tape.cpp

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#include "tape.hpp"
 
#include <algorithm>
#include <ranges>
 
Tape::Tape(String str) noexcept(false) : head_pos_(0)
{
    for (auto [idx, symbol] : std::views::enumerate(str))
    {
        // Guard against integer overflow on high-cardinality initialization streams
        if (idx > static_cast<std::size_t>(std::numeric_limits<int>::max()))
        {
            throw std::out_of_range(
                "Input string length exceeds maximum signed integer capacity of the tape."
            );
        }
        this->cells_[static_cast<int>(idx)] = symbol;
    }
}
 
Symbol Tape::read() const noexcept
{
    auto it = this->cells_.find(this->head_pos_);
    if (it == this->cells_.end())
    {
        return Symbol(kBlank);
    }
    return it->second;
}
 
void Tape::print(std::ostream &os) const noexcept
{
    os << "Tape: ";
 
    // To prevent giant memory printing overhead when head is far away,
    // visible window is clamped around the actual data limits and head position.
    int min_idx = this->head_pos_;
    int max_idx = this->head_pos_;
 
    // If there is data, expand limits to show the whole string
    if (!this->cells_.empty())
    {
        min_idx = std::min(min_idx, this->cells_.begin()->first);
        max_idx = std::max(max_idx, this->cells_.rbegin()->first);
    }
 
    // Optional safety padding to see at least 2 blank cells around boundaries
    min_idx = std::min(min_idx, this->head_pos_ - 2);
    max_idx = std::max(max_idx, this->head_pos_ + 2);
 
    // Row 1: Render structural tape cell elements sequentially
    for (int i = min_idx; i <= max_idx; ++i)
    {
        auto it = this->cells_.find(i);
        Symbol s = (it != this->cells_.end()) ? it->second : Symbol(kBlank);
        os << "| " << s << " ";
    }
    os << "|\n";
 
    // Row 2: Render alignment tracks and drop the head tracking marker (^)
    os << "      "; // Absolute padding to sync with the "Tape: " prefix layout
    for (int i = min_idx; i <= max_idx; ++i)
    {
        if (i == this->head_pos_)
        {
            os << "  ^ ";
            break; // Break execution early: markers past the head track are non-constructive
        }
        os << "    "; // Pad alignment spacing proportional to cell size metrics ("| x ")
    }
    os << "\n";
}
 
std::ostream &operator<<(std::ostream &os, const Tape &tape) noexcept
{
    tape.print(os);
    return os;
}