From da0819745a2fb5cee2297f307b4ce54dbd923528 Mon Sep 17 00:00:00 2001
From: projectmoon <projectmoon@agnos.is>
Date: Mon, 31 Aug 2020 00:07:56 +0000
Subject: [PATCH] Switch to non-macro nom parser with better text handling.

By using the alpha1 function in complete mode, we are able to handle
arbitrary single-word commands (e.g. "!help") and proprly map the
remaining input to an empty string.
---
 src/commands/parser.rs | 109 ++++++++++++++++++++++++++++++-----------
 1 file changed, 80 insertions(+), 29 deletions(-)

diff --git a/src/commands/parser.rs b/src/commands/parser.rs
index afd3e21..27fce63 100644
--- a/src/commands/parser.rs
+++ b/src/commands/parser.rs
@@ -1,10 +1,9 @@
-use nom::{alt, complete, named, tag, take_while, tuple, IResult};
-
 use crate::cofd::parser::{create_chance_die, parse_dice_pool};
 use crate::commands::{Command, HelpCommand, PoolRollCommand, RollCommand};
 use crate::dice::parser::parse_element_expression;
 use crate::help::parse_help_topic;
 use crate::parser::{eat_whitespace, trim};
+use nom::{bytes::complete::tag, character::complete::alpha1, IResult};
 
 // Parse a roll expression.
 fn parse_roll(input: &str) -> IResult<&str, Box<dyn Command>> {
@@ -30,36 +29,88 @@ fn help(topic: &str) -> IResult<&str, Box<dyn Command>> {
     Ok(("", Box::new(HelpCommand(topic))))
 }
 
-/// Potentially parse a command expression.  If we recognize the command, an error should be raised
-/// if the command is misparsed.  If we don't recognize the command, ignore it and return none
-pub fn parse_command(original_input: &str) -> IResult<&str, Option<Box<dyn Command>>> {
-    let (input, _) = eat_whitespace(original_input)?;
+/// Split an input string into its constituent command and "everything
+/// else" parts. Extracts the command separately from its input (i.e.
+/// rest of the line) and returns a tuple of (command_input, command).
+fn split_command(input: &str) -> IResult<&str, &str> {
+    let (input, _) = eat_whitespace(input)?;
+    let (input, _) = tag("!")(input)?;
+    let (command_input, command) = alpha1(input)?;
+    let (command_input, _) = eat_whitespace(command_input)?;
+    //TODO strip witespace from end of command input
+    Ok((command_input, command))
+}
 
-    //Parser understands either specific !commands with no input, or any !command with extra input.
-    named!(command(&str) -> (&str, &str), tuple!(
-        complete!(tag!("!")),
-        alt!(
-            //TODO figure out how to gracefully handle arbitrary single commands.
-            complete!(tag!("chance")) |
-            complete!(tag!("help")) |
-            complete!(take_while!(char::is_alphabetic))
-        )
-    ));
+/// Potentially parse a command expression. If we recognize the
+/// command, an error should be raised if the command is misparsed. If
+/// we don't recognize the command, ignore it and return none
+pub fn parse_command(input: &str) -> IResult<&str, Option<Box<dyn Command>>> {
+    let (cmd_input, cmd) = split_command(input)?;
 
-    let (input, command) = match command(input) {
-        // Strip the exclamation mark
-        Ok((input, (_, result))) => (input, result),
-        Err(_e) => {
-            return Ok((original_input, None));
-        }
-    };
-
-    match command {
-        "r" | "roll" => parse_roll(input).map(|(input, command)| (input, Some(command))),
-        "rp" | "pool" => parse_pool_roll(input).map(|(input, command)| (input, Some(command))),
+    match cmd {
+        "r" | "roll" => parse_roll(cmd_input).map(|(input, command)| (input, Some(command))),
+        "rp" | "pool" => parse_pool_roll(cmd_input).map(|(input, command)| (input, Some(command))),
         "chance" => chance_die().map(|(input, command)| (input, Some(command))),
-        "help" => help(input).map(|(input, command)| (input, Some(command))),
+        "help" => help(cmd_input).map(|(input, command)| (input, Some(command))),
         // No recognized command, ignore this.
-        _ => Ok((original_input, None)),
+        _ => Ok((input, None)),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn basic_command_test() {
+        assert_eq!(
+            ("1d4", "roll"),
+            split_command("!roll 1d4").expect("got parsing error")
+        );
+    }
+
+    #[test]
+    fn whitespace_at_start_test() {
+        assert_eq!(
+            ("1d4", "roll"),
+            split_command("   !roll 1d4").expect("got parsing error")
+        );
+    }
+
+    #[test]
+    fn whitespace_at_end_test() {
+        //TODO currently it does not chop whitespace off the end.
+        assert_eq!(
+            ("1d4   ", "roll"),
+            split_command("!roll 1d4   ").expect("got parsing error")
+        );
+    }
+
+    #[test]
+    fn whitespace_on_both_ends_test() {
+        //TODO currently it does not chop whitespace off the end.
+        assert_eq!(
+            ("1d4   ", "roll"),
+            split_command("   !roll 1d4   ").expect("got parsing error")
+        );
+    }
+
+    #[test]
+    fn single_command_test() {
+        assert_eq!(
+            ("", "roll"),
+            split_command("!roll").expect("got parsing error")
+        );
+
+        assert_eq!(
+            ("", "thisdoesnotexist"),
+            split_command("!thisdoesnotexist").expect("got parsing error")
+        );
+    }
+
+    #[test]
+    fn bad_command_test() {
+        assert!(split_command("roll 1d4").is_err());
+        assert!(split_command("roll").is_err());
     }
 }