//! Semantic Fact Storage
//!
//! Persistent storage for semantic facts extracted from episodic memories.
//! Facts represent durable knowledge distilled from multiple experiences.
//!
//! Storage schema:
//! - `facts:{user_id}:{fact_id}` - Primary fact storage
//! - `facts_by_entity:{user_id}:{entity}:{fact_id}` - Entity index for fast lookup
//! - `facts_by_type:{user_id}:{type}:{fact_id}` - Type index
//! - `facts_embedding:{user_id}:{fact_id}` - Pre-computed embedding vector (384-dim)

use anyhow::Result;
use rocksdb::{IteratorMode, DB};
use serde::{Deserialize, Serialize};
use std::sync::Arc;

use super::compression::{FactType, SemanticFact};

/// Response for fact queries
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct FactQueryResponse {
    pub facts: Vec<SemanticFact>,
    pub total: usize,
}

/// Statistics about semantic facts
#[derive(Debug, Clone, Default, Serialize, Deserialize)]
pub struct FactStats {
    pub total_facts: usize,
    pub by_type: std::collections::HashMap<String, usize>,
    pub avg_confidence: f32,
    pub avg_support: f32,
}

/// Storage for semantic facts with indexing
pub struct SemanticFactStore {
    db: Arc<DB>,
}

impl SemanticFactStore {
    /// Create a new fact store backed by RocksDB
    pub fn new(db: Arc<DB>) -> Self {
        Self { db }
    }

    /// Get references to all RocksDB databases for backup
    pub fn databases(&self) -> Vec<(&str, &Arc<DB>)> {
        vec![("semantic_facts", &self.db)]
    }

    /// Store a semantic fact
    pub fn store(&self, user_id: &str, fact: &SemanticFact) -> Result<()> {
        // Primary storage
        let key = format!("facts:{}:{}", user_id, fact.id);
        let value = crate::serialization::encode(fact)?;
        self.db.put(key.as_bytes(), &value)?;

        // Entity index - index by each related entity
        for entity in &fact.related_entities {
            let entity_key = format!(
                "facts_by_entity:{}:{}:{}",
                user_id,
                entity.to_lowercase(),
                fact.id
            );
            self.db.put(entity_key.as_bytes(), fact.id.as_bytes())?;
        }

        // Type index
        let type_name = format!("{:?}", fact.fact_type);
        let type_key = format!("facts_by_type:{}:{}:{}", user_id, type_name, fact.id);
        self.db.put(type_key.as_bytes(), fact.id.as_bytes())?;

        Ok(())
    }

    /// Store multiple facts in a batch
    pub fn store_batch(&self, user_id: &str, facts: &[SemanticFact]) -> Result<usize> {
        let mut stored = 0;
        for fact in facts {
            if self.store(user_id, fact).is_ok() {
                stored += 1;
            }
        }
        Ok(stored)
    }

    /// Get a fact by ID
    pub fn get(&self, user_id: &str, fact_id: &str) -> Result<Option<SemanticFact>> {
        let key = format!("facts:{}:{}", user_id, fact_id);
        match self.db.get(key.as_bytes())? {
            Some(data) => {
                let (fact, _) = crate::serialization::try_decode::<SemanticFact>(&data)?;
                Ok(Some(fact))
            }
            None => Ok(None),
        }
    }

    /// Update an existing fact (for reinforcement)
    pub fn update(&self, user_id: &str, fact: &SemanticFact) -> Result<()> {
        // Simply overwrite - indices stay valid since ID doesn't change
        let key = format!("facts:{}:{}", user_id, fact.id);
        let value = crate::serialization::encode(fact)?;
        self.db.put(key.as_bytes(), &value)?;
        Ok(())
    }

    /// Delete a fact
    pub fn delete(&self, user_id: &str, fact_id: &str) -> Result<bool> {
        // Get fact first to clean up indices
        if let Some(fact) = self.get(user_id, fact_id)? {
            // Delete entity indices
            for entity in &fact.related_entities {
                let entity_key = format!(
                    "facts_by_entity:{}:{}:{}",
                    user_id,
                    entity.to_lowercase(),
                    fact_id
                );
                self.db.delete(entity_key.as_bytes())?;
            }

