use std::{collections::HashMap, env, error::Error, sync::Arc};

use serde_json::{json, Value};
use sqlx::{postgres::PgPoolOptions, Pool, Postgres, Row, Transaction};

use crate::{embedding::embedder_trait::Embedder, vectorstore::VecStoreOptions};

use super::{
    HNSWIndex, Store, PG_LOCKID_EXTENSION, PG_LOCK_ID_COLLECTION_TABLE, PG_LOCK_ID_EMBEDDING_TABLE,
};

const DEFAULT_COLLECTION_NAME: &str = "langchain";
const DEFAULT_PRE_DELETE_COLLECTION: bool = false;
const DEFAULT_EMBEDDING_STORE_TABLE_NAME: &str = "langchain_pg_embedding";
const DEFAULT_COLLECTION_STORE_TABLE_NAME: &str = "langchain_pg_collection";

pub struct StoreBuilder {
    pool: Option<Pool<Postgres>>,
    embedder: Option<Arc<dyn Embedder>>,
    connection_url: Option<String>,
    vector_dimensions: i32,
    pre_delete_collection: bool,
    embedder_table_name: String,
    collection_name: String,
    collection_uuid: String,
    collection_table_name: String,
    collection_metadata: HashMap<String, Value>,
    vstore_options: VecStoreOptions,
    hns_index: Option<HNSWIndex>,
}

impl StoreBuilder {
    // Returns a new StoreBuilder instance with default values for each option
    pub fn new() -> Self {
        StoreBuilder {
            pool: None,
            embedder: None,
            connection_url: None,
            collection_uuid: Default::default(),
            vector_dimensions: 0,
            pre_delete_collection: DEFAULT_PRE_DELETE_COLLECTION,
            embedder_table_name: DEFAULT_EMBEDDING_STORE_TABLE_NAME.into(),
            collection_name: DEFAULT_COLLECTION_NAME.into(),
            collection_table_name: DEFAULT_COLLECTION_STORE_TABLE_NAME.into(),
            collection_metadata: HashMap::new(),
            vstore_options: VecStoreOptions::default(),
            hns_index: None,
        }
    }

    pub fn pool(mut self, pool: Pool<Postgres>) -> Self {
        self.pool = Some(pool);
        self
    }

    pub fn embedder<E: Embedder + 'static>(mut self, embedder: E) -> Self {
        self.embedder = Some(Arc::new(embedder));
        self
    }

    pub fn connection_url(mut self, connection_url: &str) -> Self {
        self.connection_url = Some(connection_url.into());
        self
    }

    pub fn vector_dimensions(mut self, vector_dimensions: i32) -> Self {
        self.vector_dimensions = vector_dimensions;
        self
    }

    pub fn pre_delete_collection(mut self, pre_delete_collection: bool) -> Self {
        self.pre_delete_collection = pre_delete_collection;
        self
    }

    pub fn embedder_table_name(mut self, embedder_table_name: &str) -> Self {
        self.embedder_table_name = embedder_table_name.into();
        self
    }

    pub fn collection_name(mut self, collection_name: &str) -> Self {
        self.collection_name = collection_name.into();
        self
    }

    pub fn collection_table_name(mut self, collection_table_name: &str) -> Self {
        self.collection_table_name = collection_table_name.into();
        self
    }

    pub fn vstore_options(mut self, vstore_options: VecStoreOptions) -> Self {
        self.vstore_options = vstore_options;
        self
    }

    fn collecion_metadata(mut self, collecion_metadata: HashMap<String, Value>) -> Self {
        self.collection_metadata = collecion_metadata;
        self
    }

    pub fn hns_index(mut self, hns_index: HNSWIndex) -> Self {
        self.hns_index = Some(hns_index);
        self
    }

    // Finalize the builder and construct the Store object
    pub async fn build(self) -> Result<Store, Box<dyn Error>> {
        if self.embedder.is_none() {
            return Err("Embedder is required".into());
        }
        let pool = self.get_pool().await?;
        let mut tx = pool.begin().await?;
        self.create_vector_extension_if_not_exists(&mut tx).await?;
        self.create_collection_table_if_not_exists(&mut tx).await?;
        self.create_embedding_table_if_not_exists(&mut tx).await?;

        if self.pre_delete_collection {
            self.remove_collection(&mut tx).await?;
        }

        let collection_uuid = self.create_or_get_collection(&mut tx).await?;

        tx.commit().await?;

        Ok(Store {
            pool,
            embedder: self.embedder.unwrap(),
            collection_name: self.collection_name,
            pre_delete_collection: self.pre_delete_collection,
            collection_uuid,
            collection_table_name: self.collection_table_name,
            collection_metadata: self.collection_metadata,
            embedder_table_name: self.embedder_table_name,
            vector_dimensions: self.vector_dimensions,
            vstore_options: self.vstore_options,
            hns_index: self.hns_index,
        })
    }

    async fn get_pool(&self) -> Result<Pool<Postgres>, Box<dyn Error>> {
        match &self.pool {
            Some(existing_pool) => {
                // If `self.pool` is Some, use the existing pool
                Ok(existing_pool.clone())
            }
            None => {
                let connection_url = match self.connection_url {
        Some(ref url) if !url.is_empty() => url.clone(),
        _ => env::var("PGVECTOR_CONNECTION_STRING")
                            .map_err(|_| "PGVECTOR_CONNECTION_STRING environment variable not set, and no connection URL provided.")?};

                // Check if the resolved `connection_url` is empty
                if connection_url.is_empty() {
                    return Err("Connection URL is empty.".into());
                }

