use async_compression::tokio::write::{ZstdDecoder, ZstdEncoder};
use chrono::{DurationRound, TimeDelta, Utc};
use eyre::{format_err, Result};
use log::{debug, error, warn};
use std::path::{Path, PathBuf};
use std::process::Stdio;
use tokio::{
    fs::{self, File},
    io::{self, AsyncBufReadExt, AsyncRead, AsyncWrite, AsyncWriteExt, BufReader, BufWriter},
    process,
    sync::mpsc,
    time::{sleep, Duration},
};

pub type Timestamp = chrono::DateTime<Utc>;

const TS_FORMAT: &str = "%Y%m%d_%H";
const PREFIX_TS_FORMAT: &str = "%H:%M:%S";
const TRUNC_DELTA: TimeDelta = TimeDelta::hours(1);
const FLUSH_INTERVAL: Duration = Duration::from_secs(1);
const WRITE_RETRY_DELAY: Duration = Duration::from_secs(1);

pub struct Logger<'t> {
    pub log_path: &'t str,
    pub log_name: &'t str,
    pub with_prefix: bool,
}

impl<'t> Logger<'t> {
    pub async fn run(&self, command: &str, args: &[String]) -> Result<()> {
        // make sure we can at least open the log before starting the command
        let archives_path = &format!("{path}/archives", path = self.log_path);
        (fs::create_dir_all(archives_path).await)
            .map_err(|e| format_err!("failed to create archives dir: {e}"))?;
        let archives_read_dir = (fs::read_dir(archives_path).await)
            .map_err(|e| format_err!("failed to list archives: {e}"))?;

        let mut prev_stamp = trunc_ts(Utc::now());
        let mut current_log = BufWriter::new(self.open_log(prev_stamp).await?);

        tokio::spawn(compress_archives(
            archives_read_dir,
            self.log_name.to_string(),
            prev_stamp.format(TS_FORMAT).to_string(),
        ));

        // start the command
        let mut child = process::Command::new(command)
            .args(args)
            .stdout(Stdio::piped())
            .stderr(Stdio::piped())
            .spawn()?;

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

        tokio::spawn(copy("stdout", child.stdout.take().unwrap(), tx.clone()));
        tokio::spawn(copy("stderr", child.stderr.take().unwrap(), tx));

        let mut flush_ticker = tokio::time::interval(FLUSH_INTERVAL);

        // handle output
        loop {
            tokio::select!(
                r = rx.recv() => {
                    let Some(log) = r else { break; };

                    while let Err(e) = self.log_item(&log, &mut prev_stamp, &mut current_log).await
                    {
                        error!("log failed: {e}");
                        sleep(WRITE_RETRY_DELAY).await;
                    }
                }
                _ = flush_ticker.tick() => {
                    if let Err(e) = current_log.flush().await {
                        warn!("log flush failed: {e}");
                    }
                }
            );
        }

        // finalize
        while let Err(e) = current_log.flush().await {
            error!("final log flush failed: {e}");
            sleep(WRITE_RETRY_DELAY).await;
        }

        let status = child.wait().await?;
        std::process::exit(status.code().unwrap_or(-1));
    }

    async fn log_item(
        &self,
        log: &LogItem,
        prev_stamp: &mut Timestamp,
        out: &mut BufWriter<File>,
    ) -> Result<()> {
        let trunc_ts = trunc_ts(log.ts);
        if *prev_stamp < trunc_ts {
            // switch log
            out.flush().await?;
            *out = BufWriter::new(self.open_log(trunc_ts).await?);

            let prev_path = self.archive_path(*prev_stamp);
            tokio::spawn(async move { compress(&prev_path).await });

            *prev_stamp = trunc_ts;
        };

        if self.with_prefix {
            let prefix = format!("{} {}| ", log.ts.format(PREFIX_TS_FORMAT), log.stream_name);
            out.write_all(prefix.as_bytes()).await?;
        }

        out.write_all(&log.line).await?;
        Ok(())
    }

    async fn open_log(&self, ts: Timestamp) -> Result<File> {
        let log_file = &self.archive_path(ts);

        let file = File::options()
            .create(true)
            .append(true)
            .write(true)
            .open(log_file)
            .await?;

        let link_src = &format!(
            "{path}/{name}.log",
            path = self.log_path,
            name = self.log_name
        );
        let link_tgt = log_file
            .strip_prefix(&format!("{}/", self.log_path))
            .unwrap_or(log_file);

        let _ = fs::remove_file(link_src).await;
        fs::symlink(link_tgt, link_src)
            .await
            .map_err(|e| format_err!("symlink {link_src} -> {link_tgt} failed: {e}",))?;

