use crate::storage::buffer_pool::ArenaBuffer;
use crate::storage::sqlite3_ondisk::WAL_FRAME_HEADER_SIZE;
use crate::{BufferPool, Result};
use bitflags::bitflags;
use cfg_block::cfg_block;
use std::fmt;
use std::ptr::NonNull;
use std::sync::Arc;
use std::{cell::Cell, fmt::Debug, pin::Pin};

pub trait File: Send + Sync {
    fn lock_file(&self, exclusive: bool) -> Result<()>;
    fn unlock_file(&self) -> Result<()>;
    fn pread(&self, pos: usize, c: Completion) -> Result<Completion>;
    fn pwrite(&self, pos: usize, buffer: Arc<Buffer>, c: Completion) -> Result<Completion>;
    fn sync(&self, c: Completion) -> Result<Completion>;
    fn pwritev(&self, pos: usize, buffers: Vec<Arc<Buffer>>, c: Completion) -> Result<Completion> {
        use std::sync::atomic::{AtomicUsize, Ordering};
        if buffers.is_empty() {
            c.complete(0);
            return Ok(c);
        }
        if buffers.len() == 1 {
            return self.pwrite(pos, buffers[0].clone(), c);
        }
        // naive default implementation can be overridden on backends where it makes sense to
        let mut pos = pos;
        let outstanding = Arc::new(AtomicUsize::new(buffers.len()));
        let total_written = Arc::new(AtomicUsize::new(0));

        for buf in buffers {
            let len = buf.len();
            let child_c = {
                let c_main = c.clone();
                let outstanding = outstanding.clone();
                let total_written = total_written.clone();
                let _cloned = buf.clone();
                Completion::new_write(move |n| {
                    // reference buffer in callback to ensure alive for async io
                    let _buf = _cloned.clone();
                    // accumulate bytes actually reported by the backend
                    total_written.fetch_add(n as usize, Ordering::Relaxed);
                    if outstanding.fetch_sub(1, Ordering::AcqRel) == 1 {
                        // last one finished
                        c_main.complete(total_written.load(Ordering::Acquire) as i32);
                    }
                })
            };
            if let Err(e) = self.pwrite(pos, buf.clone(), child_c) {
                // best-effort: mark as done so caller won't wait forever
                c.complete(-1);
                return Err(e);
            }
            pos += len;
        }
        Ok(c)
    }
    fn size(&self) -> Result<u64>;
    fn truncate(&self, len: usize, c: Completion) -> Result<Completion>;
    fn copy_to(&self, io: &dyn IO, path: &str) -> Result<()> {
        // Open or create the destination file
        let dest_file = io.open_file(path, OpenFlags::Create, false)?;
        // Get the size of the source file
        let file_size = self.size()? as usize;
        if file_size == 0 {
            return Ok(());
        }

        // use 1MB chunk size
        const BUFFER_SIZE: usize = 1024 * 1024;
        let mut pos = 0;

        while pos < file_size {
            let chunk_size = (file_size - pos).min(BUFFER_SIZE);
            // Read from source
            let read_buffer = Arc::new(Buffer::allocate(chunk_size, Rc::new(|_| {})));
            let read_completion = self.pread(
                pos,
                Completion::new_read(read_buffer.clone(), move |_, _| {}),
            )?;

            // Wait for read to complete
            io.wait_for_completion(read_completion)?;

            // Write to destination
            let write_completion =
                dest_file.pwrite(pos, read_buffer, Completion::new_write(|_| {}))?;
            io.wait_for_completion(write_completion)?;

            pos += chunk_size;
        }
        let sync_completion = dest_file.sync(Completion::new_sync(|_| {}))?;
        io.wait_for_completion(sync_completion)?;

