retroglyph-core 0.5.0

//! Stateful terminal lifecycle and double-buffering.

use crate::backend::{Backend, Output};
use crate::event::Event;
use crate::grid::{Grid, Rect, Size};
use crate::surface::Surface;
use core::time::Duration;

/// A double-buffered terminal generic over a [`Backend`].
///
/// Owns the current and previous frame grids and the backend's lifecycle (resize, present,
/// events). Drawing itself goes entirely through [`Surface`]: see [`draw`](Self::draw) for the
/// common case (draw a frame, then present it) and [`surface`](Self::surface) for manual control
/// over presenting.
///
/// # Out-of-bounds drawing
///
/// [`Surface`] clips any write that falls outside its own area rather than panicking; see
/// [`Surface`]'s own "out-of-bounds drawing" documentation.
///
/// # Examples
///
/// ```
/// use retroglyph_core::backend::Headless;
/// use retroglyph_core::{Color, Terminal};
///
/// let mut term = Terminal::new(Headless::new(20, 5));
/// term.draw(|surface| {
///     surface.put((2, 1), '@', retroglyph_core::Style::new().fg(Color::GREEN));
/// })
/// .unwrap();
/// ```
pub struct Terminal<B: Backend> {
    current: Grid,
    previous: Grid,
    /// Single-layer scratch buffers used only when the backend does not
    /// composite layers itself. `present` flattens `current` into
    /// `flattened_current`, diffs it against `flattened_previous`, and sends the
    /// result. Unused (but allocated) for compositing backends.
    flattened_current: Grid,
    flattened_previous: Grid,
    backend: B,
    queued_event: Option<Event>,
    /// `true` when the flatten buffers no longer reflect the last frame sent to
    /// the backend (because the single-layer fast path bypassed them). The next
    /// multi-layer present clears `flattened_previous` first so it does a full
    /// redraw instead of diffing against stale data.
    flattened_stale: bool,
    /// Incremented every time [`present`](Self::present) is called.
    ///
    /// Lets embedding drivers detect whether application code already presented during a frame,
    /// so they can skip a redundant driver-side present.
    present_count: u64,
}

impl<B: Backend> Terminal<B> {
    /// Create a terminal with the given backend.
    /// Grid dimensions are queried from the backend.
    #[must_use]
    pub fn new(backend: B) -> Self {
        let size = backend.size();
        let current = Grid::new(size.width(), size.height());
        let previous = Grid::new(size.width(), size.height());
        let flattened_current = Grid::new(size.width(), size.height());
        let flattened_previous = Grid::new(size.width(), size.height());
        Self {
            current,
            previous,
            flattened_current,
            flattened_previous,
            backend,
            queued_event: None,
            flattened_stale: false,
            present_count: 0,
        }
    }

    /// Draws one frame: `f` gets a [`Surface`] scoped to the whole terminal on layer 0, then the
    /// frame is presented (see [`present`](Self::present)) once `f` returns.
    ///
    /// This is the common entry point for drawing: a caller that draws every frame regardless of
    /// whether anything changed calls this once per frame. A caller that only wants to redraw
    /// when its own state changed should gate the call to `draw` itself (e.g. `if
    /// state.changed() { term.draw(|s| render(s, &state))?; }`) rather than rely on `draw`/
    /// [`present`](Self::present) to no-op. Unlike some earlier revisions of this API, presenting
    /// is unconditional here.
    ///
    /// # Errors
    ///
    /// Propagates errors from [`present`](Self::present).
    pub fn draw(&mut self, f: impl FnOnce(&mut Surface<'_>)) -> Result<(), <B as Output>::Error> {
        let area = self.area();
        let mut surface = Surface::new(&mut self.current, area, 0);
        f(&mut surface);
        self.present()
    }

    /// A [`Surface`] scoped to the whole terminal on layer 0, for manual control over presenting
    /// (e.g. partial updates spread across several calls, or conditionally skipping a present).
    /// Most callers want [`draw`](Self::draw) instead.
    pub const fn surface(&mut self) -> Surface<'_> {
        let area = self.area();
        Surface::new(&mut self.current, area, 0)
    }

