learnharness/components/ai-elements/message.tsx

"use client";

import { Button } from "@/components/ui/button";
import {
  ButtonGroup,
  ButtonGroupText,
} from "@/components/ui/button-group";
import {
  Tooltip,
  TooltipContent,
  TooltipProvider,
  TooltipTrigger,
} from "@/components/ui/tooltip";
import { cn } from "@/lib/utils";
import { cjk } from "@streamdown/cjk";
import { code } from "@streamdown/code";
import { createMathPlugin } from "@streamdown/math";

import { ChevronLeftIcon, ChevronRightIcon } from "lucide-react";
import type { ComponentProps, HTMLAttributes, ReactElement } from "react";
import type { LhViewMessage } from "@/src/core";
import {
  createContext,
  memo,
  useCallback,
  useContext,
  useEffect,
  useMemo,
  useState,
} from "react";
import remarkBreaks from "remark-breaks";
import {
  Streamdown,
  type PluginConfig,
} from "streamdown";
import { mdComponents } from "@/components/md-blocks";
import { transformMathDelimiters } from "@/src/core";

export type MessageProps = HTMLAttributes<HTMLDivElement> & {
  from: LhViewMessage["role"];
};

export const Message = ({ className, from, ...props }: MessageProps) => (
  <div
    className={cn(
      "group flex w-full max-w-[95%] flex-col gap-2",
      from === "user" ? "is-user ml-auto justify-end" : "is-assistant",
      className
    )}
    {...props}
  />
);

export type MessageContentProps = HTMLAttributes<HTMLDivElement>;

export const MessageContent = ({
  children,
  className,
  ...props
}: MessageContentProps) => (
  <div
    className={cn(
      "is-user:dark flex w-fit min-w-0 max-w-full flex-col gap-2 overflow-hidden text-sm",
      "group-[.is-user]:ml-auto group-[.is-user]:rounded-lg group-[.is-user]:bg-secondary group-[.is-user]:px-4 group-[.is-user]:py-3 group-[.is-user]:text-foreground",
      "group-[.is-assistant]:text-foreground",
      className
    )}
    {...props}
  >
    {children}
  </div>
);

export type MessageActionsProps = ComponentProps<"div">;

export const MessageActions = ({
  className,
  children,
  ...props
}: MessageActionsProps) => (
  <div className={cn("flex items-center gap-1", className)} {...props}>
    {children}
  </div>
);

export type MessageActionProps = ComponentProps<typeof Button> & {
  tooltip?: string;
  label?: string;
};

export const MessageAction = ({
  tooltip,
  children,
  label,
  variant = "ghost",
  size = "icon-sm",
  ...props
}: MessageActionProps) => {
  const button = (
    <Button size={size} type="button" variant={variant} {...props}>
      {children}
      <span className="sr-only">{label || tooltip}</span>
    </Button>
  );

  if (tooltip) {
    return (
      <TooltipProvider>
        <Tooltip>
          <TooltipTrigger asChild>{button}</TooltipTrigger>
          <TooltipContent>
            <p>{tooltip}</p>
          </TooltipContent>
        </Tooltip>
      </TooltipProvider>
    );
  }

  return button;
};

interface MessageBranchContextType {
  currentBranch: number;
  totalBranches: number;
  goToPrevious: () => void;
  goToNext: () => void;
  branches: ReactElement[];
  setBranches: (branches: ReactElement[]) => void;
}

const MessageBranchContext = createContext<MessageBranchContextType | null>(
  null
);

const useMessageBranch = () => {
  const context = useContext(MessageBranchContext);

  if (!context) {
    throw new Error(
      "MessageBranch components must be used within MessageBranch"
    );
  }

  return context;
};

export type MessageBranchProps = HTMLAttributes<HTMLDivElement> & {
  defaultBranch?: number;
  onBranchChange?: (branchIndex: number) => void;
};

export const MessageBranch = ({
  defaultBranch = 0,
  onBranchChange,
  className,
  ...props
}: MessageBranchProps) => {
  const [currentBranch, setCurrentBranch] = useState(defaultBranch);
  const [branches, setBranches] = useState<ReactElement[]>([]);

  const handleBranchChange = useCallback(
    (newBranch: number) => {
      setCurrentBranch(newBranch);
      onBranchChange?.(newBranch);
    },
    [onBranchChange]
  );

  const goToPrevious = useCallback(() => {
    const newBranch =
      currentBranch > 0 ? currentBranch - 1 : branches.length - 1;
    handleBranchChange(newBranch);
  }, [currentBranch, branches.length, handleBranchChange]);

  const goToNext = useCallback(() => {
    const newBranch =
      currentBranch < branches.length - 1 ? currentBranch + 1 : 0;
    handleBranchChange(newBranch);
  }, [currentBranch, branches.length, handleBranchChange]);

  const contextValue = useMemo<MessageBranchContextType>(
    () => ({
      branches,
      currentBranch,
      goToNext,
      goToPrevious,
      setBranches,
      totalBranches: branches.length,
    }),
    [branches, currentBranch, goToNext, goToPrevious]
  );

  return (
    <MessageBranchContext.Provider value={contextValue}>
      <div
        className={cn("grid w-full gap-2 [&>div]:pb-0", className)}
        {...props}
      />
    </MessageBranchContext.Provider>
  );
};

export type MessageBranchContentProps = HTMLAttributes<HTMLDivElement>;

export const MessageBranchContent = ({
  children,
  ...props
}: MessageBranchContentProps) => {
  const { currentBranch, setBranches, branches } = useMessageBranch();
  const childrenArray = useMemo(
    () => (Array.isArray(children) ? children : [children]),
    [children]
  );

