chronicle-graph 0.1.1

//! Validation passes: referential integrity, temporal consistency, state tracking, orphan detection.

use std::fmt;

use allen_intervals::{Interval, Meets, NonEmpty, Precedes};
use petgraph::Direction;

use crate::graph::{Chronicle, parse_references};
use crate::model::*;

// ── Report types ───────────────────────────────────────────

/// The result of running all validation passes over a [`Chronicle`].
///
/// Contains collected errors (hard violations that indicate inconsistent data)
/// and warnings (soft issues like orphan entities that may be intentional).
#[derive(Debug, Default)]
pub struct ValidationReport {
    /// Hard validation failures: dangling references, temporal impossibilities,
    /// and state violations (e.g. a dead actor participating in a future event).
    pub errors: Vec<ValidationError>,
    /// Soft issues that do not necessarily indicate broken data, such as
    /// entities with no incoming or outgoing relationships.
    pub warnings: Vec<ValidationWarning>,
}

impl ValidationReport {
    /// Returns `true` if no errors were found. Warnings alone do not cause this to return `false`.
    pub fn is_ok(&self) -> bool {
        self.errors.is_empty()
    }
}

/// A hard validation error indicating inconsistent world data.
#[derive(Debug)]
pub enum ValidationError {
    /// A reference from one entity to another that does not exist in the graph.
    DanglingReference {
        /// The ID of the entity that contains the broken reference.
        source_id: String,
        /// The ID that was referenced but not found in the graph.
        target_id: String,
        /// Human-readable label for the kind of reference (e.g. `"location"`, `"participant"`).
        context: String,
    },
    /// A temporal impossibility detected via Allen's Interval Algebra — for example,
    /// an event occurring before a participant's lifespan or after a cause.
    TemporalViolation {
        /// The ID of the entity whose timeline is violated (actor or event).
        entity_id: String,
        /// The ID of the event involved in the violation.
        event_id: String,
        /// Human-readable explanation of the temporal conflict.
        description: String,
    },
    /// An entity is used in an event despite having a terminal status
    /// (e.g. `Dead`, `Destroyed`) from a strictly earlier event.
    StateViolation {
        /// The ID of the entity in a terminal state.
        entity_id: String,
        /// The ID of the event that illegally references the terminal entity.
        event_id: String,
        /// Human-readable explanation including the terminal status and the events involved.
        description: String,
    },
}

/// A soft validation warning that does not indicate broken data but may
/// signal authoring oversights.
#[derive(Debug)]
pub enum ValidationWarning {
    /// An entity with zero incoming and zero outgoing edges — it is completely
    /// disconnected from the rest of the graph.
    OrphanEntity {
        /// The ID of the disconnected entity.
        entity_id: String,
    },
    /// A temporal relationship that is ambiguous (e.g. overlapping intervals
    /// where strict ordering was expected) but not provably wrong.
    TemporalAmbiguity {
        /// Human-readable explanation of the ambiguous temporal relationship.
        description: String,
    },
}

impl fmt::Display for ValidationError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::DanglingReference {
                source_id,
                target_id,
                context,
            } => {
                write!(
                    f,
                    "dangling reference: {source_id} -> {target_id} ({context})"
                )
            }
            Self::TemporalViolation {
                entity_id,
                event_id,
                description,
            } => {
                write!(
                    f,
                    "temporal violation: {entity_id} in {event_id}: {description}"
                )
            }
            Self::StateViolation {
                entity_id,
                event_id,
                description,
            } => {
                write!(
                    f,
                    "state violation: {entity_id} in {event_id}: {description}"
                )
            }
        }
    }
}

impl fmt::Display for ValidationWarning {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::OrphanEntity { entity_id } => {
                write!(f, "orphan entity: {entity_id} has no references in or out")
            }
            Self::TemporalAmbiguity { description } => {
                write!(f, "temporal ambiguity: {description}")
            }
        }
    }
}

