// Vector cel painting: flat polygons on the frames that get their own drawing.
//
// THIS IS A SKETCH. It exists to test whether the aesthetic holds when a human
// draws the background rather than the tracker deriving it, and it is expected
// to be replaced by a real paint surface with onion skin, undo and a proper
// tool model. Deliberately kept to one module with no dependencies on the rest
// of the pipeline so that throwing it away is a delete rather than a surgery.
//
// The data model is the part worth keeping:
//
//   cel   = Layer[]         index 0 is the BACK of the stack, last is the front
//   Layer = { name, color, pts, hidden }
//
// `color` is a PALETTE INDEX, never an RGB value - the one rule from
// docs/design.md that a paint tool could most easily break. You cannot pick a
// colour here that is not already in the take's ramp.
//
// Points are integers in 320x200 raster space. Snapping is not a convenience:
// sub-pixel vertices on a hard-edged indexed rasteriser move an edge by a whole
// pixel or not at all depending on where the polygon happens to land, so a
// shape nudged by 0.4px shimmers instead of holding still.

export const newCel = () => [];

export const cloneCel = (cel) =>
  (cel || []).map((l) => ({
    name: l.name, color: l.color, hidden: !!l.hidden,
    pts: l.pts.map((p) => ({ x: p.x, y: p.y })),
  }));

// Fill every visible layer back to front. Same rasteriser the derived parts
// use, so a painted shape and a traced one cannot look different.
export function drawCel(raster, cel, idxOf) {
  if (!cel) return;
  for (const l of cel) {
    if (l.hidden || l.pts.length < 3) continue;
    raster.fillPoly(l.pts, idxOf(l.color));
  }
}

const pointInPoly = (pts, x, y) => {
  let inside = false;
  for (let i = 0, j = pts.length - 1; i < pts.length; j = i++) {
    if ((pts[i].y > y) !== (pts[j].y > y) &&
        x < ((pts[j].x - pts[i].x) * (y - pts[i].y)) / (pts[j].y - pts[i].y) + pts[i].x) inside = !inside;
  }
  return inside;
};

// Distance from p to segment ab, and where along it the foot falls.
function segDist(p, a, b) {
  const vx = b.x - a.x, vy = b.y - a.y;
  const len = vx * vx + vy * vy;
  const t = len ? Math.max(0, Math.min(1, ((p.x - a.x) * vx + (p.y - a.y) * vy) / len)) : 0;
  const cx = a.x + t * vx, cy = a.y + t * vy;
  return { d: Math.hypot(p.x - cx, p.y - cy), t };
}

export class PaintUI {
  constructor(opts) {
    this.canvas = opts.canvas;        // where the cel is drawn and edited
    this.list = opts.list;            // layer stack DOM host
    this.info = opts.info;            // status line
    this.zoom = opts.zoom || 3;
    this.RW = opts.RW; this.RH = opts.RH;
    this.palette = opts.palette;      // [{name,hex}], index is the colour
    this.getCel = opts.getCel;        // () => Layer[]  for the frame being edited
    this.setCel = opts.setCel;        // (Layer[]) => void
    this.celAt = opts.celAt;          // (frame) => Layer[]  for drag-to-seed
    this.backing = opts.backing;      // (canvas, zoom) => void, paints what is under
    this.onChange = opts.onChange;    // commit + redraw everything else

    this.tool = 'pen';
    this.color = 1;
    this.sel = -1;                    // selected layer index
    this.draft = null;                // in-progress pen path
    this.drag = null;

    this.bind();
  }

  /* ---- geometry ---- */

  at(ev) {
    const r = this.canvas.getBoundingClientRect();
    // Snap to the raster grid. See the note at the top of the file.
    return {
      x: Math.round(((ev.clientX - r.left) / r.width) * this.RW),
      y: Math.round(((ev.clientY - r.top) / r.height) * this.RH),
    };
  }

  hit(p) {
    const cel = this.getCel();
    const near = 3;
    // Vertices of the SELECTED layer win over everything, so a vertex sitting
    // under another shape stays grabbable instead of selecting the shape on top.
    if (this.sel >= 0 && cel[this.sel]) {
      const pts = cel[this.sel].pts;
      for (let i = 0; i < pts.length; i++) {
        if (Math.hypot(pts[i].x - p.x, pts[i].y - p.y) <= near) return { layer: this.sel, vertex: i };
      }
      for (let i = 0; i < pts.length; i++) {
        const s = segDist(p, pts[i], pts[(i + 1) % pts.length]);
        if (s.d <= near / 2) return { layer: this.sel, edge: i };
      }
    }
    // Then shapes, front to back, so clicking picks what you can see.
    for (let i = cel.length - 1; i >= 0; i--) {
      if (!cel[i].hidden && cel[i].pts.length >= 3 && pointInPoly(cel[i].pts, p.x, p.y)) {
        return { layer: i };
      }
    }
    return null;
  }

