const CELL_SIZE = 20;
const DEFAULT_FG = "#cccccc";
const DEFAULT_BG = "#121212";
const decoder = new TextDecoder();
const encoder = new TextEncoder();

const BUTTON = Object.freeze({ left: 0, middle: 1, right: 2, wheelUp: 3, wheelDown: 4, wheelLeft: 5, wheelRight: 6, none: 7 });
const MOUSE = Object.freeze({ press: 0, release: 1, motion: 2, drag: 3 });
const SPECIAL_KEYS = Object.freeze({
  Enter: 0x0d,
  Backspace: 0x7f,
  Tab: 0x09,
  Escape: 0x1b,
  ArrowUp: 0xf0001,
  ArrowDown: 0xf0002,
  ArrowLeft: 0xf0003,
  ArrowRight: 0xf0004,
  Home: 0xf0005,
  End: 0xf0006,
  PageUp: 0xf0007,
  PageDown: 0xf0008,
  Delete: 0xf0009,
});

export class DomRenderer {
  constructor(root, wasm) {
    this.root = root;
    this.wasm = wasm;
    this.rows = [];
    this.cells = [];
    this.cols = 0;
    this.rowCount = 0;
    this.snapshot = null;
  }

  render() {
    const count = this.wasm.pardes_frame();
    const cols = this.wasm.pardes_frame_cols();
    const rows = this.wasm.pardes_frame_rows();
    if (count !== cols * rows) throw new Error(`bad frame: ${count} cells for ${cols}x${rows}`);
    this.ensureGrid(cols, rows);

    const ptr = this.wasm.pardes_frame_ptr();
    const view = new DataView(this.wasm.memory.buffer, ptr, count * CELL_SIZE);
    const bytes = new Uint8Array(this.wasm.memory.buffer);
    const cursorX = this.wasm.pardes_cursor_x();
    const cursorY = this.wasm.pardes_cursor_y();
    const cursorBar = this.wasm.pardes_cursor_bar() !== 0;
    const raw = new Array(count);

    for (let index = 0; index < count; index += 1) {
      const off = index * CELL_SIZE;
      const len = view.getUint8(off + 18);
      const fg = view.getUint32(off + 8, true);
      const bg = view.getUint32(off + 12, true);
      const attrs = view.getUint16(off + 16, true);
      const text = decoder.decode(bytes.subarray(ptr + off, ptr + off + len)) || " ";
      const x = index % cols;
      const y = Math.floor(index / cols);
      const cursor = x === cursorX && y === cursorY;
      const cell = this.cells[index];
      if (cell.textContent !== text) cell.textContent = text;
      const styleKey = `${fg}:${bg}:${attrs}:${cursor ? 1 : 0}:${cursorBar ? 1 : 0}`;
      if (cell.pardesStyle !== styleKey) {
        applyStyle(cell, fg, bg, attrs, cursor, cursorBar);
        cell.pardesStyle = styleKey;
      }
      raw[index] = { text, fg, bg, attrs };
    }
    this.snapshot = { cols, rows, cells: raw, cursorX, cursorY, cursorBar };
    return this.snapshot;
  }

  ensureGrid(cols, rows) {
    if (cols === this.cols && rows === this.rowCount) return;
    const document = this.root.ownerDocument;
    const rowNodes = [];
    const cells = [];
    for (let y = 0; y < rows; y += 1) {
      const row = document.createElement("div");
      row.className = "pardes-row";
      row.setAttribute("role", "row");
      row.dataset.row = String(y);
      const rowCells = [];
      for (let x = 0; x < cols; x += 1) {
        const cell = document.createElement("span");
        cell.className = "pardes-cell";
        cell.setAttribute("role", "gridcell");
        cell.dataset.col = String(x);
        cell.dataset.row = String(y);
        cell.textContent = " ";
        rowCells.push(cell);
        cells.push(cell);
      }
      row.replaceChildren(...rowCells);
      rowNodes.push(row);
    }
    this.root.replaceChildren(...rowNodes);
    this.root.setAttribute("aria-colcount", String(cols));
    this.root.setAttribute("aria-rowcount", String(rows));
    this.rows = rowNodes;
    this.cells = cells;
    this.cols = cols;
    this.rowCount = rows;
  }
}

export class PardesRuntime {
  constructor(root, wasm) {
    this.root = root;
    this.wasm = wasm;
    this.renderer = new DomRenderer(root, wasm);
    this.inputPtr = wasm.pardes_input_ptr();
    this.inputCapacity = wasm.pardes_input_capacity();
    this.cellWidth = 1;
    this.cellHeight = 1;
    this.running = false;
    this.pointer = null;
    this.frameHandle = 0;
    this.bindEvents();
  }

