// Constants ///////////////////////////////////////////////////////////////////
const kDimensions = {
  wheelSize: 96,
  leverWidth: 98,
  sausageHeight: 48,
};
const kState = {
  waiting: "waiting",
  readyToGrate: "readyToGrate",
  readyToLoad: "readyToLoad",
};
const kAction = {
  completeLoading: Symbol("completeLoading"),
  startPullingLever: Symbol("startPullingLever"),
  stopPullingLever: Symbol("stopPullingLever"),
  pullLever: Symbol("pullLever"),
  startTurningWheel: Symbol("startTurningWheel"),
  stopTurningWheel: Symbol("stopTurningWheel"),
  turnWheel: Symbol("turnWheel"),
  setIsWaitingForFrame: Symbol("setIsWaitingForFrame"),
  createSausage: Symbol("createSausage"),
  completeGrating: Symbol("completeGrating"),
};
const kRotationDirection = {
  clockwise: Symbol("clockwise"),
  counterClockwise: Symbol("counterClockwise"),
};
const kPullDirection = {
  right: Symbol("right"),
  left: Symbol("left"),
};

// Configuration ///////////////////////////////////////////////////////////////
const configuration = {
  wheelStrength: 1,
  maxLoad: 100,
  leverTravel: 80.72,
  graterTravel: 69,
  chainSpeed: 0.5,
  grateStrength: 0.01,
  defaultUrl: "/example.html",
};

// App State ///////////////////////////////////////////////////////////////////
/**
 * The main app state
 */
let appState = null;

/**
 * Functions to handle side effects: Creation or removal of HTML elements,
 * actions that occur as a result of a change in state.
 */
const middleware = [
  /**
   * Makes text unselectable while we move the lever or wheel.
   */
  function disableSelect(_, action) {
    if (
      action === kAction.startTurningWheel ||
      action === kAction.startPullingLever
    ) {
      document.querySelector(".machine")?.classList.add("no-select");
    }
  },

  /**
   * Makes text selectable when we're done moving the lever or wheel.
   */
  function enableSelect(_, action) {
    if (
      action === kAction.stopTurningWheel ||
      action === kAction.stopPullingLever
    ) {
      document.querySelector(".machine")?.classList.remove("no-select");
    }
  },

  /**
   * Cleans up the old iFrames when we load the new one, and triggers a complete.
   */
  function completeLoading(state, action) {
    if (
      action === kAction.turnWheel &&
      state.currentState === kState.readyToLoad &&
      parseFloat(state.load) >= configuration.maxLoad
    ) {
      const iframes = $iframeContainer.querySelectorAll("iframe");
      for (const iframe of iframes) {
        if (iframe !== appState.currentIframe) {
          $iframeContainer.removeChild(iframe);
        }
      }
      send(kAction.completeLoading);
    }
  },

  /**
   * Sets the individual load state to the current iframe.
   */
  function updateIframe(state, action) {
    if (
      action === kAction.turnWheel &&
      state.currentState === kState.readyToLoad &&
      parseFloat(state.load) <= configuration.maxLoad
    ) {
      state.currentIframe?.style.setProperty(
        "--loadProgress",
        `${100 - state.load}vh`,
      );
    }
  },

  /**
   * Cleans up the sausage and loads the iframe once the grating is complete.
   */
  function completeGrating(state, action) {
    if (
      action === kAction.pullLever &&
      state.currentState === kState.readyToGrate &&
      parseFloat(state.grateLevel) >= kDimensions.sausageHeight
    ) {
      removeSausages();
      const $iframe = loadIframe(state.currentUrl, 0);
      send(kAction.completeGrating, { iframe: $iframe });
    }
  },

  /**
   * Creates the sausage element if we are at the right state.
   */
  function createSausageIfWaiting(state, action, data) {
    if (
      action === kAction.createSausage &&
      state.currentState === kState.waiting
    ) {
      createSausage(data.href, data.label);
    }
  },
];

/**
 * We store the state as CSS variables and data attributes in an element
 * declared as the $stateContainer. UI updates as a result of this. We
 * try to avoid manipulating the elements with JS, except for creating and
 * removing elements.
 */
const $stateContainer = document.querySelector(".machine");
const updateState = function updateState(state) {
  for (const [key, value] of Object.entries(state)) {
    $stateContainer.style.setProperty(`--${key}`, value);
    $stateContainer.dataset[key] = value;
  }
  appState = state;
};

