//! Checking a block against the CID that claims to address it.

use crate::cid::{Cid, Multihash};

#[derive(Debug, thiserror::Error)]
pub enum BlockError {
    #[error("block hashes to {computed}, not the {claimed} it is filed under")]
    CidMismatch { claimed: Cid, computed: Cid },
    #[error("block is addressed by {found:?}, but atproto only uses sha2-256")]
    UnsupportedMultihash { found: Multihash },
}

/// Check that `block`'s contents really are for its cid.
pub fn verify_block(claimed: &Cid, block: &[u8]) -> Result<(), BlockError> {
    let found = claimed.multihash_type();
    if !matches!(found, Multihash::Sha2256) {
        return Err(BlockError::UnsupportedMultihash { found });
    }
    let computed = Cid::digest_sha2(claimed.codec(), block);
    if computed == *claimed {
        Ok(())
    } else {
        Err(BlockError::CidMismatch {
            claimed: *claimed,
            computed,
        })
    }
}