learnharness/components/md-blocks.tsx

"use client";

/**
 * MARKDOWN BLOCKS, MELTED INTO THE MESSAGE (owner wave, 2026-09-19): the
 * boxed streamdown chrome — the double-framed tables (border + sidebar bg +
 * a second inner border + copy/download/fullscreen button rows), the mermaid
 * container (border box + mono label header + action pill + inner border +
 * in-chart zoom buttons), the code header bars — is REPLACED by this
 * component set, wired into Streamdown via its `components` prop:
 *
 * - Tables: a plain PROSE table (no box, no sidebar bg, no buttons bar) —
 *   hairline row rules + a stronger header underline (globals.css), wide
 *   tables scroll inside the column.
 * - Mermaid: the bare chart, part of the message — no label, no container,
 *   no zoom pill (zoom/pan lives in the session-scoped focus overlay now).
 * - Code: streamdown's CodeBlock skeleton keeps the shiki plumbing, but the
 *   container melts (subtle bg tint, no border, no header — globals.css) and
 *   the buttons go.
 * - Display math: untouched visually, but gains the corner copy.
 *
 * THE ONE AFFORDANCE (user-decided): a small muted COPY icon at each block's
 * top-right corner, revealed on hover — copying the SOURCE (table →
 * Markdown, code → text, mermaid → chart source, math → the raw TeX). It
 * never fakes a table column or shifts layout, and hover-reveal keeps the
 * reading surface clean — the whole point of the melt. Text selection stays
 * free: the icon lives in dead corner space. Mermaid additionally gets an
 * EXPAND icon (opens the session overlay) when a chat page is mounted.
 */

import { isValidElement, useEffect, useRef, useState, type ComponentProps, type ReactNode } from "react";
import { CheckIcon, CopyIcon, MaximizeIcon } from "lucide-react";
import { cn } from "@/lib/utils";
import {
	CodeBlock,
	extractTableDataFromElement,
	tableDataToMarkdown,
	useIsCodeFenceIncomplete,
} from "streamdown";
import type { ExtraProps } from "streamdown";
import { MERMAID_FONT_SIZE, renderMermaid } from "@/components/mermaid-render";
import { MermaidError } from "@/components/mermaid-error";
import { chartSize, useSessionMermaid } from "@/components/session-overlay";

// ─── The one affordance: the hover-reveal corner copy ────────────────────────

/** Clipboard write with a fallback: navigator.clipboard needs the
 *  `clipboard-sanitized-write` permission, which Electron's deny-by-default
 *  handler (electron/main.cjs) must grant from the loopback origin — and
 *  browsers with a stale/absent API reject too. The hidden-textarea
 *  execCommand path is the belt under that: a failed write would otherwise
 *  be a silent no-op, which is exactly what the owner saw. Returns whether
 *  the copy landed (drives the Copied pill). */
async function copyText(text: string): Promise<boolean> {
	try {
		await navigator.clipboard.writeText(text);
		return true;
	} catch {
		/* fall through to the legacy path */
	}
	try {
		const ta = document.createElement("textarea");
		ta.value = text;
		ta.setAttribute("readonly", "");
		ta.style.position = "fixed";
		ta.style.opacity = "0";
		document.body.appendChild(ta);
		ta.select();
		const ok = document.execCommand("copy");
		ta.remove();
		return ok;
	} catch {
		return false;
	}
}

/** A small muted copy icon for a block's top-right corner. The CONSUMER'S
 *  wrapper carries `group/md relative` (a NAMED group — the message container
 *  is also a `group`, and an unnamed group-hover would light EVERY corner in
 *  the message at once, the all-at-once the owner saw) and positions this
 *  via className; the icon self-hides until hover (opacity-0 →
 *  group-hover/md:opacity-100). Copies getText() on click; the icon flips
 *  to a check for a beat — enough feedback on its own (a "Copied" pill was
 *  tried and removed by owner ask, 2026-09-19). */
export function CopyCorner({
	getText,
	label,
	className,
}: {
	getText: () => string;
	label: string;
	className?: string;
}) {
	const [copied, setCopied] = useState(false);
	const timerRef = useRef<number | undefined>(undefined);
	useEffect(() => () => window.clearTimeout(timerRef.current), []);
	return (
		<span className={cn("relative inline-flex", className)}>
			<button
				type="button"
				aria-label={label}
				data-testid="md-copy"
				className="flex size-6 items-center justify-center rounded-md text-muted-foreground/70 opacity-0 transition-opacity hover:bg-accent hover:text-foreground focus-visible:opacity-100 group-hover/md:opacity-100"
				onClick={() => {
					void copyText(getText()).then((ok) => {
						if (!ok) return;
						setCopied(true);
						window.clearTimeout(timerRef.current);
						timerRef.current = window.setTimeout(() => setCopied(false), 1500);
					});
				}}
			>
				{copied ? <CheckIcon className="size-3.5" /> : <CopyIcon className="size-3.5" />}
			</button>
		</span>
	);
}

