Localize all command parsing code into trait impls.

This cleans up the command parser a lot, as all of the one or two line
functions and associated imports have been removed. Unfortunately it
does make the command files larger, as two trait impls are required:
one for converting to Box<dyn Command>, and one for converting from
&str to the command type.

Fixes #66.

src/commands/basic_rolling.rs

@@ -1,11 +1,37 @@
 use super::{Command, Execution, ExecutionResult};
 use crate::basic::dice::ElementExpression;
+use crate::basic::parser::parse_element_expression;
 use crate::basic::roll::Roll;
 use crate::context::Context;
+use crate::error::BotError;
 use async_trait::async_trait;
+use nom::Err as NomErr;
+use std::convert::TryFrom;
 
 pub struct RollCommand(pub ElementExpression);
 
+impl From<RollCommand> for Box<dyn Command> {
+    fn from(cmd: RollCommand) -> Self {
+        Box::new(cmd)
+    }
+}
+
+impl TryFrom<&str> for RollCommand {
+    type Error = BotError;
+
+    fn try_from(input: &str) -> Result<Self, Self::Error> {
+        let result = parse_element_expression(input);
+        match result {
+            Ok((rest, expression)) if rest.len() == 0 => Ok(RollCommand(expression)),
+            //"Legacy code boundary": translates Nom errors into BotErrors.
+            Ok(_) => Err(BotError::NomParserIncomplete),
+            Err(NomErr::Error(e)) => Err(BotError::NomParserError(e.1)),
+            Err(NomErr::Failure(e)) => Err(BotError::NomParserError(e.1)),
+            Err(NomErr::Incomplete(_)) => Err(BotError::NomParserIncomplete),
+        }
+    }
+}
+
 #[async_trait]
 impl Command for RollCommand {
     fn name(&self) -> &'static str {

src/commands/cofd.rs

@@ -1,10 +1,35 @@
 use super::{Command, Execution, ExecutionResult};
 use crate::cofd::dice::{roll_pool, DicePool, DicePoolWithContext};
+use crate::cofd::parser::{create_chance_die, parse_dice_pool};
 use crate::context::Context;
+use crate::error::BotError;
 use async_trait::async_trait;
+use std::convert::TryFrom;
 
 pub struct PoolRollCommand(pub DicePool);
 
+impl PoolRollCommand {
+    pub fn chance_die() -> Result<PoolRollCommand, BotError> {
+        let pool = create_chance_die()?;
+        Ok(PoolRollCommand(pool))
+    }
+}
+
+impl From<PoolRollCommand> for Box<dyn Command> {
+    fn from(cmd: PoolRollCommand) -> Self {
+        Box::new(cmd)
+    }
+}
+
+impl TryFrom<&str> for PoolRollCommand {
+    type Error = BotError;
+
+    fn try_from(input: &str) -> Result<Self, Self::Error> {
+        let pool = parse_dice_pool(input)?;
+        Ok(PoolRollCommand(pool))
+    }
+}
+
 #[async_trait]
 impl Command for PoolRollCommand {
     fn name(&self) -> &'static str {

src/commands/cthulhu.rs

@@ -4,10 +4,28 @@ use crate::cthulhu::dice::{
     advancement_roll, regular_roll, AdvancementRoll, AdvancementRollWithContext, DiceRoll,
     DiceRollWithContext,
 };
+use crate::cthulhu::parser::{parse_advancement_roll, parse_regular_roll};
+use crate::error::BotError;
 use async_trait::async_trait;
+use std::convert::TryFrom;
 
 pub struct CthRoll(pub DiceRoll);
 
+impl From<CthRoll> for Box<dyn Command> {
+    fn from(cmd: CthRoll) -> Self {
+        Box::new(cmd)
+    }
+}
+
+impl TryFrom<&str> for CthRoll {
+    type Error = BotError;
+
+    fn try_from(input: &str) -> Result<Self, Self::Error> {
+        let roll = parse_regular_roll(input)?;
+        Ok(CthRoll(roll))
+    }
+}
+
 #[async_trait]
 impl Command for CthRoll {
     fn name(&self) -> &'static str {
@@ -33,6 +51,21 @@ impl Command for CthRoll {
 
 pub struct CthAdvanceRoll(pub AdvancementRoll);
 
