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// Copyright 2020 Northern.tech AS
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package doc
import (
"fmt"
"reflect"
"sort"
"go.mongodb.org/mongo-driver/bson"
)
const (
// PermutationThreshold limits the complexity of Unwound maps to the
// given array length.
PermutationThreshold = 1024
)
var (
// ErrPermutations is returned if the map contains arrays with a combined
// number of permutations than the threshold.
ErrPermutations = fmt.Errorf(
"object complexity (array permutations) exceeded threshold")
)
// item is an internally used struct to organize the output in UnwindMap
type item struct {
Key string
Value reflect.Value
}
// UnwindMap takes a string map and perform mongodb $unwind aggregation operation
// on all array entries.
// Don't return a map - but a sorted list of tuples; mongo indices are sensitive
// to order.
// Example:
// {"foo": ["1", "2"], "bar": "3"} becomes
// [ {{"foo", "1", "bar", "3"}}, {{"foo": "2", "bar": "3"}} ]
func UnwindMap(
in interface{},
) ([]bson.D, error) {
// returned bloated map
var unwoundMap []bson.D
// permutations and cumulative sum of permutations
var permutations int64 = 1
inVal := reflect.ValueOf(in)
if inVal.Kind() != reflect.Map {
return nil, fmt.Errorf(
"invalid argument type: %s != map[string]interface{}",
inVal.Kind().String())
}
mapLen := inVal.Len()
orderedMap := make([]item, mapLen)
// Compute number of permutations and initialize ordered map.
var i int
keys := inVal.MapKeys()
for _, key := range keys {
var keyStr string
var ok bool
value := inVal.MapIndex(key)
if key.Kind() == reflect.Interface {
key = key.Elem()
}
if value.Kind() == reflect.Interface {
value = value.Elem()
}
if keyStr, ok = key.Interface().(string); !ok {
return nil, fmt.Errorf("invalid argument type: "+
"%s != map[string]interface{}", inVal.Kind())
}
switch value.Kind() {
case reflect.Slice, reflect.Array:
orderedMap[i] = item{
Key: keyStr,
}
prevPermutations := permutations
permutations = permutations * int64(value.Len())
// Check with constraint or overflow
if permutations > PermutationThreshold ||
permutations < prevPermutations {
return nil, ErrPermutations
}
case reflect.String:
orderedMap[i] = item{
Key: keyStr,
}
default:
return nil, fmt.Errorf(
"cannot unwind entry %s of type: %s",
key, value.Kind().String())
}
orderedMap[i].Value = value
i++
}
sort.Slice(orderedMap, func(i, j int) bool {
return orderedMap[i].Key < orderedMap[j].Key
})
// Allocate returned map array
unwoundMap = make([]bson.D, permutations)
// Fill in the map entries
for k := int64(0); k < permutations; k++ {
var tmpPerm int64 = 1
unwoundMap[k] = make(bson.D, mapLen)
for i, item := range orderedMap {
unwoundMap[k][i].Key = item.Key
itemKind := item.Value.Kind()
if itemKind == reflect.Slice ||
itemKind == reflect.Array {
// Compute index
// - think of it as counting using array
// length as base
itemLen := item.Value.Len()
idx := (k / tmpPerm) % int64(itemLen)
unwoundMap[k][i].Value = item.Value.
Index(int(idx)).Interface()
// Update cumulative permutations
tmpPerm *= int64(itemLen)
} else {
unwoundMap[k][i].Value = item.Value.Interface()
}
}
}
return unwoundMap, nil
}
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