// Measures a rendered page and reports where the layout is wrong.
//
// This function is not run here. It is serialised with toString() and evaluated
// inside the browser by scripts/device-sweep.mjs, so it may use only what a page
// has: no imports, no Node globals, no closure over anything in this file.
//
// It measures rather than guesses. Every box is compared against its nearest
// CLIPPING ancestor instead of document.scrollWidth, which lies the moment any
// container carries overflow-x: hidden or clip — and this site's body does, so
// a page can slice content off its right edge and still report a scrollWidth
// equal to the viewport. That is exactly how the header CTA at iPad portrait
// survived a fix and a release.
//
// It reports eight kinds: clipped, past_viewport, document_scrolls,
// media_overflow, sticky_occluded, active_tab_offscreen, tiny_text and
// touch_target. Each finding carries a severity, a devtools-pasteable selector
// path, and the numbers it was decided on, so a finding can be re-measured
// rather than re-argued.
//
// Provenance: lifted from the Privacy LLC site's scripts/css-qc.mjs, which is
// where the thresholds were argued out and where the comments explaining each
// one were written. Copied rather than shared because the two repositories have
// no common package; if a threshold changes in one, it does not change in the
// other. The driver here differs from that one in a way that matters: css-qc
// declares Playwright device profiles but only ever calls setViewportSize, so
// its deviceScaleFactor, isMobile and hasTouch fields never take effect and it
// is a width sweep wearing a phone's clothes.

export const audit = function audit() {
  const EPS = 1;
  const vw = window.innerWidth;
  const vh = window.innerHeight;
  const findings = [];
  const push = (f) => findings.push(f);

  /** A selector a human can paste into devtools. Short, not unique-at-all-costs. */
  function pathOf(el) {
    const parts = [];
    let node = el;

    while (node && node.nodeType === 1 && parts.length < 4) {
      let part = node.tagName.toLowerCase();

      // `getAttribute`, not `.id`. A <form> containing <input name="id"> has
      // its `id` property clobbered by that input, so `.id` returns an element
      // and the path printed as `form#[object HTMLInputElement]`.
      const id = node.getAttribute("id");

      if (id) {
        parts.unshift(`${part}#${id}`);
        break;
      }

      const cls = (node.getAttribute("class") || "")
        .split(/\s+/)
        .filter((c) => c && !c.includes("[") && !c.includes(":"))
        .slice(0, 2)
        .join(".");

      if (cls) part += `.${cls}`;
      parts.unshift(part);
      node = node.parentElement;
    }

    return parts.join(" > ");
  }

  const text = (el) => (el.textContent || "").trim().replace(/\s+/g, " ").slice(0, 60);

  const els = Array.from(document.body.querySelectorAll("*"));
  const info = new Map();
  const ellipsis = new Set();

  /**
   * Inside a closed disclosure, and therefore not on screen at all.
   *
   * Chrome does not `display: none` a closed `<details>` — it skips the
   * subtree with `content-visibility`, and the descendants keep reporting
   * layout boxes at their unconstrained size. The signature form in the
   * documents table measured 149px wide at x=255 on a 320px screen while the
   * closed `<details>` around it correctly measured 48px. Reporting that is
   * reporting content nobody can see, and it is the third distinct class of
   * false positive this audit had to learn about.
   */
  function inClosedDisclosure(el) {
    const details = el.closest("details:not([open])");

    if (!details) return false;

    const summary = details.querySelector(":scope > summary");

    return !(summary && summary.contains(el));
  }

  for (const el of els) {
    const rect = el.getBoundingClientRect();

    if (rect.width === 0 && rect.height === 0) continue;

    const cs = getComputedStyle(el);

    if (cs.display === "none" || cs.visibility === "hidden") continue;
    if (cs.contentVisibility === "hidden") continue;
    if (inClosedDisclosure(el)) continue;

    info.set(el, { rect, cs });
    if (cs.textOverflow === "ellipsis") ellipsis.add(el);
  }

  /** The nearest ancestor that scrolls horizontally on purpose. */
  function scrollerOf(el) {
    let node = el.parentElement;

    while (node && node !== document.body) {
      const rec = info.get(node);

      if (rec && (rec.cs.overflowX === "auto" || rec.cs.overflowX === "scroll")) return node;
      node = node.parentElement;
    }

    return null;
  }

  /** The nearest ancestor that cuts content off without letting anyone scroll to it. */
  function clipperOf(el) {
    let node = el.parentElement;

    while (node && node !== document.documentElement) {
      const rec = info.get(node);

      if (!rec) { node = node.parentElement; continue; }
      if (rec.cs.overflowX === "auto" || rec.cs.overflowX === "scroll") return null;
      if (rec.cs.overflowX === "hidden" || rec.cs.overflowX === "clip") return node;
      node = node.parentElement;
    }

    return null;
  }

  // --- 1. Content past the right edge of the viewport -----------------------
  //
  // Leaves only: an element that overflows and has no overflowing descendant is
  // the thing that is actually too wide. Reporting its ancestors as well would
  // bury the one line that names the culprit under the whole chain it pushed.
  const overViewport = new Set();

  for (const [el, { rect }] of info) {
    if (rect.right <= vw + EPS && rect.left >= -EPS) continue;
    if (scrollerOf(el)) continue;

