// Package subdomain is a resolver which uses the subdomain to determine the domain to route to. It
// offloads the endpoint resolution to a child resolver which is provided in New.
package subdomain // import "go.unistack.org/micro/v3/api/resolver/subdomain"

import (
	"net"
	"net/http"
	"strings"

	"go.unistack.org/micro/v3/api/resolver"
	"go.unistack.org/micro/v3/logger"
	"golang.org/x/net/publicsuffix"
)

// NewResolver creates new subdomain api resolver
func NewResolver(parent resolver.Resolver, opts ...resolver.Option) resolver.Resolver {
	options := resolver.NewOptions(opts...)
	return &subdomainResolver{opts: options, Resolver: parent}
}

type subdomainResolver struct {
	resolver.Resolver
	opts resolver.Options
}

// Resolve resolve endpoint based on subdomain
func (r *subdomainResolver) Resolve(req *http.Request, opts ...resolver.ResolveOption) (*resolver.Endpoint, error) {
	if dom := r.Domain(req); len(dom) > 0 {
		opts = append(opts, resolver.Domain(dom))
	}

	return r.Resolver.Resolve(req, opts...)
}

// Domain returns domain
func (r *subdomainResolver) Domain(req *http.Request) string {
	// determine the host, e.g. foobar.m3o.app
	host := req.URL.Hostname()
	if len(host) == 0 {
		if h, _, err := net.SplitHostPort(req.Host); err == nil {
			host = h // host does contain a port
		} else if strings.Contains(err.Error(), "missing port in address") {
			host = req.Host // host does not contain a port
		}
	}

	// check for an ip address
	if net.ParseIP(host) != nil {
		return ""
	}

	// check for dev environment
	if host == "localhost" || host == "127.0.0.1" {
		return ""
	}

	// extract the top level domain plus one (e.g. 'myapp.com')
	domain, err := publicsuffix.EffectiveTLDPlusOne(host)
	if err != nil {
		if logger.V(logger.DebugLevel) {
			logger.Debug(r.opts.Context, "Unable to extract domain from %v", host)
		}
		return ""
	}

	// there was no subdomain
	if host == domain {
		return ""
	}

	// remove the domain from the host, leaving the subdomain, e.g. "staging.foo.myapp.com" => "staging.foo"
	subdomain := strings.TrimSuffix(host, "."+domain)

	// ignore the API subdomain
	if subdomain == "api" {
		return ""
	}

	// return the reversed subdomain as the namespace, e.g. "staging.foo" => "foo-staging"
	comps := strings.Split(subdomain, ".")
	for i := len(comps)/2 - 1; i >= 0; i-- {
		opp := len(comps) - 1 - i
		comps[i], comps[opp] = comps[opp], comps[i]
	}
	return strings.Join(comps, "-")
}

func (r *subdomainResolver) String() string {
	return "subdomain"
}