filter.go

package util

import (
	"fmt"
	"sync"
)

// StringFilterT is a tuple for a value that has not been filtered out
type StringFilterT struct {
	String string
	Err    error
}

type StringFilterWrapper []StringFilterT

func (f StringFilterWrapper) Error() error {
	var errs []error
	for _, r := range f {
		if r.Err != nil {
			errs = append(errs, fmt.Errorf("'%s': %s", r.String, r.Err))
		}
	}
	if len(errs) > 0 {
		return fmt.Errorf("%v", errs)
	}
	return nil
}

// FilterFn is a function used to filter a list of string. If the
// function returns false or a non-nil error, it will not be filtered.
type FilterFn func(string) (filter bool, err error)

// StringFilter will run fn with each element of in, filtering out elements.
// it will return a slice of results where fn returned ok, or a non-nil error.
// it will also call each instance of fn in it's own goroutine.
func StringFilter(fn FilterFn, in ...string) StringFilterWrapper {
	outCh := make(chan StringFilterT, len(in))
	var wg sync.WaitGroup
	for i, s := range in {
		wg.Add(1)
		go func(i int, s string) {
			defer wg.Done()
			if filter, err := fn(s); err != nil || !filter {
				outCh <- StringFilterT{s, err}
			}
		}(i, s)
	}
	wg.Wait()
	close(outCh)
	res := make([]StringFilterT, len(outCh))
	i := 0
	for o := range outCh {
		res[i] = o
		i++
	}
	return res
}