package services

import (
	"fmt"
	"log"
	"strings"
	"time"

	"nearle/config"
	"nearle/utils"
)

// The invitation a newly onboarded merchant receives.
//
// ── Why onboarding does not fail when this does ─────────────────────────────
//
// `Invite` never returns an error to the onboarding path. A tenant that exists
// and has not been emailed is recoverable — somebody presses resend — while a
// tenant rolled back because a mail relay was slow is a business that was
// onboarded, told it was onboarded, and is not in the system. The first is a
// task; the second is a phone call nobody can explain.
//
// So a failure is logged loudly and reported as `false`, and the caller decides
// what to tell the operator. The platform console shows "invitation not sent"
// beside the tenant, which is the state somebody can act on.
type InviteService interface {
	// Invite emails a first-password link. Reports whether it was sent, and
	// why not when it was not — a sentence for the operator, not an error.
	//
	// `businessName` may be empty: the name is then looked up from `tenantid`,
	// because most callers hold an account and a tenantid and nothing else about
	// the business. A caller that already has the name — onboarding, which was
	// handed it in the form — passes it and saves the query.
	Invite(userid, tenantid int, email, businessName string) (bool, string)
}

// TenantNamer reads a business's name for the invitation's first line.
//
// A one-method interface rather than the whole tenant repository, because that
// is all this needs and because it keeps `inviteService` testable without a
// database. `repositories.TenantRepository` satisfies it.
type TenantNamer interface {
	TenantNameByID(tenantID int) (string, error)
}

type inviteService struct {
	mailer utils.Mailer
	cfg    config.MailConfig
	// May be nil. The invitation then says "your business", which is worse copy
	// and a working link — never a reason not to send.
	names TenantNamer
}

func NewInviteService(mailer utils.Mailer, cfg config.MailConfig, names TenantNamer) InviteService {
	return &inviteService{mailer: mailer, cfg: cfg, names: names}
}

func (s *inviteService) Invite(userid, tenantid int, email, businessName string) (bool, string) {
	address := strings.TrimSpace(email)
	if address == "" {
		return false, "no email address on the account"
	}
	if s.mailer == nil {
		// Not a fault. A deployment with no mail configured still onboards; the
		// reason names the variable so it is fixable rather than mysterious.
		return false, s.cfg.Why()
	}

	token, _, err := utils.MintInviteToken(
		utils.InviteClaims{Userid: userid, Tenantid: tenantid}, time.Now())
	if err != nil {
		// Only happens with no signing secret, which is already fatal at boot
		// in production — but an invitation with no token would be a link that
		// cannot work, and sending it would be worse than not sending.
		log.Printf("invite: could not sign an invitation for user %d: %v", userid, err)
		return false, "this server cannot sign an invitation"
	}

	subject, body := inviteMessage(s.businessName(tenantid, businessName), s.cfg.InviteLink(token))

	if err := s.mailer.Send(address, subject, body); err != nil {
		log.Printf("invite: could not email user %d at %s: %v", userid, address, err)
		return false, err.Error()
	}

	log.Printf("invite: sent to user %d for tenant %d", userid, tenantid)
	return true, ""
}

// businessName is the name for the mail's first line.
//
// Looked up only when the caller did not have one. A failure is logged and
// swallowed: the alternative is refusing to send somebody their only way into
// their account because a name could not be read, and "your business has been
// set up on Nearle" is a perfectly usable sentence.
func (s *inviteService) businessName(tenantid int, given string) string {
	if name := strings.TrimSpace(given); name != "" {
		return name
	}
	if s.names == nil || tenantid <= 0 {
		return ""
	}
	name, err := s.names.TenantNameByID(tenantid)
	if err != nil {
		log.Printf("invite: could not read tenant %d's name: %v", tenantid, err)
		return ""
	}
	return strings.TrimSpace(name)
}

// inviteMessage is what the merchant reads.
//
// ── Why it says so little ───────────────────────────────────────────────────
//
// This is the first thing a new merchant receives from us and the only way into
// their account, so it has one job: make the link obvious and make it credible.
// Every extra paragraph is somewhere for the link to hide, and a mail full of
// features reads like marketing — which is the thing people delete.
//
// It states who it is for and what it does, gives the link on its own line, and
// says how long it lasts. The expiry is there because an invitation found three
// weeks later needs to explain itself rather than look broken.
//
// Plain text, not HTML. A password link that arrives as an image-heavy template
// is the shape of a phishing mail, and plain text renders identically
// everywhere.
func inviteMessage(businessName, link string) (subject, body string) {
	name := strings.TrimSpace(businessName)
	if name == "" {
		name = "your business"
	}

	subject = "Set your Nearle password"

	body = fmt.Sprintf(`%s has been set up on Nearle.

To finish, choose a password for your account:

%s

This link is for you alone and works once. It expires in 7 days — if it has,
ask whoever set you up to send another.

If you were not expecting this, you can ignore it. Nothing happens until
somebody uses the link.

— Nearle
`, name, link)

	return subject, body
}