use std::collections::HashSet;
use std::path::PathBuf;
use std::time::{SystemTime, UNIX_EPOCH};

use async_trait::async_trait;
use bson::{doc, oid::ObjectId, Document};
use dashmap::DashMap;
use tracing::{debug, warn};

use crate::adapter::StorageAdapter;
use crate::error::{StorageError, StorageResult};

/// Per-document timestamp tracking for conflict detection.
type TimestampMap = DashMap<String, i64>;

/// db -> coll -> id_hex -> Document
type DataStore = DashMap<String, DashMap<String, DashMap<String, Document>>>;

/// db -> coll -> Vec<index spec Document>
type IndexStore = DashMap<String, DashMap<String, Vec<Document>>>;

/// db -> coll -> id_hex -> last_modified_ms
type ModificationStore = DashMap<String, DashMap<String, TimestampMap>>;

fn now_ms() -> i64 {
    SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .unwrap()
        .as_millis() as i64
}

/// In-memory storage adapter backed by `DashMap`.
///
/// Optionally persists to a JSON file at a configured path.
pub struct MemoryStorageAdapter {
    data: DataStore,
    indexes: IndexStore,
    modifications: ModificationStore,
    persist_path: Option<PathBuf>,
}

impl MemoryStorageAdapter {
    /// Create a new purely in-memory adapter.
    pub fn new() -> Self {
        Self {
            data: DashMap::new(),
            indexes: DashMap::new(),
            modifications: DashMap::new(),
            persist_path: None,
        }
    }

    /// Create a new adapter that will persist state to the given JSON file.
    pub fn with_persist_path(path: PathBuf) -> Self {
        Self {
            data: DashMap::new(),
            indexes: DashMap::new(),
            modifications: DashMap::new(),
            persist_path: Some(path),
        }
    }

    /// Get or create the database entry in the data store.
    fn ensure_db(&self, db: &str) {
        self.data.entry(db.to_string()).or_insert_with(DashMap::new);
        self.indexes
            .entry(db.to_string())
            .or_insert_with(DashMap::new);
        self.modifications
            .entry(db.to_string())
            .or_insert_with(DashMap::new);
    }

    fn extract_id(doc: &Document) -> StorageResult<String> {
        match doc.get("_id") {
            Some(bson::Bson::ObjectId(oid)) => Ok(oid.to_hex()),
            _ => Err(StorageError::NotFound("document missing _id".into())),
        }
    }

    fn record_modification(&self, db: &str, coll: &str, id: &str) {
        if let Some(db_mods) = self.modifications.get(db) {
            if let Some(coll_mods) = db_mods.get(coll) {
                coll_mods.insert(id.to_string(), now_ms());
            }
        }
    }
}

#[async_trait]
impl StorageAdapter for MemoryStorageAdapter {
    async fn initialize(&self) -> StorageResult<()> {
        debug!("MemoryStorageAdapter initialized");
        Ok(())
    }

    async fn close(&self) -> StorageResult<()> {
        // Persist if configured.
        self.persist().await?;
        debug!("MemoryStorageAdapter closed");
        Ok(())
    }

    // ---- database ----

    async fn list_databases(&self) -> StorageResult<Vec<String>> {
        Ok(self.data.iter().map(|e| e.key().clone()).collect())
    }

    async fn create_database(&self, db: &str) -> StorageResult<()> {
        if self.data.contains_key(db) {
            return Err(StorageError::AlreadyExists(format!("database '{db}'")));
        }
        self.ensure_db(db);
        Ok(())
    }

    async fn drop_database(&self, db: &str) -> StorageResult<()> {
        self.data.remove(db);
        self.indexes.remove(db);
        self.modifications.remove(db);
        Ok(())
    }

    async fn database_exists(&self, db: &str) -> StorageResult<bool> {
        Ok(self.data.contains_key(db))
    }

    // ---- collection ----

    async fn list_collections(&self, db: &str) -> StorageResult<Vec<String>> {
        let db_ref = self
            .data
            .get(db)
            .ok_or_else(|| StorageError::NotFound(format!("database '{db}'")))?;
        Ok(db_ref.iter().map(|e| e.key().clone()).collect())
    }

    async fn create_collection(&self, db: &str, coll: &str) -> StorageResult<()> {
        self.ensure_db(db);
        let db_ref = self.data.get(db).unwrap();
        if db_ref.contains_key(coll) {
            return Err(StorageError::AlreadyExists(format!(
                "collection '{db}.{coll}'"
            )));
        }
        db_ref.insert(coll.to_string(), DashMap::new());
        drop(db_ref);

