pl/include/prelude/string.hpp

#pragma once
#include <cstddef>
#include <cstdio>
#include <cassert>
#include <cstdarg>
#include <cstring>
#include <cstdlib>
#include <utility>
#include <functional>

template<typename T>
struct View
{
    size_t size;
    T* data;     // owns its memory

public:
    View() : size(0), data(nullptr) {}

    // Deep copy constructor
    View(const T* src, size_t count) : size(count)
    {
        if (count == 0) { data = nullptr; return; }

        data = static_cast<T*>(::operator new[](count * sizeof(T)));
        for (size_t i = 0; i < count; ++i)
            new (&data[i]) T(src[i]);   // copy-construct
    }

    // Copy constructor
    View(const View& other) : View(other.data, other.size) {}

    // Move constructor
    View(View&& other) noexcept : size(other.size), data(other.data)
    {
        other.size = 0;
        other.data = nullptr;
    }

    View &operator=(const View &other)
    {
        if (this != &other)
        {
            // free old memory
            for (size_t i = 0; i < size; ++i)
                data[i].~T();
            ::operator delete[](data);

            // deep copy
            size = other.size;
            data = static_cast<T *>(::operator new[](size * sizeof(T)));
            for (size_t i = 0; i < size; ++i)
                new (&data[i]) T(other.data[i]);
        }
        return *this;
    }

    // Destructor
    ~View()
    {
        for (size_t i = 0; i < size; ++i)
            data[i].~T();
        ::operator delete[](data);
    }

    const T* begin() const { return data; }
    const T* end()   const { return data + size; }
};


class StringView final : public View<char>
{
public:
    StringView() : View<char>() {}

    // Construct from C-string — deep copy, including null terminator
    StringView(const char* s)
        : View<char>(s, strlen(s) + 1) {}

    // Construct from View<char> — ensure null termination
    StringView(const View<char>& v)
        : View<char>(v)
    {
        if (size == 0 || data[size - 1] != '\0')
        {
            // Reallocate and append null terminator
            size_t newSize = size + 1;
            char* newData = static_cast<char*>(::operator new[](newSize * sizeof(char)));

            for (size_t i = 0; i < size; ++i)
                newData[i] = data[i];

            newData[newSize - 1] = '\0';

            // destroy old
            // for (size_t i = 0; i < size; ++i)
            //     data[i].~char();
            ::operator delete[](data);

            data = newData;
            size = newSize;
        }
    }

    const char* c_str() const { return data; }
};

namespace std
{
    template<>
    struct hash<StringView>
    {
        size_t operator()(const StringView& sv) const noexcept
        {
            // FNV-1a hash (simple, fast, good enough)
            constexpr size_t fnv_offset = 14695981039346656037ull;
            constexpr size_t fnv_prime  = 1099511628211ull;

            size_t hash = fnv_offset;

            // Exclude the null terminator if present
            size_t len = (sv.size > 0 && sv.data[sv.size - 1] == '\0')
                         ? sv.size - 1
                         : sv.size;

            for (size_t i = 0; i < len; ++i)
            {
                hash ^= static_cast<unsigned char>(sv.data[i]);
                hash *= fnv_prime;
            }

            return hash;
        }
    };
}

inline bool operator==(const StringView& a, const StringView& b)
{
    // Sizes include null terminator; logical string length is size-1
    if (a.size != b.size) return false;
    if (a.size == 0) return true;
    return std::memcmp(a.data, b.data, a.size) == 0;
}

inline bool operator!=(const StringView& a, const StringView& b)
{
    return !(a == b);
}

template<typename T>
struct Builder
{
    size_t size = 0;
    size_t capacity = 8;
    T* data;

public:
    Builder()
    {
        data = static_cast<T*>(::operator new[](capacity * sizeof(T)));
    }

    ~Builder()
    {
        clear();
        ::operator delete[](data);
    }

protected:
    void grow(size_t newSize)
    {
        if (newSize <= capacity) return;

        size_t newCap = capacity;
        while (newCap < newSize)
            newCap += newCap / 2;

        T* newData = static_cast<T*>(::operator new[](newCap * sizeof(T)));

