/*
    This file is part of jellything (https://codeberg.org/metamuffin/jellything)
    which is licensed under the GNU Affero General Public License (version 3); see /COPYING.
    Copyright (C) 2025 metamuffin <metamuffin.org>
*/
use anyhow::anyhow;
use log::{trace, warn};
use std::{
    io::{Seek, Write},
    ops::Range,
};

pub struct TrimWriter<W> {
    inner: W,
    position: usize,
    range: Range<usize>,
}
impl<W: Write> TrimWriter<W> {
    pub fn new(inner: W, range: Range<usize>) -> Self {
        Self {
            inner,
            range,
            position: 0,
        }
    }
}

impl<W: Write> Write for TrimWriter<W> {
    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
        let start = self.range.start as isize - self.position as isize;
        let end = self.range.end as isize - self.position as isize;

        let start = start.clamp(0, buf.len() as isize) as usize;
        let end = end.clamp(0, buf.len() as isize) as usize;

        if self.position >= self.range.end {
            return Err(std::io::Error::new(
                std::io::ErrorKind::Other,
                anyhow!("range ended"),
            ));
        }

        let tbuf = &buf[start..end];
        Ok(if !tbuf.is_empty() {
            trace!("trim={start}..{end} avail={}", buf.len());
            let sz = self.inner.write(tbuf)?;
            self.position += sz;
            sz
        } else {
            trace!("skip={}", buf.len());
            buf.len()
        })
    }

    fn flush(&mut self) -> std::io::Result<()> {
        self.inner.flush()
    }
}

impl<W> Seek for TrimWriter<W> {
    fn seek(&mut self, pos: std::io::SeekFrom) -> std::io::Result<u64> {
        match pos {
            std::io::SeekFrom::Start(s) => self.position = s as usize,
            std::io::SeekFrom::End(_) => unimplemented!(),
            std::io::SeekFrom::Current(s) => self.position += s as usize,
        }
        if self.position > self.range.end {
            warn!(
                "seeked beyond end: pos={} end={}",
                self.position, self.range.end
            )
        }
        Ok(self.position as u64)
    }
}