use crate::session::Session;

#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub struct TokenUsage {
    pub input_tokens: u32,
    pub output_tokens: u32,
    pub cache_creation_input_tokens: u32,
    pub cache_read_input_tokens: u32,
}

impl TokenUsage {
    #[must_use]
    pub fn total_tokens(self) -> u32 {
        self.input_tokens
            + self.output_tokens
            + self.cache_creation_input_tokens
            + self.cache_read_input_tokens
    }
}

#[derive(Debug, Clone, Default, PartialEq, Eq)]
pub struct UsageTracker {
    latest_turn: TokenUsage,
    cumulative: TokenUsage,
    turns: u32,
}

impl UsageTracker {
    #[must_use]
    pub fn new() -> Self {
        Self::default()
    }

    #[must_use]
    pub fn from_session(session: &Session) -> Self {
        let mut tracker = Self::new();
        for message in &session.messages {
            if let Some(usage) = message.usage {
                tracker.record(usage);
            }
        }
        tracker
    }

    pub fn record(&mut self, usage: TokenUsage) {
        self.latest_turn = usage;
        self.cumulative.input_tokens += usage.input_tokens;
        self.cumulative.output_tokens += usage.output_tokens;
        self.cumulative.cache_creation_input_tokens += usage.cache_creation_input_tokens;
        self.cumulative.cache_read_input_tokens += usage.cache_read_input_tokens;
        self.turns += 1;
    }

    #[must_use]
    pub fn current_turn_usage(&self) -> TokenUsage {
        self.latest_turn
    }

    #[must_use]
    pub fn cumulative_usage(&self) -> TokenUsage {
        self.cumulative
    }

    #[must_use]
    pub fn turns(&self) -> u32 {
        self.turns
    }
}

#[cfg(test)]
mod tests {
    use super::{TokenUsage, UsageTracker};
    use crate::session::{ContentBlock, ConversationMessage, MessageRole, Session};

    #[test]
    fn tracks_true_cumulative_usage() {
        let mut tracker = UsageTracker::new();
        tracker.record(TokenUsage {
            input_tokens: 10,
            output_tokens: 4,
            cache_creation_input_tokens: 2,
            cache_read_input_tokens: 1,
        });
        tracker.record(TokenUsage {
            input_tokens: 20,
            output_tokens: 6,
            cache_creation_input_tokens: 3,
            cache_read_input_tokens: 2,
        });

        assert_eq!(tracker.turns(), 2);
        assert_eq!(tracker.current_turn_usage().input_tokens, 20);
        assert_eq!(tracker.current_turn_usage().output_tokens, 6);
        assert_eq!(tracker.cumulative_usage().output_tokens, 10);
        assert_eq!(tracker.cumulative_usage().input_tokens, 30);
        assert_eq!(tracker.cumulative_usage().total_tokens(), 48);
    }

    #[test]
    fn reconstructs_usage_from_session_messages() {
        let session = Session {
            version: 1,
            messages: vec![ConversationMessage {
                role: MessageRole::Assistant,
                blocks: vec![ContentBlock::Text {
                    text: "done".to_string(),
                }],
                usage: Some(TokenUsage {
                    input_tokens: 5,
                    output_tokens: 2,
                    cache_creation_input_tokens: 1,
                    cache_read_input_tokens: 0,
                }),
            }],
        };

        let tracker = UsageTracker::from_session(&session);
        assert_eq!(tracker.turns(), 1);
        assert_eq!(tracker.cumulative_usage().total_tokens(), 8);
    }
}