package alerts

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

// AlwaysOnDisplay sends each alert to the session API used by the wall
// display. A session is created for the alert and then given a status and log
// entry so the display can show both the current incident and its details.
type AlwaysOnDisplay struct {
	URL    string
	Client *http.Client
}

func (a *AlwaysOnDisplay) Name() string { return "always-on-display" }

type aodSession struct {
	ID string `json:"id"`
}

func (a *AlwaysOnDisplay) Send(ctx context.Context, alert Alert) error {
	client := a.Client
	if client == nil {
		client = &http.Client{Timeout: 15 * time.Second}
	}
	base := strings.TrimRight(a.URL, "/")

	var session aodSession
	name := fmt.Sprintf("%s alert: %s", strings.ToUpper(string(alert.Priority())), alert.Spike.Service)
	if alert.Test {
		name = "TEST alert: " + alert.Spike.Service
	}
	if err := postJSONDecode(ctx, client, base+"/api/sessions", nil, map[string]string{"name": name}, &session); err != nil {
		return err
	}
	if session.ID == "" {
		return fmt.Errorf("always-on-display: session response did not include an id")
	}

	status := firstLine(alert.Text(""))
	if err := postJSON(ctx, client, base+"/api/sessions/"+session.ID+"/status", nil, map[string]string{"status": status}); err != nil {
		return err
	}
	level := "info"
	if alert.Priority() == PriorityHigh {
		level = "error"
	} else if alert.Priority() == PriorityMedium {
		level = "warning"
	}
	return postJSON(ctx, client, base+"/api/sessions/"+session.ID+"/log", nil, map[string]string{
		"level":   level,
		"message": alert.Text(""),
	})
}

func firstLine(s string) string {
	if i := strings.IndexByte(s, '\n'); i >= 0 {
		return s[:i]
	}
	return s
}

func postJSONDecode(ctx context.Context, client *http.Client, target string, headers map[string]string, body any, out any) error {
	raw, err := json.Marshal(body)
	if err != nil {
		return err
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, target, strings.NewReader(string(raw)))
	if err != nil {
		return fmt.Errorf("always-on-display: invalid request")
	}
	req.Header.Set("Content-Type", "application/json")
	for k, v := range headers {
		req.Header.Set(k, v)
	}
	resp, err := client.Do(req)
	if err != nil {
		return fmt.Errorf("always-on-display: request failed: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode/100 != 2 {
		return fmt.Errorf("always-on-display: HTTP %d", resp.StatusCode)
	}
	if err := json.NewDecoder(resp.Body).Decode(out); err != nil {
		return fmt.Errorf("always-on-display: invalid session response: %w", err)
	}
	return nil
}