Chat thread

/**
 * @title Chat Thread
 * @category product
 * @description Message thread that shows three bouncing typing dots before a "them" reply, pops bubbles in, and scrolls up as it fills.
 * @duration data-driven
 * @use A DM, support chat or group thread inside a `phone-frame` or app mockup
 * @use Showing a bot or assistant "typing" before it answers
 * @avoid A single command-and-output log. Use `terminal`
 * @tags chat, messages, dm, bubbles, typing, conversation
 * @example
 * <PhoneFrame>
 *   <ChatThread
 *     messages={[
 *       { from: "me", text: "Can it render 9:16?", at: 0 },
 *       { from: "them", text: "Yes. Same component, three formats.", at: 30 },
 *     ]}
 *   />
 * </PhoneFrame>
 */
import type React from "react";
import { type MotionProps, tween, useMotion, useTheme, useViewport } from "./core";

export type ChatMessage = {
  from: "me" | "them";
  text: string;
  /** Frame this message lands, counted from `delay`. A "them" message shows typing dots for `typingDuration` frames before it. */
  at: number;
};

export type ChatThreadProps = MotionProps & {
  messages: ChatMessage[];
  /** Frames the typing dots show before a "them" message lands. Defaults to 0.6s. 0 skips the dots. */
  typingDuration?: number;
  /** Visible thread width in design units. */
  width?: number;
  /** Visible thread height in design units. Older bubbles scroll out the top once it's full. */
  height?: number;
  /** Largest font size in design units. */
  fontSize?: number;
  background?: string;
  /** "me" bubble fill. Defaults to the theme accent. */
  meColor?: string;
  meTextColor?: string;
  /** "them" bubble fill. Defaults to the theme surface. */
  themColor?: string;
  themTextColor?: string;
  radius?: number;
  style?: React.CSSProperties;
  className?: string;
};

/** Rough wrapped line count at `perLine` characters per line. Good enough to reserve bubble height without measuring the DOM. */
function wrappedLines(text: string, perLine: number): number {
  const words = text.split(" ");
  let lines = 1;
  let column = 0;
  for (const word of words) {
    const size = word.length + (column > 0 ? 1 : 0);
    if (column > 0 && column + size > perLine) {
      lines++;
      column = word.length;
    } else {
      column += size;
    }
  }
  return lines;
}

function TypingDots({ frame, color, size }: { frame: number; color: string; size: number }) {
  const dot = size * 0.22;
  return (
    <div style={{ display: "flex", gap: dot * 0.7 }}>
      {[0, 1, 2].map((index) => (
        <div
          key={index}
          style={{
            width: dot,
            height: dot,
            borderRadius: "50%",
            background: color,
            translate: `0 ${Math.sin(frame * 0.35 + index * 1.1) * dot * 0.5}px`,
          }}
        />
      ))}
    </div>
  );
}

export function ChatThread({
  messages,
  typingDuration,
  width = 460,
  height = 480,
  fontSize = 24,
  background,
  meColor,
  meTextColor,
  themColor,
  themTextColor,
  radius,
  style,
  className,
  ...motion
}: ChatThreadProps) {
  const theme = useTheme();
  const { u } = useViewport();
  const m = useMotion(motion);
  const dotsFrames = typingDuration ?? Math.round(m.fps * 0.6);
  const boxW = u(width);
  const boxH = u(height);
  const fontPx = u(fontSize);
  const padX = u(16);
  const padY = u(10);
  const gap = u(10);
  const lineH = fontPx * 1.35;
  const bubbleMaxW = boxW * 0.74;
  const perLine = Math.max(4, Math.floor((bubbleMaxW - padX * 2) / (fontPx * 0.56)));
  const appearFrames = Math.round(m.fps * 0.3);
  const popFrames = Math.round(m.fps * 0.35);

  const rows = messages.map((message) => {
    const lines = wrappedLines(message.text, perLine);
    const rowH = lines * lineH + padY * 2;
    const typingFrom = message.from === "them" ? message.at - dotsFrames : message.at;
    return { message, rowH, typingFrom };
  });

  let top = 0;
  const positioned = rows.map((row) => {
    const y = top;
    top += row.rowH + gap;
    return { ...row, y };
  });

  const appearOf = (from: number) =>
    Math.min(Math.max(tween(m.frame, m.fps, { from: m.delay + from, duration: appearFrames, motion: "smooth" }), 0), 1);

  const filled = positioned.reduce((sum, row) => sum + appearOf(row.typingFrom) * (row.rowH + gap), 0);
  const scroll = Math.max(0, filled - boxH + padY * 2);

  return (
    <div
      className={className}
      style={{
        position: "relative",
        width: boxW,
        height: boxH,
        overflow: "hidden",
        borderRadius: u(radius ?? theme.radius),
        background: background ?? theme.colors.background,
        fontFamily: theme.fonts.body,
        opacity: 1 - m.exit,
        ...style,
      }}
    >
      <div
        style={{
          position: "absolute",
          left: 0,
          right: 0,
          top: padY,
          padding: `0 ${padX}px`,
          translate: `0 ${-scroll}px`,
        }}
      >
        {positioned.map((row, index) => {
          const { message, rowH, typingFrom, y } = row;
          const isMe = message.from === "me";
          const shown = appearOf(typingFrom);
          const typing = !isMe && dotsFrames > 0 && m.frame < m.delay + message.at;
          const pop = Math.max(
            0,
            tween(m.frame, m.fps, { from: m.delay + message.at, duration: popFrames, motion: "bouncy" }),
          );
          return (
            <div
              key={index}
              style={{
                position: "absolute",
                top: y,
                left: 0,
                right: 0,
                display: "flex",
                justifyContent: isMe ? "flex-end" : "flex-start",
                opacity: shown,
                translate: `0 ${(1 - shown) * u(14)}px`,
              }}
            >
              <div
                style={{
                  maxWidth: bubbleMaxW,
                  minHeight: rowH,
                  display: "flex",
                  alignItems: "center",
                  padding: `${padY}px ${padX}px`,
                  borderRadius: u(radius ?? theme.radius * 0.9),
                  background: isMe ? (meColor ?? theme.colors.accent) : (themColor ?? theme.colors.surface),
                  color: isMe
                    ? (meTextColor ?? theme.colors.accentForeground)
                    : (themTextColor ?? theme.colors.foreground),
                  fontSize: fontPx,
                  lineHeight: `${lineH}px`,
                  scale: typing ? "1" : String(0.85 + 0.15 * pop),
                }}
              >
                {typing ? (
                  <TypingDots frame={m.frame} color={themTextColor ?? theme.colors.muted} size={fontPx} />
                ) : (
                  message.text
                )}
              </div>
            </div>
          );
        })}
      </div>
    </div>
  );
}