package daemon

import (
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"slices"
	"strings"
	"sync"

	"github.com/adrg/xdg"
)

// EnvVars are variables which are derived based on the environment which the
// process is running in.
type EnvVars struct {
	RuntimeDirPath string // TODO should be private to this package
	StateDirPath   string // TODO should be private to this package
	HTTPSocketPath string
}

func getRPCSocketDirPath() string {
	path, err := firstExistingDir(
		"/run",
		"/var/run",
		"/tmp",
		"/dev/shm",
	)
	if err != nil {
		panic(fmt.Sprintf("Failed to find directory for RPC socket: %v", err))
	}

	return path
}

// GetEnvVars will return the EnvVars of the current processes, as determined by
// the process's environment.
var GetEnvVars = sync.OnceValue(func() (v EnvVars) {
	// RUNTIME_DIRECTORY/STATE_DIRECTORY are used by the systemd service in
	// conjunction with the RuntimeDirectory/StateDirectory directives.

	v.RuntimeDirPath = envOr(
		"RUNTIME_DIRECTORY",
		func() string { return filepath.Join(xdg.RuntimeDir, "isle") },
	)

	v.StateDirPath = envOr(
		"STATE_DIRECTORY",
		func() string { return filepath.Join(xdg.StateHome, "isle") },
	)

	v.HTTPSocketPath = envOr(
		"ISLE_SOCKET_PATH",
		func() string {
			return filepath.Join(getRPCSocketDirPath(), "isle-daemon.sock")
		},
	)

	return
})

////////////////////////////////////////////////////////////////////////////////
// Jigs

func envOr(name string, fallback func() string) string {
	if v := os.Getenv(name); v != "" {
		return v
	}
	return fallback()
}

func firstExistingDir(paths ...string) (string, error) {
	var errs []error
	for _, path := range paths {
		stat, err := os.Stat(path)
		switch {
		case errors.Is(err, fs.ErrExist):
			continue
		case err != nil:
			errs = append(
				errs, fmt.Errorf("checking if path %q exists: %w", path, err),
			)
		case !stat.IsDir():
			errs = append(
				errs, fmt.Errorf("path %q exists but is not a directory", path),
			)
		default:
			return path, nil
		}
	}

	err := fmt.Errorf(
		"no directory found at any of the following paths: %s",
		strings.Join(paths, ", "),
	)
	if len(errs) > 0 {
		err = errors.Join(slices.Insert(errs, 0, err)...)
	}
	return "", err
}