  start() {
    this.measure();
    const { cols, rows } = this.gridSize();
    const error = this.wasm.pardes_init(cols, rows);
    if (error) throw new Error(`Pardes wasm init failed (${error})`);
    this.inputPtr = this.wasm.pardes_input_ptr();
    this.resize();
    this.renderer.render();
    this.drainEffects();
    this.running = true;
    this.frameHandle = requestAnimationFrame(() => this.frame());
    this.root.focus({ preventScroll: true });
  }

  stop() {
    this.running = false;
    if (this.frameHandle) cancelAnimationFrame(this.frameHandle);
    this.wasm.pardes_deinit();
  }

  frame() {
    if (!this.running) return;
    this.wasm.pardes_tick();
    this.renderer.render();
    this.drainEffects();
    this.frameHandle = requestAnimationFrame(() => this.frame());
  }

  measure() {
    const probe = this.root.ownerDocument.createElement("span");
    probe.className = "pardes-probe";
    probe.textContent = "M";
    this.root.ownerDocument.body.append(probe);
    const rect = probe.getBoundingClientRect();
    probe.remove();
    this.cellWidth = Math.max(1, rect.width);
    this.cellHeight = Math.max(1, rect.height);
  }

  gridSize() {
    return {
      cols: Math.max(1, Math.floor(this.root.clientWidth / this.cellWidth)),
      rows: Math.max(1, Math.floor(this.root.clientHeight / this.cellHeight)),
    };
  }

  resize() {
    this.measure();
    const { cols, rows } = this.gridSize();
    this.wasm.pardes_resize(cols, rows);
  }

  writeInput(text) {
    const data = encoder.encode(text);
    if (data.length > this.inputCapacity) throw new Error("browser input exceeds wasm transfer buffer");
    new Uint8Array(this.wasm.memory.buffer, this.inputPtr, data.length).set(data);
    return data.length;
  }

  key(event) {
    const mods = modifiers(event);
    let cp = SPECIAL_KEYS[event.key];
    let text = "";
    if (cp === undefined && event.key.length > 0 && [...event.key].length === 1) {
      text = mods & 3 ? "" : event.key;
      const shortcut = event.code?.match(/^Key([A-Z])$/);
      cp = shortcut && (mods & 3) ? shortcut[1].toLowerCase().codePointAt(0) : event.key.codePointAt(0);
    }
    if (cp === undefined) return;
    event.preventDefault();
    this.wasm.pardes_key(cp, this.writeInput(text), mods);
  }

  point(event) {
    const rect = this.root.getBoundingClientRect();
    return {
      col: clamp(Math.floor((event.clientX - rect.left) / this.cellWidth), 0, Math.max(0, this.wasm.pardes_frame_cols() - 1)),
      row: clamp(Math.floor((event.clientY - rect.top) / this.cellHeight), 0, Math.max(0, this.wasm.pardes_frame_rows() - 1)),
    };
  }

  cellPoint(col, row) {
    const rect = this.root.getBoundingClientRect();
    return { x: rect.left + (col + 0.5) * this.cellWidth, y: rect.top + (row + 0.5) * this.cellHeight };
  }

  pointerDown(event) {
    event.preventDefault();
    this.root.focus({ preventScroll: true });
    this.root.setPointerCapture?.(event.pointerId);
    const point = this.point(event);
    if (event.pointerType === "touch") {
      const packed = this.wasm.pardes_chrome_target(point.col, point.row) >>> 0;
      const chrome = packed !== 0xffffffff;
      const snapped = chrome ? { col: packed & 0xffff, row: packed >>> 16 } : point;
      this.pointer = { id: event.pointerId, touch: true, chrome, startX: event.clientX, startY: event.clientY, lastX: event.clientX, lastY: event.clientY, point: snapped, scrolling: false, accum: 0 };
      if (chrome) this.wasm.pardes_mouse(BUTTON.left, MOUSE.press, snapped.col, snapped.row, modifiers(event));
      return;
    }
    const button = pointerButton(event.button);
    this.pointer = { id: event.pointerId, touch: false, button };
    this.wasm.pardes_mouse(button, MOUSE.press, point.col, point.row, modifiers(event));
  }