    // Contained by something that clips: the reader does not see this past the
    // edge, they see it cut off — which check 2 reports, with the clipper named.
    // Reporting it here as well was the single largest source of noise in the
    // first run: every `truncate` in the admin has a child span whose rect runs
    // off the viewport by design, ellipsis and all.
    const clipper = clipperOf(el);

    if (clipper) {
      const box = info.get(clipper);

      if (box && box.rect.right <= vw + EPS) continue;
    }

    overViewport.add(el);
  }

  for (const el of overViewport) {
    if (Array.from(overViewport).some((other) => other !== el && el.contains(other))) continue;

    const { rect, cs } = info.get(el);

    push({
      kind: "past_viewport",
      severity: "blocking",
      path: pathOf(el),
      text: text(el),
      detail: {
        right: Math.round(rect.right),
        viewport: vw,
        over: Math.round(rect.right - vw),
        width: cs.width,
        minWidth: cs.minWidth,
        whiteSpace: cs.whiteSpace,
        position: cs.position,
      },
      says: `${Math.round(rect.right - vw)}px past the right edge`,
    });
  }

  // --- 2. Content clipped by an ancestor, with no way to scroll to it -------
  const clipped = new Map();

  for (const [el, { rect }] of info) {
    const clipper = clipperOf(el);

    if (!clipper) continue;

    const box = info.get(clipper);

    if (!box) continue;
    if (rect.right <= box.rect.right + EPS && rect.left >= box.rect.left - EPS) continue;
    // A clipper wider than the viewport is already reported by check 1.
    if (box.rect.right > vw + EPS) continue;

    const seen = clipped.get(clipper) || [];

    seen.push({ el, rect });
    clipped.set(clipper, seen);
  }

  for (const [clipper, children] of clipped) {
    const leaves = children.filter(
      ({ el }) => !children.some((other) => other.el !== el && el.contains(other.el)),
    );
    const box = info.get(clipper);
    // Overflow has two sides. Picking the right-most leaf and subtracting made
    // a left-side overflow report as "cut off by -150px", which is not a
    // sentence. Measure how far each leaf escapes in whichever direction it
    // escapes, and rank by that.
    const escape = ({ rect }) =>
      Math.max(0, rect.right - box.rect.right, box.rect.left - rect.left);
    const worst = leaves.reduce((a, b) => (escape(b) > escape(a) ? b : a), leaves[0]);
    const side = worst.rect.right - box.rect.right >= box.rect.left - worst.rect.left ? "right" : "left";

    // `text-overflow: ellipsis` is a container saying "I will cut text off and
    // show that I did". That is an affordance, not silent loss — the reader can
    // see there is more. It stops being one the moment something interactive or
    // replaced is inside, because a button behind an ellipsis is still a button
    // nobody can press.
    const INTERACTIVE = "a[href], button, summary, input, select, textarea, img, video, iframe, [role=button], [role=tab]";
    const carries = ({ el }) =>
      (el.textContent || "").trim().length > 0 || el.matches(INTERACTIVE) || el.querySelector(INTERACTIVE);

    /**
     * A control is only *swallowed* when little enough of it survives the clip
     * to stop being aimable.
     *
     * The first version of this asked whether a control was present at all, and
     * that is too coarse for the commonest shape in the admin: a truncated cell
     * whose text *is* a link. `span.block.truncate > a` reports the anchor's
     * full 189px box against a 144px cell, so the anchor counted as swallowed —
     * while on screen 161px of it is visible, ellipsised, and perfectly
     * clickable. Three blocking findings on the projects board, all of them the
     * repository link reading `null/Privacy-Period-Tr...`, none of them a fault.
     *
     * What the rule is really protecting against is a control the clip puts out
     * of reach, so measure that: how much of it is left inside the box. Below
     * the 24px WCAG floor — or its own width, for a control smaller than that —
     * there is nothing to press and the ellipsis is not an affordance any more.
     */
    const MIN_AIMABLE = 24;
    const controlsIn = (el) => [
      ...(el.matches(INTERACTIVE) ? [el] : []),
      ...el.querySelectorAll(INTERACTIVE),
    ];
    const swallowed = (control) => {
      const rect = control.getBoundingClientRect();
      const visible = Math.min(rect.right, box.rect.right) - Math.max(rect.left, box.rect.left);

      return visible < Math.min(MIN_AIMABLE, rect.width);
    };
    const swallowsControls = leaves.some(({ el }) => controlsIn(el).some(swallowed));

