use futures::stream::FuturesUnordered;
use futures::StreamExt;
use percent_encoding::percent_decode_str;
use std::io::SeekFrom;
use std::path::Path;
use std::time::SystemTime;
use tokio::io::{AsyncSeekExt, AsyncWriteExt};
use tokio::sync::mpsc;

use crate::dlreport::*;
use crate::errors::*;

struct RollingAverage {
    index: usize,
    data: Vec<f64>,
}

impl RollingAverage {
    fn new(size: usize) -> Self {
        RollingAverage {
            index: 0,
            data: Vec::with_capacity(size),
        }
    }

    fn value(&self) -> f64 {
        if self.data.len() == 0 {
            0.0
        } else {
            let mut max = self.data[0];

            for v in self.data.iter() {
                if *v > max {
                    max = *v;
                }
            }

            let mut sum: f64 = self.data.iter().sum();
            let mut count = self.data.len();

            if self.data.len() >= 3 {
                sum -= max;
                count -= 1;
            }

            sum / count as f64
        }
    }

    fn add(&mut self, val: f64) {
        if self.data.capacity() == self.data.len() {
            self.data[self.index] = val;

            self.index += 1;
            if self.index >= self.data.capacity() {
                self.index = 0;
            }
        } else {
            self.data.push(val);
        }
    }
}

/// Get the filename at the end of the given URL. This will decode the URL Encoding.
pub fn url_to_filename(url: &str) -> String {
    let url_dec = percent_decode_str(&url)
        .decode_utf8_lossy()
        .to_owned()
        .to_string();
    let file_name = std::path::Path::new(&url_dec)
        .file_name()
        .unwrap()
        .to_str()
        .unwrap();
    // Split at ? and return the first part. If no ? is present, this just returns the full string
    file_name.split("?").next().unwrap().to_string()
}

pub async fn download_feedback(
    url: &str,
    into_file: &Path,
    rep: DlReporter,
    content_length: Option<u64>,
) -> ResBE<()> {
    download_feedback_chunks(url, into_file, rep, None, content_length).await
}

pub async fn download_feedback_chunks(
    url: &str,
    into_file: &Path,
    rep: DlReporter,
    from_to: Option<(u64, u64)>,
    content_length: Option<u64>,
) -> ResBE<()> {
    let mut content_length = match content_length {
        Some(it) => it,
        None => {
            let (content_length, _) = http_get_filesize_and_range_support(url).await?;
            content_length
        }
    };

    // Send the HTTP request to download the given link
    let mut req = reqwest::Client::new().get(url);

    // Add range header if needed
    if let Some((from, to)) = from_to {
        req = req.header(reqwest::header::RANGE, format!("bytes={}-{}", from, to));
        content_length = to - from + 1;
    }

    // Actually send the request and get the response
    let mut resp = req.send().await?;

    // Error out if the server response is not success (something went wrong)
    if !resp.status().is_success() {
        return Err(DlError::BadHttpStatus.into());
    }

    // Open the local output file
    let mut opts = tokio::fs::OpenOptions::new();
    let mut ofile = opts
        .create(true)
        .write(true)
        .truncate(!from_to.is_some())
        .open(into_file)
        .await?;

    if from_to.is_some() {
        ofile.seek(SeekFrom::Start(from_to.unwrap().0)).await?;
    }

    let filename = into_file.file_name().unwrap().to_str().unwrap();

    // Report the download start
    rep.send(DlStatus::Init {
        bytes_total: content_length,
        filename: filename.to_string(),
    });

    let mut curr_progress = 0;
    let mut speed_mbps = 0.0;

    let t_start = SystemTime::now();

    let mut t_last_speed = SystemTime::now();
    let mut last_bytecount = 0;

    let mut average_speed = RollingAverage::new(10);

    let mut buff: Vec<u8> = Vec::new();

    // Read data from server as long as new data is available
    while let Some(chunk) = resp.chunk().await? {
        let datalen = chunk.len() as u64;

        buff.extend(chunk);

        // Buffer in memory first and only write to disk if the threshold is reached.
        // This reduces the number of small disk writes and thereby reduces the
        // io bottleneck that occurs on HDDs with many small writes in different
        // files and offsets at the same time
        if buff.len() >= 1_000_000 {
            // Write the received data into the file
            ofile.write_all(&buff).await?;

            buff.clear();
        }

        // Update progress
        curr_progress += datalen;

