filter/filter.go

// Copyright (C) 2017 Marius Schellenberger

// Package filter implements simple struct field filtering
package filter

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

// Filter is the filter interface to be implemented for faster non generic filtering
// Example implementation:
// type f []struct
// func (v f) Len() int                { return len(v) }
// func (v f) Index(i int) interface{} { return v[i] }
// func (v *f) Remove(i, j int)        { *v = append((*v)[:i], (*v)[j:]...) }
type Filter interface {
	Len() int
	Index(int) interface{}
	Remove(int, int)
}

type match struct {
	fields []string
	mf     func(string) bool
	bf     func(bool) bool
}

// Logic is the filter logic
type Logic int

const (
	// AND all of the queries have to match
	AND Logic = iota
	// OR only one query has to match
	OR
	// NOT none of the queries have to match
	NOT
)

// Query is 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 (use ** to match the '*' character):
// <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, float, 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}
	if s == "" {
		err = errors.New("query is empty")
		return
	}
	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], "."),
			matchFunc(m[1]),
			boolFunc(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
				return
			}
		}
	case OR:
		b = false
	case NOT:
		for _, ok := range oks {
			if ok {
				b = false
				return
			}
		}
	}
	return
}

func (q *Query) match(v reflect.Value) (ok bool) {
	if v.Kind() != reflect.Struct {
		return
	}
	ql := len(q.m)
	if ql == 0 {
		return
	}
	var (
		oks   []bool
		match bool
	)
	if q.l != OR {
		oks = make([]bool, ql)
	}
	for i, qv := range q.m {
		fl := len(qv.fields)
		if fl == 0 {
			continue
		}
		val := v.FieldByName(qv.fields[0])
		for j := 1; j < fl; j++ {
			val = val.FieldByName(qv.fields[j])
		}
		s, b, err := getValue(val)
		if err != nil {
			continue
		}
		switch s {
		case "":
			match = qv.bf(b)
		default:
			match = qv.mf(s)
		}
		if q.l == OR {
			if match {
				return true
			}
			continue
		}
		oks[i] = match
	}
	return q.check(oks)
}

// 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()
}

// Filter takes a pointer to the Filter interface as an argument.
// The original slice is modified is the filtering process.
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)
	}
}