use crate::{Completion, File, LimboError, OpenFlags, Result, IO};
use log::{debug, trace};
use std::cell::RefCell;
use std::io::{Read, Seek, Write};
use std::rc::Rc;

pub struct GenericIO {}

impl GenericIO {
    pub fn new() -> Result<Self> {
        debug!("Using IO backend 'generic'");
        Ok(Self {})
    }
}

impl IO for GenericIO {
    fn open_file(&self, path: &str, flags: OpenFlags, _direct: bool) -> Result<Rc<dyn File>> {
        trace!("open_file(path = {})", path);
        let file = std::fs::OpenOptions::new()
            .read(true)
            .write(true)
            .create(matches!(flags, OpenFlags::Create))
            .open(path)?;
        Ok(Rc::new(GenericFile {
            file: RefCell::new(file),
        }))
    }

    fn run_once(&self) -> Result<()> {
        Ok(())
    }

    fn generate_random_number(&self) -> i64 {
        let mut buf = [0u8; 8];
        getrandom::getrandom(&mut buf).unwrap();
        i64::from_ne_bytes(buf)
    }

    fn get_current_time(&self) -> String {
        chrono::Local::now().format("%Y-%m-%d %H:%M:%S").to_string()
    }
}

pub struct GenericFile {
    file: RefCell<std::fs::File>,
}

impl File for GenericFile {
    // Since we let the OS handle the locking, file locking is not supported on the generic IO implementation
    // No-op implementation allows compilation but provides no actual file locking.
    fn lock_file(&self, exclusive: bool) -> Result<()> {
        Ok(())
    }

    fn unlock_file(&self) -> Result<()> {
        Ok(())
    }

    fn pread(&self, pos: usize, c: Rc<Completion>) -> Result<()> {
        let mut file = self.file.borrow_mut();
        file.seek(std::io::SeekFrom::Start(pos as u64))?;
        {
            let r = match c.as_ref() {
                Completion::Read(r) => r,
                _ => unreachable!(),
            };
            let mut buf = r.buf_mut();
            let buf = buf.as_mut_slice();
            file.read_exact(buf)?;
        }
        c.complete(0);
        Ok(())
    }

    fn pwrite(
        &self,
        pos: usize,
        buffer: Rc<RefCell<crate::Buffer>>,
        c: Rc<Completion>,
    ) -> Result<()> {
        let mut file = self.file.borrow_mut();
        file.seek(std::io::SeekFrom::Start(pos as u64))?;
        let buf = buffer.borrow();
        let buf = buf.as_slice();
        file.write_all(buf)?;
        c.complete(buf.len() as i32);
        Ok(())
    }

    fn sync(&self, c: Rc<Completion>) -> Result<()> {
        let mut file = self.file.borrow_mut();
        file.sync_all().map_err(|err| LimboError::IOError(err))?;
        c.complete(0);
        Ok(())
    }

    fn size(&self) -> Result<u64> {
        let file = self.file.borrow();
        Ok(file.metadata().unwrap().len())
    }
}

impl Drop for GenericFile {
    fn drop(&mut self) {
        self.unlock_file().expect("Failed to unlock file");
    }
}