app/frontend/src/components/Common/DashboardMosaic.tsx

import { useQuery } from "@tanstack/react-query"
import { Link } from "@tanstack/react-router"
import { LayoutDashboard } from "lucide-react"

import type {
  DashboardDef_Output,
  DashboardSummary,
  Placement,
  WidgetDef,
} from "@/client"
import { dashboardQueryOptions } from "@/components/Dashboard/queries"
import { Skeleton } from "@/components/ui/skeleton"
import { cn } from "@/lib/utils"

/** Columns a dashboard is cut into when its document does not say. */
const DEFAULT_COLUMNS = 12

/**
 * How many tiles are worth a request of their own.
 *
 * ponytail: the list endpoint carries no placements, so a footprint means
 * reading that dashboard's document — cheap for the handful an instance
 * has, and shared with the editor's own cache. The ceiling is an instance
 * with dozens: the tiles past this show their name and nothing else, and the
 * fix would be a stored footprint on `DashboardSummary`.
 */
const PREVIEWS = 8

/** Widgets that draw a shape, and widgets that are controls. The rest read out. */
const GRAPHIC = new Set(["chart", "forecast", "bar", "gauge"])
const INPUT = new Set([
  "button",
  "switch",
  "slider",
  "input",
  "dropdown",
  "color",
])

const shade = (type: string) =>
  INPUT.has(type)
    ? "bg-muted-foreground/30"
    : GRAPHIC.has(type)
      ? "bg-primary/45"
      : "bg-primary/20"

/**
 * Where a widget sits, at the width a panel is arranged for.
 *
 * The same three-line fallback as `Dashboard/DashboardView`, written out again
 * rather than imported: that module pulls the whole dashboard chunk, and this
 * draws a schematic on a screen that shows no dashboards.
 */
const placement = (widget: WidgetDef): Placement => {
  const layout = (widget.layout ?? {}) as Record<string, Placement>
  return layout.lg ?? layout.md ?? layout.sm ?? {}
}

type Block = {
  id: string
  type: string
  x: number
  y: number
  w: number
  h: number
}

/** The dashboard's widgets as one grid. */
function blocksOf(dashboard: DashboardDef_Output): {
  blocks: Block[]
  rows: number
} {
  const blocks: Block[] = []
  let rows = 0
  for (const widget of dashboard.widgets ?? []) {
    const { x = 0, y = 0, w = 3, h = 2 } = placement(widget)
    blocks.push({
      id: widget.id,
      type: widget.type,
      x: Math.max(0, x),
      y: Math.max(0, y),
      w: Math.max(1, w),
      h: Math.max(1, h),
    })
    rows = Math.max(rows, Math.max(0, y) + Math.max(1, h))
  }
  return { blocks, rows: Math.max(1, rows) }
}

/**
 * What a dashboard looks like from across the room: its widgets as blocks,
 * shaded by what kind of thing each one is.
 *
 * A footprint rather than a live render. Nothing here subscribes to a message
 * or reads a value — recognising "the one with the big chart on the left" is
 * the whole job, and it has to cost nothing on a screen that is not the
 * dashboard.
 */
function Footprint({ dashboard }: { dashboard: DashboardDef_Output }) {
  const { blocks, rows } = blocksOf(dashboard)
  const columns = dashboard.columns || DEFAULT_COLUMNS
  // Before the editor could place things, every widget was written at 0,0;
  // honouring that would pile the whole page onto one cell.
  const placed = blocks.some((block) => block.x > 0 || block.y > 0)
  const area = blocks.reduce((sum, block) => sum + block.w * block.h, 0)

  if (blocks.length === 0) {
    return (
      <div className="flex aspect-video items-center justify-center rounded-sm bg-muted">
        <LayoutDashboard className="size-5 text-muted-foreground" />
      </div>
    )
  }

  return (
    <div
      aria-hidden
      className="grid aspect-video gap-0.5 overflow-hidden rounded-sm bg-muted p-1"
      style={{
        gridTemplateColumns: `repeat(${columns}, minmax(0, 1fr))`,
        gridTemplateRows: `repeat(${
          placed ? rows : Math.max(1, Math.ceil(area / columns))
        }, minmax(0, 1fr))`,
      }}
    >
      {blocks.map((block) => {
        const width = Math.min(columns, block.w)
        return (
          <span
            key={block.id}
            className={cn("rounded-[2px]", shade(block.type))}
            style={
              placed
                ? {
                    gridColumn: `${Math.min(columns - width, block.x) + 1} / span ${width}`,
                    gridRow: `${block.y + 1} / span ${block.h}`,
                  }
                : { gridColumn: `span ${width}`, gridRow: `span ${block.h}` }
            }
          />
        )
      })}
    </div>
  )
}