// ── Validation entry point ─────────────────────────────────

/// Run all four validation passes over the given [`Chronicle`] and return a [`ValidationReport`].
///
/// The passes, executed in order, are:
/// 1. **Referential integrity** — every ID referenced by an entity must exist in the graph.
/// 2. **Temporal consistency** — participant lifespans and causal ordering are checked
///    using Allen's Interval Algebra.
/// 3. **State tracking** — entities with terminal statuses (per [`ValidationConfig`]) cannot
///    appear in events that occur strictly after the status-changing event.
/// 4. **Orphan detection** — entities with no edges in either direction produce warnings.
pub fn validate(chronicle: &Chronicle) -> ValidationReport {
    let mut report = ValidationReport::default();
    validate_referential(chronicle, &mut report);
    validate_temporal(chronicle, &mut report);
    validate_state(chronicle, &chronicle.config, &mut report);
    validate_orphans(chronicle, &mut report);
    report
}

// ── Referential integrity ──────────────────────────────────

fn validate_referential(chronicle: &Chronicle, report: &mut ValidationReport) {
    for nx in chronicle.graph.node_indices() {
        let entity = &chronicle.graph[nx];
        match entity {
            Entity::Actor(actor) => {
                for aff in &actor.affiliations {
                    check_ref(chronicle, &actor.id, aff, "affiliation", report);
                }
                if let Some(ev) = &actor.status_since_event {
                    check_ref(chronicle, &actor.id, ev, "status_since_event", report);
                }
            }
            Entity::Place(place) => {
                if let Some(r) = &place.region {
                    check_ref(chronicle, &place.id, r, "region", report);
                }
                if let Some(ev) = &place.status_since_event {
                    check_ref(chronicle, &place.id, ev, "status_since_event", report);
                }
            }
            Entity::Event(event) => {
                if let Some(loc) = &event.location {
                    check_ref(chronicle, &event.id, loc, "location", report);
                }
                for cause in &event.caused_by {
                    check_ref(chronicle, &event.id, cause, "caused_by", report);
                }
                for p in &event.participants {
                    check_ref(chronicle, &event.id, &p.actor, "participant", report);
                }
                for sc in &event.state_changes {
                    check_ref(
                        chronicle,
                        &event.id,
                        &sc.entity,
                        "state_change target",
                        report,
                    );
                }
            }
            Entity::Concept(concept) => {
                if let Some(origin) = &concept.origin_event {
                    check_ref(chronicle, &concept.id, origin, "origin_event", report);
                }
            }
            Entity::Account(account) => {
                check_ref(chronicle, &account.id, &account.source, "source", report);
                for ev in &account.event_refs {
                    check_ref(chronicle, &account.id, ev, "event_ref", report);
                }
                for mention in parse_references(&account.text) {
                    check_ref(chronicle, &account.id, &mention, "text mention", report);
                }
            }
        }
    }
}

fn check_ref(
    chronicle: &Chronicle,
    source_id: &str,
    target_id: &str,
    context: &str,
    report: &mut ValidationReport,
) {
    if !chronicle.index.contains_key(target_id) {
        report.errors.push(ValidationError::DanglingReference {
            source_id: source_id.to_owned(),
            target_id: target_id.to_owned(),
            context: context.to_owned(),
        });
    }
}

// ── Temporal consistency ───────────────────────────────────

fn to_interval(ts: &TimeSpan) -> Option<NonEmpty<Interval<i32>>> {
    // TimeSpan uses inclusive bounds; Allen's discrete intervals use exclusive end.
    Interval {
        start: ts.start,
        end: ts.end + 1,
    }
    .try_into()
    .ok()
}

/// True if interval `a` ends strictly before `b` starts (precedes or meets in Allen's algebra).
fn strictly_before(a: &NonEmpty<Interval<i32>>, b: &NonEmpty<Interval<i32>>) -> bool {
    a.precedes(b) || a.meets(b)
}

fn validate_temporal(chronicle: &Chronicle, report: &mut ValidationReport) {
    for nx in chronicle.graph.node_indices() {
        if let Entity::Event(event) = &chronicle.graph[nx] {
            let Some(event_iv) = to_interval(&event.time_span) else {
                continue;
            };

