// Export / import of a save as a JSON or TXT file (or pasted text).
// Works on every device: download via a Blob link, import via file input or paste.

import { sanitizeState, serializeState } from '../engine/state.js';

const GAME_ID = 'idle-clicker';
const FORMAT = 1;

export class ImportError extends Error {
  /** @param {'empty'|'invalid'|'unknown_theme'|'wrong_game'} code */
  constructor(code) {
    super(code);
    this.code = code;
  }
}

/** The text a player downloads, copies or pastes back. */
export function buildExport(themeId, state, now = Date.now()) {
  return JSON.stringify(
    {
      game: GAME_ID,
      format: FORMAT,
      theme: themeId,
      exportedAt: new Date(now).toISOString(),
      state: JSON.parse(serializeState(state)),
    },
    null,
    2,
  );
}

/** Validate imported text. Throws ImportError; never trusts the content. */
export function parseImport(text, ctx, knownThemeIds) {
  const trimmed = String(text ?? '').trim().replace(/^/, '');
  if (!trimmed) throw new ImportError('empty');

  let data;
  try {
    data = JSON.parse(trimmed);
  } catch {
    throw new ImportError('invalid');
  }
  if (data?.game !== GAME_ID || data.format !== FORMAT) throw new ImportError('wrong_game');
  if (!knownThemeIds.includes(data.theme)) throw new ImportError('unknown_theme');

  const state = sanitizeState(data.state, ctx);
  if (!state) throw new ImportError('invalid');
  return { themeId: data.theme, state };
}

export function downloadText(filename, text, mime = 'application/json') {
  const url = URL.createObjectURL(new Blob([text], { type: `${mime};charset=utf-8` }));
  const link = document.createElement('a');
  link.href = url;
  link.download = filename;
  document.body.append(link);
  link.click();
  link.remove();
  setTimeout(() => URL.revokeObjectURL(url), 10_000);
}

export function readFileText(file) {
  return file.text();
}