use anyhow::{anyhow, Result};
use std::{fs::File, io::Read};

pub struct LogEntry {
    pub ts: u64,
    pub message: Vec<u8>,
}

pub fn load_raw_log(filename: &str) -> Result<Vec<LogEntry>> {
    let mut file = File::options()
        .append(true)
        .create(true)
        .read(true)
        .open(filename)?;

    let mut ts_buf: [u8; 8] = [0_u8; 8];
    let mut len_buf: [u8; 8] = [0_u8; 8];

    let mut entries = vec![];

    loop {
        match file.read(&mut ts_buf) {
            Ok(0) => return Ok(entries),
            Ok(8) => {}
            Ok(n) => return Err(anyhow!("got {} of expected 8 bytes for timestamp", n)),
            Err(e) => return Err(e.into()),
        };
        file.read_exact(&mut len_buf)?;

        let ts = u64::from_be_bytes(ts_buf);
        let len = usize::from_be_bytes(len_buf);

        let mut message = vec![0_u8; len];
        file.read_exact(message.as_mut_slice())?;

        entries.push(LogEntry { ts, message });
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    pub fn reads_entries_from_windsynth_log() {
        let filename = "assets/windsynth.log";
        let entries = load_raw_log(filename).unwrap();

        assert_eq!(1260, entries.len());
    }
}