  /* ---- editing ---- */

  commit() { this.onChange(); this.render(); }

  addLayer(pts) {
    const cel = this.getCel().slice();
    cel.push({ name: `shape ${cel.length + 1}`, color: this.color, hidden: false, pts });
    this.setCel(cel);
    this.sel = cel.length - 1;
    this.commit();
  }

  mutate(fn) {
    const cel = cloneCel(this.getCel());
    fn(cel);
    this.setCel(cel);
    this.commit();
  }

  move(from, to) {
    if (to < 0 || to >= this.getCel().length) return;
    this.mutate((cel) => { cel.splice(to, 0, cel.splice(from, 1)[0]); });
    this.sel = to;
    this.render();
  }

  bind() {
    const c = this.canvas;

    c.addEventListener('mousedown', (ev) => {
      ev.preventDefault();
      const p = this.at(ev);

      if (this.tool === 'pen') {
        if (!this.draft) { this.draft = [p]; this.render(); return; }
        const first = this.draft[0];
        // Closing on the first point is how you finish; three points minimum,
        // because a two-point "polygon" fills nothing and looks like a bug.
        if (this.draft.length >= 3 && Math.hypot(first.x - p.x, first.y - p.y) <= 3) {
          const pts = this.draft; this.draft = null; this.addLayer(pts); return;
        }
        this.draft.push(p); this.render(); return;
      }

      const h = this.hit(p);
      if (!h) { this.sel = -1; this.render(); return; }
      this.sel = h.layer;

      if (h.vertex !== undefined) {
        if (ev.altKey) {
          // Never below a triangle.
          if (this.getCel()[h.layer].pts.length > 3) {
            this.mutate((cel) => cel[h.layer].pts.splice(h.vertex, 1));
          }
          return;
        }
        this.drag = { kind: 'vertex', layer: h.layer, vertex: h.vertex };
        this.render(); return;
      }
      if (h.edge !== undefined && ev.shiftKey) {
        this.mutate((cel) => cel[h.layer].pts.splice(h.edge + 1, 0, { x: p.x, y: p.y }));
        this.drag = { kind: 'vertex', layer: h.layer, vertex: h.edge + 1 };
        return;
      }
      this.drag = { kind: 'shape', layer: h.layer, from: p };
      this.render();
    });

    window.addEventListener('mousemove', (ev) => {
      if (!this.drag) return;
      const p = this.at(ev);
      const d = this.drag;
      const cel = this.getCel();
      if (d.kind === 'vertex') {
        const v = cel[d.layer].pts[d.vertex];
        if (v.x === p.x && v.y === p.y) return;
        v.x = p.x; v.y = p.y;
      } else {
        const dx = p.x - d.from.x, dy = p.y - d.from.y;
        if (!dx && !dy) return;
        for (const q of cel[d.layer].pts) { q.x += dx; q.y += dy; }
        d.from = p;
      }
      this.render();
    });

    window.addEventListener('mouseup', () => {
      if (!this.drag) return;
      this.drag = null;
      this.commit();
    });

    c.addEventListener('dblclick', (ev) => {
      ev.preventDefault();
      if (this.tool === 'pen' && this.draft && this.draft.length >= 3) {
        const pts = this.draft; this.draft = null; this.addLayer(pts);
      }
    });

    // Seed from another frame: drag a strip thumbnail onto the canvas and take
    // a copy of whatever that frame is showing, every layer. Copy, never
    // reference - two cels sharing a layer object would edit each other and the
    // reason would be invisible.
    c.addEventListener('dragover', (ev) => { ev.preventDefault(); c.classList.add('drop'); });
    c.addEventListener('dragleave', () => c.classList.remove('drop'));
    c.addEventListener('drop', (ev) => {
      ev.preventDefault();
      c.classList.remove('drop');
      const f = +ev.dataTransfer.getData('text/plain');
      if (!Number.isFinite(f)) return;
      const src = this.celAt(f);
      if (!src || !src.length) { this.say(`f${f} has nothing to copy`); return; }
      this.setCel(cloneCel(src));
      this.sel = -1;
      this.commit();
      this.say(`seeded from f${f} — ${src.length} layers`);
    });

