#include <time.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "../xyw.h"

#define SYSTEM_STATE 0x00
#define SYSTEM_ERROR 0x01
#define SYSTEM_PAGE 0x02
#define SYSTEM_RANDOM 0x03
#define SYSTEM_ON_ERROR 0x04
#define SYSTEM_IMAGE_EXEC 0x06

#define MAX_IMAGE_EXEC_DEPTH 8
#define MAX_IMAGE_EXEC_PATH_LENGTH 256

/// Error handler tracking
static xyw_byte error_handler_entry_s = 0;

/// Exec stack management
static xyw_vm_snapshot exec_stack[MAX_IMAGE_EXEC_DEPTH];
static int exec_stack_depth = 0;
static int exec_pending = 0;
static char exec_path_buf[MAX_IMAGE_EXEC_PATH_LENGTH];

void system_setup(xyw_byte *data)
{
    (void)data;
    srand(time(NULL));
    error_handler_entry_s = 0;
}

xyw_byte system_input(xyw_byte *data, xyw_byte addr, xyw_byte *error)
{
    if (addr == SYSTEM_RANDOM)
        return (xyw_byte)(rand() & 0xFF);
    (void)error;
    return data[addr];
}

static void get_string_from_memory(xyw_word addr, char *buf, size_t bufsize)
{
    size_t i;
    for (i = 0; i < bufsize - 1 && xyw_memory[addr + i] != 0; i++)
        buf[i] = xyw_memory[addr + i];
    buf[i] = '\0';
}

static void request_exec(xyw_word path_addr)
{
    get_string_from_memory(path_addr, exec_path_buf, sizeof(exec_path_buf));
    exec_pending = 1;
}

void system_output(xyw_byte *data, xyw_byte addr, xyw_byte *error)
{
    (void)error;
    if (addr == SYSTEM_IMAGE_EXEC + 1)
    {
        xyw_word target = XYW_PEEKW(&data[SYSTEM_IMAGE_EXEC]);
        if (target != 0)
            request_exec(target);
    }
}

static void split_exec_string(char *full, char **path, char **argstart)
{
    char *sp = strchr(full, ' ');
    if (sp)
    {
        *sp = '\0';
        *argstart = sp + 1;
    }
    else
    {
        *argstart = NULL;
    }
    *path = full;
}

static void handle_exec_requests(xyw_byte *data)
{
    if (!exec_pending)
        return;
    exec_pending = 0;

    if (exec_stack_depth >= MAX_IMAGE_EXEC_DEPTH)
    {
        data[SYSTEM_ERROR] = XYW_ERROR_EXEC_DEPTH_EXCEEDED;
        return;
    }
    xyw_vm_save_snapshot(&exec_stack[exec_stack_depth++]);

    char path_copy[MAX_IMAGE_EXEC_PATH_LENGTH];
    strncpy(path_copy, exec_path_buf, sizeof(path_copy) - 1);
    path_copy[sizeof(path_copy) - 1] = '\0';
    char *path, *argstart;
    split_exec_string(path_copy, &path, &argstart);

    xyw_vm_reset();
    if (xyw_vm_load_image(path, argstart) != 0)
    {
        // Restore parent state so error handler can run in the caller's context
        xyw_vm_restore_snapshot(&exec_stack[--exec_stack_depth]);
    }
}

void system_tick(xyw_byte *data)
{
    // Check if returning from error handler (after RTS popped the frame)
    if ((data[SYSTEM_STATE] & XYW_STATE_ERROR) &&
        error_handler_entry_s != 0 &&
        xyw_vm_get_system_depth() == error_handler_entry_s)
    {
        data[SYSTEM_STATE] &= ~XYW_STATE_ERROR;
        error_handler_entry_s = 0;
    }

    // Check for new error condition
    if (data[SYSTEM_ERROR] != XYW_ERROR_NONE && !(data[SYSTEM_STATE] & XYW_STATE_ERROR))
    {
        xyw_word on_error_handler = XYW_PEEKW(&data[SYSTEM_ON_ERROR]);
        if (on_error_handler != 0)
        {
            XYW_DBG("Error occurred: %02X, jumping to error handler at %04X\n", data[SYSTEM_ERROR], on_error_handler);
            data[SYSTEM_STATE] |= XYW_STATE_ERROR;
            error_handler_entry_s = xyw_vm_get_system_depth();
            xyw_vm_push_frame(*pc);
            *pc = on_error_handler;
        }
        else
        {
            // No error handler: halt execution
            data[SYSTEM_STATE] &= ~XYW_STATE_RUNNING;
        }
    }

    // Handle exec requests
    handle_exec_requests(data);
}

void system_save(xyw_byte *data, xyw_byte *state)
{
    (void)data;
    state[0] = error_handler_entry_s;
}

void system_restore(xyw_byte *data, const xyw_byte *state)
{
    (void)data;
    error_handler_entry_s = state[0];
}

int xyw_system_try_restore_parent(void)
{
    if (exec_stack_depth > 0)
    {
        xyw_vm_restore_snapshot(&exec_stack[--exec_stack_depth]);
        return 1;
    }
    return 0;
}