From 60cc15bbb064faa704f78ca51ae60584b5f7ca31 Mon Sep 17 00:00:00 2001
From: FujiApple <fujiapple852@gmail.com>
Date: Sun, 20 Oct 2024 10:49:05 +0800
Subject: [PATCH] feat!: add support for empty bar style to `Sparkline` (#1326)

- distingiush between empty bars and bars with a value of 0
- provide custom styling for empty bars
- provide custom styling for individual bars
- inverts the rendering algorithm to be item first

Closes: #1325

BREAKING CHANGE: `Sparkline::data` takes `IntoIterator<Item = SparklineBar>`
instead of `&[u64]` and is no longer const

Co-authored-by: Josh McKinney <joshka@users.noreply.github.com>
---
 BREAKING-CHANGES.md               |  30 ++
 examples/demo2/tabs/traceroute.rs |   2 +-
 src/symbols.rs                    |   8 +
 src/widgets.rs                    |   2 +-
 src/widgets/sparkline.rs          | 475 ++++++++++++++++++++++++++----
 5 files changed, 465 insertions(+), 52 deletions(-)

diff --git a/BREAKING-CHANGES.md b/BREAKING-CHANGES.md
index ed9b2940..bd2c07a7 100644
--- a/BREAKING-CHANGES.md
+++ b/BREAKING-CHANGES.md
@@ -11,6 +11,7 @@ GitHub with a [breaking change] label.
 This is a quick summary of the sections below:
 
 - [v0.29.0](#unreleased)
+  - `Sparkline::data` takes `IntoIterator<Item = SparklineBar>` instead of `&[u64]` and is no longer const
   - Removed public fields from `Rect` iterators
   - `Line` now implements `From<Cow<str>`
   - `Table::highlight_style` is now `Table::row_highlight_style`
@@ -73,6 +74,35 @@ This is a quick summary of the sections below:
 
 ## Unreleased
 
+### `Sparkline::data` takes `IntoIterator<Item = SparklineBar>` instead of `&[u64]` and is no longer const ([#1326])
+
+[#1326]: https://github.com/ratatui/ratatui/pull/1326
+
+The `Sparkline::data` method has been modified to accept `IntoIterator<Item = SparklineBar>`
+instead of `&[u64]`.
+
+`SparklineBar` is a struct that contains an `Option<u64>` value, which represents an possible
+_absent_ value, as distinct from a `0` value. This change allows the `Sparkline` to style
+data points differently, depending on whether they are present or absent.
+
+`SparklineBar` also contains an `Option<Style>` that will be used to apply a style the bar in
+addition to any other styling applied to the `Sparkline`.
+
+Several `From` implementations have been added to `SparklineBar` to support existing callers who
+provide `&[u64]` and other types that can be converted to `SparklineBar`, such as `Option<u64>`.
+
+If you encounter any type inference issues, you may need to provide an explicit type for the data
+passed to `Sparkline::data`. For example, if you are passing a single value, you may need to use
+`into()` to convert it to form that can be used as a `SparklineBar`:
+
+```diff
+let value = 1u8;
+- Sparkline::default().data(&[value.into()]);
++ Sparkline::default().data(&[u64::from(value)]);
+```
+
+As a consequence of this change, the `data` method is no longer a `const fn`.
+
 ### `Color::from_hsl` is now behind the `palette` feature and accepts `palette::Hsl` ([#1418])
 
 [#1418]: https://github.com/ratatui/ratatui/pull/1418
diff --git a/examples/demo2/tabs/traceroute.rs b/examples/demo2/tabs/traceroute.rs
index 3cf56c30..845e8396 100644
--- a/examples/demo2/tabs/traceroute.rs
+++ b/examples/demo2/tabs/traceroute.rs
@@ -99,7 +99,7 @@ pub fn render_ping(progress: usize, area: Rect, buf: &mut Buffer) {
                 .title_alignment(Alignment::Center)
                 .border_type(BorderType::Thick),
         )
-        .data(&data)
+        .data(data)
         .style(THEME.traceroute.ping)
         .render(area, buf);
 }
diff --git a/src/symbols.rs b/src/symbols.rs
index e0ec9bc2..8d39e825 100644
--- a/src/symbols.rs
+++ b/src/symbols.rs
@@ -203,6 +203,14 @@ pub mod scrollbar {
     };
 }
 