            // Check participants' lifespans
            for p in &event.participants {
                if let Some(&actor_nx) = chronicle.index.get(&p.actor)
                    && let Entity::Actor(actor) = &chronicle.graph[actor_nx]
                    && let Some(lifespan) = &actor.lifespan
                    && let Some(life_iv) = to_interval(lifespan)
                {
                    if strictly_before(&event_iv, &life_iv) {
                        report.errors.push(ValidationError::TemporalViolation {
                            entity_id: actor.id.clone(),
                            event_id: event.id.clone(),
                            description: format!(
                                "event at {}-{} precedes actor lifespan {}-{}",
                                event.time_span.start,
                                event.time_span.end,
                                lifespan.start,
                                lifespan.end,
                            ),
                        });
                    }
                    if strictly_before(&life_iv, &event_iv) {
                        report.errors.push(ValidationError::TemporalViolation {
                            entity_id: actor.id.clone(),
                            event_id: event.id.clone(),
                            description: format!(
                                "actor lifespan {}-{} ends before event at {}-{}",
                                lifespan.start,
                                lifespan.end,
                                event.time_span.start,
                                event.time_span.end,
                            ),
                        });
                    }
                }
            }

            // Check causal ordering: cause must not be after effect
            for cause_id in &event.caused_by {
                if let Some(&cause_nx) = chronicle.index.get(cause_id)
                    && let Entity::Event(cause_event) = &chronicle.graph[cause_nx]
                    && let Some(cause_iv) = to_interval(&cause_event.time_span)
                    && strictly_before(&event_iv, &cause_iv)
                {
                    report.errors.push(ValidationError::TemporalViolation {
                        entity_id: event.id.clone(),
                        event_id: cause_event.id.clone(),
                        description: format!(
                            "effect {}-{} precedes its cause {}-{}",
                            event.time_span.start,
                            event.time_span.end,
                            cause_event.time_span.start,
                            cause_event.time_span.end,
                        ),
                    });
                    // cause precedes/meets effect = valid; overlap/equal = ambiguous, not error
                }
            }
        }
    }
}

// ── State tracking ─────────────────────────────────────────

fn validate_state(chronicle: &Chronicle, config: &ValidationConfig, report: &mut ValidationReport) {
    let state_changes = collect_state_changes(chronicle);

    for nx in chronicle.graph.node_indices() {
        if let Entity::Event(event) = &chronicle.graph[nx] {
            let Some(event_iv) = to_interval(&event.time_span) else {
                continue;
            };

            // Check participants aren't in a terminal state from a strictly earlier event
            for p in &event.participants {
                for (entity_id, status, change_time, change_event_id) in &state_changes {
                    if *entity_id == p.actor
                        && config.terminal_statuses.contains(status)
                        && let Some(change_iv) = to_interval(change_time)
                        && strictly_before(&change_iv, &event_iv)
                    {
                        report.errors.push(ValidationError::StateViolation {
                            entity_id: p.actor.clone(),
                            event_id: event.id.clone(),
                            description: format!(
                                "actor '{}' has status {:?} as of '{}' (year {}-{}), \
                                 cannot participate in '{}' (year {}-{})",
                                p.actor,
                                status,
                                change_event_id,
                                change_time.start,
                                change_time.end,
                                event.id,
                                event.time_span.start,
                                event.time_span.end,
                            ),
                        });
                    }
                }
            }

