use std::env;
use std::io::{Error, ErrorKind, Result};
use std::path::PathBuf;

pub struct Configuration {
    // Default Base Directories, default to XDG dirs but can be
    pub output_directory: PathBuf,
}

impl Configuration {
    pub fn new() -> Result<Self> {
        let output_directory =
            Configuration::directory("PAGE_OUTPUT_DIRECTORY", "XDG_CACHE_HOME", ".cache", "page")?;

        Ok(Configuration { output_directory })
    }

    fn directory(
        user_override: &str,
        default_value: &str,
        home_fallback: &str,
        path: &str,
    ) -> Result<PathBuf> {
        match env::var(user_override) {
            Ok(directory) => Ok(PathBuf::from(directory).join(path)),
            Err(_) => match env::var(default_value) {
                Ok(directory) => Ok(PathBuf::from(directory).join(path)),
                Err(_) => match env::var("HOME") {
                    Ok(directory) => Ok(PathBuf::from(directory).join(home_fallback).join(path)),
                    Err(_) => Err(Error::new(
                        ErrorKind::NotFound,
                        format!(
                            "Could not find required directory, {user_override} or {default_value} should be set and readable"
                        ),
                    )),
                },
            },
        }
    }
}

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

    use test_utilities::*;

    #[test]
    fn test_sets_correct_configuration_directories() {
        let default_configuration = Configuration::new().unwrap();

        let test_dir = setup_test_dir();

        // SAFETY: Run only in single-threaded mode
        unsafe {
            env::set_var("PAGE_OUTPUT_DIRECTORY", test_dir.join("output"));
        }
        let override_configuration = Configuration::new().unwrap();

        // Ensure our overrides were applied

        assert_eq!(
            override_configuration.output_directory,
            test_dir.join("output/page")
        );

        // Ensure all the defaults are different from defaults

        assert_ne!(
            default_configuration.output_directory,
            override_configuration.output_directory
        );

        cleanup_test_dir(&test_dir);
    }
}