    /// Returns the current grid dimensions.
    #[must_use]
    pub const fn size(&self) -> Size {
        Size::new(self.current.width(), self.current.height())
    }

    /// Returns the full drawing surface as a [`Rect`] at the origin.
    ///
    /// Equivalent to `Rect::new(0, 0, width, height)`. Handy for passing the
    /// whole terminal to layout helpers or region-based drawing.
    #[must_use]
    pub const fn area(&self) -> Rect {
        Rect::new(0, 0, self.current.width(), self.current.height())
    }

    /// Resize both grids to `width` × `height` cells.
    ///
    /// Content within the overlapping region is preserved in the current grid.
    /// The previous grid is cleared so the next [`present`](Self::present) redraws
    /// the entire new surface rather than diffing stale data.
    pub fn resize(&mut self, width: u16, height: u16) {
        self.current.resize(width, height);
        self.previous.resize(width, height);
        self.flattened_current.resize(width, height);
        self.flattened_previous.resize(width, height);
        // Clearing previous forces a full redraw next present(), ensuring no
        // stale cells bleed into the resized layout.
        self.previous.clear_all();
        self.flattened_previous.clear_all();
        self.backend.resize(Size::new(width, height));
    }

    /// Returns a reference to the current grid.
    #[must_use]
    pub const fn grid(&self) -> &Grid {
        &self.current
    }

    /// Returns a mutable reference to the current grid, with no clipping or layer scoping.
    ///
    /// Escape hatch for whole-grid operations that don't fit [`Surface`]'s clipped,
    /// single-layer model (e.g. [`Grid::blit`]). Most drawing should go through
    /// [`draw`](Self::draw)/[`surface`](Self::surface) instead.
    pub const fn grid_mut(&mut self) -> &mut Grid {
        &mut self.current
    }

    /// Returns a reference to the backend.
    #[must_use]
    pub const fn backend(&self) -> &B {
        &self.backend
    }

    /// Returns a mutable reference to the backend.
    pub const fn backend_mut(&mut self) -> &mut B {
        &mut self.backend
    }

    /// Number of times [`present`](Self::present) has been called so far.
    ///
    /// Wraps on overflow; intended for detecting whether `present` was called *at all* between two
    /// points in time (compare a saved count against the current one), not as a precise total.
    /// Embedding drivers (e.g. `retroglyph-window`'s windowed drivers) use this to decide whether
    /// application code already presented during a frame, so they can skip a redundant
    /// driver-side present.
    #[must_use]
    pub const fn present_count(&self) -> u64 {
        self.present_count
    }

