use crate::core::types::ConversationMessage;

/// The in-memory conversation history for the current session.
///
/// Stores messages as a flat ordered list. Each [`push`][`Self::push`] appends
/// one message; [`messages`][`Self::messages`] returns a slice over all of them.
///
/// This is a flat list for Phase 1. Phases 3+ will introduce a tree structure
/// (each event carrying a `parent_id`) to support conversation branching and
/// sub-agent threads. The flat model is upward-compatible: a tree is just a
/// linear chain of parent IDs when there is no branching.
pub struct ConversationHistory {
    messages: Vec<ConversationMessage>,
}

impl ConversationHistory {
    /// Create an empty history.
    pub fn new() -> Self {
        Self {
            messages: Vec::new(),
        }
    }

    /// Append one message to the end of the history.
    pub fn push(&mut self, message: ConversationMessage) {
        self.messages.push(message);
    }

    /// Return the full ordered message list, oldest-first.
    ///
    /// This slice is what gets serialised and sent to the provider on each
    /// turn -- the provider needs the full prior context to generate a coherent
    /// continuation.
    pub fn messages(&self) -> &[ConversationMessage] {
        &self.messages
    }

    /// Remove all messages from the history.
    pub fn clear(&mut self) {
        self.messages.clear();
    }
}

impl Default for ConversationHistory {
    fn default() -> Self {
        Self::new()
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::core::types::Role;

    #[test]
    fn new_history_is_empty() {
        let history = ConversationHistory::new();
        assert!(history.messages().is_empty());
    }

    #[test]
    fn push_and_read_roundtrip() {
        let mut history = ConversationHistory::new();
        history.push(ConversationMessage {
            role: Role::User,
            content: "hello".to_string(),
        });
        history.push(ConversationMessage {
            role: Role::Assistant,
            content: "hi there".to_string(),
        });

        let msgs = history.messages();
        assert_eq!(msgs.len(), 2);
        assert_eq!(msgs[0].role, Role::User);
        assert_eq!(msgs[0].content, "hello");
        assert_eq!(msgs[1].role, Role::Assistant);
        assert_eq!(msgs[1].content, "hi there");
    }

    #[test]
    fn clear_empties_history() {
        let mut history = ConversationHistory::new();
        history.push(ConversationMessage {
            role: Role::User,
            content: "hello".to_string(),
        });
        history.clear();
        assert!(history.messages().is_empty());
    }

    #[test]
    fn messages_preserves_insertion_order() {
        let mut history = ConversationHistory::new();
        for i in 0u32..5 {
            history.push(ConversationMessage {
                role: Role::User,
                content: format!("msg {i}"),
            });
        }
        for (i, msg) in history.messages().iter().enumerate() {
            assert_eq!(msg.content, format!("msg {i}"));
        }
    }
}