use rusqlite::{Connection, OpenFlags, params};
use std::sync::{Arc, Mutex};

use crate::error::AppError;

#[derive(Debug, Clone)]
pub struct Record {
    pub key: String,
    pub volumes: Vec<String>,
    pub size: Option<i64>,
}

fn apply_pragmas(conn: &Connection) {
    conn.execute_batch(
        "PRAGMA journal_mode = WAL;
         PRAGMA synchronous = NORMAL;
         PRAGMA busy_timeout = 5000;
         PRAGMA temp_store = memory;
         PRAGMA cache_size = -64000;
         PRAGMA mmap_size = 268435456;",
    )
    .expect("failed to set pragmas");
}

fn parse_volumes(s: &str) -> Vec<String> {
    serde_json::from_str(s).unwrap_or_default()
}

fn encode_volumes(v: &[String]) -> String {
    serde_json::to_string(v).unwrap()
}

/// A single SQLite connection behind a mutex, used for both reads and writes.
#[derive(Clone)]
pub struct Db {
    conn: Arc<Mutex<Connection>>,
}

impl Db {
    pub fn new(path: &str) -> Self {
        let conn = Connection::open_with_flags(
            path,
            OpenFlags::SQLITE_OPEN_READ_WRITE
                | OpenFlags::SQLITE_OPEN_CREATE
                | OpenFlags::SQLITE_OPEN_NO_MUTEX
                | OpenFlags::SQLITE_OPEN_URI,
        )
        .expect("failed to open database");
        apply_pragmas(&conn);
        conn.execute_batch(
            "CREATE TABLE IF NOT EXISTS kv (
                key         TEXT PRIMARY KEY,
                volumes     TEXT NOT NULL,
                size        INTEGER,
                created_at  INTEGER DEFAULT (unixepoch())
            );",
        )
        .expect("failed to create tables");
        Self {
            conn: Arc::new(Mutex::new(conn)),
        }
    }

    pub async fn get(&self, key: &str) -> Result<Record, AppError> {
        let conn = self.conn.clone();
        let key = key.to_string();
        tokio::task::spawn_blocking(move || {
            let conn = conn.lock().unwrap();
            let mut stmt =
                conn.prepare_cached("SELECT key, volumes, size FROM kv WHERE key = ?1")?;
            Ok(stmt.query_row(params![key], |row| {
                let vj: String = row.get(1)?;
                Ok(Record {
                    key: row.get(0)?,
                    volumes: parse_volumes(&vj),
                    size: row.get(2)?,
                })
            })?)
        })
        .await
        .unwrap()
    }

    pub async fn list_keys(&self, prefix: &str) -> Result<Vec<String>, AppError> {
        let conn = self.conn.clone();
        let prefix = prefix.to_string();
        tokio::task::spawn_blocking(move || {
            let conn = conn.lock().unwrap();
            if prefix.is_empty() {
                let mut stmt = conn.prepare_cached("SELECT key FROM kv ORDER BY key")?;
                let keys = stmt
                    .query_map([], |row| row.get(0))?
                    .collect::<Result<Vec<String>, _>>()?;
                return Ok(keys);
            }
            // Compute exclusive upper bound: increment last non-0xFF byte
            let upper = {
                let mut bytes = prefix.as_bytes().to_vec();
                let mut result = None;
                while let Some(last) = bytes.pop() {
                    if last < 0xFF {
                        bytes.push(last + 1);
                        result = Some(String::from_utf8_lossy(&bytes).into_owned());
                        break;
                    }
                }
                result
            };
            let keys = match &upper {
                Some(end) => {
                    let mut stmt = conn.prepare_cached(
                        "SELECT key FROM kv WHERE key >= ?1 AND key < ?2 ORDER BY key",
                    )?;
                    stmt.query_map(params![prefix, end], |row| row.get(0))?
                        .collect::<Result<Vec<String>, _>>()?
                }
                None => {
                    let mut stmt =
                        conn.prepare_cached("SELECT key FROM kv WHERE key >= ?1 ORDER BY key")?;
                    stmt.query_map(params![prefix], |row| row.get(0))?
                        .collect::<Result<Vec<String>, _>>()?
                }
            };
            Ok(keys)
        })
        .await
        .unwrap()
    }

    pub async fn put(
        &self,
        key: String,
        volumes: Vec<String>,
        size: Option<i64>,
    ) -> Result<(), AppError> {
        let conn = self.conn.clone();
        tokio::task::spawn_blocking(move || {
            let conn = conn.lock().unwrap();
            conn.prepare_cached(
                "INSERT INTO kv (key, volumes, size) VALUES (?1, ?2, ?3)
                 ON CONFLICT(key) DO UPDATE SET volumes = ?2, size = ?3",
            )?
            .execute(params![key, encode_volumes(&volumes), size])?;
            Ok(())
        })
        .await
        .unwrap()
    }

    pub async fn delete(&self, key: String) -> Result<(), AppError> {
        let conn = self.conn.clone();
        tokio::task::spawn_blocking(move || {
            let conn = conn.lock().unwrap();
            conn.prepare_cached("DELETE FROM kv WHERE key = ?1")?
                .execute(params![key])?;
            Ok(())
        })
        .await
        .unwrap()
    }

    pub async fn bulk_put(
        &self,
        records: Vec<(String, Vec<String>, Option<i64>)>,
    ) -> Result<(), AppError> {
        let conn = self.conn.clone();
        tokio::task::spawn_blocking(move || {
            let conn = conn.lock().unwrap();
            conn.execute_batch("BEGIN")?;
            let mut stmt = conn.prepare_cached(
                "INSERT INTO kv (key, volumes, size) VALUES (?1, ?2, ?3)
                 ON CONFLICT(key) DO UPDATE SET volumes = ?2, size = ?3",
            )?;
            for (key, volumes, size) in &records {
                stmt.execute(params![key, encode_volumes(volumes), size])?;
            }
            drop(stmt);
            conn.execute_batch("COMMIT")?;
            Ok(())
        })
        .await
        .unwrap()
    }

    pub fn all_records_sync(&self) -> Result<Vec<Record>, AppError> {
        let conn = self.conn.lock().unwrap();
        let mut stmt = conn.prepare_cached("SELECT key, volumes, size FROM kv")?;
        let records = stmt
            .query_map([], |row| {
                let vj: String = row.get(1)?;
                Ok(Record {
                    key: row.get(0)?,
                    volumes: parse_volumes(&vj),
                    size: row.get(2)?,
                })
            })?
            .collect::<Result<Vec<_>, _>>()?;
        Ok(records)
    }
}