use core::fmt;
use std::{
    cmp,
    fs::File,
    future::Future,
    io,
    path::PathBuf,
    pin::Pin,
    task::{Context, Poll},
};

use actix_web::error::{Error, ErrorInternalServerError};
use bytes::Bytes;
use futures_core::{ready, Stream};
use inotify::{Inotify, WatchMask};
use log::trace;
use pin_project_lite::pin_project;
use serde::{de, Deserialize, Deserializer};
use std::{os::unix::fs::MetadataExt, time::SystemTime};
use time::OffsetDateTime;

use actix_web::{
    body::{self, BoxBody, SizedStream},
    http::{
        header::{
            self, ContentDisposition, DispositionParam, DispositionType, EntityTag, HeaderValue,
            HttpDate, IfMatch, IfModifiedSince, IfNoneMatch, IfUnmodifiedSince,
        },
        StatusCode,
    },
    HttpMessage, HttpRequest, HttpResponse, Responder,
};

use actix_files::HttpRange;

use crate::{store::StoredFile, upload::UploadedFile};

#[derive(Clone, Copy)]
pub enum DownloadSelection {
    One(usize),
    All,
}

impl fmt::Display for DownloadSelection {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            DownloadSelection::All => write!(f, "all"),
            DownloadSelection::One(n) => n.fmt(f),
        }
    }
}

struct SelectionVisitor;

impl<'de> de::Visitor<'de> for SelectionVisitor {
    type Value = DownloadSelection;

    fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(formatter, r#"a nonnegative integer or the string "all""#)
    }

    fn visit_u64<E>(self, v: u64) -> Result<Self::Value, E> {
        Ok(DownloadSelection::One(v as usize))
    }

    fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
    where
        E: de::Error,
    {
        if v == "all" {
            Ok(DownloadSelection::All)
        } else if let Ok(n) = v.parse::<usize>() {
            Ok(DownloadSelection::One(n))
        } else {
            Err(de::Error::invalid_value(de::Unexpected::Str(v), &self))
        }
    }
}

impl<'de> Deserialize<'de> for DownloadSelection {
    fn deserialize<D: Deserializer<'de>>(de: D) -> Result<DownloadSelection, D::Error> {
        de.deserialize_any(SelectionVisitor)
    }
}

// This is copied substantially from actix-files, with some tweaks

pub(crate) struct DownloadingFile {
    pub(crate) file: File,
    pub(crate) storage_path: PathBuf,
    pub(crate) info: StoredFile,
    pub(crate) selection: DownloadSelection,
}

impl DownloadingFile {
    fn selected(&self) -> Option<&UploadedFile> {
        match self.selection {
            DownloadSelection::All => None,
            DownloadSelection::One(n) => Some(self.info.contents.as_ref()?.files.get(n)?),
        }
    }

    fn name(&self) -> &str {
        match self.selected() {
            None => &self.info.name,
            Some(f) => &f.name,
        }
    }

    fn size(&self) -> u64 {
        match self.selected() {
            None => self.info.size,
            Some(f) => f.size,
        }
    }

    fn modtime(&self) -> OffsetDateTime {
        match self.selected() {
            None => self.info.modtime,
            Some(f) => f.modtime,
        }
    }

    fn baseline_offset(&self) -> u64 {
        if let (DownloadSelection::One(n), Some(files)) =
            (self.selection, self.info.contents.as_ref())
        {
            crate::zip::file_data_offset(files, n)
        } else {
            0
        }
    }

    fn etag(&self) -> EntityTag {
        let ino = self.file.metadata().map(|md| md.ino()).unwrap_or_default();
        let modtime = self.modtime();
        EntityTag::new_strong(format!(
            "{:x}:{}:{:x}:{:x}:{:x}",
            ino,
            self.selection,
            self.size(),
            modtime.unix_timestamp() as u64,
            modtime.nanosecond(),
        ))
    }

