// Copyright 2017 The Prometheus Authors
// 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 labels

import (
	"bytes"
	"encoding/json"
	"sort"
	"strconv"

	"github.com/cespare/xxhash"
)

const sep = '\xff'

// Well-known label names used by Prometheus components.
const (
	MetricName   = "__name__"
	AlertName    = "alertname"
	BucketLabel  = "le"
	InstanceName = "instance"
)

// Label is a key/value pair of strings.
type Label struct {
	Name, Value string
}

// Labels is a sorted set of labels. Order has to be guaranteed upon
// instantiation.
type Labels []Label

func (ls Labels) Len() int           { return len(ls) }
func (ls Labels) Swap(i, j int)      { ls[i], ls[j] = ls[j], ls[i] }
func (ls Labels) Less(i, j int) bool { return ls[i].Name < ls[j].Name }

func (ls Labels) String() string {
	var b bytes.Buffer

	b.WriteByte('{')
	for i, l := range ls {
		if i > 0 {
			b.WriteByte(',')
			b.WriteByte(' ')
		}
		b.WriteString(l.Name)
		b.WriteByte('=')
		b.WriteString(strconv.Quote(l.Value))
	}
	b.WriteByte('}')

	return b.String()
}

// MarshalJSON implements json.Marshaler.
func (ls Labels) MarshalJSON() ([]byte, error) {
	return json.Marshal(ls.Map())
}

// UnmarshalJSON implements json.Unmarshaler.
func (ls *Labels) UnmarshalJSON(b []byte) error {
	var m map[string]string

	if err := json.Unmarshal(b, &m); err != nil {
		return err
	}

	*ls = FromMap(m)
	return nil
}

// MarshalYAML implements yaml.Marshaler.
func (ls Labels) MarshalYAML() (interface{}, error) {
	return ls.Map(), nil
}

// UnmarshalYAML implements yaml.Unmarshaler.
func (ls *Labels) UnmarshalYAML(unmarshal func(interface{}) error) error {
	var m map[string]string

	if err := unmarshal(&m); err != nil {
		return err
	}

	*ls = FromMap(m)
	return nil
}

// MatchLabels returns a subset of Labels that matches/does not match with the provided label names based on the 'on' boolean.
// If on is set to true, it returns the subset of labels that match with the provided label names and its inverse when 'on' is set to false.
func (ls Labels) MatchLabels(on bool, names ...string) Labels {
	matchedLabels := Labels{}

	nameSet := map[string]struct{}{}
	for _, n := range names {
		nameSet[n] = struct{}{}
	}

	for _, v := range ls {
		if _, ok := nameSet[v.Name]; on == ok && (on || v.Name != MetricName) {
			matchedLabels = append(matchedLabels, v)
		}
	}

	return matchedLabels
}

// Hash returns a hash value for the label set.
func (ls Labels) Hash() uint64 {
	b := make([]byte, 0, 1024)

	for _, v := range ls {
		b = append(b, v.Name...)
		b = append(b, sep)
		b = append(b, v.Value...)
		b = append(b, sep)
	}
	return xxhash.Sum64(b)
}

// HashForLabels returns a hash value for the labels matching the provided names.
// 'names' have to be sorted in ascending order.
func (ls Labels) HashForLabels(b []byte, names ...string) (uint64, []byte) {
	b = b[:0]
	i, j := 0, 0
	for i < len(ls) && j < len(names) {
		if names[j] < ls[i].Name {
			j++
		} else if ls[i].Name < names[j] {
			i++
		} else {
			b = append(b, ls[i].Name...)
			b = append(b, sep)
			b = append(b, ls[i].Value...)
			b = append(b, sep)
			i++
			j++
		}
	}
	return xxhash.Sum64(b), b
}

// HashWithoutLabels returns a hash value for all labels except those matching
// the provided names.
// 'names' have to be sorted in ascending order.
func (ls Labels) HashWithoutLabels(b []byte, names ...string) (uint64, []byte) {
	b = b[:0]
	j := 0
	for i := range ls {
		for j < len(names) && names[j] < ls[i].Name {
			j++
		}
		if ls[i].Name == MetricName || (j < len(names) && ls[i].Name == names[j]) {
			continue
		}
		b = append(b, ls[i].Name...)
		b = append(b, sep)
		b = append(b, ls[i].Value...)
		b = append(b, sep)
	}
	return xxhash.Sum64(b), b
}

// Copy returns a copy of the labels.
func (ls Labels) Copy() Labels {
	res := make(Labels, len(ls))
	copy(res, ls)
	return res
}

// Get returns the value for the label with the given name.
// Returns an empty string if the label doesn't exist.
func (ls Labels) Get(name string) string {
	for _, l := range ls {
		if l.Name == name {
			return l.Value
		}
	}
	return ""
}

