use std::collections::HashMap;
use std::io::{self, Seek, SeekFrom, Write};
use std::pin::Pin;
use std::task::{Context, Poll};

use bytes::Bytes;
use futures_util::io::AsyncRead;
use futures_util::stream::Stream;
use multer::{Constraints, Multipart, SizeLimit};
use pin_project_lite::pin_project;

use crate::{BatchRequest, ParseRequestError, UploadValue};

/// Options for `receive_multipart`.
#[derive(Default, Clone, Copy)]
#[non_exhaustive]
#[cfg_attr(feature = "nightly", doc(cfg(feature = "multipart")))]
pub struct MultipartOptions {
    /// The maximum file size.
    pub max_file_size: Option<usize>,
    /// The maximum number of files.
    pub max_num_files: Option<usize>,
}

impl MultipartOptions {
    /// Set maximum file size.
    pub fn max_file_size(self, size: usize) -> Self {
        MultipartOptions {
            max_file_size: Some(size),
            ..self
        }
    }

    /// Set maximum number of files.
    pub fn max_num_files(self, n: usize) -> Self {
        MultipartOptions {
            max_num_files: Some(n),
            ..self
        }
    }
}

pub(super) async fn receive_batch_multipart(
    body: impl AsyncRead + Send + 'static,
    boundary: impl Into<String>,
    opts: MultipartOptions,
) -> Result<BatchRequest, ParseRequestError> {
    let mut multipart = Multipart::new_with_constraints(
        ReaderStream::new(body),
        boundary,
        Constraints::new().size_limit({
            let mut limit = SizeLimit::new();
            if let (Some(max_file_size), Some(max_num_files)) =
                (opts.max_file_size, opts.max_file_size)
            {
                limit = limit.whole_stream((max_file_size * max_num_files) as u64);
            }
            if let Some(max_file_size) = opts.max_file_size {
                limit = limit.per_field(max_file_size as u64);
            }
            limit
        }),
    );

    let mut request = None;
    let mut map = None;
    let mut files = Vec::new();

    while let Some(mut field) = multipart.next_field().await? {
        match field.name() {
            Some("operations") => {
                let request_str = field.text().await?;
                request = Some(
                    serde_json::from_str::<BatchRequest>(&request_str)
                        .map_err(ParseRequestError::InvalidRequest)?,
                );
            }
            Some("map") => {
                let map_str = field.text().await?;
                map = Some(
                    serde_json::from_str::<HashMap<String, Vec<String>>>(&map_str)
                        .map_err(ParseRequestError::InvalidFilesMap)?,
                );
            }
            _ => {
                if let Some(name) = field.name().map(ToString::to_string) {
                    if let Some(filename) = field.file_name().map(ToString::to_string) {
                        let content_type = field.content_type().map(|mime| mime.to_string());
                        let mut file = tempfile::tempfile().map_err(ParseRequestError::Io)?;
                        while let Some(chunk) = field.chunk().await.unwrap() {
                            file.write(&chunk).map_err(ParseRequestError::Io)?;
                        }
                        file.seek(SeekFrom::Start(0))?;
                        files.push((name, filename, content_type, file));
                    }
                }
            }
        }
    }

    let mut request: BatchRequest = request.ok_or(ParseRequestError::MissingOperatorsPart)?;
    let map = map.as_mut().ok_or(ParseRequestError::MissingMapPart)?;

    for (name, filename, content_type, file) in files {
        if let Some(var_paths) = map.remove(&name) {
            let upload = UploadValue {
                filename,
                content_type,
                content: file,
            };

            for var_path in var_paths {
                match &mut request {
                    BatchRequest::Single(request) => {
                        request.set_upload(&var_path, upload.try_clone()?);
                    }
                    BatchRequest::Batch(requests) => {
                        let mut s = var_path.splitn(2, '.');
                        let idx = s.next().and_then(|idx| idx.parse::<usize>().ok());
                        let path = s.next();

                        if let (Some(idx), Some(path)) = (idx, path) {
                            if let Some(request) = requests.get_mut(idx) {
                                request.set_upload(path, upload.try_clone()?);
                            }
                        }
                    }
                }
            }
        }
    }

    if !map.is_empty() {
        return Err(ParseRequestError::MissingFiles);
    }

    Ok(request)
}

pin_project! {
    pub(crate) struct ReaderStream<T> {
        buf: [u8; 2048],
        #[pin]
        reader: T,
    }
}

impl<T> ReaderStream<T> {
    pub(crate) fn new(reader: T) -> Self {
        Self {
            buf: [0; 2048],
            reader,
        }
    }
}

impl<T: AsyncRead> Stream for ReaderStream<T> {
    type Item = io::Result<Bytes>;

    fn poll_next(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
        let this = self.project();

        Poll::Ready(
            match futures_util::ready!(this.reader.poll_read(cx, this.buf)?) {
                0 => None,
                size => Some(Ok(Bytes::copy_from_slice(&this.buf[..size]))),
            },
        )
    }
}