use serde::{de::DeserializeOwned, Serialize};
use std::{
io::Write,
sync::{RwLock, RwLockReadGuard, RwLockWriteGuard},
};
use std::{
ops::{Deref, DerefMut},
path::{Path, PathBuf},
sync::Arc,
};
use thiserror::Error;
#[derive(Error, Debug)]
pub enum AcidJsonError {
#[error("I/O error: {0}")]
IoError(#[from] std::io::Error),
#[error("JSON parsing error: {0}")]
JsonError(#[from] serde_json::Error),
}
#[derive(Clone, Debug)]
pub struct AcidJson<T: Serialize + DeserializeOwned + Sync> {
cached: Arc<RwLock<T>>,
fname: PathBuf,
}
impl<T: Serialize + DeserializeOwned + Sync> AcidJson<T> {
pub fn open(fname: &Path) -> Result<Self, AcidJsonError> {
let file_contents = std::fs::read(fname)?;
let parsed: T = serde_json::from_slice(&file_contents)?;
Ok(Self {
cached: RwLock::new(parsed).into(),
fname: fname.to_owned(),
})
}
pub fn open_or_else(fname: &Path, gen_def: impl FnOnce() -> T) -> Result<Self, AcidJsonError> {
if !fname.exists() {
std::fs::write(fname, serde_json::to_vec(&gen_def())?)?;
}
let file_contents = std::fs::read(fname)?;
let parsed: T = serde_json::from_slice(&file_contents)?;
Ok(Self {
cached: RwLock::new(parsed).into(),
fname: fname.to_owned(),
})
}
pub fn read(&self) -> AcidJsonReadGuard<T> {
let inner = self.cached.read().unwrap();
AcidJsonReadGuard { inner }
}
pub fn write(&self) -> AcidJsonWriteGuard<T> {
let inner = self.cached.write().unwrap();
let init_serialized = serde_json::to_vec(inner.deref()).expect("cannot serialize");
AcidJsonWriteGuard {
inner,
fname: self.fname.clone(),
init_serialized,
}
}
}
pub struct AcidJsonReadGuard<'a, T: Serialize + DeserializeOwned + Sync> {
inner: RwLockReadGuard<'a, T>,
}
impl<'a, T: Serialize + DeserializeOwned + Sync> Deref for AcidJsonReadGuard<'a, T> {
type Target = T;
fn deref(&self) -> &Self::Target {
&self.inner
}
}
pub struct AcidJsonWriteGuard<'a, T: Serialize + DeserializeOwned + Sync> {
inner: RwLockWriteGuard<'a, T>,
fname: PathBuf,
init_serialized: Vec<u8>,
}
impl<'a, T: Serialize + DeserializeOwned + Sync> Deref for AcidJsonWriteGuard<'a, T> {
type Target = T;
fn deref(&self) -> &Self::Target {
self.inner.deref()
}
}
impl<'a, T: Serialize + DeserializeOwned + Sync> DerefMut for AcidJsonWriteGuard<'a, T> {
fn deref_mut(&mut self) -> &mut Self::Target {
self.inner.deref_mut()
}
}
impl<'a, T: Serialize + DeserializeOwned + Sync> Drop for AcidJsonWriteGuard<'a, T> {
fn drop(&mut self) {
let serialized = serde_json::to_vec(self.inner.deref()).expect("cannot serialize");
if serialized != self.init_serialized {
atomicwrites::AtomicFile::new(
&self.fname,
atomicwrites::OverwriteBehavior::AllowOverwrite,
)
.write(|f| f.write_all(&serialized))
.expect("could not write acidjson");
log::debug!(
"wrote {} bytes to {}",
serialized.len(),
self.fname.as_os_str().to_string_lossy()
);
} else {
log::debug!("not writing because nothing changed")
}
}
}