    /// Present the current frame: computes the diff against the previous frame, sends changed
    /// cells to the backend, flushes, then swaps buffers. Always presents unconditionally, even
    /// if nothing was drawn since the last call; most callers want [`draw`](Self::draw) instead
    /// of calling this directly.
    ///
    /// When the backend requires a full frame (see
    /// [`crate::Output::needs_full_frame`]), all cells from every allocated layer are
    /// sent rather than just the diff, so pixel-based backends can clear and
    /// redraw to avoid orphaned pixels from sub-cell offsets.
    ///
    /// After a present, the new current buffer is cleared so the next frame starts empty.
    /// Callers should not draw into a frame and skip presenting it: the next [`draw`](Self::draw)
    /// call starts from an empty grid regardless.
    ///
    /// # Immediate mode
    ///
    /// This is an immediate-mode API (the same trade [ratatui] makes): the
    /// current buffer is wiped after every present, so each frame must redraw
    /// its entire scene from scratch. Cells are **not** retained between
    /// frames. The diff only bounds what is sent to the backend (terminal or
    /// pixel I/O); it does not bound the CPU cost of your redraw.
    ///
    /// [ratatui]: https://docs.rs/ratatui
    ///
    /// # Errors
    ///
    /// Propagates errors from the backend's [`draw_layers`](crate::Output::draw_layers) or
    /// [`flush`](crate::Output::flush) operations. Either failure returns before the
    /// current/previous buffers are swapped, so the cells from the failed frame stay marked
    /// dirty and are resent the next time `present` succeeds; the caller doesn't need to
    /// redraw anything to recover, just call `draw`/`present` again.
    pub fn present(&mut self) -> Result<(), <B as Output>::Error> {
        self.present_count = self.present_count.wrapping_add(1);
        if self.backend.composites_layers() {
            // Pixel/GPU backends composite the raw layered stream themselves.
            if self.backend.needs_full_frame() {
                let all = self.current.layers();
                self.backend.draw_layers(all)?;
            } else {
                let diff = self.current.diff(&self.previous);
                self.backend.draw_layers(diff)?;
            }
        } else if self.current.max_layer() == 0 && self.previous.max_layer() == 0 {
            // Fast path: only layer 0 is in play, so flattening would be an exact
            // copy of `current`. Diff the real grids directly and skip the
            // flatten buffers entirely.
            let diff = self.current.diff(&self.previous);
            self.backend.draw_layers(diff)?;
            self.flattened_stale = true;
        } else {
            // Cell backends receive a pre-flattened, single-layer diff so layers
            // 1+ appear everywhere, not just on pixel backends.
            if self.flattened_stale {
                // The previous frame used the fast path, so `flattened_previous`
                // is stale. Clear it to force a full redraw this frame.
                self.flattened_previous.clear_all();
                self.flattened_stale = false;
            }
            self.current.flatten_into(&mut self.flattened_current);
            let diff = self.flattened_current.diff(&self.flattened_previous);
            self.backend.draw_layers(diff)?;
            core::mem::swap(&mut self.flattened_current, &mut self.flattened_previous);
        }
        self.backend.flush()?;
        core::mem::swap(&mut self.current, &mut self.previous);
        self.current.clear_all();
        Ok(())
    }

    /// Polls for an input event, waiting up to `timeout`.
    ///
    /// If an event was previously buffered by [`has_input`](Self::has_input), it is
    /// returned immediately. Otherwise, the backend is polled for a new event.
    ///
    /// [`Event::Resize`] events are automatically applied: both grids are resized
    /// before the event is returned to the caller, so the game loop can immediately
    /// redraw at the new size.
    pub fn poll(&mut self, timeout: Duration) -> Option<Event> {
        let event = self
            .queued_event
            .take()
            .or_else(|| self.backend.poll_event(timeout))?;
        if let Event::Resize(w, h) = event {
            self.resize(w, h);
        }
        Some(event)
    }

    /// Reads an input event, blocking indefinitely until one is available.
    ///
    /// Only call this on backends that genuinely block (e.g. crossterm, window). Backends
    /// that never block (e.g. [`Headless`](crate::backend::Headless), which returns
    /// immediately regardless of timeout) will panic here once their event queue is
    /// empty; use [`poll`](Self::poll) or [`drain_events`](Self::drain_events) instead if
    /// that is a possibility.
    ///
    /// # Panics
    ///
    /// Panics if the backend's [`poll_event`](crate::Input::poll_event) returns
    /// `None` even with an unbounded timeout.
    pub fn read_blocking(&mut self) -> Event {
        self.poll(Duration::MAX)
            .expect("read_blocking() called but no events available")
    }

    /// Drains all available events without blocking.
    ///
    /// Returns an iterator that yields every pending event — the internal queued event
    /// followed by all events buffered in the backend. The iterator polls the backend
    /// with zero timeout repeatedly until `None` is returned.
    ///
    /// This is needed for frame-based game loops (e.g. software backend + WASM, where
    /// frames are gated by `requestAnimationFrame`). Multiple keypresses can arrive
    /// between frames; draining all of them ensures accumulated input doesn't replay in
    /// slow motion.
    ///
    /// Crossterm and headless backends can also use this, but the single-event `poll`
    /// pattern works for them because their loops aren't frame-capped.
    pub fn drain_events(&mut self) -> impl Iterator<Item = Event> + use<'_, B> {
        struct DrainEvents<'a, B: Backend> {
            terminal: &'a mut Terminal<B>,
        }

