// Copyright 2013 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 model

import (
	"bytes"
	"encoding/json"
	"fmt"
	"slices"
	"sort"
	"strconv"
)

// A LabelSet is a collection of LabelName and LabelValue pairs.  The LabelSet
// may be fully-qualified down to the point where it may resolve to a single
// Metric in the data store or not.  All operations that occur within the realm
// of a LabelSet can emit a vector of Metric entities to which the LabelSet may
// match.
type LabelSet map[LabelName]LabelValue

// Validate checks whether all names and values in the label set
// are valid.
func (ls LabelSet) Validate() error {
	for ln, lv := range ls {
		if !ln.IsValid() {
			return fmt.Errorf("invalid name %q", ln)
		}
		if !lv.IsValid() {
			return fmt.Errorf("invalid value %q", lv)
		}
	}
	return nil
}

// Equal returns true iff both label sets have exactly the same key/value pairs.
func (ls LabelSet) Equal(o LabelSet) bool {
	if len(ls) != len(o) {
		return false
	}
	for ln, lv := range ls {
		olv, ok := o[ln]
		if !ok {
			return false
		}
		if olv != lv {
			return false
		}
	}
	return true
}

// Before compares the metrics, using the following criteria:
//
// If m has fewer labels than o, it is before o. If it has more, it is not.
//
// If the number of labels is the same, the superset of all label names is
// sorted alphanumerically. The first differing label pair found in that order
// determines the outcome: If the label does not exist at all in m, then m is
// before o, and vice versa. Otherwise the label value is compared
// alphanumerically.
//
// If m and o are equal, the method returns false.
func (ls LabelSet) Before(o LabelSet) bool {
	if len(ls) < len(o) {
		return true
	}
	if len(ls) > len(o) {
		return false
	}

	lns := make(LabelNames, 0, len(ls)+len(o))
	for ln := range ls {
		lns = append(lns, ln)
	}
	for ln := range o {
		lns = append(lns, ln)
	}
	// It's probably not worth it to de-dup lns.
	sort.Sort(lns)
	for _, ln := range lns {
		mlv, ok := ls[ln]
		if !ok {
			return true
		}
		olv, ok := o[ln]
		if !ok {
			return false
		}
		if mlv < olv {
			return true
		}
		if mlv > olv {
			return false
		}
	}
	return false
}

// Clone returns a copy of the label set.
func (ls LabelSet) Clone() LabelSet {
	lsn := make(LabelSet, len(ls))
	for ln, lv := range ls {
		lsn[ln] = lv
	}
	return lsn
}

// Merge is a helper function to non-destructively merge two label sets.
func (l LabelSet) Merge(other LabelSet) LabelSet {
	result := make(LabelSet, len(l))

	for k, v := range l {
		result[k] = v
	}

	for k, v := range other {
		result[k] = v
	}

	return result
}

// String will look like `{foo="bar", more="less"}`. Names are sorted alphabetically.
func (l LabelSet) String() string {
	var lna [32]LabelName // On stack to avoid memory allocation for sorting names.
	labelNames := lna[:0]
	for name := range l {
		labelNames = append(labelNames, name)
	}
	slices.Sort(labelNames)
	var bytea [1024]byte // On stack to avoid memory allocation while building the output.
	b := bytes.NewBuffer(bytea[:0])
	b.WriteByte('{')
	for i, name := range labelNames {
		if i > 0 {
			b.WriteString(", ")
		}
		b.WriteString(string(name))
		b.WriteByte('=')
		b.Write(strconv.AppendQuote(b.AvailableBuffer(), string(l[name])))
	}
	b.WriteByte('}')
	return b.String()
}

// Fingerprint returns the LabelSet's fingerprint.
func (ls LabelSet) Fingerprint() Fingerprint {
	return labelSetToFingerprint(ls)
}

// FastFingerprint returns the LabelSet's Fingerprint calculated by a faster hashing
// algorithm, which is, however, more susceptible to hash collisions.
func (ls LabelSet) FastFingerprint() Fingerprint {
	return labelSetToFastFingerprint(ls)
}

// UnmarshalJSON implements the json.Unmarshaler interface.
func (l *LabelSet) UnmarshalJSON(b []byte) error {
	var m map[LabelName]LabelValue
	if err := json.Unmarshal(b, &m); err != nil {
		return err
	}
	// encoding/json only unmarshals maps of the form map[string]T. It treats
	// LabelName as a string and does not call its UnmarshalJSON method.
	// Thus, we have to replicate the behavior here.
	for ln := range m {
		if !ln.IsValid() {
			return fmt.Errorf("%q is not a valid label name", ln)
		}
	}
	*l = LabelSet(m)
	return nil
}
