//! NPC-to-NPC knowledge transfer system (D-080, ticket #548).
//!
//! When an NPC-to-NPC conversation starts (`Added<NpcConversation>`), this system
//! transfers a sample of the speaker's KG entries to the listener (ToldBy source).
//! Transfer eligibility and volume are gated by the trust level between the two NPCs
//! from `RelationshipGraph`. The confidence cap (max KnowsOf) ensures information
//! degrades as it propagates through social networks.
//!
//! Player overhear: if the player is within VOICE_RANGE_TILES of the conversation,
//! they gain entity-level knowledge about both NPCs at Suspects confidence
//! (Heard source). This models ambient social information gathering.
//!
//! Closes Q-024: NPC-to-NPC propagation rate.

use bevy_ecs::prelude::*;
use rand::Rng;
use std::cmp::Reverse;
use std::collections::BTreeMap;

use crate::knowledge::registry::StableEntityId;
use crate::knowledge::types::{
    EntityKnowledge, FactId, FactKnowledge, KnowledgeConfidence, KnowledgeSource, KnowledgeState,
    RelationshipState, SoundRange, StableId,
};
use crate::knowledge::{
    KnowledgeEvent, KnowledgeEventQueue, KnowledgeEventType, KnowledgeGraph, ProcessedEntityGrant,
    ProcessedKnowledgeGrant,
};
use crate::npc::relationships::RelationshipGraph;
use crate::npc::Npc;
use crate::simulation::movement::{PlayerCharacter, TilePosition};
use crate::simulation::npc_components::NpcConversation;
use crate::simulation::rng::SimRng;
use crate::simulation::tier::ActiveSim;
use crate::simulation::time::SimulationTime;

// ---------------------------------------------------------------------------
// Constants
// ---------------------------------------------------------------------------

/// Range within which player can overhear NPC-to-NPC knowledge exchange.
/// Matches VOICE_RANGE_TILES in conversation.rs (D-018 Medium = 8 tiles).
const VOICE_RANGE_TILES: u32 = 8;

// ---------------------------------------------------------------------------
// Trust tier (NPC-to-NPC, D-080)
// ---------------------------------------------------------------------------

/// Trust tier for NPC-to-NPC knowledge transfer.
/// Derived from `RelationshipEdge.trust` (i8 in -10..+10).
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum NpcTransferTier {
    /// trust < 0: no knowledge flows.
    None,
    /// trust 0..=2: Active facts at KnowsOf+ confidence only.
    Surface,
    /// trust 3..=6: Active facts at any confidence + entity observations.
    Real,
    /// trust 7..=10: All Active entries (facts at any confidence + all entities).
    Secret,
}

/// Map a raw trust score to the NPC transfer tier (D-080 boundaries).
fn trust_to_tier(trust: i8) -> NpcTransferTier {
    if trust < 0 {
        NpcTransferTier::None
    } else if trust >= 7 {
        NpcTransferTier::Secret
    } else if trust >= 3 {
        NpcTransferTier::Real
    } else {
        NpcTransferTier::Surface
    }
}

// ---------------------------------------------------------------------------
// Transfer candidate pool
// ---------------------------------------------------------------------------

/// Tagged entry in the transfer candidate pool.
/// Used to sort facts and entity entries by recency before drawing.
enum TransferCandidate {
    Fact {
        id: FactId,
        confidence: KnowledgeConfidence,
        acquired_tick: u64,
    },
    Entity {
        id: StableId,
        ek: EntityKnowledge,
    },
}

impl TransferCandidate {
    /// Sort key: most recently updated entries are preferred.
    fn sort_key(&self) -> u64 {
        match self {
            Self::Fact { acquired_tick, .. } => *acquired_tick,
            Self::Entity { ek, .. } => ek.last_updated_tick,
        }
    }
}

// ---------------------------------------------------------------------------
// System
// ---------------------------------------------------------------------------

