// The only way we can provide values to wasm_bindgen's generated code is to set globals
function setGlobalsForWasmBindgen() {
  window.js_create_app = js_create_app;
  window.js_run_app = js_run_app;
  window.js_get_result_and_memory = js_get_result_and_memory;

  // The only place we use console.error is in wasm_bindgen, where it gets a single string argument.
  console.error = function displayErrorInHistoryPanel(string) {
    const html = `<div class="panic">${string}</div>`;
    updateHistoryEntry(repl.inputHistoryIndex, false, html);
  };
}
setGlobalsForWasmBindgen();

import * as roc_repl_wasm from "./roc_repl_wasm.js";
import { getMockWasiImports } from "./wasi.js";

// ----------------------------------------------------------------------------
// REPL state
// ----------------------------------------------------------------------------

const repl = {
  elemHistory: document.getElementById("history-text"),
  elemSourceInput: document.getElementById("source-input"),

  inputQueue: [],
  inputHistory: [],
  inputHistoryIndex: 0,
  inputStash: "", // stash the user input while we're toggling through history with up/down arrows

  textDecoder: new TextDecoder(),
  textEncoder: new TextEncoder(),

  compiler: null,
  app: null,

  // Temporary storage for values passing back and forth between JS and Wasm
  result: { addr: 0, buffer: new ArrayBuffer() },
};

// Initialise
repl.elemSourceInput.addEventListener("change", onInputChange);
repl.elemSourceInput.addEventListener("keyup", onInputKeyup);
roc_repl_wasm.default("/repl/roc_repl_wasm_bg.wasm").then((instance) => {
  repl.elemHistory.querySelector('#loading-message').remove();
  repl.elemSourceInput.disabled = false;
  repl.elemSourceInput.placeholder =
    "Type some Roc code and press Enter. (Use Shift+Enter for multi-line input)";
  repl.compiler = instance;
});

// ----------------------------------------------------------------------------
// Handle inputs
// ----------------------------------------------------------------------------

function onInputChange(event) {
  const inputText = event.target.value;
  if (!inputText) return;

  event.target.value = "";

  repl.inputQueue.push(inputText);
  if (repl.inputQueue.length === 1) {
    processInputQueue();
  }
}

function onInputKeyup(event) {
  const UP = 38;
  const DOWN = 40;
  const ENTER = 13;

  const { keyCode } = event;

  const el = repl.elemSourceInput;

  switch (keyCode) {
    case UP:
      if (repl.inputHistoryIndex == repl.inputHistory.length - 1) {
        repl.inputStash = el.value;
      }
      setInput(repl.inputHistory[repl.inputHistoryIndex]);

      if (repl.inputHistoryIndex > 0) {
        repl.inputHistoryIndex--;
      }
      break;

    case DOWN:
      if (repl.inputHistoryIndex === repl.inputHistory.length - 1) {
        setInput(repl.inputStash);
      } else {
        repl.inputHistoryIndex++;
        setInput(repl.inputHistory[repl.inputHistoryIndex]);
      }
      break;

    case ENTER:
      if (!event.shiftKey) {
        onInputChange({ target: repl.elemSourceInput });
      }
      break;

    default:
      break;
  }
}

function setInput(value) {
  const el = repl.elemSourceInput;
  el.value = value;
  el.selectionStart = value.length;
  el.selectionEnd = value.length;
}

// Use a queue just in case we somehow get inputs very fast
// We want the REPL to only process one at a time, since we're using some global state.
// In normal usage we shouldn't see this edge case anyway. Maybe with copy/paste?
async function processInputQueue() {
  while (repl.inputQueue.length) {
    const inputText = repl.inputQueue[0];
    repl.inputHistoryIndex = createHistoryEntry(inputText);
    repl.inputStash = "";

    let outputText;
    let ok = true;
    try {
      outputText = await roc_repl_wasm.entrypoint_from_js(inputText);
    } catch (e) {
      outputText = `${e}`;
      ok = false;
    }

    updateHistoryEntry(repl.inputHistoryIndex, ok, outputText);
    repl.inputQueue.shift();
  }
}

// ----------------------------------------------------------------------------
// Callbacks to JS from Rust
// ----------------------------------------------------------------------------

// Create an executable Wasm instance from an array of bytes
// (Browser validates the module and does the final compilation.)
async function js_create_app(wasm_module_bytes) {
  const wasiLinkObject = {}; // gives the WASI functions a reference to the app so they can write to its memory
  const importObj = getMockWasiImports(wasiLinkObject);
  const { instance } = await WebAssembly.instantiate(
    wasm_module_bytes,
    importObj
  );
  wasiLinkObject.instance = instance;
  repl.app = instance;
}

// Call the main function of the app, via the test wrapper
// Cache the result and return the size of the app's memory
function js_run_app() {
  const { wrapper, memory } = repl.app.exports;
  const addr = wrapper();
  const { buffer } = memory;
  repl.result = { addr, buffer };

  // Tell Rust how much space to reserve for its copy of the app's memory buffer.
  // This is not predictable, since the app can resize its own memory via malloc.
  return buffer.byteLength;
}

// After the Rust app has allocated space for the app's memory buffer,
// it calls this function and we copy it, and return the result too
function js_get_result_and_memory(buffer_alloc_addr) {
  const { addr, buffer } = repl.result;
  const appMemory = new Uint8Array(buffer);
  const compilerMemory = new Uint8Array(repl.compiler.memory.buffer);
  compilerMemory.set(appMemory, buffer_alloc_addr);
  return addr;
}

// ----------------------------------------------------------------------------
// Rendering
// ----------------------------------------------------------------------------

function createHistoryEntry(inputText) {
  const historyIndex = repl.inputHistory.length;
  repl.inputHistory.push(inputText);

  const firstLinePrefix = '<span class="input-line-prefix">» </span>';
  const otherLinePrefix = '\n<span class="input-line-prefix">… </span>';
  const inputLines = inputText.split("\n");
  if (inputLines[inputLines.length - 1] === "") {
    inputLines.pop();
  }
  const inputWithPrefixes = firstLinePrefix + inputLines.join(otherLinePrefix);

  const inputElem = document.createElement("pre");
  inputElem.innerHTML = inputWithPrefixes;
  inputElem.classList.add("input");

  const historyItem = document.createElement("div");
  historyItem.appendChild(inputElem);
  historyItem.classList.add("history-item");

  repl.elemHistory.appendChild(historyItem);
  repl.elemHistory.scrollTop = repl.elemHistory.scrollHeight;

  return historyIndex;
}

function updateHistoryEntry(index, ok, outputText) {
  const outputElem = document.createElement("pre");
  outputElem.innerHTML = outputText;
  outputElem.classList.add("output");
  outputElem.classList.add(ok ? "output-ok" : "output-error");

  const historyItem = repl.elemHistory.children[index];
  historyItem.appendChild(outputElem);

  repl.elemHistory.scrollTop = repl.elemHistory.scrollHeight;
}