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

struct stack{
    char data[100];
    int size;
}stack;

///add bracket to stack and increment size

void push(char ch){
    if(stack.size < 100){
        stack.size++;
        stack.data[stack.size] = ch;
    }
    else
        exit(0);
}

///if i have opening bracket in stack, then decrement size

void pop(){
    if(stack.size >= 0)
        stack.size--;
    else 
        exit(0);
}

///compare brackets

bool find_pair(char a, char b){
    if(a == '(' && b == ')') 
        return true;
    if(a == '{' && b == '}')
        return true;
    if(a == '<' && b == '>')
        return true;
    if(a == '[' && b == ']')
        return true;

    return false;
}

///function to find right pair

char right_pair(char a){
    char b;
    if(a == '(')
        b = ')';
    if(a == '{')
        b = '}';
    if(a == '[')
        b = ']';
    if(a == '<')
        b = '>';

    return b;    
}

///find the last opening bracket in the stack

char gettop(){
    return stack.data[stack.size];
}

int main(){
    
    
    char line[100];
    stack.size = -1;

    printf("Read: ");
    char *x = fgets(line, 100, stdin);
    printf("%s", line);

    int l = strlen(line);
    int i, j = -1, f = -1;;
    char *o_bracket = calloc(l, sizeof(char));
    char *c_bracket = calloc(l, sizeof(char));
     
    for(i = 0; i < l; i++){
        if(line[i] == '{' || line[i] == '(' || line[i] == '[' || line[i] == '<'){
            push(line[i]);
            j++;
            f++;
            o_bracket[j] = gettop();                   //get opening bracket from the stack
            c_bracket[f] = right_pair(o_bracket[j]);   //get closing bracket 
        }
        if(line[i] == '}' || line[i] == ')' || line[i] == ']' || line[i] == '>'){

            if(stack.size == -1){                      //if there is no opening bracket in the stack
                printf("Unexpected closing bracket %c in %d\n", line[i], i);
                return 0; 

            }
            else if(!find_pair(gettop(), line[i])){    //if there is another closing bracket 
                printf("Crossed bracket %c in %d, expected %c \n", line[i], i, c_bracket[f]);
                return 0;            
            }
            else{
                 c_bracket[f] = 0;                     //if closing bracket is correct then reducee array
                 f--;                                  //if i didn't find a correct bracket, then keep it in the array c_bracket
                 pop();
            }
        }
    }
   
    int begin = 0;
    int end = strlen(c_bracket);
    int temp;

    //now i have all missing closing brackets in array
 
    //flip array
    while(begin < end){
        temp = c_bracket[begin];
        c_bracket[begin++] = c_bracket[--end];
        c_bracket[end] = temp;
    }

    //if program pop all opening brackets from the stack, then stack size must be -1;
    if(stack.size == -1){
        printf("All brackets OK\n");
    }
    //if no, then program didn't find closing bracket
    else {
        printf("Missing closing brackets: %s\n", c_bracket);        
    }

    free(o_bracket);
    free(c_bracket);
    
    return 0;
}