    // Clipping only costs something when something was in it. A decorative
    // element parked outside its box is the technique, not a fault: the hover
    // shimmer on the radar capture button is `absolute inset-0 -translate-x-full`
    // and lives entirely to the left of the button until you hover it, which
    // this reported as "148px past the left edge" at every width for twenty
    // runs. An `aria-hidden` span with no text and no controls has nothing to
    // lose.
    if (!leaves.some(carries)) continue;

    if (ellipsis.has(clipper) && !swallowsControls) continue;

    push({
      kind: "clipped",
      severity: "blocking",
      path: pathOf(clipper),
      text: text(worst.el),
      detail: {
        side,
        clipper: [Math.round(box.rect.left), Math.round(box.rect.right)],
        child: [Math.round(worst.rect.left), Math.round(worst.rect.right)],
        over: Math.round(escape(worst)),
        overflowX: box.cs.overflowX,
        childPath: pathOf(worst.el),
        hiddenChildren: leaves.length,
      },
      says:
        `${leaves.length} element(s) cut off by ${Math.round(escape(worst))}px past the ${side} edge ` +
        `of an overflow-x:${box.cs.overflowX} box — no scrollbar, no hint`,
    });
  }

  // --- 3. The weakest signal, kept for completeness -------------------------
  const doc = document.documentElement;

  if (doc.scrollWidth > doc.clientWidth + EPS) {
    push({
      kind: "document_scrolls",
      severity: "blocking",
      path: "html",
      text: "",
      detail: { scrollWidth: doc.scrollWidth, clientWidth: doc.clientWidth },
      says: `the page itself scrolls sideways by ${doc.scrollWidth - doc.clientWidth}px`,
    });
  }

  // --- 4. Touch targets ------------------------------------------------------
  //
  // 44px is the number both platform guidelines land on. Elements nested inside
  // a larger tappable ancestor are skipped: the ancestor is the target.
  const TAPPABLE = "a[href], button, summary, input, select, textarea, [role=button], [role=tab]";

  for (const el of document.body.querySelectorAll(TAPPABLE)) {
    const rec = info.get(el);

    if (!rec) continue;

    // A control inside a <label> is aimed at through the label, so the label is
    // what gets measured. Skipping it outright — which this did first — means
    // wrapping a 16px checkbox in a label silences the check without making the
    // target any bigger, and the fix for the one real instance of that was
    // exactly such a wrapper. A checker you can satisfy by adding an element is
    // not a checker.
    const label = el.closest("label");
    const measured = label ? info.get(label) : null;
    const rect = measured ? measured.rect : rec.rect;

    if (label && !measured) continue;

    const parent = el.parentElement && el.parentElement.closest(TAPPABLE);

    if (parent) continue;

    // Two rules, because a link and a button are not the same shape of target.
    //
    // A control must be at least **32px thick and 44px long** — not 44x44.
    //
    // 44x44 is WCAG 2.5.5, the AAA figure, and applying it to anything matching
    // `button` produced ninety findings that all said the same thing: the admin
    // renders lists whose rows are controls. A milestone row is 300px wide and
    // 20px tall; taking it to 44 doubles the height of a twenty-item list, and
    // that is a decision about how much the board shows per screen rather than
    // a fix. 2.5.8 (AA) sets the floor at 24.
    //
    // So the rule is about the shape of a finger, not a square: you need
    // thickness in whichever axis is scarce, and length in the other. An icon
    // button is 44x44 and passes on both counts; a list row at 300x32 passes;
    // a row at 300x20 fails on thickness; a 40x40 icon button fails on length,
    // which is what caught `size="icon"` being `size-10`. Decided deliberately,
    // and 32 rather than 24 so there is margin above the AA floor.
    //
    // A text link is judged on height and on its smaller dimension only. The
    // first version demanded 44px in both axes and duly reported "FAQ" — 27px
    // wide, 44px tall, with 24px of gap either side — as a defect on nine
    // routes. Padding a three-letter word out to 44px to satisfy a checker is
    // the checker driving the design. WCAG 2.5.8 sets 24px as the floor and
    // exempts inline links in text for exactly this reason; the axis that is
    // actually scarce in a horizontal nav row is the vertical one.
    //
    // A link inside a sentence is exempt, and this is not a loophole — WCAG
    // 2.5.8 says so in as many words. Its height is the line height of the
    // prose around it; the only way to give it 44px is to break the paragraph.
    // Nine of these were being reported on the FAQ and the legal pages.
    if (el.tagName === "A") {
      const parent = el.parentElement;
      const around = parent ? parent.textContent.trim().length : 0;

