import { CACHE_MANAGER } from '@nestjs/cache-manager';
import { Inject, Injectable, Logger } from '@nestjs/common';
import { Cache } from 'cache-manager';
import { randomBytes, createHash } from 'crypto';


@Injectable()
export class PowService {
    private readonly logger = new Logger(PowService.name);
    private difficulty = 5;

    constructor(
        @Inject(CACHE_MANAGER) private cacheManager: Cache,
    ) { }

    /**
     * Generate a proof of work challenge, stored to redis for verification within
     * the next 10 seconds.
     */
    async generateChallenge() {
        const challenge = this.generateRandom256BitString();
        console.log(challenge)
        await this.cacheManager.set(challenge, true, 60 * 1000);
        return challenge;
    }

    generateRandom256BitString() {
        const randomString = randomBytes(32).toString('hex');
        return randomString;
    }


    hashAndCheck(string: string) {
        return this.hashPassesDifficulty(this.hashString(string), this.difficulty);
    }

    hashPassesDifficulty(hash: string, difficulty: number) {
        return hash.startsWith('0'.repeat(difficulty));
    }

    /**
     * Verify that the proof of work submitted has a leading number of
     * zeroes equal to the challenge length and the challenge exists.
     */
    async verifyChallenge(challenge: string, proof: string): Promise<boolean> {
        const expected = await this.cacheManager.get<boolean>(challenge);
        return expected ? this.hashAndCheck(proof + challenge) : false;
    }

    async markChallengeAsComplete(challenge: string) {
        await this.cacheManager.del(challenge);
    }

    /**
     * Perform a proof of work challenge to find a proof that hashes to a value
     */
    async performChallenge(challenge: string) {
        let proof = this.generateRandom256BitString();
        let hash = this.hashString(proof + challenge);
        while (!this.hashPassesDifficulty(hash, this.difficulty)) {
            proof = this.generateRandom256BitString();
            hash = this.hashString(proof + challenge);
        }
        return { proof, hash };
    }

    /**
     * sha512 the provided string and return the result.
     */
    hashString(input: string) {
        return createHash('sha512').update(input).digest('hex');
    }

    /**
     * Set the difficulty of the proof of work challenge.
     */
    setDifficulty(difficulty: number) {
        this.difficulty = difficulty;
    }

    /**
     * Get the current difficulty of the proof of work challenge.
     */
    getDifficulty() {
        return this.difficulty;
    }

}