package notification

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"time"
)

// ResendConfig configures the Resend HTTP sender. APIKey is required;
// FromEmail is the sending address on a domain you've verified in the
// Resend dashboard.
type ResendConfig struct {
	APIKey    string
	FromEmail string
	FromName  string

	// HTTPClient overrides the default client (mostly so tests can point
	// at httptest.Server). Leave nil for production.
	HTTPClient *http.Client
	BaseURL    string // overrideable for tests; defaults to https://api.resend.com
}

// ResendEmailSender posts emails through https://api.resend.com/emails.
// Implements auth.EmailSender + GuestEmailDispatcher.
type ResendEmailSender struct {
	cfg    ResendConfig
	tpls   *Templates
	from   string
	client *http.Client
	url    string
}

func NewResendEmailSender(cfg ResendConfig, tpls *Templates) (*ResendEmailSender, error) {
	if cfg.APIKey == "" {
		return nil, errors.New("resend: APIKey required")
	}
	if cfg.FromEmail == "" {
		return nil, errors.New("resend: FromEmail required")
	}
	from := cfg.FromEmail
	if cfg.FromName != "" {
		from = fmt.Sprintf("%s <%s>", cfg.FromName, cfg.FromEmail)
	}
	cli := cfg.HTTPClient
	if cli == nil {
		cli = &http.Client{Timeout: 15 * time.Second}
	}
	base := cfg.BaseURL
	if base == "" {
		base = "https://api.resend.com"
	}
	return &ResendEmailSender{cfg: cfg, tpls: tpls, from: from, client: cli, url: base + "/emails"}, nil
}

// --- auth.EmailSender ---

func (s *ResendEmailSender) SendVerification(ctx context.Context, to, name, link string) error {
	_, err := s.sendTemplated(ctx, to, "Verify your GuestGuard email",
		TmplVerification, map[string]any{"Name": name, "Link": link})
	return err
}

func (s *ResendEmailSender) SendPasswordReset(ctx context.Context, to, name, link string) error {
	_, err := s.sendTemplated(ctx, to, "Reset your GuestGuard password",
		TmplPasswordReset, map[string]any{"Name": name, "Link": link, "ExpiryHumane": "1 hour"})
	return err
}

func (s *ResendEmailSender) SendCollaboratorInvite(ctx context.Context, to, inviterName, eventName, role, link string) error {
	_, err := s.sendTemplated(ctx, to,
		inviterName+" invited you to "+eventName,
		TmplCollaboratorInvite, map[string]any{
			"InviterName": inviterName,
			"EventName":   eventName,
			"Role":        role,
			"Link":        link,
		})
	return err
}

func (s *ResendEmailSender) SendRSVPEditLink(ctx context.Context, to, guestName, eventName, link string) error {
	_, err := s.sendTemplated(ctx, to,
		"Edit your RSVP for "+eventName,
		TmplRSVPEditLink, map[string]any{
			"GuestName": guestName,
			"EventName": eventName,
			"Link":      link,
		})
	return err
}

// --- GuestEmailDispatcher ---

func (s *ResendEmailSender) SendGuest(ctx context.Context, to, subject string, name TemplateName, data map[string]any) (string, error) {
	return s.sendTemplated(ctx, to, subject, name, data)
}

// --- internals ---

type resendRequest struct {
	From    string   `json:"from"`
	To      []string `json:"to"`
	Subject string   `json:"subject"`
	HTML    string   `json:"html"`
	Text    string   `json:"text"`
}

type resendResponse struct {
	ID      string `json:"id"`
	Message string `json:"message,omitempty"`
}

func (s *ResendEmailSender) sendTemplated(ctx context.Context, to, subject string, name TemplateName, data map[string]any) (string, error) {
	if data == nil {
		data = map[string]any{}
	}
	data["Subject"] = subject
	html, text, err := s.tpls.Render(name, data)
	if err != nil {
		return "", err
	}

	body, _ := json.Marshal(resendRequest{
		From:    s.from,
		To:      []string{to},
		Subject: subject,
		HTML:    html,
		Text:    text,
	})
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, s.url, bytes.NewReader(body))
	if err != nil {
		return "", err
	}
	req.Header.Set("Authorization", "Bearer "+s.cfg.APIKey)
	req.Header.Set("Content-Type", "application/json")

	resp, err := s.client.Do(req)
	if err != nil {
		return "", fmt.Errorf("resend: do: %w", err)
	}
	defer resp.Body.Close()

	respBody, _ := io.ReadAll(io.LimitReader(resp.Body, 64*1024))
	if resp.StatusCode >= 300 {
		return "", fmt.Errorf("resend: status %d: %s", resp.StatusCode, string(respBody))
	}
	var parsed resendResponse
	if err := json.Unmarshal(respBody, &parsed); err != nil {
		return "", fmt.Errorf("resend: parse: %w", err)
	}
	return parsed.ID, nil
}