README.md

@@ -118,8 +118,16 @@ expressions.
 !r 3d12 - 5d2 + 3 - 7d3 + 20d20
 ```
 
-This system does not yet have the capability to handle things like D&D
-5e advantage or disadvantage.
+#### Keep/Drop Dice
+The bot supports either keeping the highest dice in a roll, or
+dropping the highest dice in a roll.  This allows the bot to handle 
+things like D&D 5e advantage or disadvantage.
+
+```
+!roll 2d20k1
+!r 2d20dh1 + 5
+!r 10d10k5 + 10d10dh5 - 2
+```
 
 ### Storytelling System
 

dicebot/src/basic/dice.rs

@@ -12,17 +12,29 @@ use std::ops::{Deref, DerefMut};
 pub struct Dice {
     pub(crate) count: u32,
     pub(crate) sides: u32,
+    pub(crate) keep_drop: KeepOrDrop,
 }
 
 impl fmt::Display for Dice {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "{}d{}", self.count, self.sides)
+        match self.keep_drop {
+            KeepOrDrop::Keep(keep) => write!(f, "{}d{}k{}", self.count, self.sides, keep),
+            KeepOrDrop::Drop(drop) => write!(f, "{}d{}dh{}", self.count, self.sides, drop),
+            KeepOrDrop::None       => write!(f, "{}d{}", self.count, self.sides),
+        }
     }
 }
 
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+pub enum KeepOrDrop {
+    Keep (u32),
+    Drop (u32),
+    None,
+}
+
 impl Dice {
-    pub fn new(count: u32, sides: u32) -> Dice {
-        Dice { count, sides }
+    pub fn new(count: u32, sides: u32, keep_drop: KeepOrDrop) -> Dice {
+        Dice { count, sides, keep_drop }
     }
 }
 

dicebot/src/basic/parser.rs

@@ -31,12 +31,53 @@ enum Sign {
     Minus,
 }
 
-// Parse a dice expression.  Does not eat whitespace
+/// Parse a dice expression.  Does not eat whitespace
 fn parse_dice(input: &str) -> IResult<&str, Dice> {
+    // parse main dice expression
     let (input, (count, _, sides)) = tuple((digit1, tag("d"), digit1))(input)?;
+
+    // check for keep expression to keep highest dice (2d20k1)
+    let (keep, input) = match tuple::<&str, _, (_, _), _>((tag("k"), digit1))(input) {
+        // if ok, keep expression is present
+        Ok((rest, (_, keep_amount))) => (keep_amount, rest),
+        // otherwise absent and keep all dice
+        Err(_) => ("", input)
+    };
+
+    // check for drop expression to drop highest dice (2d20dh1)
+    let (drop, input) = match tuple::<&str, _, (_, _), _>((tag("dh"), digit1))(input) {
+        // if ok, keep expression is present
+        Ok((rest, (_, drop_amount))) => (drop_amount, rest),
+        // otherwise absent and keep all dice
+        Err(_) => ("", input)
+    };
+
+    let count: u32 = count.parse().unwrap();
+
+    // don't allow keep greater than number of dice, and don't allow keep zero
+    let keep_drop = match keep.parse::<u32>() {
+        // Ok, there's a keep value, check and create Keep
+        Ok(i) => match i {
+            _i if _i > count || _i == 0 => KeepOrDrop::None,
+            i => KeepOrDrop::Keep(i),
+        },
+        // Err, check if drop works
+        Err(_) => {
+            match drop.parse::<u32>() {
+                // Ok, there's a drop value, check and create Drop
+                Ok(i) => match i {
+                    _i if i >= count => KeepOrDrop::None,
+                    i => KeepOrDrop::Drop(i),
+                },
+                // Err, there's neither keep nor drop
+                Err(_) => KeepOrDrop::None,
+            }
+        },
+    };
+
     Ok((
         input,
-        Dice::new(count.parse().unwrap(), sides.parse().unwrap()),
+        Dice::new(count, sides.parse().unwrap(), keep_drop),
     ))
 }
 
@@ -108,16 +149,29 @@ mod tests {
     use super::*;
     #[test]
     fn dice_test() {
-        assert_eq!(parse_dice("2d4"), Ok(("", Dice::new(2, 4))));
-        assert_eq!(parse_dice("20d40"), Ok(("", Dice::new(20, 40))));
-        assert_eq!(parse_dice("8d7"), Ok(("", Dice::new(8, 7))));
+        assert_eq!(parse_dice("2d4"), Ok(("", Dice::new(2, 4, KeepOrDrop::None))));
+        assert_eq!(parse_dice("20d40"), Ok(("", Dice::new(20, 40, KeepOrDrop::None))));
+        assert_eq!(parse_dice("8d7"), Ok(("", Dice::new(8, 7, KeepOrDrop::None))));
+        assert_eq!(parse_dice("2d20k1"), Ok(("", Dice::new(2, 20, KeepOrDrop::Keep(1)))));
