use crate::AssetLocationExt;
use base64::Engine;
use jellycommon::AssetLocation;
use std::{future::Future, sync::LazyLock};
use tokio::sync::Mutex;

pub fn cache_location(seed: &[&str]) -> (usize, AssetLocation) {
    use sha2::Digest;
    let mut d = sha2::Sha512::new();
    for s in seed {
        d.update(s.as_bytes());
        d.update(b"\0");
    }
    let d = d.finalize();
    let n = d[0] as usize | (d[1] as usize) << 8 | (d[2] as usize) << 16 | (d[3] as usize) << 24;
    let fname = base64::engine::general_purpose::URL_SAFE.encode(d);
    let fname = &fname[..22]; // about 128 bits
    (n, AssetLocation::Cache(fname.into()))
}

const CACHE_GENERATION_BUCKET_COUNT: usize = 1024;
pub static CACHE_GENERATION_LOCKS: LazyLock<[Mutex<()>; CACHE_GENERATION_BUCKET_COUNT]> =
    LazyLock::new(|| [(); CACHE_GENERATION_BUCKET_COUNT].map(|_| Mutex::new(())));

pub async fn async_cache_file<Fun, Fut>(
    seed: &[&str],
    generate: Fun,
) -> Result<AssetLocation, anyhow::Error>
where
    Fun: FnOnce(tokio::fs::File) -> Fut,
    Fut: Future<Output = Result<(), anyhow::Error>>,
{
    let (bucket, location) = cache_location(seed);
    // we need a lock even if it exists since somebody might be still in the process of writing.
    let _guard = CACHE_GENERATION_LOCKS[bucket % CACHE_GENERATION_BUCKET_COUNT].lock();
    let exists = tokio::fs::try_exists(location.path()).await?;
    if !exists {
        let f = tokio::fs::File::create(location.path()).await?;
        generate(f).await?;
    }
    drop(_guard);
    Ok(location)
}

pub fn cache_file<Fun>(seed: &[&str], mut generate: Fun) -> Result<AssetLocation, anyhow::Error>
where
    Fun: FnMut(std::fs::File) -> Result<(), anyhow::Error>,
{
    let (bucket, location) = cache_location(seed);
    // we need a lock even if it exists since somebody might be still in the process of writing.
    let _guard = CACHE_GENERATION_LOCKS[bucket % CACHE_GENERATION_BUCKET_COUNT].blocking_lock();
    let exists = location.path().exists();
    if !exists {
        let f = std::fs::File::create(location.path())?;
        generate(f)?;
    }
    drop(_guard);
    Ok(location)
}