// Package notify posts owner-notice embeds to a Discord webhook. It is
// deliberately small and stdlib-only: one POST of a JSON body needs no
// Discord library, and the path imports nothing of this repo's session or
// OAuth packages — that independence is why a webhook was chosen over a bot
// (issue #171, AC9).
package notify

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

	"bookmarkmanager/backend/internal/latest"
)

// dangerColor is the dark design branch's --danger, #cf5c4d = 13589581. The
// integer is unreadable, so a future edit will otherwise "fix" it — do not:
// --ember means new chapter only, and a fault wearing ember would tell the
// owner a stall is a release. This is the one colour a fault wears.
const dangerColor = 13589581

// Client posts owner notices to one Discord webhook. The webhook address is a
// secret in the class of TOKEN_KEY: it is never logged, never rendered, and
// never carried in a returned error, which the poller logs.
type Client struct {
	webhookURL string
	baseURL    string // the deployment's public origin; embed URLs resolve against it
	http       *http.Client
}

// New returns a Client posting to webhookURL. baseURL is the deployment's
// public origin (Config.PublicBaseURL); the embed's deep-linked title is
// built from it.
func New(webhookURL, baseURL string) *Client {
	return &Client{
		webhookURL: webhookURL,
		baseURL:    strings.TrimSuffix(baseURL, "/"),
		http:       &http.Client{Timeout: 10 * time.Second},
	}
}

// Notify posts one owner notice as a Discord embed: the danger colour, the
// subject as a deep-linked title, the sentence as the description, the pass
// time as the timestamp and the machine word in the footer. The send is
// wrapped in a deadline so a hanging Discord cannot hold a poller Lane. On
// failure the error carries no part of the webhook address (the poller logs
// it), and the caller leaves the suppression row unwritten so the next pass
// retries while the condition holds.
func (c *Client) Notify(ctx context.Context, f latest.Fault, sentence, href string) error {
	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()

	body, err := json.Marshal(c.payload(f, sentence, href))
	if err != nil {
		return fmt.Errorf("owner notice: marshal: %w", err)
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.webhookURL, strings.NewReader(string(body)))
	if err != nil {
		return errors.New("owner notice: build request")
	}
	req.Header.Set("Content-Type", "application/json")
	resp, err := c.http.Do(req)
	if err != nil {
		// The transport error embeds the webhook address; the address is a
		// secret in the class of TOKEN_KEY and the poller logs this error.
		return errors.New("owner notice: send failed")
	}
	defer resp.Body.Close()
	// Cap the read: a Discord error page is enough, and draining the body
	// lets the connection be reused.
	io.Copy(io.Discard, io.LimitReader(resp.Body, 4096))
	if resp.StatusCode < 200 || resp.StatusCode > 299 {
		return fmt.Errorf("owner notice: webhook status %d", resp.StatusCode)
	}
	return nil
}

// payload is the webhook body: one embed and nothing else. No fields, no
// thumbnail, no author block — the wire shape is what Discord reads.
func (c *Client) payload(f latest.Fault, sentence, href string) webhookPayload {
	return webhookPayload{Embeds: []embed{{
		Color:       dangerColor,
		Title:       subject(f),
		URL:         c.baseURL + href,
		Description: sentence,
		Timestamp:   time.UnixMilli(f.Since).UTC().Format(time.RFC3339),
		Footer:      embedFooter{Text: f.Condition},
	}}}
}

// subject renders the embed's title: the Site the fault is about, with the
// machine word so the title needs no per-condition wording here — #172's
// conditions pass different sentences, not a different builder. For a fault
// that is not one Site's, the machine word stands alone.
func subject(f latest.Fault) string {
	if f.Site == "" {
		return f.Condition
	}
	return f.Site + ": " + f.Condition
}

type webhookPayload struct {
	Embeds []embed `json:"embeds"`
}

type embed struct {
	Color       int         `json:"color"`
	Title       string      `json:"title"`
	URL         string      `json:"url"`
	Description string      `json:"description"`
	Timestamp   string      `json:"timestamp"`
	Footer      embedFooter `json:"footer"`
}

type embedFooter struct {
	Text string `json:"text"`
}