            // Delete type index
            let type_name = format!("{:?}", fact.fact_type);
            let type_key = format!("facts_by_type:{}:{}:{}", user_id, type_name, fact_id);
            self.db.delete(type_key.as_bytes())?;

            // Delete primary record
            let key = format!("facts:{}:{}", user_id, fact_id);
            self.db.delete(key.as_bytes())?;

            // Delete embedding if present
            let _ = self.delete_embedding(user_id, fact_id);

            Ok(true)
        } else {
            Ok(false)
        }
    }

    /// List all facts for a user
    pub fn list(&self, user_id: &str, limit: usize) -> Result<Vec<SemanticFact>> {
        let prefix = format!("facts:{}:", user_id);
        let mut facts = Vec::new();

        let iter = self.db.iterator(IteratorMode::From(
            prefix.as_bytes(),
            rocksdb::Direction::Forward,
        ));

        for item in iter {
            let (key, value) = item?;
            let key_str = String::from_utf8_lossy(&key);

            // Stop when we leave the prefix
            if !key_str.starts_with(&prefix) {
                break;
            }

            // Skip index keys (they contain extra colons)
            if key_str.matches(':').count() > 2 {
                continue;
            }

            if let Ok((fact, _)) = crate::serialization::try_decode::<SemanticFact>(&value) {
                facts.push(fact);
                if facts.len() >= limit {
                    break;
                }
            }
        }

        // Sort by confidence (highest first)
        facts.sort_by(|a, b| b.confidence.total_cmp(&a.confidence));

        Ok(facts)
    }

    /// Find facts by related entity
    pub fn find_by_entity(
        &self,
        user_id: &str,
        entity: &str,
        limit: usize,
    ) -> Result<Vec<SemanticFact>> {
        let prefix = format!("facts_by_entity:{}:{}:", user_id, entity.to_lowercase());
        let mut facts = Vec::new();
        let mut seen_ids = std::collections::HashSet::new();

        let iter = self.db.iterator(IteratorMode::From(
            prefix.as_bytes(),
            rocksdb::Direction::Forward,
        ));

        for item in iter {
            let (key, value) = item?;
            let key_str = String::from_utf8_lossy(&key);

            if !key_str.starts_with(&prefix) {
                break;
            }

            let fact_id = String::from_utf8_lossy(&value);
            if seen_ids.insert(fact_id.to_string()) {
                if let Some(fact) = self.get(user_id, &fact_id)? {
                    facts.push(fact);
                    if facts.len() >= limit {
                        break;
                    }
                }
            }
        }

        Ok(facts)
    }

    /// Find facts by type
    pub fn find_by_type(
        &self,
        user_id: &str,
        fact_type: FactType,
        limit: usize,
    ) -> Result<Vec<SemanticFact>> {
        let type_name = format!("{:?}", fact_type);
        let prefix = format!("facts_by_type:{}:{}:", user_id, type_name);
        let mut facts = Vec::new();

        let iter = self.db.iterator(IteratorMode::From(
            prefix.as_bytes(),
            rocksdb::Direction::Forward,
        ));

        for item in iter {
            let (key, value) = item?;
            let key_str = String::from_utf8_lossy(&key);

            if !key_str.starts_with(&prefix) {
                break;
            }

            let fact_id = String::from_utf8_lossy(&value);
            if let Some(fact) = self.get(user_id, &fact_id)? {
                facts.push(fact);
                if facts.len() >= limit {
                    break;
                }
            }
        }

