = *(s++);
    }
}
#endif

#ifndef UVM32_MEMSET
#define UVM32_MEMSET uvm32_memset
void uvm32_memset(void *buf, int c, int len) {
    uint8_t *b = (uint8_t *)buf;
    while(len--) {
        *(b++) = c;
    }
}
#endif

#include "mini-rv32ima.h"

#define X(name) #name,
static const char *errNames[] = {
    LIST_OF_UVM32_ERRS
};
#undef X

static void setup_err_evt(uvm32_state_t *vmst, uvm32_evt_t *evt) {
    evt->typ = UVM32_EVT_ERR;
    evt->data.err.errcode = vmst->err;
    evt->data.err.errstr = errNames[vmst->err];
}

static void setStatus(uvm32_state_t *vmst, uvm32_status_t newStatus) {
    if (vmst->status == UVM32_STATUS_ERROR) {
        // always stay in error state until a uvm32_init()
        return;
    } else {
        vmst->status = newStatus;
    }
}

static void setStatusErr(uvm32_state_t *vmst, uvm32_err_t err) {
    // if already in error state, stay in the first error state
    if (vmst->status != UVM32_STATUS_ERROR) {
        setStatus(vmst, UVM32_STATUS_ERROR);
        vmst->err = err;
    }
}

void uvm32_init(uvm32_state_t *vmst) {
    UVM32_MEMSET(vmst, 0x00, sizeof(uvm32_state_t));
    vmst->status = UVM32_STATUS_PAUSED;

    vmst->core.pc = MINIRV32_RAM_IMAGE_OFFSET;
    // https://projectf.io/posts/riscv-cheat-sheet/
    // setup stack pointer
    // la	sp, _sstack
    // addi	sp,sp,-16
    vmst->core.regs[2] = (MINIRV32_RAM_IMAGE_OFFSET + UVM32_MEMORY_SIZE) - 16;
    vmst->core.regs[10] = 0x00;  //hart ID
    vmst->core.regs[11] = 0;
    vmst->core.extraflags |= 3;  // Machine-mode.
}

bool uvm32_load(uvm32_state_t *vmst, const uint8_t *rom, int len) {
    if (len > UVM32_MEMORY_SIZE) {
        // too big
        return false;
    }

    UVM32_MEMCPY(vmst->memory, rom, len);
    return true;
}

// Read C-string up to terminator and return len,ptr
bool get_safeptr_null_terminated(uvm32_state_t *vmst, uint32_t addr, uvm32_evt_syscall_buf_t *buf) {
    uint32_t ptrstart = addr - MINIRV32_RAM_IMAGE_OFFSET;
    uint32_t p = ptrstart;
    if (p >= UVM32_MEMORY_SIZE) {
        setStatusErr(vmst, UVM32_ERR_MEM_RD);
        buf->ptr = (uint8_t *)UVM32_NULL;
        buf->len = 0;
        return false;
    }
    while(vmst->memory[p] != '\0') {
        p++;
        if (p >= UVM32_MEMORY_SIZE) {
            setStatusErr(vmst, UVM32_ERR_MEM_RD);
            buf->ptr = (uint8_t *)UVM32_NULL;
            buf->len = 0;
            return false;
        }
    }
    buf->ptr = &vmst->memory[ptrstart];
    buf->len = p - ptrstart;
    return true;
}

bool get_safeptr(uvm32_state_t *vmst, uint32_t addr, uint32_t len, uvm32_evt_syscall_buf_t *buf) {
    uint32_t ptrstart = addr - MINIRV32_RAM_IMAGE_OFFSET;
    if ((ptrstart > UVM32_MEMORY_SIZE) || (ptrstart + len >= UVM32_MEMORY_SIZE)) {
        setStatusErr(vmst, UVM32_ERR_MEM_RD);
        buf->ptr = (uint8_t *)UVM32_NULL;
        buf->len = 0;
        return false;
    }
    buf->ptr = &vmst->memory[ptrstart];
    buf->len = len;
    return true;
}

void uvm32_clearError(uvm32_state_t *vmst) {
    if (vmst->status == UVM32_STATUS_ERROR) {
        // vm is in an error state, but user wants to continue
        // most likely after UVM32_ERR_HUNG
        vmst->status = UVM32_STATUS_PAUSED;
    }
}

uint32_t uvm32_run(uvm32_state_t *vmst, uvm32_evt_t *evt, uint32_t instr_meter) {
    uint32_t num_instr = 0;

    if (vmst->status != UVM32_STATUS_PAUSED) {
        setStatusErr(vmst, UVM32_ERR_NOTREADY);
        setup_err_evt(vmst, evt);
        return num_instr;
    }

    setStatus(vmst, UVM32_STATUS_RUNNING);

