luci_config/server/cfgclient/backend/format/formatters.go

// Copyright 2017 The LUCI Authors. All rights reserved.
// Use of this source code is governed under the Apache License, Version 2.0
// that can be found in the LICENSE file.

package format

import (
	"fmt"
	"sync"

	"github.com/luci/luci-go/common/errors"
)

// registry is a registry of Resolver key mapped to the Formatter to use to
// format that key.
var registry struct {
	sync.RWMutex
	r map[string]Formatter
}

// Formatter applies a transformation to the data's cached representation.
//
// The Formatter is supplied with the content to format along with the
// formatter-specific metadata, fd.
//
// Formatter operates on a backend.Item's Content via the "format" Backend.
type Formatter interface {
	FormatItem(c, fd string) (string, error)
}

// Register registers a Formatter implementation for given format.
//
// If the supplied key is already registered, Register will panic.
func Register(rk string, f Formatter) {
	if rk == "" {
		panic("cannot register empty key")
	}

	registry.Lock()
	defer registry.Unlock()

	if _, ok := registry.r[rk]; ok {
		panic(fmt.Errorf("key %q is already registered", rk))
	}
	if registry.r == nil {
		registry.r = map[string]Formatter{}
	}
	registry.r[rk] = f
}

// ClearRegistry removes all registered formatters.
//
// Useful in tests that call Register to setup initial state.
func ClearRegistry() {
	registry.Lock()
	defer registry.Unlock()
	registry.r = nil
}

// getFormatter returns the Formatter associated with the provided Format.
func getFormatter(f string) (Formatter, error) {
	registry.RLock()
	defer registry.RUnlock()

	formatter := registry.r[f]
	if formatter == nil {
		return nil, errors.Reason("unknown formatter: %(formatter)q").D("formatter", f).Err()
	}
	return formatter, nil
}