// ─── Code + mermaid fences (the Streamdown `code` override) ──────────────────

/** The fence source from a code element's children — a bare string in the
 *  common case; an element wrapping a string when rehype nests it. Pure. */
export function codeSource(children: ReactNode): string {
	if (typeof children === "string") return children;
	if (typeof children === "number") return String(children);
	if (isValidElement(children)) {
		const inner = (children.props as { children?: ReactNode }).children;
		if (typeof inner === "string") return inner;
	}
	return "";
}

/** Mermaid, in the message flow: the bare chart (dark theme, rendered via
 *  the app's own plugin — components/mermaid-render.ts), the hover corner
 *  with copy + expand, the house error fallback. No container chrome, no
 *  zoom pill — the zoom/pan home is the session overlay. While the fence is
 *  still streaming (the trailing open fence), a quiet skeleton instead of a
 *  doomed parse. */
function MermaidInline({ chart }: { chart: string }) {
	const [svg, setSvg] = useState<string | null>(null);
	const [error, setError] = useState<string | null>(null);
	const [attempt, setAttempt] = useState(0);
	const overlay = useSessionMermaid();
	const incomplete = useIsCodeFenceIncomplete();
	// The font-parity cap (owner rule, 2026-09-19): the house CSS
	// (`max-width: 100% !important`) overrides mermaid's own natural-size cap,
	// so a chart would otherwise stretch to the full column and render its
	// text larger than the session's own text. Cap the holder at the width
	// where the chart's 16px base font lands at the SESSION font (measured
	// live from the wrapper — --lh-prose-size today): a chart may shrink to
	// fit the column, but never blow its text up past the chat's.
	const holderRef = useRef<HTMLDivElement>(null);
	const [capW, setCapW] = useState<number | null>(null);
	useEffect(() => {
		if (!svg || !holderRef.current) return;
		const fs = Number.parseFloat(getComputedStyle(holderRef.current).fontSize);
		if (!Number.isFinite(fs) || fs <= 0) return;
		const { w } = chartSize(svg);
		setCapW((w * fs) / MERMAID_FONT_SIZE);
	}, [svg]);

	useEffect(() => {
		if (incomplete) return;
		let cancelled = false;
		setSvg(null);
		setError(null);
		renderMermaid(chart)
			.then((s) => {
				if (!cancelled) setSvg(s);
			})
			.catch((e) => {
				if (!cancelled) setError(e instanceof Error ? e.message : String(e));
			});
		return () => {
			cancelled = true;
		};
	}, [chart, attempt, incomplete]);

	if (incomplete || (svg === null && error === null)) {
		return (
			<div data-testid="md-mermaid" className="my-4 flex justify-center p-4" aria-busy="true">
				<span className="inline-block size-4 animate-spin rounded-full border border-current border-b-2 text-muted-foreground" />
			</div>
		);
	}
	if (error !== null) {
		return <MermaidError chart={chart} error={error} retry={() => setAttempt((a) => a + 1)} />;
	}
	return (
		// data-streamdown="mermaid" keeps the house CSS hook (the svg
		// max-width rule in globals.css) alive for this app-owned block.
		<div data-testid="md-mermaid" data-streamdown="mermaid" className="group/md relative my-4">
			<div
				ref={holderRef}
				className="mx-auto flex w-full justify-center"
				style={capW === null ? undefined : { maxWidth: `${capW}px` }}
				dangerouslySetInnerHTML={{ __html: svg ?? "" }}
			/>
			<div className="absolute top-0 right-0 flex items-start gap-0.5">
				<CopyCorner getText={() => chart} label="Copy diagram source" />
				{overlay && (
					<button
						type="button"
						aria-label="Expand diagram"
						data-testid="md-mermaid-expand"
						title="Expand into the session view"
						className="flex size-6 items-center justify-center rounded-md text-muted-foreground/70 opacity-0 transition-opacity hover:bg-accent hover:text-foreground group-hover/md:opacity-100"
						onClick={() => overlay.openMermaid(chart)}
					>
						<MaximizeIcon className="size-3.5" />
					</button>
				)}
			</div>
		</div>
	);
}

/** The Streamdown `code` override: inline code passes through with the
 *  house inline classes; block fences split — mermaid renders as the bare
 *  chart above, everything else delegates to streamdown's exported
 *  CodeBlock (shiki highlighting + line numbers preserved) inside a
 *  hover-copy wrapper, with NO children so its sticky button row never
 *  mounts. The container/look is CSS-melted in globals.css
 *  (data-streamdown="code-block"…). */
export function MarkdownCode(props: ComponentProps<"code"> & ExtraProps) {
	const incomplete = useIsCodeFenceIncomplete();
	const { children, className, node, ...rest } = props;

