use super::MemoryIO;
use crate::{Clock, Completion, File, Instant, LimboError, OpenFlags, Result, IO};
use std::cell::RefCell;
use std::io::{Read, Seek, Write};
use std::sync::Arc;
use tracing::{debug, trace};

pub struct GenericIO {}

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

unsafe impl Send for GenericIO {}
unsafe impl Sync for GenericIO {}

impl IO for GenericIO {
    fn open_file(&self, path: &str, flags: OpenFlags, _direct: bool) -> Result<Arc<dyn File>> {
        trace!("open_file(path = {})", path);
        let mut file = std::fs::File::options();
        file.read(true);

        if !flags.contains(OpenFlags::ReadOnly) {
            file.write(true);
            file.create(flags.contains(OpenFlags::Create));
        }

        let file = file.open(path)?;
        Ok(Arc::new(GenericFile {
            file: RefCell::new(file),
            memory_io: Arc::new(MemoryIO::new()),
        }))
    }

    fn wait_for_completion(&self, c: Arc<Completion>) -> Result<()> {
        while !c.is_completed() {
            self.run_once()?;
        }
        Ok(())
    }

    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_memory_io(&self) -> Arc<MemoryIO> {
        Arc::new(MemoryIO::new())
    }
}

impl Clock for GenericIO {
    fn now(&self) -> Instant {
        let now = chrono::Local::now();
        Instant {
            secs: now.timestamp(),
            micros: now.timestamp_subsec_micros(),
        }
    }
}

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

unsafe impl Send for GenericFile {}
unsafe impl Sync for GenericFile {}

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: Arc<Completion>) -> Result<()> {
        let mut file = self.file.borrow_mut();
        file.seek(std::io::SeekFrom::Start(pos as u64))?;
        {
            let r = match *c {
                Completion::Read(ref 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: Arc<RefCell<crate::Buffer>>, c: Arc<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: Arc<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");
    }
}