  // Use useEffect to update branches when they change
  useEffect(() => {
    if (branches.length !== childrenArray.length) {
      setBranches(childrenArray);
    }
  }, [childrenArray, branches, setBranches]);

  return childrenArray.map((branch, index) => (
    <div
      className={cn(
        "grid gap-2 overflow-hidden [&>div]:pb-0",
        index === currentBranch ? "block" : "hidden"
      )}
      key={branch.key}
      {...props}
    >
      {branch}
    </div>
  ));
};

export type MessageBranchSelectorProps = ComponentProps<typeof ButtonGroup>;

export const MessageBranchSelector = ({
  className,
  ...props
}: MessageBranchSelectorProps) => {
  const { totalBranches } = useMessageBranch();

  // Don't render if there's only one branch
  if (totalBranches <= 1) {
    return null;
  }

  return (
    <ButtonGroup
      className={cn(
        "[&>*:not(:first-child)]:rounded-l-md [&>*:not(:last-child)]:rounded-r-md",
        className
      )}
      orientation="horizontal"
      {...props}
    />
  );
};

export type MessageBranchPreviousProps = ComponentProps<typeof Button>;

export const MessageBranchPrevious = ({
  children,
  ...props
}: MessageBranchPreviousProps) => {
  const { goToPrevious, totalBranches } = useMessageBranch();

  return (
    <Button
      aria-label="Previous branch"
      disabled={totalBranches <= 1}
      onClick={goToPrevious}
      size="icon-sm"
      type="button"
      variant="ghost"
      {...props}
    >
      {children ?? <ChevronLeftIcon size={14} />}
    </Button>
  );
};

export type MessageBranchNextProps = ComponentProps<typeof Button>;

export const MessageBranchNext = ({
  children,
  ...props
}: MessageBranchNextProps) => {
  const { goToNext, totalBranches } = useMessageBranch();

  return (
    <Button
      aria-label="Next branch"
      disabled={totalBranches <= 1}
      onClick={goToNext}
      size="icon-sm"
      type="button"
      variant="ghost"
      {...props}
    >
      {children ?? <ChevronRightIcon size={14} />}
    </Button>
  );
};

export type MessageBranchPageProps = HTMLAttributes<HTMLSpanElement>;

export const MessageBranchPage = ({
  className,
  ...props
}: MessageBranchPageProps) => {
  const { currentBranch, totalBranches } = useMessageBranch();

  return (
    <ButtonGroupText
      className={cn(
        "border-none bg-transparent text-muted-foreground shadow-none",
        className
      )}
      {...props}
    >
      {currentBranch + 1} of {totalBranches}
    </ButtonGroupText>
  );
};

export type MessageResponseProps = ComponentProps<typeof Streamdown>;

// Type-only version skew: @streamdown/code bundles shiki@3 types while
// streamdown@2.5 expects shiki@4 types. Both work at runtime (each ships its
// own highlighter); the cast papers over the .d.ts mismatch.
//
// singleDollarTextMath: false — a bare $ is ALWAYS literal currency (the
// teacher-prompt contract). Inline math arrives as \(...\) and display math
// as \[...\]; transformMathDelimiters (below) rewrites both to the
// two-dollar forms remark-math still parses. $ can never start math.
//
// remark-breaks rides in the cjk plugin's remarkPluginsAfter slot (public
// PluginConfig API): Streamdown's bare `remarkPlugins` PROP would REPLACE the
// defaults ([remark-gfm, codeMeta]), silently dropping GFM and code-fence
// metastring parsing. The slot appends after the defaults, which is the
// standard remark-gfm → remark-breaks order.
//
// MERMAID is app-owned since the chrome-melt wave (2026-09-19): the md-blocks
// `code` override intercepts mermaid fences and renders via
// components/mermaid-render.ts — streamdown's internal mermaid machinery
// (the plugin entry + the `mermaid` prop) is retired with it.
export const streamdownPlugins = {
  cjk: {
    ...cjk,
    remarkPluginsAfter: [...cjk.remarkPluginsAfter, remarkBreaks],
  },
  code,
  math: createMathPlugin({ singleDollarTextMath: false }),
} as unknown as PluginConfig;

export const MessageResponse = memo(
  ({ className, children, ...props }: MessageResponseProps) => {
    // Delimiter preprocessing is a single linear scan (no markdown parsing)
    // — cheap enough for the render path of this children-memoized
    // component. Unbalanced delimiters pass through untouched, so mid-stream
    // chunks render literally until the closing delimiter arrives and the
    // full text is re-transformed.
    const content =
      typeof children === "string"
        ? transformMathDelimiters(children)
        : children;

    return (
      <Streamdown
        className={cn(
          // Source Sans 3 + emphasis-color tokens on every markdown surface
          // (labels stay JetBrains Mono). Unlayered plain CSS wins over text-sm.
          "lh-prose size-full [&>*:first-child]:mt-0 [&>*:last-child]:mb-0",
          className
        )}
        components={mdComponents}
        plugins={streamdownPlugins}
        {...props}
      >
        {content}
      </Streamdown>
    );
  },
  (prevProps, nextProps) =>
    prevProps.children === nextProps.children &&
    nextProps.isAnimating === prevProps.isAnimating
);

MessageResponse.displayName = "MessageResponse";

export type MessageToolbarProps = ComponentProps<"div">;

export const MessageToolbar = ({
  className,
  children,
  ...props
}: MessageToolbarProps) => (
  <div
    className={cn(
      "mt-4 flex w-full items-center justify-between gap-4",
      className
    )}
    {...props}
  >
    {children}
  </div>
);