+impl From<CthAdvanceRoll> for Box<dyn Command> {
+    fn from(cmd: CthAdvanceRoll) -> Self {
+        Box::new(cmd)
+    }
+}
+
+impl TryFrom<&str> for CthAdvanceRoll {
+    type Error = BotError;
+
+    fn try_from(input: &str) -> Result<Self, Self::Error> {
+        let roll = parse_advancement_roll(input)?;
+        Ok(CthAdvanceRoll(roll))
+    }
+}
+
 #[async_trait]
 impl Command for CthAdvanceRoll {
     fn name(&self) -> &'static str {

src/commands/management.rs

@@ -1,13 +1,28 @@
 use super::{Command, Execution, ExecutionResult};
-use crate::context::Context;
 use crate::db::Users;
 use crate::error::BotError::{AccountDoesNotExist, AuthenticationError, PasswordCreationError};
 use crate::logic::hash_password;
 use crate::models::{AccountStatus, User};
+use crate::{context::Context, error::BotError};
 use async_trait::async_trait;
+use std::convert::{Into, TryFrom};
 
 pub struct RegisterCommand(pub String);
 
+impl From<RegisterCommand> for Box<dyn Command> {
+    fn from(cmd: RegisterCommand) -> Self {
+        Box::new(cmd)
+    }
+}
+
+impl TryFrom<&str> for RegisterCommand {
+    type Error = BotError;
+
+    fn try_from(value: &str) -> Result<Self, Self::Error> {
+        Ok(RegisterCommand(value.to_owned()))
+    }
+}
+
 #[async_trait]
 impl Command for RegisterCommand {
     fn name(&self) -> &'static str {
@@ -38,6 +53,20 @@ impl Command for RegisterCommand {
 
 pub struct CheckCommand(pub String);
 
+impl From<CheckCommand> for Box<dyn Command> {
+    fn from(cmd: CheckCommand) -> Self {
+        Box::new(cmd)
+    }
+}
+
+impl TryFrom<&str> for CheckCommand {
+    type Error = BotError;
+
+    fn try_from(value: &str) -> Result<Self, Self::Error> {
+        Ok(CheckCommand(value.to_owned()))
+    }
+}
+
 #[async_trait]
 impl Command for CheckCommand {
     fn name(&self) -> &'static str {
@@ -60,6 +89,20 @@ impl Command for CheckCommand {
 
 pub struct UnregisterCommand;
 
+impl From<UnregisterCommand> for Box<dyn Command> {
+    fn from(cmd: UnregisterCommand) -> Self {
+        Box::new(cmd)
+    }
+}
+
+impl TryFrom<&str> for UnregisterCommand {
+    type Error = BotError;
+
+    fn try_from(_: &str) -> Result<Self, Self::Error> {
+        Ok(UnregisterCommand)
+    }
+}
+
 #[async_trait]
 impl Command for UnregisterCommand {
     fn name(&self) -> &'static str {

src/commands/misc.rs

@@ -1,10 +1,27 @@
 use super::{Command, Execution, ExecutionResult};
 use crate::context::Context;
-use crate::help::HelpTopic;
+use crate::error::BotError;
+use crate::help::{parse_help_topic, HelpTopic};
 use async_trait::async_trait;
+use std::convert::TryFrom;
 
 pub struct HelpCommand(pub Option<HelpTopic>);
 
+impl From<HelpCommand> for Box<dyn Command> {
+    fn from(cmd: HelpCommand) -> Self {
+        Box::new(cmd)
+    }
+}
+
+impl TryFrom<&str> for HelpCommand {
+    type Error = BotError;
+
+    fn try_from(input: &str) -> Result<Self, Self::Error> {
+        let topic = parse_help_topic(input);
+        Ok(HelpCommand(topic))
+    }
+}
+
 #[async_trait]
 impl Command for HelpCommand {
     fn name(&self) -> &'static str {

src/commands/parser.rs

@@ -3,8 +3,6 @@
  * governed by the terms of the MIT license, from the original
  * axfive-matrix-dicebot project.
  */
-use crate::basic::parser::parse_element_expression;
-use crate::cofd::parser::{create_chance_die, parse_dice_pool};
 use crate::commands::{
     basic_rolling::RollCommand,
     cofd::PoolRollCommand,
@@ -16,13 +14,10 @@ use crate::commands::{
     },
     Command,
 };
-use crate::cthulhu::parser::{parse_advancement_roll, parse_regular_roll};
 use crate::error::BotError;
-use crate::help::parse_help_topic;
-use crate::parser::variables::parse_set_variable;
 use combine::parser::char::{char, letter, space};
 use combine::{any, many1, optional, Parser};
-use nom::Err as NomErr;
+use std::convert::TryFrom;
 use thiserror::Error;
 