        impl<B: Backend> Iterator for DrainEvents<'_, B> {
            type Item = Event;

            fn next(&mut self) -> Option<Event> {
                self.terminal.poll(Duration::ZERO)
            }
        }

        impl<B: Backend> core::iter::FusedIterator for DrainEvents<'_, B> {}

        DrainEvents { terminal: self }
    }

    /// Checks if a pending input event is available without blocking.
    ///
    /// If an event is already buffered, returns `true`. Otherwise, polls the backend
    /// with zero timeout. If the backend returns an event, it is stored in the internal
    /// buffer and `true` is returned; otherwise, returns `false`.
    pub fn has_input(&mut self) -> bool {
        if self.queued_event.is_some() {
            true
        } else if let Some(event) = self.backend.poll_event(Duration::ZERO) {
            self.queued_event = Some(event);
            true
        } else {
            false
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::backend::Headless;
    use crate::color::Color;
    use crate::grid::Pos;
    use crate::style::Style;
    use crate::tile::Tile;

    #[test]
    fn test_terminal_grid_mut() {
        let backend = Headless::new(10, 10);
        let mut terminal = Terminal::new(backend);

        assert_eq!(terminal.grid()[Pos::new(0, 0)].glyph(), ' ');

        terminal
            .grid_mut()
            .put_tile(0, (0, 0), Tile::new('X', Style::default()));

        assert_eq!(terminal.grid()[Pos::new(0, 0)].glyph(), 'X');
    }

    #[test]
    fn test_terminal_poll_and_read() {
        let backend = Headless::new(10, 10);
        let mut terminal = Terminal::new(backend);

        assert_eq!(terminal.poll(Duration::ZERO), None);

        terminal.backend_mut().push_event(Event::Close);
        assert_eq!(terminal.poll(Duration::ZERO), Some(Event::Close));

        terminal.backend_mut().push_event(Event::Resize(80, 25));
        assert_eq!(terminal.read_blocking(), Event::Resize(80, 25));
    }

    #[test]
    fn test_terminal_has_input() {
        let backend = Headless::new(10, 10);
        let mut terminal = Terminal::new(backend);

        assert!(!terminal.has_input());

        terminal.backend_mut().push_event(Event::Close);
        assert!(terminal.has_input());
        assert!(terminal.has_input()); // Repeated calls should still be true

        // Read/Poll should retrieve the buffered event
        assert_eq!(terminal.poll(Duration::ZERO), Some(Event::Close));

        // After taking, it should be false again
        assert!(!terminal.has_input());
    }

    #[test]
    #[should_panic(expected = "read_blocking() called but no events available")]
    fn test_terminal_read_panic() {
        let backend = Headless::new(10, 10);
        let mut terminal = Terminal::new(backend);
        let _ = terminal.read_blocking();
    }

    #[test]
    fn test_draw_composites_layers_for_cell_backend() {
        // A cell backend (Headless) must see layers 1+ composited, not
        // dropped. Terrain on layer 0, entity on layer 1.
        let mut term = Terminal::new(Headless::new(3, 1));
        term.draw(|s| {
            s.put((0, 0), '.', Style::default());
            s.put((1, 0), '.', Style::default());
            s.on_layer(1).put((1, 0), '@', Style::default());
        })
        .expect("draw failed");
        assert_eq!(term.backend().grid()[Pos::new(0, 0)].glyph(), '.');
        // Layer 1's glyph wins at (1, 0).
        assert_eq!(term.backend().grid()[Pos::new(1, 0)].glyph(), '@');
    }

    #[test]
    fn test_draw_explicit_space_on_higher_layer_erases_and_sets_bg() {
        // An explicit space on a higher layer is opaque: it overwrites the
        // glyph beneath (erase) and applies its background. This is the
        // deliberate consequence of the explicit-EMPTY transparency model.
        let mut term = Terminal::new(Headless::new(2, 1));
        term.draw(|s| {
            s.put((0, 0), 'x', Style::default());
            s.on_layer(1).put((0, 0), ' ', Style::new().bg(Color::RED));
        })
        .expect("draw failed");
        let cell = term.backend().grid()[Pos::new(0, 0)];
        assert_eq!(cell.glyph(), ' ');
        assert_eq!(cell.style().background(), Color::RED);
    }

