package originclient

import (
	"errors"
	"os"
	"path/filepath"
	"strings"

	"github.com/google/uuid"
)

// errMachineIDUnavailable is returned by the OS-specific machineID() when
// no real machine ID could be read.
var errMachineIDUnavailable = errors.New("originclient: OS machine id unavailable")

// machineIDFunc is a variable indirection over the OS-specific machineID()
// so tests can stub OS machine-id lookup without depending on the actual
// host's state.
var machineIDFunc = machineID

// ResolveMachineID returns the unique install ID to report to Origin, in
// priority order:
//
//  1. explicit, if non-empty — a caller-supplied override.
//  2. the real OS machine ID (/etc/machine-id on Linux, IOPlatformUUID on
//     macOS, MachineGuid on Windows), if readable.
//  3. the ID already persisted at path, if present.
//  4. a newly generated UUID, which ResolveMachineID attempts to persist to
//     path for future runs.
//
// OS-ID and persistence failures are logged as warnings, not returned as
// errors: ResolveMachineID always returns a usable ID, falling back to one
// that only lives for this process if it cannot be read from the OS or
// saved to disk. logger may be nil.
func ResolveMachineID(explicit, path string, logger Logger) string {
	if logger == nil {
		logger = noopLogger{}
	}

	if id := strings.TrimSpace(explicit); id != "" {
		return id
	}

	if id, err := machineIDFunc(); err == nil {
		if id = strings.TrimSpace(id); id != "" {
			return id
		}
	} else {
		logger.Warn("machine id: OS machine id unavailable, falling back to a generated id", err)
	}

	if path == "" {
		path = defaultInstallIDPath()
	}

	if data, err := os.ReadFile(path); err == nil {
		if id := strings.TrimSpace(string(data)); id != "" {
			return id
		}
	}

	id := uuid.NewString()
	if err := persistInstallID(path, id); err != nil {
		logger.Warn("machine id: failed to persist generated id, using an ephemeral id for this run", err)
	}
	return id
}

func persistInstallID(path, id string) error {
	if dir := filepath.Dir(path); dir != "." && dir != "" {
		if err := os.MkdirAll(dir, 0o750); err != nil {
			return err
		}
	}
	return os.WriteFile(path, []byte(id+"\n"), 0o600)
}

// defaultInstallIDPath returns the fallback-UUID persistence path used when
// Config.InstallIDPath is unset: the OS user-config directory, or the OS
// temp directory if that cannot be determined.
func defaultInstallIDPath() string {
	dir, err := os.UserConfigDir()
	if err != nil || dir == "" {
		dir = os.TempDir()
	}
	return filepath.Join(dir, "origin-client", "install-id")
}