use chrono::Utc;

pub struct Personality {
    template: String,
}

impl Personality {
    pub fn new(system_prompt: String) -> Self {
        Self {
            template: system_prompt,
        }
    }

    pub fn build_system_prompt(
        &self,
        room_name: &str,
        members: &[String],
        ) -> String {
        let date = Utc::now().format("%Y-%m-%d").to_string();
        let members_str = members.join(", ");

        self.template
            .replace("{date}", &date)
            .replace("{room_name}", room_name)
            .replace("{members}", &members_str)
    }
}

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

    #[test]
    fn test_date_substitution() {
        let p = Personality::new("Today is {date}.".to_string());
        let result = p.build_system_prompt("general", &[]);
        let today = Utc::now().format("%Y-%m-%d").to_string();
        assert_eq!(result, format!("Today is {today}."));
    }

    #[test]
    fn test_room_name_substitution() {
        let p = Personality::new("You are in {room_name}.".to_string());
        let result = p.build_system_prompt("design-chat", &[]);
        assert!(result.contains("design-chat"));
    }

    #[test]
    fn test_members_substitution() {
        let p = Personality::new("Members: {members}".to_string());
        let members = vec!["Alice".to_string(), "Bob".to_string(), "Carol".to_string()];
        let result = p.build_system_prompt("room", &members);
        assert_eq!(result, "Members: Alice, Bob, Carol");
    }

    #[test]
    fn test_empty_members() {
        let p = Personality::new("Members: {members}".to_string());
        let result = p.build_system_prompt("room", &[]);
        assert_eq!(result, "Members: ");
    }

    #[test]
    fn test_all_placeholders() {
        let template = "Date: {date}, Room: {room_name}, People: {members}".to_string();
        let p = Personality::new(template);
        let members = vec!["Sienna".to_string(), "Lonni".to_string()];
        let result = p.build_system_prompt("studio", &members);

        let today = Utc::now().format("%Y-%m-%d").to_string();
        assert!(result.starts_with(&format!("Date: {today}")));
        assert!(result.contains("Room: studio"));
        assert!(result.contains("People: Sienna, Lonni"));
    }

    #[test]
    fn test_no_placeholders_passthrough() {
        let p = Personality::new("Static prompt with no variables.".to_string());
        let result = p.build_system_prompt("room", &["Alice".to_string()]);
        assert_eq!(result, "Static prompt with no variables.");
    }

    #[test]
    fn test_multiple_same_placeholder() {
        let p = Personality::new("{room_name} is great. I love {room_name}.".to_string());
        let result = p.build_system_prompt("lounge", &[]);
        assert_eq!(result, "lounge is great. I love lounge.");
    }
}