/**
 * Codex-style light-sweep text shimmer.
 *
 * Vendored from pi-topping (`src/format.ts`, `shimmerString`) rather than
 * depended on, so the extensions stay independently installable. The sweep
 * geometry — band half-width, padding, speed scaling — is load-bearing for
 * visual parity, so port changes upstream rather than tuning them here.
 * test/shimmer.test.ts mirrors the upstream tests to catch drift.
 */

import type { ThemeColor } from "@earendil-works/pi-coding-agent";

const SHIMMER_SWEEP_S = 2.0;
const SHIMMER_BAND_HALF = 5.0;
const SHIMMER_PADDING = 10;

/** The slice of pi's `Theme` shimmerString needs. Structural so callers can supply a stub. */
export interface ShimmerTheme {
  getFgAnsi(color: ThemeColor): string;
  fg(color: ThemeColor, text: string): string;
}

/**
 * With `invert=true`, the text color is used at rest and the sweep moves toward
 * the theme's dim color.
 */
export function shimmerString(
  text: string,
  elapsedMs: number,
  theme: ShimmerTheme,
  direction: "ltr" | "rtl" = "ltr",
  speed: "slow" | "normal" | "fast" = "normal",
  invert = false,
): string {
  const chars = [...text];
  if (chars.length === 0) return "";
  const shimmerBase = ansiToRgb(theme.getFgAnsi(invert ? "text" : "dim"));
  const shimmerHighlight = ansiToRgb(theme.getFgAnsi(invert ? "dim" : "text"));
  if (!shimmerBase || !shimmerHighlight) return theme.fg("text", text);
  const period = chars.length + SHIMMER_PADDING * 2;
  const unitsPerS = period / SHIMMER_SWEEP_S;
  // The band crosses padding at either end while every character is still dim. Scaling only
  // the stretch where it actually overlaps the text keeps that dark pause identical at every
  // speed, so `speed` changes the sweep alone rather than the whole cycle.
  const litEnter = SHIMMER_PADDING - SHIMMER_BAND_HALF;
  const litExit = SHIMMER_PADDING + chars.length - 1 + SHIMMER_BAND_HALF;
  const enterS = litEnter / unitsPerS;
  const litS = (litExit - litEnter) / unitsPerS / (speed === "slow" ? 0.5 : speed === "fast" ? 2 : 1);
  const phase = (elapsedMs / 1000) % (enterS + litS + (period - litExit) / unitsPerS);
  const linear =
    phase < enterS
      ? phase * unitsPerS
      : phase < enterS + litS
        ? litEnter + ((phase - enterS) / litS) * (litExit - litEnter)
        : litExit + (phase - enterS - litS) * unitsPerS;
  const pos = direction === "rtl" ? period - linear : linear;

  let out = "";
  for (let i = 0; i < chars.length; i++) {
    const ch = chars[i]!;
    const dist = Math.abs(i + SHIMMER_PADDING - pos);
    const t = dist <= SHIMMER_BAND_HALF ? 0.5 * (1 + Math.cos((Math.PI * dist) / SHIMMER_BAND_HALF)) : 0;
    const alpha = t * 0.9;
    const r = Math.round(shimmerHighlight[0] * alpha + shimmerBase[0] * (1 - alpha));
    const g = Math.round(shimmerHighlight[1] * alpha + shimmerBase[1] * (1 - alpha));
    const b = Math.round(shimmerHighlight[2] * alpha + shimmerBase[2] * (1 - alpha));
    const bold = !invert && t > 0.2 ? "\x1b[1m" : "";
    out += `${bold}\x1b[38;2;${r};${g};${b}m${ch}\x1b[22m`;
  }
  return out + "\x1b[0m";
}

function ansiToRgb(ansi: string): [number, number, number] | null {
  const match = ansi.match(/^\x1b\[38;2;(\d+);(\d+);(\d+)m$/);
  if (!match) return null;
  return [Number(match[1]), Number(match[2]), Number(match[3])];
}