use std::borrow::Cow;
use std::io::{self, IoSliceMut};
use std::iter::FusedIterator;
#[cfg(feature = "tokio")]
use std::pin::Pin;
#[cfg(feature = "tokio")]
use std::task::{Context, Poll};
use std::time::Duration;

#[cfg(feature = "tokio")]
use tokio::io::{ReadBuf, SeekFrom};

use crate::progress_bar::ProgressBar;
use crate::state::ProgressFinish;
use crate::style::ProgressStyle;

/// Wraps an iterator to display its progress.
pub trait ProgressIterator
where
    Self: Sized + Iterator,
{
    /// Wrap an iterator with default styling. Uses [`Iterator::size_hint()`] to get length.
    /// Returns `Some(..)` only if `size_hint.1` is [`Some`]. If you want to create a progress bar
    /// even if `size_hint.1` returns [`None`] use [`progress_count()`](ProgressIterator::progress_count)
    /// or [`progress_with()`](ProgressIterator::progress_with) instead.
    fn try_progress(self) -> Option<ProgressBarIter<Self>> {
        self.size_hint()
            .1
            .map(|len| self.progress_count(u64::try_from(len).unwrap()))
    }

    /// Wrap an iterator with default styling.
    fn progress(self) -> ProgressBarIter<Self>
    where
        Self: ExactSizeIterator,
    {
        let len = u64::try_from(self.len()).unwrap();
        self.progress_count(len)
    }

    /// Wrap an iterator with an explicit element count.
    fn progress_count(self, len: u64) -> ProgressBarIter<Self> {
        self.progress_with(ProgressBar::new(len))
    }

    /// Wrap an iterator with a custom progress bar.
    fn progress_with(self, progress: ProgressBar) -> ProgressBarIter<Self>;

    /// Wrap an iterator with a progress bar and style it.
    fn progress_with_style(self, style: crate::ProgressStyle) -> ProgressBarIter<Self>
    where
        Self: ExactSizeIterator,
    {
        let len = u64::try_from(self.len()).unwrap();
        let bar = ProgressBar::new(len).with_style(style);
        self.progress_with(bar)
    }
}

/// Wraps an iterator to display its progress.
#[derive(Debug)]
pub struct ProgressBarIter<T> {
    pub(crate) it: T,
    pub progress: ProgressBar,
}

impl<T> ProgressBarIter<T> {
    /// Builder-like function for setting underlying progress bar's style.
    ///
    /// See [`ProgressBar::with_style()`].
    pub fn with_style(mut self, style: ProgressStyle) -> Self {
        self.progress = self.progress.with_style(style);
        self
    }

    /// Builder-like function for setting underlying progress bar's prefix.
    ///
    /// See [`ProgressBar::with_prefix()`].
    pub fn with_prefix(mut self, prefix: impl Into<Cow<'static, str>>) -> Self {
        self.progress = self.progress.with_prefix(prefix);
        self
    }

    /// Builder-like function for setting underlying progress bar's message.
    ///
    /// See [`ProgressBar::with_message()`].
    pub fn with_message(mut self, message: impl Into<Cow<'static, str>>) -> Self {
        self.progress = self.progress.with_message(message);
        self
    }

    /// Builder-like function for setting underlying progress bar's position.
    ///
    /// See [`ProgressBar::with_position()`].
    pub fn with_position(mut self, position: u64) -> Self {
        self.progress = self.progress.with_position(position);
        self
    }

    /// Builder-like function for setting underlying progress bar's elapsed time.
    ///
    /// See [`ProgressBar::with_elapsed()`].
    pub fn with_elapsed(mut self, elapsed: Duration) -> Self {
        self.progress = self.progress.with_elapsed(elapsed);
        self
    }

    /// Builder-like function for setting underlying progress bar's finish behavior.
    ///
    /// See [`ProgressBar::with_finish()`].
    pub fn with_finish(mut self, finish: ProgressFinish) -> Self {
        self.progress = self.progress.with_finish(finish);
        self
    }
}

impl<S, T: Iterator<Item = S>> Iterator for ProgressBarIter<T> {
    type Item = S;

    fn next(&mut self) -> Option<Self::Item> {
        let item = self.it.next();

        if item.is_some() {
            self.progress.inc(1);
        } else if !self.progress.is_finished() {
            self.progress.finish_using_style();
        }

        item
    }
}

impl<T: ExactSizeIterator> ExactSizeIterator for ProgressBarIter<T> {
    fn len(&self) -> usize {
        self.it.len()
    }
}

impl<T: DoubleEndedIterator> DoubleEndedIterator for ProgressBarIter<T> {
    fn next_back(&mut self) -> Option<Self::Item> {
        let item = self.it.next_back();

        if item.is_some() {
            self.progress.inc(1);
        } else if !self.progress.is_finished() {
            self.progress.finish_using_style();
        }

        item
    }
}

impl<T: FusedIterator> FusedIterator for ProgressBarIter<T> {}

impl<R: io::Read> io::Read for ProgressBarIter<R> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        let inc = self.it.read(buf)?;
        self.progress.inc(inc as u64);
        Ok(inc)
    }

    fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
        let inc = self.it.read_vectored(bufs)?;
        self.progress.inc(inc as u64);
        Ok(inc)
    }

    fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize> {
        let inc = self.it.read_to_string(buf)?;
        self.progress.inc(inc as u64);
        Ok(inc)
    }

    fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<()> {
        self.it.read_exact(buf)?;
        self.progress.inc(buf.len() as u64);
        Ok(())
    }
}

impl<R: io::BufRead> io::BufRead for ProgressBarIter<R> {
    fn fill_buf(&mut self) -> io::Result<&[u8]> {
        self.it.fill_buf()
    }

    fn consume(&mut self, amt: usize) {
        self.it.consume(amt);
        self.progress.inc(amt as u64);
    }
}

impl<S: io::Seek> io::Seek for ProgressBarIter<S> {
    fn seek(&mut self, f: io::SeekFrom) -> io::Result<u64> {
        self.it.seek(f).map(|pos| {
            self.progress.set_position(pos);
            pos
        })
    }
    // Pass this through to preserve optimizations that the inner I/O object may use here
    // Also avoid sending a set_position update when the position hasn't changed
    fn stream_position(&mut self) -> io::Result<u64> {
        self.it.stream_position()
    }
}