      if (around > (el.textContent || "").trim().length + 3) continue;
    }

    const isControl = el.matches("button, summary, input, select, textarea, [role=button]");
    const thickness = Math.min(rect.width, rect.height);
    const length = Math.max(rect.width, rect.height);
    // Row-shaped: twice as wide as it is tall. A list row, not a thing you aim
    // at. This is what separates "the milestone row" from "the icon button",
    // and it has to be measured rather than guessed from the tag, because both
    // are `<button>`.
    // 1.5x, not 2x. A 60x32 link in a dashboard widget is a row by every
    // sensible reading and missed a 2x test by four pixels. "FAQ" at 27x44 is
    // still nowhere near it, which is the case this threshold exists to keep out.
    const rowShaped = rect.width >= rect.height * 1.5;

    let short;
    let narrow;

    if (isControl && rowShaped) {
      // A control that is a row. Thickness is what a thumb needs; the length
      // takes care of itself.
      short = thickness < 32 - EPS;
      narrow = length < 44 - EPS;
    } else if (isControl) {
      // A compact control — an icon button, a checkbox. You aim at a point, so
      // it needs the full 44 in both axes. The 32px relaxation above is for
      // rows and must not leak here: it would accept `size="icon"` back at
      // 40x44, which is the exact defect this caught a few commits ago.
      short = thickness < 44 - EPS;
      narrow = length < 44 - EPS;
    } else if (rowShaped) {
      // A link that is a row obeys the row rule. The docs file list and the
      // dashboard's widget links are links by tag and rows by shape.
      short = rect.height < 32 - EPS;
      narrow = false;
    } else {
      // A link that is a word in a nav. Judged on height, because the vertical
      // axis is the scarce one in a horizontal row, and on 24px of thickness —
      // demanding 32 here would report "FAQ" at 27px wide, which is the
      // checker driving the design again.
      short = rect.height < 44 - EPS;
      narrow = thickness < 24 - EPS;
    }

    if (!short && !narrow) continue;

    push({
      kind: "touch_target",
      severity: "high",
      path: pathOf(el),
      text: text(el),
      detail: { width: Math.round(rect.width), height: Math.round(rect.height) },
      says:
        `${Math.round(rect.width)}x${Math.round(rect.height)}px — ` +
        (short
          ? `thinner than the ${isControl && !rowShaped ? 44 : rowShaped ? 32 : 44}px a touch target needs`
          : `shorter than the ${isControl ? 44 : 24}px minimum`),
    });
  }

  // --- 5. Text too small to read --------------------------------------------
  for (const [el, { cs }] of info) {
    const own = Array.from(el.childNodes).some(
      (n) => n.nodeType === 3 && n.textContent.trim().length > 3,
    );

    if (!own) continue;

    const size = parseFloat(cs.fontSize);

    if (size >= 12 - 0.01) continue;

    // Visually hidden. `sr-only` clips text to a 1px box so a screen reader
    // still reads it and nobody sees it — its font-size is not a legibility
    // question, and 28 of the 87 findings here were the Ripley quote's
    // `sr-only` companion saying the same thing on every admin screen.
    const box = info.get(el).rect;

    if (box.width <= 1 || box.height <= 1) continue;

    // Small uppercase tracked text is a label, not prose.
    //
    // This codebase writes badges, eyebrows and machine values as 10-11px mono
    // uppercase with positive letter-spacing — a deliberate typographic
    // register, used in over two hundred places. Reporting every one of them at
    // "high" produces a list nobody will ever work through, which is how a
    // report stops being read. What actually harms a reader is small *prose*,
    // so that is what this reports. There is no WCAG minimum font size to
    // appeal to here; this is a judgement, and it is written down so the next
    // person can disagree with it on purpose.
    const tracked = parseFloat(cs.letterSpacing) > 0;

    if (cs.textTransform === "uppercase" && tracked) continue;

    push({
      kind: "tiny_text",
      severity: "high",
      path: pathOf(el),
      text: text(el),
      detail: { fontSize: cs.fontSize },
      says: `${cs.fontSize} text`,
    });
  }