        Ok(facts)
    }

    /// Search facts by keyword in fact content
    pub fn search(&self, user_id: &str, query: &str, limit: usize) -> Result<Vec<SemanticFact>> {
        let query_lower = query.to_lowercase();
        let all_facts = self.list(user_id, 1000)?; // Get all facts

        let mut matching: Vec<SemanticFact> = all_facts
            .into_iter()
            .filter(|f| f.fact.to_lowercase().contains(&query_lower))
            .collect();

        matching.truncate(limit);
        Ok(matching)
    }

    /// Get statistics about stored facts
    pub fn stats(&self, user_id: &str) -> Result<FactStats> {
        let facts = self.list(user_id, 10000)?;

        if facts.is_empty() {
            return Ok(FactStats::default());
        }

        let mut by_type: std::collections::HashMap<String, usize> =
            std::collections::HashMap::new();
        let mut total_confidence: f32 = 0.0;
        let mut total_support: usize = 0;

        for fact in &facts {
            let type_name = format!("{:?}", fact.fact_type);
            *by_type.entry(type_name).or_insert(0) += 1;
            total_confidence += fact.confidence;
            total_support += fact.support_count;
        }

        let count = facts.len();
        Ok(FactStats {
            total_facts: count,
            by_type,
            avg_confidence: total_confidence / count as f32,
            avg_support: total_support as f32 / count as f32,
        })
    }

    /// Find the creation timestamp of the most recent fact for a user.
    ///
    /// Used at startup to initialize the fact extraction watermark when no
    /// persisted watermark exists. Returns None if user has no facts.
    pub fn latest_fact_created_at(&self, user_id: &str) -> Option<i64> {
        let prefix = format!("facts:{user_id}:");
        let mut max_millis: Option<i64> = None;

        let iter = self.db.iterator(IteratorMode::From(
            prefix.as_bytes(),
            rocksdb::Direction::Forward,
        ));

        for item in iter {
            let (key, value) = match item {
                Ok(kv) => kv,
                Err(_) => break,
            };
            let key_str = String::from_utf8_lossy(&key);
            if !key_str.starts_with(&prefix) {
                break;
            }
            // Skip index keys (entity/type sub-keys have extra colons)
            if key_str.matches(':').count() > 2 {
                continue;
            }
            if let Ok((fact, _)) = crate::serialization::try_decode::<SemanticFact>(&value) {
                let millis = fact.created_at.timestamp_millis();
                max_millis = Some(max_millis.map_or(millis, |cur| cur.max(millis)));
            }
        }

        max_millis
    }

    /// Find facts that should decay (no reinforcement for too long)
    pub fn find_decaying_facts(
        &self,
        user_id: &str,
        max_age_days: i64,
    ) -> Result<Vec<SemanticFact>> {
        let cutoff = chrono::Utc::now() - chrono::Duration::days(max_age_days);
        let all_facts = self.list(user_id, 10000)?;

        let decaying: Vec<SemanticFact> = all_facts
            .into_iter()
            .filter(|f| f.last_reinforced < cutoff)
            .collect();

        Ok(decaying)
    }

    /// Check if a similar fact already exists (hybrid dedup)
    ///
    /// Multi-gate pipeline when embedding is provided:
    /// 1. Entity gate: at least 1 shared entity, OR both have zero entities
    /// 2. Polarity gate: same negation polarity (prevents merging contradictions)
    /// 3. Cosine gate: embedding similarity >= FACT_DEDUP_COSINE_THRESHOLD
    /// 4. Jaccard floor: word overlap >= FACT_DEDUP_JACCARD_FLOOR
    ///
    /// Falls back to pure Jaccard (0.70) if no embedding is provided.
    pub fn find_similar(
        &self,
        user_id: &str,
        fact_content: &str,
        fact_entities: &[String],
        new_embedding: Option<&[f32]>,
    ) -> Result<Option<SemanticFact>> {
        use crate::constants::{
            FACT_DEDUP_COSINE_THRESHOLD, FACT_DEDUP_JACCARD_FALLBACK, FACT_DEDUP_JACCARD_FLOOR,
        };
        use crate::similarity::cosine_similarity;

        let facts = self.list(user_id, 1000)?;
        let query_lower = fact_content.to_lowercase();
        let query_words: std::collections::HashSet<&str> = query_lower.split_whitespace().collect();
        let new_polarity = detect_polarity(&query_lower);
        let new_entity_set: std::collections::HashSet<&str> =
            fact_entities.iter().map(|s| s.as_str()).collect();

        let use_hybrid = new_embedding.is_some();
        let mut best_match: Option<(f32, SemanticFact)> = None;

        for fact in facts {
            let fact_lower = fact.fact.to_lowercase();
            let fact_words: std::collections::HashSet<&str> =
                fact_lower.split_whitespace().collect();

