settled-reach/server/src/npc/interaction.rs

//! Interaction tracking component — ticket #325.
//!
//! `InteractionMemory` is a per-NPC component tracking the player's interaction
//! history with that NPC. Drives D-028 Layer 2 situation activation:
//!   - `interaction_count == 0` → `Situation::FirstMeeting`
//!   - `interaction_count >= 3` → `Situation::RepeatedVisit`
//!
//! Populated by `process_talk_interaction` in `dialogue.rs` each time a talk
//! line is selected. Walk-away and confrontation events appended to
//! `notable_events` for fast per-pair access (complements the KnowledgeGraph).
//!
//! No HashMap. No floats. Deterministic (no random access to notable_events).

use bevy_ecs::prelude::*;

/// Notable event kinds recorded per player-NPC interaction.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum InteractionEventKind {
    /// Player walked away during active dialogue (D-064).
    WalkAway,
    /// Player delivered a confrontation (D-063).
    Confrontation,
}

/// A single notable event in an interaction history.
#[derive(Debug, Clone)]
pub struct InteractionEvent {
    /// Simulation tick the event occurred.
    pub tick: u64,
    /// The kind of event.
    pub kind: InteractionEventKind,
}

/// Per-NPC interaction history with the player (#325, D-028 Layer 2).
///
/// Spawned on every NPC entity. Drives situation derivation for Layer 2
/// dialogue selection: `first_meeting` (count == 0), `repeated_visit`
/// (count >= 3). `notable_events` stores walk-aways and confrontations for
/// fast lookup without a full KnowledgeGraph query.
#[derive(Component, Debug, Default)]
pub struct InteractionMemory {
    /// Total number of completed Talk interactions with the player.
    /// Incremented each time a dialogue line is selected in `process_talk_interaction`.
    pub interaction_count: u32,
    /// Tick of the most recent completed Talk interaction.
    /// Used for trust decay baseline (D-028 trust progression, #324).
    pub last_interaction_tick: u64,
    /// Notable events: walk-aways and confrontations.
    /// Bounded by `MAX_NOTABLE_EVENTS` — oldest entries dropped when full.
    pub notable_events: std::collections::VecDeque<InteractionEvent>,
}

/// Maximum number of notable events retained per NPC pair.
pub const MAX_NOTABLE_EVENTS: usize = 16;

impl InteractionMemory {
    /// Record a completed Talk interaction.
    ///
    /// Increments `interaction_count` and stamps `last_interaction_tick`.
    pub fn record_talk(&mut self, tick: u64) {
        self.interaction_count = self.interaction_count.saturating_add(1);
        self.last_interaction_tick = tick;
    }

    /// Append a notable event, dropping the oldest if at capacity.
    pub fn push_event(&mut self, event: InteractionEvent) {
        if self.notable_events.len() >= MAX_NOTABLE_EVENTS {
            self.notable_events.pop_front();
        }
        self.notable_events.push_back(event);
    }

    /// Returns `true` if this is the first meeting (count == 0).
    pub fn is_first_meeting(&self) -> bool {
        self.interaction_count == 0
    }

    /// Returns `true` if this qualifies as a repeated visit (count >= 3).
    pub fn is_repeated_visit(&self) -> bool {
        self.interaction_count >= 3
    }

    /// Count notable events of a given kind.
    pub fn count_events(&self, kind: InteractionEventKind) -> usize {
        self.notable_events.iter().filter(|e| e.kind == kind).count()
    }
}

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

    #[test]
    fn default_is_first_meeting() {
        let mem = InteractionMemory::default();
        assert!(mem.is_first_meeting());
        assert!(!mem.is_repeated_visit());
    }

    #[test]
    fn record_talk_increments_count() {
        let mut mem = InteractionMemory::default();
        mem.record_talk(10);
        assert_eq!(mem.interaction_count, 1);
        assert_eq!(mem.last_interaction_tick, 10);
        assert!(!mem.is_first_meeting());
    }

    #[test]
    fn repeated_visit_threshold_at_three() {
        let mut mem = InteractionMemory::default();
        assert!(!mem.is_repeated_visit());
        mem.record_talk(10);
        mem.record_talk(20);
        assert!(!mem.is_repeated_visit());
        mem.record_talk(30);
        assert!(mem.is_repeated_visit());
    }

    #[test]
    fn push_event_appends() {
        let mut mem = InteractionMemory::default();
        mem.push_event(InteractionEvent {
            tick: 5,
            kind: InteractionEventKind::WalkAway,
        });
        assert_eq!(mem.notable_events.len(), 1);
        assert_eq!(mem.notable_events[0].kind, InteractionEventKind::WalkAway);
    }

    #[test]
    fn push_event_drops_oldest_when_full() {
        let mut mem = InteractionMemory::default();
        for i in 0..MAX_NOTABLE_EVENTS {
            mem.push_event(InteractionEvent {
                tick: i as u64,
                kind: InteractionEventKind::WalkAway,
            });
        }
        assert_eq!(mem.notable_events.len(), MAX_NOTABLE_EVENTS);
        // Pushing one more should drop the oldest (tick=0)
        mem.push_event(InteractionEvent {
            tick: 99,
            kind: InteractionEventKind::Confrontation,
        });
        assert_eq!(mem.notable_events.len(), MAX_NOTABLE_EVENTS);
        assert_eq!(mem.notable_events[0].tick, 1); // tick=0 dropped
        assert_eq!(mem.notable_events.back().unwrap().tick, 99);
    }

    #[test]
    fn count_events_filters_by_kind() {
        let mut mem = InteractionMemory::default();
        mem.push_event(InteractionEvent {
            tick: 1,
            kind: InteractionEventKind::WalkAway,
        });
        mem.push_event(InteractionEvent {
            tick: 2,
            kind: InteractionEventKind::Confrontation,
        });
        mem.push_event(InteractionEvent {
            tick: 3,
            kind: InteractionEventKind::WalkAway,
        });
        assert_eq!(mem.count_events(InteractionEventKind::WalkAway), 2);
        assert_eq!(mem.count_events(InteractionEventKind::Confrontation), 1);
    }

    #[test]
    fn record_talk_saturates_on_overflow() {
        let mut mem = InteractionMemory {
            interaction_count: u32::MAX,
            ..Default::default()
        };
        mem.record_talk(1);
        assert_eq!(mem.interaction_count, u32::MAX); // saturating_add
    }
}