/// System: transfer NPC knowledge at conversation start (D-080).
///
/// Fires once per conversation (triggered by `Added<NpcConversation>`).
/// Reads the trust level between the two NPCs from `RelationshipGraph` and
/// transfers a sample (1–3 entries) of the speaker's eligible KG entries to
/// the listener's KG with `ToldBy` source and confidence capped at `KnowsOf`.
///
/// If the player is within VOICE_RANGE_TILES, they gain entity-level knowledge
/// about both NPCs at `Suspects` confidence (`Heard` source).
///
/// System ordering: after(run_npc_conversations).
#[allow(clippy::too_many_arguments)]
pub fn transfer_npc_knowledge(
    time: Res<SimulationTime>,
    mut rng: ResMut<SimRng>,
    relationship_graph: Res<RelationshipGraph>,
    mut event_queue: ResMut<KnowledgeEventQueue>,
    // NPCs that just started a conversation — Added fires once per conversation.
    new_conv_query: Query<
        (
            Entity,
            &NpcConversation,
            &TilePosition,
            Option<&StableEntityId>,
        ),
        (With<Npc>, With<ActiveSim>, Added<NpcConversation>),
    >,
    // Read-only StableEntityId on NPC partner (distinct query, no KG conflict).
    partner_sid_query: Query<Option<&StableEntityId>, With<Npc>>,
    // Mutable KG access — get_many_mut for dual-entity borrow safety.
    mut kg_query: Query<&mut KnowledgeGraph>,
    // Player position for overhear radius check.
    player_query: Query<(Entity, &TilePosition), With<PlayerCharacter>>,
) {
    let tick = time.tick;

    for (speaker_entity, conv, speaker_pos, speaker_sid_opt) in new_conv_query.iter() {
        let partner_entity = conv.partner;

        // --- Resolve stable IDs ---

        let speaker_sid = match speaker_sid_opt.map(|s| s.0) {
            Some(sid) => sid,
            None => {
                tracing::debug!(
                    "NPC transfer: speaker {:?} has no StableEntityId, skipping",
                    speaker_entity
                );
                continue;
            }
        };

        let partner_sid = match partner_sid_query
            .get(partner_entity)
            .ok()
            .and_then(|opt| opt.map(|s| s.0))
        {
            Some(sid) => sid,
            None => {
                tracing::debug!(
                    "NPC transfer: partner {:?} has no StableEntityId, skipping",
                    partner_entity
                );
                continue;
            }
        };

        // --- Trust level → transfer tier ---
        //
        // Use the speaker's trust in the listener: the speaker decides what to share
        // based on how much they trust this particular person. Defaults to 0 (Surface)
        // when no relationship edge exists — strangers can still overhear ambient facts.
        let trust = relationship_graph
            .get_relationship(&speaker_sid, &partner_sid)
            .map(|e| e.trust)
            .unwrap_or(0);
        let tier = trust_to_tier(trust);

        if tier == NpcTransferTier::None {
            tracing::debug!(
                "NPC transfer: trust={} (None tier) between {:?} ↔ {:?}, skipping",
                trust,
                speaker_entity,
                partner_entity
            );
            // Still do player overhear (NPCs are audibly talking even if not exchanging info)
            emit_player_overhear_grants(
                &player_query,
                speaker_pos,
                tick,
                speaker_sid,
                partner_sid,
                &mut event_queue,
            );
            continue;
        }

        // --- Dual-mutable KG access ---
        // Transfer is one-directional per conversation tick: speaker → partner.
        // If both participants are Active NPCs, each fires as "speaker" in
        // separate conversation pairs (run_npc_conversations creates symmetric
        // pairs), so both directions are covered across two iterations.

        let Ok([speaker_kg, mut partner_kg]) =
            kg_query.get_many_mut([speaker_entity, partner_entity])
        else {
            tracing::debug!(
                "NPC transfer: couldn't get KGs for {:?} / {:?}, skipping",
                speaker_entity,
                partner_entity
            );
            continue;
        };

        // --- Build candidate pool from speaker's KG ---

        let mut candidates: Vec<TransferCandidate> = Vec::new();

        // Facts: always eligible (filtered by tier and disclosure_blocked)
        for (fid, fk) in speaker_kg.facts.iter() {
            if fk.disclosure_blocked || fk.state != KnowledgeState::Active {
                continue;
            }
            let eligible = match tier {
                NpcTransferTier::Surface => fk.confidence >= KnowledgeConfidence::KnowsOf,
                NpcTransferTier::Real | NpcTransferTier::Secret => true,
                NpcTransferTier::None => unreachable!("None tier handled above"),
            };
            if eligible {
                candidates.push(TransferCandidate::Fact {
                    id: fid.clone(),
                    confidence: fk.confidence,
                    acquired_tick: fk.acquired_tick,
                });
            }
        }

