/*
    This file is part of jellything (https://codeberg.org/metamuffin/jellything)
    which is licensed under the GNU Affero General Public License (version 3); see /COPYING.
    Copyright (C) 2025 metamuffin <metamuffin.org>
*/
use crate::{CACHE_GENERATION_BUCKET_COUNT, CONF};
use anyhow::bail;
use base64::{Engine, prelude::BASE64_URL_SAFE};
use sha2::Sha256;
use std::{
    fmt::Display,
    hash::{Hash, Hasher},
    str::FromStr,
};

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct CacheKey(pub [u8; 32]);

impl CacheKey {
    pub fn new(ty: CacheContentType, seed: impl Hash) -> Self {
        use sha2::Digest;
        struct ShaHasher(Sha256);
        impl Hasher for ShaHasher {
            fn finish(&self) -> u64 {
                unreachable!()
            }
            fn write(&mut self, bytes: &[u8]) {
                self.0.update(bytes);
            }
        }
        let mut d = ShaHasher(sha2::Sha256::new());
        d.0.update(CONF.secret.as_bytes());
        seed.hash(&mut d);
        let d = d.0.finalize();
        let mut key: [u8; 32] = d.as_slice().try_into().unwrap();
        key[0] = ty as u8;
        Self(key)
    }
    pub fn new_json(seed: impl Hash) -> Self {
        Self::new(CacheContentType::Json, seed)
    }
    pub fn new_image(seed: impl Hash) -> Self {
        Self::new(CacheContentType::Image, seed)
    }
    pub fn content_type(&self) -> CacheContentType {
        match self.0[0] {
            1 => CacheContentType::Image,
            2 => CacheContentType::Json,
            _ => CacheContentType::Unknown,
        }
    }
    pub(super) fn bucket(&self) -> usize {
        (self.0[1] as usize
            | ((self.0[2] as usize) << 8)
            | ((self.0[3] as usize) << 16)
            | ((self.0[4] as usize) << 24))
            % CACHE_GENERATION_BUCKET_COUNT
    }
}

impl Display for CacheKey {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_str(&BASE64_URL_SAFE.encode(self.0))
    }
}
impl FromStr for CacheKey {
    type Err = anyhow::Error;
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let mut out = [0; 32];
        let size = BASE64_URL_SAFE.decode_slice(s, &mut out)?;
        if size != out.len() {
            bail!("cache key parse invalid size")
        }
        Ok(Self(out))
    }
}

#[repr(u8)]
pub enum CacheContentType {
    Unknown = 0,
    Image = 1,
    Json = 2,
}