    #[test]
    fn test_draw_single_layer_fast_path_matches_backend() {
        // Only layer 0 is ever touched: the fast path must still deliver the
        // correct cells to a cell backend across multiple frames.
        let mut term = Terminal::new(Headless::new(3, 1));
        term.draw(|s| s.put((0, 0), 'a', Style::default()))
            .expect("draw failed");
        assert_eq!(term.backend().grid()[Pos::new(0, 0)].glyph(), 'a');

        // Immediate mode: redraw 'a' and add 'c'.
        term.draw(|s| {
            s.put((0, 0), 'a', Style::default());
            s.put((2, 0), 'c', Style::default());
        })
        .expect("draw failed");
        assert_eq!(term.backend().grid()[Pos::new(0, 0)].glyph(), 'a');
        assert_eq!(term.backend().grid()[Pos::new(2, 0)].glyph(), 'c');

        // A cell that is not redrawn is erased (immediate mode).
        term.draw(|s| s.put((0, 0), 'a', Style::default()))
            .expect("draw failed");
        assert_eq!(term.backend().grid()[Pos::new(0, 0)].glyph(), 'a');
        assert_eq!(term.backend().grid()[Pos::new(2, 0)].glyph(), ' ');
    }

    #[test]
    fn test_present_transition_single_to_multi_layer() {
        // Start single-layer (fast path), then introduce layer 1. The frame
        // that adds the layer must composite correctly despite the fast path
        // having bypassed the flatten buffers.
        let mut term = Terminal::new(Headless::new(2, 1));
        term.draw(|s| {
            s.put((0, 0), '.', Style::default());
            s.put((1, 0), '.', Style::default());
        })
        .expect("draw failed");

        term.draw(|s| {
            s.put((0, 0), '.', Style::default());
            s.put((1, 0), '.', Style::default());
            s.on_layer(1).put((1, 0), '@', Style::default());
        })
        .expect("draw failed");
        assert_eq!(term.backend().grid()[Pos::new(0, 0)].glyph(), '.');
        assert_eq!(term.backend().grid()[Pos::new(1, 0)].glyph(), '@');
    }

    #[test]
    fn test_present_untouched_higher_layer_is_transparent() {
        // A higher layer that was allocated but not written at this cell must
        // not disturb the lower layer's glyph or background.
        let mut term = Terminal::new(Headless::new(2, 1));
        term.draw(|s| {
            s.put((0, 0), 'x', Style::default());
            // Allocate layer 1 by writing elsewhere, leaving (0, 0) empty.
            s.on_layer(1).put((1, 0), 'y', Style::default());
        })
        .expect("draw failed");
        assert_eq!(term.backend().grid()[Pos::new(0, 0)].glyph(), 'x');
    }

    #[test]
    fn test_terminal_size() {
        let term = Terminal::new(Headless::new(40, 20));
        assert_eq!(term.size(), Size::new(40, 20));
    }

    #[test]
    fn test_terminal_area() {
        let term = Terminal::new(Headless::new(40, 20));
        assert_eq!(term.area(), Rect::new(0, 0, 40, 20));
    }

    #[test]
    fn test_terminal_resize_changes_dimensions() {
        let mut term = Terminal::new(Headless::new(10, 10));
        term.resize(30, 15);
        assert_eq!(term.size(), Size::new(30, 15));
        assert_eq!(term.grid().width(), 30);
        assert_eq!(term.grid().height(), 15);
    }