/**
 * One dashboard in the mosaic.
 *
 * Its own query, so the tiles fill in as their documents arrive instead of the
 * whole panel waiting for the slowest of them.
 */
function Tile({
  dashboard,
  preview,
  className,
}: {
  dashboard: DashboardSummary
  /** Read the document for a footprint, or settle for the name alone. */
  preview: boolean
  /** What the layout needs of it — a width, in the scrolling strip. */
  className?: string
}) {
  // The working copy, which is what the list itself is a summary of, so the
  // preview shows what an editor would open rather than the last publish.
  const { data, isPending } = useQuery({
    ...dashboardQueryOptions(dashboard.name, true),
    enabled: preview,
  })

  return (
    <Link
      to="/dashboards/$name"
      params={{ name: dashboard.name }}
      data-testid="home-dashboard-tile"
      className={cn(
        "grid content-start gap-2 rounded-lg border border-border p-2 transition-colors hover:bg-accent/50",
        className,
      )}
    >
      {preview && isPending ? (
        <Skeleton className="aspect-video rounded-sm" />
      ) : data ? (
        <Footprint dashboard={data} />
      ) : (
        <div className="flex aspect-video items-center justify-center rounded-sm bg-muted">
          <LayoutDashboard className="size-5 text-muted-foreground" />
        </div>
      )}
      <span className="flex items-center gap-2">
        <span className="truncate text-sm font-medium">
          {dashboard.title || dashboard.name}
        </span>
        {dashboard.has_draft ? (
          <span className="size-1.5 shrink-0 rounded-full bg-primary">
            <span className="sr-only">Unpublished changes</span>
          </span>
        ) : null}
      </span>
    </Link>
  )
}

/**
 * Which of two documents was worked on more recently.
 *
 * ponytail: neither `FlowSummary` nor `DashboardSummary` carries a modified
 * time, so this reads the two things that come close — an unpublished edit is
 * the one someone has open, and a higher version counter has been saved more
 * often. An `updated_at` on both summaries is what would make it exact.
 */
export function byRecency<
  T extends { name: string; has_draft?: boolean; version?: number },
>(a: T, b: T): number {
  return (
    Number(b.has_draft ?? false) - Number(a.has_draft ?? false) ||
    (b.version ?? 0) - (a.version ?? 0) ||
    a.name.localeCompare(b.name)
  )
}

/**
 * The dashboards, as the shapes they are.
 *
 * Two layouts, because it is read two ways: a column of pairs where it sits
 * beside something else, and one wide strip where it has the page to itself.
 * A tile is `content-start` around an `aspect-video` footprint and so has no
 * width of its own — the strip has to give it one.
 */
export function DashboardMosaic({
  dashboards,
  isPending,
  row = false,
}: {
  dashboards: DashboardSummary[]
  isPending: boolean
  /** One scrolling strip instead of a two-column grid. */
  row?: boolean
}) {
  const container = row
    ? "flex snap-x snap-mandatory gap-3 overflow-x-auto p-3"
    : "grid gap-3 p-3 sm:grid-cols-2"
  const tile = row ? "w-56 shrink-0 snap-start" : ""

  if (isPending) {
    return (
      <div className={container}>
        {Array.from({ length: 2 }).map((_, index) => (
          <Skeleton
            key={index}
            className={cn("aspect-[4/3] rounded-lg", tile)}
          />
        ))}
      </div>
    )
  }

  if (dashboards.length === 0) {
    return (
      <div className="flex flex-col items-center gap-3 px-5 py-10 text-center">
        <span className="flex size-12 items-center justify-center rounded-full bg-muted text-muted-foreground">
          <LayoutDashboard className="size-5" />
        </span>
        <p className="text-sm text-muted-foreground">
          Dashboards you build show up here, as the shapes they are.
        </p>
        <Link to="/dashboards" className="text-sm font-medium underline">
          Go to dashboards
        </Link>
      </div>
    )
  }

  return (
    <div className={container}>
      {dashboards.map((dashboard, index) => (
        <Tile
          key={dashboard.name}
          dashboard={dashboard}
          preview={index < PREVIEWS}
          className={tile}
        />
      ))}
    </div>
  )
}