    /// Creates an `HttpResponse` with file as a streaming body.
    pub fn into_response(self, req: &HttpRequest) -> HttpResponse<BoxBody> {
        let total_size = self.size();
        let etag = self.etag();
        let last_modified = HttpDate::from(SystemTime::from(self.modtime()));

        let precondition_failed = precondition_failed(req, &etag, &last_modified);
        let not_modified = not_modified(req, &etag, &last_modified);

        let mut res = HttpResponse::build(StatusCode::OK);

        res.insert_header((header::CONTENT_SECURITY_POLICY, "sandbox"));
        res.insert_header((header::CONTENT_TYPE, mime::APPLICATION_OCTET_STREAM));
        res.insert_header((
            header::CONTENT_DISPOSITION,
            ContentDisposition {
                disposition: DispositionType::Attachment,
                parameters: vec![DispositionParam::Filename(self.name().to_string())],
            },
        ));
        res.insert_header((header::LAST_MODIFIED, last_modified));
        res.insert_header((header::ETAG, etag));
        res.insert_header((header::ACCEPT_RANGES, "bytes"));

        let mut length = total_size;
        let mut offset = 0;

        // check for range header
        if let Some(ranges) = req.headers().get(header::RANGE) {
            if let Ok(ranges_header) = ranges.to_str() {
                if let Ok(ranges) = HttpRange::parse(ranges_header, length) {
                    length = ranges[0].length;
                    offset = ranges[0].start;

                    // don't allow compression middleware to modify partial content
                    res.insert_header((
                        header::CONTENT_ENCODING,
                        HeaderValue::from_static("identity"),
                    ));

                    res.insert_header((
                        header::CONTENT_RANGE,
                        format!("bytes {}-{}/{}", offset, offset + length - 1, total_size,),
                    ));
                } else {
                    res.insert_header((header::CONTENT_RANGE, format!("bytes */{}", length)));
                    return res.status(StatusCode::RANGE_NOT_SATISFIABLE).finish();
                };
            } else {
                return res.status(StatusCode::BAD_REQUEST).finish();
            };
        };

        if precondition_failed {
            return res.status(StatusCode::PRECONDITION_FAILED).finish();
        } else if not_modified {
            return res
                .status(StatusCode::NOT_MODIFIED)
                .body(body::None::new())
                .map_into_boxed_body();
        }

        let reader = new_live_reader(
            length,
            self.baseline_offset() + offset,
            self.file,
            self.storage_path,
        );

        if offset != 0 || length != total_size {
            res.status(StatusCode::PARTIAL_CONTENT);
        }

        res.body(SizedStream::new(length, reader))
    }
}

fn precondition_failed(req: &HttpRequest, etag: &EntityTag, last_modified: &HttpDate) -> bool {
    if let Some(IfMatch::Items(ref items)) = req.get_header() {
        if !items.iter().any(|item| item.strong_eq(etag)) {
            return true;
        }
    }
    if let Some(IfUnmodifiedSince(ref since)) = req.get_header() {
        if last_modified > since {
            return true;
        }
    }
    false
}

fn not_modified(req: &HttpRequest, etag: &EntityTag, last_modified: &HttpDate) -> bool {
    match req.get_header::<IfNoneMatch>() {
        Some(IfNoneMatch::Any) => {
            return true;
        }
        Some(IfNoneMatch::Items(ref items)) => {
            return items.iter().any(|item| item.weak_eq(etag));
        }
        None => (),
    }
    if let Some(IfModifiedSince(ref since)) = req.get_header() {
        if last_modified < since {
            return true;
        }
    }
    false
}

impl Responder for DownloadingFile {
    type Body = BoxBody;

    fn respond_to(self, req: &HttpRequest) -> HttpResponse<Self::Body> {
        self.into_response(req)
    }
}

pin_project! {
    pub struct LiveFileReader<F, Fut> {
        size: u64,
        offset: u64,
        #[pin]
        state: LiveFileReaderState<Fut>,
        counter: u64,
        available_file_size: u64,
        callback: F,
        #[pin]
        events: inotify::EventStream<[u8; 1024]>,
    }
}