        // Entity observations: Real and Secret tiers only
        if tier == NpcTransferTier::Real || tier == NpcTransferTier::Secret {
            for (sid, ek) in speaker_kg.entities.iter() {
                if ek.state != KnowledgeState::Active {
                    continue;
                }
                candidates.push(TransferCandidate::Entity {
                    id: *sid,
                    ek: ek.clone(),
                });
            }
        }

        if candidates.is_empty() {
            tracing::debug!(
                "NPC transfer: no eligible entries in speaker {:?} KG at {:?} tier",
                speaker_entity,
                tier
            );
            emit_player_overhear_grants(
                &player_query,
                speaker_pos,
                tick,
                speaker_sid,
                partner_sid,
                &mut event_queue,
            );
            continue;
        }

        // Sort by most recently updated (deterministic: descending tick, stable by BTreeMap key order)
        candidates.sort_by_key(|c| Reverse(c.sort_key()));

        // Take top 1–3 entries by recency (random count, deterministic selection).
        // The random element is HOW MANY facts transfer, not WHICH ones.
        let count = rng.rng.random_range(1u32..=3u32) as usize;
        let count = count.min(candidates.len());

        tracing::debug!(
            "NPC transfer: {:?} → {:?}, tier={:?}, trust={}, drawing {}/{}",
            speaker_entity,
            partner_entity,
            tier,
            trust,
            count,
            candidates.len(),
        );

        // --- Apply transfers to partner's KG ---

        for candidate in candidates.into_iter().take(count) {
            match candidate {
                TransferCandidate::Fact { id, confidence, .. } => {
                    // Confidence cap: speaker's knowledge degrades to at most KnowsOf.
                    let capped = confidence.min(KnowledgeConfidence::KnowsOf);

                    // Upgrade-only: never downgrade existing knowledge.
                    let should_write = partner_kg
                        .facts
                        .get(&id)
                        .map(|existing| existing.confidence < capped)
                        .unwrap_or(true);

                    if should_write {
                        partner_kg.facts.insert(
                            id.clone(),
                            FactKnowledge {
                                confidence: capped,
                                source: KnowledgeSource::ToldBy {
                                    source_id: speaker_sid,
                                    tick,
                                },
                                state: KnowledgeState::Active,
                                acquired_tick: tick,
                                disclosure_blocked: false,
                            },
                        );
                        tracing::debug!(
                            "NPC transfer: fact {:?} at {:?} → {:?}",
                            id,
                            capped,
                            partner_entity
                        );
                    }
                }

                TransferCandidate::Entity { id, ek } => {
                    // Confidence cap: at most KnowsOf.
                    let capped = ek.confidence.min(KnowledgeConfidence::KnowsOf);

                    // Preserve existing relationship state if the partner already knows this entity.
                    let (should_write, existing_relationship) = match partner_kg.entities.get(&id) {
                        None => (true, RelationshipState::Unknown),
                        Some(existing) => (existing.confidence < capped, existing.relationship),
                    };

                    if should_write {
                        partner_kg.entities.insert(
                            id,
                            EntityKnowledge {
                                last_known_position: ek.last_known_position,
                                last_observed_tick: ek.last_observed_tick,
                                last_updated_tick: tick,
                                confidence: capped,
                                source: KnowledgeSource::ToldBy {
                                    source_id: speaker_sid,
                                    tick,
                                },
                                state: KnowledgeState::Active,
                                relationship: existing_relationship,
                                known_attributes: ek.known_attributes.clone(),
                                contradicted_claim: None,
                            },
                        );
                        tracing::debug!(
                            "NPC transfer: entity {:?} at {:?} → {:?}",
                            id,
                            capped,
                            partner_entity
                        );
                    }
                }
            }
        }

        // --- Player overhear grants ---

        emit_player_overhear_grants(
            &player_query,
            speaker_pos,
            tick,
            speaker_sid,
            partner_sid,
            &mut event_queue,
        );
    }
}

/// Emit `Heard` entity grants to all players within VOICE_RANGE_TILES of a conversation.
///
/// Called regardless of transfer tier — even if the NPCs aren't sharing information,
/// the player can still learn that these two entities exist from overhearing them talk.
fn emit_player_overhear_grants(
    player_query: &Query<(Entity, &TilePosition), With<PlayerCharacter>>,
    speaker_pos: &TilePosition,
    tick: u64,
    speaker_sid: StableId,
    partner_sid: StableId,
    event_queue: &mut KnowledgeEventQueue,
) {
    for (player_entity, player_pos) in player_query.iter() {
        let distance = speaker_pos
            .manhattan_distance(player_pos)
            .unwrap_or(u32::MAX);

