import { RULER_ICON } from "/js/icons.js";
import { NoteSaveForm } from "/js/notes.js";
import { isLoggedIn } from "/js/auth.js";

const SOURCE_ID = "measure";
const LINE_LAYER_ID = "measure-line";
const FILL_LAYER_ID = "measure-fill";
const POINT_LAYER_ID = "measure-points";
const SEGMENT_LABEL_LAYER_ID = "measure-segment-labels";
const EARTH_RADIUS_M = 6378137; // WGS84 equatorial radius, matches turf.js's area formula

// A distance/area measuring tool, matching the ruler button in NPS's own
// map controls (Home/zoom/ruler, screenshot). Click to add vertices,
// distance sums the haversine length of the resulting line; area uses the
// standard spherical-excess polygon formula (Chamberlain & Duquette, the
// same one turf.js's `area()` uses) rather than a flat-plane shoelace,
// since a flat approximation drifts at the scale this app's park-sized
// areas can reach. SI units throughout (m/km, m²/km²) — no imperial toggle.
export class MeasureControl {
  constructor() {
    this._mode = "distance";
    this._active = false;
    this._points = [];
    this._selectedIndex = null; // which vertex Delete/Backspace acts on
    this._draggingIndex = null;
    this._suppressNextClick = false; // a mousedown on a vertex already handled this click; don't also add a new point
  }

  onAdd(map) {
    this._map = map;

    this._container = document.createElement("div");
    this._container.className = "maplibregl-ctrl maplibregl-ctrl-group measure-ctrl";
    this._container.innerHTML = `
      <button type="button" class="measure-ctrl__button" title="Measure" aria-label="Measure">${RULER_ICON}</button>
      <div class="measure-panel" hidden>
        <div class="measure-panel__controls">
          <button type="button" class="measure-panel__mode active" data-mode="distance">Distance</button>
          <button type="button" class="measure-panel__mode" data-mode="area">Area</button>
          <span class="measure-panel__result"></span>
          <button type="button" class="measure-panel__save" title="Save as a note" aria-label="Save as a note" disabled>📍</button>
          <button type="button" class="measure-panel__clear" title="Clear" aria-label="Clear">×</button>
        </div>
      </div>
    `;
    this._button = this._container.querySelector(".measure-ctrl__button");
    this._panel = this._container.querySelector(".measure-panel");
    this._controls = this._container.querySelector(".measure-panel__controls");
    this._result = this._container.querySelector(".measure-panel__result");
    this._saveButton = this._container.querySelector(".measure-panel__save");
    // Same "hide the write-only affordance for a logged-out viewer" story
    // as notes.js's own button not being added at all — Measure itself
    // stays available either way, only saving needs a login.
    if (!isLoggedIn()) this._saveButton.hidden = true;

    this._noteForm = new NoteSaveForm(this._panel, {
      onSaved: () => {
        this._controls.hidden = false;
        this._clear();
      },
      onCancel: () => (this._controls.hidden = false),
    });

    this._button.addEventListener("click", () => this._setActive(!this._active));
    this._panel.querySelectorAll(".measure-panel__mode").forEach((button) => {
      button.addEventListener("click", () => this._setMode(button.dataset.mode));
    });
    this._saveButton.addEventListener("click", () => this._saveAsNote());
    this._panel.querySelector(".measure-panel__clear").addEventListener("click", () => this._clear());

    this._onClick = (event) => {
      if (!this._active || this._noteForm.isOpen) return;
      // A mousedown on an existing vertex (below) already selected/started
      // dragging it — without this, that same click would also land here
      // and add a brand new point right on top of it.
      if (this._suppressNextClick) {
        this._suppressNextClick = false;
        return;
      }
      this._selectedIndex = null;
      this._points.push([event.lngLat.lng, event.lngLat.lat]);
      this._render();
    };
    map.on("click", this._onClick);

    // Vertex drag: mousedown on a point starts it, a map-wide mousemove
    // follows the cursor while dragging, mouseup anywhere ends it — not
    // scoped to the layer since the cursor is very likely to leave the
    // (few-pixel) vertex circle mid-drag. preventDefault on the mousedown
    // is what stops MapLibre's own drag-to-pan from also engaging for the
    // same gesture (its documented way to opt out per-interaction).
    this._onVertexMouseDown = (event) => {
      if (!this._active || this._noteForm.isOpen) return;
      const index = event.features[0]?.properties?.index;
      if (index === undefined) return;
      event.preventDefault();
      this._draggingIndex = index;
      this._selectedIndex = index;
      this._suppressNextClick = true;
      this._map.getCanvas().style.cursor = "grabbing";
      this._render();
    };
    map.on("mousedown", POINT_LAYER_ID, this._onVertexMouseDown);

