package console

import (
	"context"
	"errors"
	"log"
	"strings"
	"time"
)

// deliveryChannel names how deliver got a message out.
type deliveryChannel string

const (
	deliveredKeymail deliveryChannel = "keymail"
	deliveredEmail   deliveryChannel = "email"
)

// domainOf is the lowercased part of addr after its last "@", "" if none.
func domainOf(addr string) string {
	i := strings.LastIndex(addr, "@")
	if i < 0 {
		return ""
	}
	return strings.ToLower(addr[i+1:])
}

// deliver sends one message to an address the person did not just type (an
// invite, a notice): Keymail federation first, then the console mailer (SES).
// The fall-through rule (spec 4.3):
//
//   - a definite "no mailbox" (ErrNoKeymailMailbox) goes to the mailer;
//   - an unreachable lookup stops when the address is at the Keymail host
//     (it IS a Keymail mailbox, so SES must not be used), and otherwise goes
//     to the mailer;
//   - a block, a price above the cap, or any failure after a successful
//     lookup stops with that error: the address is a Keymail mailbox.
//
// keymailShare bounds Keymail's part of ctx so the mailer keeps the rest.
// On error the channel is "".
func (s *Server) deliver(ctx context.Context, to, subject, body string, keymailShare time.Duration) (deliveryChannel, error) {
	if s.sendFederated != nil {
		kctx, cancel := context.WithTimeout(ctx, keymailShare)
		_, err := s.sendFederated(kctx, to, subject, body)
		cancel()
		if err == nil {
			return deliveredKeymail, nil
		}
		switch {
		case IsKeymailBlocked(err):
			// The recipient blocked the console. That is their answer;
			// email to the same address would go round it.
			log.Printf("console: delivery to %s: the recipient blocked the console on keymail; not emailing", to)
			return "", err
		case errors.Is(err, ErrNoKeymailMailbox):
			log.Printf("console: delivery to %s: no keymail mailbox, trying email", to)
		case errors.Is(err, ErrKeymailUnreachable):
			if s.km != nil && domainOf(to) == s.km.Host() {
				log.Printf("console: delivery to %s: keymail lookup unreachable for a keymail address; not emailing: %v", to, err)
				return "", err
			}
			log.Printf("console: delivery to %s: keymail lookup unreachable, trying email: %v", to, err)
		default:
			// ErrFederationPriceTooHigh, or a failure after the lookup
			// said the mailbox exists.
			log.Printf("console: delivery to %s by keymail: %v", to, err)
			return "", err
		}
	}
	if s.consoleMail == nil {
		return "", errors.New("console: no email sender is configured")
	}
	if err := s.consoleMail.Send(ctx, to, subject, body); err != nil {
		log.Printf("console: delivery to %s by email: %v", to, err)
		return "", err
	}
	return deliveredEmail, nil
}