package appdata

import (
	"os"
	"os/user"
	"path/filepath"
	"runtime"
	"strings"
	"unicode"
)

// GetDataDir returns an operating system specific directory to be used for
// storing application data for an application.
// See Dir for more details. This unexported version takes an operating system argument primarily to enable the testing
// package to properly test the function by forcing an operating system that is not the currently one.
func GetDataDir(goos, appName string, roaming bool) string {
	if appName == "" || appName == "." {
		return "."
	}
	// The caller really shouldn't prepend the appName with a period, but if they do, handle it gracefully by trimming
	// it.
	appName = strings.TrimPrefix(appName, ".")
	appNameUpper := string(unicode.ToUpper(rune(appName[0]))) + appName[1:]
	appNameLower := string(unicode.ToLower(rune(appName[0]))) + appName[1:]
	// Get the OS specific home directory via the Go standard lib.
	var homeDir string
	var usr *user.User
	var e error
	if usr, e = user.Current(); e == nil {
		homeDir = usr.HomeDir
	}
	// Fall back to standard HOME environment variable that works for most POSIX OSes if the directory from the Go
	// standard lib failed.
	if e != nil || homeDir == "" {
		homeDir = os.Getenv("HOME")
	}
	switch goos {
	// Attempt to use the LOCALAPPDATA or APPDATA environment variable on Windows.
	case "windows":
		// Windows XP and before didn't have a LOCALAPPDATA, so fallback to regular APPDATA when LOCALAPPDATA is not
		// set.
		appData := os.Getenv("LOCALAPPDATA")
		if roaming || appData == "" {
			appData = os.Getenv("APPDATA")
		}
		if appData != "" {
			return filepath.Join(appData, appNameUpper)
		}
	case "darwin":
		if homeDir != "" {
			return filepath.Join(
				homeDir, "Library",
				"Application Support", appNameUpper,
			)
		}
	case "plan9":
		if homeDir != "" {
			return filepath.Join(homeDir, appNameLower)
		}
	default:
		if homeDir != "" {
			return filepath.Join(homeDir, "."+appNameLower)
		}
	}
	// Fall back to the current directory if all else fails.
	return "."
}

// Dir returns an operating system specific directory to be used for storing application data for an application. The
// appName parameter is the name of the application the data directory is being requested for.  This function will
// prepend a period to the appName for POSIX style operating systems since that is standard practice.
//
// An empty appName or one with a single dot is treated as requesting the current directory so only "." will be
// returned. Further, the first character of appName will be made lowercase for POSIX style operating systems and
// uppercase for Mac and Windows since that is standard practice.
//
// The roaming parameter only applies to Windows where it specifies the roaming application data profile (%APPDATA%)
// should be used instead of the local one (%LOCALAPPDATA%) that is used by default. Example results:
//
//	dir := Dir("myapp", false)
//
//	 POSIX (Linux/BSD): ~/.myapp
//	 Mac OS: $HOME/Library/Application Support/Myapp
//	 Windows: %LOCALAPPDATA%\Myapp
//	 Plan 9: $home/myapp
func Dir(appName string, roaming bool) string {
	return GetDataDir(runtime.GOOS, appName, roaming)
}