        Ok(file)
    }

    fn archive_path(&self, ts: Timestamp) -> String {
        format!(
            "{path}/archives/{file}",
            path = self.log_path,
            file = self.archive_file(ts)
        )
    }
    fn archive_file(&self, ts: Timestamp) -> String {
        format!(
            "{name}.{ts}.log",
            name = self.log_name,
            ts = ts.format(TS_FORMAT),
        )
    }
}

struct LogItem {
    stream_name: &'static str,
    ts: chrono::DateTime<chrono::Utc>,
    line: Vec<u8>,
}

async fn copy(
    stream_name: &'static str,
    out: impl AsyncRead + Unpin,
    tx: mpsc::UnboundedSender<LogItem>,
) {
    let mut out = BufReader::new(out);
    let buf_size = page_size::get();
    loop {
        let mut line = Vec::with_capacity(buf_size);
        if let Err(e) = out.read_until(b'\n', &mut line).await {
            warn!("read {stream_name} failed: {e}");
            return;
        }
        if line.is_empty() {
            break;
        }

        let log = LogItem {
            stream_name,
            ts: chrono::Utc::now(),
            line,
        };
        if let Err(e) = tx.send(log) {
            warn!("send line failed: {e}");
            return;
        }
    }
}

pub fn trunc_ts(ts: Timestamp) -> Timestamp {
    ts.duration_trunc(TRUNC_DELTA)
        .expect("duration_trunc failed")
}

async fn compress_archives(mut read_dir: fs::ReadDir, log_name: String, exclude_ts: String) {
    loop {
        let Ok(Some(entry)) =
            (read_dir.next_entry().await).inspect_err(|e| error!("archive dir read failed: {e}"))
        else {
            return;
        };

        let file_name = entry.file_name();
        let Some(file_name) = file_name.to_str() else {
            continue;
        };
        let Some(name) = file_name.strip_suffix(".log") else {
            continue;
        };
        let Some((name, ts)) = name.rsplit_once('.') else {
            continue;
        };
        if name != log_name {
            continue;
        }
        if ts == exclude_ts {
            continue;
        }

        let file_path = entry.path();
        let Some(file_path) = file_path.to_str() else {
            continue;
        };

        compress(file_path).await;
    }
}

async fn compress(path: impl AsRef<Path>) {
    let path = path.as_ref();

    let result = async {
        let path_str = path.to_string_lossy();
        debug!("compressing {path_str}");

        let mut input = File::open(path)
            .await
            .map_err(|e| format_err!("open {path_str} failed: {e}"))?;

        let out_path = path.with_extension("zstd");
        let out = (File::create(&out_path).await) // create output
            .map_err(|e| format_err!("create {} failed: {e}", out_path.to_string_lossy()))?;

        let mut out = ZstdEncoder::new(out);
        async {
            tokio::io::copy(&mut input, &mut out).await?;
            out.flush().await
        }
        .await
        .map_err(|e| format_err!("compression of {path_str} failed: {e}"))?;

        fs::remove_file(path)
            .await
            .map_err(|e| format_err!("remove {path_str} failed: {e}"))
    }
    .await;

    if let Err(e) = result {
        warn!("{e}");
    }
}

pub fn parse_ts(ts: &str) -> std::result::Result<Timestamp, chrono::ParseError> {
    let dt =
        chrono::NaiveDateTime::parse_from_str(&format!("{ts}0000"), &format!("{TS_FORMAT}%M%S"))?;
    Ok(Timestamp::from_naive_utc_and_offset(dt, Utc))
}

pub async fn log_files(log_path: &str, log_name: &str) -> std::io::Result<Vec<LogFile>> {
    let mut dir = PathBuf::from(log_path);
    dir.push("archives");

    let mut entries = Vec::new();
    let mut read_dir = fs::read_dir(dir).await?;

    while let Some(entry) = read_dir.next_entry().await? {
        let file_name = entry.file_name();
        let Some(file_name) = file_name.to_str() else {
            continue;
        };

        let (name, compressed) = file_name
            .strip_suffix(".zstd")
            .map_or((file_name, false), |s| (s, true));

        let Some(name) = name.strip_suffix(".log") else {
            continue;
        };

        let Some((name, timestamp)) = name.rsplit_once('.') else {
            continue;
        };
        if name != log_name {
            continue;
        };

        let Ok(timestamp) =
            parse_ts(timestamp).inspect_err(|e| debug!("invalid timestamp: {timestamp}: {e}"))
        else {
            continue;
        };

        entries.push(LogFile {
            path: entry.path(),
            compressed,
            timestamp,
        });
    }

    Ok(entries)
}

#[derive(Debug, PartialEq, Eq, Ord)]
pub struct LogFile {
    pub path: PathBuf,
    pub compressed: bool,
    pub timestamp: Timestamp,
}

impl PartialOrd for LogFile {
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        self.timestamp.partial_cmp(&other.timestamp)
    }
}

impl LogFile {
    pub async fn copy_to(&self, out: &mut (impl AsyncWrite + Unpin)) -> io::Result<u64> {
        let input = &mut File::open(&self.path).await?;
        if self.compressed {
            let out = &mut ZstdDecoder::new(out);
            tokio::io::copy(input, out).await
        } else {
            tokio::io::copy(input, out).await
        }
    }
}