        // Create modification tracker for this collection.
        if let Some(db_mods) = self.modifications.get(db) {
            db_mods.insert(coll.to_string(), DashMap::new());
        }

        // Auto-create _id index spec.
        let idx_spec = doc! { "name": "_id_", "key": { "_id": 1 } };
        if let Some(db_idx) = self.indexes.get(db) {
            db_idx.insert(coll.to_string(), vec![idx_spec]);
        }

        Ok(())
    }

    async fn drop_collection(&self, db: &str, coll: &str) -> StorageResult<()> {
        if let Some(db_ref) = self.data.get(db) {
            db_ref.remove(coll);
        }
        if let Some(db_idx) = self.indexes.get(db) {
            db_idx.remove(coll);
        }
        if let Some(db_mods) = self.modifications.get(db) {
            db_mods.remove(coll);
        }
        Ok(())
    }

    async fn collection_exists(&self, db: &str, coll: &str) -> StorageResult<bool> {
        Ok(self
            .data
            .get(db)
            .map(|db_ref| db_ref.contains_key(coll))
            .unwrap_or(false))
    }

    async fn rename_collection(
        &self,
        db: &str,
        old_name: &str,
        new_name: &str,
    ) -> StorageResult<()> {
        let db_ref = self
            .data
            .get(db)
            .ok_or_else(|| StorageError::NotFound(format!("database '{db}'")))?;
        if db_ref.contains_key(new_name) {
            return Err(StorageError::AlreadyExists(format!(
                "collection '{db}.{new_name}'"
            )));
        }
        let (_, coll_data) = db_ref
            .remove(old_name)
            .ok_or_else(|| StorageError::NotFound(format!("collection '{db}.{old_name}'")))?;
        db_ref.insert(new_name.to_string(), coll_data);
        drop(db_ref);

        // Rename in indexes.
        if let Some(db_idx) = self.indexes.get(db) {
            if let Some((_, idx_data)) = db_idx.remove(old_name) {
                db_idx.insert(new_name.to_string(), idx_data);
            }
        }
        // Rename in modifications.
        if let Some(db_mods) = self.modifications.get(db) {
            if let Some((_, mod_data)) = db_mods.remove(old_name) {
                db_mods.insert(new_name.to_string(), mod_data);
            }
        }

        Ok(())
    }

    // ---- document writes ----

    async fn insert_one(
        &self,
        db: &str,
        coll: &str,
        mut doc: Document,
    ) -> StorageResult<String> {
        // Ensure _id exists.
        if !doc.contains_key("_id") {
            doc.insert("_id", ObjectId::new());
        }
        let id = Self::extract_id(&doc)?;

        let db_ref = self
            .data
            .get(db)
            .ok_or_else(|| StorageError::NotFound(format!("database '{db}'")))?;
        let coll_ref = db_ref
            .get(coll)
            .ok_or_else(|| StorageError::NotFound(format!("collection '{db}.{coll}'")))?;

        if coll_ref.contains_key(&id) {
            return Err(StorageError::AlreadyExists(format!("document '{id}'")));
        }
        coll_ref.insert(id.clone(), doc);
        drop(coll_ref);
        drop(db_ref);

        self.record_modification(db, coll, &id);
        Ok(id)
    }

    async fn insert_many(
        &self,
        db: &str,
        coll: &str,
        docs: Vec<Document>,
    ) -> StorageResult<Vec<String>> {
        let mut ids = Vec::with_capacity(docs.len());
        for doc in docs {
            let id = self.insert_one(db, coll, doc).await?;
            ids.push(id);
        }
        Ok(ids)
    }

    async fn update_by_id(
        &self,
        db: &str,
        coll: &str,
        id: &str,
        doc: Document,
    ) -> StorageResult<()> {
        let db_ref = self
            .data
            .get(db)
            .ok_or_else(|| StorageError::NotFound(format!("database '{db}'")))?;
        let coll_ref = db_ref
            .get(coll)
            .ok_or_else(|| StorageError::NotFound(format!("collection '{db}.{coll}'")))?;

        if !coll_ref.contains_key(id) {
            return Err(StorageError::NotFound(format!("document '{id}'")));
        }
        coll_ref.insert(id.to_string(), doc);
        drop(coll_ref);
        drop(db_ref);

        self.record_modification(db, coll, id);
        Ok(())
    }

    async fn delete_by_id(
        &self,
        db: &str,
        coll: &str,
        id: &str,
    ) -> StorageResult<()> {
        let db_ref = self
            .data
            .get(db)
            .ok_or_else(|| StorageError::NotFound(format!("database '{db}'")))?;
        let coll_ref = db_ref
            .get(coll)
            .ok_or_else(|| StorageError::NotFound(format!("collection '{db}.{coll}'")))?;

        coll_ref
            .remove(id)
            .ok_or_else(|| StorageError::NotFound(format!("document '{id}'")))?;
        drop(coll_ref);
        drop(db_ref);

        self.record_modification(db, coll, id);
        Ok(())
    }

    async fn delete_by_ids(
        &self,
        db: &str,
        coll: &str,
        ids: &[String],
    ) -> StorageResult<()> {
        for id in ids {
            self.delete_by_id(db, coll, id).await?;
        }
        Ok(())
    }

