package mail

import (
	"context"
	"fmt"
	"html"
	"os"
	"strings"

	"github.com/resend/resend-go/v3"
)

// QuestionAnswered is the payload for notifying a question author of a reply.
type QuestionAnswered struct {
	ToEmail       string
	ToName        string
	QuestionID    string
	QuestionTitle string
	AnswerBody    string
}

// Notifier sends transactional email about answered questions.
type Notifier interface {
	NotifyQuestionAnswered(ctx context.Context, msg QuestionAnswered) error
}

// Nop is a no-op Notifier used when Resend is not configured.
type Nop struct{}

func (Nop) NotifyQuestionAnswered(context.Context, QuestionAnswered) error { return nil }

// Resend sends via the Resend HTTP API.
type Resend struct {
	client  *resend.Client
	from    string
	baseURL string
}

// FromEnv builds a Notifier from RESEND_* and APP_BASE_URL.
// Returns Nop when RESEND_API_KEY is unset.
func FromEnv() (Notifier, error) {
	key := strings.TrimSpace(os.Getenv("RESEND_API_KEY"))
	if key == "" {
		return Nop{}, nil
	}
	from := strings.TrimSpace(os.Getenv("RESEND_FROM"))
	base := strings.TrimRight(strings.TrimSpace(os.Getenv("APP_BASE_URL")), "/")
	if from == "" {
		return nil, fmt.Errorf("RESEND_FROM is required when RESEND_API_KEY is set")
	}
	if base == "" {
		return nil, fmt.Errorf("APP_BASE_URL is required when RESEND_API_KEY is set")
	}
	return &Resend{
		client:  resend.NewClient(key),
		from:    from,
		baseURL: base,
	}, nil
}

func (r *Resend) NotifyQuestionAnswered(ctx context.Context, msg QuestionAnswered) error {
	if r == nil || r.client == nil {
		return nil
	}
	to := strings.TrimSpace(msg.ToEmail)
	if to == "" {
		return nil
	}
	link := r.baseURL + "/questions/" + msg.QuestionID
	title := strings.TrimSpace(msg.QuestionTitle)
	if title == "" {
		title = "your question"
	}
	text := fmt.Sprintf(
		"Hi%s,\n\nYour question %q has an answer from a plumber:\n\n%s\n\nView it here:\n%s\n",
		greetingName(msg.ToName),
		title,
		msg.AnswerBody,
		link,
	)
	htmlBody := fmt.Sprintf(
		`<p>Hi%s,</p><p>Your question <strong>%s</strong> has an answer from a plumber:</p><blockquote style="margin:1em 0;padding:0.75em 1em;border-left:3px solid #ccc;white-space:pre-wrap">%s</blockquote><p><a href="%s">View the answer</a></p>`,
		html.EscapeString(greetingName(msg.ToName)),
		html.EscapeString(title),
		html.EscapeString(msg.AnswerBody),
		html.EscapeString(link),
	)
	params := &resend.SendEmailRequest{
		From:    r.from,
		To:      []string{to},
		Subject: "Your question was answered",
		Text:    text,
		Html:    htmlBody,
	}
	opts := &resend.SendEmailOptions{
		IdempotencyKey: "answer-notify:" + msg.QuestionID,
	}
	_, err := r.client.Emails.SendWithOptions(ctx, params, opts)
	return err
}

func greetingName(name string) string {
	name = strings.TrimSpace(name)
	if name == "" {
		return ""
	}
	return " " + name
}