/**
 * We modify a copy of the state and return it.
 */
const reduce = function reduce(stateReference, action, data) {
  let state = Object.assign({}, stateReference);

  switch (action) {
    case kAction.turnWheel:
      state.wheelRotation = `${data.angle}rad`;
      if (state.currentState === kState.readyToLoad) {
        const sign = data.direction === kRotationDirection.clockwise ? 1 : -1;
        const load = Math.max(
          Math.min(
            state.load - sign * data.magnitude * configuration.wheelStrength,
            configuration.maxLoad,
          ),
          0,
        );
        state.load = load;
        if (load < configuration.maxLoad && load > 0) {
          const chainOffset =
            parseFloat(state.chainOffset) +
            sign * data.magnitude * configuration.chainSpeed;
          state.chainOffset = `${chainOffset}%`;
        }
      }
      break;
    case kAction.pullLever:
      const diff = Math.abs(state.leverTravel - data.magnitude);
      state.leverTravel = data.magnitude;
      const rotation = (data.magnitude * configuration.leverTravel) / 100;
      state.leverRotation = `${rotation}deg`;
      const gratingTravel = (data.magnitude * configuration.graterTravel) / 100;
      state.graterTravel = `${gratingTravel}px`;
      if (state.currentState === kState.readyToGrate) {
        const grateLevel = Math.min(
          parseFloat(state.grateLevel) + diff * configuration.grateStrength,
          kDimensions.sausageHeight,
        );
        state.grateLevel = `${grateLevel}px`;
      }
      break;
    case kAction.createSausage:
      state.currentUrl = data.href;
      state.grateLevel = "0%";
      state.currentState = kState.readyToGrate;
      break;
    case kAction.startTurningWheel:
      state.isTurningWheel = true;
      break;
    case kAction.stopTurningWheel:
      state.isTurningWheel = false;
      break;
    case kAction.startPullingLever:
      state.isPullingLever = true;
      break;
    case kAction.stopPullingLever:
      state.isPullingLever = false;
      break;
    case kAction.completeLoading:
      state.currentState = kState.waiting;
      state.currentIframe = null;
      state.load = 0;
      break;
    case kAction.completeGrating:
      state.currentState = kState.readyToLoad;
      state.currentIframe = data.iframe;
      state.grateLevel = "0%";
      state.load = 0;
      break;
  }

  return state;
};

/**
 * The main mechanism for view changes to trigger updates.
 * It receives an action and its payload.
 * It queues the middleware to run after this.
 */
const send = function send(action, data) {
  const state = Object.assign({}, appState);
  for (const m of middleware) {
    setTimeout(() => m(state, action, data), 0);
  }
  const newState = reduce(state, action, data);
  updateState(newState);
};

// Initializzation /////////////////////////////////////////////////////////////

/**
 * Initializes state and events.
 */
const initialize = function initialize() {
  const state = {
    currentState: kState.waiting,
    isPullingLever: false,
    isTurningWheel: false,
    leverTravel: 0,
    grateLevel: 0,
    leverRotation: "0deg",
    graterTravel: "0rem",
    wheelRotation: "0deg",
    chainOffset: "0%",
    load: 0,
  };
  updateState(state);

  // Reset interaction with widgets if we lift a mouse button.
  document.addEventListener("mouseup", () => {
    send(kAction.stopTurningWheel);
    send(kAction.stopPullingLever);
  });

  // The lever handle initiates interactions with the lever.
  document
    .querySelector(".lever .handle")
    ?.addEventListener("mousedown", () => {
      send(kAction.startPullingLever);
    });

  // The wheel handle initiates interactions with the wheel.
  document
    .querySelector(".wheel .handle")
    ?.addEventListener("mousedown", () => {
      send(kAction.startTurningWheel);
    });

  // Rotation is calculated relatively to the whole wheel.
  // And travel based no the full arc of the lever
  const $wheel = document.querySelector(".wheel");
  const $lever = document.querySelector(".lever");
  document.addEventListener("mousemove", (event) => {
    if (appState.isTurningWheel && !appState.waitingForFrame) {
      requestAnimationFrame(() => {
        const elementPosition = $wheel.getBoundingClientRect();
        const x = event.clientX - elementPosition.left;
        const y = event.clientY - elementPosition.top;
        const angle = angleFromCenter(
          x,
          y,
          kDimensions.wheelSize,
          kDimensions.wheelSize,
        );
        const oldAngle = parseFloat(appState.wheelRotation);
        const { direction, magnitude } = rotationDirection(oldAngle, angle);
        send(kAction.turnWheel, { angle, direction, magnitude });
        send(kAction.setIsWaitingForFrame, { state: false });
      });
      send(kAction.setIsWaitingForFrame, { state: true });
    }
    if (appState.isPullingLever && !appState.waitingForFrame) {
      requestAnimationFrame(() => {
        const elementPosition = $lever.getBoundingClientRect();
        const x = event.clientX - elementPosition.left;
        const magnitude = Math.max(
          Math.min((x * 100) / kDimensions.leverWidth, 100),
          0,
        );
        const direction =
          magnitude >= appState.leverTravel
            ? kPullDirection.right
            : kPullDirection.left;
        send(kAction.pullLever, { magnitude, direction });
        send(kAction.setIsWaitingForFrame, { state: false });
      });
      send(kAction.setIsWaitingForFrame, { state: true });
    }
  });

