use std::sync::Arc;

use mistralai_client::v1::{
    chat::{ChatMessage, ChatParams, ResponseFormat},
    constants::Model,
};
use regex::Regex;
use tracing::{debug, warn};

use crate::config::Config;

#[derive(Debug)]
pub enum Engagement {
    MustRespond { reason: MustRespondReason },
    MaybeRespond { relevance: f32, hook: String },
    Ignore,
}

#[derive(Debug)]
pub enum MustRespondReason {
    DirectMention,
    DirectMessage,
    NameInvocation,
}

pub struct Evaluator {
    config: Arc<Config>,
    mention_regex: Regex,
    name_regex: Regex,
}

impl Evaluator {
    // todo(sienna): regex must be configrable
    pub fn new(config: Arc<Config>) -> Self {
        let user_id = &config.matrix.user_id;
        let mention_pattern = regex::escape(user_id);
        let mention_regex = Regex::new(&mention_pattern).expect("Failed to compile mention regex");
        let name_regex =
            Regex::new(r"(?i)(?:^|\bhey\s+)\bsol\b").expect("Failed to compile name regex");

        Self {
            config,
            mention_regex,
            name_regex,
        }
    }

    pub async fn evaluate(
        &self,
        sender: &str,
        body: &str,
        is_dm: bool,
        recent_messages: &[String],
        mistral: &Arc<mistralai_client::v1::client::Client>,
    ) -> Engagement {
        // Don't respond to ourselves
        if sender == self.config.matrix.user_id {
            return Engagement::Ignore;
        }

        // Direct mention: @sol:sunbeam.pt
        if self.mention_regex.is_match(body) {
            return Engagement::MustRespond {
                reason: MustRespondReason::DirectMention,
            };
        }

        // DM
        if is_dm {
            return Engagement::MustRespond {
                reason: MustRespondReason::DirectMessage,
            };
        }

        // Name invocation: "sol ..." or "hey sol ..."
        if self.name_regex.is_match(body) {
            return Engagement::MustRespond {
                reason: MustRespondReason::NameInvocation,
            };
        }

        // Cheap evaluation call for spontaneous responses
        self.evaluate_relevance(body, recent_messages, mistral)
            .await
    }

    /// Check rule-based engagement (without calling Mistral). Returns Some(Engagement)
    /// if a rule matched, None if we need to fall through to the LLM evaluation.
    pub fn evaluate_rules(
        &self,
        sender: &str,
        body: &str,
        is_dm: bool,
    ) -> Option<Engagement> {
        if sender == self.config.matrix.user_id {
            return Some(Engagement::Ignore);
        }
        if self.mention_regex.is_match(body) {
            return Some(Engagement::MustRespond {
                reason: MustRespondReason::DirectMention,
            });
        }
        if is_dm {
            return Some(Engagement::MustRespond {
                reason: MustRespondReason::DirectMessage,
            });
        }
        if self.name_regex.is_match(body) {
            return Some(Engagement::MustRespond {
                reason: MustRespondReason::NameInvocation,
            });
        }
        None
    }

    async fn evaluate_relevance(
        &self,
        body: &str,
        recent_messages: &[String],
        mistral: &Arc<mistralai_client::v1::client::Client>,
    ) -> Engagement {
        let context = recent_messages
            .iter()
            .rev()
            .take(5) //todo(sienna): must be configurable
            .rev()
            .cloned()
            .collect::<Vec<_>>()
            .join("\n");

        let prompt = format!(
            "You are evaluating whether a virtual librarian named Sol should spontaneously join \
             a conversation. Sol has deep knowledge of the group's message archive and helps \
             people find information.\n\n\
             Recent conversation:\n{context}\n\n\
             Latest message: {body}\n\n\
             Respond ONLY with JSON: {{\"relevance\": 0.0-1.0, \"hook\": \"brief reason or empty string\"}}\n\
             relevance=1.0 means Sol absolutely should respond, 0.0 means irrelevant."
        );

        let messages = vec![ChatMessage::new_user_message(&prompt)];
        let params = ChatParams {
            response_format: Some(ResponseFormat::json_object()),
            temperature: Some(0.1),
            max_tokens: Some(100),
            ..Default::default()
        };

        let model = Model::new(&self.config.mistral.evaluation_model);
        let client = Arc::clone(mistral);
        let result = tokio::task::spawn_blocking(move || {
            client.chat(model, messages, Some(params))
        })
        .await
        .unwrap_or_else(|e| Err(mistralai_client::v1::error::ApiError {
            message: format!("spawn_blocking join error: {e}"),
        }));

        match result {
            Ok(response) => {
                let text = &response.choices[0].message.content;
                match serde_json::from_str::<serde_json::Value>(text) {
                    Ok(val) => {
                        let relevance = val["relevance"].as_f64().unwrap_or(0.0) as f32;
                        let hook = val["hook"].as_str().unwrap_or("").to_string();

