src/components/ai-elements/context.tsx

import { Button } from '@/components/ui/button';
import { HoverCard, HoverCardContent, HoverCardTrigger } from '@/components/ui/hover-card';
import { Progress } from '@/components/ui/progress';
import { cn } from '@/lib/utils';
import type { LanguageModelUsage } from 'ai';
import { type ComponentProps, createContext, useContext } from 'react';
import { getUsage } from 'tokenlens';

const PERCENT_MAX = 100;
const ICON_RADIUS = 10;
const ICON_VIEWBOX = 24;
const ICON_CENTER = 12;
const ICON_STROKE_WIDTH = 2;

type ModelId = string;

type ContextSchema = {
  usedTokens: number;
  maxTokens: number;
  usage?: LanguageModelUsage;
  modelId?: ModelId;
};

const ContextContext = createContext<ContextSchema | null>(null);

const useContextValue = () => {
  const context = useContext(ContextContext);

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

  return context;
};

export type ContextProps = ComponentProps<typeof HoverCard> & ContextSchema;

export const Context = ({ usedTokens, maxTokens, usage, modelId, ...props }: ContextProps) => (
  <ContextContext.Provider
    value={{
      usedTokens,
      maxTokens,
      usage,
      modelId,
    }}
  >
    <HoverCard closeDelay={0} openDelay={0} {...props} />
  </ContextContext.Provider>
);

const ContextIcon = () => {
  const { usedTokens, maxTokens } = useContextValue();
  const circumference = 2 * Math.PI * ICON_RADIUS;
  const usedPercent = usedTokens / maxTokens;
  const dashOffset = circumference * (1 - usedPercent);

  return (
    <svg
      aria-label="Model context usage"
      height="20"
      role="img"
      style={{ color: 'currentcolor' }}
      viewBox={`0 0 ${ICON_VIEWBOX} ${ICON_VIEWBOX}`}
      width="20"
    >
      <circle
        cx={ICON_CENTER}
        cy={ICON_CENTER}
        fill="none"
        opacity="0.25"
        r={ICON_RADIUS}
        stroke="currentColor"
        strokeWidth={ICON_STROKE_WIDTH}
      />
      <circle
        cx={ICON_CENTER}
        cy={ICON_CENTER}
        fill="none"
        opacity="0.7"
        r={ICON_RADIUS}
        stroke="currentColor"
        strokeDasharray={`${circumference} ${circumference}`}
        strokeDashoffset={dashOffset}
        strokeLinecap="round"
        strokeWidth={ICON_STROKE_WIDTH}
        style={{ transformOrigin: 'center', transform: 'rotate(-90deg)' }}
      />
    </svg>
  );
};

export type ContextTriggerProps = ComponentProps<typeof Button>;

export const ContextTrigger = ({ children, ...props }: ContextTriggerProps) => {
  const { usedTokens, maxTokens } = useContextValue();
  const usedPercent = usedTokens / maxTokens;
  const renderedPercent = new Intl.NumberFormat('en-US', {
    style: 'percent',
    maximumFractionDigits: 1,
  }).format(usedPercent);

  return (
    <HoverCardTrigger asChild>
      {children ?? (
        <Button type="button" variant="ghost" {...props}>
          <span className="font-medium text-muted-foreground">{renderedPercent}</span>
          <ContextIcon />
        </Button>
      )}
    </HoverCardTrigger>
  );
};

export type ContextContentProps = ComponentProps<typeof HoverCardContent>;

export const ContextContent = ({ className, ...props }: ContextContentProps) => (
  <HoverCardContent className={cn('min-w-60 divide-y overflow-hidden p-0', className)} {...props} />
);

export type ContextContentHeaderProps = ComponentProps<'div'>;

export const ContextContentHeader = ({
  children,
  className,
  ...props
}: ContextContentHeaderProps) => {
  const { usedTokens, maxTokens } = useContextValue();
  const usedPercent = usedTokens / maxTokens;
  const displayPct = new Intl.NumberFormat('en-US', {
    style: 'percent',
    maximumFractionDigits: 1,
  }).format(usedPercent);
  const used = new Intl.NumberFormat('en-US', {
    notation: 'compact',
  }).format(usedTokens);
  const total = new Intl.NumberFormat('en-US', {
    notation: 'compact',
  }).format(maxTokens);

  return (
    <div className={cn('w-full space-y-2 p-3', className)} {...props}>
      {children ?? (
        <>
          <div className="flex items-center justify-between gap-3 text-xs">
            <p>{displayPct}</p>
            <p className="font-mono text-muted-foreground">
              {used} / {total}
            </p>
          </div>
          <div className="space-y-2">
            <Progress className="bg-muted" value={usedPercent * PERCENT_MAX} />
          </div>
        </>
      )}
    </div>
  );
};

export type ContextContentBodyProps = ComponentProps<'div'>;

export const ContextContentBody = ({ children, className, ...props }: ContextContentBodyProps) => (
  <div className={cn('w-full p-3', className)} {...props}>
    {children}
  </div>
);