    this._onMouseMove = (event) => {
      if (this._draggingIndex === null) return;
      this._points[this._draggingIndex] = [event.lngLat.lng, event.lngLat.lat];
      this._render();
    };
    map.on("mousemove", this._onMouseMove);

    this._onMouseUp = () => {
      if (this._draggingIndex === null) return;
      this._draggingIndex = null;
      this._map.getCanvas().style.cursor = this._active ? "crosshair" : "";
    };
    map.on("mouseup", this._onMouseUp);

    map.on("mouseenter", POINT_LAYER_ID, () => {
      if (this._draggingIndex === null) this._map.getCanvas().style.cursor = "grab";
    });
    map.on("mouseleave", POINT_LAYER_ID, () => {
      if (this._draggingIndex === null) this._map.getCanvas().style.cursor = this._active ? "crosshair" : "";
    });

    this._onKeyDown = (event) => {
      if (!this._active || this._selectedIndex === null) return;
      if (event.key !== "Delete" && event.key !== "Backspace") return;
      // Don't eat Backspace while the note-text form (or anything else on
      // the page) actually has focus for typing.
      if (["INPUT", "TEXTAREA"].includes(document.activeElement?.tagName)) return;
      event.preventDefault();
      this._points.splice(this._selectedIndex, 1);
      this._selectedIndex = null;
      this._render();
    };
    document.addEventListener("keydown", this._onKeyDown);

    // setStyle() (switching Online/Offline) tears down all sources/layers —
    // same re-add-on-reload pattern as radar.js/gpx.js.
    map.on("style.load", () => {
      if (this._active) this._addLayers();
    });

    return this._container;
  }

  onRemove() {
    this._map.off("click", this._onClick);
    this._map.off("mousedown", POINT_LAYER_ID, this._onVertexMouseDown);
    this._map.off("mousemove", this._onMouseMove);
    this._map.off("mouseup", this._onMouseUp);
    document.removeEventListener("keydown", this._onKeyDown);
    this._removeLayers();
    this._container.remove();
  }

  getDefaultPosition() {
    return "top-left";
  }

  _setActive(active) {
    this._active = active;
    this._button.classList.toggle("active", active);
    this._panel.hidden = !active;
    this._map.getCanvas().style.cursor = active ? "crosshair" : "";
    if (active) {
      this._addLayers();
    } else {
      this._noteForm.close();
      this._controls.hidden = false;
      this._clear();
    }
  }

  // The same shape _render() draws — a distance line (2+ points) or a
  // closed area polygon (3+ points), or null while there isn't yet enough
  // to measure — extracted so "Save as note" saves exactly what's on
  // screen rather than recomputing it slightly differently.
  _currentShapeGeometry() {
    if (this._mode === "area") {
      return this._points.length >= 3 ? { type: "Polygon", coordinates: [[...this._points, this._points[0]]] } : null;
    }
    return this._points.length >= 2 ? { type: "LineString", coordinates: this._points } : null;
  }

  _saveAsNote() {
    const geometry = this._currentShapeGeometry();
    if (!geometry) return;
    this._controls.hidden = true;
    this._noteForm.open(geometry);
  }

  _setMode(mode) {
    this._mode = mode;
    this._panel.querySelectorAll(".measure-panel__mode").forEach((button) => {
      button.classList.toggle("active", button.dataset.mode === mode);
    });
    this._points = [];
    this._selectedIndex = null;
    this._render();
  }

  _clear() {
    this._points = [];
    this._selectedIndex = null;
    this._draggingIndex = null;
    this._render();
  }

  _addLayers() {
    if (this._map.getSource(SOURCE_ID)) return;

    this._map.addSource(SOURCE_ID, { type: "geojson", data: emptyCollection() });
    this._map.addLayer({
      id: FILL_LAYER_ID,
      type: "fill",
      source: SOURCE_ID,
      filter: ["==", ["geometry-type"], "Polygon"],
      paint: { "fill-color": "#1e5fbf", "fill-opacity": 0.15 },
    });
    this._map.addLayer({
      id: LINE_LAYER_ID,
      type: "line",
      source: SOURCE_ID,
      filter: ["!=", ["geometry-type"], "Point"],
      paint: { "line-color": "#1e5fbf", "line-width": 2 },
    });
    // "role" alone (not also a geometry-type check) — it's only ever set on
    // Point features to begin with (the line/polygon shape feature has no
    // "role" property at all), so it already implies the geometry type.
    // Mixing the legacy "$type" filter syntax with an expression like
    // ["get", "role"] in the same filter logs as unsupported in newer
    // MapLibre — this sidesteps that rather than fixing it by switching
    // "$type" to ["geometry-type"] and keeping both checks.
    this._map.addLayer({
      id: POINT_LAYER_ID,
      type: "circle",
      source: SOURCE_ID,
      filter: ["==", ["get", "role"], "vertex"],
      paint: {
        "circle-radius": ["case", ["get", "selected"], 6, 4],
        "circle-color": ["case", ["get", "selected"], "#ffd43b", "#fff"],
        "circle-stroke-color": "#1e5fbf",
        "circle-stroke-width": 2,
      },
    });
    // Distance mode only (see _render) — each segment's own length, not
    // just the running total, matching how a typical measure tool
    // (Google Maps, QGIS) labels every leg of a multi-point line.
    this._map.addLayer({
      id: SEGMENT_LABEL_LAYER_ID,
      type: "symbol",
      source: SOURCE_ID,
      filter: ["==", ["get", "role"], "segment-label"],
      layout: {
        "text-field": ["get", "label"],
        "text-font": ["Noto Sans Regular"],
        "text-size": 11,
        "text-allow-overlap": true,
      },
      paint: { "text-color": "#1e5fbf", "text-halo-color": "#fff", "text-halo-width": 1.5 },
    });

