par-term-render 0.7.3

use super::{BackgroundInstance, CellRenderer, TextInstance};
use anyhow::Result;

/// Number of extra background instance slots reserved for cursor overlays
/// (beam/underline, guide line, shadow, boost glow, hollow outline sides).
/// Layout: [0] cursor overlay, [1] guide, [2] shadow, [3] boost glow, [4-7] hollow outline.
pub(crate) const CURSOR_OVERLAY_SLOTS: usize = 10;

/// Width of gutter indicator bars in terminal cell columns.
/// Each gutter indicator occupies this many cell-widths on the left side.
pub(crate) const GUTTER_WIDTH_CELLS: f32 = 2.0;

/// Underline thickness as a fraction of cell height.
/// Scaled at render time so underlines remain proportional across font sizes.
pub(crate) const UNDERLINE_HEIGHT_RATIO: f32 = 0.07;

/// Pixel tolerance for snapping glyphs to cell boundaries during rendering.
/// Glyphs within this many pixels of a cell edge are snapped to it.
pub(crate) const GLYPH_SNAP_THRESHOLD_PX: f32 = 3.0;

/// Sub-pixel extension applied when snapping glyphs to cell boundaries.
/// Prevents hairline gaps between adjacent block-drawing characters.
pub(crate) const GLYPH_SNAP_EXTENSION_PX: f32 = 0.5;

/// Floating-point epsilon for color component comparisons.
/// Used to detect when a cell's background matches the default terminal background.
pub(crate) const COLOR_COMPONENT_EPSILON: f32 = 0.001;

/// Brightness threshold for automatic cursor text-contrast selection.
/// Cursors brighter than this use dark text; darker cursors use light text.
pub(crate) const CURSOR_BRIGHTNESS_THRESHOLD: f32 = 0.5;

/// Maximum alpha for cursor boost glow effect (as a multiplier of boost intensity).
/// Keeps the glow subtle even at full boost strength.
pub(crate) const CURSOR_BOOST_MAX_ALPHA: f32 = 0.3;

/// Width of the hollow-cursor border in pixels.
/// Used for the four thin rectangles that form the hollow block cursor outline.
pub(crate) const HOLLOW_CURSOR_BORDER_PX: f32 = 1.0;

/// Stipple on-length in pixels for dashed link underlines.
pub(crate) const STIPPLE_ON_PX: f32 = 2.0;

/// Stipple off-length in pixels for dashed link underlines.
pub(crate) const STIPPLE_OFF_PX: f32 = 2.0;

/// Number of text instances pre-allocated per terminal cell.
/// 2× because wide (double-width) characters can emit two instances.
pub(crate) const TEXT_INSTANCES_PER_CELL: usize = 2;

/// Compute the text foreground color when a block cursor covers a cell.
///
/// If the cursor has an explicit `text_color` (RGB, 3 components), that is used
/// directly with `text_alpha` appended.  Otherwise, a simple luminance-based
/// auto-contrast rule is applied: cursors brighter than `CURSOR_BRIGHTNESS_THRESHOLD`
/// get dark text; darker cursors get light text.
///
/// `cursor_color` and `cursor_text_color` are 3-component RGB (no alpha) as stored in
/// `CursorState`. The returned value is a 4-component RGBA with `text_alpha` as alpha.
///
/// This is a free function rather than a method so it can be called from
/// both `text_instance_builder.rs` and `pane_render/mod.rs` without any
/// borrowing conflicts.
pub(crate) fn compute_cursor_text_color(
    cursor_color: [f32; 3],
    cursor_text_color: Option<[f32; 3]>,
    text_alpha: f32,
) -> [f32; 4] {
    if let Some(cursor_text) = cursor_text_color {
        [cursor_text[0], cursor_text[1], cursor_text[2], text_alpha]
    } else {
        let cursor_brightness = (cursor_color[0] + cursor_color[1] + cursor_color[2]) / 3.0;
        if cursor_brightness > CURSOR_BRIGHTNESS_THRESHOLD {
            [0.0, 0.0, 0.0, text_alpha] // Dark text on bright cursor
        } else {
            [1.0, 1.0, 1.0, text_alpha] // Bright text on dark cursor
        }
    }
}

impl CellRenderer {
    /// Orchestrate a full instance-buffer update for the current frame.
    ///
    /// **This method is used exclusively by the custom shader / cursor shader path**
    /// (`render_to_texture` → intermediate texture → shader effect). Normal terminal
    /// rendering always goes through `build_pane_instance_buffers` (in `pane_render.rs`)
    /// via `render_pane_to_view`, because `pane_manager` is always initialized.
    ///
    /// For each dirty row the per-row background and text instance builders are called
    /// (see `instance_builders.rs`) and the results are written to the GPU buffers
    /// incrementally. After processing all rows, cursor overlay, separator, and gutter
    /// instances are built and uploaded in a single write per region.
    pub(crate) fn build_instance_buffers(&mut self) -> Result<()> {
        for row in 0..self.grid.rows {
            if self.dirty_rows[row] || self.row_cache[row].is_none() {
                let start = row * self.grid.cols;
                let end = (row + 1) * self.grid.cols;