+pub mod shade {
+    pub const EMPTY: &str = " ";
+    pub const LIGHT: &str = "░";
+    pub const MEDIUM: &str = "▒";
+    pub const DARK: &str = "▓";
+    pub const FULL: &str = "█";
+}
+
 #[cfg(test)]
 mod tests {
     use strum::ParseError;
diff --git a/src/widgets.rs b/src/widgets.rs
index 28afc893..0234de03 100644
--- a/src/widgets.rs
+++ b/src/widgets.rs
@@ -50,7 +50,7 @@ pub use self::{
     logo::{RatatuiLogo, Size as RatatuiLogoSize},
     paragraph::{Paragraph, Wrap},
     scrollbar::{ScrollDirection, Scrollbar, ScrollbarOrientation, ScrollbarState},
-    sparkline::{RenderDirection, Sparkline},
+    sparkline::{RenderDirection, Sparkline, SparklineBar},
     table::{Cell, HighlightSpacing, Row, Table, TableState},
     tabs::Tabs,
 };
diff --git a/src/widgets/sparkline.rs b/src/widgets/sparkline.rs
index 3be46ef3..7c45251c 100644
--- a/src/widgets/sparkline.rs
+++ b/src/widgets/sparkline.rs
@@ -12,10 +12,29 @@ use crate::{
 
 /// Widget to render a sparkline over one or more lines.
 ///
+/// Each bar in a `Sparkline` represents a value from the provided dataset. The height of the bar
+/// is determined by the value in the dataset.
+///
 /// You can create a `Sparkline` using [`Sparkline::default`].
 ///
+/// The data is set using [`Sparkline::data`]. The data can be a slice of `u64`, `Option<u64>`, or a
+/// [`SparklineBar`].  For the `Option<u64>` and [`SparklineBar`] cases, a data point with a value
+/// of `None` is interpreted an as the _absence_ of a value.
+///
 /// `Sparkline` can be styled either using [`Sparkline::style`] or preferably using the methods
-/// provided by the [`Stylize`](crate::style::Stylize) trait.
+/// provided by the [`Stylize`](crate::style::Stylize) trait.  The style may be set for the entire
+/// widget or for individual bars by setting individual [`SparklineBar::style`].
+///
+/// The bars are rendered using a set of symbols. The default set is [`symbols::bar::NINE_LEVELS`].
+/// You can change the set using [`Sparkline::bar_set`].
+///
+/// If the data provided is a slice of `u64` or `Option<u64>`, the bars will be styled with the
+/// style of the sparkline. If the data is a slice of [`SparklineBar`], the bars will be
+/// styled with the style of the sparkline combined with the style provided in the [`SparklineBar`]
+/// if it is set, otherwise the sparkline style will be used.
+///
+/// Absent values and will be rendered with the style set by [`Sparkline::absent_value_style`] and
+/// the symbol set by [`Sparkline::absent_value_symbol`].
 ///
 /// # Setter methods
 ///
@@ -37,7 +56,9 @@ use crate::{
 ///     .data(&[0, 2, 3, 4, 1, 4, 10])
 ///     .max(5)
 ///     .direction(RenderDirection::RightToLeft)
-///     .style(Style::default().red().on_white());
+///     .style(Style::default().red().on_white())
+///     .absent_value_style(Style::default().fg(Color::Red))
+///     .absent_value_symbol(symbols::shade::FULL);
 /// ```
 #[derive(Debug, Default, Clone, Eq, PartialEq)]
 pub struct Sparkline<'a> {
@@ -45,14 +66,18 @@ pub struct Sparkline<'a> {
     block: Option<Block<'a>>,
     /// Widget style
     style: Style,
+    /// Style of absent values
+    absent_value_style: Style,
+    /// The symbol to use for absent values
+    absent_value_symbol: AbsentValueSymbol,
     /// A slice of the data to display
-    data: &'a [u64],
+    data: Vec<SparklineBar>,
     /// The maximum value to take to compute the maximum bar height (if nothing is specified, the
     /// widget uses the max of the dataset)
     max: Option<u64>,
     /// A set of bar symbols used to represent the give data
     bar_set: symbols::bar::Set,
-    // The direction to render the sparkine, either from left to right, or from right to left
+    /// The direction to render the sparkline, either from left to right, or from right to left
     direction: RenderDirection,
 }
 