            // Check locations aren't in a terminal state
            if let Some(loc) = &event.location {
                for (entity_id, status, change_time, change_event_id) in &state_changes {
                    if entity_id == loc.as_str()
                        && config.terminal_statuses.contains(status)
                        && let Some(change_iv) = to_interval(change_time)
                        && strictly_before(&change_iv, &event_iv)
                    {
                        report.errors.push(ValidationError::StateViolation {
                            entity_id: loc.clone(),
                            event_id: event.id.clone(),
                            description: format!(
                                "location '{}' has status {:?} as of '{}' (year {}-{}), \
                                 cannot host '{}' (year {}-{})",
                                loc,
                                status,
                                change_event_id,
                                change_time.start,
                                change_time.end,
                                event.id,
                                event.time_span.start,
                                event.time_span.end,
                            ),
                        });
                    }
                }
            }
        }
    }
}

// ── Orphan detection ───────────────────────────────────────

fn validate_orphans(chronicle: &Chronicle, report: &mut ValidationReport) {
    for nx in chronicle.graph.node_indices() {
        let in_deg = chronicle
            .graph
            .neighbors_directed(nx, Direction::Incoming)
            .count();
        let out_deg = chronicle
            .graph
            .neighbors_directed(nx, Direction::Outgoing)
            .count();
        if in_deg == 0 && out_deg == 0 {
            report.warnings.push(ValidationWarning::OrphanEntity {
                entity_id: chronicle.graph[nx].id().to_owned(),
            });
        }
    }
}

// ── Shared helpers ─────────────────────────────────────────

/// Collect all status changes from events: (entity_id, status, time_span, event_id).
fn collect_state_changes(chronicle: &Chronicle) -> Vec<(String, Status, TimeSpan, String)> {
    let mut changes = Vec::new();
    for nx in chronicle.graph.node_indices() {
        if let Entity::Event(event) = &chronicle.graph[nx] {
            for sc in &event.state_changes {
                if let StateChange::StatusChange(status) = &sc.change {
                    changes.push((
                        sc.entity.clone(),
                        status.clone(),
                        event.time_span.clone(),
                        event.id.clone(),
                    ));
                }
            }
        }
    }
    changes
}

// ── can_add_event ──────────────────────────────────────────

/// Check whether a proposed [`Event`] is consistent with the existing graph.
///
/// Runs referential, temporal, and state checks against the current [`Chronicle`]
/// without modifying it. This is the pre-flight check for inserting new narrative content.
///
/// Returns `Ok(())` if the event can be safely added, or `Err` containing every
/// detected [`ValidationError`] (the list is exhaustive, not short-circuited).
pub fn can_add_event(chronicle: &Chronicle, event: &Event) -> Result<(), Vec<ValidationError>> {
    let mut errors = Vec::new();

    // Duplicate ID check
    if chronicle.index.contains_key(&event.id) {
        errors.push(ValidationError::DanglingReference {
            source_id: event.id.clone(),
            target_id: event.id.clone(),
            context: format!(
                "proposed event '{}' has the same ID as an existing entity",
                event.id
            ),
        });
    }

    // Referential: all referenced entities must exist
    if let Some(loc) = &event.location
        && !chronicle.index.contains_key(loc.as_str())
    {
        errors.push(ValidationError::DanglingReference {
            source_id: event.id.clone(),
            target_id: loc.clone(),
            context: "location".to_owned(),
        });
    }
    for cause_id in &event.caused_by {
        if !chronicle.index.contains_key(cause_id.as_str()) {
            errors.push(ValidationError::DanglingReference {
                source_id: event.id.clone(),
                target_id: cause_id.clone(),
                context: "caused_by".to_owned(),
            });
        }
    }
    for p in &event.participants {
        if !chronicle.index.contains_key(p.actor.as_str()) {
            errors.push(ValidationError::DanglingReference {
                source_id: event.id.clone(),
                target_id: p.actor.clone(),
                context: "participant".to_owned(),
            });
        }
    }
    for sc in &event.state_changes {
        if !chronicle.index.contains_key(sc.entity.as_str()) {
            errors.push(ValidationError::DanglingReference {
                source_id: event.id.clone(),
                target_id: sc.entity.clone(),
                context: "state_change target".to_owned(),
            });
        }
    }

