scan.go

package deepclean

import (
	"io/fs"
	"path/filepath"
	"runtime"
	"sync"
)

// Scanner contains fields to access the results of an ongoing Scan.
//
// If the underlying filepath Walk encounters a fatal error, the results
// channel will be closed and Err() will return a non-nil value. Always
// drain (*Scanner).C prior to checking Err().
//
// If the underlying filepath Walk encounters a non-fatal error, the
// walked directory will be silently skipped (for now).
type Scanner struct {
	C   <-chan Result
	err error
}

// Err returns the error status of the underlying filepath Walk performed by the
// scanner. This will only be set once the Walk has exited, indicated by the
// Results channel being closed.
func (s Scanner) Err() error {
	return s.err
}

// Scan walks the path searching for directories matching the targets strings,
// and then initiates a DirStats on the directory, returning the Results as they
// occur on the returned channel.
func Scan(path string, targets []string) *Scanner {
	resultsChan := make(chan Result)
	scanner := Scanner{C: resultsChan}

	go func() {
		defer close(resultsChan)

		// spawn worker pool to perform stating of matched target directories
		matchedDirs := make(chan string)
		var wg sync.WaitGroup
		for i := 0; i < runtime.NumCPU(); i++ {
			wg.Add(1)
			go func() {
				defer wg.Done()
				for path := range matchedDirs {
					if s, err := Stat(path); err == nil {
						resultsChan <- Result{Path: path, Stats: s}
					}
				}
			}()
		}

		// primary file system walk looking for target directories
		scanner.err = filepath.WalkDir(path, func(fpath string, d fs.DirEntry, err error) error {
			if err != nil && path == fpath {
				// error on initial directory should be fatal
				return err
			} else if err != nil {
				// error anywhere else should skip the file, but not abort the scan
				// TODO: log only if verbose
				// fmt.Fprintf(os.Stderr, "ERROR: %s\n", err)
				return nil
			}

			// Positives are directories matching any target string. For each
			// match, send to the worker pool to gather stats, but skip further
			// walking of the subdir in this primary scan thread.
			if d.IsDir() && inTargets(targets, fpath) {
				matchedDirs <- fpath
				return fs.SkipDir
			}
			return nil
		})
		close(matchedDirs)
		wg.Wait()
	}()

	return &scanner
}

func inTargets(targets []string, path string) bool {
	for _, t := range targets {
		if t == filepath.Base(path) {
			return true
		}
	}
	return false
}

// Stat walks the directory at path collecting the aggregate DirStats.
func Stat(path string) (DirStats, error) {
	var t DirStats
	err := filepath.WalkDir(path, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}

		fi, err := d.Info()
		if err != nil {
			return err
		}

		t.Files++
		if !d.IsDir() {
			t.Bytes += uint64(fi.Size())
		}
		return nil
	})
	return t, err
}