// ── Logic Sections — labelled polygonal areas on the algorithm canvas ────
//
// Users draw labelled polygons (grid-snapped, 0/45/90° edges) to group
// related blocks. Sections sit in #connections behind blocks/links.
//
// Dependencies: dom.js ($id, svgNamespace), draw.js (drawpath), helpers.js
// Load order: after draw.js, before app.js (add toolbar button handler)

/**
 * Internal state for the sections subsystem.
 * @type {{
 *   list: Array<{id:string, points:Array<{x:number,y:number}>, title:string}>,
 *   nextId: number,
 *   creating: boolean,
 *   curPoints: Array<{x:number,y:number}>,
 *   editingId: string|null,
 *   editOverlay: HTMLElement|null,
 *   previewPoly: SVGPolygonElement|null,
 *   previewLine: SVGLineElement|null,
 *   ghostCircles: SVGCircleElement[]
 * }}
 */
const _sec = {
  list: [],
  nextId: 1,
  creating: false,
  curPoints: [],
  editingId: null,
  editOverlay: null,
  previewPoly: null,
  previewLine: null,
  ghostCircles: [],
};

// ── Helpers ────────────────────────────────────────────────────────────

/** @returns {number} The CSS `--grid-size` value, defaulting to 25. */
function _gridSize() {
  const el = document.querySelector("[data-block]");
  if (!el) return 25;
  return parseInt(window.getComputedStyle(el).getPropertyValue("--grid-size")) || 25;
}

/**
 * Snaps a coordinate value to the nearest grid multiple.
 * @param {number} v
 * @returns {number}
 */
function _snap(v) { const g = _gridSize(); return Math.round(v / g) * g; }

/**
 * Constrains a new point to 0°, 45°, or 90° relative to the previous point.
 * @param {{x:number,y:number}} prev
 * @param {{x:number,y:number}} raw
 * @returns {{x:number,y:number}}
 */
function _snapAngle(prev, raw) {
  const dx = raw.x - prev.x, dy = raw.y - prev.y;
  const adx = Math.abs(dx), ady = Math.abs(dy);
  let sx = dx >= 0 ? 1 : -1, sy = dy >= 0 ? 1 : -1;
  if (adx === 0 && ady === 0) return { x: prev.x, y: prev.y };
  if (adx > ady * 2)   return { x: raw.x, y: prev.y };
  if (ady > adx * 2)   return { x: prev.x, y: raw.y };
  const m = Math.max(adx, ady);
  return { x: prev.x + sx * m, y: prev.y + sy * m };
}

/**
 * Converts a mouse event to grid-snapped coordinates relative to #draw-area.
 * @param {MouseEvent} ev
 * @returns {{x:number, y:number}}
 */
function _xy(ev) {
  const area = $id("draw-area");
  if (!area) return { x: 0, y: 0 };
  const r = area.getBoundingClientRect();
  return { x: _snap(ev.clientX - r.left + area.scrollLeft), y: _snap(ev.clientY - r.top + area.scrollTop) };
}

/**
 * Converts absolute page coordinates to SVG-relative coordinates.
 * @param {number} x
 * @param {number} y
 * @returns {{x:number, y:number}}
 */
function _svgPt(x, y) {
  const svg = $id("connections");
  if (!svg) return { x: 0, y: 0 };
  const r = svg.getBoundingClientRect();
  return { x: x - r.left, y: y - r.top };
}

/**
 * Computes the signed area of a polygon via the shoelace formula.
 * Used to reject tiny/collinear sections.
 * @param {Array<{x:number,y:number}>} pts
 * @returns {number}
 */
function _shoelace(pts) {
  if (pts.length < 3) return 0;
  let s = 0;
  for (let i = 0; i < pts.length; i++) {
    const j = (i + 1) % pts.length;
    s += pts[i].x * pts[j].y - pts[j].x * pts[i].y;
  }
  return Math.abs(s) / 2;
}