                // Create a new pool
                let new_pool = PgPoolOptions::new()
                    .connect(&connection_url)
                    .await
                    .map_err(|e| format!("Failed to create a new connection pool: {}", e))?;
                Ok(new_pool)
            }
        }
    }

    async fn create_or_get_collection(
        &self,
        tx: &mut Transaction<'_, Postgres>,
    ) -> Result<String, Box<dyn Error>> {
        let sql = format!(
            r#"INSERT INTO {} (uuid, name, cmetadata)
        VALUES($1, $2, $3) ON CONFLICT (name) DO
        UPDATE SET cmetadata = $3"#,
            self.collection_table_name
        );
        sqlx::query(&sql)
            .bind(uuid::Uuid::new_v4().to_string())
            .bind(&self.collection_name)
            .bind(json!(&self.collection_metadata))
            .execute(&mut **tx)
            .await?;

        let sql = format!(
            r#"SELECT uuid FROM {} WHERE name = $1 ORDER BY name limit 1"#,
            self.collection_table_name
        );
        let row = sqlx::query(&sql)
            .bind(&self.collection_name)
            .fetch_one(&mut **tx)
            .await?;

        Ok(row.get(0))
    }

    async fn remove_collection(
        &self,
        tx: &mut Transaction<'_, Postgres>,
    ) -> Result<(), Box<dyn Error>> {
        sqlx::query(&format!(
            "DELETE FROM {} WHERE name = $1",
            self.collection_table_name
        ))
        .bind(&self.collection_name)
        .execute(&mut **tx)
        .await?;

        Ok(())
    }

    pub async fn create_vector_extension_if_not_exists(
        &self,
        tx: &mut Transaction<'_, Postgres>,
    ) -> Result<(), Box<dyn Error>> {
        // Acquire an advisory lock to prevent concurrent creation of the vector extension
        sqlx::query("SELECT pg_advisory_xact_lock($1)")
            .bind(PG_LOCKID_EXTENSION)
            .execute(&mut **tx)
            .await?;

        // Create the vector extension if it doesn't already exist
        sqlx::query("CREATE EXTENSION IF NOT EXISTS vector")
            .execute(&mut **tx)
            .await?;

        Ok(())
    }

    async fn create_collection_table_if_not_exists(
        &self,
        tx: &mut Transaction<'_, Postgres>,
    ) -> Result<(), Box<dyn Error>> {
        // inspired by
        // https://github.com/langchain-ai/langchain/blob/v0.0.340/libs/langchain/langchain/vectorstores/pgvector.py#L167
        // The advisor lock fixes issue arising from concurrent
        // creation of the vector extension.
        // https://github.com/langchain-ai/langchain/issues/12933
        // For more information see:
        // https://www.postgresql.org/docs/16/explicit-locking.html#ADVISORY-LOCKS
        let create_extension_sql = format!("CREATE EXTENSION IF NOT EXISTS vector");
        sqlx::query(&create_extension_sql)
            .execute(&mut **tx)
            .await?;

        // Use advisory lock as before
        sqlx::query("SELECT pg_advisory_xact_lock($1)")
            .bind(PG_LOCK_ID_COLLECTION_TABLE)
            .execute(&mut **tx)
            .await?;

        // Now, create the table
        let create_table_sql = format!(
            r#"CREATE TABLE IF NOT EXISTS {} (
        name VARCHAR,
        cmetadata JSON,
        "uuid" TEXT NOT NULL,
        UNIQUE (name),
        PRIMARY KEY (uuid)
    )"#,
            self.collection_table_name
        );
        sqlx::query(&create_table_sql).execute(&mut **tx).await?;

        Ok(())
    }

    async fn create_embedding_table_if_not_exists(
        &self,
        tx: &mut Transaction<'_, Postgres>,
    ) -> Result<(), Box<dyn Error>> {
        sqlx::query("SELECT pg_advisory_xact_lock($1)")
            .bind(PG_LOCK_ID_EMBEDDING_TABLE)
            .execute(&mut **tx)
            .await?;

        let mut vector_dimensions = String::from("");
        if self.vector_dimensions > 0 {
            vector_dimensions = format!("({})", self.vector_dimensions);
        }

        let sql = format!(
            r#"CREATE TABLE IF NOT EXISTS {}
             (collection_id TEXT,
             embedding VECTOR{},
             document VARCHAR,
             cmetadata JSON,
             "uuid" TEXT NOT NULL,
             CONSTRAINT langchain_pg_embedding_collection_id_fkey
             FOREIGN KEY (collection_id) REFERENCES {}("uuid") ON DELETE CASCADE,
             PRIMARY KEY ("uuid"))"#,
            self.embedder_table_name, vector_dimensions, self.collection_table_name
        );

        sqlx::query(&sql).execute(&mut **tx).await?;

        let sql = format!(
            r#"CREATE INDEX IF NOT EXISTS {}_collection_id ON {} (collection_id)"#,
            self.embedder_table_name, self.embedder_table_name
        );
        sqlx::query(&sql).execute(&mut **tx).await?;

        // See this for more details on HNWS indexes: https://github.com/pgvector/pgvector#hnsw
        match &self.hns_index {
            Some(hns_index) => {
                let mut sql = format!(
                    r#"CREATE INDEX IF NOT EXISTS {}_embedding_hnsw ON {} USING hnsw (embedding {})"#,
                    self.embedder_table_name, self.embedder_table_name, hns_index.distance_function
                );
                if hns_index.m > 0 && hns_index.ef_construction > 0 {
                    sql = format!(
                        "{} WITH (m={}, ef_construction = {})",
                        sql, hns_index.m, hns_index.ef_construction
                    );
                }
                sqlx::query(&sql).execute(&mut **tx).await?;
            }
            None => {}
        }

        Ok(())
    }
}