pin_project! {
    #[project = LiveFileReaderStateProj]
    #[project_replace = LiveFileReaderStateProjReplace]
    enum LiveFileReaderState<Fut> {
        File { file: Option<File>, },
        Future { #[pin] fut: Fut },
    }
}

pub(crate) fn new_live_reader(
    size: u64,
    offset: u64,
    file: File,
    storage_path: PathBuf,
) -> impl Stream<Item = Result<Bytes, Error>> {
    let mut inotify = Inotify::init().expect("failed to init inotify");
    inotify
        .add_watch(storage_path, WatchMask::MODIFY | WatchMask::CLOSE_WRITE)
        .expect("Failed to add inotify watch");
    let events = inotify
        .event_stream([0; 1024])
        .expect("failed to set up event stream");
    LiveFileReader {
        size,
        offset,
        state: LiveFileReaderState::File { file: Some(file) },
        counter: 0,
        available_file_size: 0,
        callback: live_file_reader_callback,
        events,
    }
}

async fn live_file_reader_callback(
    mut file: File,
    offset: u64,
    max_bytes: usize,
) -> Result<(File, Bytes), Error> {
    use io::{Read as _, Seek as _};

    let res = actix_web::web::block(move || {
        trace!(
            "reading up to {} bytes of file starting at {}",
            max_bytes,
            offset
        );

        let mut buf = Vec::with_capacity(max_bytes);

        file.seek(io::SeekFrom::Start(offset))?;

        let n_bytes = std::io::Read::by_ref(&mut file)
            .take(max_bytes as u64)
            .read_to_end(&mut buf)?;
        trace!("got {} bytes from file", n_bytes);
        if n_bytes == 0 {
            Err(io::Error::from(io::ErrorKind::UnexpectedEof))
        } else {
            Ok((file, Bytes::from(buf)))
        }
    })
    .await??;

    Ok(res)
}

impl<F, Fut> Stream for LiveFileReader<F, Fut>
where
    F: Fn(File, u64, usize) -> Fut,
    Fut: Future<Output = Result<(File, Bytes), Error>>,
{
    type Item = Result<Bytes, Error>;

    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        let mut this = self.as_mut().project();
        match this.state.as_mut().project() {
            LiveFileReaderStateProj::File { file } => {
                let size = *this.size;
                let offset = *this.offset;
                let counter = *this.counter;

                if size == counter {
                    Poll::Ready(None)
                } else {
                    let inner_file = file.take().expect("LiveFileReader polled after completion");

                    if offset >= *this.available_file_size {
                        trace!(
                            "offset {} has reached available file size {}, updating metadata",
                            offset,
                            this.available_file_size
                        );
                        // If we've hit the end of what was available
                        // last time we checked, check again
                        *this.available_file_size = match inner_file.metadata() {
                            Ok(md) => md.len(),
                            Err(e) => {
                                return Poll::Ready(Some(Err(e.into())));
                            }
                        };
                        trace!("new available file size: {}", this.available_file_size);

                        // If we're still at the end, inotify time
                        if offset >= *this.available_file_size {
                            trace!("waiting for inotify events");
                            file.get_or_insert(inner_file);
                            if ready!(this.events.poll_next(cx)).is_none() {
                                return Poll::Ready(Some(Err(ErrorInternalServerError(
                                    "inotify stream empty",
                                ))));
                            }
                            return self.poll_next(cx);
                        }
                    }

                    let max_bytes = cmp::min(
                        65_536,
                        cmp::min(
                            size.saturating_sub(counter),
                            this.available_file_size.saturating_sub(offset),
                        ),
                    ) as usize;

                    let fut = (this.callback)(inner_file, offset, max_bytes);

                    this.state
                        .project_replace(LiveFileReaderState::Future { fut });

                    self.poll_next(cx)
                }
            }
            LiveFileReaderStateProj::Future { fut } => {
                let (file, bytes) = ready!(fut.poll(cx))?;

                this.state
                    .project_replace(LiveFileReaderState::File { file: Some(file) });

                *this.offset += bytes.len() as u64;
                *this.counter += bytes.len() as u64;

                Poll::Ready(Some(Ok(bytes)))
            }
        }
    }
}