import * as bip39 from 'bip39';

export class EnglishMnemonic {
    public static readonly wordlist: readonly string[] = bip39.wordlists.english;

    // list of space separated lower case words (1 or more)
    private static readonly mnemonicMatcher = /^[a-z]+( [a-z]+)*$/;

    private readonly data: string;

    public constructor(mnemonic: string) {
        if (!EnglishMnemonic.mnemonicMatcher.test(mnemonic)) {
            throw new Error('Invalid mnemonic format');
        }

        const words = mnemonic.split(' ');
        const allowedWordsLengths: readonly number[] = [12, 15, 18, 21, 24];
        if (allowedWordsLengths.indexOf(words.length) === -1) {
            throw new Error(`Invalid word count in mnemonic (allowed: ${allowedWordsLengths} got: ${words.length})`);
        }

        for (const word of words) {
            if (EnglishMnemonic.wordlist.indexOf(word) === -1) {
                throw new Error('Mnemonic contains invalid word');
            }
        }

        // Throws with informative error message if mnemonic is not valid
        bip39.mnemonicToEntropy(mnemonic);

        this.data = mnemonic;
    }

    public toString(): string {
        return this.data;
    }
}