/**
 * KHAELOR
 * File: src/tui/renderer/capabilities.ts
 * Description: Terminal capability detection — color depth ladder, NO_COLOR, DEC 2026 probe, OSC 11 background query.
 *
 * Author: Simon-Pierre Boucher
 * Contact: contact@spboucher.ai
 */

export type ColorDepth = "truecolor" | "ansi256" | "ansi16" | "mono";
export type Background = "dark" | "light";

export interface TerminalCapabilities {
  colorDepth: ColorDepth;
  /** DEC 2026 synchronized-output supported (probed; false when unknown). */
  syncUpdates: boolean;
  background: Background;
}

/**
 * Color capability ladder (TUI_DESIGN §12): truecolor → ANSI-256 → ANSI-16 →
 * monochrome. `NO_COLOR` and `TERM=dumb` are honored absolutely; non-TTY
 * output is monochrome.
 */
export function detectColorDepth(env: NodeJS.ProcessEnv, isTty: boolean): ColorDepth {
  if (!isTty) return "mono";
  if (env["NO_COLOR"] !== undefined && env["NO_COLOR"] !== "") return "mono";
  const term = env["TERM"] ?? "";
  if (term === "dumb" || term === "") return "mono";
  const colorterm = env["COLORTERM"] ?? "";
  if (colorterm === "truecolor" || colorterm === "24bit") return "truecolor";
  if (term.includes("256color")) return "ansi256";
  return "ansi16";
}

/**
 * Parse a DECRQM reply for mode 2026: `CSI ? 2026 ; Ps $ y`.
 * Ps 1 (set) / 2 (reset) / 3 (permanently set) mean the mode is recognized →
 * synchronized updates are supported. Ps 0 (unrecognized) / 4 (permanently
 * reset) mean unsupported. Returns null when no complete reply is present.
 */
export function parseDecrqmReply(data: string): boolean | null {
  const m = /\x1b\[\?2026;(\d+)\$y/.exec(data);
  if (!m) return null;
  const ps = Number(m[1]);
  return ps === 1 || ps === 2 || ps === 3;
}

/**
 * Parse an OSC 11 background-color reply (`OSC 11 ; rgb:RRRR/GGGG/BBBB ST|BEL`)
 * into light/dark via relative luma. Returns null when no complete reply is present.
 */
export function parseOsc11Reply(data: string): Background | null {
  const m = /\x1b\]11;rgb:([0-9a-fA-F]+)\/([0-9a-fA-F]+)\/([0-9a-fA-F]+)(?:\x07|\x1b\\)/.exec(data);
  if (!m) return null;
  const channel = (hex: string): number => {
    const max = Math.pow(16, hex.length) - 1;
    return parseInt(hex, 16) / max;
  };
  const r = channel(m[1] as string);
  const g = channel(m[2] as string);
  const b = channel(m[3] as string);
  const luma = 0.2126 * r + 0.7152 * g + 0.0722 * b;
  return luma > 0.5 ? "light" : "dark";
}

export interface ProbeStreams {
  stdin: NodeJS.ReadStream;
  stdout: NodeJS.WriteStream;
}

/**
 * Probe the terminal for DEC 2026 support and background color. Requires raw
 * mode to already be active (replies arrive on stdin without a newline).
 * Resolves within `timeoutMs` (default 100 ms — TUI_DESIGN §12) with whatever
 * was learned; absence of a reply degrades to `{ syncUpdates: false,
 * background: null }` — never a hang, never a guess presented as fact.
 */
export function probeTerminal(
  streams: ProbeStreams,
  timeoutMs = 100,
): Promise<{ syncUpdates: boolean; background: Background | null }> {
  const { stdin, stdout } = streams;
  if (!stdin.isTTY || !stdout.isTTY) {
    return Promise.resolve({ syncUpdates: false, background: null });
  }
  return new Promise((resolve) => {
    let buffer = "";
    let sync: boolean | null = null;
    let background: Background | null = null;
    let done = false;

    const finish = (): void => {
      if (done) return;
      done = true;
      stdin.off("data", onData);
      clearTimeout(timer);
      resolve({ syncUpdates: sync ?? false, background });
    };

    const onData = (chunk: Buffer | string): void => {
      buffer += chunk.toString("utf8");
      if (sync === null) sync = parseDecrqmReply(buffer);
      if (background === null) background = parseOsc11Reply(buffer);
      if (sync !== null && background !== null) finish();
    };

    const timer = setTimeout(finish, timeoutMs);
    timer.unref();
    stdin.on("data", onData);
    // DECRQM for mode 2026, then OSC 11 background query.
    stdout.write("\x1b[?2026$p\x1b]11;?\x07");
  });
}