package discovery

import (
	"net/url"
	"os"
	"path"

	"git.twelvetwelve.org/library/core/json"
)

type LocalDiscovery struct {
}

func lookup(kv map[string]string, serviceUrn string) *url.URL {
	rawURL, ok := kv[serviceUrn]
	if !ok {
		return nil
	}

	u, err := url.Parse(rawURL)
	if err != nil {
		return nil
	}
	return u
}

func lookupFrom(path string, serviceUrn string) *url.URL {
	services := make(map[string]string)
	err := json.ReadFromFile(path, &services)
	if err != nil {
		return nil
	}
	return lookup(services, serviceUrn)
}

func (ld *LocalDiscovery) Discover(serviceUrn string) (*url.URL, error) {
	if url := lookupFrom("discovery.json", serviceUrn); url != nil {
		return url, nil
	}

	home, err := os.UserHomeDir()
	if err != nil {
		homeConf := path.Join(home, ".config", "discovery.json")
		if url := lookupFrom(homeConf, serviceUrn); url != nil {
			return url, nil
		}
	}

	if url := lookupFrom("/etc/discovery/discovery.json", serviceUrn); url != nil {
		return url, nil
	}

	return nil, os.ErrNotExist
}

func NewLocalDiscovery() *LocalDiscovery {
	return &LocalDiscovery{}
}