/*
    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 crate::backends::ReadTransaction;
use anyhow::Result;
use std::{borrow::Cow, ops::Range};

pub struct PrefixIterator<'a> {
    db: &'a dyn ReadTransaction,
    prefix: &'a [u8],
    cursor: Cow<'a, [u8]>,
}
impl Iterator for PrefixIterator<'_> {
    type Item = Result<Vec<u8>>;
    fn next(&mut self) -> Option<Self::Item> {
        match self.db.next(&self.cursor) {
            Err(e) => Some(Err(e)),
            Ok(None) => None,
            Ok(Some(next)) => {
                if next.starts_with(self.prefix) {
                    self.cursor = next.clone().into();
                    Some(Ok(next))
                } else {
                    None
                }
            }
        }
    }
}

pub struct RangeIterator<'a> {
    db: &'a dyn ReadTransaction,
    range: Range<Cow<'a, [u8]>>,
}
impl Iterator for RangeIterator<'_> {
    type Item = Result<Vec<u8>>;
    fn next(&mut self) -> Option<Self::Item> {
        match self.db.next(&self.range.start) {
            Err(e) => Some(Err(e)),
            Ok(None) => None,
            Ok(Some(next)) => {
                if next.as_slice() < self.range.end.as_ref() {
                    self.range.start = next.clone().into();
                    Some(Ok(next))
                } else {
                    None
                }
            }
        }
    }
}
impl DoubleEndedIterator for RangeIterator<'_> {
    fn next_back(&mut self) -> Option<Self::Item> {
        match self.db.prev(&self.range.end) {
            Err(e) => Some(Err(e)),
            Ok(None) => None,
            Ok(Some(prev)) => {
                if prev.as_slice() >= self.range.start.as_ref() {
                    self.range.end = prev.clone().into();
                    Some(Ok(prev))
                } else {
                    None
                }
            }
        }
    }
}