//! Cause-link recorder: every death, injury, and major event stores the
//! rule chain that produced it (docs/04 §4.2 phase 12, docs/03 §3.9).
//! Powers epitaphs, death replays, and tutorial subtitles.

/// One link in a causal chain: `rule` names the law (e.g. "rooms breathe"),
/// `detail` is the NetHack-voice line shown to the player.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct CauseLink {
    pub tick: u64,
    pub rule: &'static str,
    pub detail: String,
}

impl CauseLink {
    pub fn new(tick: u64, rule: &'static str, detail: impl Into<String>) -> Self {
        Self {
            tick,
            rule,
            detail: detail.into(),
        }
    }
}

/// Ordered record of what happened, oldest first.
#[derive(Clone, Debug, Default)]
pub struct CauseChain {
    links: Vec<CauseLink>,
}

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

    pub fn push(&mut self, link: CauseLink) {
        self.links.push(link);
    }

    /// Reserve cause capacity before an atomic multi-link transaction mutates.
    pub(crate) fn try_reserve(
        &mut self,
        additional: usize,
    ) -> Result<(), std::collections::TryReserveError> {
        self.links.try_reserve(additional)
    }

    /// Links in canonical occurrence order (oldest first).
    pub fn links(&self) -> &[CauseLink] {
        &self.links
    }

    pub fn is_empty(&self) -> bool {
        self.links.is_empty()
    }

    pub fn len(&self) -> usize {
        self.links.len()
    }

    /// NetHack-voice epitaph fragment, e.g.
    /// "Slain by own cleverness, via falling boulder, while overburdened".
    pub fn epitaph(&self) -> String {
        if self.links.is_empty() {
            return "Died without witnesses, which is also a story.".to_string();
        }
        self.links
            .iter()
            .map(|l| l.detail.clone())
            .collect::<Vec<_>>()
            .join(", via ")
    }
}

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

    #[test]
    fn epitaph_joins_chain() {
        let mut c = CauseChain::new();
        c.push(CauseLink::new(1, "gravity", "own cleverness"));
        c.push(CauseLink::new(2, "gravity", "falling boulder"));
        assert!(c.epitaph().contains("falling boulder"));
    }
}