use crate::blocks::block::{VrfBlock, VRF_BLOCK_BYTES};
use crate::common::network_paths_and_settings::block_extension_and_paths;
use crate::AsyncReadExt;
use crate::File;
use crate::PathBuf;

pub async fn load_block_header(block_number: u32) -> Result<VrfBlock, String> {
    // Header-only loads avoid reading the full block when only chain metadata
    // is needed.
    let (
        _network_name,
        _padded_base_coin,
        block_ext,
        _torrent_path,
        _wallet_path,
        block_path,
        _db_path,
        _balance_path,
        _log_path,
    ) = block_extension_and_paths();
    let file_name = PathBuf::from(block_path)
        .join(format!("{block_number}.{block_ext}"))
        .to_string_lossy()
        .into_owned();
    let file = match File::open(&file_name).await {
        Ok(file) => file,
        Err(err) => {
            return Err(format!(
                "Error opening block file for height {block_number}: {err:?}"
            ));
        }
    };

    let mut binary_data = Vec::with_capacity(VRF_BLOCK_BYTES);
    // Only read the fixed VrfBlock prefix from the block file.
    if let Err(err) = file
        .take(VRF_BLOCK_BYTES as u64)
        .read_to_end(&mut binary_data)
        .await
    {
        return Err(format!(
            "Error reading block header for height {block_number}: {err:?}"
        ));
    }

    // The stored header format is the same VrfBlock prefix used at the
    // beginning of every block file.
    match VrfBlock::from_bytes(&binary_data).await {
        Ok(block) => Ok(block),
        Err(err) => Err(format!("Error parsing block: {err:?}")),
    }
}