'use strict';

const config = require('config');
const bhttp = require('bhttp');
const blake2 = require('blake2');
const phash = require('sharp-phash');
// const phashDistance = require('sharp-phash/distance');

const { agentFor } = require('../proxy');
const logger = require('../logger')(__filename);
const limiterFor = require('../limiter');

async function fetchItem(url, attempt, context) {
    async function retry(error) {
        logger.warn(`Failed to fetch '${url}', ${attempt < config.fetch.retries ? 'retrying' : 'giving up'}: ${error.message} (${context.post ? context.post.permalink : 'no post'})`);

        if (attempt < config.fetch.retries) {
            return fetchItem(url, attempt + 1, context);
        }

        return null;
    }

    try {
        // throw new Error('Failed it!');
        // config.proxy.retryFlipped: once this url has already failed once, retry it via
        // whichever of proxied/direct is NOT what it'd normally get - see resolveProxyUrl()
        const flip = config.proxy.retryFlipped && attempt > 0;

        const res = await limiterFor(url).schedule(() => bhttp.get(url, {
            headers: context.headers,
            agent: agentFor(url, { flip }),
            // bhttp has no timeout at all by default - a server (or, more likely, a proxy
            // tunnel) that connects fine but then just stops responding would otherwise hang
            // forever. This isn't just a wall-clock ceiling on the *promise* (an external
            // Promise.race achieves that, but leaves the real connection dangling) - bhttp
            // calls req.abort() itself when this fires, actually releasing the socket. Without
            // that, every stalled attempt leaks one connection onto the shared agent for that
            // host; enough of those piling up (e.g. after several retries against a host that's
            // currently black-holing everything, as seen with i.redd.it) exhausts it, and every
            // *future* request to that host silently queues forever waiting for a socket that's
            // never coming back - a freeze with no further log lines, not just a slow retry.
            responseTimeout: config.fetch.timeout,
        }));

        if (res.statusCode !== 200) {
            throw new Error(`Response not OK for ${url} (${res.statusCode})`);
        }

        if (!Buffer.isBuffer(res.body)) {
            throw new Error(`Unexpected response for ${url} (${res.statusCode}): ${res.body}`);
        }

        logger.debug(`Fetched '${context.host?.url || url}' (${context.post?.permalink || 'no post'})`);

        const hash = blake2.createHash('blake2b', { digestLength: 24 });
        hash.update(res.body);
        const contentHash = hash.digest('hex');

        const phashResult = context.item?.type?.includes('image/')
            ? await phash(res.body)
            : null;

        return {
            buffer: res.body,
            hash: contentHash,
            phash: phashResult,
        };
    } catch (error) {
        return retry(error);
    }
}

module.exports = fetchItem;