+        assert_eq!(parse_dice("100d10k90"), Ok(("", Dice::new(100, 10, KeepOrDrop::Keep(90)))));
+        assert_eq!(parse_dice("11d10k10"), Ok(("", Dice::new(11, 10, KeepOrDrop::Keep(10)))));
+        assert_eq!(parse_dice("12d10k11"), Ok(("", Dice::new(12, 10, KeepOrDrop::Keep(11)))));
+        assert_eq!(parse_dice("12d10k13"), Ok(("", Dice::new(12, 10, KeepOrDrop::None))));
+        assert_eq!(parse_dice("12d10k0"), Ok(("", Dice::new(12, 10, KeepOrDrop::None))));
+        assert_eq!(parse_dice("20d40dh5"), Ok(("", Dice::new(20, 40, KeepOrDrop::Drop(5)))));
+        assert_eq!(parse_dice("8d7dh9"), Ok(("", Dice::new(8, 7, KeepOrDrop::None))));
+        assert_eq!(parse_dice("8d7dh8"), Ok(("", Dice::new(8, 7, KeepOrDrop::None))));
     }
 
     #[test]
     fn element_test() {
         assert_eq!(
             parse_element("  \t\n\r\n 8d7 \n"),
-            Ok((" \n", Element::Dice(Dice::new(8, 7))))
+            Ok((" \n", Element::Dice(Dice::new(8, 7, KeepOrDrop::None))))
+        );
+        assert_eq!(
+            parse_element("  \t\n\r\n 3d20k2 \n"),
+            Ok((" \n", Element::Dice(Dice::new(3, 20, KeepOrDrop::Keep(2)))))
         );
         assert_eq!(
             parse_element("  \t\n\r\n 8 \n"),
@@ -139,14 +193,21 @@ mod tests {
             parse_signed_element("  \t\n\r\n- 8d4 \n"),
             Ok((
                 " \n",
-                SignedElement::Negative(Element::Dice(Dice::new(8, 4)))
+                SignedElement::Negative(Element::Dice(Dice::new(8, 4, KeepOrDrop::None)))
+            ))
+        );
+        assert_eq!(
+            parse_signed_element("  \t\n\r\n- 8d4k4 \n"),
+            Ok((
+                " \n",
+                SignedElement::Negative(Element::Dice(Dice::new(8, 4, KeepOrDrop::Keep(4))))
             ))
         );
         assert_eq!(
             parse_signed_element("  \t\n\r\n+ 8d4 \n"),
             Ok((
                 " \n",
-                SignedElement::Positive(Element::Dice(Dice::new(8, 4)))
+                SignedElement::Positive(Element::Dice(Dice::new(8, 4, KeepOrDrop::None)))
             ))
         );
     }
@@ -158,29 +219,39 @@ mod tests {
             Ok((
                 "",
                 ElementExpression(vec![SignedElement::Positive(Element::Dice(Dice::new(
-                    8, 4
+                    8, 4, KeepOrDrop::None
                 )))])
             ))
         );
+        assert_eq!(
+            parse_element_expression("\t2d20k1 + 5"),
+            Ok((
+                "",
+                ElementExpression(vec![
+                    SignedElement::Positive(Element::Dice(Dice::new(2, 20, KeepOrDrop::Keep(1)))),
+                    SignedElement::Positive(Element::Bonus(5)),
+                ])
+            ))
+        );
         assert_eq!(
             parse_element_expression(" -  8d4 \n "),
             Ok((
                 " \n ",
                 ElementExpression(vec![SignedElement::Negative(Element::Dice(Dice::new(
-                    8, 4
+                    8, 4, KeepOrDrop::None
                 )))])
             ))
         );
         assert_eq!(
-            parse_element_expression("\t3d4 + 7 - 5 - 6d12 + 1d1 + 53 1d5 "),
+            parse_element_expression("\t3d4k2 + 7 - 5 - 6d12dh3 + 1d1 + 53 1d5 "),
             Ok((
                 " 1d5 ",
                 ElementExpression(vec![
-                    SignedElement::Positive(Element::Dice(Dice::new(3, 4))),
+                    SignedElement::Positive(Element::Dice(Dice::new(3, 4, KeepOrDrop::Keep(2)))),
                     SignedElement::Positive(Element::Bonus(7)),
                     SignedElement::Negative(Element::Bonus(5)),
-                    SignedElement::Negative(Element::Dice(Dice::new(6, 12))),
-                    SignedElement::Positive(Element::Dice(Dice::new(1, 1))),
+                    SignedElement::Negative(Element::Dice(Dice::new(6, 12, KeepOrDrop::Drop(3)))),
+                    SignedElement::Positive(Element::Dice(Dice::new(1, 1, KeepOrDrop::None))),
                     SignedElement::Positive(Element::Bonus(53)),
                 ])
             ))

dicebot/src/basic/roll.rs

@@ -4,6 +4,7 @@
  * project.
