use super::*;

/// What determines one rendered row's pixels: its cells, the cursor on it, the
/// selection span over it, and the blink phase. Two equal `RowSnap`s render
/// identically, so a buffer holding an equal snapshot needs no repaint.
#[derive(Clone, PartialEq, Debug)]
struct RowSnap {
    cells: Vec<Cell>,
    /// `(col, shape, focused)` when the cursor is drawn on this row.
    cursor: Option<(usize, CursorShape, bool)>,
    /// Inclusive selected column span on this row.
    sel: Option<(usize, usize)>,
    /// Search-match spans `(lo, hi, is_current)` highlighted on this row.
    search: Vec<(usize, usize, bool)>,
    /// Search-prompt text drawn over this row (only the bottom row, when active).
    overlay: Option<String>,
    /// IME preedit `(start_col, text)` drawn inline over this row (cursor row).
    preedit: Option<(usize, String)>,
    /// Blink phase, but only varied when the row actually has blinking ink, so
    /// non-blinking rows stay equal across phase toggles.
    blink: bool,
}

/// One shm buffer plus the per-row snapshot of what it currently displays.
#[derive(Debug)]
pub(super) struct FrameBuf {
    buffer: Buffer,
    rows: Vec<RowSnap>,
}

/// Snapshot the determinants of viewport row `y`'s pixels.
fn row_snap(grid: &Grid, y: usize, focused: bool, blink_on: bool) -> RowSnap {
    let abs = grid.view_to_abs(y);
    let cells = grid.view_row(y).to_vec();
    let cursor = if grid.view_at_bottom() && grid.cursor().1 == y {
        let visible = grid.cursor_visible() && (!grid.cursor_blink() || blink_on);
        visible.then(|| (grid.cursor().0, grid.cursor_shape(), focused))
    } else {
        None
    };
    let has_blink = cells
        .iter()
        .any(|c| c.flags.contains(crate::grid::Flags::BLINK));
    RowSnap {
        cells,
        cursor,
        sel: grid.selection_span_on(abs),
        search: grid.search_spans_on(abs),
        overlay: None,
        preedit: None,
        blink: if has_blink { blink_on } else { true },
    }
}
impl App {
    /// Render only the rows that changed since the chosen buffer last displayed
    /// them, damage just those rows, and commit with a frame-callback request.
    pub(super) fn present(&mut self) {
        self.needs_draw = false;
        // URL hint labels overlay the grid but are not part of the row snapshot,
        // so force a full redraw while the labels are showing.
        if self.url_mode {
            self.frames.clear();
        }
        // Render into a buffer sized in physical pixels (logical × scale); the
        // viewport presents it back at the logical surface size.
        let (w, h) = self.phys_dims();
        let m = self.renderer.metrics();
        let (focused, blink_on) = (self.focused, self.blink_on);

        // A resize invalidates every buffer's contents and size.
        if self.buf_dims != (w, h) {
            self.frames.clear();
            self.buf_dims = (w, h);
        }

        let Some(session) = self.session.as_ref() else {
            return;
        };
        let grid = session.term.grid();
        // The visual bell inverts fg/bg for the duration of the flash.
        let flashed = self.flashing.then(|| session.term.theme().inverted());
        let theme = flashed.as_ref().unwrap_or(session.term.theme());
        let rows = grid.rows();
        let mut cur: Vec<RowSnap> = (0..rows)
            .map(|y| row_snap(grid, y, focused, blink_on))
            .collect();

        // The search prompt occupies the bottom row while search mode is active.
        // Recording it in the snapshot keeps the row's damage/diff correct.
        let bar_text = if let Some(hex) = &self.unicode_input {
            Some(format!("unicode: U+{}", hex.to_uppercase()))
        } else {
            self.searching.then(|| {
                let (n, total) = grid.search_count();
                format!(
                    "search: {}  [{n}/{total}]",
                    grid.search_query().unwrap_or("")
                )
            })
        };
        if let Some(text) = &bar_text
            && rows > 0
        {
            cur[rows - 1].overlay = Some(text.clone());
        }

