use anyhow::{anyhow, Result};
use std::alloc::{alloc, dealloc, Layout};
use std::collections::HashMap;
use std::fs::File;
use std::fs::OpenOptions;
use std::io;
use std::io::{Read, Seek};
use std::os::unix::fs::OpenOptionsExt;
use std::os::unix::io::AsRawFd;
use std::path::Path;
use std::sync::{Arc, Mutex};
use io_uring::opcode::{self, types};
use io_uring::IoUring;

//------------------------------------------

pub const BLOCK_SIZE: usize = 4096;
const ALIGN: usize = 4096;

#[derive(Debug)]
pub struct Block {
    pub loc: u64,
    data: *mut u8,
}

impl Block {
    pub fn new(loc: u64) -> Block {
        let layout = Layout::from_size_align(BLOCK_SIZE, ALIGN).unwrap();
        let ptr = unsafe { alloc(layout) };
        assert!(!ptr.is_null(), "out of memory");
        Block { loc, data: ptr }
    }

    pub fn get_data<'a>(&self) -> &'a mut [u8] {
        unsafe { std::slice::from_raw_parts_mut::<'a>(self.data, BLOCK_SIZE) }
    }
}

impl Drop for Block {
    fn drop(&mut self) {
        let layout = Layout::from_size_align(BLOCK_SIZE, ALIGN).unwrap();
        unsafe {
            dealloc(self.data, layout);
        }
    }
}

//------------------------------------------

pub trait IoEngine {
    fn get_nr_blocks(&self) -> u64;
    fn read(&mut self, block: &mut Block) -> Result<()>;
    fn read_many(&mut self, blocks: &mut Vec<Block>) -> Result<()>;
}

fn get_nr_blocks(path: &Path) -> io::Result<u64> {
    let metadata = std::fs::metadata(path)?;
    Ok(metadata.len() / (BLOCK_SIZE as u64))
}

//------------------------------------------

pub struct SyncIoEngine {
    nr_blocks: u64,
    input: File,
}

impl SyncIoEngine {
    pub fn new(path: &Path) -> Result<SyncIoEngine> {
        let input = OpenOptions::new()
            .read(true)
            .write(false)
            .custom_flags(libc::O_DIRECT)
            .open(path)?;

        Ok(SyncIoEngine {
            nr_blocks: get_nr_blocks(path)?,
            input,
        })
    }
}

impl IoEngine for SyncIoEngine {
    fn get_nr_blocks(&self) -> u64 {
        self.nr_blocks
    }

    fn read(&mut self, b: &mut Block) -> Result<()> {
        self.input
            .seek(io::SeekFrom::Start(b.loc * BLOCK_SIZE as u64))?;
        self.input.read_exact(&mut b.get_data())?;

        Ok(())
    }

    fn read_many(&mut self, blocks: &mut Vec<Block>) -> Result<()> {
        for b in blocks {
            self.read(b);
        }

        Ok(())
    }
}

//------------------------------------------

pub struct AsyncIoEngine {
    ring: IoUring,
    nr_blocks: u64,
    input: File,
}

impl AsyncIoEngine {
    pub fn new(path: &Path, queue_len: u32) -> Result<AsyncIoEngine> {
        let input = OpenOptions::new()
            .read(true)
            .write(false)
            .custom_flags(libc::O_DIRECT)
            .open(path)?;

        Ok(AsyncIoEngine {
            ring: IoUring::new(queue_len)?,
            nr_blocks: get_nr_blocks(path)?,
            input,
        })
    }
}

impl IoEngine for AsyncIoEngine {
    fn get_nr_blocks(&self) -> u64 {
        self.nr_blocks
    }

    fn read(&mut self, b: &mut Block) -> Result<()> {
        let fd = types::Target::Fd(self.input.as_raw_fd());
        let read_e = opcode::Read::new(fd, b.data, BLOCK_SIZE as u32).offset(b.loc as i64 * BLOCK_SIZE as i64);

        unsafe {
            let mut queue = self.ring.submission().available();
            queue.push(read_e.build().user_data(1))
                .ok()
                .expect("queue is full");
        }

        self.ring.submit_and_wait(1)?;

        let cqes = self.ring.completion().available().collect::<Vec<_>>();

	// FIXME: return proper errors
         assert_eq!(cqes.len(), 1);
         assert_eq!(cqes[0].user_data(), 1);
         assert_eq!(cqes[0].result(), BLOCK_SIZE as i32);

        Ok(())
    }

    fn read_many(&mut self, blocks: &mut Vec<Block>) -> Result<()> {
        let count = blocks.len();
        let fd = types::Target::Fd(self.input.as_raw_fd());

        for b in blocks.into_iter() {
            let read_e = opcode::Read::new(fd, b.data, BLOCK_SIZE as u32).offset(b.loc as i64 * BLOCK_SIZE as i64);

            unsafe {
                let mut queue = self.ring.submission().available();
                queue.push(read_e.build().user_data(1))
                    .ok()
                    .expect("queue is full");
            }
        }

        self.ring.submit_and_wait(count)?;

        let cqes = self.ring.completion().available().collect::<Vec<_>>();

        // FIXME: return proper errors
        assert_eq!(cqes.len(), count);
        for c in &cqes {
            assert_eq!(c.result(), BLOCK_SIZE as i32);
        }

        Ok(())
    }
}

//------------------------------------------