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use std::{io, mem, ptr, slice, sync::Arc};

use crate::buffer;
use crate::device::Handle;
use crate::memory::Memory;
use crate::v4l2;
use crate::v4l_sys::*;

/// Manage mapped buffers
///
/// All buffers are unmapped in the Drop impl.
/// In case of errors during unmapping, we panic because there is memory corruption going on.
pub struct Arena<'a> {
    handle: Arc<Handle>,
    pub bufs: Vec<&'a mut [u8]>,
    pub buf_type: buffer::Type,
}

impl<'a> Arena<'a> {
    /// Returns a new buffer manager instance
    ///
    /// You usually do not need to use this directly.
    /// A MappedBufferStream creates its own manager instance by default.
    ///
    /// # Arguments
    ///
    /// * `handle` - Device handle to get its file descriptor
    /// * `buf_type` - Type of the buffers
    pub fn new(handle: Arc<Handle>, buf_type: buffer::Type) -> Self {
        Arena {
            handle,
            bufs: Vec::new(),
            buf_type,
        }
    }

    fn buffer_desc(&self) -> v4l2_buffer {
        v4l2_buffer {
            type_: self.buf_type as u32,
            memory: Memory::Mmap as u32,
            ..unsafe { mem::zeroed() }
        }
    }

    fn requestbuffers_desc(&self) -> v4l2_requestbuffers {
        v4l2_requestbuffers {
            type_: self.buf_type as u32,
            memory: Memory::Mmap as u32,
            ..unsafe { mem::zeroed() }
        }
    }

    pub fn allocate(&mut self, count: u32) -> io::Result<u32> {
        let mut v4l2_reqbufs = v4l2_requestbuffers {
            count,
            ..self.requestbuffers_desc()
        };
        unsafe {
            v4l2::ioctl(
                self.handle.fd(),
                v4l2::vidioc::VIDIOC_REQBUFS,
                &mut v4l2_reqbufs as *mut _ as *mut std::os::raw::c_void,
            )?;
        }

        for index in 0..v4l2_reqbufs.count {
            let mut v4l2_buf = v4l2_buffer {
                index,
                ..self.buffer_desc()
            };
            unsafe {
                v4l2::ioctl(
                    self.handle.fd(),
                    v4l2::vidioc::VIDIOC_QUERYBUF,
                    &mut v4l2_buf as *mut _ as *mut std::os::raw::c_void,
                )?;

                let ptr = v4l2::mmap(
                    ptr::null_mut(),
                    v4l2_buf.length as usize,
                    libc::PROT_READ | libc::PROT_WRITE,
                    libc::MAP_SHARED,
                    self.handle.fd(),
                    v4l2_buf.m.offset as libc::off_t,
                )?;

                let slice =
                    slice::from_raw_parts_mut::<u8>(ptr as *mut u8, v4l2_buf.length as usize);
                self.bufs.push(slice);
            }
        }

        Ok(v4l2_reqbufs.count)
    }

    pub fn release(&mut self) -> io::Result<()> {
        for buf in &self.bufs {
            unsafe {
                v4l2::munmap(buf.as_ptr() as *mut core::ffi::c_void, buf.len())?;
            }
        }

        // free all buffers by requesting 0
        let mut v4l2_reqbufs = v4l2_requestbuffers {
            count: 0,
            ..self.requestbuffers_desc()
        };
        unsafe {
            v4l2::ioctl(
                self.handle.fd(),
                v4l2::vidioc::VIDIOC_REQBUFS,
                &mut v4l2_reqbufs as *mut _ as *mut std::os::raw::c_void,
            )?;
        }

        self.bufs.clear();
        Ok(())
    }
}

impl<'a> Drop for Arena<'a> {
    fn drop(&mut self) {
        if self.bufs.is_empty() {
            // nothing to do
            return;
        }

        if let Err(e) = self.release() {
            if let Some(code) = e.raw_os_error() {
                // ENODEV means the file descriptor wrapped in the handle became invalid, most
                // likely because the device was unplugged or the connection (USB, PCI, ..)
                // broke down. Handle this case gracefully by ignoring it.
                if code == 19 {
                    /* ignore */
                    return;
                }
            }

            panic!("{:?}", e)
        }
    }
}