  pointerMove(event) {
    const point = this.point(event);
    const active = this.pointer?.id === event.pointerId ? this.pointer : null;
    if (!active) {
      if (event.pointerType !== "touch") this.wasm.pardes_mouse(BUTTON.none, MOUSE.motion, point.col, point.row, modifiers(event));
      return;
    }
    event.preventDefault();
    if (!active.touch) {
      this.wasm.pardes_mouse(active.button, MOUSE.drag, point.col, point.row, modifiers(event));
      return;
    }
    if (active.chrome) {
      this.wasm.pardes_mouse(BUTTON.left, MOUSE.drag, point.col, point.row, modifiers(event));
      return;
    }
    const travel = Math.hypot(event.clientX - active.startX, event.clientY - active.startY);
    if (travel > 8) active.scrolling = true;
    if (active.scrolling) {
      const dy = event.clientY - active.lastY;
      active.accum += dy / this.cellHeight;
      while (active.accum <= -1) {
        this.wasm.pardes_mouse(BUTTON.wheelDown, MOUSE.press, point.col, point.row, 0);
        active.accum += 1;
      }
      while (active.accum >= 1) {
        this.wasm.pardes_mouse(BUTTON.wheelUp, MOUSE.press, point.col, point.row, 0);
        active.accum -= 1;
      }
      this.wasm.pardes_touch_scroll(dy / this.cellHeight);
    }
    active.lastX = event.clientX;
    active.lastY = event.clientY;
  }

  pointerUp(event) {
    const active = this.pointer?.id === event.pointerId ? this.pointer : null;
    if (!active) return;
    event.preventDefault();
    const point = this.point(event);
    if (active.touch) {
      if (active.chrome) this.wasm.pardes_mouse(BUTTON.left, MOUSE.release, point.col, point.row, modifiers(event));
      else if (!active.scrolling) {
        this.wasm.pardes_mouse(BUTTON.right, MOUSE.press, point.col, point.row, 0);
        this.wasm.pardes_mouse(BUTTON.right, MOUSE.release, point.col, point.row, 0);
      }
    } else {
      this.wasm.pardes_mouse(active.button, MOUSE.release, point.col, point.row, modifiers(event));
    }
    if (this.root.hasPointerCapture?.(event.pointerId)) this.root.releasePointerCapture(event.pointerId);
    this.pointer = null;
  }

  wheel(event) {
    event.preventDefault();
    const point = this.point(event);
    if (event.deltaY) this.wasm.pardes_mouse(event.deltaY < 0 ? BUTTON.wheelUp : BUTTON.wheelDown, MOUSE.press, point.col, point.row, modifiers(event));
    if (event.deltaX) this.wasm.pardes_mouse(event.deltaX < 0 ? BUTTON.wheelLeft : BUTTON.wheelRight, MOUSE.press, point.col, point.row, modifiers(event));
  }

  paste(event) {
    const text = event.clipboardData?.getData("text/plain");
    if (text === undefined) return;
    event.preventDefault();
    this.wasm.pardes_paste(this.writeInput(text));
  }

  bindEvents() {
    this.root.addEventListener("keydown", (event) => this.key(event));
    this.root.addEventListener("paste", (event) => this.paste(event));
    this.root.addEventListener("contextmenu", (event) => event.preventDefault());
    this.root.addEventListener("pointerdown", (event) => this.pointerDown(event));
    this.root.addEventListener("pointermove", (event) => this.pointerMove(event));
    this.root.addEventListener("pointerup", (event) => this.pointerUp(event));
    this.root.addEventListener("pointercancel", (event) => this.pointerUp(event));
    this.root.addEventListener("wheel", (event) => this.wheel(event), { passive: false });
    globalThis.addEventListener?.("resize", () => this.resize());
  }

  drainEffects() {
    for (;;) {
      const kind = this.wasm.pardes_effect_next();
      if (!kind) return;
      const ptr = this.wasm.pardes_effect_ptr();
      const len = this.wasm.pardes_effect_len();
      const data = new Uint8Array(len);
      if (len) data.set(new Uint8Array(this.wasm.memory.buffer, ptr, len));
      const aux0 = this.wasm.pardes_effect_aux0();
      const aux1 = this.wasm.pardes_effect_aux1();
      this.handleEffect(kind, data, aux0, aux1);
    }
  }

  handleEffect(kind, data, aux0, aux1) {
    if (kind === 4) {
      globalThis.open?.(decoder.decode(data), "_blank", "noopener,noreferrer");
    } else if (kind === 5) {
      const view = new DataView(data.buffer, data.byteOffset, data.byteLength);
      const pathLength = data.length >= 4 ? view.getUint32(0, true) : 0;
      const path = decoder.decode(data.subarray(4, 4 + pathLength));
      download(data.subarray(4 + pathLength), path.split("/").pop() || "pardes.txt", "text/plain;charset=utf-8");
    } else if (kind === 6) {
      download(data, "pardes-dump.zon", "text/plain;charset=utf-8");
    } else if (kind === 7) {
      navigator.clipboard?.writeText(decoder.decode(data)).catch(() => {});
    } else if (kind === 13) {
      // Async and permission-gated, unlike every other effect here: a refused
      // or unsupported read is simply a paste that never happens, which is
      // what the core already tolerates from an empty clipboard.
      navigator.clipboard?.readText().then((text) => this.wasm.pardes_paste(this.writeInput(text))).catch(() => {});
    } else if (kind === 10) {
      this.running = false;
    } else {
      this.root.dispatchEvent(new CustomEvent("pardes-io", { detail: { kind, data, aux0, aux1 } }));
    }
  }
}