@@ -90,9 +115,51 @@ impl<'a> Sparkline<'a> {
         self
     }
 
+    /// Sets the style to use for absent values.
+    ///
+    /// Absent values are values in the dataset that are `None`.
+    ///
+    /// `style` accepts any type that is convertible to [`Style`] (e.g. [`Style`], [`Color`], or
+    /// your own type that implements [`Into<Style>`]).
+    ///
+    /// The foreground corresponds to the bars while the background is everything else.
+    #[must_use = "method moves the value of self and returns the modified value"]
+    pub fn absent_value_style<S: Into<Style>>(mut self, style: S) -> Self {
+        self.absent_value_style = style.into();
+        self
+    }
+
+    /// Sets the symbol to use for absent values.
+    ///
+    /// Absent values are values in the dataset that are `None`.
+    ///
+    /// The default is [`symbols::shade::EMPTY`].
+    #[must_use = "method moves the value of self and returns the modified value"]
+    pub fn absent_value_symbol(mut self, symbol: impl Into<String>) -> Self {
+        self.absent_value_symbol = AbsentValueSymbol(symbol.into());
+        self
+    }
+
     /// Sets the dataset for the sparkline.
     ///
-    /// # Example
+    /// Each item in the dataset is a bar in the sparkline. The height of the bar is determined by
+    /// the value in the dataset.
+    ///
+    /// The data can be a slice of `u64`, `Option<u64>`, or a [`SparklineBar`].  For the
+    /// `Option<u64>` and [`SparklineBar`] cases, a data point with a value of `None` is
+    /// interpreted an as the _absence_ of a value.
+    ///
+    /// If the data provided is a slice of `u64` or `Option<u64>`, the bars will be styled with the
+    /// style of the sparkline. If the data is a slice of [`SparklineBar`], the bars will be
+    /// styled with the style of the sparkline combined with the style provided in the
+    /// [`SparklineBar`] if it is set, otherwise the sparkline style will be used.
+    ///
+    /// Absent values and will be rendered with the style set by [`Sparkline::absent_value_style`]
+    /// and the symbol set by [`Sparkline::absent_value_symbol`].
+    ///
+    /// # Examples
+    ///
+    /// Create a `Sparkline` from a slice of `u64`:
     ///
     /// ```
     /// use ratatui::{layout::Rect, widgets::Sparkline, Frame};
@@ -103,9 +170,41 @@ impl<'a> Sparkline<'a> {
     /// frame.render_widget(sparkline, area);
     /// # }
     /// ```
+    ///
+    /// Create a `Sparkline` from a slice of `Option<u64>` such that some bars are absent:
+    ///
+    /// ```
+    /// # use ratatui::{prelude::*, widgets::*};
+    /// # fn ui(frame: &mut Frame) {
+    /// # let area = Rect::default();
+    /// let data = vec![Some(1), None, Some(3)];
+    /// let sparkline = Sparkline::default().data(data);
+    /// frame.render_widget(sparkline, area);
+    /// # }
+    /// ```
+    ///
+    /// Create a [`Sparkline`] from a a Vec of [`SparklineBar`] such that some bars are styled:
+    ///
+    /// ```
+    /// # use ratatui::{prelude::*, widgets::*};
+    /// # fn ui(frame: &mut Frame) {
+    /// # let area = Rect::default();
+    /// let data = vec![
+    ///     SparklineBar::from(1).style(Some(Style::default().fg(Color::Red))),
+    ///     SparklineBar::from(2),
+    ///     SparklineBar::from(3).style(Some(Style::default().fg(Color::Blue))),
+    /// ];
+    /// let sparkline = Sparkline::default().data(data);
+    /// frame.render_widget(sparkline, area);
+    /// # }
+    /// ```
     #[must_use = "method moves the value of self and returns the modified value"]
-    pub const fn data(mut self, data: &'a [u64]) -> Self {
-        self.data = data;
+    pub fn data<T>(mut self, data: T) -> Self
+    where
+        T: IntoIterator,
+        T::Item: Into<SparklineBar>,
+    {
+        self.data = data.into_iter().map(Into::into).collect();
         self
     }
 
