src/app/compare/loading.tsx

import {
  Skeleton,
  SkeletonTable,
  SkeletonText,
} from "@/components/ui/LoadingSkeleton";

/* Route-level loading state for /compare — mirrors the page's structure
   (heading + dataset chips, Pareto canvas, head-to-head card, efficiency
   canvas) so content streams in without layout shift. Server-safe: all
   shimmer comes from the .skeleton class, which collapses to a static
   block under prefers-reduced-motion. */

function HeadingSkeleton({ titleWidth = 320 }: { titleWidth?: number }) {
  return (
    <div className="hairline-b flex flex-col gap-3 pb-6">
      <Skeleton className="h-3" width={130} />
      <Skeleton className="h-9" width={titleWidth} />
      <SkeletonText className="max-w-2xl" lines={2} lastLineWidth="45%" />
    </div>
  );
}

function ChartCardSkeleton({ height }: { height: number }) {
  return (
    <div className="glass depth-2 rounded-sm p-5">
      {/* control row: legend chips left, toggle right */}
      <div className="flex flex-wrap items-center justify-between gap-3">
        <div className="flex flex-wrap items-center gap-4">
          {[72, 96, 64, 88].map((w, i) => (
            <Skeleton key={i} className="h-3" width={w} />
          ))}
        </div>
        <Skeleton className="h-7" width={140} />
      </div>
      {/* chart canvas */}
      <Skeleton className="mt-4 w-full" height={height} />
      {/* caption */}
      <div className="hairline-t mt-4 pt-3">
        <Skeleton className="h-3.5" width="70%" />
      </div>
    </div>
  );
}

export default function CompareLoading() {
  return (
    <div
      aria-busy="true"
      aria-label="Loading model comparison"
      className="flex flex-col gap-12 md:gap-16"
    >
      {/* 02 · Compare heading + dataset-scope chips */}
      <div className="flex flex-col gap-5">
        <HeadingSkeleton titleWidth={340} />
        <div className="flex flex-wrap items-center gap-2">
          <Skeleton className="h-3" width={96} />
          {[88, 76, 112].map((w, i) => (
            <Skeleton key={i} className="h-6 rounded-sm" width={w} />
          ))}
        </div>
      </div>

      {/* pulse line strip */}
      <Skeleton className="h-6 w-full" />

      {/* Pareto frontier card */}
      <ChartCardSkeleton height={440} />

      {/* 02.1 · Head-to-head */}
      <HeadingSkeleton titleWidth={300} />
      <div className="glass depth-2 rounded-sm p-5">
        {/* three model selectors */}
        <div className="flex flex-wrap items-end gap-4">
          {[0, 1, 2].map((i) => (
            <div key={i} className="flex min-w-52 flex-1 flex-col gap-1.5">
              <Skeleton className="h-3" width="45%" />
              <Skeleton className="h-9 w-full" />
            </div>
          ))}
        </div>
        {/* delta table */}
        <SkeletonTable className="mt-5" rows={6} columns={4} />
        {/* profile bars */}
        <div className="mt-5 grid gap-x-10 gap-y-5 sm:grid-cols-2">
          {[0, 1, 2, 3].map((i) => (
            <div key={i} className="flex flex-col gap-2">
              <Skeleton className="h-3" width="35%" />
              <Skeleton className="h-1.5 w-full" />
              <Skeleton className="h-1.5 w-4/5" />
            </div>
          ))}
        </div>
      </div>

      {/* 02.2 · Efficiency */}
      <HeadingSkeleton titleWidth={360} />
      <ChartCardSkeleton height={360} />
    </div>
  );
}