        // Move-construct into the new buffer
        for (size_t i = 0; i < size; ++i)
            new (&newData[i]) T(std::move(data[i]));

        // Destroy old items
        for (size_t i = 0; i < size; ++i)
            data[i].~T();

        ::operator delete[](data);

        data = newData;
        capacity = newCap;
    }

public:
    void Push(const T& value)
    {
        grow(size + 1);
        new (&data[size]) T(value);
        size++;
    }

    void Push(T&& value)
    {
        grow(size + 1);
        new (&data[size]) T(std::move(value));
        size++;
    }

    // Clear Builder storage but keep capacity
    void clear()
    {
        for (size_t i = 0; i < size; ++i)
            data[i].~T();
        size = 0;
    }

    // ALWAYS produce a deep-copied View
    View<T> view() const
    {
        return View<T>(data, size);
    }
};

// using StringBuilder = Builder<char>;

class StringBuilder final : public Builder<char>
{
public:
    StringBuilder() : Builder<char>() {}

    // Ensure there is room for `n` more characters (not counting terminator)
    void ensure_extra(size_t n)
    {
        // grow size + n (but not including terminator)
        this->grow(this->size + n);
    }

    // Append raw C string (WITHOUT copying terminator)
    void Extend(const char* str)
    {
        if (!str) return;

        size_t len = strlen(str);
        ensure_extra(len);

        for (size_t i = 0; i < len; ++i)
            this->Push(str[i]);
    }

    // Append a single char
    void Append(char c)
    {
        this->Push(c);
    }

    void AppendIndent(int indent) {
        grow(size + indent);
        memset(data + size, ' ', indent);
        size += indent;
    }

    void VAppendFormat(const char* fmt, va_list args)
    {
        // Make a copy because vsnprintf consumes the va_list
        va_list argsCopy;
        va_copy(argsCopy, args);

        int len = std::vsnprintf(nullptr, 0, fmt, argsCopy);
        va_end(argsCopy);

        if (len <= 0)
            return;

        this->grow(this->size + len + 1);

        std::vsnprintf(this->data + this->size, len + 1, fmt, args);
        this->size += len;
    }


    void AppendFormat(const char* fmt, ...)
    {
        va_list args;
        va_start(args, fmt);

        // 1) compute length (excluding terminator)
        va_list argsCopy;
        va_copy(argsCopy, args);
        int len = std::vsnprintf(nullptr, 0, fmt, argsCopy);
        va_end(argsCopy);

        if (len <= 0)
        {
            va_end(args);
            return;
        }

        // 2) reserve space
        this->grow(this->size + len + 1);

        // 3) write formatted string
        std::vsnprintf(this->data + this->size, len + 1, fmt, args);
        this->size += len;

        va_end(args);
    }

    // Return a null-terminated string pointer owned by builder
    const char* c_str()
    {
        // ensure space for terminator
        this->grow(this->size + 1);

        // add terminator (overwrite or place it at end)
        if (this->size == 0 || this->data[this->size - 1] != '\0')
        {
            // If already ended with \0, fine
            this->Push('\0');
        }
        return this->data;
    }

    // Produce a deep-copied StringView
    StringView view()
    {
        return StringView(this->c_str());
    }

    // streaming operators
    StringBuilder& operator<<(const char* s)
    {
        Extend(s);
        return *this;
    }

    StringBuilder& operator<<(const StringView& sv)
    {
        Extend(sv.c_str());
        return *this;
    }

    StringBuilder& operator<<(char c)
    {
        Append(c);
        return *this;
    }

    StringBuilder& operator<<(int v)
    {
        char buf[32];
        snprintf(buf, sizeof(buf), "%d", v);
        Extend(buf);
        return *this;
    }

    StringBuilder& operator<<(long v)
    {
        char buf[32];
        snprintf(buf, sizeof(buf), "%ld", v);
        Extend(buf);
        return *this;
    }

    StringBuilder& operator<<(unsigned int v)
    {
        char buf[32];
        snprintf(buf, sizeof(buf), "%d", v);
        Extend(buf);
        return *this;
    }
};