// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
//!  This example shows you how to define ops in Rust and then call them from
//!  JavaScript.

use anyhow::anyhow;
use deno_core::json_op_sync;
use deno_core::JsRuntime;
use deno_core::Op;
use serde_json::Value;
use std::io::Write;

fn main() {
  // Initialize a runtime instance
  let mut runtime = JsRuntime::new(Default::default());

  // The first thing we do is define two ops.  They will be used to show how to
  // pass data to Rust and back to JavaScript.
  //
  // The first one is used to print data to stdout, because by default the
  // JavaScript console functions are just stubs (they don't do anything).
  //
  // The second one just transforms some input and returns it to JavaScript.

  // Register the op for outputting bytes to stdout.
  // It can be invoked with Deno.core.dispatch and the id this method returns
  // or Deno.core.dispatchByName and the name provided.
  runtime.register_op(
    "op_print",
    // The op_fn callback takes a state object OpState
    // and a vector of ZeroCopyBuf's, which are mutable references
    // to ArrayBuffer's in JavaScript.
    |_state, zero_copy| {
      let mut out = std::io::stdout();

      // Write the contents of every buffer to stdout
      for buf in zero_copy {
        out.write_all(&buf).unwrap();
      }

      Op::Sync(Box::new([])) // No meaningful result
    },
  );

  // Register the JSON op for summing a number array.
  // A JSON op is just an op where the first ZeroCopyBuf is a serialized JSON
  // value, the return value is also a serialized JSON value.  It can be invoked
  // with Deno.core.jsonOpSync and the name.
  runtime.register_op(
    "op_sum",
    // The json_op_sync function automatically deserializes
    // the first ZeroCopyBuf and serializes the return value
    // to reduce boilerplate
    json_op_sync(|_state, json: Vec<f64>, zero_copy| {
      // We check that we only got the JSON value.
      if !zero_copy.is_empty() {
        Err(anyhow!("Expected exactly one argument"))
      } else {
        // And if we did, do our actual task
        let sum = json.iter().fold(0.0, |a, v| a + v);

        // Finally we return a JSON value
        Ok(Value::from(sum))
      }
    }),
  );

  // Now we see how to invoke the ops we just defined. The runtime automatically
  // contains a Deno.core object with several functions for interacting with it.
  // You can find its definition in core.js.
  runtime.execute(
    "<init>",
    r#"
// First we initialize the ops cache.
// This maps op names to their id's.
Deno.core.ops();

// Then we define a print function that uses
// our op_print op to display the stringified argument.
const _newline = new Uint8Array([10]);
function print(value) {
  Deno.core.dispatchByName('op_print', Deno.core.encode(value.toString()), _newline);
}

// Finally we register the error class used by op_sum
// so that it throws the correct class.
Deno.core.registerErrorClass('Error', Error);
"#,
  ).unwrap();

  // Now we can finally use this in an example.
  runtime
    .execute(
      "<usage>",
      r#"
const arr = [1, 2, 3];
print("The sum of");
print(arr);
print("is");
print(Deno.core.jsonOpSync('op_sum', arr));

// And incorrect usage
try {
  print(Deno.core.jsonOpSync('op_sum', 0));
} catch(e) {
  print('Exception:');
  print(e);
}
"#,
    )
    .unwrap();
}