  */
 use crate::basic::dice;
+use crate::basic::dice::KeepOrDrop;
 use rand::prelude::*;
 use std::fmt;
 use std::ops::{Deref, DerefMut};
@@ -19,15 +20,27 @@ pub trait Rolled {
 }
 
 #[derive(Debug, PartialEq, Eq, Clone)]
-pub struct DiceRoll(pub Vec<u32>);
+/// array of rolls in order, how many dice to keep, and how many to drop
+///   keep indicates how many of the highest dice to keep
+///   drop indicates how many of the highest dice to drop
+pub struct DiceRoll (pub Vec<u32>, usize, usize);
 
 impl DiceRoll {
     pub fn rolls(&self) -> &[u32] {
         &self.0
     }
 
+    pub fn keep(&self) -> usize {
+        self.1
+    }
+
+    pub fn drop(&self) -> usize {
+        self.2
+    }
+
+    // only count kept dice in total
     pub fn total(&self) -> u32 {
-        self.0.iter().sum()
+        self.0[self.2..self.1].iter().sum()
     }
 }
 
@@ -41,11 +54,21 @@ impl fmt::Display for DiceRoll {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "{}", self.rolled_value())?;
         let rolls = self.rolls();
-        let mut iter = rolls.iter();
+        let keep  = self.keep();
+        let drop  = self.drop();
+        let mut iter = rolls.iter().enumerate();
         if let Some(first) = iter.next() {
-            write!(f, " ({}", first)?;
+            if drop != 0 {
+                write!(f, " ([{}]", first.1)?;
+            } else {
+                write!(f, " ({}", first.1)?;
+            }
             for roll in iter {
-                write!(f, " + {}", roll)?;
+                if roll.0 >= keep || roll.0 < drop {
+                    write!(f, " + [{}]", roll.1)?;
+                } else {
+                    write!(f, " + {}", roll.1)?;
+                }
             }
             write!(f, ")")?;
         }
@@ -58,11 +81,17 @@ impl Roll for dice::Dice {
 
     fn roll(&self) -> DiceRoll {
         let mut rng = rand::thread_rng();
-        let rolls: Vec<_> = (0..self.count)
+        let mut rolls: Vec<_> = (0..self.count)
             .map(|_| rng.gen_range(1..=self.sides))
             .collect();
+        // sort rolls in descending order
+        rolls.sort_by(|a, b| b.cmp(a));
 
-        DiceRoll(rolls)
+        match self.keep_drop {
+            KeepOrDrop::Keep(k)  => DiceRoll(rolls,k as usize, 0),
+            KeepOrDrop::Drop(dh) => DiceRoll(rolls,self.count as usize, dh as usize),
+            KeepOrDrop::None     => DiceRoll(rolls,self.count as usize, 0),
+        }
     }
 }
 
@@ -198,18 +227,26 @@ mod tests {
     use super::*;
     #[test]
     fn dice_roll_display_test() {
-        assert_eq!(DiceRoll(vec![1, 3, 4]).to_string(), "8 (1 + 3 + 4)");
-        assert_eq!(DiceRoll(vec![]).to_string(), "0");
+        assert_eq!(DiceRoll(vec![1, 3, 4], 3, 0).to_string(), "8 (1 + 3 + 4)");
+        assert_eq!(DiceRoll(vec![], 0, 0).to_string(), "0");
         assert_eq!(
-            DiceRoll(vec![4, 7, 2, 10]).to_string(),
+            DiceRoll(vec![4, 7, 2, 10], 4, 0).to_string(),
             "23 (4 + 7 + 2 + 10)"
         );
+        assert_eq!(
+            DiceRoll(vec![20, 13, 11, 10], 3, 0).to_string(),
+            "44 (20 + 13 + 11 + [10])"
+        );
+        assert_eq!(
+            DiceRoll(vec![20, 13, 11, 10], 4, 1).to_string(),
+            "34 ([20] + 13 + 11 + 10)"
+        );
     }
 
     #[test]
     fn element_roll_display_test() {
         assert_eq!(
-            ElementRoll::Dice(DiceRoll(vec![1, 3, 4])).to_string(),
+            ElementRoll::Dice(DiceRoll(vec![1, 3, 4], 3, 0)).to_string(),
             "8 (1 + 3 + 4)"
         );
         assert_eq!(ElementRoll::Bonus(7).to_string(), "7");
