// Package notify shows desktop notifications: best effort, through the
// operating system's own tools, without a library dependency and without
// CGO (the same line as provider/osbuiltin):
//
//	Linux:   notify-send (libnotify; needs a notification daemon)
//	macOS:   osascript `display notification`
//	Windows: PowerShell toast (Windows.UI.Notifications)
//
// 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
// (binary present; whether a daemon listens only Show reveals).
func Available() bool {
	_, err := exec.LookPath(tool())
	return err == nil
}

// Describe names the path for `talk doctor`.
func Describe() string {
	t := tool()
	if _, err := exec.LookPath(t); err != nil {
		return t + " not found"
	}
	switch runtime.GOOS {
	case "darwin":
		return "osascript (Notification Center)"
	case "windows":
		return "powershell (Windows toast)"
	default:
		return "notify-send (libnotify)"
	}
}

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

// Show shows a notification with Title and text and waits for the OS call
// to finish (not for the notification to be closed).
func Show(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)
}