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use crate::Result;

#[derive(Default)]
pub struct MMRBatch<Elem, Store: MMRStore<Elem>> {
    memory_batch: Vec<(u64, Vec<Elem>)>,
    store: Store,
}

impl<Elem: Clone, Store: MMRStore<Elem>> MMRBatch<Elem, Store> {
    pub fn new(store: Store) -> Self {
        MMRBatch {
            memory_batch: Vec::new(),
            store,
        }
    }

    pub fn append(&mut self, pos: u64, elems: Vec<Elem>) {
        self.memory_batch.push((pos, elems));
    }

    pub fn get_elem(&self, pos: u64) -> Result<Option<Elem>> {
        for (start_pos, elems) in self.memory_batch.iter().rev() {
            if pos < *start_pos {
                continue;
            } else if pos < start_pos + elems.len() as u64 {
                return Ok(elems.get((pos - start_pos) as usize).cloned());
            } else {
                break;
            }
        }
        self.store.get_elem(pos)
    }

    pub fn commit(self) -> Result<()> {
        let Self {
            mut store,
            memory_batch,
        } = self;
        for (pos, elems) in memory_batch {
            store.append(pos, elems)?;
        }
        Ok(())
    }
}

impl<Elem, Store: MMRStore<Elem>> IntoIterator for MMRBatch<Elem, Store> {
    type Item = (u64, Vec<Elem>);
    type IntoIter = ::std::vec::IntoIter<Self::Item>;

    fn into_iter(self) -> Self::IntoIter {
        self.memory_batch.into_iter()
    }
}

pub trait MMRStore<Elem> {
    fn get_elem(&self, pos: u64) -> Result<Option<Elem>>;
    fn append(&mut self, pos: u64, elems: Vec<Elem>) -> Result<()>;
}