        // The IME preedit is drawn inline at the cursor while composing.
        if !self.preedit.is_empty() && grid.view_at_bottom() {
            let (cx, cy) = grid.cursor();
            if cy < rows {
                cur[cy].preedit = Some((cx, self.preedit.clone()));
            }
        }

        // Reuse a buffer the compositor has released, else grow the ring.
        let stride = w as i32 * 4;
        let mut idx = None;
        for i in 0..self.frames.len() {
            if self.pool.canvas(&self.frames[i].buffer).is_some() {
                idx = Some(i);
                break;
            }
        }
        let idx = match idx {
            Some(i) => i,
            None if self.frames.len() < MAX_BUFFERS => {
                match self
                    .pool
                    .create_buffer(w as i32, h as i32, stride, wl_shm::Format::Argb8888)
                {
                    Ok((buffer, _)) => {
                        self.frames.push(FrameBuf {
                            buffer,
                            rows: Vec::new(),
                        });
                        self.frames.len() - 1
                    }
                    Err(err) => {
                        tracing::error!("allocate shm buffer: {err}");
                        return;
                    }
                }
            }
            // All buffers are still held by the compositor; a release event will
            // wake us and `needs_draw` (re-set below) retries then.
            None => {
                self.needs_draw = true;
                return;
            }
        };

        // Rows that differ from what this buffer last showed (all, if fresh).
        let prev = &self.frames[idx].rows;
        let dirty: Vec<usize> = (0..rows)
            .filter(|&y| prev.get(y) != Some(&cur[y]))
            .collect();
        if dirty.is_empty() {
            return;
        }

        // A buffer used for the first time has uninitialized margins; paint the
        // whole thing (background + padding) once, then damage it in full below.
        let fresh = self.frames[idx].rows.is_empty();
        let pad_y = self.to_phys(self.config.main.pad_y) as i32;
        let Some(canvas) = self.pool.canvas(&self.frames[idx].buffer) else {
            return;
        };
        let dims = (w as usize, h as usize);
        let frame = crate::render::Frame {
            theme,
            focused,
            blink_on,
            hovered_link: self.hovered_link,
        };
        if fresh {
            self.renderer.clear(canvas, dims, theme);
        }
        for &y in &dirty {
            self.renderer.render_row(canvas, dims, grid, &frame, y);
        }
        // Draw the search prompt over the (now repainted) bottom row.
        if let Some(text) = &bar_text
            && dirty.contains(&(rows - 1))
        {
            self.renderer
                .render_search_bar(canvas, dims, theme, rows - 1, text);
        }
        // Draw the IME preedit inline over its (repainted) cursor row.
        for &y in &dirty {
            if let Some((col, text)) = &cur[y].preedit {
                self.renderer
                    .render_preedit(canvas, dims, theme, y, *col, text);
            }
        }
        // Draw URL hint labels on top, narrowing to those matching the input.
        if self.url_mode {
            for (hit, label) in self.url_hits.iter().zip(&self.url_labels) {
                if label.starts_with(&self.url_input) {
                    self.renderer
                        .render_label(canvas, dims, theme, hit.row, hit.col, label);
                }
            }
        }
        self.frames[idx].rows = cur;

        let surface = self.window.wl_surface();
        if let Err(err) = self.frames[idx].buffer.attach_to(surface) {
            tracing::error!("attach buffer: {err}");
            return;
        }
        // With a viewport the buffer is presented at the logical destination, so
        // its own scale stays 1; without one, fall back to integer buffer scale.
        if let Some(vp) = &self.viewport {
            surface.set_buffer_scale(1);
            vp.set_destination(self.width.max(1) as i32, self.height.max(1) as i32);
        } else {
            surface.set_buffer_scale((self.scale120 / 120).max(1) as i32);
        }
        if fresh {
            surface.damage_buffer(0, 0, w as i32, h as i32);
        } else {
            for &y in &dirty {
                let top = pad_y + y as i32 * m.height as i32;
                surface.damage_buffer(0, top, w as i32, m.height as i32);
            }
        }
        surface.frame(&self.qh, surface.clone());
        self.window.commit();
        self.frame_pending = true;
    }
}