/*
 * Equi platform reference implementation
 *
 * Created in 2022 by Luxferre, released into public domain
 *
 * See equi.md file for the specification and manual
 *
 * @license Unlicense <https://unlicense.org>
 * @author Luxferre
 */

/* Standard includes with size optimizations for TCC */

#ifdef __TINYC__
#include <tcclib.h>
#else
#include <stdlib.h>
#include <stdio.h>
#endif

/*
 * Non-standard includes
 * To save space, we emulate necessary conio functions on non-6502 systems, not vice versa
 */

#ifdef __CC65__
#include <conio.h>
#else

#define cgetc() (fgetc(stdin))

#endif

/* Definitions section */

#define ushort unsigned short /* basic 16-bit integer */
#define uchar unsigned char /* basic 8-bit integer */
#define WS sizeof(ushort) /* Equi word size in bytes */
#define CLT_ENTRY_LEN 6u /* Amount of significant compiled word characters */
#define CLT_ENTRY_SIZE (CLT_ENTRY_LEN + WS) /* Full size in bytes taken by one CLT entry */

/* Configuration section (constants overridable at compile-time) */

/* Main and return stack size in bytes */
#ifndef STACK_SIZE
#define STACK_SIZE 256u
#endif

/* Literal stack size in bytes */
#ifndef LIT_STACK_SIZE
#define LIT_STACK_SIZE 32u
#endif

/* GPD (general purpose data) area start address */
#ifndef GPD_AREA_START
#define GPD_AREA_START 0x2300u
#endif

/* Command buffer start address */
#ifndef CMD_BUF_START
#define CMD_BUF_START 0x3b80u
#endif

/* Command buffer size in bytes */
#ifndef CMD_BUF_SIZE
#define CMD_BUF_SIZE 15600u
#endif

/* Some necessary constants and offsets derived from the above values */
#define STACK_SIZE_WORDS (STACK_SIZE / WS) /* Main and return stack size in words */
#define MAIN_STACK_ADDR 0u /* Main stack address */
#define RETURN_STACK_ADDR STACK_SIZE /* Return stack address */
#define LIT_STACK_ADDR (RETURN_STACK_ADDR + STACK_SIZE) /* Literal stack address */
#define PC_ADDR (LIT_STACK_ADDR + LIT_STACK_SIZE) /* Program counter address */
#define CBP_ADDR (PC_ADDR + WS) /* Compilation buffer pointer location address */
#define CLTP_ADDR (CBP_ADDR + WS) /* Compilation lookup table pointer location address */
#define FLAGS_ADDR (CLTP_ADDR + WS) /* Flags register address */
#define GPD_START_LOC_ADDR (FLAGS_ADDR + 1u) /* Location where GPD_AREA_START value is stored */
#define CMD_START_LOC_ADDR (GPD_START_LOC_ADDR + WS) /* Location where CMD_BUF_START value is stored */
#define CMD_SIZE_LOC_ADDR (CMD_START_LOC_ADDR + WS) /* Location where CMD_BUF_SIZE value is stored */
#define CLT_START (CMD_SIZE_LOC_ADDR + 213u) /* should be 0x300 by default */
#define CLT_SIZE (GPD_AREA_START - CLT_START) /* Compilation lookup table size in bytes */
#define CLT_ENTRIES_MAX (CLT_SIZE / CLT_ENTRY_SIZE) /* Maximum amount of entries in CLT, must be integer */
#define GPD_AREA_SIZE (CMD_BUF_START - GPD_AREA_START) /* GPD area size in bytes */

/*
 * Structures that describe Equi machine RAM using the above configuration
 */

struct EquiFlags {
  unsigned int II:1; /* instruction ignore mode */
  unsigned int CM:1; /* compilation mode */
  unsigned int IM:1; /* interpretation mode */
};

struct CLTEntry {
  uchar name[CLT_ENTRY_LEN]; /* compiled word name */
  ushort loc;    /* compiled word location */
};

struct EquiRAM { 
  ushort main_stack[STACK_SIZE_WORDS];
  ushort return_stack[STACK_SIZE_WORDS];
  uchar literal_stack[LIT_STACK_SIZE];
  ushort pc; /* program counter */
  ushort msp; /* main stack pointer */
  ushort rsp; /* return stack pointer */
  uchar lsp; /* literal stack pointer */
  ushort cbp; /* compilation buffer pointer */
  ushort cltp; /* compilation lookup table pointer */
  struct EquiFlags flags;
  ushort gpd_start;
  ushort cmd_start;
  ushort cmd_size;
  uchar reserved[206u]; /* reserved space */
  struct CLTEntry clt[CLT_ENTRIES_MAX]; /* compilation lookup table */
  uchar gpd[GPD_AREA_SIZE];
  uchar cmdbuf[CMD_BUF_SIZE];
};


/* Before running the main code, instantiate the machine RAM */
static struct EquiRAM ram;

/* Also create an alternative view of the same RAM area for direct offset-based access */
static uchar* flatram = (uchar *)&ram;

int main(int argc, char* argv[]) {
  /* initialize the RAM in the most standard way */
  ram.gpd_start = GPD_AREA_START;
  ram.cmd_start = CMD_BUF_START;
  ram.cmd_size = CMD_BUF_SIZE;

  printf("Equi command buffer: 0x%X\n", ram.cmd_size);
 
  cgetc();


  return 0;
}