export type ContextContentFooterProps = ComponentProps<'div'>;

export const ContextContentFooter = ({
  children,
  className,
  ...props
}: ContextContentFooterProps) => {
  const { modelId, usage } = useContextValue();
  const costUSD = modelId
    ? getUsage({
        modelId,
        usage: {
          input: usage?.inputTokens ?? 0,
          output: usage?.outputTokens ?? 0,
        },
      }).costUSD?.totalUSD
    : undefined;
  const totalCost = new Intl.NumberFormat('en-US', {
    style: 'currency',
    currency: 'USD',
  }).format(costUSD ?? 0);

  return (
    <div
      className={cn(
        'flex w-full items-center justify-between gap-3 bg-secondary p-3 text-xs',
        className,
      )}
      {...props}
    >
      {children ?? (
        <>
          <span className="text-muted-foreground">Total cost</span>
          <span>{totalCost}</span>
        </>
      )}
    </div>
  );
};

export type ContextInputUsageProps = ComponentProps<'div'>;

export const ContextInputUsage = ({ className, children, ...props }: ContextInputUsageProps) => {
  const { usage, modelId } = useContextValue();
  const inputTokens = usage?.inputTokens ?? 0;

  if (children) {
    return children;
  }

  if (!inputTokens) {
    return null;
  }

  const inputCost = modelId
    ? getUsage({
        modelId,
        usage: { input: inputTokens, output: 0 },
      }).costUSD?.totalUSD
    : undefined;
  const inputCostText = new Intl.NumberFormat('en-US', {
    style: 'currency',
    currency: 'USD',
  }).format(inputCost ?? 0);

  return (
    <div className={cn('flex items-center justify-between text-xs', className)} {...props}>
      <span className="text-muted-foreground">Input</span>
      <TokensWithCost costText={inputCostText} tokens={inputTokens} />
    </div>
  );
};

export type ContextOutputUsageProps = ComponentProps<'div'>;

export const ContextOutputUsage = ({ className, children, ...props }: ContextOutputUsageProps) => {
  const { usage, modelId } = useContextValue();
  const outputTokens = usage?.outputTokens ?? 0;

  if (children) {
    return children;
  }

  if (!outputTokens) {
    return null;
  }

  const outputCost = modelId
    ? getUsage({
        modelId,
        usage: { input: 0, output: outputTokens },
      }).costUSD?.totalUSD
    : undefined;
  const outputCostText = new Intl.NumberFormat('en-US', {
    style: 'currency',
    currency: 'USD',
  }).format(outputCost ?? 0);

  return (
    <div className={cn('flex items-center justify-between text-xs', className)} {...props}>
      <span className="text-muted-foreground">Output</span>
      <TokensWithCost costText={outputCostText} tokens={outputTokens} />
    </div>
  );
};

export type ContextReasoningUsageProps = ComponentProps<'div'>;

export const ContextReasoningUsage = ({
  className,
  children,
  ...props
}: ContextReasoningUsageProps) => {
  const { usage, modelId } = useContextValue();
  const reasoningTokens = usage?.reasoningTokens ?? 0;

  if (children) {
    return children;
  }

  if (!reasoningTokens) {
    return null;
  }

  const reasoningCost = modelId
    ? getUsage({
        modelId,
        usage: { reasoningTokens },
      }).costUSD?.totalUSD
    : undefined;
  const reasoningCostText = new Intl.NumberFormat('en-US', {
    style: 'currency',
    currency: 'USD',
  }).format(reasoningCost ?? 0);

  return (
    <div className={cn('flex items-center justify-between text-xs', className)} {...props}>
      <span className="text-muted-foreground">Reasoning</span>
      <TokensWithCost costText={reasoningCostText} tokens={reasoningTokens} />
    </div>
  );
};

export type ContextCacheUsageProps = ComponentProps<'div'>;

export const ContextCacheUsage = ({ className, children, ...props }: ContextCacheUsageProps) => {
  const { usage, modelId } = useContextValue();
  const cacheTokens = usage?.cachedInputTokens ?? 0;

  if (children) {
    return children;
  }

  if (!cacheTokens) {
    return null;
  }

  const cacheCost = modelId
    ? getUsage({
        modelId,
        usage: { cacheReads: cacheTokens, input: 0, output: 0 },
      }).costUSD?.totalUSD
    : undefined;
  const cacheCostText = new Intl.NumberFormat('en-US', {
    style: 'currency',
    currency: 'USD',
  }).format(cacheCost ?? 0);

  return (
    <div className={cn('flex items-center justify-between text-xs', className)} {...props}>
      <span className="text-muted-foreground">Cache</span>
      <TokensWithCost costText={cacheCostText} tokens={cacheTokens} />
    </div>
  );
};

const TokensWithCost = ({ tokens, costText }: { tokens?: number; costText?: string }) => (
  <span>
    {tokens === undefined
      ? '—'
      : new Intl.NumberFormat('en-US', {
          notation: 'compact',
        }).format(tokens)}
    {costText ? <span className="ml-2 text-muted-foreground">• {costText}</span> : null}
  </span>
);