package app

import (
	"fmt"
	"strings"
)

type vpnLocationChoice struct {
	ISO       string
	Label     string
	RawTarget string
	Name      string
	Connect   string
}

func resolveVPNLocationSelection(
	reqTarget string,
	reqISO string,
	reqLabel string,
	locs []vpnLocationItem,
) (target string, iso string, label string, validated bool, err error) {
	targetReq := strings.TrimSpace(reqTarget)
	isoReq := strings.ToUpper(strings.TrimSpace(reqISO))
	labelReq := strings.TrimSpace(reqLabel)

	choices := buildVPNLocationChoices(locs)
	if len(choices) == 0 {
		if isISO2(isoReq) {
			return isoReq, isoReq, "", false, nil
		}
		if isISO2(targetReq) {
			t := strings.ToUpper(strings.TrimSpace(targetReq))
			return t, t, "", false, nil
		}
		return "", "", "", false, fmt.Errorf("location catalog unavailable; use ISO code")
	}

	findBy := func(pred func(vpnLocationChoice) bool) *vpnLocationChoice {
		for i := range choices {
			if pred(choices[i]) {
				return &choices[i]
			}
		}
		return nil
	}

	var chosen *vpnLocationChoice

	if labelReq != "" {
		chosen = findBy(func(it vpnLocationChoice) bool {
			return equalsFoldTrim(labelReq, it.Label)
		})
	}

	if chosen == nil && targetReq != "" {
		chosen = findBy(func(it vpnLocationChoice) bool {
			return equalsFoldTrim(targetReq, it.Connect) ||
				equalsFoldTrim(targetReq, it.Name) ||
				equalsFoldTrim(targetReq, it.RawTarget) ||
				equalsFoldTrim(targetReq, it.Label)
		})
	}

	if chosen == nil && isISO2(isoReq) {
		chosen = findBy(func(it vpnLocationChoice) bool {
			return it.ISO == isoReq
		})
	}

	if chosen == nil && isISO2(targetReq) {
		isoByTarget := strings.ToUpper(strings.TrimSpace(targetReq))
		chosen = findBy(func(it vpnLocationChoice) bool {
			return it.ISO == isoByTarget
		})
	}

	if chosen == nil {
		return "", "", "", false, fmt.Errorf("location not recognized; current connection kept")
	}

	connectArg := strings.TrimSpace(chosen.Connect)
	if connectArg == "" {
		connectArg = chosen.ISO
	}

	isValidated := true
	if targetReq != "" &&
		!equalsFoldTrim(targetReq, connectArg) &&
		!equalsFoldTrim(targetReq, chosen.ISO) &&
		!equalsFoldTrim(targetReq, chosen.Name) &&
		!equalsFoldTrim(targetReq, chosen.RawTarget) &&
		!equalsFoldTrim(targetReq, chosen.Label) {
		isValidated = false
	}

	return connectArg, chosen.ISO, chosen.Label, isValidated, nil
}

func buildVPNLocationChoices(locs []vpnLocationItem) []vpnLocationChoice {
	choices := make([]vpnLocationChoice, 0, len(locs))
	namesByISO := map[string][][]string{}
	countByISO := map[string]int{}

	for _, it := range locs {
		iso := strings.ToUpper(strings.TrimSpace(it.ISO))
		if !isISO2(iso) {
			continue
		}
		label := strings.TrimSpace(it.Label)
		rawTarget := strings.TrimSpace(it.Target)

		name := inferVPNLocationTargetFromLabel(label, iso)
		if name == "" {
			name = rawTarget
		}
		if name == "" {
			name = iso
		}

		namesByISO[iso] = append(namesByISO[iso], strings.Fields(name))
		countByISO[iso]++
		choices = append(choices, vpnLocationChoice{
			ISO:       iso,
			Label:     label,
			RawTarget: rawTarget,
			Name:      name,
		})
	}

	commonByISO := map[string][]string{}
	for iso, names := range namesByISO {
		if len(names) < 2 {
			continue
		}
		pfx := commonPrefixTokens(names)
		if len(pfx) > 0 {
			commonByISO[iso] = pfx
		}
	}

	for i := range choices {
		iso := choices[i].ISO
		if countByISO[iso] <= 1 {
			choices[i].Connect = iso
			continue
		}
		tokens := strings.Fields(choices[i].Name)
		pfx := commonByISO[iso]
		if len(pfx) > 0 && len(tokens) > len(pfx) {
			choices[i].Connect = strings.TrimSpace(strings.Join(tokens[len(pfx):], " "))
		} else if choices[i].Name != "" {
			choices[i].Connect = choices[i].Name
		}
		if choices[i].Connect == "" {
			choices[i].Connect = iso
		}
	}

	return choices
}

func equalsFoldTrim(a, b string) bool {
	return strings.EqualFold(strings.TrimSpace(a), strings.TrimSpace(b))
}