2022-2-WS_group_project_pmuw-project/src/preprocess.rs

use crate::error::ShellError;
use once_cell::unsync::Lazy;
use regex::Regex;
use std::env;

const ENV_SET: Lazy<Regex> = Lazy::new(|| Regex::new(r#"(?P<key>\w+)=(?P<value>\w*)"#).unwrap());
const ENV_VARIABLE: Lazy<Regex> = Lazy::new(|| Regex::new(r"(\\\$|\$(?P<env>\w+))").unwrap());

/// Returns `Ok(Some(...))` if a command should be triggered after calling this functions. If it
/// returns `Ok(None)`, do not execute a command.
pub fn preprocess(mut line: String) -> Result<Option<String>, ShellError> {
    if let Some(capture) = ENV_SET.captures(&line) {
        let key = capture.name("key").unwrap().as_str();
        let value = capture
            .name("value")
            .map_or("".to_string(), |v| v.as_str().to_string());

        env::set_var(key, value);
        return Ok(None);
    }

    for capture in ENV_VARIABLE.captures_iter(&line.clone()) {
        let variable_name = capture.name("env").unwrap().as_str();
        if variable_name.is_empty() {
            continue;
        }
        let value = env::var(variable_name).unwrap_or_default();

        line = ENV_VARIABLE.replacen(&line, 1, &value).to_string();
    }

    Ok(Some(line))
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_preprocess_env_variable() {
        assert_eq!(preprocess("key=value".to_string()), Ok(None));
        assert_eq!(env::var("key").unwrap_or_default(), "value".to_string())
    }

    #[test]
    fn test_preprocessing_resolve_env_variable() {
        assert_eq!(preprocess("key=value".to_string()), Ok(None));
        assert_eq!(preprocess("$key".to_string()), Ok(Some("value".to_string())))
    }

    #[test]
    fn test_preprocessing_resolve_non_existent_env_variable() {
        assert_eq!(preprocess("$nonexitent".to_string()), Ok(Some("".to_string())))
    }
}