@@ -139,6 +238,73 @@ impl<'a> Sparkline<'a> {
     }
 }
 
+/// An bar in a `Sparkline`.
+///
+/// The height of the bar is determined by the value and a value of `None` is interpreted as the
+/// _absence_ of a value, as distinct from a value of `Some(0)`.
+#[derive(Debug, Default, Copy, Clone, Eq, PartialEq)]
+pub struct SparklineBar {
+    /// The value of the bar.
+    ///
+    /// If `None`, the bar is absent.
+    value: Option<u64>,
+    /// The style of the bar.
+    ///
+    /// If `None`, the bar will use the style of the sparkline.
+    style: Option<Style>,
+}
+
+impl SparklineBar {
+    /// Sets the style of the bar.
+    ///
+    /// `style` accepts any type that is convertible to [`Style`] (e.g. [`Style`], [`Color`], or
+    /// your own type that implements [`Into<Style>`]).
+    ///
+    /// If not set, the default style of the sparkline will be used.
+    ///
+    /// As well as the style of the sparkline, each [`SparklineBar`] may optionally set its own
+    /// style.  If set, the style of the bar will be the style of the sparkline combined with
+    /// the style of the bar.
+    #[must_use = "method moves the value of self and returns the modified value"]
+    pub fn style<S: Into<Option<Style>>>(mut self, style: S) -> Self {
+        self.style = style.into();
+        self
+    }
+}
+
+impl From<Option<u64>> for SparklineBar {
+    fn from(value: Option<u64>) -> Self {
+        Self { value, style: None }
+    }
+}
+
+impl From<u64> for SparklineBar {
+    fn from(value: u64) -> Self {
+        Self {
+            value: Some(value),
+            style: None,
+        }
+    }
+}
+
+impl From<&u64> for SparklineBar {
+    fn from(value: &u64) -> Self {
+        Self {
+            value: Some(*value),
+            style: None,
+        }
+    }
+}
+
+impl From<&Option<u64>> for SparklineBar {
+    fn from(value: &Option<u64>) -> Self {
+        Self {
+            value: *value,
+            style: None,
+        }
+    }
+}
+
 impl<'a> Styled for Sparkline<'a> {
     type Item = Self;
 