        if distance <= VOICE_RANGE_TILES {
            // Player overhears both participants — learns they exist at Suspects level.
            for npc_sid in [speaker_sid, partner_sid] {
                event_queue.push(KnowledgeEvent {
                    observer: player_entity,
                    tick,
                    event_type: KnowledgeEventType::KnowledgeGranted {
                        grant: ProcessedKnowledgeGrant::Entity(ProcessedEntityGrant {
                            target_id: npc_sid,
                            attributes: BTreeMap::new(),
                            confidence: KnowledgeConfidence::Suspects,
                        }),
                        source: KnowledgeSource::Heard {
                            tick,
                            range: SoundRange::Medium,
                        },
                    },
                });
            }
            tracing::debug!(
                "Player {:?} overhears conversation at distance {} tiles (D-080)",
                player_entity,
                distance
            );
        }
    }
}

// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------

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

    use crate::knowledge::types::{FactId, KnowledgeConfidence, KnowledgeState, StableId};
    use crate::knowledge::{EntityRegistry, KnowledgeGraph};
    use crate::npc::relationships::{RelationshipEdge, RelationshipGraph};
    use crate::npc::RelationshipKind;
    use crate::simulation::movement::TilePosition;
    use crate::simulation::npc_components::NpcConversation;
    use crate::simulation::rng::SimRng;
    use crate::simulation::tier::ActiveSim;
    use crate::simulation::time::SimulationTime;

    fn build_test_world() -> App {
        let mut app = App::new();
        app.init_resource::<SimulationTime>();
        app.insert_resource(SimRng::new(42));
        app.init_resource::<EntityRegistry>();
        app.init_resource::<RelationshipGraph>();
        app.init_resource::<KnowledgeEventQueue>();
        app.add_systems(Update, transfer_npc_knowledge);
        app
    }

    /// Spawn a minimal NPC entity with the required components.
    /// The StableEntityId component is what the transfer system reads — no registry needed.
    fn spawn_npc(world: &mut World, sid: StableId, kg: KnowledgeGraph) -> Entity {
        world
            .spawn((
                crate::npc::Npc,
                ActiveSim,
                StableEntityId(sid),
                TilePosition { x: 0, y: 0, z: 0 },
                kg,
            ))
            .id()
    }

    fn make_fact_kg(fact_id: &str, confidence: KnowledgeConfidence) -> KnowledgeGraph {
        let mut kg = KnowledgeGraph::new();
        kg.facts.insert(
            FactId(fact_id.to_string()),
            FactKnowledge {
                confidence,
                source: KnowledgeSource::Background,
                state: KnowledgeState::Active,
                acquired_tick: 1,
                disclosure_blocked: false,
            },
        );
        kg
    }

    // --- Trust tier mapping ---

    #[test]
    fn trust_none_below_zero() {
        assert_eq!(trust_to_tier(-1), NpcTransferTier::None);
        assert_eq!(trust_to_tier(-10), NpcTransferTier::None);
    }

    #[test]
    fn trust_surface_zero_to_two() {
        assert_eq!(trust_to_tier(0), NpcTransferTier::Surface);
        assert_eq!(trust_to_tier(2), NpcTransferTier::Surface);
    }

    #[test]
    fn trust_real_three_to_six() {
        assert_eq!(trust_to_tier(3), NpcTransferTier::Real);
        assert_eq!(trust_to_tier(6), NpcTransferTier::Real);
    }

    #[test]
    fn trust_secret_seven_plus() {
        assert_eq!(trust_to_tier(7), NpcTransferTier::Secret);
        assert_eq!(trust_to_tier(10), NpcTransferTier::Secret);
    }

    // --- Confidence cap ---

    #[test]
    fn confidence_cap_downgrades_details_to_knows_of() {
        let capped = KnowledgeConfidence::KnowsDetails.min(KnowledgeConfidence::KnowsOf);
        assert_eq!(capped, KnowledgeConfidence::KnowsOf);
    }

    #[test]
    fn confidence_cap_preserves_lower_confidence() {
        let capped = KnowledgeConfidence::Suspects.min(KnowledgeConfidence::KnowsOf);
        assert_eq!(capped, KnowledgeConfidence::Suspects);
    }

    // --- Surface tier: KnowsOf+ facts only ---

    #[test]
    fn surface_tier_transfers_knows_of_fact() {
        let mut app = build_test_world();

        let sid_a = StableId(1);
        let sid_b = StableId(2);
        let kg_a = make_fact_kg("test.fact", KnowledgeConfidence::KnowsOf);
        let kg_b = KnowledgeGraph::new();

        let entity_a = spawn_npc(app.world_mut(), sid_a, kg_a);
        let entity_b = spawn_npc(app.world_mut(), sid_b, kg_b);