    // ---- document reads ----

    async fn find_all(
        &self,
        db: &str,
        coll: &str,
    ) -> StorageResult<Vec<Document>> {
        let db_ref = self
            .data
            .get(db)
            .ok_or_else(|| StorageError::NotFound(format!("database '{db}'")))?;
        let coll_ref = db_ref
            .get(coll)
            .ok_or_else(|| StorageError::NotFound(format!("collection '{db}.{coll}'")))?;

        Ok(coll_ref.iter().map(|e| e.value().clone()).collect())
    }

    async fn find_by_ids(
        &self,
        db: &str,
        coll: &str,
        ids: HashSet<String>,
    ) -> StorageResult<Vec<Document>> {
        let db_ref = self
            .data
            .get(db)
            .ok_or_else(|| StorageError::NotFound(format!("database '{db}'")))?;
        let coll_ref = db_ref
            .get(coll)
            .ok_or_else(|| StorageError::NotFound(format!("collection '{db}.{coll}'")))?;

        let mut results = Vec::with_capacity(ids.len());
        for id in &ids {
            if let Some(doc) = coll_ref.get(id) {
                results.push(doc.value().clone());
            }
        }
        Ok(results)
    }

    async fn find_by_id(
        &self,
        db: &str,
        coll: &str,
        id: &str,
    ) -> StorageResult<Option<Document>> {
        let db_ref = self
            .data
            .get(db)
            .ok_or_else(|| StorageError::NotFound(format!("database '{db}'")))?;
        let coll_ref = db_ref
            .get(coll)
            .ok_or_else(|| StorageError::NotFound(format!("collection '{db}.{coll}'")))?;

        Ok(coll_ref.get(id).map(|e| e.value().clone()))
    }

    async fn count(
        &self,
        db: &str,
        coll: &str,
    ) -> StorageResult<u64> {
        let db_ref = self
            .data
            .get(db)
            .ok_or_else(|| StorageError::NotFound(format!("database '{db}'")))?;
        let coll_ref = db_ref
            .get(coll)
            .ok_or_else(|| StorageError::NotFound(format!("collection '{db}.{coll}'")))?;

        Ok(coll_ref.len() as u64)
    }

    // ---- indexes ----

    async fn save_index(
        &self,
        db: &str,
        coll: &str,
        name: &str,
        spec: Document,
    ) -> StorageResult<()> {
        let db_idx = self
            .indexes
            .get(db)
            .ok_or_else(|| StorageError::NotFound(format!("database '{db}'")))?;

        let mut specs = db_idx
            .get_mut(coll)
            .ok_or_else(|| StorageError::NotFound(format!("collection '{db}.{coll}'")))?;

        // Remove existing index with same name, then add.
        specs.retain(|s| s.get_str("name").unwrap_or("") != name);
        let mut full_spec = spec;
        full_spec.insert("name", name);
        specs.push(full_spec);
        Ok(())
    }

    async fn get_indexes(
        &self,
        db: &str,
        coll: &str,
    ) -> StorageResult<Vec<Document>> {
        let db_idx = self
            .indexes
            .get(db)
            .ok_or_else(|| StorageError::NotFound(format!("database '{db}'")))?;

        let specs = db_idx
            .get(coll)
            .ok_or_else(|| StorageError::NotFound(format!("collection '{db}.{coll}'")))?;

        Ok(specs.clone())
    }

    async fn drop_index(
        &self,
        db: &str,
        coll: &str,
        name: &str,
    ) -> StorageResult<()> {
        let db_idx = self
            .indexes
            .get(db)
            .ok_or_else(|| StorageError::NotFound(format!("database '{db}'")))?;

        let mut specs = db_idx
            .get_mut(coll)
            .ok_or_else(|| StorageError::NotFound(format!("collection '{db}.{coll}'")))?;

        let before = specs.len();
        specs.retain(|s| s.get_str("name").unwrap_or("") != name);
        if specs.len() == before {
            return Err(StorageError::NotFound(format!("index '{name}'")));
        }
        Ok(())
    }