            // Compute Jaccard (needed in both modes)
            let intersection = query_words.intersection(&fact_words).count();
            let union = query_words.union(&fact_words).count();
            let jaccard = if union > 0 {
                intersection as f32 / union as f32
            } else {
                0.0
            };

            if use_hybrid {
                // Gate 1: Entity overlap — at least 1 shared entity, or both empty
                let existing_entity_set: std::collections::HashSet<&str> =
                    fact.related_entities.iter().map(|s| s.as_str()).collect();
                let both_empty = new_entity_set.is_empty() && existing_entity_set.is_empty();
                let has_overlap = !new_entity_set.is_disjoint(&existing_entity_set);
                if !both_empty && !has_overlap {
                    continue;
                }

                // Gate 2: Polarity match — prevents merging contradictions
                let existing_polarity = detect_polarity(&fact_lower);
                if new_polarity != existing_polarity {
                    continue;
                }

                // Gate 3: Cosine similarity
                let new_emb = new_embedding.unwrap();
                match self.get_embedding(user_id, &fact.id) {
                    Ok(Some(existing_emb)) => {
                        let cosine = cosine_similarity(new_emb, &existing_emb);
                        if cosine < FACT_DEDUP_COSINE_THRESHOLD {
                            continue;
                        }

                        // Gate 4: Jaccard sanity floor
                        if jaccard < FACT_DEDUP_JACCARD_FLOOR {
                            continue;
                        }

                        // Passed all gates — rank by cosine
                        if best_match.as_ref().map_or(true, |(s, _)| cosine > *s) {
                            best_match = Some((cosine, fact));
                        }
                    }
                    _ => {
                        // No stored embedding — fall back to Jaccard-only for this candidate
                        if jaccard >= FACT_DEDUP_JACCARD_FALLBACK
                            && best_match.as_ref().map_or(true, |(s, _)| jaccard > *s)
                        {
                            best_match = Some((jaccard, fact));
                        }
                    }
                }
            } else {
                // Fallback: pure Jaccard (legacy behavior when embedder unavailable)
                if jaccard >= FACT_DEDUP_JACCARD_FALLBACK {
                    return Ok(Some(fact));
                }
            }
        }

        Ok(best_match.map(|(_, fact)| fact))
    }

    // =========================================================================
    // EMBEDDING PERSISTENCE
    // =========================================================================

    /// Store pre-computed embedding vector for a fact
    ///
    /// Key format: `facts_embedding:{user_id}:{fact_id}` → bincode Vec<f32>
    /// Stored separately from SemanticFact struct for backward compatibility.
    pub fn store_embedding(&self, user_id: &str, fact_id: &str, embedding: &[f32]) -> Result<()> {
        let key = format!("facts_embedding:{user_id}:{fact_id}");
        let value = crate::serialization::encode(embedding)?;
        self.db.put(key.as_bytes(), &value)?;
        Ok(())
    }

    /// Get pre-computed embedding vector for a fact
    pub fn get_embedding(&self, user_id: &str, fact_id: &str) -> Result<Option<Vec<f32>>> {
        let key = format!("facts_embedding:{user_id}:{fact_id}");
        match self.db.get(key.as_bytes())? {
            Some(data) => {
                let (embedding, _) = crate::serialization::try_decode::<Vec<f32>>(&data)?;
                Ok(Some(embedding))
            }
            None => Ok(None),
        }
    }

    /// Delete embedding for a fact (called during fact deletion)
    pub fn delete_embedding(&self, user_id: &str, fact_id: &str) -> Result<()> {
        let key = format!("facts_embedding:{user_id}:{fact_id}");
        self.db.delete(key.as_bytes())?;
        Ok(())
    }

    /// List all unique user IDs that have facts
    pub fn list_users(&self, limit: usize) -> Result<Vec<String>> {
        let prefix = "facts:";
        let mut users = std::collections::HashSet::new();

        let iter = self.db.iterator(IteratorMode::From(
            prefix.as_bytes(),
            rocksdb::Direction::Forward,
        ));

        for item in iter {
            let (key, _) = item?;
            let key_str = String::from_utf8_lossy(&key);

            if !key_str.starts_with(prefix) {
                break;
            }

            // Key format: facts:{user_id}:{fact_id}
            // Skip index keys (facts_by_entity, facts_by_type)
            if key_str.starts_with("facts_by_") {
                continue;
            }

