// Geometry shared by the on-screen overlay and the pdf-lib writer.
//
// Both need to agree exactly on where an arrowhead's barbs land, where each
// line of a text stamp sits, and how a normalised signature stroke maps into
// its placed box. Keeping that arithmetic in one place is what makes "what I
// drew" and "what got saved" the same picture; two copies of it drift the
// first time either side is touched.
//
// Everything here works in PDF user space: points, origin bottom-left, y up.

/** Approximate ascent as a fraction of font size, for Helvetica. */
export const ASCENT = 0.76;
/** Line advance as a fraction of font size. */
export const LINE_GAP = 1.2;

/**
 * Where each line of a text stamp is drawn. `a.y` is the TOP of the block —
 * that is what the user clicked — so every baseline hangs below it.
 * @returns {{text:string, x:number, y:number}[]} y is the baseline.
 */
export function textLayout(a) {
  const lines = String(a.text ?? "").split("\n");
  const size = a.size || 12;
  return lines.map((text, i) => ({
    text,
    x: a.x,
    y: a.y - size * ASCENT - i * size * LINE_GAP,
  }));
}

/** Height of a text stamp's block, for hit-testing and the selection box. */
export function textBlockHeight(a) {
  const lines = String(a.text ?? "").split("\n").length;
  const size = a.size || 12;
  return size * ASCENT + (lines - 1) * size * LINE_GAP + size * 0.24;
}

/**
 * The two barb points of an arrowhead at (x2,y2) coming from (x1,y1).
 * Head length scales with stroke width but is floored so a thin arrow still
 * reads as an arrow.
 */
export function arrowBarbs(x1, y1, x2, y2, width) {
  const dx = x2 - x1, dy = y2 - y1;
  const len = Math.hypot(dx, dy) || 1;
  const head = Math.max(6, Math.min(len * 0.34, (width || 2) * 4.5));
  const ux = dx / len, uy = dy / len;
  // 24° either side of the shaft.
  const cos = Math.cos(0.42), sin = Math.sin(0.42);
  return [
    { x: x2 - head * (ux * cos - uy * sin), y: y2 - head * (uy * cos + ux * sin) },
    { x: x2 - head * (ux * cos + uy * sin), y: y2 - head * (uy * cos - ux * sin) },
  ];
}

/**
 * A placed signature's strokes in user space. Strokes are stored normalised
 * (0..1, y measured DOWN from the top of the pad) so the same drawing can be
 * dropped at any size, on any page, any number of times.
 */
export function signatureStrokes(a) {
  const { x, y, w, h } = a;
  return (a.strokes || []).map((s) => s.map(([nx, ny]) => [x + nx * w, y + (1 - ny) * h]));
}

/** Normalise a box that may have been dragged right-to-left or bottom-to-top. */
export function normBox(x0, y0, x1, y1) {
  return { x: Math.min(x0, x1), y: Math.min(y0, y1), w: Math.abs(x1 - x0), h: Math.abs(y1 - y0) };
}

/**
 * Where a rule sits inside a line's rectangle, as a fraction of its height
 * from the baseline side. Shared by the renderer and the writer so that what
 * is on screen and what lands in the file are the same picture — two copies of
 * this number is two pictures the first time either is touched.
 */
export const RULE_OFFSET = { underline: 0.06, strikeout: 0.42 };

/** Marks whose geometry is a list of text-line rectangles. */
export const RECT_LIST_KINDS = new Set(["highlight", "underline", "strikeout"]);
/** Marks whose geometry is a single box. */
export const BOX_KINDS = new Set(["rect", "ellipse", "redact", "signature"]);
/** Marks defined by two endpoints. */
export const SEGMENT_KINDS = new Set(["arrow", "line"]);

export function boundsOf(a) {
  if (RECT_LIST_KINDS.has(a.kind)) {
    const rs = a.rects || [];
    if (!rs.length) return { x: 0, y: 0, w: 0, h: 0 };
    const x0 = Math.min(...rs.map((r) => r.x)), y0 = Math.min(...rs.map((r) => r.y));
    const x1 = Math.max(...rs.map((r) => r.x + r.w)), y1 = Math.max(...rs.map((r) => r.y + r.h));
    return { x: x0, y: y0, w: x1 - x0, h: y1 - y0 };
  }
  if (SEGMENT_KINDS.has(a.kind)) return normBox(a.x1, a.y1, a.x2, a.y2);
  switch (a.kind) {
    case "pen": {
      const pts = a.pts || [];
      if (!pts.length) return { x: 0, y: 0, w: 0, h: 0 };
      const xs = pts.map((p) => p[0]), ys = pts.map((p) => p[1]);
      const pad = (a.width || 2) / 2;
      return { x: Math.min(...xs) - pad, y: Math.min(...ys) - pad,
               w: Math.max(...xs) - Math.min(...xs) + pad * 2, h: Math.max(...ys) - Math.min(...ys) + pad * 2 };
    }
    case "text": {
      // Width is unknown without measuring the font; the renderer measures it
      // and caches it on the mark as `_w` so selection boxes are tight.
      return { x: a.x, y: a.y - textBlockHeight(a), w: a._w || (a.size || 12) * 6, h: textBlockHeight(a) };
    }
    default: return { x: a.x, y: a.y, w: a.w, h: a.h };
  }
}

