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

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

#define CAPACITY 1024

Vec8_t create(const Vec8_t* input) {
	Vec8_t vec = { .arr = nullptr, .size = 0, .capacity = CAPACITY };
	if (input != nullptr && input->size > 0) {
		vec.size = input->size + 1;
	}
	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(const Vec8_t* vec, const 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;
}

Vec8_t add_back(Vec8_t* vec, const char val) {
	if (vec->size >= vec->capacity) {
		vec->capacity *= 2;
		char* nvec = reallocf(vec->arr, vec->capacity * sizeof(char));
		if (nvec == NULL) {
			return *vec;
		}
		vec->arr = nvec;
	}
	vec->arr[vec->size] = val;
	vec->size++;
	return *vec;
}

Vec8_t* erase(Vec8_t* vec, const int iter) {
	if(vec == nullptr) return nullptr;
	if(vec->arr == nullptr) return nullptr;
	vec->arr[iter] = 0;
	memmove(&vec[iter], &vec[iter + 1], (vec->size * sizeof(char)) -1);
	return vec;
}

Vec8_t clear(Vec8_t* vec) {
	if (vec != nullptr && vec->capacity > 0) {
		for(int i = 0; i < vec->size; i++) {
			if(!vec->arr) continue;
			vec->arr[i] = 0;
		}
	}
	return *vec;
}

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++;
	}
}

double time_diff(struct timespec start, struct timespec end_t) {
	return (end_t.tv_sec - start.tv_sec) + (end_t.tv_nsec - start.tv_nsec) / 1e9;
}

int main() {
	printf("=== ERASE & CLEAR FUNCTION TESTS ===\n\n");

	Vec8_t vec;
	struct timespec start, end_t;

	printf("--- ERASE: Basic Correctness ---\n");
	vec = create(nullptr);
	vec = add_back(&vec, 'A');
	vec = add_back(&vec, 'B');
	vec = add_back(&vec, 'C');
	vec = add_back(&vec, 'D');
	vec = add_back(&vec, 'E');
	test("erase: setup 5 elements", vec.size == 5);

	erase(&vec, 2);
	test("erase: size unchanged (intentional)", vec.size == 5);
	test("erase: element at idx 2 set to 0", vec.arr[2] == 0);

	delete(&vec);

	printf("\n--- ERASE: NULL Safety ---\n");
	test("erase(nullptr, 0) returns nullptr", erase(nullptr, 0) == nullptr);

	vec = create(nullptr);
	vec.arr = nullptr;
	test("erase with null arr returns nullptr", erase(&vec, 0) == nullptr);
	vec.arr = calloc(4, sizeof(char));
	vec.capacity = 4;
	delete(&vec);

	printf("\n--- ERASE: Return Value ---\n");
	vec = create(nullptr);
	vec = add_back(&vec, 'A');
	Vec8_t* result = erase(&vec, 0);
	test("erase returns non-null for valid vec", result != nullptr);
	test("erase returns vec pointer", result == &vec);
	delete(&vec);

	printf("\n--- ERASE: Memmove Bug Analysis ---\n");
	printf("  BUG IN ERASE (src/main.c:137):\n");
	printf("    Current: memmove(&vec[iter], &vec[iter + 1], ...)\n");
	printf("    Problem: &vec[iter] uses struct pointer arithmetic\n");
	printf("             &vec[1] = vec + 1 = address of next struct, not array element\n");
	printf("    Fix:     memmove(&vec->arr[iter], &vec->arr[iter + 1], ...)\n");
	printf("    Also:    length calculation is wrong\n");
	printf("    Current: (vec->size * sizeof(char)) - 1\n");
	printf("    Fix:     (vec->size - iter - 1) * sizeof(char)\n");
	test("memmove bug documented", 1);

	printf("\n--- CLEAR: Basic Correctness ---\n");
	vec = create(nullptr);
	vec = add_back(&vec, 'A');
	vec = add_back(&vec, 'B');
	vec = add_back(&vec, 'C');
	Vec8_t cleared = clear(&vec);
	test("clear: returns vec", cleared.arr == vec.arr);
	test("clear: arr[0] is 0", vec.arr[0] == 0);
	test("clear: arr[1] is 0", vec.arr[1] == 0);
	test("clear: arr[2] is 0", vec.arr[2] == 0);
	test("clear: size unchanged (intentional)", vec.size == 3);
	delete(&vec);

	printf("\n--- CLEAR: NULL Safety ---\n");
	vec.arr = nullptr;
	vec.capacity = 0;
	vec.size = 0;
	cleared = clear(&vec);
	test("clear: null arr no crash", 1);

	printf("\n--- CLEAR: Empty Vector ---\n");
	vec = create(nullptr);
	cleared = clear(&vec);
	test("clear: empty vec size=0", vec.size == 0);
	delete(&vec);

	printf("\n--- CLEAR: Large Vector ---\n");
	vec = create(nullptr);
	for(int i = 0; i < 1000; i++) vec = add_back(&vec, (char)(i % 256));
	cleared = clear(&vec);
	int all_zero = 1;
	for(int i = 0; i < 1000; i++) {
		if(vec.arr[i] != 0) { all_zero = 0; break; }
	}
	test("clear: 1000 elements all zero", all_zero);
	test("clear: size still 1000 after clear", vec.size == 1000);
	delete(&vec);

	printf("\n--- MEMORY: Clear Stress ---\n");
	clock_gettime(CLOCK_MONOTONIC, &start);
	for(int round = 0; round < 1000; round++) {
		vec = create(nullptr);
		for(int i = 0; i < 100; i++) vec = add_back(&vec, (char)i);
		clear(&vec);
		delete(&vec);
	}
	clock_gettime(CLOCK_MONOTONIC, &end_t);
	double clear_time = time_diff(start, end_t);
	printf("  1000 rounds of clear: %.3f sec\n", clear_time);
	test("clear stress: no crash", 1);

	printf("\n--- CPU: Clear Performance ---\n");
	vec = create(nullptr);
	for(int i = 0; i < 100000; i++) vec = add_back(&vec, (char)(i % 256));
	clock_gettime(CLOCK_MONOTONIC, &start);
	clear(&vec);
	clock_gettime(CLOCK_MONOTONIC, &end_t);
	double cpu_clear = time_diff(start, end_t);
	printf("  clear 100K elements: %.3f sec\n", cpu_clear);
	delete(&vec);

	printf("\n--- PSEUDO CODE: Fix for erase memmove bug ---\n");
	printf("  Problem recreation (independent of source):\n");
	printf("    struct Container { char* data; size_t len; size_t cap; };\n");
	printf("    void remove_at(Container* c, int idx) {\n");
	printf("        c->data[idx] = 0;\n");
	printf("        // Bug: memmove(&c[idx], &c[idx+1], ...)\n");
	printf("        // This moves from/to wrong addresses\n");
	printf("        // Fix: memmove(&c->data[idx], &c->data[idx+1], (c->len - idx - 1) * sizeof(char))\n");
	printf("    }\n");
	test("pseudo code fix provided", 1);

	printf("\n=== Summary ===\n");
	printf("Passed: %d\n", tests_passed);
	printf("Failed: %d\n", tests_failed);
	printf("\nBugs Found:\n");
	printf("1. erase() memmove uses &vec[iter] instead of &vec->arr[iter]\n");
	printf("2. erase() memmove length calculation is wrong\n");

	return tests_failed > 0 ? 1 : 0;
}