tenquestionmarks/src/modules/loader.rs

use std::collections::BTreeMap;
use std::error::Error;
use std::fmt;

use toml::Table;

use modules::Module;
use modules::discord::DiscordModule;
use modules::lua::LuaModule;
use modules::stdin::StdinModule;
use modules::echo::EchoModule;
use modules::random::RandomModule;

pub struct ModuleLoader {
    types: BTreeMap<&'static str, fn(&Table) -> Box<Module>>
}

impl ModuleLoader {
    pub fn new () -> ModuleLoader {
        let mut types = BTreeMap::new();
        types.insert("discord", DiscordModule::new as fn(&Table) -> Box<Module>);
        types.insert("lua", LuaModule::new as fn(&Table) -> Box<Module>);
        types.insert("stdin", StdinModule::new as fn(&Table) -> Box<Module>);
        types.insert("echo", EchoModule::new as fn(&Table) -> Box<Module>);
        types.insert("random", RandomModule::new as fn(&Table) -> Box<Module>);
        ModuleLoader {
            types: types
        }
    }

    pub fn load_from_configuration (&self, configuration: Table) -> Result<BTreeMap<String, Box<Module>>, ModuleLoaderError> {
        configuration.into_iter().map(|(key, value)| {
            match value.as_table() {
                Some(table) => {
                    let module = self.load_single_module(&key, table)?;
                    Result::Ok((key, module))
                },
                None => Result::Err(ModuleLoaderError { message: format!("Bad configuration parameters for module instance: {}. Configuration for a Module must be a table.", key) })
            }
        }).collect()
    }

    pub fn load_single_module (&self, name: &str, configuration: &Table) -> Result<Box<Module>, ModuleLoaderError> {
        /*
         * The Module type defaults to the instance name (in the tenquestionmarks configuration)
         * but can explicitly be set by using the special "type" parameter.
         */
        let module_type: &str = configuration.get("type")
                                             .and_then(|value| value.as_str())
                                             .unwrap_or(name);

        match self.types.get(module_type) {
           Some(constructor) => Result::Ok(constructor(configuration)),
           None => Result::Err(ModuleLoaderError { message: format!("No such module type: {}", module_type) })
        }
    }
}

#[derive(Debug)]
pub struct ModuleLoaderError {
    message: String
}

impl Error for ModuleLoaderError {
    fn description(&self) -> &str {
        &self.message[..]
    }
}

impl fmt::Display for ModuleLoaderError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "ModuleLoaderError: {}", self.message)
    }
}