src/components/ai-elements/reasoning.tsx

import { useControllableState } from '@radix-ui/react-use-controllable-state';
import { Collapsible, CollapsibleContent, CollapsibleTrigger } from '@/components/ui/collapsible';
import { cn } from '@/lib/utils';
import { BrainIcon, ChevronDownIcon } from 'lucide-react';
import type { ComponentProps, ReactNode } from 'react';
import { createContext, memo, useContext, useEffect, useState } from 'react';
import { Streamdown } from 'streamdown';
import { Shimmer } from './shimmer';

type ReasoningContextValue = {
  isStreaming: boolean;
  isOpen: boolean;
  setIsOpen: (open: boolean) => void;
  duration: number | undefined;
};

const ReasoningContext = createContext<ReasoningContextValue | null>(null);

export const useReasoning = () => {
  const context = useContext(ReasoningContext);
  if (!context) {
    throw new Error('Reasoning components must be used within Reasoning');
  }
  return context;
};

export type ReasoningProps = ComponentProps<typeof Collapsible> & {
  isStreaming?: boolean;
  open?: boolean;
  defaultOpen?: boolean;
  onOpenChange?: (open: boolean) => void;
  duration?: number;
};

const AUTO_CLOSE_DELAY = 1000;
const MS_IN_S = 1000;

export const Reasoning = memo(
  ({
    className,
    isStreaming = false,
    open,
    defaultOpen = true,
    onOpenChange,
    duration: durationProp,
    children,
    ...props
  }: ReasoningProps) => {
    const [isOpen, setIsOpen] = useControllableState({
      prop: open,
      defaultProp: defaultOpen,
      onChange: onOpenChange,
    });
    const [duration, setDuration] = useControllableState({
      prop: durationProp,
      defaultProp: undefined,
    });

    const [hasAutoClosed, setHasAutoClosed] = useState(false);
    const [startTime, setStartTime] = useState<number | null>(null);

    // Track duration when streaming starts and ends
    useEffect(() => {
      if (isStreaming) {
        if (startTime === null) {
          // eslint-disable-next-line react-hooks/set-state-in-effect -- Tracking streaming duration requires effect
          setStartTime(Date.now());
        }
      } else if (startTime !== null) {
        setDuration(Math.ceil((Date.now() - startTime) / MS_IN_S));
        setStartTime(null);
      }
    }, [isStreaming, startTime, setDuration]);

    // Auto-open when streaming starts, auto-close when streaming ends (once only)
    useEffect(() => {
      if (defaultOpen && !isStreaming && isOpen && !hasAutoClosed) {
        // Add a small delay before closing to allow user to see the content
        const timer = setTimeout(() => {
          setIsOpen(false);
          setHasAutoClosed(true);
        }, AUTO_CLOSE_DELAY);

        return () => clearTimeout(timer);
      }
    }, [isStreaming, isOpen, defaultOpen, setIsOpen, hasAutoClosed]);

    const handleOpenChange = (newOpen: boolean) => {
      setIsOpen(newOpen);
    };

    return (
      <ReasoningContext.Provider value={{ isStreaming, isOpen, setIsOpen, duration }}>
        <Collapsible
          className={cn('not-prose mb-4', className)}
          onOpenChange={handleOpenChange}
          open={isOpen}
          {...props}
        >
          {children}
        </Collapsible>
      </ReasoningContext.Provider>
    );
  },
);

export type ReasoningTriggerProps = ComponentProps<typeof CollapsibleTrigger> & {
  getThinkingMessage?: (isStreaming: boolean, duration?: number) => ReactNode;
};

const defaultGetThinkingMessage = (isStreaming: boolean, duration?: number) => {
  if (isStreaming || duration === 0) {
    return <Shimmer duration={1}>Thinking...</Shimmer>;
  }
  if (duration === undefined) {
    return <p>Thought for a few seconds</p>;
  }
  return <p>Thought for {duration} seconds</p>;
};

export const ReasoningTrigger = memo(
  ({
    className,
    children,
    getThinkingMessage = defaultGetThinkingMessage,
    ...props
  }: ReasoningTriggerProps) => {
    const { isStreaming, isOpen, duration } = useReasoning();

    return (
      <CollapsibleTrigger
        className={cn(
          'flex w-full items-center gap-2 text-muted-foreground text-sm transition-colors hover:text-foreground',
          className,
        )}
        {...props}
      >
        {children ?? (
          <>
            <BrainIcon className="size-4" />
            {getThinkingMessage(isStreaming, duration)}
            <ChevronDownIcon
              className={cn('size-4 transition-transform', isOpen ? 'rotate-180' : 'rotate-0')}
            />
          </>
        )}
      </CollapsibleTrigger>
    );
  },
);

export type ReasoningContentProps = ComponentProps<typeof CollapsibleContent> & {
  children: string;
};

export const ReasoningContent = memo(({ className, children, ...props }: ReasoningContentProps) => (
  <CollapsibleContent
    className={cn(
      'mt-4 text-sm',
      'data-[state=closed]:fade-out-0 data-[state=closed]:slide-out-to-top-2 data-[state=open]:slide-in-from-top-2 text-muted-foreground outline-none data-[state=closed]:animate-out data-[state=open]:animate-in',
      className,
    )}
    {...props}
  >
    <Streamdown>{children}</Streamdown>
  </CollapsibleContent>
));

Reasoning.displayName = 'Reasoning';
ReasoningTrigger.displayName = 'ReasoningTrigger';
ReasoningContent.displayName = 'ReasoningContent';