    #[test]
    fn test_terminal_resize_preserves_current_content() {
        // Writes through `surface()` rather than `draw()`, so `current` is inspected before any
        // `present()` clears it: `draw()` always presents, which would swap this content out to
        // `previous` and clear the new `current` before the assertions below could see it.
        let mut term = Terminal::new(Headless::new(10, 10));
        term.surface().put((2, 2), 'X', Style::default());
        term.resize(20, 20);
        assert_eq!(term.grid()[Pos::new(2, 2)].glyph(), 'X');
        assert_eq!(term.grid()[Pos::new(15, 15)].glyph(), ' ');
    }

    #[test]
    fn test_terminal_resize_event_auto_applies() {
        let mut term = Terminal::new(Headless::new(10, 10));
        term.backend_mut().push_event(Event::Resize(80, 25));
        let event = term.poll(Duration::ZERO);
        assert_eq!(event, Some(Event::Resize(80, 25)));
        assert_eq!(term.size(), Size::new(80, 25));
    }

    #[test]
    fn test_terminal_resize_new_cells_accessible() {
        // Resize to a larger area, then draw into the newly created region.
        let mut term = Terminal::new(Headless::new(3, 3));
        term.draw(|s| s.put((0, 0), 'A', Style::default()))
            .expect("draw failed");

        term.resize(5, 5);

        // Draw into the expanded region and verify it reaches the backend.
        term.draw(|s| s.put((4, 4), 'B', Style::default()))
            .expect("draw failed");

        assert_eq!(term.backend().grid()[Pos::new(4, 4)].glyph(), 'B');
        // (0,0) was not redrawn this frame; backend retains 'A' from before resize.
        assert_eq!(term.backend().grid()[Pos::new(0, 0)].glyph(), 'A');
    }

    // --- unicode width ---

    #[test]
    fn test_put_wide_char_sets_continuation() {
        let mut term = Terminal::new(Headless::new(10, 3));
        term.surface().put((0, 0), '\u{4e2d}', Style::default()); // '中', width 2
        assert_eq!(term.grid()[Pos::new(0, 0)].glyph(), '\u{4e2d}');
        // With egc: spacer uses WIDE_CHAR_SPACER flag, glyph is space.
        // Without egc: spacer is '\0'.
        #[cfg(feature = "egc")]
        {
            use crate::tile::TileFlags;
            assert!(
                term.grid()[Pos::new(1, 0)]
                    .flags()
                    .contains(TileFlags::WIDE_CHAR_SPACER)
            );
            assert_eq!(term.grid()[Pos::new(1, 0)].glyph(), ' ');
        }
        #[cfg(not(feature = "egc"))]
        assert_eq!(term.grid()[Pos::new(1, 0)].glyph(), '\0');
        assert_eq!(term.grid()[Pos::new(2, 0)].glyph(), ' '); // untouched
    }

    #[test]
    fn test_print_advances_by_char_width() {
        let mut term = Terminal::new(Headless::new(10, 3));
        term.surface().print((0, 0), "\u{4e2d}x", Style::default()); // '中' (2) then 'x' at col 2
        assert_eq!(term.grid()[Pos::new(0, 0)].glyph(), '\u{4e2d}');
        #[cfg(feature = "egc")]
        {
            use crate::tile::TileFlags;
            assert!(
                term.grid()[Pos::new(1, 0)]
                    .flags()
                    .contains(TileFlags::WIDE_CHAR_SPACER)
            );
        }
        #[cfg(not(feature = "egc"))]
        assert_eq!(term.grid()[Pos::new(1, 0)].glyph(), '\0');
        assert_eq!(term.grid()[Pos::new(2, 0)].glyph(), 'x');
    }

    #[test]
    fn test_put_accepts_a_pos_or_a_tuple() {
        // `put` takes `impl Into<Pos>`, so a `Pos` and an equivalent `(u16, u16)` tuple must
        // write the same cell.
        let mut term = Terminal::new(Headless::new(10, 3));
        let mut s = term.surface();
        s.put(Pos::new(2, 1), 'X', Style::default());
        s.put((3, 1), 'Y', Style::default());
        assert_eq!(term.grid()[Pos::new(2, 1)].glyph(), 'X');
        assert_eq!(term.grid()[Pos::new(3, 1)].glyph(), 'Y');
    }