        Ok(())
    }
}

#[derive(Debug, Copy, Clone, PartialEq)]
pub struct OpenFlags(i32);

bitflags! {
    impl OpenFlags: i32 {
        const None = 0b00000000;
        const Create = 0b0000001;
        const ReadOnly = 0b0000010;
    }
}

impl Default for OpenFlags {
    fn default() -> Self {
        Self::Create
    }
}

pub trait IO: Clock + Send + Sync {
    fn open_file(&self, path: &str, flags: OpenFlags, direct: bool) -> Result<Arc<dyn File>>;

    fn run_once(&self) -> Result<()>;

    fn wait_for_completion(&self, c: Completion) -> Result<()>;

    fn generate_random_number(&self) -> i64;

    fn get_memory_io(&self) -> Arc<MemoryIO>;

    fn register_fixed_buffer(&self, _ptr: NonNull<u8>, _len: usize) -> Result<u32> {
        Err(crate::LimboError::InternalError(
            "unsupported operation".to_string(),
        ))
    }
}

pub type Complete = dyn Fn(Arc<Buffer>, i32);
pub type WriteComplete = dyn Fn(i32);
pub type SyncComplete = dyn Fn(i32);
pub type TruncateComplete = dyn Fn(i32);

#[must_use]
#[derive(Clone)]
pub struct Completion {
    inner: Arc<CompletionInner>,
}

struct CompletionInner {
    pub completion_type: CompletionType,
    is_completed: Cell<bool>,
}

pub enum CompletionType {
    Read(ReadCompletion),
    Write(WriteCompletion),
    Sync(SyncCompletion),
    Truncate(TruncateCompletion),
}

pub struct ReadCompletion {
    pub buf: Arc<Buffer>,
    pub complete: Box<Complete>,
}

impl Completion {
    pub fn new(completion_type: CompletionType) -> Self {
        Self {
            inner: Arc::new(CompletionInner {
                completion_type,
                is_completed: Cell::new(false),
            }),
        }
    }

    pub fn new_write<F>(complete: F) -> Self
    where
        F: Fn(i32) + 'static,
    {
        Self::new(CompletionType::Write(WriteCompletion::new(Box::new(
            complete,
        ))))
    }

    pub fn new_read<F>(buf: Arc<Buffer>, complete: F) -> Self
    where
        F: Fn(Arc<Buffer>, i32) + 'static,
    {
        Self::new(CompletionType::Read(ReadCompletion::new(
            buf,
            Box::new(complete),
        )))
    }
    pub fn new_sync<F>(complete: F) -> Self
    where
        F: Fn(i32) + 'static,
    {
        Self::new(CompletionType::Sync(SyncCompletion::new(Box::new(
            complete,
        ))))
    }

    pub fn new_trunc<F>(complete: F) -> Self
    where
        F: Fn(i32) + 'static,
    {
        Self::new(CompletionType::Truncate(TruncateCompletion::new(Box::new(
            complete,
        ))))
    }
    pub fn is_completed(&self) -> bool {
        self.inner.is_completed.get()
    }

    pub fn complete(&self, result: i32) {
        if !self.inner.is_completed.get() {
            match &self.inner.completion_type {
                CompletionType::Read(r) => r.complete(result),
                CompletionType::Write(w) => w.complete(result),
                CompletionType::Sync(s) => s.complete(result), // fix
                CompletionType::Truncate(t) => t.complete(result),
            };
            self.inner.is_completed.set(true);
        }
    }

    /// only call this method if you are sure that the completion is
    /// a ReadCompletion, panics otherwise
    pub fn as_read(&self) -> &ReadCompletion {
        match self.inner.completion_type {
            CompletionType::Read(ref r) => r,
            _ => unreachable!(),
        }
    }