 #[derive(Debug, Clone, PartialEq, Error)]
@@ -34,73 +29,6 @@ pub enum CommandParsingError {
     InternalParseError(#[from] combine::error::StringStreamError),
 }
 
-// Parse a roll expression.
-fn parse_roll(input: &str) -> Result<Box<dyn Command>, BotError> {
-    let result = parse_element_expression(input);
-    match result {
-        Ok((rest, expression)) if rest.len() == 0 => Ok(Box::new(RollCommand(expression))),
-        //Legacy code boundary translates nom errors into BotErrors.
-        Ok(_) => Err(BotError::NomParserIncomplete),
-        Err(NomErr::Error(e)) => Err(BotError::NomParserError(e.1)),
-        Err(NomErr::Failure(e)) => Err(BotError::NomParserError(e.1)),
-        Err(NomErr::Incomplete(_)) => Err(BotError::NomParserIncomplete),
-    }
-}
-
-fn parse_register_command(input: &str) -> Result<Box<dyn Command>, BotError> {
-    Ok(Box::new(RegisterCommand(input.to_owned())))
-}
-
-fn parse_check_command(input: &str) -> Result<Box<dyn Command>, BotError> {
-    Ok(Box::new(CheckCommand(input.to_owned())))
-}
-
-fn parse_unregister_command() -> Result<Box<dyn Command>, BotError> {
-    Ok(Box::new(UnregisterCommand))
-}
-
-fn parse_get_variable_command(input: &str) -> Result<Box<dyn Command>, BotError> {
-    Ok(Box::new(GetVariableCommand(input.to_owned())))
-}
-
-fn parse_set_variable_command(input: &str) -> Result<Box<dyn Command>, BotError> {
-    let (variable_name, value) = parse_set_variable(input)?;
-    Ok(Box::new(SetVariableCommand(variable_name, value)))
-}
-
-fn parse_delete_variable_command(input: &str) -> Result<Box<dyn Command>, BotError> {
-    Ok(Box::new(DeleteVariableCommand(input.to_owned())))
-}
-
-fn parse_pool_roll(input: &str) -> Result<Box<dyn Command>, BotError> {
-    let pool = parse_dice_pool(input)?;
-    Ok(Box::new(PoolRollCommand(pool)))
-}
-
-fn parse_cth_roll(input: &str) -> Result<Box<dyn Command>, BotError> {
-    let roll = parse_regular_roll(input)?;
-    Ok(Box::new(CthRoll(roll)))
-}
-
-fn parse_cth_advancement_roll(input: &str) -> Result<Box<dyn Command>, BotError> {
-    let roll = parse_advancement_roll(input)?;
-    Ok(Box::new(CthAdvanceRoll(roll)))
-}
-
-fn chance_die() -> Result<Box<dyn Command>, BotError> {
-    let pool = create_chance_die()?;
-    Ok(Box::new(PoolRollCommand(pool)))
-}
-
-fn get_all_variables() -> Result<Box<dyn Command>, BotError> {
-    Ok(Box::new(GetAllVariablesCommand))
-}
-
-fn help(topic: &str) -> Result<Box<dyn Command>, BotError> {
-    let topic = parse_help_topic(topic);
-    Ok(Box::new(HelpCommand(topic)))
-}
-
 /// 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).
@@ -132,25 +60,34 @@ fn split_command(input: &str) -> Result<(String, String), CommandParsingError> {
     Ok((command, command_input))
 }
 