        // Update the number of bytes downloaded since the last report
        last_bytecount += datalen;

        let t_elapsed = t_last_speed.elapsed()?.as_secs_f64();

        // Update the reported download speed after every 3MB or every second
        // depending on what happens first
        if last_bytecount >= 3_000_000 || t_elapsed >= 0.8 {
            // Update rolling average
            average_speed.add(((last_bytecount as f64) / t_elapsed) / 1_000_000.0);

            speed_mbps = average_speed.value() as f32;

            // Reset the time and bytecount
            last_bytecount = 0;
            t_last_speed = SystemTime::now();
        }

        // Send status update report
        rep.send(DlStatus::Update {
            speed_mbps,
            bytes_curr: curr_progress,
        });
    }

    if buff.len() > 0 {
        ofile.write_all(&buff).await?;
    }

    if curr_progress != content_length {
        return Err(DlError::HttpNoData.into());
    }

    // Ensure that IO is completed
    //ofile.flush().await?;

    let duration_ms = t_start.elapsed()?.as_millis() as u64;

    // Send report that the download is finished
    rep.send(DlStatus::Done { duration_ms });

    Ok(())
}

// This will spin up multiple tasks that and manage the status updates for them.
// The combined status will be reported back to the caller
pub async fn download_feedback_multi(
    url: &str,
    into_file: &Path,
    rep: DlReporter,
    conn_count: u32,
    content_length: Option<u64>,
) -> ResBE<()> {
    let content_length = match content_length {
        Some(it) => it,
        None => http_get_filesize_and_range_support(url).await?.0,
    };

    // Create zeroed file with 1 byte too much. This will be truncated on download
    // completion and can indicate that the file is not suitable for continuation
    create_zeroed_file(into_file, content_length as usize + 1).await?;

    let chunksize = content_length / conn_count as u64;
    let rest = content_length % conn_count as u64;

    let mut joiners = Vec::new();

    let (tx, mut rx) = mpsc::unbounded_channel::<DlReport>();

    let t_start = SystemTime::now();

    for index in 0..conn_count {
        let url = url.clone().to_owned();
        let into_file = into_file.clone().to_owned();

        let tx = tx.clone();

        joiners.push(tokio::spawn(async move {
            let rep = DlReporter::new(index, tx.clone());

            let mut from_to = (index as u64 * chunksize, (index + 1) as u64 * chunksize - 1);

            if index == conn_count - 1 {
                from_to.1 += rest;
            }

            let specific_content_length = from_to.1 - from_to.0 + 1;

            // Delay each chunk-download to reduce the number of simultanious connection attempts
            tokio::time::sleep(tokio::time::Duration::from_millis(50 * index as u64)).await;

            download_feedback_chunks(
                &url,
                &into_file,
                rep,
                Some(from_to),
                Some(specific_content_length),
            )
            .await
            .map_err(|e| e.to_string())
        }))
    }

    drop(tx);

    let filename = Path::new(into_file).file_name().unwrap().to_str().unwrap();

    rep.send(DlStatus::Init {
        bytes_total: content_length,
        filename: filename.to_string(),
    });

    let rep_task = rep.clone();

    let mut t_last = t_start.clone();

    let manager_handle = tokio::task::spawn(async move {
        let rep = rep_task;
        //let mut dl_speeds = vec![0.0_f32; conn_count as usize];
        let mut progresses = vec![0; conn_count as usize];

        let mut progress_last: u64 = 0;

        let mut average_speed = RollingAverage::new(10);

        while let Some(update) = rx.recv().await {
            match update.status {
                DlStatus::Init {
                    bytes_total: _,
                    filename: _,
                } => {}
                DlStatus::Update {
                    speed_mbps: _,
                    bytes_curr,
                } => {
                    //dl_speeds[update.id as usize] = speed_mbps;
                    progresses[update.id as usize] = bytes_curr;

                    let progress_curr = progresses.iter().sum();
                    let progress_delta = progress_curr - progress_last;
                    let t_elapsed = t_last.elapsed().unwrap().as_secs_f64();

                    let speed_mbps = average_speed.value() as f32;