export async function instantiate(url = "./pardes.wasm") {
  const response = await fetch(url);
  if (!response.ok) throw new Error(`fetch ${url}: HTTP ${response.status}`);
  if (WebAssembly.instantiateStreaming) {
    try {
      return (await WebAssembly.instantiateStreaming(response.clone(), {})).instance.exports;
    } catch (error) {
      if (!/mime|content-type/i.test(String(error))) throw error;
    }
  }
  return (await WebAssembly.instantiate(await response.arrayBuffer(), {})).instance.exports;
}

export async function boot(root, url = "./pardes.wasm") {
  if (!root) throw new Error("Pardes DOM root is missing");
  const wasm = await instantiate(url);
  const runtime = new PardesRuntime(root, wasm);
  runtime.start();
  const test = {
    grid: () => runtime.renderer.snapshot,
    cellPoint: (col, row) => runtime.cellPoint(col, row),
  };
  globalThis.pardes = { runtime, wasm, test };
  return runtime;
}

function applyStyle(cell, fgCode, bgCode, attrs, cursor, cursorBar) {
  let fg = color(fgCode, DEFAULT_FG);
  let bg = color(bgCode, DEFAULT_BG);
  if (attrs & (1 << 4)) [fg, bg] = [bg, fg];
  if (attrs & (1 << 5)) fg = bg;
  if (attrs & (1 << 1)) fg = dim(fg);
  cell.style.color = fg;
  cell.style.backgroundColor = bg;
  cell.style.fontWeight = attrs & 1 ? "700" : "400";
  cell.style.fontStyle = attrs & (1 << 2) ? "italic" : "normal";
  const underline = (attrs >>> 8) & 7;
  cell.style.textDecorationLine = `${underline ? "underline " : ""}${attrs & (1 << 6) ? "line-through" : ""}`.trim() || "none";
  cell.style.textDecorationStyle = ["solid", "solid", "double", "wavy", "dotted", "dashed"][underline] || "solid";
  cell.style.setProperty("--cell-fg", fg);
  cell.style.setProperty("--cell-bg", bg);
  cell.classList.toggle("is-cursor", cursor);
  cell.classList.toggle("is-bar", cursor && cursorBar);
  cell.classList.toggle("is-blinking", Boolean(attrs & (1 << 3)));
}

function color(encoded, fallback) {
  if (encoded === 0x01000000) return fallback;
  if ((encoded & 0xff000000) === 0x02000000) return indexedColor(encoded & 0xff);
  return `#${(encoded & 0xffffff).toString(16).padStart(6, "0")}`;
}

function indexedColor(index) {
  const ansi = [
    "#000000", "#cc0000", "#4e9a06", "#c4a000", "#3465a4", "#75507b", "#06989a", "#d3d7cf",
    "#555753", "#ef2929", "#8ae234", "#fce94f", "#729fcf", "#ad7fa8", "#34e2e2", "#eeeeec",
  ];
  if (index < 16) return ansi[index];
  if (index >= 232) {
    const level = 8 + (index - 232) * 10;
    return rgb(level, level, level);
  }
  const n = index - 16;
  const level = (part) => part === 0 ? 0 : 55 + part * 40;
  return rgb(level(Math.floor(n / 36)), level(Math.floor(n / 6) % 6), level(n % 6));
}

function dim(value) {
  const n = Number.parseInt(value.slice(1), 16);
  return rgb(((n >>> 16) & 0xff) * 0.6, ((n >>> 8) & 0xff) * 0.6, (n & 0xff) * 0.6);
}

function rgb(r, g, b) {
  return `#${[r, g, b].map((part) => Math.round(part).toString(16).padStart(2, "0")).join("")}`;
}

function modifiers(event) {
  return (event.ctrlKey ? 1 : 0) | (event.altKey ? 2 : 0) | (event.shiftKey ? 4 : 0);
}

function pointerButton(button) {
  return button === 1 ? BUTTON.middle : button === 2 ? BUTTON.right : BUTTON.left;
}

function clamp(value, low, high) {
  return Math.max(low, Math.min(high, value));
}

function download(bytes, name, type) {
  if (typeof document === "undefined") return;
  const url = URL.createObjectURL(new Blob([bytes], { type }));
  const anchor = document.createElement("a");
  anchor.href = url;
  anchor.download = name;
  anchor.click();
  setTimeout(() => URL.revokeObjectURL(url), 0);
}