@@ -165,57 +331,100 @@ impl WidgetRef for Sparkline<'_> {
     }
 }
 
+/// A newtype wrapper for the symbol to use for absent values.
+#[derive(Debug, Clone, Eq, PartialEq)]
+struct AbsentValueSymbol(String);
+
+impl Default for AbsentValueSymbol {
+    fn default() -> Self {
+        Self(symbols::shade::EMPTY.to_string())
+    }
+}
+
 impl Sparkline<'_> {
     fn render_sparkline(&self, spark_area: Rect, buf: &mut Buffer) {
         if spark_area.is_empty() {
             return;
         }
-
-        let max = self
+        // determine the maximum height across all bars
+        let max_height = self
             .max
-            .unwrap_or_else(|| *self.data.iter().max().unwrap_or(&1));
+            .unwrap_or_else(|| self.data.iter().filter_map(|s| s.value).max().unwrap_or(1));
+
+        // determine the maximum index to render
         let max_index = min(spark_area.width as usize, self.data.len());
-        let mut data = self
-            .data
-            .iter()
-            .take(max_index)
-            .map(|e| {
-                if max == 0 {
-                    0
-                } else {
-                    e * u64::from(spark_area.height) * 8 / max
+
+        // render each item in the data
+        for (i, item) in self.data.iter().take(max_index).enumerate() {
+            let x = match self.direction {
+                RenderDirection::LeftToRight => spark_area.left() + i as u16,
+                RenderDirection::RightToLeft => spark_area.right() - i as u16 - 1,
+            };
+
+            // determine the height, symbol and style to use for the item
+            //
+            // if the item is not absent:
+            // - the height is the value of the item scaled to the height of the spark area
+            // - the symbol is determined by the scaled height
+            // - the style is the style of the item, if one is set
+            //
+            // otherwise:
+            // - the height is the total height of the spark area
+            // - the symbol is the absent value symbol
+            // - the style is the absent value style
+            let (mut height, symbol, style) = match item {
+                SparklineBar {
+                    value: Some(value),
+                    style,
+                } => {
+                    let height = if max_height == 0 {
+                        0
+                    } else {
+                        *value * u64::from(spark_area.height) * 8 / max_height
+                    };
+                    (height, None, *style)
+                }
+                _ => (
+                    u64::from(spark_area.height) * 8,
+                    Some(self.absent_value_symbol.0.as_str()),
+                    Some(self.absent_value_style),
+                ),
+            };
+
+            // render the item from top to bottom
+            //
+            // if the symbol is set it will be used for the entire height of the bar, otherwise the
+            // symbol will be determined by the _remaining_ height.
+            //
+            // if the style is set it will be used for the entire height of the bar, otherwise the
+            // sparkline style will be used.
+            for j in (0..spark_area.height).rev() {
+                let symbol = symbol.unwrap_or_else(|| self.symbol_for_height(height));
+                if height > 8 {
+                    height -= 8;
+                } else {
+                    height = 0;
                 }
-            })
-            .collect::<Vec<u64>>();
-        for j in (0..spark_area.height).rev() {
-            for (i, d) in data.iter_mut().enumerate() {
-                let symbol = match *d {
-                    0 => self.bar_set.empty,
-                    1 => self.bar_set.one_eighth,
-                    2 => self.bar_set.one_quarter,
-                    3 => self.bar_set.three_eighths,
-                    4 => self.bar_set.half,
-                    5 => self.bar_set.five_eighths,
-                    6 => self.bar_set.three_quarters,
-                    7 => self.bar_set.seven_eighths,
-                    _ => self.bar_set.full,
-                };
-                let x = match self.direction {
-                    RenderDirection::LeftToRight => spark_area.left() + i as u16,
-                    RenderDirection::RightToLeft => spark_area.right() - i as u16 - 1,
-                };
                 buf[(x, spark_area.top() + j)]
                     .set_symbol(symbol)
-                    .set_style(self.style);
-
-                if *d > 8 {
-                    *d -= 8;
-                } else {
-                    *d = 0;
-                }
+                    .set_style(self.style.patch(style.unwrap_or_default()));
             }
         }
     }
+
+    const fn symbol_for_height(&self, height: u64) -> &str {
+        match height {
+            0 => self.bar_set.empty,
+            1 => self.bar_set.one_eighth,
+            2 => self.bar_set.one_quarter,
+            3 => self.bar_set.three_eighths,
+            4 => self.bar_set.half,
+            5 => self.bar_set.five_eighths,
+            6 => self.bar_set.three_quarters,
+            7 => self.bar_set.seven_eighths,
+            _ => self.bar_set.full,
+        }
+    }
 }
 
