use std::collections::HashMap;
use parking_lot::RwLock;

/// per-session 的用户模型覆盖选择存储。
///
/// 与 ExpertRuntime 的 session_experts 平级独立，职责单一：
/// 只负责存储 session_id -> (provider, model) 的映射，不依赖任何业务模块。
#[derive(Debug, Default)]
pub struct ModelSelectionStore {
    selections: RwLock<HashMap<String, (Option<String>, Option<String>)>>,
}

impl ModelSelectionStore {
    pub fn new() -> Self {
        Self::default()
    }

    /// 设置 session 的用户模型覆盖。provider 和 model 均为 None 时清除该 session 的选择。
    pub fn set(&self, session_id: &str, provider: Option<String>, model: Option<String>) {
        let mut selections = self
            .selections
            .write();
        if provider.is_none() && model.is_none() {
            selections.remove(session_id);
        } else {
            selections.insert(session_id.to_string(), (provider, model));
        }
    }

    /// 读取 session 的用户模型覆盖。
    pub fn get(&self, session_id: &str) -> Option<(Option<String>, Option<String>)> {
        self.selections
            .read()
            .get(session_id)
            .cloned()
    }
}

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

    #[test]
    fn set_and_get() {
        let store = ModelSelectionStore::new();
        store.set("s1", Some("p1".to_string()), Some("m1".to_string()));
        assert_eq!(
            store.get("s1"),
            Some((Some("p1".to_string()), Some("m1".to_string())))
        );
    }

    #[test]
    fn get_missing_returns_none() {
        let store = ModelSelectionStore::new();
        assert_eq!(store.get("missing"), None);
    }

    #[test]
    fn set_none_none_removes_entry() {
        let store = ModelSelectionStore::new();
        store.set("s1", Some("p1".to_string()), Some("m1".to_string()));
        assert!(store.get("s1").is_some());
        store.set("s1", None, None);
        assert!(store.get("s1").is_none());
    }

    #[test]
    fn set_only_provider_keeps_entry() {
        let store = ModelSelectionStore::new();
        store.set("s1", Some("p1".to_string()), None);
        assert_eq!(store.get("s1"), Some((Some("p1".to_string()), None)));
    }
}