package config

import (
	"fmt"
	"strconv"
	"strings"
)

// Sending email.
//
// ── Why this exists at all ──────────────────────────────────────────────────
//
// A newly onboarded merchant's admin account arrives with no password, and the
// only safe way to let them set one is a signed invitation sent to the primary
// email they gave us. Until this, the server could not send email: no library,
// no configuration, and `NotifyUser` is Firebase push rather than mail.
//
// ── Shaped like AssistantConfig, for the same reasons ───────────────────────
//
// Unconfigured is a deployment choice and not a fault, so `Enabled` reports it
// and `Why` says which variable is missing. A server with no mail still boots
// and still onboards tenants — the invitation is recorded as unsent rather than
// failing the creation, because a tenant that exists and cannot be reached is
// recoverable and a tenant that was rolled back by a mail outage is confusing.
type MailConfig struct {
	// SMTP, because it is the one protocol every provider speaks. A transactional
	// service (SES, SendGrid, Resend) is reached the same way, with its own host
	// and an API key as the password — so choosing one later is configuration
	// rather than code.
	Host     string
	Port     int
	Username string
	Password string
	// Who the invitation appears to come from. Separate from the username
	// because most providers authenticate as one identity and send as another,
	// and using the login as the From address is how mail ends up in spam.
	FromAddress string
	FromName    string
	// Where the invitation link points. The merchant console, always — a
	// merchant sets their password there and nowhere else — and a build
	// variable rather than a constant because the site can move.
	ConsoleURL string
}

func (m MailConfig) Enabled() bool { return m.Why() == "" }

// Why says what is missing, or "" when mail can be sent.
//
// A sentence rather than a bool. "Off" is the same answer for five different
// mistakes, and the difference between "we have not set this up" and "somebody
// misspelled a variable" is invisible from outside — which is exactly how the
// assistant sat switched off for two days.
func (m MailConfig) Why() string {
	if strings.TrimSpace(m.Host) == "" {
		return "MAIL_HOST is not set, so no invitation can be sent"
	}
	if m.Port <= 0 {
		return "MAIL_PORT is not a usable port number"
	}
	if strings.TrimSpace(m.FromAddress) == "" {
		return "MAIL_FROM is not set; an invitation needs a sender address"
	}
	// Username and password are deliberately NOT required. An internal relay
	// that authenticates by network is a real deployment, and demanding
	// credentials would refuse it.
	if strings.TrimSpace(m.ConsoleURL) == "" {
		return "MAIL_CONSOLE_URL is not set; the invitation would have nowhere to point"
	}
	return ""
}

// Address is host:port, as the SMTP client wants it.
func (m MailConfig) Address() string { return fmt.Sprintf("%s:%d", m.Host, m.Port) }

// InviteLink is where an invitation sends somebody.
//
// Built here rather than in the mailer so the shape is decided once, beside the
// console URL it depends on. The token is the whole credential, so it is the
// only thing in the query string — never an email address or a userid, which
// would put both halves of an account into a URL that lands in server logs,
// browser history and whatever proxy sits between.
func (m MailConfig) InviteLink(token string) string {
	base := strings.TrimRight(strings.TrimSpace(m.ConsoleURL), "/")
	return base + "/set-password?t=" + token
}

// MailFromEnv reads the mail settings.
func MailFromEnv() MailConfig {
	port, err := strconv.Atoi(strings.TrimSpace(env("MAIL_PORT", "587")))
	if err != nil {
		// Zero rather than the default, so `Why` reports it instead of the
		// server quietly dialling a port nobody asked for.
		port = 0
	}

	return MailConfig{
		Host:     env("MAIL_HOST", ""),
		Port:     port,
		Username: env("MAIL_USERNAME", ""),
		Password: env("MAIL_PASSWORD", ""),
		// A name is optional; an address is not.
		FromAddress: env("MAIL_FROM", ""),
		FromName:    env("MAIL_FROM_NAME", "Nearle"),
		ConsoleURL:  env("MAIL_CONSOLE_URL", "https://app.nearledaily.com"),
	}
}