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//! ## Usage
//!
//! Cargo.toml:
//!
//! ```toml
//! [dependencies]
//! tauri-async-handler = "0.4"
//! ```
//!
//! src-tauri/main.rs:
//!
//! ```rust
//! mod cmd;
//!
//!
//! use serde_json::json;
//! use tauri_async_handler::*;
//!
//! fn main() {
//!   tauri::AppBuilder::new()
//!     .async_handler(None, |cmd: cmd::Cmd| async {
//!       use cmd::Cmd::*;
//!       Ok(match cmd {
//!         MyCustomCommand{ argument } => {
//!           println!("arg {}", argument);
//!           let world = "world";
//!           json!({
//!             "hello": world
//!           })
//!         }
//!       })
//!     })
//!     .build()
//!     .run();
//! }
//!
//! ```
//!
//! JavaScript:
//!
//! ```javascript
//! const myCustomCommand = (argument) => {
//!   return window.tauri.promisified({
//!     cmd: 'myCustomCommand',
//!     argument,
//!   })
//! }
//! myCustomCommand.then((r) => console.log('myCustomCommand', r))
//! ```

use async_std::task::spawn;
use futures_channel::mpsc;
use futures_util::stream::StreamExt;
use serde_derive::Deserialize;
use serde_json::Value;
use tauri::AppBuilder;
use tauri::{Result, WebviewMut};

fn map_err<E: std::error::Error>(e: E) -> String {
    e.to_string()
}

#[derive(Deserialize)]
#[serde(rename_all = "camelCase")]
struct CallbackCmd<T> {
    #[serde(flatten)]
    cmd: T,
    callback: String,
    error: String,
}

struct Command<T>(T, WebviewMut);

pub trait AppBuilderExt {
    fn async_handler<C, F, Fut>(self, limit: impl Into<Option<usize>>, invoke_handler: F) -> Self
    where
        C: serde::de::DeserializeOwned + Send + 'static,
        F: FnMut(C) -> Fut + Send + 'static,
        Fut: std::future::Future<Output = Result<Value>> + Send;
}

fn json_string(value: Value) -> String {
    serde_json::to_string(&value).expect("Failed to encode json")
}

fn execute_callback(
    mut handle: WebviewMut,
    result: Result<Value>,
    callback: String,
    error: String,
) {
    handle
        .dispatch(|mut webview| {
            tauri::execute_promise_sync(&mut webview, || result.map(json_string), callback, error)
                .expect("Failed to execute promise");
        })
        .expect("Failed to dispatch");
}

impl AppBuilderExt for AppBuilder {
    fn async_handler<C, F, Fut>(
        self,
        limit: impl Into<Option<usize>>,
        mut invoke_handler: F,
    ) -> Self
    where
        C: serde::de::DeserializeOwned + Send + 'static,
        F: FnMut(C) -> Fut + Send + 'static,
        Fut: std::future::Future<Output = Result<Value>> + Send,
    {
        let limit = limit.into();
        let (mut tx, rx) = mpsc::channel::<Command<CallbackCmd<C>>>(10);

        spawn(async move {
            rx.for_each_concurrent(limit, move |command| {
                let Command(
                    CallbackCmd {
                        cmd,
                        callback,
                        error,
                    },
                    handle,
                ) = command;
                let fut = invoke_handler(cmd);
                async {
                    execute_callback(handle, fut.await, callback, error);
                }
            })
            .await
        });
        self.invoke_handler(move |webview, arg| {
            let handle = webview.as_mut();
            let command: CallbackCmd<C> = serde_json::from_str(arg).map_err(map_err)?;
            if let Err(e) = tx.try_send(Command(command, handle.clone())) {
                let command = e.into_inner();
                execute_callback(
                    handle,
                    Err(anyhow::anyhow!("Failed to execute command")),
                    command.0.callback,
                    command.0.error,
                );
            }
            Ok(())
        })
    }
}