            // Extract user_id from key
            let parts: Vec<&str> = key_str.splitn(3, ':').collect();
            if parts.len() >= 2 {
                users.insert(parts[1].to_string());
                if users.len() >= limit {
                    break;
                }
            }
        }

        Ok(users.into_iter().collect())
    }
}

/// Detect negation polarity of a fact statement.
///
/// Returns `true` for positive polarity (even negation count, including 0),
/// `false` for negative polarity (odd negation count).
/// Handles double-negation: "not unlike" = positive.
fn detect_polarity(text_lower: &str) -> bool {
    use crate::constants::FACT_NEGATION_MARKERS;
    let words: Vec<&str> = text_lower.split_whitespace().collect();
    let negation_count = words
        .iter()
        .filter(|w| FACT_NEGATION_MARKERS.iter().any(|marker| *w == marker))
        .count();
    negation_count % 2 == 0
}

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

    fn create_test_store() -> (SemanticFactStore, TempDir) {
        let temp_dir = TempDir::new().unwrap();
        let db = Arc::new(DB::open_default(temp_dir.path()).unwrap());
        (SemanticFactStore::new(db), temp_dir)
    }

    fn create_test_fact(id: &str, content: &str) -> SemanticFact {
        SemanticFact {
            id: id.to_string(),
            fact: content.to_string(),
            confidence: 0.8,
            support_count: 3,
            source_memories: vec![],
            related_entities: vec!["rust".to_string(), "memory".to_string()],
            created_at: chrono::Utc::now(),
            last_reinforced: chrono::Utc::now(),
            fact_type: FactType::Pattern,
        }
    }

    #[test]
    fn test_store_and_get() {
        let (store, _dir) = create_test_store();
        let fact = create_test_fact("fact-1", "Rust is a systems programming language");

        store.store("user-1", &fact).unwrap();
        let retrieved = store.get("user-1", "fact-1").unwrap();

        assert!(retrieved.is_some());
        assert_eq!(
            retrieved.unwrap().fact,
            "Rust is a systems programming language"
        );
    }

    #[test]
    fn test_find_by_entity() {
        let (store, _dir) = create_test_store();
        let fact = create_test_fact("fact-1", "Rust has efficient memory management");

        store.store("user-1", &fact).unwrap();
        let results = store.find_by_entity("user-1", "rust", 10).unwrap();

        assert_eq!(results.len(), 1);
        assert_eq!(results[0].id, "fact-1");
    }

    #[test]
    fn test_find_by_type() {
        let (store, _dir) = create_test_store();
        let fact = create_test_fact("fact-1", "Pattern detected in codebase");

        store.store("user-1", &fact).unwrap();
        let results = store.find_by_type("user-1", FactType::Pattern, 10).unwrap();

        assert_eq!(results.len(), 1);
    }

    #[test]
    fn test_delete() {
        let (store, _dir) = create_test_store();
        let fact = create_test_fact("fact-1", "Test fact");

        store.store("user-1", &fact).unwrap();
        assert!(store.get("user-1", "fact-1").unwrap().is_some());

        store.delete("user-1", "fact-1").unwrap();
        assert!(store.get("user-1", "fact-1").unwrap().is_none());

        // Entity index should also be cleaned up
        let by_entity = store.find_by_entity("user-1", "rust", 10).unwrap();
        assert!(by_entity.is_empty());
    }

    #[test]
    fn test_stats() {
        let (store, _dir) = create_test_store();

        store
            .store("user-1", &create_test_fact("fact-1", "Fact one"))
            .unwrap();
        store
            .store("user-1", &create_test_fact("fact-2", "Fact two"))
            .unwrap();

        let stats = store.stats("user-1").unwrap();
        assert_eq!(stats.total_facts, 2);
        assert!(stats.avg_confidence > 0.0);
    }
}
