package audit

import (
	"context"
	"fmt"
	"net/http"
	"strings"
	"time"
)

// NtfyNotifier posts alerts to an ntfy topic URL. Used to surface a
// degraded audit state (records buffered locally during a loki outage).
type NtfyNotifier struct {
	topicURL string
	token    string
	http     *http.Client
}

// NewNtfyNotifier constructs a notifier for the given ntfy topic URL
// (e.g. https://ntfy.sh/my-topic). token is an optional bearer for
// protected ntfy instances; it is held here and only sent in the
// Authorization header, never logged. Returns nil when topicURL is empty.
func NewNtfyNotifier(topicURL, token string) *NtfyNotifier {
	if topicURL == "" {
		return nil
	}
	return &NtfyNotifier{
		topicURL: strings.TrimRight(topicURL, "/"),
		token:    token,
		http:     &http.Client{Timeout: 10 * time.Second},
	}
}

// Notify posts a message to the ntfy topic.
func (n *NtfyNotifier) Notify(ctx context.Context, msg string) error {
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, n.topicURL, strings.NewReader(msg))
	if err != nil {
		return err
	}
	req.Header.Set("Title", "brain-capture audit degraded")
	req.Header.Set("Priority", "high")
	req.Header.Set("Tags", "warning,brain")
	if n.token != "" {
		req.Header.Set("Authorization", "Bearer "+n.token)
	}
	resp, err := n.http.Do(req)
	if err != nil {
		return fmt.Errorf("ntfy notify: %w", err)
	}
	defer func() { _ = resp.Body.Close() }()
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return &RejectedError{Status: resp.StatusCode}
	}
	return nil
}

// RejectedError is a non-2xx ntfy response.
type RejectedError struct{ Status int }

func (e *RejectedError) Error() string { return fmt.Sprintf("ntfy notify: status %d", e.Status) }

// Permanent reports whether resending the same message cannot succeed: a 4xx
// other than 429 (rate limited). Callers may drop such a message; anything
// else (5xx, 429, transport errors) is an outage and must be retried.
func (e *RejectedError) Permanent() bool {
	return e.Status >= 400 && e.Status < 500 && e.Status != http.StatusTooManyRequests
}