    /// only call this method if you are sure that the completion is
    /// a WriteCompletion, panics otherwise
    pub fn as_write(&self) -> &WriteCompletion {
        match self.inner.completion_type {
            CompletionType::Write(ref w) => w,
            _ => unreachable!(),
        }
    }
}

pub struct WriteCompletion {
    pub complete: Box<WriteComplete>,
}

pub struct SyncCompletion {
    pub complete: Box<SyncComplete>,
}

impl ReadCompletion {
    pub fn new(buf: Arc<Buffer>, complete: Box<Complete>) -> Self {
        Self { buf, complete }
    }

    pub fn buf(&self) -> &Buffer {
        &self.buf
    }

    pub fn complete(&self, bytes_read: i32) {
        (self.complete)(self.buf.clone(), bytes_read);
    }
}

impl WriteCompletion {
    pub fn new(complete: Box<WriteComplete>) -> Self {
        Self { complete }
    }

    pub fn complete(&self, bytes_written: i32) {
        (self.complete)(bytes_written);
    }
}

impl SyncCompletion {
    pub fn new(complete: Box<SyncComplete>) -> Self {
        Self { complete }
    }

    pub fn complete(&self, res: i32) {
        (self.complete)(res);
    }
}

pub struct TruncateCompletion {
    pub complete: Box<TruncateComplete>,
}

impl TruncateCompletion {
    pub fn new(complete: Box<TruncateComplete>) -> Self {
        Self { complete }
    }

    pub fn complete(&self, res: i32) {
        (self.complete)(res);
    }
}

pub type BufferData = Pin<Box<[u8]>>;

pub enum Buffer {
    Heap(BufferData),
    Pooled(ArenaBuffer),
}

impl Debug for Buffer {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Pooled(p) => write!(f, "{p:?}"),
            Self::Heap(buf) => write!(f, "{buf:?}: {}", buf.len()),
        }
    }
}

impl Clone for Buffer {
    fn clone(&self) -> Self {
        match self {
            Self::Heap(buf) => {
                let len = buf.len();
                Self::Heap(Vec::from(&buf[..len]).into_boxed_slice().into())
            }
            Self::Pooled(buf) => {
                // Clone pooled buffers as heap buffers
                let data = Vec::from(buf.as_slice());
                Self::Heap(Pin::new(data.into_boxed_slice()))
            }
        }
    }
}

impl Drop for Buffer {
    fn drop(&mut self) {
        let len = self.len();
        if let Self::Heap(buf) = self {
            TEMP_BUFFER_CACHE.with(|cache| {
                let mut cache = cache.borrow_mut();
                // take ownership of the buffer by swapping it with a dummy
                let buffer = std::mem::replace(buf, Pin::new(vec![].into_boxed_slice()));
                cache.return_buffer(buffer, len);
            });
        }
    }
}

impl Buffer {
    pub fn new(data: Vec<u8>) -> Self {
        tracing::trace!("buffer::new({:?})", data);
        Self::Heap(Pin::new(data.into_boxed_slice()))
    }
    pub fn fixed_id(&self) -> Option<u32> {
        match self {
            Self::Heap { .. } => None,
            Self::Pooled(buf) => buf.fixed_id(),
        }
    }

    pub fn new_pooled(buf: ArenaBuffer) -> Self {
        tracing::trace!("new_pooled({:?})", buf);
        Self::Pooled(buf)
    }

    pub fn new_temporary(size: usize) -> Self {
        TEMP_BUFFER_CACHE.with(|cache| {
            if let Some(buffer) = cache.borrow_mut().get_buffer(size) {
                Self::Heap(buffer)
            } else {
                Self::Heap(Pin::new(vec![0; size].into_boxed_slice()))
            }
        })
    }

    pub fn len(&self) -> usize {
        match self {
            Self::Heap(buf) => buf.len(),
            Self::Pooled(buf) => buf.logical_len(),
        }
    }

    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    pub fn as_slice(&self) -> &[u8] {
        match self {
            Self::Heap(buf) => {
                // SAFETY: The buffer is guaranteed to be valid for the lifetime of the slice
                unsafe { std::slice::from_raw_parts(buf.as_ptr(), buf.len()) }
            }
            Self::Pooled(buf) => buf,
        }
    }

