//! Blob utilities which do not require RPC calls.
//!
//! Offers the following functions:
//!
//! - [`get_blob_path()`]
//! - [`hash_blob()`]

use base64;
use sha2::{Digest, Sha256};

use crate::error::GolgiError;

/// Lookup the filepath for a blob.
///
/// # Example
///
/// ```rust
/// use golgi::blobs;
///
/// fn lookup_blob_path() -> Result<(), GolgiError> {
///     let blob_ref = "&JlJHc9yeG1EpZA9fIPGLzUKDH0FeR39Ai57euhKT1G8=.sha256";
///
///     let blob_path = blobs::get_blob_path(blob_ref)?;
///
///     println!("{}", blob_path);
///
///     // 26/524773dc9e1b5129640f5f20f18bcd42831f415e477f408b9edeba1293d46f
///
///     Ok(())
/// }
/// ```
pub fn get_blob_path(blob_id: &str) -> Result<String, GolgiError> {
    let dot_index = blob_id.rfind('.').ok_or_else(|| {
        GolgiError::SigilLink(format!(
            "Invalid blob ID; no dot index was found: {}",
            blob_id
        ))
    })?;

    // obtain the base64 portion (substring) of the blob id
    let base64_str = &blob_id[1..dot_index];

    // decode blob substring from base64 (to bytes)
    let blob_bytes = base64::decode_config(base64_str, base64::STANDARD)?;

    // represent the blob bytes as hex, removing all unnecessary characters
    let blob_hex = format!("{:02x?}", blob_bytes)
        .replace('[', "")
        .replace(']', "")
        .replace(',', "")
        .replace(' ', "");

    // split the hex representation of the decoded base64
    // this is how paths are formatted for the blobstore
    // e.g. 26/524773dc9e1b5129640f5f20f18bcd42831f415e477f408b9edeba1293d46f
    // full path would be: `/home/user/.ssb-go/blobs/sha256/26/524773dc...`
    let blob_path = format!("{}/{}", &blob_hex[..2], &blob_hex[2..]);

    Ok(blob_path)
}

/// Hash the given blob byte slice and return the hex representation and
/// blob ID (sigil-link).
///
/// This function can be used when adding a blob to the local blobstore.
pub fn hash_blob(buffer: &[u8]) -> Result<(String, String), GolgiError> {
    // hash the bytes
    let hash = Sha256::digest(buffer);

    // generate a hex representation of the hash
    let hex_hash = format!("{:02x?}", hash)
        .replace('[', "")
        .replace(']', "")
        .replace(',', "")
        .replace(' ', "");

    // encode the hash
    let b64_hash = base64::encode(&hash[..]);

    // format the base64 encoding as a blob sigil-link (blob id)
    let blob_id = format!("&{}.sha256", b64_hash);

    Ok((hex_hash, blob_id))
}