/**
 * Ray-casting point-in-polygon test.
 * @param {number} px
 * @param {number} py
 * @param {Array<{x:number,y:number}>} pts Polygon vertices in order
 * @returns {boolean}
 */
function _ptInPoly(px, py, pts) {
  let inside = false;
  for (let i = 0, j = pts.length - 1; i < pts.length; j = i++) {
    const xi = pts[i].x, yi = pts[i].y, xj = pts[j].x, yj = pts[j].y;
    if ((yi > py) !== (yj > py) && px < (xj - xi) * (py - yi) / (yj - yi) + xi)
      inside = !inside;
  }
  return inside;
}

/**
 * Checks whether two line segments AB and CD intersect (including endpoints).
 * @param {{x:number,y:number}} a
 * @param {{x:number,y:number}} b
 * @param {{x:number,y:number}} c
 * @param {{x:number,y:number}} d
 * @returns {boolean}
 */
function _segmentsIntersect(a, b, c, d) {
  const det = (b.y - a.y) * (d.x - c.x) - (b.x - a.x) * (d.y - c.y);
  if (Math.abs(det) < 1) return false;
  const t = ((c.y - a.y) * (d.x - c.x) - (c.x - a.x) * (d.y - c.y)) / det;
  const u = ((b.x - a.x) * (c.y - a.y) - (b.y - a.y) * (c.x - a.x)) / det;
  return t >= 0 && t <= 1 && u >= 0 && u <= 1;
}

/**
 * Checks whether a rectangle overlaps a polygon (any edge crossing or
 * one fully containing the other).
 * @param {number} rx Rectangle left
 * @param {number} ry Rectangle top
 * @param {number} rw Rectangle width
 * @param {number} rh Rectangle height
 * @param {Array<{x:number,y:number}>} pts Polygon vertices
 * @returns {boolean}
 */
function _rectPolyOverlap(rx, ry, rw, rh, pts) {
  const corners = [
    { x: rx, y: ry }, { x: rx + rw, y: ry },
    { x: rx + rw, y: ry + rh }, { x: rx, y: ry + rh }
  ];
  for (let i = 0; i < pts.length; i++) {
    const j = (i + 1) % pts.length;
    for (const c of corners) {
      if (_segmentsIntersect(pts[i], pts[j], { x: rx, y: ry }, c)) return true;
    }
  }
  for (let i = 0; i < corners.length; i++) {
    const j = (i + 1) % corners.length;
    for (let k = 0; k < pts.length; k++) {
      const l = (k + 1) % pts.length;
      if (_segmentsIntersect(corners[i], corners[j], pts[k], pts[l])) return true;
    }
  }
  for (const c of corners) { if (_ptInPoly(c.x, c.y, pts)) return true; }
  for (const p of pts) { if (p.x >= rx && p.x <= rx + rw && p.y >= ry && p.y <= ry + rh) return true; }
  return false;
}

/**
 * Converts a points array to an SVG `points` attribute string ("x,y x2,y2 …").
 * @param {Array<{x:number,y:number}>} pts
 * @returns {string}
 */
function _pointsAttr(pts) {
  return pts.map(p => `${p.x},${p.y}`).join(" ");
}

/**
 * Returns the top-left-most point in a polygon (used for label positioning).
 * @param {Array<{x:number,y:number}>} pts
 * @returns {{x:number,y:number}}
 */
function _topLeftOf(pts) {
  if (!pts.length) return { x: 0, y: 0 };
  let tl = pts[0];
  for (const p of pts) { if (p.x < tl.x || (p.x === tl.x && p.y < tl.y)) tl = p; }
  return tl;
}

// ── SVG rendering ──────────────────────────────────────────────────────

/** @returns {SVGGElement|null} The `<g class="sections-group">`, creating it if needed. */
function _ensureSectionGroup() {
  const svg = $id("connections");
  if (!svg) return null;
  let g = svg.querySelector(".sections-group");
  if (!g) {
    g = document.createElementNS(svgNamespace, "g");
    g.classList.add("sections-group");
    svg.insertBefore(g, svg.firstChild);
  }
  return g;
}

