use crate::error::{DownloadError, DownloadResult};
use futures::{stream, StreamExt, TryStreamExt};
use sha1::Digest;
use sha1::Sha1;
use std::cmp::min;
use std::path::PathBuf;
use tokio::fs::create_dir_all;
use tokio::fs::File;
use tokio::io::AsyncWriteExt;
use tokio::sync::mpsc::channel;
use tokio::sync::mpsc::Receiver;
use tokio::sync::mpsc::Sender;
use tokio::task;

#[derive(Clone, Debug)]
pub struct Download {
    pub url: String,
    pub file: PathBuf,
    pub sha1: Option<Vec<u8>>,
}

impl Download {
    #[instrument(
        name = "download_file",
        level = "trace",
        skip_all,
        fields(
            url = self.url,
            file = %self.file.to_string_lossy(),
            current_file,
            total_files,
        )
    )]
    pub async fn download(
        &self,
        client: reqwest::Client,
        mut progress_sender: Option<Sender<DownloadProgress>>,
        current_file: usize,
        total_files: usize,
    ) -> DownloadResult<()> {
        // Create parent folder
        if let Some(parent) = self.file.parent() {
            trace!("Creating parent folder");
            create_dir_all(parent).await?;
        }

        // Setup request
        let response = client.get(&self.url).send().await?.error_for_status()?;

        // Progress Update
        trace!("Sending request to get content-length");
        let total_bytes = response
            .content_length()
            .ok_or(DownloadError::NoContentLength)?;
        let mut progress = DownloadProgress {
            url: self.url.clone(),
            file: self.file.clone(),
            current_file,
            total_files,
            downloaded_bytes: 0,
            total_bytes,
        };

        trace!("Send initial progress");
        progress.send(&mut progress_sender).await;

        let mut file = File::create(&self.file).await?;
        let mut stream = response.bytes_stream();

        trace!("Writing content to disk.");
        while let Some(item) = stream.next().await {
            let chunk = item?;
            file.write_all(&chunk).await?;
            progress.downloaded_bytes = min(
                progress.downloaded_bytes + (chunk.len() as u64),
                progress.total_bytes,
            );

            trace!("Send progress");
            progress.send(&mut progress_sender).await;
        }

        file.sync_all().await?;

        Ok(())
    }

    #[instrument(
        name = "verify_file",
        level = "trace",
        skip_all,
        fields(
            url = self.url,
            file = %self.file.to_string_lossy(),
        )
    )]
    pub async fn verify(&self) -> DownloadResult<bool> {
        let this = self.clone();

        task::spawn_blocking(move || this.blocking_verify())
            .await
            .unwrap()
    }

    fn blocking_verify(self) -> DownloadResult<bool> {
        if let Some(sha) = self.sha1 {
            if !self.file.is_file() {
                return Ok(false);
            }

            let mut file = std::fs::File::open(self.file)?;
            let mut hasher = Sha1::new();
            std::io::copy(&mut file, &mut hasher)?;
            let hash = hasher.finalize().to_vec();

            Ok(sha == hash)
        } else {
            Ok(self.file.is_file())
        }
    }
}

/// Progress of an ongoing download.
#[derive(Clone, Debug)]
pub struct DownloadProgress {
    /// The URL of the download.
    pub url: String,
    /// The path where the file is saved.
    pub file: PathBuf,
    /// Current file index.
    pub current_file: usize,
    /// Number of files that are being downloaded.
    pub total_files: usize,
    /// Bytes that already got downloaded.
    pub downloaded_bytes: u64,
    /// Total bytes of the file.
    pub total_bytes: u64,
}

impl DownloadProgress {
    pub(crate) async fn send(&self, sender: &mut Option<Sender<Self>>) {
        if let Some(s) = &sender {
            if s.send(self.clone()).await.is_err() {
                trace!("Sending failed because receiver is no longer around. Dropping sender...");
                *sender = None;
            }
        }
    }
}

#[instrument(
    name = "download",
    level = "trace",
    skip_all,
    fields(parallel_downloads, verify)
)]
pub async fn download(
    downloads: Vec<Download>,
    progress_sender: Option<Sender<DownloadProgress>>,
    parallel_downloads: u16,
    retries: u16,
    verify: bool,
) -> DownloadResult<()> {
    let client = reqwest::Client::new();
    let total = downloads.len();
    let downloads = downloads.into_iter().enumerate();

    stream::iter(downloads)
        .map(move |(n, d)| {
            let client = client.clone();
            let mut sender = progress_sender.clone();
            async move {
                // Retries
                for x in 0..=retries {
                    if x > 0 {
                        trace!("Retrying to download file for the {}th time", x);
                    }

                    // Download file
                    if !d.file.exists() || x > 0 {
                        trace!("File does not exist or retrying");
                        d.download(client.clone(), sender.clone(), n, total).await?;
                    } else {
                        trace!("File does exist, sending progress update");
                        let file = File::open(&d.file).await?;
                        let size = file.metadata().await?.len();

                        // Send progress
                        DownloadProgress {
                            url: d.url.clone(),
                            file: d.file.clone(),
                            current_file: n,
                            total_files: total,
                            downloaded_bytes: size,
                            total_bytes: size,
                        }
                        .send(&mut sender)
                        .await;
                    }

                    // Verify file
                    if verify && !d.verify().await? {
                        // Checksum does not match
                        if x == retries {
                            debug!("Verification of file failed");
                            return Err(DownloadError::ChecksumMismatch);
                        } else {
                            debug!("Verification of file failed, retrying...");
                        }
                    } else {
                        // Success
                        return Ok(());
                    }
                }

                Ok(())
            }
        })
        .buffer_unordered(parallel_downloads as usize)
        .try_collect::<()>()
        .await?;

    Ok(())
}

pub fn download_progress_channel(
    buffer: usize,
) -> (Sender<DownloadProgress>, Receiver<DownloadProgress>) {
    channel(buffer)
}