	// Inline code: no data-block (the pre handler stamps block fences only).
	if (!("data-block" in props)) {
		return (
			<code className={cn("rounded bg-muted px-1.5 py-0.5 font-mono text-sm", className)} data-streamdown="inline-code" {...rest}>
				{children}
			</code>
		);
	}

	const language = /language-([^\s]+)/.exec(className ?? "")?.[1] ?? "";
	const meta = (node?.properties?.metastring as string | undefined) ?? "";
	const source = codeSource(children);

	if (language === "mermaid") return <MermaidInline chart={source} />;

	const startMatch = /startLine=(\d+)/.exec(meta);
	const startLine = startMatch ? Number.parseInt(startMatch[1]!, 10) : undefined;
	const lineNumbers = !/\bnoLineNumbers\b/.test(meta);
	return (
		<div className="group/md relative" data-testid="md-code">
			<CopyCorner className="absolute top-1.5 right-2 z-10" getText={() => source} label="Copy code" />
			<CodeBlock
				code={source}
				language={language}
				className={className}
				isIncomplete={incomplete}
				startLine={startLine !== undefined && startLine >= 1 ? startLine : undefined}
				lineNumbers={lineNumbers}
			/>
		</div>
	);
}

// ─── Tables (the Streamdown `table` override) ────────────────────────────────

/** A plain PROSE table: no wrapper box, no button rows — just the table
 *  (streamdown's inner cells keep their padding/typography; the hairline
 *  rules live in globals.css on the data-streamdown attributes) inside a
 *  horizontal-scroller for wide ones, with the corner copy. The copy
 *  serializes the REAL DOM table (the library's own extractor → Markdown). */
export function MarkdownTable(props: ComponentProps<"table"> & ExtraProps) {
	const { children, node, ...rest } = props;
	const ref = useRef<HTMLTableElement>(null);
	return (
		<div className="group/md relative my-4" data-testid="md-table">
			<CopyCorner
				// Contained in the table's top-right corner (owner note, 2026-09-19:
				// the old -top-3 lifted only half the 24px button above the 12px
				// offset, so it straddled the top outline). 4px inset, z above the
				// cells it hovers over; the scroll container stays under it (the
				// corner is fixed to the wrapper, not the scrolling table).
				className="absolute top-1 right-1 z-10"
				label="Copy table"
				getText={() => (ref.current ? tableDataToMarkdown(extractTableDataFromElement(ref.current)) : "")}
			/>
			<div className="overflow-x-auto">
				<table
					ref={ref}
					// No text-sm here — the table text runs at the session prose size
				// (owner note, 2026-09-19: streamdown's cells pin their own text-sm
				// 12.5px; globals.css overrides cells to inherit, so tables match the
				// 16px chat text for a consistent look).
					className="w-full border-collapse"
					data-streamdown="table"
					{...rest}
				>
					{children}
				</table>
			</div>
		</div>
	);
}

// ─── Display math (the Streamdown `span` override) ────────────────────────────

/** KaTeX display equations are wrapped in a SPAN.katex-display (rehype-katex
 *  renders them as spans with display:block CSS — NOT divs; verified in the
 *  static render). They gain the corner copy (the raw TeX — KaTeX embeds it
 *  in the MathML <annotation>; read from the DOM on click, no re-parse).
 *  Every other span passes through untouched. */
export function MathDisplay(props: ComponentProps<"span"> & ExtraProps) {
	const { children, className, node, ...rest } = props;
	const ref = useRef<HTMLSpanElement>(null);
	if (!className?.includes("katex-display")) {
		return (
			<span className={className} {...rest}>
				{children}
			</span>
		);
	}
	return (
		// BLOCK, not inline: the katex-display child is itself display:block
		// (KaTeX's CSS), and an inline wrapper around a block child gets
		// FRAGMENTED by the anonymous-block rules — the absolutely positioned
		// corner then has no clean containing block and pointer events never
		// land on it (owner report: the math corner neither highlights on hover
		// nor copies; everything else works). display:block gives the corner a
		// real box; z-10 keeps it above the equation spans it overlays.
		<span className="group/md relative block z-0" data-testid="md-math">
			<CopyCorner
				className="absolute top-0 right-0 z-10"
				label="Copy equation source"
				getText={() => ref.current?.querySelector("annotation")?.textContent ?? ""}
			/>
			<span ref={ref} className={className} {...rest}>
				{children}
			</span>
		</span>
	);
}

// ─── The stable override set (module identity: Streamdown is memoized) ────────

export const mdComponents = {
	code: MarkdownCode,
	table: MarkdownTable,
	span: MathDisplay,
};