/**
 * Renders one section as SVG polygon + text label.
 * @param {{id:string, points:Array<{x:number,y:number}>, title:string}} s
 */
function renderSection(s) {
  const g = _ensureSectionGroup();
  if (!g) return;
  let poly = g.querySelector(`polygon[data-section-id="${s.id}"]`);
  if (!poly) {
    poly = document.createElementNS(svgNamespace, "polygon");
    poly.dataset.sectionId = s.id;
    poly.classList.add("section-bg");
    g.appendChild(poly);
  }
  poly.setAttribute("points", _pointsAttr(s.points));

  let label = g.querySelector(`text[data-section-id="${s.id}"]`);
  if (!label) {
    label = document.createElementNS(svgNamespace, "text");
    label.dataset.sectionId = s.id;
    label.classList.add("section-label");
    label.addEventListener("click", ev => { ev.stopPropagation(); _editTitle(s.id); });
    g.appendChild(label);
  }
  const tl = _topLeftOf(s.points);
  label.setAttribute("x", tl.x + 6);
  label.setAttribute("y", tl.y + 14);
  label.textContent = s.title;
}

/** Removes all SVG elements for a given section ID. @param {string} id */
function _removeSectionEls(id) {
  const g = _ensureSectionGroup();
  if (!g) return;
  for (const el of g.querySelectorAll(`[data-section-id="${id}"]`)) el.remove();
}

/** Re-renders every section from scratch. */
function renderAllSections() {
  const g = _ensureSectionGroup();
  if (g) g.innerHTML = "";
  for (const s of _sec.list) renderSection(s);
}

// ── Create / edit mode overlay ─────────────────────────────────────────

/** Shows the dimming overlay that blocks interaction with blocks/links during section editing. */
function _showOverlay() {
  if (_sec.editOverlay) return;
  const area = $id("draw-area");
  if (!area) return;
  const ov = document.createElement("div");
  ov.className = "section-edit-overlay";
  area.appendChild(ov);
  _sec.editOverlay = ov;
  area.classList.add("section-editing");
}

/** Hides the dimming overlay. */
function _hideOverlay() {
  if (_sec.editOverlay) {
    _sec.editOverlay.remove();
    _sec.editOverlay = null;
  }
  const area = $id("draw-area");
  if (area) area.classList.remove("section-editing");
}

// ── Point placement preview helpers ────────────────────────────────────

/** Removes all preview visuals (polygon, line, ghost circles). */
function _clearPreview() {
  const svg = $id("connections");
  if (!svg) return;
  if (_sec.previewPoly) { _sec.previewPoly.remove(); _sec.previewPoly = null; }
  if (_sec.previewLine) { _sec.previewLine.remove(); _sec.previewLine = null; }
  for (const c of _sec.ghostCircles) c.remove();
  _sec.ghostCircles = [];
}

/**
 * Updates the visual preview during polygon point placement.
 * @param {Array<{x:number,y:number}>} pts Points placed so far
 * @param {{x:number,y:number}|null} mouse Current snapped mouse position
 */
function _updatePreview(pts, mouse) {
  _clearPreview();
  const svg = $id("connections");
  if (!svg) return;
  const g = _ensureSectionGroup();

  if (pts.length >= 3) {
    const poly = document.createElementNS(svgNamespace, "polygon");
    poly.classList.add("section-preview-bg");
    poly.setAttribute("points", _pointsAttr([...pts, pts[0]]));
    g.appendChild(poly);
    _sec.previewPoly = poly;
  }

  if (pts.length > 0 && mouse) {
    const line = document.createElementNS(svgNamespace, "line");
    line.classList.add("section-preview-line");
    line.setAttribute("x1", pts[pts.length - 1].x);
    line.setAttribute("y1", pts[pts.length - 1].y);
    line.setAttribute("x2", mouse.x);
    line.setAttribute("y2", mouse.y);
    g.appendChild(line);
    _sec.previewLine = line;
  }

  for (const p of pts) {
    const circ = document.createElementNS(svgNamespace, "circle");
    circ.classList.add("section-ghost");
    circ.setAttribute("cx", p.x);
    circ.setAttribute("cy", p.y);
    circ.setAttribute("r", 4);
    g.appendChild(circ);
    _sec.ghostCircles.push(circ);
  }
}

