import { CID } from 'multiformats/cid'
import { Logger } from 'besonders-logger'

const { WARN, LOG, DEBUG } = Logger.setup(Logger.INFO) // eslint-disable-line unused-imports/no-unused-vars

/**
 * Resolve an IPNS name to a CID using a public IPFS gateway's HTTP HEAD response.
 *
 * Mechanism: per the IPFS HTTP Gateway spec, `HEAD <gateway>/ipns/<name>/` returns the
 * IPNS-resolved root CID in the `X-Ipfs-Roots` response header (space-separated, ordered
 * from root to leaf). The first entry is the IPNS-resolved CID.
 *
 * This works against any gateway that follows the spec and exposes CORS for HEAD
 * (most public gateways do, e.g. ipfs.zt.ax, ipfs.io, dweb.link).
 *
 * The legacy w3name HTTP endpoint (`GET <base>/name/<ipns>` returning `{value: "/ipfs/<cid>"}`)
 * is also supported here for back-compat with self-hosted w3name-like services — but the
 * X-Ipfs-Roots path is preferred since it's the standardised gateway mechanism.
 *
 * @param ipns - The IPNS name (k51... string)
 * @param gateways - List of gateway base URLs (e.g. `["https://ipfs.zt.ax"]`)
 * @returns The resolved CID, or null if no gateway could resolve the name
 */
export async function resolveIPNSViaGateway(ipns: string, gateways: string[]): Promise<CID | null> {
	if (!ipns.startsWith('k51')) return null // only IPNS libp2p-key names go through gateway
	if (!gateways?.length) return null

	for (const rawGateway of gateways) {
		const gateway = rawGateway.replace(/\/+$/, '')
		const url = `${gateway}/ipns/${ipns}/`
		try {
			DEBUG(`[resolveIPNSViaGateway] HEAD ${url}`)
			const response = await fetch(url, { method: 'HEAD' })
			if (!response.ok) {
				DEBUG(`[resolveIPNSViaGateway] ${gateway} returned ${response.status}`)
				continue
			}
			const roots = response.headers.get('x-ipfs-roots') ?? response.headers.get('X-Ipfs-Roots')
			if (roots) {
				const first = roots.split(/[\s,]+/)[0]?.trim()
				if (first) {
					const cid = CID.parse(first)
					DEBUG(`[resolveIPNSViaGateway] resolved via ${gateway} x-ipfs-roots:`, cid.toString())
					return cid
				}
			}
			// Some gateways omit X-Ipfs-Roots but put the CID in etag (e.g. `<cid>.dag-json`)
			const etag = response.headers.get('etag')
			if (etag) {
				const m = etag.match(/^"?([a-z0-9]+)/i)
				if (m) {
					const cid = CID.parse(m[1])
					DEBUG(`[resolveIPNSViaGateway] resolved via ${gateway} etag:`, cid.toString())
					return cid
				}
			}
			WARN(`[resolveIPNSViaGateway] ${gateway} returned 200 but no usable CID header`)
		} catch (err) {
			WARN(`[resolveIPNSViaGateway] ${gateway} failed:`, err)
		}
	}
	return null
}