// Package userlogdir has a single function, UserLogDir, that returns
// an OS-specific path for storing user logs.
package userlogdir

import (
	"errors"
	"os"
	"runtime"
)

// UserLogDir returns the default root directory to use for user-specific
// log data. Users should create their own application-specific subdirectory
// within this one and use that.
//
// On Unix systems, it returns $XDG_CACHE_HOME as specified by
// https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if
// non-empty, else $HOME/.cache.
// On Darwin, it returns $HOME/Library/Logs.
// On Windows, it returns %LocalAppData%.
// On Plan 9, it returns $home/lib/cache.
//
// If the location cannot be determined (for example, $HOME is not defined),
// then it will return an error.
func UserLogDir() (string, error) {
	var dir string

	switch runtime.GOOS {
	case "windows":
		dir = os.Getenv("LocalAppData")
		if dir == "" {
			return "", errors.New("%LocalAppData% is not defined")
		}

	case "darwin", "ios":
		dir = os.Getenv("HOME")
		if dir == "" {
			return "", errors.New("$HOME is not defined")
		}
		dir += "/Library/Logs"

	case "plan9":
		dir = os.Getenv("home")
		if dir == "" {
			return "", errors.New("$home is not defined")
		}
		dir += "/lib/cache"

	default: // Unix
		dir = os.Getenv("XDG_CACHE_HOME")
		if dir == "" {
			dir = os.Getenv("HOME")
			if dir == "" {
				return "", errors.New("neither $XDG_CACHE_HOME nor $HOME are defined")
			}
			dir += "/.cache"
		}
	}

	return dir, nil
}