/** Shift a mark by (dx,dy) in user space. Returns the patch, does not mutate. */
export function translatePatch(a, dx, dy) {
  if (RECT_LIST_KINDS.has(a.kind)) {
    return { rects: (a.rects || []).map((r) => ({ ...r, x: r.x + dx, y: r.y + dy })) };
  }
  if (SEGMENT_KINDS.has(a.kind)) {
    return { x1: a.x1 + dx, y1: a.y1 + dy, x2: a.x2 + dx, y2: a.y2 + dy };
  }
  if (a.kind === "pen") return { pts: (a.pts || []).map(([x, y]) => [x + dx, y + dy]) };
  return { x: a.x + dx, y: a.y + dy };
}

// ---- resizing ---------------------------------------------------------
//
// Handles are named by the corner or edge they sit on, in screen terms: "nw"
// is top-left as the reader sees it. User space has y running the other way,
// so "n" moves the box's y + h and "s" moves its y. Keeping the names in
// reader terms means the cursor CSS and the drag maths agree with what the
// user is doing with the mouse.

export const BOX_HANDLES = ["nw", "n", "ne", "e", "se", "s", "sw", "w"];
export const CORNER_HANDLES = ["nw", "ne", "se", "sw"];

/** Smallest box a resize may produce, in points. */
export const MIN_EXTENT = 4;
export const MIN_FONT = 4;
export const MAX_FONT = 288;

/** Which handles a mark offers. Segments get their two endpoints instead. */
export function handlesFor(a) {
  if (SEGMENT_KINDS.has(a.kind)) return ["p1", "p2"];
  if (a.kind === "text") return CORNER_HANDLES;   // uniform scale only
  return BOX_HANDLES;
}

/**
 * The box a drag of `handle` produces, given the mark's current bounds and a
 * user-space delta. Anchors the opposite corner or edge, and never inverts:
 * dragging the top edge past the bottom stops at the minimum rather than
 * flipping the mark over, which is disorienting mid-gesture.
 */
export function resizeBox(b, handle, dx, dy, { uniform = false } = {}) {
  let { x, y, w, h } = b;
  const east = handle.includes("e"), west = handle.includes("w");
  const north = handle.includes("n"), south = handle.includes("s");
  if (uniform && (east || west) && (north || south)) {
    // Corner drag on a uniform mark: one scale factor, taken from whichever
    // axis moved further, so the mark never distorts.
    const sx = (w + (east ? dx : -dx)) / (w || 1);
    const sy = (h + (north ? dy : -dy)) / (h || 1);
    const k = Math.max(MIN_EXTENT / Math.max(w, h, 1), Math.abs(sx) > Math.abs(sy) ? sx : sy);
    const nw = Math.max(MIN_EXTENT, w * k), nh = Math.max(MIN_EXTENT, h * k);
    return {
      x: west ? x + w - nw : x,
      y: south ? y + h - nh : y,
      w: nw, h: nh,
    };
  }
  if (east) w = Math.max(MIN_EXTENT, w + dx);
  if (west) { const nw2 = Math.max(MIN_EXTENT, w - dx); x = x + w - nw2; w = nw2; }
  if (north) h = Math.max(MIN_EXTENT, h + dy);
  if (south) { const nh2 = Math.max(MIN_EXTENT, h - dy); y = y + h - nh2; h = nh2; }
  return { x, y, w, h };
}

/**
 * Map a mark from one bounding box to another. One function for every kind,
 * so a new mark type gets resizing for free as long as boundsOf knows it.
 */
export function scaleToBox(a, from, to) {
  const sx = from.w > 0.001 ? to.w / from.w : 1;
  const sy = from.h > 0.001 ? to.h / from.h : 1;
  const fx = (x) => to.x + (x - from.x) * sx;
  const fy = (y) => to.y + (y - from.y) * sy;

  if (RECT_LIST_KINDS.has(a.kind)) {
    return { rects: (a.rects || []).map((r) => ({ x: fx(r.x), y: fy(r.y), w: r.w * sx, h: r.h * sy })) };
  }
  if (SEGMENT_KINDS.has(a.kind)) {
    return { x1: fx(a.x1), y1: fy(a.y1), x2: fx(a.x2), y2: fy(a.y2) };
  }
  if (a.kind === "pen") {
    return { pts: (a.pts || []).map(([x, y]) => [fx(x), fy(y)]) };
  }
  if (a.kind === "text") {
    // Text scales by font size, not by stretching glyphs. `y` is the top of
    // the block, which is where the new box's top is.
    const size = clampFont((a.size || 12) * (sy || 1));
    return { size, x: to.x, y: to.y + to.h };
  }
  return { x: to.x, y: to.y, w: Math.max(MIN_EXTENT, to.w), h: Math.max(MIN_EXTENT, to.h) };
}

export function clampFont(n) {
  return Math.min(MAX_FONT, Math.max(MIN_FONT, Math.round(n * 10) / 10));
}