CPP-Queue/include/queue.h

#ifndef QUEUE_H
#define QUEUE_H

#include <cstdint>
#include <new>
#include <print>
#include <format>
#include <expected>

#define DEFAULT_QUEUE_SIZE 4

enum class QueueErr {
    ok,
    bad_alloc,
    empty,
};

template <typename T>
requires std::formattable<T, char>
class Queue {
private:
    uint64_t len;
    uint64_t cap;
    uint64_t head;
    uint64_t tail;
    T *data;
public:
    Queue();
    Queue(uint64_t size);

    ~Queue();

    QueueErr enqueue(T value);

    std::expected<T, QueueErr> peek();

    std::expected<T, QueueErr> dequeue();

    void display();
};

template <typename T>
requires std::formattable<T, char>
Queue<T>::Queue() {
    this->cap = 0;
    this->len = 0;
    this->head = 0;
    this->tail = 0;
    this->data = new T[DEFAULT_QUEUE_SIZE];
}

template <typename T>
requires std::formattable<T, char>
Queue<T>::Queue(uint64_t size) {
    this->cap = 0;
    this->len = 0;
    this->head = 0;
    this->tail = 0;
    this->data = new T[size];

}


template <typename T>
requires std::formattable<T, char>
QueueErr Queue<T>::enqueue(T value) {
    if (this->len >= this->cap) {
        uint64_t new_cap = this->cap * 2;
        T *tmp;

        try {
            T *tmp = new T[new_cap];
        } catch(const std::bad_alloc& e) {
            return QueueErr::bad_alloc;
        }

        for (uint64_t i = 0; i < this->len; i++) {
            uint64_t index = (this->tail) % this->cap;
            tmp[i] = this->data[index];
        }

        delete[] this->data;
        this->data = tmp;
        this->cap = new_cap;
        this->tail = 0;
        this->head = this->len;
    }

    this->data[this->head] = value;
    this->len++;
    this->head = (this->head + 1) % this->cap;
    return QueueErr::ok;
}

template <typename T>
requires std::formattable<T, char>
std::expected<T, QueueErr> Queue<T>::dequeue() {
    if (this->len == 0) {
        return std::unexpected(QueueErr::empty);
    }

    if (this->cap > DEFAULT_QUEUE_SIZE && this->cap / 4 > this->len) {
        uint64_t new_cap = this->cap / 2;
        if (new_cap < DEFAULT_QUEUE_SIZE) {
            new_cap = DEFAULT_QUEUE_SIZE;
        }

        T *tmp;
        try {
            tmp = new T[new_cap];
        } catch(const std::bad_alloc& e) {
            return std::unexpected(QueueErr::bad_alloc);
        }

        for (uint64_t i = 0; i < this->len; i++) {
            uint64_t index = (this->tail) % this->cap;
            tmp[i] = this->data[index];
        }

        delete[] this->data;
        this->data = tmp;
        this->cap = new_cap;
        this->tail = 0;
        this->head = this->len;

    }

    T out;
    out = this->data[this->tail];
    this->len--;
    this->tail = (this->tail + 1) % this->cap;

    return out;
}

template <typename T>
requires std::formattable<T, char>
std::expected<T, QueueErr> Queue<T>::peek() {
    if (this->len == 0) {
        return std::unexpected(QueueErr::empty);
    }

    T out;
    out = this->data[this->tail];
    this->len--;
    this->tail = (this->tail + 1) % this->cap;

    return out;
}
#endif // !QUEUE_H