        // Trust = 1 → Surface tier
        {
            let mut rel = app.world_mut().resource_mut::<RelationshipGraph>();
            rel.set_relationship(
                sid_a,
                sid_b,
                RelationshipEdge {
                    kind: RelationshipKind::Colleague,
                    trust: 1,
                    history: vec![],
                    last_interaction_tick: 0,
                },
            );
        }

        // Start conversation — tick 0, so started_tick == 0
        app.world_mut()
            .entity_mut(entity_a)
            .insert(NpcConversation {
                partner: entity_b,
                started_tick: 0,
                end_tick: 100,
                ticks_since_last_line: 0,
            });

        app.update();

        // Partner should now know the fact
        let partner_kg = app
            .world()
            .entity(entity_b)
            .get::<KnowledgeGraph>()
            .expect("partner has KG");
        assert!(
            partner_kg.knows_fact(&FactId("test.fact".to_string())),
            "partner should know test.fact after surface-tier transfer"
        );
    }

    #[test]
    fn surface_tier_blocks_suspects_fact() {
        let mut app = build_test_world();

        let sid_a = StableId(1);
        let sid_b = StableId(2);
        // Suspects confidence — below KnowsOf threshold for Surface tier
        let kg_a = make_fact_kg("test.secret", KnowledgeConfidence::Suspects);
        let kg_b = KnowledgeGraph::new();

        let entity_a = spawn_npc(app.world_mut(), sid_a, kg_a);
        let entity_b = spawn_npc(app.world_mut(), sid_b, kg_b);

        {
            let mut rel = app.world_mut().resource_mut::<RelationshipGraph>();
            rel.set_relationship(
                sid_a,
                sid_b,
                RelationshipEdge {
                    kind: RelationshipKind::Colleague,
                    trust: 1,
                    history: vec![],
                    last_interaction_tick: 0,
                },
            );
        }

        app.world_mut()
            .entity_mut(entity_a)
            .insert(NpcConversation {
                partner: entity_b,
                started_tick: 0,
                end_tick: 100,
                ticks_since_last_line: 0,
            });

        app.update();

        let partner_kg = app
            .world()
            .entity(entity_b)
            .get::<KnowledgeGraph>()
            .expect("partner has KG");
        assert!(
            !partner_kg.knows_fact(&FactId("test.secret".to_string())),
            "Suspects fact should not transfer at Surface tier"
        );
    }

    #[test]
    fn none_tier_does_not_transfer() {
        let mut app = build_test_world();

        let sid_a = StableId(1);
        let sid_b = StableId(2);
        let kg_a = make_fact_kg("test.fact", KnowledgeConfidence::KnowsOf);
        let kg_b = KnowledgeGraph::new();

        let entity_a = spawn_npc(app.world_mut(), sid_a, kg_a);
        let entity_b = spawn_npc(app.world_mut(), sid_b, kg_b);

        {
            let mut rel = app.world_mut().resource_mut::<RelationshipGraph>();
            rel.set_relationship(
                sid_a,
                sid_b,
                RelationshipEdge {
                    kind: RelationshipKind::Colleague,
                    trust: -1, // None tier
                    history: vec![],
                    last_interaction_tick: 0,
                },
            );
        }

        app.world_mut()
            .entity_mut(entity_a)
            .insert(NpcConversation {
                partner: entity_b,
                started_tick: 0,
                end_tick: 100,
                ticks_since_last_line: 0,
            });

        app.update();

        let partner_kg = app
            .world()
            .entity(entity_b)
            .get::<KnowledgeGraph>()
            .expect("partner has KG");
        assert!(
            !partner_kg.knows_fact(&FactId("test.fact".to_string())),
            "No transfer should occur at None tier"
        );
    }

    #[test]
    fn disclosure_blocked_fact_never_transfers() {
        let mut app = build_test_world();

        let sid_a = StableId(1);
        let sid_b = StableId(2);

        // KnowledgeGraph with disclosure_blocked fact
        let mut kg_a = KnowledgeGraph::new();
        kg_a.facts.insert(
            FactId("secret.blocked".to_string()),
            FactKnowledge {
                confidence: KnowledgeConfidence::KnowsDetails,
                source: KnowledgeSource::Background,
                state: KnowledgeState::Active,
                acquired_tick: 1,
                disclosure_blocked: true, // blocks NPC transfer
            },
        );
        let kg_b = KnowledgeGraph::new();

        let entity_a = spawn_npc(app.world_mut(), sid_a, kg_a);
        let entity_b = spawn_npc(app.world_mut(), sid_b, kg_b);