    window.addEventListener('keydown', (ev) => {
      if (ev.target.tagName === 'INPUT' || ev.target.tagName === 'SELECT') return;
      if (!this.focused) return;
      if (ev.key === 'Escape' && this.draft) { this.draft = null; this.render(); ev.preventDefault(); }
      else if (ev.key === 'Enter' && this.draft && this.draft.length >= 3) {
        const pts = this.draft; this.draft = null; this.addLayer(pts); ev.preventDefault();
      } else if (ev.key === 'Backspace' && this.draft) {
        this.draft.pop(); if (!this.draft.length) this.draft = null;
        this.render(); ev.preventDefault();
      } else if ((ev.key === 'Delete' || ev.key === 'Backspace') && this.sel >= 0) {
        this.mutate((cel) => cel.splice(this.sel, 1));
        this.sel = -1; ev.preventDefault();
      }
    });

    // The paint canvas takes the keyboard only while the pointer is over it, so
    // the main window's frame stepping keeps working everywhere else.
    c.addEventListener('mouseenter', () => { this.focused = true; });
    c.addEventListener('mouseleave', () => { this.focused = false; });
  }

  say(msg) { if (this.info) this.info.textContent = msg; }

  /* ---- drawing ---- */

  render() {
    const z = this.zoom, c = this.canvas;
    this.backing(c, z);                       // the composited frame, cels included
    const g = c.getContext('2d');

    const cel = this.getCel();
    g.lineWidth = 1;
    cel.forEach((l, i) => {
      if (l.pts.length < 2) return;
      const on = i === this.sel;
      // Unselected outlines stay faint: they are there so you can find a shape
      // to click, not so you can read them.
      g.strokeStyle = l.hidden ? '#f8717166' : (on ? '#fbbf24' : '#ffffff33');
      g.beginPath();
      l.pts.forEach((p, k) => (k ? g.lineTo(p.x * z, p.y * z) : g.moveTo(p.x * z, p.y * z)));
      g.closePath(); g.stroke();
      if (!on) return;
      g.fillStyle = '#fbbf24';
      for (const p of l.pts) g.fillRect(p.x * z - 2, p.y * z - 2, 5, 5);
    });

    if (this.draft) {
      g.strokeStyle = '#4ade80';
      g.beginPath();
      this.draft.forEach((p, k) => (k ? g.lineTo(p.x * z, p.y * z) : g.moveTo(p.x * z, p.y * z)));
      g.stroke();
      g.fillStyle = '#4ade80';
      for (const p of this.draft) g.fillRect(p.x * z - 2, p.y * z - 2, 5, 5);
      // The closing target, so "click here to finish" is visible rather than
      // something you have to know.
      if (this.draft.length >= 3) {
        g.strokeStyle = '#4ade80';
        g.strokeRect(this.draft[0].x * z - 4, this.draft[0].y * z - 4, 9, 9);
      }
    }
    this.renderList();
  }

  renderList() {
    const cel = this.getCel();
    this.list.innerHTML = '';
    // Top of the list is the FRONT of the stack, the way a layers panel reads.
    for (let i = cel.length - 1; i >= 0; i--) {
      const l = cel[i];
      const row = document.createElement('div');
      row.className = 'lay' + (i === this.sel ? ' sel' : '');

      const sw = document.createElement('select');
      this.palette.forEach((p, k) => {
        const o = document.createElement('option');
        o.value = k; o.textContent = p.name;
        sw.append(o);
      });
      sw.value = l.color;
      sw.onchange = () => this.mutate((cc) => { cc[i].color = +sw.value; });

      const chip = document.createElement('i');
      chip.style.background = this.palette[l.color] ? this.palette[l.color].hex : '#f0f';

      const nm = document.createElement('b');
      nm.textContent = l.name;
      nm.onclick = () => { this.sel = i; this.render(); };

      const btn = (txt, title, fn) => {
        const b = document.createElement('button');
        b.textContent = txt; b.title = title;
        b.onclick = (e) => { e.stopPropagation(); fn(); };
        return b;
      };

      row.append(chip, sw, nm,
        btn('↑', 'forward', () => this.move(i, i + 1)),
        btn('↓', 'back', () => this.move(i, i - 1)),
        btn(l.hidden ? '◻' : '◼', 'show/hide', () => this.mutate((cc) => { cc[i].hidden = !cc[i].hidden; })),
        btn('✕', 'delete', () => { this.mutate((cc) => cc.splice(i, 1)); this.sel = -1; }));
      row.onclick = () => { this.sel = i; this.render(); };
      this.list.append(row);
    }
    if (!cel.length) {
      const e = document.createElement('div');
      e.className = 'legend';
      e.textContent = 'no layers — draw with the pen, or drag a frame here to copy its drawing';
      this.list.append(e);
    }
  }
}