#if !defined PREFIX
#   error("PREFIX")
#endif

#if !defined ITEM
#   error("ITEM")
#endif
#if !defined NAME
#   error("NAME")
#endif

#define FUNC(ACTION) PREFIX#_##ACTION


typedef struct NAME {
    ITEM* buffer;
    int capacity;
    ITEM* front;
    ITEM* back;
} NAME;

NAME FUNC(new)(int capacity){
    assert(capacity > 0);
    ITEM* buffer = (ITEM*)malloc(capacity*sizeof(ITEM));
    assert(buffer);
    NAME vector = { buffer, capacity, buffer, buffer};
    return vector;
}
void FUNC(delete)(NAME* vec){
    free(vec->buffer);
    vec->capacity = 0;
    vec->buffer = NULL;
    vec->front = NULL;
    vec->back = NULL;
}
void FUNC(as_queue)(NAME* vec){
    assert(vec);
    assert(vec->buffer);
    assert(vec->capacity > 0);
    vec->front = vec->buffer + vec->capacity/2;
    vec->back = vec->front + 1;
}
void FUNC(push_back)(NAME* vec, ITEM item){
    assert(vec);
    assert(vec->buffer);
    assert(vec->back);
    assert(vec->back < vec->buffer + vec->capacity);
    *vec->back = item;
    vec->back++;
}

ITEM FUNC(pop_back)(NAME* vec){
    assert(vec);
    assert(vec->buffer);
    assert(vec->back);
    assert(vec->back > vec->buffer);
    vec->back--;
    return *(vec->back + 1);
}

void FUNC(push_front)(NAME* vec, ITEM item){
    assert(vec);
    assert(vec->buffer);
    assert(vec->front);
    assert(vec->front > vec->buffer);
    vec->front--;
    *vec->front = item;
}

ITEM FUNC(pop_front)(NAME* vec){
    assert(vec);
    assert(vec->buffer);
    assert(vec->front);
    assert(vec->front < vec->buffer + vec->capacity);
    vec->front++;
    return *(vec->front - 1);
}

ITEM FUNC(get)(NAME* vec, int idx){
    assert(vec->front + idx < vec->buffer + vec->capacity);
    return *(vec->front + idx);
}

ITEM* FUNC(top)(NAME* vec){
    assert(vec);
    assert(vec->buffer);
    assert(vec->back);
    return vec->back-1;
}

#define FOR_EACH_IN_VECTOR(VEC, VAR, STMT)                               \
    { ITEM *__p##VAR, VAR;                                              \
        for(__p##VAR = (VEC)->front; __p##VAR < (VEC)->back; __p##VAR++){ \
            VAR = *__p##VAR;                                            \
            STMT;                                                       \
        }                                                               \
    }