#ifndef BU_PARSER_HG
#define BU_PARSER_HG

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "tree.h"

/* PRODUCTION RULES
  <expr> ::= <expr> <binary_op> <expr> | <unary_op> <expr> | "(" <expr> ")" | <var>
  <binary_op> ::= "*" | "+"
  <unary_op> ::= "!"
  <var> ::= r#[a-z]
 */

enum parser_state {
  PARSER_ERR = -1,
  PARSER_READY = 0,
  PARSER_ACCEPT,
};

enum token_id {
  TOKEN_INVALID = 0,
  TOKEN_BINARY_OPERATOR,
  TOKEN_UNARY_OPERATOR,
  TOKEN_VARIABLE,
  TOKEN_OPEN_PAREN,
  TOKEN_CLOSE_PAREN,
  TOKEN_EOS,
  TOKEN_OOB,
  TOKEN_MAX,
};

enum stackmember_id {
  // all token ids
  STACKMEMBER_INVALID = TOKEN_INVALID,
  // ...
  STACKMEMBER_EXPR = TOKEN_MAX + 1,
  STACKMEMBER_MAX,
};

struct chartoken { enum token_id id; char c; };
typedef struct chartoken(*lexer_fn)(void*);

struct stackmember {
  enum stackmember_id id;
  union {
    char terminal;
    node *expr;
  };
};

struct expr_parser {
  lexer_fn lex;
  void *lex_data;
  // since tokens are 1-to-1 maps to chars,
  // we're fine making this type assumption
  struct chartoken lahead;
  enum parser_state st;
  // (and 1024 oughta be enough, FIXME if not)
  struct stackmember stack[1024];
  size_t stack_idx;
};

struct expr_parser expr_parser_init(lexer_fn src, void* lex_data);
void expr_parser_finish(struct expr_parser *ep);
int expr_parser_run(struct expr_parser *ep);
void expr_parser_debug_print(FILE *stream, struct expr_parser *ep);

#endif // BU_PARSER_HG