gabrielsimmer.com/src/cache/mod.rs

mod memory;
mod sqlite;

use std::{time::{SystemTime, UNIX_EPOCH}, fmt};
use async_trait::async_trait;
use sqlx::FromRow;

use self::{memory::Memory, sqlite::Sqlite};

#[derive(Clone, Debug)]
pub struct Cache {
    memory: Memory,
    sqlite: Option<Sqlite>,
}

pub async fn init_cache() -> Cache {
    Cache{ memory: memory::new(), sqlite: sqlite::new().await }
}

/// Tier enums take an i64, which is the amount of time in seconds
/// the tier should consider the contents of the cache valid.
#[derive(Clone, Debug, sqlx::Type)]
pub enum Tier {
    Memory,
    Sqlite,
    External,
    None
}

impl fmt::Display for Tier {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Tier::Memory => write!(f, "memory"),
            Tier::Sqlite => write!(f, "sqlite"),
            Tier::External => write!(f, "external"),
            Tier::None => write!(f, ""),
        }
    }
}

#[derive(Clone, Debug, FromRow)]
pub struct CachedItem {
    pub content_type: String,
    pub content: String,
    cached: i64,
    #[sqlx(default)]
    tier: Option<Tier>
}

impl CachedItem {
    pub fn tier(&self) -> Tier {
        self.tier.clone().unwrap_or(Tier::None)
    }
}

#[async_trait]
pub trait CacheMechanism: Sized + Clone + Send + Sync + 'static  {
    async fn get(&self, key: &String) -> Option<CachedItem>;
    async fn rm(&mut self, key: String);
    async fn set(&self, key: String, item: CachedItem);
}

impl Cache {
    pub async fn get(&self, key: &String) -> Option<CachedItem> {
        let m = self.memory.get(key).await;
        if m.is_some() {
            return m;
        }
        if self.sqlite.is_some() {
            let sq = self.sqlite.clone().unwrap();
            let s = sq.get(key).await; if s.is_some() {
                let current_time = SystemTime::now()
                    .duration_since(UNIX_EPOCH)
                    .expect("SystemTime before UNIX EPOCH!")
                    .as_secs()
                    .try_into()
                    .unwrap();
                let mut refresh_memory = s.clone().unwrap();
                refresh_memory.cached = current_time;
                let _ = self.memory.set(key.clone(), refresh_memory).await;
                return s
            }
        }

        return None
    }

     pub async fn set(&self, key: String, content_type: String, content: String) -> bool {
        let current_time = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .expect("SystemTime before UNIX EPOCH!")
            .as_secs()
            .try_into()
            .unwrap();
         let cached_item = CachedItem{ content_type, content, cached: current_time, tier: None };
         self.memory.set(key.clone(), cached_item.clone()).await;
         if self.sqlite.is_some() {
             let sq = self.sqlite.clone().unwrap();
             sq.set(key.clone(), cached_item.clone()).await;
         }
         true
     }
}

/// Determine whether we should actually use the cached item or not.
fn should_use(item: &CachedItem, tier: Tier) -> bool {
    // TODO: Make configurable.
    let cache_time = match tier {
        Tier::Memory => 2*60,
        Tier::Sqlite => 10*60,
        Tier::External => 0,
        Tier::None => 0,
    };
    
    let current_time: i64 = SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .expect("SystemTime before UNIX EPOCH!")
        .as_secs().try_into().unwrap();

    current_time <= (item.cached + cache_time) && item.content != ""
}