use etcetera::BaseStrategy;
use std::path::PathBuf;

use crate::path_ext::PathExt;

fn xdg_dir(env: &str) -> Option<PathBuf> {
    if cfg!(windows) {
        let env_var = std::env::var(env).ok()?;
        Some(PathBuf::from(env_var))
    } else {
        // On non-Windows platforms, `etcetera` already handles XDG variables
        None
    }
}

fn runtime_dir(basedirs: &impl BaseStrategy) -> Option<PathBuf> {
    xdg_dir("XDG_RUNTIME_DIR").or_else(|| basedirs.runtime_dir())
}

fn state_dir(basedirs: &impl BaseStrategy) -> Option<PathBuf> {
    xdg_dir("XDG_STATE_HOME").or_else(|| basedirs.state_dir())
}

fn cache_dir(basedirs: &impl BaseStrategy) -> PathBuf {
    xdg_dir("XDG_CACHE_HOME").unwrap_or_else(|| basedirs.cache_dir())
}

/// A helper struct for directories in fnm that uses XDG Base Directory Specification
/// if applicable for the platform.
#[derive(Debug)]
pub struct Directories(
    #[cfg(windows)] etcetera::base_strategy::Windows,
    #[cfg(not(windows))] etcetera::base_strategy::Xdg,
);

impl Default for Directories {
    fn default() -> Self {
        Self(etcetera::choose_base_strategy().expect("choosing base strategy"))
    }
}

impl Directories {
    pub fn strategy(&self) -> &impl BaseStrategy {
        &self.0
    }

    pub fn default_base_dir(&self) -> PathBuf {
        let strategy = self.strategy();
        let modern = strategy.data_dir().join("fnm");
        if modern.exists() {
            return modern;
        }

        let legacy = strategy.home_dir().join(".fnm");
        if legacy.exists() {
            return legacy;
        }

        #[cfg(target_os = "macos")]
        {
            let basedirs = etcetera::base_strategy::Apple::new().expect("Can't get home directory");
            let legacy = basedirs.data_dir().join("fnm");
            if legacy.exists() {
                return legacy;
            }
        }

        modern.ensure_exists_silently()
    }

    pub fn multishell_storage(&self) -> PathBuf {
        let basedirs = self.strategy();
        let dir = runtime_dir(basedirs)
            .or_else(|| state_dir(basedirs))
            .unwrap_or_else(|| cache_dir(basedirs));
        dir.join("fnm_multishells")
    }
}