/**
 * peachScript.ts — PeachScript encoding/decoding.
 *
 * PeachScript is the device-to-device export format. Each byte of an
 * encrypted vault payload maps to one Unicode Private Use Area code point
 * in U+E000..U+E0FF. The bundled `PeachScript-Regular.otf` renders those
 * 256 code points as the visual script. Outside Peach the string renders
 * as boxes — that is the desired property: PeachScript is meant to be
 * read by Peach, not by humans.
 *
 * The encoding is trivially reversible: byte 0 → U+E000, byte 255 →
 * U+E0FF. No padding, no base conversion, no alignment fix-ups. The font
 * does the visual work; this module is the codec.
 */

const BASE = 0xe000;

/** Encode a binary payload to a PeachScript string (one byte per code point). */
export function encodePeachScript(bytes: Uint8Array): string {
  const out: string[] = [];
  for (let i = 0; i < bytes.length; i++) {
    out.push(String.fromCodePoint(BASE + bytes[i]));
  }
  return out.join("");
}

/**
 * Decode a PeachScript string back to bytes. Throws
 * `INVALID_PEACHSCRIPT_CHARACTER` when any character is outside the
 * allotted PUA range — i.e. the string was edited, truncated mid-pair,
 * or is not PeachScript at all.
 */
export function decodePeachScript(str: string): Uint8Array {
  const codePoints = Array.from(str);
  const bytes = new Uint8Array(codePoints.length);
  for (let i = 0; i < codePoints.length; i++) {
    const cp = codePoints[i].codePointAt(0)!;
    if (cp < BASE || cp > BASE + 0xff) {
      throw new Error("INVALID_PEACHSCRIPT_CHARACTER");
    }
    bytes[i] = cp - BASE;
  }
  return bytes;
}

/** Strip whitespace from a PeachScript string before decoding. */
export function normalisePeachScript(str: string): string {
  return str.replace(/\s+/g, "");
}

/**
 * Cheap pre-flight: every non-whitespace char must be in the PUA range and
 * the string must be non-empty. Used by the import UI to gate the decode
 * button without throwing.
 */
export function isPeachScript(str: string): boolean {
  const trimmed = normalisePeachScript(str);
  if (trimmed.length === 0) return false;
  for (const ch of trimmed) {
    const cp = ch.codePointAt(0)!;
    if (cp < BASE || cp > BASE + 0xff) return false;
  }
  return true;
}