    this._render();
  }

  _removeLayers() {
    [FILL_LAYER_ID, LINE_LAYER_ID, POINT_LAYER_ID, SEGMENT_LABEL_LAYER_ID].forEach((id) => {
      if (this._map.getLayer(id)) this._map.removeLayer(id);
    });
    if (this._map.getSource(SOURCE_ID)) this._map.removeSource(SOURCE_ID);
  }

  _render() {
    const source = this._map.getSource(SOURCE_ID);
    if (!source) return;

    const pointFeatures = this._points.map((coord, index) => ({
      type: "Feature",
      properties: { role: "vertex", index, selected: index === this._selectedIndex },
      geometry: { type: "Point", coordinates: coord },
    }));
    const geometry = this._currentShapeGeometry();
    const shapeFeature = geometry && { type: "Feature", geometry };
    this._saveButton.disabled = !geometry;
    // Area mode has no equivalent yet — only asked for distance's own
    // per-leg labels, and a polygon's edges read differently (perimeter
    // segments, not a path) if this ever extends there.
    const segmentLabels =
      this._mode === "distance"
        ? this._points.slice(1).map((point, i) => ({
            type: "Feature",
            properties: { role: "segment-label", label: formatDistance(haversine(this._points[i], point)) },
            geometry: { type: "Point", coordinates: midpoint(this._points[i], point) },
          }))
        : [];

    source.setData({
      type: "FeatureCollection",
      features: [...(shapeFeature ? [shapeFeature] : []), ...pointFeatures, ...segmentLabels],
    });

    this._result.textContent = this._mode === "area" ? formatArea(polygonArea(this._points)) : formatDistance(lineLength(this._points));
  }
}

function emptyCollection() {
  return { type: "FeatureCollection", features: [] };
}

function haversine([lng1, lat1], [lng2, lat2]) {
  const rad = Math.PI / 180;
  const dLat = (lat2 - lat1) * rad;
  const dLng = (lng2 - lng1) * rad;
  const a = Math.sin(dLat / 2) ** 2 + Math.cos(lat1 * rad) * Math.cos(lat2 * rad) * Math.sin(dLng / 2) ** 2;
  return 2 * EARTH_RADIUS_M * Math.asin(Math.sqrt(a));
}

function lineLength(points) {
  let total = 0;
  for (let i = 1; i < points.length; i++) total += haversine(points[i - 1], points[i]);
  return total;
}

// A plain coordinate average, not the geodesic midpoint — this only
// positions a text label, and the two differ by nothing worth computing a
// great-circle formula for at the segment lengths this tool measures.
function midpoint([lng1, lat1], [lng2, lat2]) {
  return [(lng1 + lng2) / 2, (lat1 + lat2) / 2];
}

// Spherical polygon area (Chamberlain & Duquette, 2007) — the same formula
// turf.js's area() uses. A flat shoelace formula would drift noticeably at
// the scale a park boundary can reach; this accounts for the sphere.
function polygonArea(points) {
  if (points.length < 3) return 0;
  const rad = (deg) => (deg * Math.PI) / 180;
  let area = 0;
  const n = points.length;
  for (let i = 0; i < n; i++) {
    const [, lat] = points[i];
    const [lng1] = points[(i + n - 1) % n];
    const [lng2] = points[(i + 1) % n];
    area += (rad(lng2) - rad(lng1)) * Math.sin(rad(lat));
  }
  return Math.abs((area * EARTH_RADIUS_M * EARTH_RADIUS_M) / 2);
}

function formatDistance(meters) {
  if (meters === 0) return "";
  return meters >= 1000 ? `${(meters / 1000).toFixed(2)} km` : `${Math.round(meters)} m`;
}

function formatArea(squareMeters) {
  if (squareMeters === 0) return "";
  return squareMeters >= 1e6 ? `${(squareMeters / 1e6).toFixed(2)} km²` : `${Math.round(squareMeters)} m²`;
}