// ── Create mode ────────────────────────────────────────────────────────

/** @param {MouseEvent} ev Handles a click during polygon creation (adds point or closes polygon). */
function _onCreateClick(ev) {
  if (!_sec.creating) return;
  const pos = _xy(ev);
  const pts = _sec.curPoints;

  if (pts.length > 0) {
    const snapped = _snapAngle(pts[pts.length - 1], pos);
    if (pts.length >= 3) {
      const first = pts[0];
      if (Math.abs(snapped.x - first.x) < _gridSize() && Math.abs(snapped.y - first.y) < _gridSize()) {
        _finishSection(pts);
        return;
      }
    }
    pts.push(snapped);
  } else {
    pts.push(pos);
  }
  _updatePreview(pts, null);
}

/** @param {MouseEvent} ev Updates the preview line during mouse movement in create mode. */
function _onCreateMove(ev) {
  if (!_sec.creating || _sec.curPoints.length === 0) return;
  const pos = _xy(ev);
  const snapped = _snapAngle(_sec.curPoints[_sec.curPoints.length - 1], pos);
  _updatePreview(_sec.curPoints, snapped);
}

/** @param {MouseEvent} ev Finishes polygon creation on double-click. */
function _onCreateDblClick(ev) {
  if (!_sec.creating) return;
  if (_sec.curPoints.length >= 3) _finishSection(_sec.curPoints);
}

/**
 * Finalises a section from the placed points, adds it to the list, renders it,
 * and exits create mode.
 * @param {Array<{x:number,y:number}>} pts
 */
function _finishSection(pts) {
  if (pts.length < 3) return;
  if (_shoelace(pts) < 100) { _cancelCreate(); return; }
  const id = "section-" + (_sec.nextId++);
  _sec.list.push({ id, points: pts.map(p => ({ x: p.x, y: p.y })), title: "Section" });
  renderSection(_sec.list[_sec.list.length - 1]);
  _exitCreateMode();
  setTimeout(() => _editTitle(id), 100);
}

/** Cancels section creation without saving. */
function _cancelCreate() {
  _exitCreateMode();
}

/** Cleans up all create-mode event listeners and preview elements. */
function _exitCreateMode() {
  _sec.creating = false;
  _sec.curPoints = [];
  _clearPreview();
  _hideOverlay();
  const area = $id("draw-area");
  if (area) {
    area.removeEventListener("click", _onCreateClick);
    area.removeEventListener("mousemove", _onCreateMove);
    area.removeEventListener("dblclick", _onCreateDblClick);
  }
  document.removeEventListener("keydown", _onCreateKey);
}

/** @param {KeyboardEvent} ev Handles Escape (cancel) / Enter (finish) during creation. */
function _onCreateKey(ev) {
  if (!_sec.creating) return;
  if (ev.key === "Escape") _cancelCreate();
  if (ev.key === "Enter" && _sec.curPoints.length >= 3) _finishSection(_sec.curPoints);
}

/** Enters polygon creation mode: sets up event listeners and the dimming overlay. */
function enterCreateMode() {
  if (_sec.creating) return;
  _sec.creating = true;
  _sec.curPoints = [];
  _showOverlay();
  const area = $id("draw-area");
  if (!area) return;
  area.addEventListener("click", _onCreateClick);
  area.addEventListener("mousemove", _onCreateMove);
  area.addEventListener("dblclick", _onCreateDblClick);
  document.addEventListener("keydown", _onCreateKey);
}