        {
            let mut rel = app.world_mut().resource_mut::<RelationshipGraph>();
            rel.set_relationship(
                sid_a,
                sid_b,
                RelationshipEdge {
                    kind: RelationshipKind::Colleague,
                    trust: 10, // Max trust — still blocked
                    history: vec![],
                    last_interaction_tick: 0,
                },
            );
        }

        app.world_mut()
            .entity_mut(entity_a)
            .insert(NpcConversation {
                partner: entity_b,
                started_tick: 0,
                end_tick: 100,
                ticks_since_last_line: 0,
            });

        app.update();

        let partner_kg = app
            .world()
            .entity(entity_b)
            .get::<KnowledgeGraph>()
            .expect("partner has KG");
        assert!(
            !partner_kg.knows_fact(&FactId("secret.blocked".to_string())),
            "disclosure_blocked fact must never transfer regardless of trust"
        );
    }

    #[test]
    fn confidence_cap_applied_on_transfer() {
        let mut app = build_test_world();

        let sid_a = StableId(1);
        let sid_b = StableId(2);
        // KnowsDetails — should be capped to KnowsOf after transfer
        let kg_a = make_fact_kg("test.detail", KnowledgeConfidence::KnowsDetails);
        let kg_b = KnowledgeGraph::new();

        let entity_a = spawn_npc(app.world_mut(), sid_a, kg_a);
        let entity_b = spawn_npc(app.world_mut(), sid_b, kg_b);

        {
            let mut rel = app.world_mut().resource_mut::<RelationshipGraph>();
            rel.set_relationship(
                sid_a,
                sid_b,
                RelationshipEdge {
                    kind: RelationshipKind::Colleague,
                    trust: 8, // Secret tier
                    history: vec![],
                    last_interaction_tick: 0,
                },
            );
        }

        app.world_mut()
            .entity_mut(entity_a)
            .insert(NpcConversation {
                partner: entity_b,
                started_tick: 0,
                end_tick: 100,
                ticks_since_last_line: 0,
            });

        app.update();

        let partner_kg = app
            .world()
            .entity(entity_b)
            .get::<KnowledgeGraph>()
            .expect("partner has KG");
        let fact = partner_kg
            .facts
            .get(&FactId("test.detail".to_string()))
            .expect("fact should be transferred");
        assert_eq!(
            fact.confidence,
            KnowledgeConfidence::KnowsOf,
            "transferred confidence must be capped at KnowsOf"
        );
    }

    #[test]
    fn upgrade_only_never_downgrades_existing_knowledge() {
        let mut app = build_test_world();

        let sid_a = StableId(1);
        let sid_b = StableId(2);

        // Speaker knows fact at KnowsOf
        let kg_a = make_fact_kg("test.fact", KnowledgeConfidence::KnowsOf);

        // Partner already knows fact at KnowsDetails (higher than speaker)
        let mut kg_b = KnowledgeGraph::new();
        kg_b.facts.insert(
            FactId("test.fact".to_string()),
            FactKnowledge {
                confidence: KnowledgeConfidence::KnowsDetails,
                source: KnowledgeSource::Background,
                state: KnowledgeState::Active,
                acquired_tick: 0,
                disclosure_blocked: false,
            },
        );

        let entity_a = spawn_npc(app.world_mut(), sid_a, kg_a);
        let entity_b = spawn_npc(app.world_mut(), sid_b, kg_b);

        {
            let mut rel = app.world_mut().resource_mut::<RelationshipGraph>();
            rel.set_relationship(
                sid_a,
                sid_b,
                RelationshipEdge {
                    kind: RelationshipKind::Colleague,
                    trust: 5,
                    history: vec![],
                    last_interaction_tick: 0,
                },
            );
        }

        app.world_mut()
            .entity_mut(entity_a)
            .insert(NpcConversation {
                partner: entity_b,
                started_tick: 0,
                end_tick: 100,
                ticks_since_last_line: 0,
            });

        app.update();

        let partner_kg = app
            .world()
            .entity(entity_b)
            .get::<KnowledgeGraph>()
            .expect("partner has KG");
        let fact = partner_kg
            .facts
            .get(&FactId("test.fact".to_string()))
            .expect("fact exists");
        assert_eq!(
            fact.confidence,
            KnowledgeConfidence::KnowsDetails,
            "existing higher confidence must not be downgraded"
        );
    }
}