// Copyright 2013 Prometheus Team
// 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 model

import (
	"encoding/binary"
	"fmt"
	"hash/fnv"
	"sort"
	"strconv"
)

// Fingerprint provides a hash-capable representation of a Metric.
// For our purposes, FNV-1A 64-bit is used.
type Fingerprint uint64

func (f Fingerprint) String() string {
	return fmt.Sprintf("%016x", uint64(f))
}

// Less implements sort.Interface.
func (f Fingerprint) Less(o Fingerprint) bool {
	return f < o
}

// Equal implements sort.Interface.
func (f Fingerprint) Equal(o Fingerprint) bool {
	return f == o
}

// LoadFromString transforms a string representation into a Fingerprint.
func (f *Fingerprint) LoadFromString(s string) error {
	num, err := strconv.ParseUint(s, 16, 64)
	if err != nil {
		return err
	}
	*f = Fingerprint(num)
	return nil
}

// MustLoadFromString works like LoadFromString but panics in case of an error.
func (f *Fingerprint) MustLoadFromString(s string) {
	if err := f.LoadFromString(s); err != nil {
		panic(err)
	}
}

// LoadFromMetric decomposes a Metric into this Fingerprint
func (f *Fingerprint) LoadFromMetric(m Metric) {
	labelLength := len(m)
	labelNames := make([]string, 0, labelLength)

	for labelName := range m {
		labelNames = append(labelNames, string(labelName))
	}

	sort.Strings(labelNames)

	summer := fnv.New64a()

	for _, labelName := range labelNames {
		labelValue := m[LabelName(labelName)]

		summer.Write([]byte(labelName))
		summer.Write([]byte{0})
		summer.Write([]byte(labelValue))
	}

	*f = Fingerprint(binary.LittleEndian.Uint64(summer.Sum(nil)))
}

// Fingerprints represents a collection of Fingerprint subject to a given
// natural sorting scheme. It implements sort.Interface.
type Fingerprints []Fingerprint

// Len implements sort.Interface.
func (f Fingerprints) Len() int {
	return len(f)
}

// Less implements sort.Interface.
func (f Fingerprints) Less(i, j int) bool {
	return f[i] < f[j]
}

// Swap implements sort.Interface.
func (f Fingerprints) Swap(i, j int) {
	f[i], f[j] = f[j], f[i]
}

// FingerprintSet is a set of Fingerprints.
type FingerprintSet map[Fingerprint]struct{}

// Equal returns true if both sets contain the same elements (and not more).
func (s FingerprintSet) Equal(o FingerprintSet) bool {
	if len(s) != len(o) {
		return false
	}

	for k := range s {
		if _, ok := o[k]; !ok {
			return false
		}
	}

	return true
}

// Intersection returns the elements contained in both sets.
func (s FingerprintSet) Intersection(o FingerprintSet) FingerprintSet {
	myLength, otherLength := len(s), len(o)
	if myLength == 0 || otherLength == 0 {
		return FingerprintSet{}
	}

	subSet := s
	superSet := o

	if otherLength < myLength {
		subSet = o
		superSet = s
	}

	out := FingerprintSet{}

	for k := range subSet {
		if _, ok := superSet[k]; ok {
			out[k] = struct{}{}
		}
	}

	return out
}