filter/filter.go

// Copyright (C) 2017 Marius Schellenberger

// Package filter implements simple struct field filtering
package filter

import (
	"errors"
	"reflect"
	"strconv"
	"strings"
)

const any = '*'

type Filter interface {
	Len() int
	Index(int) interface{}
	Remove(int, int)
}

type match struct {
	fields []string
	value  string
}

type Logic int

const (
	AND Logic = iota
	OR
	NOT
)

// Query implements the filter query
type Query struct {
	m []match
	l Logic
}

// NewQuery parses the filter query and match logic
// Examples:
// Explicit match: <struct field>:<struct value>
// Wildcard match:
// <struct field>:*<part of struct value>
// <struct field>:<part of struct value>*
// <struct field>:*<middl of struct value>*
// Nested structs:
// <struct field>.<struct field>:<struct value>
// Multiple matches:
// <struct field>:<struct value> <struct field>:<struct value>*
// Supported data types are: string, int, bool
// Bool does not support the wildcard operator
func NewQuery(s string, l Logic) (q *Query, err error) {
	if l > 2 || l < 0 {
		l = AND
	}
	q = &Query{l: l}
	qm := make(map[string]struct{})
	fields := strings.Split(s, " ")
	for _, v := range fields {
		if v == "" {
			continue
		}
		m := strings.SplitN(v, ":", 2)
		if len(m) != 2 {
			err = errors.New("invalid match: " + v)
			return
		}
		if l == AND {
			if _, ok := qm[m[0]]; ok {
				err = errors.New("field for AND matching used more than once: " + m[0])
				return
			}
			qm[m[0]] = struct{}{}
		}
		q.m = append(q.m, match{strings.Split(m[0], "."), m[1]})
	}
	return
}

func (q *Query) check(oks []bool) (b bool) {
	b = true
	switch q.l {
	case AND:
		for _, ok := range oks {
			if !ok {
				b = false
			}
		}
	case NOT:
		for _, ok := range oks {
			if ok {
				b = false
			}
		}
	}
	return
}

func (q *Query) match(v reflect.Value) bool {
	if q.l == OR {
		return q.orMatch(v)
	}
	return q.allMatch(v)
}

func (q *Query) allMatch(v reflect.Value) (ok bool) {
	if v.Kind() != reflect.Struct {
		return
	}
	ql := len(q.m)
	if ql == 0 {
		return
	}
	oks := make([]bool, ql)
	for i, qv := range q.m {
		s := ""
		fl := len(qv.fields)
		vl := len(qv.value)
		if fl == 0 {
			continue
		}
		val := v.FieldByName(qv.fields[0])
		for j := 1; j < fl; j++ {
			val = val.FieldByName(qv.fields[j])
		}
		switch val.Kind() {
		case reflect.Int, reflect.Int8, reflect.Int16,
			reflect.Int32, reflect.Int64:
			s = strconv.Itoa(int(val.Int()))
		case reflect.String:
			s = val.String()
		case reflect.Bool:
			if vl == 0 {
				continue
			}
			b := val.Bool()
			if b && qv.value[0] == 't' {
				oks[i] = true
				continue
			}
			if !b && qv.value[0] == 'f' {
				oks[i] = true
			}
			continue
		default:
			continue
		}
		switch {
		case vl >= 3:
			if qv.value[0] == any && qv.value[vl-1] == any {
				if strings.Contains(s, qv.value[1:vl-1]) {
					oks[i] = true
					continue
				}
			}
			fallthrough
		case vl >= 2:
			switch {
			case qv.value[0] == any:
				if strings.HasSuffix(s, qv.value[1:]) {
					oks[i] = true
					continue
				}
			case qv.value[vl-1] == any:
				if strings.HasPrefix(s, qv.value[:vl-1]) {
					oks[i] = true
					continue
				}
			}
		}
		if s == qv.value {
			oks[i] = true
		}
	}
	return q.check(oks)
}

func (q *Query) orMatch(v reflect.Value) bool {
	if v.Kind() != reflect.Struct {
		return false
	}
	ql := len(q.m)
	if ql == 0 {
		return false
	}
	for _, qv := range q.m {
		s := ""
		fl := len(qv.fields)
		vl := len(qv.value)
		if fl == 0 {
			continue
		}
		val := v.FieldByName(qv.fields[0])
		for j := 1; j < fl; j++ {
			val = val.FieldByName(qv.fields[j])
		}
		switch val.Kind() {
		case reflect.Int, reflect.Int8, reflect.Int16,
			reflect.Int32, reflect.Int64:
			s = strconv.Itoa(int(val.Int()))
		case reflect.String:
			s = val.String()
		case reflect.Bool:
			if vl == 0 {
				continue
			}
			b := val.Bool()
			if b && qv.value[0] == 't' {
				return true
			}
			if !b && qv.value[0] == 'f' {
				return true
			}
			continue
		default:
			continue
		}
		switch {
		case vl >= 3:
			if qv.value[0] == any && qv.value[vl-1] == any {
				if strings.Contains(s, qv.value[1:vl-1]) {
					return true
				}
			}
			fallthrough
		case vl >= 2:
			switch {
			case qv.value[0] == any:
				if strings.HasSuffix(s, qv.value[1:]) {
					return true
				}
			case qv.value[vl-1] == any:
				if strings.HasPrefix(s, qv.value[:vl-1]) {
					return true
				}
			}
		}
		if s == qv.value {
			return true
		}
	}
	return false
}

// GenericFilter takes any slice of structs value and returns the same slice type containing only the filter matches.
// Returns nil if interface{} is not a slice.
func (q *Query) GenericFilter(i interface{}) interface{} {
	v := reflect.ValueOf(i)
	if v.Kind() != reflect.Slice {
		return nil
	}
	ret := reflect.MakeSlice(v.Type(), 0, 0)
	for i := 0; i < v.Len(); i++ {
		val := v.Index(i)
		if q.match(val) {
			ret = reflect.Append(ret, val)
		}
	}
	return ret.Interface()
}

func (q Query) Filter(f Filter) {
	count := 0
	i := 0
	for ; i < f.Len(); i++ {
		if q.match(reflect.ValueOf(f.Index(i))) {
			if count > 0 {
				f.Remove(i-count, i)
				i -= count
			}
			count = 0
		} else {
			count++
		}
	}
	if count > 0 {
		f.Remove(i-count, i)
	}
}