package notification

import (
	"context"
	"log/slog"
)

// EmailBackend names the chosen email delivery channel for telemetry +
// startup logging. Mostly a debugging aid — code paths don't branch on
// this value.
type EmailBackend string

const (
	BackendResend EmailBackend = "resend"
	BackendSMTP   EmailBackend = "smtp"
	BackendSES    EmailBackend = "ses"
	BackendLog    EmailBackend = "log"
)

// EmailSenderConfig collects every email-related env var so the picker
// has a single, ordered place to decide which backend wins. Priority is
// Resend > SMTP > SES > Log — the first one with non-empty creds is used.
type EmailSenderConfig struct {
	Resend ResendConfig
	SMTP   SMTPConfig
	SES    SESConfig
}

// CombinedEmailSender satisfies both the auth.EmailSender interface (for
// verification + reset emails) and GuestEmailDispatcher (for invitation,
// confirmation, reminder). One concrete value handles both audiences so
// callers don't end up with two configurations.
type CombinedEmailSender interface {
	SendVerification(ctx context.Context, to, name, link string) error
	SendPasswordReset(ctx context.Context, to, name, link string) error
	SendGuest(ctx context.Context, to, subject string, name TemplateName, data map[string]any) (string, error)
}

// PickEmailSender returns the configured email sender + which backend was
// chosen. Falls back to a logger stub if nothing is configured, so the
// service stays bootable in stripped-down dev environments.
func PickEmailSender(ctx context.Context, cfg EmailSenderConfig, tpls *Templates, logger *slog.Logger) (CombinedEmailSender, EmailBackend, error) {
	switch {
	case cfg.Resend.APIKey != "":
		s, err := NewResendEmailSender(cfg.Resend, tpls)
		if err != nil {
			return nil, "", err
		}
		return s, BackendResend, nil
	case cfg.SMTP.Host != "":
		s, err := NewSMTPEmailSender(cfg.SMTP, tpls)
		if err != nil {
			return nil, "", err
		}
		return s, BackendSMTP, nil
	case cfg.SES.FromEmail != "":
		s, err := NewSESEmailSender(ctx, cfg.SES, tpls)
		if err != nil {
			return nil, "", err
		}
		return s, BackendSES, nil
	}
	return &logCombinedSender{logger: logger, tpls: tpls}, BackendLog, nil
}

// logCombinedSender is the dev fallback. Verification + reset emails come
// through as structured log lines (preserving the Block A behaviour);
// guest emails get rendered + dumped so engineers can eyeball the output.
type logCombinedSender struct {
	logger *slog.Logger
	tpls   *Templates
}

func (l *logCombinedSender) SendVerification(_ context.Context, to, name, link string) error {
	l.logger.Info("auth email (stub): verification", "to", to, "name", name, "link", link)
	return nil
}

func (l *logCombinedSender) SendPasswordReset(_ context.Context, to, name, link string) error {
	l.logger.Info("auth email (stub): password reset", "to", to, "name", name, "link", link)
	return nil
}

func (l *logCombinedSender) SendGuest(_ context.Context, to, subject string, name TemplateName, data map[string]any) (string, error) {
	if data == nil {
		data = map[string]any{}
	}
	data["Subject"] = subject
	_, text, err := l.tpls.Render(name, data)
	if err != nil {
		return "", err
	}
	l.logger.Info("guest email (stub)",
		"to", to, "subject", subject, "template", string(name), "text_body", text,
	)
	return "log:" + string(name), nil
}