  // --- 6. Media wider than the box holding it -------------------------------
  for (const el of document.body.querySelectorAll("img, video, iframe, canvas, svg")) {
    const rec = info.get(el);
    const parent = el.parentElement && info.get(el.parentElement);

    if (!rec || !parent) continue;
    if (rec.rect.width <= parent.rect.width + EPS) continue;

    push({
      kind: "media_overflow",
      severity: "high",
      path: pathOf(el),
      text: el.getAttribute("alt") || el.getAttribute("src") || "",
      detail: {
        mediaWidth: Math.round(rec.rect.width),
        containerWidth: Math.round(parent.rect.width),
      },
      says: `${Math.round(rec.rect.width - parent.rect.width)}px wider than its container`,
    });
  }

  // --- 7. Two sticky boxes fighting over the same edge ----------------------
  //
  // The project header is `sticky top-0 z-20` under a shell bar that is also
  // stuck at 0 with an opaque background and z-40. Nothing errors; the header
  // just slides underneath and is never seen again.
  const sticky = [];

  for (const [el, { cs, rect }] of info) {
    if (cs.position !== "sticky" && cs.position !== "fixed") continue;
    if (cs.top === "auto") continue;
    // A decoration cannot occlude anything: it does not take clicks and it is
    // not what the reader is looking for. The navigation progress bar is
    // `pointer-events-none fixed top-0 z-[100] h-[3px]`, and without this it
    // reported the entire admin header as hidden behind it on all 25 screens.
    if (cs.pointerEvents === "none") continue;
    sticky.push({ el, top: parseFloat(cs.top) || 0, z: parseInt(cs.zIndex, 10) || 0, rect, cs });
  }

  for (const a of sticky) {
    for (const b of sticky) {
      if (a === b || a.el.contains(b.el) || b.el.contains(a.el)) continue;
      if (Math.abs(a.top - b.top) > EPS) continue;
      if (a.z >= b.z) continue;

      // Same offset and behind only matters if the thing in front actually
      // covers it, in both axes.
      //
      // Vertically, a quarter is enough: what a stuck header loses first is its
      // top, which is where its title is. A 50% threshold — the first version
      // of this — let the real case through, because the project header is
      // 294px tall and the bar over it is 132px, so it was "only" 45% hidden.
      //
      // Horizontally is not optional. The admin sidebar is `fixed inset-y-0
      // z-40` and overlaps every sticky header on the page vertically while
      // sitting entirely to their left, which without this reads as the whole
      // admin being permanently occluded by its own navigation.
      const vertical =
        Math.min(a.rect.bottom, b.rect.bottom) - Math.max(a.rect.top, b.rect.top);
      const horizontal =
        Math.min(a.rect.right, b.rect.right) - Math.max(a.rect.left, b.rect.left);

      if (vertical < Math.max(24, a.rect.height * 0.25)) continue;
      if (horizontal < a.rect.width * 0.5) continue;
      // a is behind b at the same offset: a is the one that disappears.
      push({
        kind: "sticky_occluded",
        severity: "high",
        path: pathOf(a.el),
        text: text(a.el),
        detail: { top: a.top, zIndex: a.z, coveredBy: pathOf(b.el), coveredByZ: b.z },
        says: `sticky at top:${a.top}px with z-index ${a.z}, behind another stuck at the same offset with z-index ${b.z}`,
      });
      break;
    }
  }

  // --- 8. The selected tab is scrolled out of sight -------------------------
  for (const el of document.body.querySelectorAll('[aria-selected="true"], [data-state="active"]')) {
    const rec = info.get(el);

    if (!rec) continue;

    const scroller = scrollerOf(el);

    if (!scroller) continue;

    const box = info.get(scroller);

    if (!box) continue;
    if (rec.rect.left >= box.rect.left - EPS && rec.rect.right <= box.rect.right + EPS) continue;

    push({
      kind: "active_tab_offscreen",
      severity: "high",
      path: pathOf(el),
      text: text(el),
      detail: { tabLeft: Math.round(rec.rect.left), visibleFrom: Math.round(box.rect.left), visibleTo: Math.round(box.rect.right) },
      says: "the selected tab is outside the visible part of its scroller, so nothing on screen looks selected",
    });
  }

  // There is no check here for `100vh`.
  //
  // There was, and it could never fire: `getComputedStyle` resolves `100vh` to
  // a pixel value, so nothing in the browser can tell it apart from a height
  // that was written in pixels. A check that cannot fail is worse than no check
  // — it reads as coverage. The rule it was reaching for ("use dvh, because
  // 100vh is the viewport with the mobile URL bar hidden") is a property of the
  // source, so it lives in `tests/responsive-guards.test.ts` where a source
  // grep is the honest instrument.

  return findings;
};