  // The URL Grater is the drop area.
  const $grater = document.querySelector(".grater-bed");
  $grater.addEventListener("dragenter", (event) => {
    event.preventDefault();
    if (appState.currentState === kState.waiting) {
      $grater.classList.add("drag-over");
    }
  });
  $grater.addEventListener("dragover", (event) => event.preventDefault());
  $grater.addEventListener("dragleave", (event) => {
    if (!$grater.contains(event.relatedTarget)) {
      $grater.classList.remove("drag-over");
    }
  });
  $grater.addEventListener("drop", (event) => {
    event.preventDefault();
    if (appState.currentState !== kState.waiting) {
      return;
    }
    const href = event.dataTransfer.getData("text/uri-list");
    const label = event.dataTransfer.getData("text/plain");
    $grater.classList.remove("drag-over");
    send(kAction.createSausage, { href, label });
  });

  const params = new URLSearchParams(window.location.search);
  const urlFromQuery = params.get("url");
  const url = urlFromQuery ?? configuration.defaultUrl;
  loadIframe(url, 100);
};

// Utility Functions ///////////////////////////////////////////////////////////

/**
 * Calculates the angle of a point (x,y) relative to the center of a square
 * with dimensions (w, h). The result is in radians.
 */
const angleFromCenter = function angleFromCenter(x, y, w, h) {
  const centerX = w / 2;
  const centerY = h / 2;
  const dx = x - centerX;
  const dy = y - centerY;
  return Math.atan2(dy, dx);
};

/**
 * Given two angles, calculates the direction of the rotation.
 */
const rotationDirection = function rotationDirection(angle1, angle2) {
  let diff = angle2 - angle1;

  if (diff > Math.PI) diff -= 2 * Math.PI;
  if (diff < -Math.PI) diff += 2 * Math.PI;

  const magnitude = Math.abs(diff);
  const direction =
    diff > 0
      ? kRotationDirection.counterClockwise
      : kRotationDirection.clockwise;

  return {
    direction,
    magnitude,
  };
};

/**
 * Loads an iframe and appends it into the body.
 */
const $iframeContainer = document.querySelector(".web-content");
const loadIframe = function loadIframe(url, loadProgress) {
  const $iframe = document.createElement("iframe");
  $iframe.src = url;
  $iframe.style.setProperty("--loadProgress", `${100 - loadProgress}vh`);
  $iframeContainer.appendChild($iframe);

  $iframe.addEventListener("load", () => {
    const iframeDocument = $iframe.contentDocument;

    iframeDocument.querySelectorAll("a").forEach(($link) => {
      $link.addEventListener("click", (event) => event.preventDefault());
      $link.draggable = true;
      $link.addEventListener("dragstart", (event) => {
        event.dataTransfer.setData("text/uri-list", $link.href);
        event.dataTransfer.setData("text/plain", $link.textContent.trim());
        const ghost = $link.cloneNode(true);
        ghost.style.background = "url('/images/Sausage.svg')";
        ghost.style.backgroundRepeat = "no-repeat";
        ghost.style.cursor = "grabbing";
        ghost.style.display = "block";
        ghost.style.height = "3rem";
        ghost.style.width = "8.125rem";
        ghost.style.color = "#fff";
        ghost.style.textAlign = "center";
        ghost.style.fontSize = "0.625rem";
        ghost.style.fontFamily = "sans-serif";
        ghost.style.textTransform = "uppercase";
        ghost.style.paddingTop = "1rem";

        document.body.appendChild(ghost);
        event.dataTransfer.setDragImage(ghost, 10, 10);
      });
    });
  });

  return $iframe;
};

/**
 * Creates a sausage link for grating.
 */
const createSausage = function createSausage(href, label) {
  const $sausage = document.createElement("article");
  $sausage.classList.add("sausage");
  $sausage.dataset.href = href;
  $sausage.innerText = label;
  const $graterBed = document.querySelector(".grater-bed");
  $graterBed?.appendChild($sausage);
};

/**
 * Removes a completely grated sausage link.
 */
const removeSausages = function removeSausages() {
  const $graterBed = document.querySelector(".grater-bed");
  const $existingSausages = $graterBed.querySelectorAll(".sausage");
  for (const $existingSausage of $existingSausages) {
    $graterBed?.removeChild($existingSausage);
  }
};

initialize();