package config

import (
	"errors"
	"path/filepath"
	"runtime"
)

// fileName is the config file's name inside the config directory.
const fileName = "config.toml"

// ErrNoHome reports that the home directory cannot be determined (no HOME or
// APPDATA environment variable).
var ErrNoHome = errors.New("config directory unknown (HOME or APPDATA not set)")

// Dir returns talk's platform-native config directory: ~/.config/talk on
// Linux (or $XDG_CONFIG_HOME/talk), ~/Library/Application Support/talk on
// macOS, %APPDATA%\talk on Windows.
func Dir(getenv func(string) string) (string, error) {
	return dirFor(runtime.GOOS, getenv)
}

// dirFor is the testable platform logic behind Dir: goos is a parameter so
// all platforms can be table-tested from one host.
//
// XDG_CONFIG_HOME is honoured only when it holds an absolute path (XDG
// spec); relative values are ignored.
func dirFor(goos string, getenv func(string) string) (string, error) {
	if getenv == nil {
		return "", ErrNoHome
	}
	switch goos {
	case "windows":
		appdata := getenv("APPDATA")
		if appdata == "" {
			return "", ErrNoHome
		}
		return filepath.Join(appdata, "talk"), nil
	case "darwin":
		home := getenv("HOME")
		if home == "" {
			return "", ErrNoHome
		}
		return filepath.Join(home, "Library", "Application Support", "talk"), nil
	default: // linux and other unix-likes
		if xdg := getenv("XDG_CONFIG_HOME"); xdg != "" && filepath.IsAbs(xdg) {
			return filepath.Join(xdg, "talk"), nil
		}
		home := getenv("HOME")
		if home == "" {
			return "", ErrNoHome
		}
		return filepath.Join(home, ".config", "talk"), nil
	}
}

// Path returns the full path of config.toml in the config directory
// (diagnostics, setup).
func Path(getenv func(string) string) (string, error) {
	dir, err := Dir(getenv)
	if err != nil {
		return "", err
	}
	return filepath.Join(dir, fileName), nil
}