                        debug!(relevance, hook = hook.as_str(), "Evaluation result");

                        if relevance >= self.config.behavior.spontaneous_threshold {
                            Engagement::MaybeRespond { relevance, hook }
                        } else {
                            Engagement::Ignore
                        }
                    }
                    Err(e) => {
                        warn!("Failed to parse evaluation response: {e}");
                        Engagement::Ignore
                    }
                }
            }
            Err(e) => {
                warn!("Evaluation call failed: {e}");
                Engagement::Ignore
            }
        }
    }
}

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

    fn test_config() -> Arc<Config> {
        let toml = r#"
[matrix]
homeserver_url = "https://chat.sunbeam.pt"
user_id = "@sol:sunbeam.pt"
state_store_path = "/tmp/sol"

[opensearch]
url = "http://localhost:9200"
index = "test"

[mistral]
[behavior]
"#;
        Arc::new(Config::from_str(toml).unwrap())
    }

    fn evaluator() -> Evaluator {
        Evaluator::new(test_config())
    }

    #[test]
    fn test_ignore_own_messages() {
        let ev = evaluator();
        let result = ev.evaluate_rules("@sol:sunbeam.pt", "hello everyone", false);
        assert!(matches!(result, Some(Engagement::Ignore)));
    }

    #[test]
    fn test_direct_mention() {
        let ev = evaluator();
        let result = ev.evaluate_rules("@alice:sunbeam.pt", "hey @sol:sunbeam.pt what's up?", false);
        assert!(matches!(
            result,
            Some(Engagement::MustRespond { reason: MustRespondReason::DirectMention })
        ));
    }

    #[test]
    fn test_dm_detection() {
        let ev = evaluator();
        let result = ev.evaluate_rules("@alice:sunbeam.pt", "random message", true);
        assert!(matches!(
            result,
            Some(Engagement::MustRespond { reason: MustRespondReason::DirectMessage })
        ));
    }

    #[test]
    fn test_name_invocation_start_of_message() {
        let ev = evaluator();
        let result = ev.evaluate_rules("@alice:sunbeam.pt", "sol, can you find that link?", false);
        assert!(matches!(
            result,
            Some(Engagement::MustRespond { reason: MustRespondReason::NameInvocation })
        ));
    }

    #[test]
    fn test_name_invocation_hey_sol() {
        let ev = evaluator();
        let result = ev.evaluate_rules("@alice:sunbeam.pt", "hey sol do you remember?", false);
        assert!(matches!(
            result,
            Some(Engagement::MustRespond { reason: MustRespondReason::NameInvocation })
        ));
    }

    #[test]
    fn test_name_invocation_case_insensitive() {
        let ev = evaluator();
        let result = ev.evaluate_rules("@alice:sunbeam.pt", "Hey Sol, help me", false);
        assert!(matches!(
            result,
            Some(Engagement::MustRespond { reason: MustRespondReason::NameInvocation })
        ));
    }

    #[test]
    fn test_name_invocation_sol_uppercase() {
        let ev = evaluator();
        let result = ev.evaluate_rules("@alice:sunbeam.pt", "SOL what do you think?", false);
        assert!(matches!(
            result,
            Some(Engagement::MustRespond { reason: MustRespondReason::NameInvocation })
        ));
    }

    #[test]
    fn test_no_false_positive_solstice() {
        let ev = evaluator();
        // "solstice" should NOT trigger name invocation — \b boundary prevents it
        let result = ev.evaluate_rules("@alice:sunbeam.pt", "the solstice is coming", false);
        assert!(result.is_none());
    }

    #[test]
    fn test_random_message_falls_through() {
        let ev = evaluator();
        let result = ev.evaluate_rules("@alice:sunbeam.pt", "what's for lunch?", false);
        assert!(result.is_none());
    }

    #[test]
    fn test_priority_mention_over_dm() {
        // When both mention and DM are true, mention should match first
        let ev = evaluator();
        let result = ev.evaluate_rules("@alice:sunbeam.pt", "hi @sol:sunbeam.pt", true);
        assert!(matches!(
            result,
            Some(Engagement::MustRespond { reason: MustRespondReason::DirectMention })
        ));
    }
}