// ── Title editing ──────────────────────────────────────────────────────

/**
 * Shows an inline text input (via SVG foreignObject) to edit a section's title.
 * @param {string} id Section ID
 */
function _editTitle(id) {
  const s = _sec.list.find(x => x.id === id);
  if (!s) return;
  _showOverlay();

  const svg = $id("connections");
  if (!svg) return;
  const existing = svg.querySelector(`foreignObject[data-section-id="${id}"]`);
  if (existing) return;

  const tl = _topLeftOf(s.points);
  const fo = document.createElementNS(svgNamespace, "foreignObject");
  fo.dataset.sectionId = id;
  fo.setAttribute("x", tl.x + 4);
  fo.setAttribute("y", tl.y + 2);
  fo.setAttribute("width", "200");
  fo.setAttribute("height", "28");

  const input = document.createElement("input");
  input.className = "section-title-input";
  input.type = "text";
  input.value = s.title;
  input.style.width = "192px";
  input.addEventListener("blur", () => _commitTitle(id, input.value, fo));
  input.addEventListener("keydown", ev => {
    if (ev.key === "Enter") input.blur();
    if (ev.key === "Escape") { _cancelEdit(id); }
  });
  fo.appendChild(input);
  svg.appendChild(fo);
  setTimeout(() => input.focus(), 0);
}

/**
 * Commits an edited section title and removes the editing foreignObject.
 * @param {string} id
 * @param {string} title
 * @param {SVGForeignObjectElement} fo
 */
function _commitTitle(id, title, fo) {
  const s = _sec.list.find(x => x.id === id);
  if (s) {
    s.title = title || "Section";
    renderSection(s);
  }
  if (fo) fo.remove();
  _hideOverlayIfIdle();
}

/**
 * Cancels section title editing without saving.
 * @param {string} id
 */
function _cancelEdit(id) {
  const svg = $id("connections");
  if (svg) {
    const fo = svg.querySelector(`foreignObject[data-section-id="${id}"]`);
    if (fo) fo.remove();
  }
  _hideOverlayIfIdle();
}

/** Hides the overlay if neither creation nor editing is active. */
function _hideOverlayIfIdle() {
  if (!_sec.creating && !_sec.editingId) _hideOverlay();
}

// ── Block border collision ─────────────────────────────────────────────

/**
 * Checks whether a block's bounding rectangle overlaps any section polygon.
 * Called during drag to prevent blocks from sitting on section borders.
 * @param {HTMLElement} block A WCBlock element
 * @returns {boolean}
 */
function blockOnSectionBorder(block) {
  const rx = block.offsetLeft, ry = block.offsetTop;
  const rw = block.offsetWidth, rh = block.offsetHeight;
  if (!rw || !rh) return false;
  for (const s of _sec.list) {
    if (_rectPolyOverlap(rx, ry, rw, rh, s.points)) return true;
  }
  return false;
}

// ── Persistence ────────────────────────────────────────────────────────

/** @returns {Array<{id:string, title:string, points:Array<{x:number,y:number}>}>} */
function saveSections() {
  return _sec.list.map(s => ({
    id: s.id, title: s.title, points: s.points.map(p => ({ x: p.x, y: p.y }))
  }));
}

/**
 * Deserialises and restores sections from saved data.
 * @param {Array<{id?:string, title?:string, points?:Array<{x:number,y:number}>}>} data
 */
function restoreSections(data) {
  if (!Array.isArray(data)) return;
  _sec.list = [];
  for (const s of data) {
    _sec.list.push({ id: s.id || ("section-" + _sec.nextId), title: s.title || "Section", points: s.points || [] });
    _sec.nextId = Math.max(_sec.nextId, (parseInt(s.id.split("-")[1]) || 0) + 1);
  }
  renderAllSections();
}

// ── Selection / deletion (user clicks on section) ──────────────────────

/**
 * Handles a click on a section polygon: selects it, shows draggable vertex handles.
 * @param {MouseEvent} ev
 */
function _onSectionClick(ev) {
  const poly = ev.target.closest(".section-bg");
  if (!poly) return;
  const id = poly.dataset.sectionId;
  if (!id) return;
  ev.stopPropagation();

  for (const el of document.querySelectorAll(".section-bg.selected-section")) el.classList.remove("selected-section");
  poly.classList.add("selected-section");