    #[allow(clippy::mut_from_ref)]
    pub fn as_mut_slice(&self) -> &mut [u8] {
        match self {
            Self::Heap(buf) => {
                // SAFETY: The buffer is guaranteed to be valid for the lifetime of the slice
                unsafe { std::slice::from_raw_parts_mut(buf.as_ptr() as *mut u8, buf.len()) }
            }
            Self::Pooled(buf) => unsafe {
                std::slice::from_raw_parts_mut(buf.as_ptr() as *mut u8, buf.len())
            },
        }
    }
    pub fn as_mut_ptr(&mut self) -> *mut u8 {
        match self {
            Self::Heap(buf) => buf.as_mut_ptr(),
            Self::Pooled(buf) => buf.as_mut_ptr(),
        }
    }
}

thread_local! {
    /// thread local cache to re-use temporary buffers to prevent churn when pool overflows
    pub static TEMP_BUFFER_CACHE: RefCell<TempBufferCache> = RefCell::new(TempBufferCache::new());
}

pub(crate) struct TempBufferCache {
    // Buffers indexed by size, we only cache common sizes
    page_size: usize,
    page_buffers: Vec<BufferData>,
    wal_frame_buffers: Vec<BufferData>,
    max_cached: usize,
}

impl TempBufferCache {
    fn new() -> Self {
        Self {
            page_size: BufferPool::DEFAULT_PAGE_SIZE,
            page_buffers: Vec::with_capacity(8),
            wal_frame_buffers: Vec::with_capacity(8),
            max_cached: 512,
        }
    }

    pub fn reinit_cache(&mut self, page_size: usize) {
        self.page_buffers.clear();
        self.wal_frame_buffers.clear();
        self.page_size = page_size;
    }

    fn get_buffer(&mut self, size: usize) -> Option<BufferData> {
        match size {
            sz if sz == self.page_size => self.page_buffers.pop(),
            sz if sz == (self.page_size + WAL_FRAME_HEADER_SIZE) => self.wal_frame_buffers.pop(),
            _ => None,
        }
    }

    fn return_buffer(&mut self, buff: BufferData, len: usize) {
        let sz = self.page_size;
        let cache = match len {
            n if n.eq(&sz) => &mut self.page_buffers,
            n if n.eq(&(sz + WAL_FRAME_HEADER_SIZE)) => &mut self.wal_frame_buffers,
            _ => return,
        };
        if self.max_cached > cache.len() {
            cache.push(buff);
        }
    }
}

cfg_block! {
    #[cfg(all(target_os = "linux", feature = "io_uring"))] {
        mod io_uring;
        #[cfg(feature = "fs")]
        pub use io_uring::UringIO;
    }

    #[cfg(target_family = "unix")] {
        mod unix;
        #[cfg(feature = "fs")]
        pub use unix::UnixIO;
        pub use unix::UnixIO as PlatformIO;
        pub use PlatformIO as SyscallIO;
    }

    #[cfg(any(target_os = "android", target_os = "ios"))] {
        mod unix;
        #[cfg(feature = "fs")]
        pub use unix::UnixIO;
        pub use unix::UnixIO as SyscallIO;
        pub use unix::UnixIO as PlatformIO;
    }

     #[cfg(target_os = "windows")] {
        mod windows;
        pub use windows::WindowsIO as PlatformIO;
         pub use PlatformIO as SyscallIO;
    }

    #[cfg(not(any(target_os = "linux", target_os = "macos", target_os = "windows", target_os = "android", target_os = "ios")))] {
        mod generic;
        pub use generic::GenericIO as PlatformIO;
        pub use PlatformIO as SyscallIO;
    }
}

mod memory;
#[cfg(feature = "fs")]
mod vfs;
pub use memory::MemoryIO;
pub mod clock;
mod common;
pub use clock::Clock;