/**
 * @file terminalTheme.ts
 * @description The xterm colour theme for lane terminals. The terminal is
 * ALWAYS dark — Claude Code's TUI picks its own colours for a dark background,
 * so a light terminal would make its text unreadable — and is painted with the
 * palette of the DARK theme the user picked (`themeFor.dark`). Colours are read
 * from the CSS variables in `index.css` on a hidden probe carrying
 * `class="dark" data-theme=<id>`, so no hex is duplicated here.
 * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
 */
import type { ITheme } from "@xterm/xterm";

/** Reads one CSS variable (an RGB triplet like `17 17 19`) by name. */
export type VarReader = (name: string) => string;

function toHex(triplet: string): string | undefined {
  const parts = triplet
    .trim()
    .split(/[\s,]+/)
    .map(Number);
  if (parts.length !== 3 || parts.some((n) => !Number.isFinite(n))) return undefined;
  return "#" + parts.map((n) => Math.round(n).toString(16).padStart(2, "0")).join("");
}

/** Mix a hex colour toward white by `amount` (0..1) — the ANSI "bright" twin. */
function lighten(hex: string | undefined, amount: number): string | undefined {
  if (!hex) return undefined;
  const rgb = [1, 3, 5].map((i) => parseInt(hex.slice(i, i + 2), 16));
  return (
    "#" +
    rgb
      .map((c) =>
        Math.round(c + (255 - c) * amount)
          .toString(16)
          .padStart(2, "0")
      )
      .join("")
  );
}

/**
 * Build an xterm theme from a theme's CSS variables. red/green/yellow come from
 * `--status-*`, blue from `--accent`, black/white from the surface/fg ramp.
 * Magenta and cyan stay the classic ANSI hues: no token keeps that hue in every
 * theme (darcula's keyword is orange), and a program printing "magenta" should
 * get magenta.
 */
export function buildTerminalTheme(read: VarReader): ITheme {
  const v = (name: string) => toHex(read(name));
  const red = v("--status-danger");
  const green = v("--status-success");
  const yellow = v("--status-warning");
  const blue = v("--accent");
  const magenta = "#c678dd";
  const cyan = "#56b6c2";
  return {
    // The page's colour: the console sits on the page, with no card or frame.
    background: v("--surface-0"),
    foreground: v("--fg-primary"),
    cursor: v("--fg-primary"),
    cursorAccent: v("--surface-0"),
    selectionBackground: v("--border-light"),
    black: v("--border-light"),
    red,
    green,
    yellow,
    blue,
    magenta,
    cyan,
    white: v("--fg-secondary"),
    brightBlack: v("--fg-muted"),
    brightRed: lighten(red, 0.25),
    brightGreen: lighten(green, 0.25),
    brightYellow: lighten(yellow, 0.25),
    brightBlue: lighten(blue, 0.25),
    brightMagenta: lighten(magenta, 0.25),
    brightCyan: lighten(cyan, 0.25),
    brightWhite: v("--fg-primary"),
  };
}

/** Resolve the dark theme `id`'s variables on a hidden probe and build the theme. */
export function terminalThemeFor(id: string): ITheme {
  const probe = document.createElement("div");
  probe.className = "dark";
  if (id !== "default") probe.dataset.theme = id;
  probe.style.display = "none";
  document.body.appendChild(probe);
  try {
    const style = getComputedStyle(probe);
    return buildTerminalTheme((name) => style.getPropertyValue(name));
  } finally {
    probe.remove();
  }
}