// Package notify shows desktop notifications: best effort, never a reason to
// abort an announcement.
//
//	Linux:   the freedesktop Notifications D-Bus service (org.freedesktop.
//	         Notifications, pure Go via godbus): notifications with a Cancel
//	         action, closed again when the announcement ends. Fallback when
//	         no session bus is reachable: notify-send (no action).
//	macOS:   osascript `display notification` (no action).
//	Windows: PowerShell toast (Windows.UI.Notifications) with a Cancel
//	         button that opens a talk: link; the talk: protocol handler
//	         (registered in HKCU, `talk uri`) relays the click to the daemon.
//
// Missing tools are a clear error for the caller (log), never an abort: a
// notification is an extra, not a contract.
package notify

import (
	"bytes"
	"context"
	"encoding/base64"
	"encoding/binary"
	"fmt"
	"os/exec"
	"runtime"
	"strings"
	"time"
	"unicode/utf16"
)

// Title is the title of all talk notifications.
const Title = "talk"

// timeout bounds the call of the OS tool.
const timeout = 10 * time.Second

// Available reports whether a notification path exists on this system: a
// reachable notification service on the session bus, or the OS tool.
func Available() bool {
	if dbusAvailable() {
		return true
	}
	_, err := exec.LookPath(tool())
	return err == nil
}

// Describe names the path for `talk doctor`: the notification service with
// name and version and whether it supports a Cancel action, or the OS tool.
func Describe() string {
	if info, ok := dbusDescribe(); ok {
		return info
	}
	t := tool()
	if _, err := exec.LookPath(t); err != nil {
		if runtime.GOOS == "linux" {
			return "no notification service on the session bus and " + t + " not found"
		}
		return t + " not found"
	}
	switch runtime.GOOS {
	case "darwin":
		return "osascript (Notification Center; no cancel button)"
	case "windows":
		return "powershell (Windows toast with cancel button via the talk: link)"
	default:
		return "notify-send (libnotify; no session bus, so no cancel button)"
	}
}

// SupportsCancel reports whether notifications on this system can carry a
// Cancel button that reaches talk: Linux with a notification service that
// has the "actions" capability, or Windows (toast button via the talk:
// protocol handler).
func SupportsCancel() bool {
	return dbusSupportsActions() || runtime.GOOS == "windows"
}

func tool() string {
	switch runtime.GOOS {
	case "darwin":
		return "osascript"
	case "windows":
		return "powershell"
	default:
		return "notify-send"
	}
}

// Show shows a plain notification with Title and text (no action) and waits
// for the handover to finish, not for the notification to be closed. Used
// for the quiet-hours toast.
func Show(ctx context.Context, text string) error {
	if dbusAvailable() {
		id, err := dbusNotify(ctx, text, nil, nil)
		if err == nil {
			_ = id
			return nil
		}
	}
	return showWithTool(ctx, text)
}

// Announcement is what Announce shows for a playing announcement.
type Announcement struct {
	// Text is the announcement text (the notification body).
	Text string

	// CancelLabel is the button label ("Cancel", "Abbrechen").
	CancelLabel string

	// CancelURI is the talk: link the button opens where the click cannot
	// reach the daemon directly (Windows toast): talk:cancel?id=…&port=….
	// The talk: protocol handler (talk uri) turns it into POST /cancel-item.
	CancelURI string

	// Tag identifies the notification for closing it again where the
	// platform needs a tag (Windows); typically the announcement id.
	Tag string
}

// Announce shows the notification for an announcement that is playing: the
// text plus a Cancel button where the platform supports it. onCancel runs
// when the user clicks it on platforms that report the click back (Linux
// D-Bus); on Windows the click opens CancelURI instead. The returned close
// function dismisses the notification (call it when the announcement
// ends); it is never nil. Platforms without actions show a plain
// notification and the close function does nothing.
func Announce(ctx context.Context, a Announcement, onCancel func()) (close func(), err error) {
	noop := func() {}
	if dbusAvailable() {
		id, err := dbusNotify(ctx, a.Text, []string{"cancel", a.CancelLabel}, func(action string) {
			if action == "cancel" && onCancel != nil {
				onCancel()
			}
		})
		if err == nil {
			return func() { dbusClose(id) }, nil
		}
		// fall through to the tool on a bus error
	}
	if runtime.GOOS == "windows" && a.CancelURI != "" {
		return announceWindows(ctx, a)
	}
	return noop, showWithTool(ctx, a.Text)
}

// showWithTool shows a notification through the OS tool (no action).
func showWithTool(ctx context.Context, text string) error {
	ctx, cancel := context.WithTimeout(ctx, timeout)
	defer cancel()
	var cmd *exec.Cmd
	switch runtime.GOOS {
	case "darwin":
		script := fmt.Sprintf("display notification %s with title %s", appleString(text), appleString(Title))
		cmd = exec.CommandContext(ctx, "osascript", "-e", script)
	case "windows":
		cmd = exec.CommandContext(ctx, "powershell", "-NoProfile", "-NonInteractive", "-EncodedCommand", psEncode(toastScript(text)))
	default:
		cmd = exec.CommandContext(ctx, "notify-send", "--app-name="+Title, "--urgency=normal", Title, text)
	}
	if out, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("notify: %s failed: %w: %s", tool(), err, bytes.TrimSpace(out))
	}
	return nil
}

// appleString turns s into an AppleScript string literal.
func appleString(s string) string {
	return `"` + strings.NewReplacer(`\`, `\\`, `"`, `\"`).Replace(s) + `"`
}

// toastScript is the PowerShell toast (Windows 10/11); the text is passed
// base64-encoded so there is no quoting problem.
func toastScript(text string) string {
	return fmt.Sprintf(`$ErrorActionPreference = 'Stop'
[Windows.UI.Notifications.ToastNotificationManager, Windows.UI.Notifications, ContentType = WindowsRuntime] | Out-Null
$msg = [System.Text.Encoding]::UTF8.GetString([Convert]::FromBase64String('%s'))
$xml = [Windows.UI.Notifications.ToastNotificationManager]::GetTemplateContent([Windows.UI.Notifications.ToastTemplateType]::ToastText02)
$nodes = $xml.GetElementsByTagName('text')
$nodes.Item(0).AppendChild($xml.CreateTextNode('%s')) | Out-Null
$nodes.Item(1).AppendChild($xml.CreateTextNode($msg)) | Out-Null
[Windows.UI.Notifications.ToastNotificationManager]::CreateToastNotifier('%s').Show([Windows.UI.Notifications.ToastNotification]::new($xml))
`, base64.StdEncoding.EncodeToString([]byte(text)), Title, Title)
}

// psEncode encodes a script for -EncodedCommand (UTF-16LE + base64).
func psEncode(script string) string {
	runes := utf16.Encode([]rune(script))
	buf := make([]byte, len(runes)*2)
	for i, r := range runes {
		binary.LittleEndian.PutUint16(buf[i*2:], r)
	}
	return base64.StdEncoding.EncodeToString(buf)
}