package console

import (
	"net"

	"github.com/carlosframework/platform/internal/geo"
)

// guessInput carries a request's location hints for ONE call. Neither
// field is ever stored, logged, audited or echoed (spec §6.5).
type guessInput struct {
	TZ string
	IP net.IP
}

// guessResult is a guess in the record vocabulary and its source word.
type guessResult struct{ Code, Source string }

// guessRegion is spec §6.4:
//
//  1. filter candidates to eligible ones the policy allows;
//  2. nearest among those with a point, from the timezone, else (only
//     when the timezone is unmappable) the IP;
//  3. else the home, ONLY if the home is itself a filtered candidate;
//  4. else no guess.
func guessRegion(cands []regionCandidate, allows func(code string) bool, in guessInput, loc geo.Locator) (guessResult, bool) {
	var pick []geo.Candidate
	homeIn := false
	for _, c := range cands {
		if !c.Eligible || !allows(c.Code) {
			continue
		}
		pick = append(pick, geo.Candidate{Code: c.Code, Home: c.Home, AWSRegion: c.AWSRegion})
		homeIn = homeIn || c.Home
	}
	if len(pick) == 0 {
		return guessResult{}, false
	}
	if p, ok := geo.ZonePoint(in.TZ); ok {
		if code, ok := geo.Nearest(p, pick); ok {
			return guessResult{code, "timezone"}, true
		}
	} else if loc != nil && in.IP != nil {
		if p, ok := loc.Locate(in.IP); ok {
			if code, ok := geo.Nearest(p, pick); ok {
				return guessResult{code, "ip"}, true
			}
		}
	}
	if homeIn {
		return guessResult{"", "default"}, true
	}
	return guessResult{}, false
}