// Has returns true if the label with the given name is present.
func (ls Labels) Has(name string) bool {
	for _, l := range ls {
		if l.Name == name {
			return true
		}
	}
	return false
}

// HasDuplicateLabelNames returns whether ls has duplicate label names.
// It assumes that the labelset is sorted.
func (ls Labels) HasDuplicateLabelNames() (string, bool) {
	for i, l := range ls {
		if i == 0 {
			continue
		}
		if l.Name == ls[i-1].Name {
			return l.Name, true
		}
	}
	return "", false
}

// WithoutEmpty returns the labelset without empty labels.
// May return the same labelset.
func (ls Labels) WithoutEmpty() Labels {
	for _, v := range ls {
		if v.Value != "" {
			continue
		}
		els := make(Labels, 0, len(ls)-1)
		for _, v := range ls {
			if v.Value != "" {
				els = append(els, v)
			}
		}
		return els
	}
	return ls
}

// Equal returns whether the two label sets are equal.
func Equal(ls, o Labels) bool {
	if len(ls) != len(o) {
		return false
	}
	for i, l := range ls {
		if l.Name != o[i].Name || l.Value != o[i].Value {
			return false
		}
	}
	return true
}

// Map returns a string map of the labels.
func (ls Labels) Map() map[string]string {
	m := make(map[string]string, len(ls))
	for _, l := range ls {
		m[l.Name] = l.Value
	}
	return m
}

// New returns a sorted Labels from the given labels.
// The caller has to guarantee that all label names are unique.
func New(ls ...Label) Labels {
	set := make(Labels, 0, len(ls))
	for _, l := range ls {
		set = append(set, l)
	}
	sort.Sort(set)

	return set
}

// FromMap returns new sorted Labels from the given map.
func FromMap(m map[string]string) Labels {
	l := make([]Label, 0, len(m))
	for k, v := range m {
		l = append(l, Label{Name: k, Value: v})
	}
	return New(l...)
}

// FromStrings creates new labels from pairs of strings.
func FromStrings(ss ...string) Labels {
	if len(ss)%2 != 0 {
		panic("invalid number of strings")
	}
	var res Labels
	for i := 0; i < len(ss); i += 2 {
		res = append(res, Label{Name: ss[i], Value: ss[i+1]})
	}

	sort.Sort(res)
	return res
}

// Compare compares the two label sets.
// The result will be 0 if a==b, <0 if a < b, and >0 if a > b.
func Compare(a, b Labels) int {
	l := len(a)
	if len(b) < l {
		l = len(b)
	}

	for i := 0; i < l; i++ {
		if a[i].Name != b[i].Name {
			if a[i].Name < b[i].Name {
				return -1
			} else {
				return 1
			}
		}
		if a[i].Value != b[i].Value {
			if a[i].Value < b[i].Value {
				return -1
			} else {
				return 1
			}
		}
	}
	// If all labels so far were in common, the set with fewer labels comes first.
	return len(a) - len(b)
}

// Builder allows modifying Labels.
type Builder struct {
	base Labels
	del  []string
	add  []Label
}

// NewBuilder returns a new LabelsBuilder.
func NewBuilder(base Labels) *Builder {
	b := &Builder{
		del: make([]string, 0, 5),
		add: make([]Label, 0, 5),
	}
	b.Reset(base)
	return b
}

// Reset clears all current state for the builder.
func (b *Builder) Reset(base Labels) {
	b.base = base
	b.del = b.del[:0]
	b.add = b.add[:0]
	for _, l := range b.base {
		if l.Value == "" {
			b.del = append(b.del, l.Name)
		}
	}
}

// Del deletes the label of the given name.
func (b *Builder) Del(ns ...string) *Builder {
	for _, n := range ns {
		for i, a := range b.add {
			if a.Name == n {
				b.add = append(b.add[:i], b.add[i+1:]...)
			}
		}
		b.del = append(b.del, n)
	}
	return b
}

// Set the name/value pair as a label.
func (b *Builder) Set(n, v string) *Builder {
	if v == "" {
		// Empty labels are the same as missing labels.
		return b.Del(n)
	}
	for i, a := range b.add {
		if a.Name == n {
			b.add[i].Value = v
			return b
		}
	}
	b.add = append(b.add, Label{Name: n, Value: v})

	return b
}

// Labels returns the labels from the builder. If no modifications
// were made, the original labels are returned.
func (b *Builder) Labels() Labels {
	if len(b.del) == 0 && len(b.add) == 0 {
		return b.base
	}

	// In the general case, labels are removed, modified or moved
	// rather than added.
	res := make(Labels, 0, len(b.base))
Outer:
	for _, l := range b.base {
		for _, n := range b.del {
			if l.Name == n {
				continue Outer
			}
		}
		for _, la := range b.add {
			if l.Name == la.Name {
				continue Outer
			}
		}
		res = append(res, l)
	}
	res = append(res, b.add...)
	sort.Sort(res)

	return res
}