    // Temporal: lifespan checks for participants
    if let Some(event_iv) = to_interval(&event.time_span) {
        for p in &event.participants {
            if let Some(&actor_nx) = chronicle.index.get(&p.actor)
                && let Entity::Actor(actor) = &chronicle.graph[actor_nx]
                && let Some(lifespan) = &actor.lifespan
                && let Some(life_iv) = to_interval(lifespan)
            {
                if strictly_before(&event_iv, &life_iv) {
                    errors.push(ValidationError::TemporalViolation {
                        entity_id: actor.id.clone(),
                        event_id: event.id.clone(),
                        description: format!(
                            "proposed event '{}' (year {}-{}) precedes actor '{}' lifespan ({}-{})",
                            event.id,
                            event.time_span.start,
                            event.time_span.end,
                            actor.id,
                            lifespan.start,
                            lifespan.end,
                        ),
                    });
                }
                if strictly_before(&life_iv, &event_iv) {
                    errors.push(ValidationError::TemporalViolation {
                        entity_id: actor.id.clone(),
                        event_id: event.id.clone(),
                        description: format!(
                            "actor '{}' lifespan ({}-{}) ends before proposed event '{}' (year {}-{})",
                            actor.id, lifespan.start, lifespan.end,
                            event.id, event.time_span.start, event.time_span.end,
                        ),
                    });
                }
            }
        }

        // Temporal: causal ordering
        for cause_id in &event.caused_by {
            if let Some(&cause_nx) = chronicle.index.get(cause_id.as_str())
                && let Entity::Event(cause_event) = &chronicle.graph[cause_nx]
                && let Some(cause_iv) = to_interval(&cause_event.time_span)
                && strictly_before(&event_iv, &cause_iv)
            {
                errors.push(ValidationError::TemporalViolation {
                    entity_id: event.id.clone(),
                    event_id: cause_event.id.clone(),
                    description: format!(
                        "proposed event '{}' (year {}-{}) precedes its cause '{}' (year {}-{})",
                        event.id,
                        event.time_span.start,
                        event.time_span.end,
                        cause_event.id,
                        cause_event.time_span.start,
                        cause_event.time_span.end,
                    ),
                });
            }
        }

        // State: check participants and location against terminal statuses
        let state_changes = collect_state_changes(chronicle);

        for p in &event.participants {
            for (entity_id, status, change_time, change_event_id) in &state_changes {
                if *entity_id == p.actor
                    && chronicle.config.terminal_statuses.contains(status)
                    && let Some(change_iv) = to_interval(change_time)
                    && strictly_before(&change_iv, &event_iv)
                {
                    errors.push(ValidationError::StateViolation {
                        entity_id: p.actor.clone(),
                        event_id: event.id.clone(),
                        description: format!(
                            "actor '{}' has status {:?} as of '{}' (year {}-{}), \
                             cannot participate in proposed event '{}' (year {}-{})",
                            p.actor,
                            status,
                            change_event_id,
                            change_time.start,
                            change_time.end,
                            event.id,
                            event.time_span.start,
                            event.time_span.end,
                        ),
                    });
                }
            }
        }

        if let Some(loc) = &event.location {
            for (entity_id, status, change_time, change_event_id) in &state_changes {
                if entity_id == loc.as_str()
                    && chronicle.config.terminal_statuses.contains(status)
                    && let Some(change_iv) = to_interval(change_time)
                    && strictly_before(&change_iv, &event_iv)
                {
                    errors.push(ValidationError::StateViolation {
                        entity_id: loc.clone(),
                        event_id: event.id.clone(),
                        description: format!(
                            "location '{}' has status {:?} as of '{}' (year {}-{}), \
                             cannot host proposed event '{}' (year {}-{})",
                            loc,
                            status,
                            change_event_id,
                            change_time.start,
                            change_time.end,
                            event.id,
                            event.time_span.start,
                            event.time_span.end,
                        ),
                    });
                }
            }
        }
    }

    if errors.is_empty() {
        Ok(())
    } else {
        Err(errors)
    }
}