/**
 * Forth runtime internals
 *
 * Created on 2021/11/13.
 */

#ifndef FORTH_FH_RUNTIME_H
#define FORTH_FH_RUNTIME_H

#include <stdint.h>
#include <stddef.h>
#include <stdint.h>
#include <stdbool.h>

#include "fh_config.h"

struct fh_word_s;
struct fh_instruction_s;
struct fh_thread_s;

/** Word handler typedef */
typedef enum fh_error (*word_exec_t)(struct fh_thread_s *fh, const struct fh_word_s *w);

/** Bytecode instruction type marker */
enum fh_instruction_kind {
  /* Data = word pointer (dict index) */
  FH_INSTR_WORD,

  /* Data = numeric value to push onto the data stack */
  FH_INSTR_NUMBER,

  /** End of a user defined word, pop address and jump back */
  FH_INSTR_ENDWORD,

  /** This is the `s"` instruction, the length (u32) and string data immediately follow */
  FH_INSTR_ALLOCSTR,

  /** This is the `."` instruction, same format as above. */
  FH_INSTR_TYPESTR,

  /* Unconditional jump */
  FH_INSTR_JUMP,

  /* Jump if zero */
  FH_INSTR_JUMPZERO,

  /* Loop exit */
  FH_INSTR_LEAVE,

  /* DO loop initializer */
  FH_INSTR_DO,

  /* value TO var */
  FH_INSTR_TO,

  /* ?DO short-circuiting loop */
  FH_INSTR_DO_QUESTION,

  /* Loop end instr */
  FH_INSTR_LOOP,

  /* Loop end instr with custom step */
  FH_INSTR_LOOP_PLUS,

  /* Postponed word */
  FH_INSTR_POSTPONED_WORD,

  FH_INSTR_MAX,
};

const char *instr_name(enum fh_instruction_kind kind);

/** One instruction in bytecode */
struct fh_instruction_s {
  /** What is the meaning of data? */
  enum fh_instruction_kind kind;
  /** Data word */
  uint32_t data;
};

#define INSTR_SIZE (sizeof(struct fh_instruction_s))

_Static_assert(sizeof(struct fh_instruction_s) % 4 == 0, "Instruction struct is aligned");

/** Forth runtime major state */
enum fh_state {
  /** Interactive interpret mode */
  FH_STATE_INTERPRET = 0,
  /** Compiling */
  FH_STATE_COMPILE,
  /** Quit from RUN to interpret */
  FH_STATE_QUIT,
  /** Shutting down the runtime */
  FH_STATE_SHUTDOWN,
  FH_STATE_MAX,
};

/** Forth runtime minor state */
enum fh_substate {
  FH_SUBSTATE_NONE = 0,
  FH_SUBSTATE_PAREN_COMMENT,
  FH_SUBSTATE_LINE_COMMENT,
  FH_SUBSTATE_EXIT,
  FH_SUBSTATE_SKIP_IF,
  FH_SUBSTATE_MAX,
};

extern const char *substatenames[FH_SUBSTATE_MAX];

/** Marks a dictionary entry that is a word */
#define WORDFLAG_WORD      0x01
/** Indicates that this is a built-in instruction and not a word call */
#define WORDFLAG_BUILTIN   0x02
/** Indicates that this instruction should always be treated as interpreted */
#define WORDFLAG_IMMEDIATE 0x04
/** Variable or value stored in the dictionary */
#define WORDFLAG_VARIABLE  0x08
/** Constant with a value assigned */
#define WORDFLAG_CONSTANT  0x10
/** Something CREATEd. When executed, put the data field address on stack */
#define WORDFLAG_CREATED  0x20

/** Word struct as they are stored in the dictionary */
struct fh_word_s {
  /**
   * Start address in case of user words, or param for builtins.
   * Param must be the first for convenience in variable code!
   */
  uint32_t param;

  /**
   * Handler function.
   * Builtin functions use pre-defined native handlers.
   * User words use a shared handler that executes compiled
   * bytecode at 'start' address of the compile-memory area.
   */
  word_exec_t handler;

  /** Word flags, using WORDFLAG_ defines */
  uint32_t flags;

  /** Linked list pointer to previous word */
  uint32_t previous;

  /** Word name */
  char name[MAX_NAME_LEN]; // XXX this wastes RAM!
};

#define DICTWORD_SIZE sizeof(struct fh_word_s)

/**
 * Forth runtime instance - state variables and memory areas.
 *
 * Some memory areas, such as the dict or heap, could be moved
 * to a shared pointer if multi-threading and synchronization is added.
 */
struct fh_thread_s {
  // TODO stacks could live on heap too and share space with some other structures

  /** Data stack */
  uint32_t data_stack[DATA_STACK_DEPTH];
  size_t data_stack_top;
  size_t data_stack_hwm;

  /** Return stack */
  uint32_t return_stack[RETURN_STACK_DEPTH];
  size_t return_stack_top;
  size_t return_stack_hwm;

  /** Data buffer used for everything */
  uint8_t heap[HEAP_SIZE];
  size_t here;

  /** Pointer into the compile buffer for execution */
  uint32_t execptr;
  /** Address of the last dict word */
  uint32_t dict_last;

  /** Pictured numeric output buffer write cursor (used for prepend) */
  uint32_t pictnumptr;

  /** Input buffer parse position */
  uint32_t inputptr;
  /** Input buffer total content size */
  uint32_t inputlen;

  /** Forth state */
  enum fh_state state;

  /** Forth sub-state */
  enum fh_substate substate;

  /** The numeric base register */
  uint32_t base;

  /** Loop variable I */
  uint32_t loop_i;

  /** Loop variable J */
  uint32_t loop_j;

  /** Nesting level of [if] */
  uint32_t parse_if_level;
  
  bool executing_compiled;
};

enum fh_error fh_loop_nest(struct fh_thread_s *fh, uint32_t indexvalue);

enum fh_error fh_loop_unnest(struct fh_thread_s *fh);

enum fh_error fh_add_word(const struct fh_word_s *w, struct fh_thread_s *fh);

void fh_setstate(struct fh_thread_s *fh, enum fh_state state, enum fh_substate substate);

void fh_setsubstate(struct fh_thread_s *fh, enum fh_substate substate);

enum fh_error w_user_word(struct fh_thread_s *fh, const struct fh_word_s *w);

enum fh_error fh_postpone_word(
    struct fh_thread_s *fh,
    const char *name,
    size_t wordlen
);

/** Show disassembly of a dictionary word */
enum fh_error fh_see_word(
    struct fh_thread_s *fh,
    const char *name,
    size_t wordlen
);

/**
 * Execute a dictionary word from a definition stored at the given address
 * @param fh
 * @param addr
 * @return
 */
enum fh_error fh_handle_word(struct fh_thread_s *fh, uint32_t addr);

/**
 * Find a word in the dict
 *
 * @param fh
 * @param name - name, may be NUL terminated
 * @param wordlen - length, use 0 for strlen
 * @param addr_out the word address is output here, if given
 * @return success
 */
enum fh_error fh_find_word(struct fh_thread_s *fh, const char *name, size_t wordlen, uint32_t *addr_out);

enum fh_error fh_init(struct fh_thread_s *fh);

enum fh_error fh_process_line(struct fh_thread_s *fh, const char *linebuf, size_t len);

static inline uint32_t word_addr(struct fh_thread_s *fh, const struct fh_word_s *w) {
  return (uint32_t) ((void*)w - (void*)&fh->heap[0]);
}

#endif //FORTH_FH_RUNTIME_H