+/// Atempt to convert text input to a Boxed command type. Shortens
+/// boilerplate.
+macro_rules! convert_to {
+    ($type:ident, $input: expr) => {
+        $type::try_from($input.as_str()).map(Into::into)
+    };
+}
+
 /// 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, return an error.
 pub fn parse_command(input: &str) -> Result<Box<dyn Command>, BotError> {
     match split_command(input) {
         Ok((cmd, cmd_input)) => match cmd.to_lowercase().as_ref() {
-            "variables" => get_all_variables(),
-            "get" => parse_get_variable_command(&cmd_input),
-            "set" => parse_set_variable_command(&cmd_input),
-            "del" => parse_delete_variable_command(&cmd_input),
-            "r" | "roll" => parse_roll(&cmd_input),
-            "rp" | "pool" => parse_pool_roll(&cmd_input),
-            "cthroll" => parse_cth_roll(&cmd_input),
-            "cthadv" | "ctharoll" => parse_cth_advancement_roll(&cmd_input),
-            "chance" => chance_die(),
-            "help" => help(&cmd_input),
-            "register" => parse_register_command(&cmd_input),
-            "check" => parse_check_command(&cmd_input),
-            "unregister" => parse_unregister_command(),
+            // "variables" => GetAllVariablesCommand::try_from(input).map(Into::into),
+            "variables" => convert_to!(GetAllVariablesCommand, cmd_input),
+            "get" => convert_to!(GetVariableCommand, cmd_input),
+            "set" => convert_to!(SetVariableCommand, cmd_input),
+            "del" => convert_to!(DeleteVariableCommand, cmd_input),
+            "r" | "roll" => convert_to!(RollCommand, cmd_input),
+            "rp" | "pool" => convert_to!(PoolRollCommand, cmd_input),
+            "chance" => PoolRollCommand::chance_die().map(Into::into),
+            "cthroll" => convert_to!(CthRoll, cmd_input),
+            "cthadv" | "ctharoll" => convert_to!(CthAdvanceRoll, cmd_input),
+            "help" => convert_to!(HelpCommand, cmd_input),
+            "register" => convert_to!(RegisterCommand, cmd_input),
+            "check" => convert_to!(CheckCommand, cmd_input),
+            "unregister" => convert_to!(UnregisterCommand, cmd_input),
             _ => Err(CommandParsingError::UnrecognizedCommand(cmd).into()),
         },
         //All other errors passed up.

src/commands/variables.rs

@@ -2,10 +2,26 @@ use super::{Command, Execution, ExecutionResult};
 use crate::context::Context;
 use crate::db::errors::DataError;
 use crate::db::Variables;
+use crate::error::BotError;
 use async_trait::async_trait;
+use std::convert::TryFrom;
 
 pub struct GetAllVariablesCommand;
 
+impl From<GetAllVariablesCommand> for Box<dyn Command> {
+    fn from(cmd: GetAllVariablesCommand) -> Self {
+        Box::new(cmd)
+    }
+}
+
+impl TryFrom<&str> for GetAllVariablesCommand {
+    type Error = BotError;
+
+    fn try_from(_: &str) -> Result<Self, Self::Error> {
+        Ok(GetAllVariablesCommand)
+    }
+}
+
 #[async_trait]
 impl Command for GetAllVariablesCommand {
     fn name(&self) -> &'static str {
@@ -41,6 +57,20 @@ impl Command for GetAllVariablesCommand {
 
 pub struct GetVariableCommand(pub String);
 
+impl From<GetVariableCommand> for Box<dyn Command> {
+    fn from(cmd: GetVariableCommand) -> Self {
+        Box::new(cmd)
+    }
+}
+
+impl TryFrom<&str> for GetVariableCommand {
+    type Error = BotError;
+
+    fn try_from(input: &str) -> Result<Self, Self::Error> {
+        Ok(GetVariableCommand(input.to_owned()))
+    }
+}
+
 #[async_trait]
 impl Command for GetVariableCommand {
     fn name(&self) -> &'static str {
@@ -71,6 +101,21 @@ impl Command for GetVariableCommand {
 
 pub struct SetVariableCommand(pub String, pub i32);
 
+impl From<SetVariableCommand> for Box<dyn Command> {
+    fn from(cmd: SetVariableCommand) -> Self {
+        Box::new(cmd)
+    }
+}
+
+impl TryFrom<&str> for SetVariableCommand {
+    type Error = BotError;
+
+    fn try_from(input: &str) -> Result<Self, Self::Error> {
+        let (variable_name, value) = crate::parser::variables::parse_set_variable(input)?;
+        Ok(SetVariableCommand(variable_name, value))
+    }
+}
+
 #[async_trait]
 impl Command for SetVariableCommand {
     fn name(&self) -> &'static str {
@@ -97,6 +142,20 @@ impl Command for SetVariableCommand {
 
 pub struct DeleteVariableCommand(pub String);
 
+impl From<DeleteVariableCommand> for Box<dyn Command> {
+    fn from(cmd: DeleteVariableCommand) -> Self {
+        Box::new(cmd)
+    }
+}
+
+impl TryFrom<&str> for DeleteVariableCommand {
+    type Error = BotError;
+
+    fn try_from(input: &str) -> Result<Self, Self::Error> {
+        Ok(DeleteVariableCommand(input.to_owned()))
+    }
+}
+
 #[async_trait]
 impl Command for DeleteVariableCommand {
     fn name(&self) -> &'static str {