// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package tag provides support for telemetry tagging.
package tag

import (
	"context"

	"golang.org/x/tools/internal/telemetry"
)

// Key represents the key for a context tag.
// It is a helper to make use of context tagging slightly easier to read, it is
// not strictly needed to use it at all.
// It is intended that your common tagging keys are declared as constants of
// this type, and then you can use the methods of this type to apply and find
// those values in the context.
type Key string

// Of returns a Tag for a key and value.
// This is a trivial helper that makes common logging easier to read.
func Of(key interface{}, value interface{}) telemetry.Tag {
	return telemetry.Tag{Key: key, Value: value}
}

// Of creates a new Tag with this key and the supplied value.
// You can use this when building a tag list.
func (k Key) Of(v interface{}) telemetry.Tag {
	return telemetry.Tag{Key: k, Value: v}
}

// Tag can be used to get a tag for the key from a context.
// It makes Key conform to the Tagger interface.
func (k Key) Tag(ctx context.Context) telemetry.Tag {
	return telemetry.Tag{Key: k, Value: ctx.Value(k)}
}

// With applies sets this key to the supplied value on the context and
// returns the new context generated.
// It uses the With package level function so that observers are also notified.
func (k Key) With(ctx context.Context, v interface{}) context.Context {
	return With(ctx, telemetry.Tag{Key: k, Value: v})
}