#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

typedef struct {
    char* arr;
    size_t size;
    size_t capacity;
} Vec8_t;

Vec8_t create(Vec8_t* input) {
    Vec8_t vec = { .arr = nullptr, .size = 0, .capacity = 4 };
    if(input == nullptr) {
        vec.arr = calloc(vec.capacity, sizeof(char));
        return vec;
    }
    if (input->size > 0) {
        vec.size = input->size + 1;
    }
    if (input->capacity >= vec.capacity) {
        vec.capacity = 2 * input->capacity;
    }
    vec.arr = calloc(vec.capacity, sizeof(char));
    return vec;
}

void delete(Vec8_t* vec) {
    if (vec->arr != nullptr) free(vec->arr);
    vec->arr = nullptr;
}

char at(Vec8_t* vec, int idx) {
    if (vec == nullptr) return -2;
    if (vec->arr == nullptr) return -3;
    if (vec->size <= idx) return -4;
    if (vec != nullptr && vec->arr != nullptr && vec->size > idx) {
        return vec->arr[idx];
    }
    return -1;
}

int begin(Vec8_t* vec) {
    if (vec != nullptr && vec->arr != nullptr && vec->size > 0) return 0;
    return -1;
}

int end(Vec8_t* vec) {
    if (vec != nullptr && vec->arr != nullptr && vec->size > 0) return (int)(vec->size - 1);
    return -1;
}

char front(Vec8_t* vec) {
    return at(vec, 0);
}

char back(Vec8_t* vec) {
    if (vec) return at(vec, (int)vec->size - 1);
    return -1;
}

Vec8_t add_back(Vec8_t* vec, char val) {
    Vec8_t ret = { .arr = nullptr, .capacity = 0, .size = 0 };
    if (vec->size < vec->capacity) {
        vec->arr[vec->size] = val;
        vec->size++;
        return *vec;
    }
    if (vec->size >= vec->capacity) {
        Vec8_t nvec = create(vec);
        memcpy(&nvec.arr[0], &vec->arr[0], vec->size * sizeof(char));
        if (nvec.arr && (nvec.size > 0 || nvec.size > vec->size)) {
            nvec.arr[vec->size] = val;
        }
        free(vec->arr);
        return nvec;
    }
    return ret;
}

int tests_passed = 0;
int tests_failed = 0;
int test_num = 0;

void test(const char* name, int passed) {
    test_num++;
    if (passed) { 
        printf("[PASS] #%d: %s\n", test_num, name); 
        tests_passed++; 
    } else { 
        printf("[FAIL] #%d: %s\n", test_num, name); 
        tests_failed++; 
    }
}

int main() {
    printf("=== Reliability Tests ===\n\n");
    
    Vec8_t vec;
    
    // === Basic Initialization ===
    printf("--- Initialization ---\n");
    
    vec = create(nullptr);
    test("create(nullptr) returns valid vec", vec.arr != nullptr);
    test("create(nullptr) capacity = 4", vec.capacity == 4);
    test("create(nullptr) size = 0", vec.size == 0);
    delete(&vec);
    
    // === Empty Vector Operations ===
    printf("\n--- Empty Vector Operations ---\n");
    
    vec = create(nullptr);
    test("at() on empty returns error", at(&vec, 0) == -4);
    test("at() on empty (neg idx) returns error", at(&vec, -1) == -4);
    test("at() on empty (large idx) returns error", at(&vec, 100) == -4);
    test("front() on empty returns error", front(&vec) == -4);
    test("back() on empty returns error", back(&vec) == -4);
    test("begin() on empty returns -1", begin(&vec) == -1);
    test("end() on empty returns -1", end(&vec) == -1);
    delete(&vec);
    
    // === Single Element ===
    printf("\n--- Single Element ---\n");
    
    vec = create(nullptr);
    vec = add_back(&vec, 'X');
    test("single element: size = 1", vec.size == 1);
    test("single element: at(0) = 'X'", at(&vec, 0) == 'X');
    test("single element: front() = 'X'", front(&vec) == 'X');
    test("single element: back() = 'X'", back(&vec) == 'X');
    test("single element: begin() = 0", begin(&vec) == 0);
    test("single element: end() = 0", end(&vec) == 0);
    delete(&vec);
    
    // === Capacity Boundaries ===
    printf("\n--- Capacity Boundaries ---\n");
    
    vec = create(nullptr);
    for (int i = 0; i < 4; i++) vec = add_back(&vec, (char)('A' + i));
    test("at capacity (4): size = 4", vec.size == 4);
    test("at capacity (4): capacity = 4", vec.capacity == 4);
    
    vec = add_back(&vec, 'E');
    test("at capacity (4): size = 5", vec.size == 5);
    test("at capacity (4): capacity doubled = 8", vec.capacity == 8);
    test("at capacity (4): arr[4] = 'E'", vec.arr[4] == 'E');
    delete(&vec);
    
