// Buffer.h

#include <vector>
#include <string>

class Buffer
{
public:
    void display() const;
    void erase();
    const std::string & get_file_name() const { return file_name; }
    void insert(const std::string & new_line);
    void move_to_next_line();
    void move_to_previous_line();
    bool open(const std::string & new_file_name);
    bool save(const std::string & new_file_name);
    void set_window_height(int h) { window_height = h; }

private:
    std::vector<std::string> v_lines;
    int ix_current_line = 0;
    int ix_top_line = 0;
    std::string file_name;
    int window_height;
};

inline void Buffer::erase()
{
    if (ix_current_line < v_lines.size())
        v_lines.erase(v_lines.begin() + ix_current_line);
}

inline void Buffer::insert(const std::string & new_line)
{
    v_lines.insert(v_lines.begin() + ix_current_line, new_line);
    move_to_next_line();
}

inline void Buffer::move_to_next_line()
{
    if (ix_current_line < v_lines.size()) {
        ++ix_current_line;
        // check if window needs to be scrolled down
        if (ix_current_line >= ix_top_line + window_height)
            ++ix_top_line;
    }
}

inline void Buffer::move_to_previous_line()
{
    if (ix_current_line > 0) {
        --ix_current_line;
        // check if window needs to be scrolled up
        if (ix_current_line < ix_top_line)
            --ix_top_line;
    }
}