                // Copy the row's cells into the scratch buffer.  We can't pass a slice
                // of `self.cells` directly because `build_row_*` methods take `&mut self`,
                // creating a conflicting mutable borrow.  Taking `scratch_row_cells` out
                // via `std::mem::take` releases that field's borrow so we can re-borrow
                // the rest of `self` mutably while holding the row data.
                let mut row_cells = std::mem::take(&mut self.scratch_row_cells);
                row_cells.clear();
                row_cells.extend_from_slice(&self.cells[start..end]);

                self.scratch_row_bg.clear();
                self.scratch_row_text.clear();

                // --- Background instances (RLE-merged) ---
                self.build_row_bg_instances(row, &row_cells);

                // --- Text + underline instances ---
                self.build_row_text_instances(row, &row_cells, start);

                // Update CPU-side buffers
                let bg_start = row * self.grid.cols;
                self.bg_instances[bg_start..bg_start + self.grid.cols]
                    .copy_from_slice(&self.scratch_row_bg);

                let text_start = row * self.grid.cols * 2;
                // Clear row text segment first
                for i in 0..(self.grid.cols * 2) {
                    self.text_instances[text_start + i].size = [0.0, 0.0];
                }
                // Copy new text instances
                let text_count = self.scratch_row_text.len().min(self.grid.cols * 2);
                self.text_instances[text_start..text_start + text_count]
                    .copy_from_slice(&self.scratch_row_text[..text_count]);

                // Update GPU-side buffers incrementally
                self.queue.write_buffer(
                    &self.buffers.bg_instance_buffer,
                    (bg_start * std::mem::size_of::<BackgroundInstance>()) as u64,
                    bytemuck::cast_slice(&self.scratch_row_bg),
                );
                self.queue.write_buffer(
                    &self.buffers.text_instance_buffer,
                    (text_start * std::mem::size_of::<TextInstance>()) as u64,
                    bytemuck::cast_slice(
                        &self.text_instances[text_start..text_start + self.grid.cols * 2],
                    ),
                );

                self.row_cache[row] = Some(true);
                self.dirty_rows[row] = false;

                // Restore the scratch buffer so its capacity is retained for the next row.
                self.scratch_row_cells = row_cells;
            }
        }

        // --- Cursor overlay instances ---
        // Write cursor-related overlays to extra slots at the end of bg_instances.
        // Slot layout: [0] cursor overlay (beam/underline), [1] guide, [2] shadow,
        //              [3] boost glow, [4-7] hollow outline.
        let base_overlay_index = self.grid.cols * self.grid.rows;
        let overlay_instances = self.build_cursor_overlay_instances();

        for (i, instance) in overlay_instances.iter().enumerate() {
            self.bg_instances[base_overlay_index + i] = *instance;
        }
        self.queue.write_buffer(
            &self.buffers.bg_instance_buffer,
            (base_overlay_index * std::mem::size_of::<BackgroundInstance>()) as u64,
            bytemuck::cast_slice(&overlay_instances),
        );

        // --- Separator line instances ---
        // Write command separator line instances after cursor overlay slots.
        let separator_base = self.grid.cols * self.grid.rows + CURSOR_OVERLAY_SLOTS;
        let separator_instances = self.build_separator_instances();

        for (i, instance) in separator_instances.iter().enumerate() {
            if separator_base + i < self.buffers.max_bg_instances {
                self.bg_instances[separator_base + i] = *instance;
            }
        }
        let separator_byte_offset = separator_base * std::mem::size_of::<BackgroundInstance>();
        let separator_byte_count =
            separator_instances.len() * std::mem::size_of::<BackgroundInstance>();
        if separator_byte_offset + separator_byte_count
            <= self.buffers.max_bg_instances * std::mem::size_of::<BackgroundInstance>()
        {
            self.queue.write_buffer(
                &self.buffers.bg_instance_buffer,
                separator_byte_offset as u64,
                bytemuck::cast_slice(&separator_instances),
            );
        }

        // --- Gutter indicator instances ---
        // Write gutter indicator background instances after separator slots.
        let gutter_base = separator_base + self.grid.rows;
        let gutter_instances = self.build_gutter_instances();

        for (i, instance) in gutter_instances.iter().enumerate() {
            if gutter_base + i < self.buffers.max_bg_instances {
                self.bg_instances[gutter_base + i] = *instance;
            }
        }
        let gutter_byte_offset = gutter_base * std::mem::size_of::<BackgroundInstance>();
        let gutter_byte_count = gutter_instances.len() * std::mem::size_of::<BackgroundInstance>();
        if gutter_byte_offset + gutter_byte_count
            <= self.buffers.max_bg_instances * std::mem::size_of::<BackgroundInstance>()
        {
            self.queue.write_buffer(
                &self.buffers.bg_instance_buffer,
                gutter_byte_offset as u64,
                bytemuck::cast_slice(&gutter_instances),
            );
        }

        // Update actual instance counts for draw calls.
        // Layout: [0..cols*rows] cells + [cols*rows..+CURSOR_OVERLAY_SLOTS] overlays
        //         + [+CURSOR_OVERLAY_SLOTS..+rows] separators + [..+rows] gutters
        self.buffers.actual_bg_instances = self.grid.cols * self.grid.rows
            + CURSOR_OVERLAY_SLOTS
            + self.grid.rows
            + self.grid.rows;
        self.buffers.actual_text_instances =
            self.grid.cols * self.grid.rows * TEXT_INSTANCES_PER_CELL;

        Ok(())
    }
}