#[cfg(feature = "tokio")]
#[cfg_attr(docsrs, doc(cfg(feature = "tokio")))]
impl<W: tokio::io::AsyncWrite + Unpin> tokio::io::AsyncWrite for ProgressBarIter<W> {
    fn poll_write(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &[u8],
    ) -> Poll<io::Result<usize>> {
        Pin::new(&mut self.it).poll_write(cx, buf).map(|poll| {
            poll.map(|inc| {
                self.progress.inc(inc as u64);
                inc
            })
        })
    }

    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        Pin::new(&mut self.it).poll_flush(cx)
    }

    fn poll_shutdown(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        Pin::new(&mut self.it).poll_shutdown(cx)
    }
}

#[cfg(feature = "tokio")]
#[cfg_attr(docsrs, doc(cfg(feature = "tokio")))]
impl<W: tokio::io::AsyncRead + Unpin> tokio::io::AsyncRead for ProgressBarIter<W> {
    fn poll_read(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>,
    ) -> Poll<io::Result<()>> {
        let prev_len = buf.filled().len() as u64;
        if let Poll::Ready(e) = Pin::new(&mut self.it).poll_read(cx, buf) {
            self.progress.inc(buf.filled().len() as u64 - prev_len);
            Poll::Ready(e)
        } else {
            Poll::Pending
        }
    }
}

#[cfg(feature = "tokio")]
#[cfg_attr(docsrs, doc(cfg(feature = "tokio")))]
impl<W: tokio::io::AsyncSeek + Unpin> tokio::io::AsyncSeek for ProgressBarIter<W> {
    fn start_seek(mut self: Pin<&mut Self>, position: SeekFrom) -> io::Result<()> {
        Pin::new(&mut self.it).start_seek(position)
    }

    fn poll_complete(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
        Pin::new(&mut self.it).poll_complete(cx)
    }
}

#[cfg(feature = "tokio")]
#[cfg_attr(docsrs, doc(cfg(feature = "tokio")))]
impl<W: tokio::io::AsyncBufRead + Unpin + tokio::io::AsyncRead> tokio::io::AsyncBufRead
    for ProgressBarIter<W>
{
    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
        let this = self.get_mut();
        let result = Pin::new(&mut this.it).poll_fill_buf(cx);
        if let Poll::Ready(Ok(buf)) = &result {
            this.progress.inc(buf.len() as u64);
        }
        result
    }

    fn consume(mut self: Pin<&mut Self>, amt: usize) {
        Pin::new(&mut self.it).consume(amt);
    }
}

#[cfg(feature = "futures")]
#[cfg_attr(docsrs, doc(cfg(feature = "futures")))]
impl<S: futures_core::Stream + Unpin> futures_core::Stream for ProgressBarIter<S> {
    type Item = S::Item;

    fn poll_next(
        self: std::pin::Pin<&mut Self>,
        cx: &mut std::task::Context<'_>,
    ) -> std::task::Poll<Option<Self::Item>> {
        let this = self.get_mut();
        let item = std::pin::Pin::new(&mut this.it).poll_next(cx);
        match &item {
            std::task::Poll::Ready(Some(_)) => this.progress.inc(1),
            std::task::Poll::Ready(None) => this.progress.finish_using_style(),
            std::task::Poll::Pending => {}
        }
        item
    }
}

impl<W: io::Write> io::Write for ProgressBarIter<W> {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.it.write(buf).map(|inc| {
            self.progress.inc(inc as u64);
            inc
        })
    }

    fn write_vectored(&mut self, bufs: &[io::IoSlice]) -> io::Result<usize> {
        self.it.write_vectored(bufs).map(|inc| {
            self.progress.inc(inc as u64);
            inc
        })
    }

    fn flush(&mut self) -> io::Result<()> {
        self.it.flush()
    }

    // write_fmt can not be captured with reasonable effort.
    // as it uses write_all internally by default that should not be a problem.
    // fn write_fmt(&mut self, fmt: fmt::Arguments) -> io::Result<()>;
}

impl<S, T: Iterator<Item = S>> ProgressIterator for T {
    fn progress_with(self, progress: ProgressBar) -> ProgressBarIter<Self> {
        ProgressBarIter { it: self, progress }
    }
}

#[cfg(test)]
mod test {
    use crate::iter::{ProgressBarIter, ProgressIterator};
    use crate::progress_bar::ProgressBar;
    use crate::ProgressStyle;

    #[test]
    fn it_can_wrap_an_iterator() {
        let v = [1, 2, 3];
        let wrap = |it: ProgressBarIter<_>| {
            assert_eq!(it.map(|x| x * 2).collect::<Vec<_>>(), vec![2, 4, 6]);
        };

        wrap(v.iter().progress());
        wrap(v.iter().progress_count(3));
        wrap({
            let pb = ProgressBar::new(v.len() as u64);
            v.iter().progress_with(pb)
        });
        wrap({
            let style = ProgressStyle::default_bar()
                .template("{wide_bar:.red} {percent}/100%")
                .unwrap();
            v.iter().progress_with_style(style)
        });
    }
}