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use super::Style;
/// When printing out one coloured string followed by another, use one of
/// these rules to figure out which *extra* control codes need to be sent.
#[derive(PartialEq, Clone, Copy, Debug)]
pub enum Difference {
/// Print out the control codes specified by this style to end up looking
/// like the second string's styles.
ExtraStyles(Style),
/// Converting between these two is impossible, so just send a reset
/// command and then the second string's styles.
Reset,
/// The before style is exactly the same as the after style, so no further
/// control codes need to be printed.
NoDifference,
}
impl Difference {
/// Compute the 'style difference' required to turn an existing style into
/// the given, second style.
///
/// For example, to turn green text into green bold text, it's redundant
/// to write a reset command then a second green+bold command, instead of
/// just writing one bold command. This method should see that both styles
/// use the foreground colour green, and reduce it to a single command.
///
/// This method returns an enum value because it's not actually always
/// possible to turn one style into another: for example, text could be
/// made bold and underlined, but you can't remove the bold property
/// without also removing the underline property. So when this has to
/// happen, this function returns None, meaning that the entire set of
/// styles should be reset and begun again.
pub fn between(first: &Style, next: &Style) -> Difference {
use self::Difference::*;
// XXX(Havvy): This algorithm is kind of hard to replicate without
// having the Plain/Foreground enum variants, so I'm just leaving
// it commented out for now, and defaulting to Reset.
if first == next {
return NoDifference;
}
// Cannot un-bold, so must Reset.
if first.is_bold && !next.is_bold {
return Reset;
}
if first.is_dimmed && !next.is_dimmed {
return Reset;
}
if first.is_italic && !next.is_italic {
return Reset;
}
// Cannot un-underline, so must Reset.
if first.is_underline && !next.is_underline {
return Reset;
}
if first.is_blink && !next.is_blink {
return Reset;
}
if first.is_reverse && !next.is_reverse {
return Reset;
}
if first.is_hidden && !next.is_hidden {
return Reset;
}
if first.is_strikethrough && !next.is_strikethrough {
return Reset;
}
// Cannot go from foreground to no foreground, so must Reset.
if first.foreground.is_some() && next.foreground.is_none() {
return Reset;
}
// Cannot go from background to no background, so must Reset.
if first.background.is_some() && next.background.is_none() {
return Reset;
}
let mut extra_styles = Style::default();
if first.is_bold != next.is_bold {
extra_styles.is_bold = true;
}
if first.is_dimmed != next.is_dimmed {
extra_styles.is_dimmed = true;
}
if first.is_italic != next.is_italic {
extra_styles.is_italic = true;
}
if first.is_underline != next.is_underline {
extra_styles.is_underline = true;
}
if first.is_blink != next.is_blink {
extra_styles.is_blink = true;
}
if first.is_reverse != next.is_reverse {
extra_styles.is_reverse = true;
}
if first.is_hidden != next.is_hidden {
extra_styles.is_hidden = true;
}
if first.is_strikethrough != next.is_strikethrough {
extra_styles.is_strikethrough = true;
}
if first.foreground != next.foreground {
extra_styles.foreground = next.foreground;
}
if first.background != next.background {
extra_styles.background = next.background;
}
ExtraStyles(extra_styles)
}
}
#[cfg(test)]
mod test {
use super::*;
use super::Difference::*;
use style::Colour::*;
use style::Style;
fn style() -> Style {
Style::new()
}
macro_rules! test {
($name: ident: $first: expr; $next: expr => $result: expr) => {
#[test]
fn $name() {
assert_eq!($result, Difference::between(&$first, &$next));
}
};
}
test!(nothing: Green.normal(); Green.normal() => NoDifference);
test!(uppercase: Green.normal(); Green.bold() => ExtraStyles(style().bold()));
test!(lowercase: Green.bold(); Green.normal() => Reset);
test!(nothing2: Green.bold(); Green.bold() => NoDifference);
test!(colour_change: Red.normal(); Blue.normal() => ExtraStyles(Blue.normal()));
test!(addition_of_blink: style(); style().blink() => ExtraStyles(style().blink()));
test!(addition_of_dimmed: style(); style().dimmed() => ExtraStyles(style().dimmed()));
test!(addition_of_hidden: style(); style().hidden() => ExtraStyles(style().hidden()));
test!(addition_of_reverse: style(); style().reverse() => ExtraStyles(style().reverse()));
test!(addition_of_strikethrough: style(); style().strikethrough() => ExtraStyles(style().strikethrough()));
test!(removal_of_strikethrough: style().strikethrough(); style() => Reset);
test!(removal_of_reverse: style().reverse(); style() => Reset);
test!(removal_of_hidden: style().hidden(); style() => Reset);
test!(removal_of_dimmed: style().dimmed(); style() => Reset);
test!(removal_of_blink: style().blink(); style() => Reset);
}