    #[test]
    fn test_put_offset_accepts_pos_and_offset_tuples() {
        // `put_offset` takes `impl Into<Pos>` and `impl Into<Offset>`, so `Pos`/`Offset` values
        // and equivalent tuples must produce the same tile.
        let mut term = Terminal::new(Headless::new(4, 1));
        let mut s = term.surface();
        s.put_offset(
            Pos::new(1, 0),
            crate::grid::Offset::new(3, -2),
            'X',
            Style::default(),
        );
        s.put_offset((2, 0), (-1, 4), 'Y', Style::default());
        assert_eq!(term.grid()[Pos::new(1, 0)].glyph(), 'X');
        assert_eq!(term.grid()[Pos::new(1, 0)].dx(), 3);
        assert_eq!(term.grid()[Pos::new(1, 0)].dy(), -2);

        assert_eq!(term.grid()[Pos::new(2, 0)].glyph(), 'Y');
        assert_eq!(term.grid()[Pos::new(2, 0)].dx(), -1);
        assert_eq!(term.grid()[Pos::new(2, 0)].dy(), 4);
    }

    #[test]
    fn test_put_wide_char_at_last_column_does_not_overflow() {
        // Wide char placed at the last column: can't place a spacer.
        // write_grapheme silently refuses rather than leaving an orphan.
        let mut term = Terminal::new(Headless::new(4, 1));
        term.surface().put((3, 0), '\u{4e2d}', Style::default()); // col 3 is last; need col 4 for spacer
        assert_eq!(term.grid()[Pos::new(3, 0)].glyph(), ' '); // nothing written
    }

    // --- styled spans ---

    #[test]
    fn test_print_styled_basic() {
        use crate::text::{Line, Span};
        let mut term = Terminal::new(Headless::new(20, 3));
        let line = Line::from(vec![
            Span::raw("HP: "),
            Span::styled("100", Style::new().fg(Color::GREEN)),
        ]);
        term.surface().print_line((0, 0), &line);
        assert_eq!(term.grid()[Pos::new(0, 0)].glyph(), 'H');
        assert_eq!(term.grid()[Pos::new(3, 0)].glyph(), ' ');
        assert_eq!(term.grid()[Pos::new(4, 0)].glyph(), '1');
        assert_eq!(term.grid()[Pos::new(4, 0)].style.fg, Color::GREEN);
        assert_eq!(term.grid()[Pos::new(6, 0)].glyph(), '0');
    }

    #[test]
    fn test_print_styled_wide_chars() {
        use crate::text::Line;
        let mut term = Terminal::new(Headless::new(10, 3));
        let line = Line::from(vec![crate::text::Span::raw("\u{4e2d}x")]);
        term.surface().print_line((0, 0), &line);
        assert_eq!(term.grid()[Pos::new(0, 0)].glyph(), '\u{4e2d}');
        #[cfg(feature = "egc")]
        {
            use crate::tile::TileFlags;
            assert!(
                term.grid()[Pos::new(1, 0)]
                    .flags()
                    .contains(TileFlags::WIDE_CHAR_SPACER)
            );
        }
        #[cfg(not(feature = "egc"))]
        assert_eq!(term.grid()[Pos::new(1, 0)].glyph(), '\0');
        assert_eq!(term.grid()[Pos::new(2, 0)].glyph(), 'x');
    }

    #[test]
    fn test_print_str_styled_applies_style_to_every_cell() {
        let mut term = Terminal::new(Headless::new(20, 3));
        term.surface()
            .print((0, 0), "HP", Style::new().fg(Color::GREEN));
        assert_eq!(term.grid()[Pos::new(0, 0)].glyph(), 'H');
        assert_eq!(term.grid()[Pos::new(0, 0)].style.fg, Color::GREEN);
        assert_eq!(term.grid()[Pos::new(1, 0)].glyph(), 'P');
        assert_eq!(term.grid()[Pos::new(1, 0)].style.fg, Color::GREEN);
    }
}