#include <ctype.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>

#define ARR_LEN(X) (sizeof(X) / sizeof(X[0]))

typedef enum {
  STATE_START,
  STATE_INVALID,
  STATE_KEY,
  STATE_STRING,
  STATE_KEY_END,
  STATE_END,
} states;

typedef states (*state_handler)(char input);

states handle_start(char input);
states handle_key(char input);
states handle_string(char input);
states handle_key_end(char input);

states state_machine(states current, char input);

bool check_input(const char *text);

// clang-format off
const char *inputs[] = {
	"",
	"{\"kjehu efhkwejhf wkehjf iyg\"}",
	"{",
	"}",
	"{\"lkhefhkjhefhjjrj}",
	"{jhejhuef hkwehj fwe}",
	"{'wuy iygef'}",
	"{\"hwekhewf'}",
};
// clang-format on

int main(int argc, char *argv[]) {
  for (int i = 0; i < ARR_LEN(inputs); ++i) {
    printf("%32s is %s\n", inputs[i],
           check_input(inputs[i]) ? "VALID" : "INVALID");
  }

  return EXIT_SUCCESS;
}

bool check_input(const char *text) {
  states current = STATE_START;

  for (const char *c = &(text[0]); *c != '\0'; ++c) {
    current = state_machine(current, *c);
  }

  return current == STATE_END;
}

states state_machine(states current, char input) {
  switch (current) {
  case STATE_START:
    return handle_start(input);
  case STATE_KEY:
    return handle_key(input);
  case STATE_STRING:
    return handle_string(input);
  case STATE_KEY_END:
    return handle_key_end(input);
  case STATE_INVALID:
  case STATE_END:
    return current;
  }
}

states handle_start(char input) {
  if (isspace(input)) {
    return STATE_START;
  } else if (input == '{') {
    return STATE_KEY;
  }

  return STATE_INVALID;
}

states handle_key(char input) {
  if (isspace(input)) {
    return STATE_KEY;
  } else if (input == '"') {
    return STATE_STRING;
  }

  return STATE_INVALID;
}

states handle_string(char input) {
  if (input == '"') {
    return STATE_KEY_END;
  }

  return STATE_STRING;
}

states handle_key_end(char input) {
  if (input == '}') {
    return STATE_END;
  }

  return STATE_INVALID;
}