                    // currently executes always, but might change
                    if progress_delta >= 5_000_000 {
                        average_speed.add(((progress_delta as f64) / 1_000_000.0) / t_elapsed);

                        progress_last = progress_curr;
                        t_last = SystemTime::now();
                    }

                    rep.send(DlStatus::Update {
                        speed_mbps: speed_mbps,
                        bytes_curr: progress_curr,
                    });
                }
                DlStatus::Done { duration_ms: _ } => {

                    //dl_speeds[update.id as usize] = 0.0;
                }

                // Just forwared everything else to the calling receiver
                _ => rep.send(update.status),
            }
        }
    });

    let mut joiners: FuturesUnordered<_> = joiners.into_iter().collect();
    // Validate if the tasks were successful. This will always grab the next completed
    // task, independent from the original order in the joiners list
    while let Some(output) = joiners.next().await {
        // If any of the download tasks fail, abort the rest and delete the file
        // since it is non-recoverable anyways
        if let Err(e) = output? {
            for handle in joiners.iter() {
                handle.abort();
            }

            manager_handle.abort();

            tokio::fs::remove_file(&into_file).await?;

            return Err(e.into());
        }
    }

    manager_handle.await?;

    // Remove the additional byte at the file end
    let ofile = tokio::fs::OpenOptions::new()
        .create(false)
        .write(true)
        .truncate(false)
        .open(&into_file)
        .await?;

    ofile.set_len(content_length).await?;

    rep.send(DlStatus::Done {
        duration_ms: t_start.elapsed()?.as_millis() as u64,
    });

    Ok(())
}

async fn create_zeroed_file(file: &Path, filesize: usize) -> ResBE<()> {
    let ofile = tokio::fs::OpenOptions::new()
        .create(true)
        // Open in write mode
        .write(true)
        // Delete and overwrite the file
        .truncate(true)
        .open(file)
        .await?;

    ofile.set_len(filesize as u64).await?;

    Ok(())
}

pub async fn http_get_filesize_and_range_support(url: &str) -> ResBE<(u64, bool)> {
    let resp = reqwest::Client::new().head(url).send().await?;

    if let Some(filesize) = resp.headers().get(reqwest::header::CONTENT_LENGTH) {
        if let Ok(val_str) = filesize.to_str() {
            if let Ok(val) = val_str.parse::<u64>() {
                let mut range_supported = false;

                if let Some(range) = resp.headers().get(reqwest::header::ACCEPT_RANGES) {
                    if let Ok(range) = range.to_str() {
                        if range == "bytes" {
                            range_supported = true;
                        }
                    }
                }

                return Ok((val, range_supported));
            }
        }
    }

    Err(DlError::ContentLengthUnknown.into())
}

#[cfg(test)]
mod tests {

    use super::*;

    #[test]
    fn rolling_average() {
        let mut ra = RollingAverage::new(3);

        assert_eq!(0, ra.data.len());
        assert_eq!(3, ra.data.capacity());

        assert_eq!(0.0, ra.value());

        // 10 / 1 = 10
        ra.add(10.0);
        assert_eq!(1, ra.data.len());
        assert_eq!(10.0, ra.value());

        // (10 + 20) / 2 = 15
        ra.add(20.0);
        assert_eq!(2, ra.data.len());
        assert_eq!(15.0, ra.value());

        // (10 + 20 + 30) / 3 = 20
        ra.add(30.0);
        assert_eq!(3, ra.data.len());
        assert_eq!(20.0, ra.value());

        assert_eq!(10.0, ra.data[0]);
        assert_eq!(20.0, ra.data[1]);
        assert_eq!(30.0, ra.data[2]);

        // This should replace the oldest value (index 1)
        ra.add(40.0);

        assert_eq!(3, ra.data.len());
        assert_eq!(3, ra.data.capacity());

        // (40 + 20 + 30) / 3 = 30
        assert_eq!(30.0, ra.value());

        assert_eq!(40.0, ra.data[0]);
        assert_eq!(20.0, ra.data[1]);
        assert_eq!(30.0, ra.data[2]);

        ra.add(50.0);
        ra.add(60.0);
        ra.add(70.0);

        assert_eq!(70.0, ra.data[0]);
        assert_eq!(50.0, ra.data[1]);
        assert_eq!(60.0, ra.data[2]);
    }
}