    // ---- snapshot / conflict detection ----

    async fn create_snapshot(
        &self,
        _db: &str,
        _coll: &str,
    ) -> StorageResult<i64> {
        Ok(now_ms())
    }

    async fn has_conflicts(
        &self,
        db: &str,
        coll: &str,
        ids: &HashSet<String>,
        snapshot_time: i64,
    ) -> StorageResult<bool> {
        if let Some(db_mods) = self.modifications.get(db) {
            if let Some(coll_mods) = db_mods.get(coll) {
                for id in ids {
                    if let Some(ts) = coll_mods.get(id) {
                        if *ts.value() > snapshot_time {
                            return Ok(true);
                        }
                    }
                }
            }
        }
        Ok(false)
    }

    // ---- persistence ----

    async fn persist(&self) -> StorageResult<()> {
        let path = match &self.persist_path {
            Some(p) => p,
            None => return Ok(()),
        };

        // Serialize the entire data store to JSON.
        let mut db_map = serde_json::Map::new();
        for db_entry in self.data.iter() {
            let db_name = db_entry.key().clone();
            let mut coll_map = serde_json::Map::new();
            for coll_entry in db_entry.value().iter() {
                let coll_name = coll_entry.key().clone();
                let mut docs_map = serde_json::Map::new();
                for doc_entry in coll_entry.value().iter() {
                    let id = doc_entry.key().clone();
                    // Convert bson::Document -> serde_json::Value via bson's
                    // built-in extended-JSON serialization.
                    let json_val: serde_json::Value =
                        bson::to_bson(doc_entry.value())
                            .map_err(|e| StorageError::SerializationError(e.to_string()))
                            .and_then(|b| {
                                serde_json::to_value(&b)
                                    .map_err(|e| StorageError::SerializationError(e.to_string()))
                            })?;
                    docs_map.insert(id, json_val);
                }
                coll_map.insert(coll_name, serde_json::Value::Object(docs_map));
            }
            db_map.insert(db_name, serde_json::Value::Object(coll_map));
        }

        let json = serde_json::to_string_pretty(&serde_json::Value::Object(db_map))?;
        if let Some(parent) = path.parent() {
            tokio::fs::create_dir_all(parent).await?;
        }
        tokio::fs::write(path, json).await?;
        debug!("MemoryStorageAdapter persisted to {:?}", path);
        Ok(())
    }

    async fn restore(&self) -> StorageResult<()> {
        let path = match &self.persist_path {
            Some(p) => p,
            None => return Ok(()),
        };

        if !path.exists() {
            warn!("persist file not found at {:?}, skipping restore", path);
            return Ok(());
        }

        let json = tokio::fs::read_to_string(path).await?;
        let root: serde_json::Value = serde_json::from_str(&json)?;

        let root_obj = root
            .as_object()
            .ok_or_else(|| StorageError::SerializationError("expected object".into()))?;

        self.data.clear();
        self.indexes.clear();
        self.modifications.clear();

        for (db_name, colls_val) in root_obj {
            self.ensure_db(db_name);
            let db_ref = self.data.get(db_name).unwrap();
            let colls = colls_val
                .as_object()
                .ok_or_else(|| StorageError::SerializationError("expected object".into()))?;

            for (coll_name, docs_val) in colls {
                let coll_map: DashMap<String, Document> = DashMap::new();
                let docs = docs_val
                    .as_object()
                    .ok_or_else(|| StorageError::SerializationError("expected object".into()))?;

                for (id, doc_val) in docs {
                    let bson_val: bson::Bson = serde_json::from_value(doc_val.clone())
                        .map_err(|e| StorageError::SerializationError(e.to_string()))?;
                    let doc = bson_val
                        .as_document()
                        .ok_or_else(|| {
                            StorageError::SerializationError("expected document".into())
                        })?
                        .clone();
                    coll_map.insert(id.clone(), doc);
                }
                db_ref.insert(coll_name.clone(), coll_map);

                // Restore modification tracker and default _id index.
                if let Some(db_mods) = self.modifications.get(db_name) {
                    db_mods.insert(coll_name.clone(), DashMap::new());
                }
                if let Some(db_idx) = self.indexes.get(db_name) {
                    let idx_spec = doc! { "name": "_id_", "key": { "_id": 1 } };
                    db_idx.insert(coll_name.clone(), vec![idx_spec]);
                }
            }
        }

        debug!("MemoryStorageAdapter restored from {:?}", path);
        Ok(())
    }
}

impl Default for MemoryStorageAdapter {
    fn default() -> Self {
        Self::new()
    }
}