    // === Data Integrity ===
    printf("\n--- Data Integrity ---\n");
    
    vec = create(nullptr);
    for (int i = 0; i < 100; i++) vec = add_back(&vec, (char)i);
    test("data integrity: size = 100", vec.size == 100);
    for (int i = 0; i < 100; i++) {
        test("data integrity: arr[i] = i", vec.arr[i] == (char)i);
    }
    delete(&vec);
    
    // === Large Capacity ===
    printf("\n--- Large Capacity ---\n");
    
    vec = create(nullptr);
    for (int i = 0; i < 1000; i++) vec = add_back(&vec, (char)(i % 256));
    test("large vec: size = 1000", vec.size == 1000);
    test("large vec: capacity >= size", vec.capacity >= 1000);
    test("large vec: first preserved", vec.arr[0] == 0);
    test("large vec: last preserved", vec.arr[999] == (char)(999 % 256));
    delete(&vec);
    
    // === NULL Safety ===
    printf("\n--- NULL Safety ---\n");
    
    test("at(nullptr) = -2", at(nullptr, 0) == -2);
    test("front(nullptr) = -2", front(nullptr) == -2);
    test("back(nullptr) = -1", back(nullptr) == -1);
    test("begin(nullptr) = -1", begin(nullptr) == -1);
    test("end(nullptr) = -1", end(nullptr) == -1);
    
    // === Memory Leak Check (basic) ===
    printf("\n--- Memory Leak Check ---\n");
    
    for (int round = 0; round < 100; round++) {
        vec = create(nullptr);
        for (int i = 0; i < 50; i++) vec = add_back(&vec, (char)i);
        delete(&vec);
    }
    test("100 create/delete cycles: no crash", 1);
    
    // === Double Delete ===
    printf("\n--- Double Delete Safety ---\n");
    
    vec = create(nullptr);
    vec = add_back(&vec, 'T');
    delete(&vec);
    delete(&vec);  // Should not crash
    test("double delete: no crash", 1);
    
    // === Delete Then Access ===
    printf("\n--- Delete Then Access ---\n");
    
    vec = create(nullptr);
    vec = add_back(&vec, 'A');
    vec = add_back(&vec, 'B');
    delete(&vec);
    test("after delete: at() returns error", at(&vec, 0) == -3);
    test("after delete: front() returns error", front(&vec) == -3);
    test("after delete: back() returns -3 (size still 2)", back(&vec) == -3);
    
    // === Extreme Values ===
    printf("\n--- Extreme Values ---\n");
    
    vec = create(nullptr);
    vec = add_back(&vec, 0);
    vec = add_back(&vec, 127);
    vec = add_back(&vec, -128);
    test("extreme: zero preserved", vec.arr[0] == 0);
    test("extreme: max char preserved", vec.arr[1] == 127);
    test("extreme: min char preserved", vec.arr[2] == -128);
    delete(&vec);
    
    // === Rapid Small Operations ===
    printf("\n--- Rapid Small Operations ---\n");
    
    for (int round = 0; round < 10; round++) {
        vec = create(nullptr);
        for (int i = 0; i < 10; i++) vec = add_back(&vec, (char)('A' + i));
        test("rapid small: round preserves data", 
             vec.arr[0] == 'A' && vec.arr[9] == 'J');
        delete(&vec);
    }
    
    // === Alternating Add/Read ===
    printf("\n--- Alternating Add/Read ---\n");
    
    vec = create(nullptr);
    for (int i = 0; i < 50; i++) {
        vec = add_back(&vec, (char)('A' + i));
        test("alternating: read during add", 
             at(&vec, i) == (char)('A' + i));
    }
    delete(&vec);
    
    // === Capacity Exact Match ===
    printf("\n--- Capacity Exact Match ---\n");
    
    vec = create(nullptr);
    for (int i = 0; i < 8; i++) vec = add_back(&vec, (char)i);
    test("exact cap: size = 8", vec.size == 8);
    test("exact cap: capacity = 8", vec.capacity == 8);
    vec = add_back(&vec, 'X');
    test("exact cap +1: size = 9", vec.size == 9);
    test("exact cap +1: capacity = 16", vec.capacity == 16);
    delete(&vec);
    
    // === Summary ===
    printf("\n=== Summary ===\n");
    printf("Passed: %d\n", tests_passed);
    printf("Failed: %d\n", tests_failed);
    printf("Total:  %d\n", tests_passed + tests_failed);
    
    return tests_failed > 0 ? 1 : 0;
}