 #[cfg(test)]
@@ -250,6 +459,78 @@ mod tests {
         );
     }
 
+    #[test]
+    fn it_can_be_created_from_vec_of_u64() {
+        let data = vec![1_u64, 2, 3];
+        let spark_data = Sparkline::default().data(data).data;
+        let expected = vec![
+            SparklineBar::from(1),
+            SparklineBar::from(2),
+            SparklineBar::from(3),
+        ];
+        assert_eq!(spark_data, expected);
+    }
+
+    #[test]
+    fn it_can_be_created_from_vec_of_option_u64() {
+        let data = vec![Some(1_u64), None, Some(3)];
+        let spark_data = Sparkline::default().data(data).data;
+        let expected = vec![
+            SparklineBar::from(1),
+            SparklineBar::from(None),
+            SparklineBar::from(3),
+        ];
+        assert_eq!(spark_data, expected);
+    }
+
+    #[test]
+    fn it_can_be_created_from_array_of_u64() {
+        let data = [1_u64, 2, 3];
+        let spark_data = Sparkline::default().data(data).data;
+        let expected = vec![
+            SparklineBar::from(1),
+            SparklineBar::from(2),
+            SparklineBar::from(3),
+        ];
+        assert_eq!(spark_data, expected);
+    }
+
+    #[test]
+    fn it_can_be_created_from_array_of_option_u64() {
+        let data = [Some(1_u64), None, Some(3)];
+        let spark_data = Sparkline::default().data(data).data;
+        let expected = vec![
+            SparklineBar::from(1),
+            SparklineBar::from(None),
+            SparklineBar::from(3),
+        ];
+        assert_eq!(spark_data, expected);
+    }
+
+    #[test]
+    fn it_can_be_created_from_slice_of_u64() {
+        let data = vec![1_u64, 2, 3];
+        let spark_data = Sparkline::default().data(&data).data;
+        let expected = vec![
+            SparklineBar::from(1),
+            SparklineBar::from(2),
+            SparklineBar::from(3),
+        ];
+        assert_eq!(spark_data, expected);
+    }
+
+    #[test]
+    fn it_can_be_created_from_slice_of_option_u64() {
+        let data = vec![Some(1_u64), None, Some(3)];
+        let spark_data = Sparkline::default().data(&data).data;
+        let expected = vec![
+            SparklineBar::from(1),
+            SparklineBar::from(None),
+            SparklineBar::from(3),
+        ];
+        assert_eq!(spark_data, expected);
+    }
+
     // Helper function to render a sparkline to a buffer with a given width
     // filled with x symbols to make it easier to assert on the result
     fn render(widget: Sparkline<'_>, width: u16) -> Buffer {
@@ -261,7 +542,7 @@ mod tests {
 
     #[test]
     fn it_does_not_panic_if_max_is_zero() {
-        let widget = Sparkline::default().data(&[0, 0, 0]);
+        let widget = Sparkline::default().data([0, 0, 0]);
         let buffer = render(widget, 6);
         assert_eq!(buffer, Buffer::with_lines(["   xxx"]));
     }
@@ -270,22 +551,31 @@ mod tests {
     fn it_does_not_panic_if_max_is_set_to_zero() {
         // see https://github.com/rust-lang/rust-clippy/issues/13191
         #[allow(clippy::unnecessary_min_or_max)]
-        let widget = Sparkline::default().data(&[0, 1, 2]).max(0);
+        let widget = Sparkline::default().data([0, 1, 2]).max(0);
         let buffer = render(widget, 6);
         assert_eq!(buffer, Buffer::with_lines(["   xxx"]));
     }
 
     #[test]
     fn it_draws() {
-        let widget = Sparkline::default().data(&[0, 1, 2, 3, 4, 5, 6, 7, 8]);
+        let widget = Sparkline::default().data([0, 1, 2, 3, 4, 5, 6, 7, 8]);
         let buffer = render(widget, 12);
         assert_eq!(buffer, Buffer::with_lines([" ▁▂▃▄▅▆▇█xxx"]));
     }
 
+    #[test]
+    fn it_draws_double_height() {
+        let widget = Sparkline::default().data([0, 1, 2, 3, 4, 5, 6, 7, 8]);
+        let area = Rect::new(0, 0, 12, 2);
+        let mut buffer = Buffer::filled(area, Cell::new("x"));
+        widget.render(area, &mut buffer);
+        assert_eq!(buffer, Buffer::with_lines(["     ▂▄▆█xxx", " ▂▄▆█████xxx"]));
+    }
+
     #[test]
     fn it_renders_left_to_right() {
         let widget = Sparkline::default()
-            .data(&[0, 1, 2, 3, 4, 5, 6, 7, 8])
+            .data([0, 1, 2, 3, 4, 5, 6, 7, 8])
             .direction(RenderDirection::LeftToRight);
         let buffer = render(widget, 12);
         assert_eq!(buffer, Buffer::with_lines([" ▁▂▃▄▅▆▇█xxx"]));
@@ -294,12 +584,97 @@ mod tests {
     #[test]
     fn it_renders_right_to_left() {
         let widget = Sparkline::default()
-            .data(&[0, 1, 2, 3, 4, 5, 6, 7, 8])
+            .data([0, 1, 2, 3, 4, 5, 6, 7, 8])
             .direction(RenderDirection::RightToLeft);
         let buffer = render(widget, 12);
         assert_eq!(buffer, Buffer::with_lines(["xxx█▇▆▅▄▃▂▁ "]));
     }
 