  _sec.editingId = id;
  const s = _sec.list.find(x => x.id === id);
  if (!s) return;

  _showOverlay();

  const svg = $id("connections");
  if (!svg) return;

  for (let i = 0; i < s.points.length; i++) {
    const p = s.points[i];
    const circ = document.createElementNS(svgNamespace, "circle");
    circ.classList.add("section-handle");
    circ.dataset.sectionId = id;
    circ.dataset.idx = i;
    circ.setAttribute("cx", p.x);
    circ.setAttribute("cy", p.y);
    circ.setAttribute("r", 5);
    const g = _ensureSectionGroup();
    g.appendChild(circ);

    let dragged = false, startX, startY, origPts;
    const down = de => {
      de.stopPropagation();
      dragged = false;
      startX = de.clientX;
      startY = de.clientY;
      origPts = s.points.map(pt => ({ x: pt.x, y: pt.y }));
      document.addEventListener("mousemove", move);
      document.addEventListener("mouseup", up);
    };
    const move = me => {
      dragged = true;
      const curId = circ.dataset.sectionId;
      const sec = _sec.list.find(x => x.id === curId);
      if (!sec) return;
      const idx = parseInt(circ.dataset.idx);
      if (idx < 0 || idx >= sec.points.length) return;
      const prevPt = sec.points[(idx - 1 + sec.points.length) % sec.points.length];
      const newPos = { x: _snap(origPts[idx].x + me.clientX - startX), y: _snap(origPts[idx].y + me.clientY - startY) };
      sec.points[idx] = _snapAngle(prevPt, newPos);
      renderSection(sec);
      circ.setAttribute("cx", sec.points[idx].x);
      circ.setAttribute("cy", sec.points[idx].y);
    };
    const up = () => {
      document.removeEventListener("mousemove", move);
      document.removeEventListener("mouseup", up);
    };
    circ.addEventListener("mousedown", down);
  }
}

/**
 * Deselects a section when clicking outside all section elements.
 * @param {MouseEvent} ev
 */
function _deselectSection(ev) {
  if (ev.target.closest(".section-bg") || ev.target.closest(".section-label") || ev.target.closest(".section-handle") || ev.target.closest(".section-title-input")) return;
  if (_sec.editingId) {
    _sec.editingId = null;
    _hideOverlayIfIdle();
    for (const el of document.querySelectorAll(".section-bg.selected-section")) el.classList.remove("selected-section");
    for (const el of document.querySelectorAll(".section-handle")) el.remove();
  }
}

/** Deletes the currently selected/editing section. */
function deleteSelectedSection() {
  if (!_sec.editingId) return;
  const idx = _sec.list.findIndex(x => x.id === _sec.editingId);
  if (idx < 0) return;
  _sec.list.splice(idx, 1);
  _removeSectionEls(_sec.editingId);
  _sec.editingId = null;
  _hideOverlayIfIdle();
  for (const el of document.querySelectorAll(".section-handle")) el.remove();
}

// ── Initialisation ─────────────────────────────────────────────────────

/** Wires up section-related event listeners (SVG click, document click, delete key). */
function initSections() {
  const svg = $id("connections");
  if (svg) {
    svg.addEventListener("click", _onSectionClick);
    document.addEventListener("click", _deselectSection);
    document.addEventListener("keydown", ev => {
      if (ev.key === "Delete" || ev.key === "Del" || ev.key === "Backspace") {
        if (_sec.editingId && !ev.target.closest("input") && !ev.target.closest("textarea")) {
          ev.preventDefault();
          deleteSelectedSection();
        }
      }
    });
  }
}

// Expose global API
window.LOGIC_SECTIONS = _sec;
window.enterSectionCreateMode = enterCreateMode;
window.saveSections = saveSections;
window.restoreSections = restoreSections;
window.renderAllSections = renderAllSections;
window.blockOnSectionBorder = blockOnSectionBorder;
window.initSections = initSections;

if (document.readyState === "loading") {
  document.addEventListener("DOMContentLoaded", initSections);
} else {
  initSections();
}