    // run CPU until no longer in running state
    while(vmst->status == UVM32_STATUS_RUNNING) {
        uint64_t elapsedUs = 1;
        uint32_t ret;
        ret = MiniRV32IMAStep(vmst, &vmst->core, vmst->memory, 0, elapsedUs, 1);
        if (3 == ret) {
            // Fetch registers used by syscall
            const uint32_t syscall = vmst->core.regs[17];  // a7
            // on exception we should jump to mtvec, but we handle directly
            // and skip over the ecall instruction
            vmst->core.pc += 4;
            switch(syscall) {
                // inbuilt syscalls
                 case UVM32_SYSCALL_HALT:
                    setStatus(vmst, UVM32_STATUS_ENDED);
                break;
                case UVM32_SYSCALL_YIELD:
                    vmst->ioevt.typ = UVM32_EVT_YIELD;
                    setStatus(vmst, UVM32_STATUS_PAUSED);
                break;
                default:
                    // user defined syscalls
                    vmst->ioevt.typ = UVM32_EVT_SYSCALL;
                    vmst->ioevt.data.syscall.code = syscall;
                    vmst->ioevt.data.syscall.ret = &vmst->core.regs[12];        // a2
                    vmst->ioevt.data.syscall.params[0] = &vmst->core.regs[10];  // a0
                    vmst->ioevt.data.syscall.params[1] = &vmst->core.regs[11];  // a1
                    setStatus(vmst, UVM32_STATUS_PAUSED);
                break;
            }
        } else if (ret != 0) {
            // unhandled exception
            setStatusErr(vmst, UVM32_ERR_INTERNAL_CORE);
            setup_err_evt(vmst, evt);
        }

        num_instr++;

        // check instruction meter, in case of hang/infinite loop
        if (instr_meter-- == 0) {
            setStatusErr(vmst, UVM32_ERR_HUNG);
            setup_err_evt(vmst, evt);
            return num_instr;
        }
    }

    if (vmst->status == UVM32_STATUS_ENDED) {
        evt->typ = UVM32_EVT_END;
        return num_instr;
    }

    // an event is ready
    if (vmst->status == UVM32_STATUS_PAUSED) {
        // send back the built up event
        UVM32_MEMCPY(evt, &vmst->ioevt, sizeof(uvm32_evt_t));
        return num_instr;
    } else {
        if (vmst->status == UVM32_STATUS_ERROR) {
            setup_err_evt(vmst, evt);
        } else {
            setStatusErr(vmst, UVM32_ERR_INTERNAL_STATE);
            setup_err_evt(vmst, evt);
        }
        return num_instr;
    }
}

bool uvm32_hasEnded(const uvm32_state_t *vmst) {
    return vmst->status == UVM32_STATUS_ENDED;
}

static uint32_t *arg_to_ptr(uvm32_state_t *vmst, uvm32_evt_t *evt, uvm32_arg_t arg) {
    switch(arg) {
        case ARG0:
            return evt->data.syscall.params[0];
        break;
        case ARG1:
            return evt->data.syscall.params[1];
        break;
        case RET:
            return evt->data.syscall.ret;
        break;
        default:
            // if something invalid is passed to arg, we should never crash
            // return a pointer to something readable
            setStatusErr(vmst, UVM32_ERR_ARGS);
            garbage = 0;
            return &garbage;
        break;
    }
}

void uvm32_setval(uvm32_state_t *vmst, uvm32_evt_t *evt, uvm32_arg_t arg, uint32_t val) {
    *arg_to_ptr(vmst, evt, arg) = val;
}

uint32_t uvm32_getval(uvm32_state_t *vmst, uvm32_evt_t *evt, uvm32_arg_t arg) {
    return *arg_to_ptr(vmst, evt, arg);
}

const char *uvm32_getcstr(uvm32_state_t *vmst, uvm32_evt_t *evt, uvm32_arg_t arg) {
    uvm32_evt_syscall_buf_t scb;
    if (get_safeptr_null_terminated(vmst, uvm32_getval(vmst, evt, arg), &scb)) {
        return (const char *)scb.ptr; // we know the buffer in cpu memory is null terminated, so safe to pass back
    } else {
        setStatusErr(vmst, UVM32_ERR_MEM_RD);
        garbage = 0;
        return (const char *)&garbage;
    }
}

uvm32_evt_syscall_buf_t uvm32_getbuf(uvm32_state_t *vmst, uvm32_evt_t *evt, uvm32_arg_t argPtr, uvm32_arg_t argLen) {
    uvm32_evt_syscall_buf_t scb;
    if (!get_safeptr(vmst, uvm32_getval(vmst, evt, argPtr), uvm32_getval(vmst, evt, argLen), &scb)) {
        setStatusErr(vmst, UVM32_ERR_MEM_RD);
        garbage = 0;
        scb.ptr = (uint8_t *)&garbage;
        scb.len = 0;
    }
    return scb;
}