@@ -218,11 +255,11 @@ mod tests {
     #[test]
     fn signed_element_roll_display_test() {
         assert_eq!(
-            SignedElementRoll::Positive(ElementRoll::Dice(DiceRoll(vec![1, 3, 4]))).to_string(),
+            SignedElementRoll::Positive(ElementRoll::Dice(DiceRoll(vec![1, 3, 4], 3, 0))).to_string(),
             "8 (1 + 3 + 4)"
         );
         assert_eq!(
-            SignedElementRoll::Negative(ElementRoll::Dice(DiceRoll(vec![1, 3, 4]))).to_string(),
+            SignedElementRoll::Negative(ElementRoll::Dice(DiceRoll(vec![1, 3, 4], 3, 0))).to_string(),
             "-8 (1 + 3 + 4)"
         );
         assert_eq!(
@@ -239,14 +276,14 @@ mod tests {
     fn element_expression_roll_display_test() {
         assert_eq!(
             ElementExpressionRoll(vec![SignedElementRoll::Positive(ElementRoll::Dice(
-                DiceRoll(vec![1, 3, 4])
+                DiceRoll(vec![1, 3, 4], 3, 0)
             )),])
             .to_string(),
             "8 (1 + 3 + 4)"
         );
         assert_eq!(
             ElementExpressionRoll(vec![SignedElementRoll::Negative(ElementRoll::Dice(
-                DiceRoll(vec![1, 3, 4])
+                DiceRoll(vec![1, 3, 4], 3, 0)
             )),])
             .to_string(),
             "-8 (1 + 3 + 4)"
@@ -263,8 +300,8 @@ mod tests {
         );
         assert_eq!(
             ElementExpressionRoll(vec![
-                SignedElementRoll::Positive(ElementRoll::Dice(DiceRoll(vec![1, 3, 4]))),
-                SignedElementRoll::Negative(ElementRoll::Dice(DiceRoll(vec![1, 2]))),
+                SignedElementRoll::Positive(ElementRoll::Dice(DiceRoll(vec![1, 3, 4], 3, 0))),
+                SignedElementRoll::Negative(ElementRoll::Dice(DiceRoll(vec![1, 2], 2, 0))),
                 SignedElementRoll::Positive(ElementRoll::Bonus(4)),
                 SignedElementRoll::Negative(ElementRoll::Bonus(7)),
             ])
@@ -273,13 +310,33 @@ mod tests {
         );
         assert_eq!(
             ElementExpressionRoll(vec![
-                SignedElementRoll::Negative(ElementRoll::Dice(DiceRoll(vec![1, 3, 4]))),
-                SignedElementRoll::Positive(ElementRoll::Dice(DiceRoll(vec![1, 2]))),
+                SignedElementRoll::Negative(ElementRoll::Dice(DiceRoll(vec![1, 3, 4], 3, 0))),
+                SignedElementRoll::Positive(ElementRoll::Dice(DiceRoll(vec![1, 2], 2, 0))),
                 SignedElementRoll::Negative(ElementRoll::Bonus(4)),
                 SignedElementRoll::Positive(ElementRoll::Bonus(7)),
             ])
             .to_string(),
             "-2 (-8 (1 + 3 + 4) + 3 (1 + 2) - 4 + 7)"
         );
+        assert_eq!(
+            ElementExpressionRoll(vec![
+                SignedElementRoll::Negative(ElementRoll::Dice(DiceRoll(vec![4, 3, 1], 3, 0))),
+                SignedElementRoll::Positive(ElementRoll::Dice(DiceRoll(vec![12, 2], 1, 0))),
+                SignedElementRoll::Negative(ElementRoll::Bonus(4)),
+                SignedElementRoll::Positive(ElementRoll::Bonus(7)),
+            ])
+            .to_string(),
+            "7 (-8 (4 + 3 + 1) + 12 (12 + [2]) - 4 + 7)"
+        );
+        assert_eq!(
+            ElementExpressionRoll(vec![
+                SignedElementRoll::Negative(ElementRoll::Dice(DiceRoll(vec![4, 3, 1], 3, 1))),
+                SignedElementRoll::Positive(ElementRoll::Dice(DiceRoll(vec![12, 2], 2, 0))),
+                SignedElementRoll::Negative(ElementRoll::Bonus(4)),
+                SignedElementRoll::Positive(ElementRoll::Bonus(7)),
+            ])
+            .to_string(),
+            "13 (-4 ([4] + 3 + 1) + 14 (12 + 2) - 4 + 7)"
+        );
     }
 }