+    #[test]
+    fn it_renders_with_absent_value_style() {
+        let widget = Sparkline::default()
+            .absent_value_style(Style::default().fg(Color::Red))
+            .absent_value_symbol(symbols::shade::FULL)
+            .data([
+                None,
+                Some(1),
+                Some(2),
+                Some(3),
+                Some(4),
+                Some(5),
+                Some(6),
+                Some(7),
+                Some(8),
+            ]);
+        let buffer = render(widget, 12);
+        let mut expected = Buffer::with_lines(["█▁▂▃▄▅▆▇█xxx"]);
+        expected.set_style(Rect::new(0, 0, 1, 1), Style::default().fg(Color::Red));
+        assert_eq!(buffer, expected);
+    }
+
+    #[test]
+    fn it_renders_with_absent_value_style_double_height() {
+        let widget = Sparkline::default()
+            .absent_value_style(Style::default().fg(Color::Red))
+            .absent_value_symbol(symbols::shade::FULL)
+            .data([
+                None,
+                Some(1),
+                Some(2),
+                Some(3),
+                Some(4),
+                Some(5),
+                Some(6),
+                Some(7),
+                Some(8),
+            ]);
+        let area = Rect::new(0, 0, 12, 2);
+        let mut buffer = Buffer::filled(area, Cell::new("x"));
+        widget.render(area, &mut buffer);
+        let mut expected = Buffer::with_lines(["█    ▂▄▆█xxx", "█▂▄▆█████xxx"]);
+        expected.set_style(Rect::new(0, 0, 1, 2), Style::default().fg(Color::Red));
+        assert_eq!(buffer, expected);
+    }
+
+    #[test]
+    fn it_renders_with_custom_absent_value_style() {
+        let widget = Sparkline::default().absent_value_symbol('*').data([
+            None,
+            Some(1),
+            Some(2),
+            Some(3),
+            Some(4),
+            Some(5),
+            Some(6),
+            Some(7),
+            Some(8),
+        ]);
+        let buffer = render(widget, 12);
+        let expected = Buffer::with_lines(["*▁▂▃▄▅▆▇█xxx"]);
+        assert_eq!(buffer, expected);
+    }
+
+    #[test]
+    fn it_renders_with_custom_bar_styles() {
+        let widget = Sparkline::default().data(vec![
+            SparklineBar::from(Some(0)).style(Some(Style::default().fg(Color::Red))),
+            SparklineBar::from(Some(1)).style(Some(Style::default().fg(Color::Red))),
+            SparklineBar::from(Some(2)).style(Some(Style::default().fg(Color::Red))),
+            SparklineBar::from(Some(3)).style(Some(Style::default().fg(Color::Green))),
+            SparklineBar::from(Some(4)).style(Some(Style::default().fg(Color::Green))),
+            SparklineBar::from(Some(5)).style(Some(Style::default().fg(Color::Green))),
+            SparklineBar::from(Some(6)).style(Some(Style::default().fg(Color::Blue))),
+            SparklineBar::from(Some(7)).style(Some(Style::default().fg(Color::Blue))),
+            SparklineBar::from(Some(8)).style(Some(Style::default().fg(Color::Blue))),
+        ]);
+        let buffer = render(widget, 12);
+        let mut expected = Buffer::with_lines([" ▁▂▃▄▅▆▇█xxx"]);
+        expected.set_style(Rect::new(0, 0, 3, 1), Style::default().fg(Color::Red));
+        expected.set_style(Rect::new(3, 0, 3, 1), Style::default().fg(Color::Green));
+        expected.set_style(Rect::new(6, 0, 3, 1), Style::default().fg(Color::Blue));
+        assert_eq!(buffer, expected);
+    }
+
     #[test]
     fn can_be_stylized() {
         assert_eq!(