#pragma once

#include <cstddef>

namespace fgc {

// Viewport arithmetic for the scrollable TUI panes. Pure integer math with no
// FTXUI types, so it lives in fgc_core and is unit-testable without a terminal -
// mirroring UiSnapshot's formatting helpers.
//
// The model is a line-anchored viewport: `top` is the first body LINE we want
// visible. Heights come from the previous frame's measurements, so every entry
// point has to tolerate `view_h == 0` (nothing measured yet) without dividing by
// zero or handing back a position the renderer can't honour.

// Largest valid `top` for a body of `content_h` lines in a `view_h` window.
// 0 when it all fits, and 0 while the view is still unmeasured.
int scrollMax(int content_h, int view_h);

int scrollClamp(int top, int content_h, int view_h);

// One line per keypress; `delta` is +/-1.
int scrollBy(int top, int delta, int content_h, int view_h);

// A screenful less two lines of overlap, so the eye keeps its place. `dir` is
// +/-1; the step is at least 1 even in a one-line pane.
int scrollPage(int top, int dir, int content_h, int view_h);

// Rows per column for a wrapped grid. Short grids keep a compact multi-column
// look (at least `min_rows` per column); past `max_cols` columns the grid grows
// DOWNWARD instead of off the right edge, where vertical scrolling can reach it.
std::size_t gridRowsPerColumn(std::size_t item_count, std::size_t max_cols, std::size_t min_rows);

}  // namespace fgc