//! The DAG-CBOR wire schema for MST nodes.
//!
//! ```text
//! {
//!   l: Cid | null      // subtree left of the first entry
//!   e: [
//!     { p: uint        // bytes shared with the previous key in this node
//!     , k: bytes       // the rest of this key
//!     , v: Cid         // the record this key points at
//!     , t: Cid | null  // subtree between this key and the next
//!     }
//!     ...
//!   ]
//! }
//! ```
//!
//! note: `l` and `t` are nullable, not optional.
//!
//! Prefix compression resets per node: the first entry has `p = 0` and carries
//! its whole key.

use serde::{Deserialize, Serialize};

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

/// Fields are declared in canonical DAG-CBOR map order (`k`, `p`, `t`, `v`),
/// so the encoding is canonical whether or not the codec sorts for us (but...
/// to even be DAG-CBOR it has to sort??)
#[derive(Debug, Serialize, Deserialize)]
pub(crate) struct EntryData {
    #[serde(rename = "k", with = "serde_bytes")]
    pub key_suffix: Vec<u8>,
    #[serde(rename = "p")]
    pub prefix_len: usize,
    #[serde(rename = "t")]
    pub right: Option<Cid>,
    #[serde(rename = "v")]
    pub value: Cid,
}

/// Canonical map order again: `e` before `l`.
#[derive(Debug, Serialize, Deserialize)]
pub(crate) struct NodeData {
    #[serde(rename = "e")]
    pub entries: Vec<EntryData>,
    #[serde(rename = "l")]
    pub left: Option<Cid>,
}

/// The CID of a block of DAG-CBOR, which is how every MST node is addressed.
pub(crate) fn cid_for(block: &[u8]) -> Cid {
    Cid::digest_sha2(Codec::Drisl, block)
}