/*
 *
 * Copyright 2023 gRPC 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 audit contains interfaces for audit logging during authorization.
package audit

import (
	"encoding/json"
	"sync"
)

// loggerBuilderRegistry holds a map of audit logger builders and a mutex
// to facilitate thread-safe reading/writing operations.
type loggerBuilderRegistry struct {
	mu       sync.Mutex
	builders map[string]LoggerBuilder
}

var (
	registry = loggerBuilderRegistry{
		builders: make(map[string]LoggerBuilder),
	}
)

// RegisterLoggerBuilder registers the builder in a global map
// using b.Name() as the key.
//
// This should only be called during initialization time (i.e. in an init()
// function). If multiple builders are registered with the same name,
// the one registered last will take effect.
func RegisterLoggerBuilder(b LoggerBuilder) {
	registry.mu.Lock()
	defer registry.mu.Unlock()
	registry.builders[b.Name()] = b
}

// GetLoggerBuilder returns a builder with the given name.
// It returns nil if the builder is not found in the registry.
func GetLoggerBuilder(name string) LoggerBuilder {
	registry.mu.Lock()
	defer registry.mu.Unlock()
	return registry.builders[name]
}

// Event contains information passed to the audit logger as part of an
// audit logging event.
type Event struct {
	// FullMethodName is the full method name of the audited RPC, in the format
	// of "/pkg.Service/Method". For example, "/helloworld.Greeter/SayHello".
	FullMethodName string
	// Principal is the identity of the caller. Currently it will only be
	// available in certificate-based TLS authentication.
	Principal string
	// PolicyName is the authorization policy name or the xDS RBAC filter name.
	PolicyName string
	// MatchedRule is the matched rule or policy name in the xDS RBAC filter.
	// It will be empty if there is no match.
	MatchedRule string
	// Authorized indicates whether the audited RPC is authorized or not.
	Authorized bool
}

// LoggerConfig represents an opaque data structure holding an audit
// logger configuration. Concrete types representing configuration of specific
// audit loggers must embed this interface to implement it.
type LoggerConfig interface {
	loggerConfig()
}

// Logger is the interface to be implemented by audit loggers.
//
// An audit logger is a logger instance that can be configured via the
// authorization policy API or xDS HTTP RBAC filters. When the authorization
// decision meets the condition for audit, all the configured audit loggers'
// Log() method will be invoked to log that event.
//
// TODO(lwge): Change the link to the merged gRFC once it's ready.
// Please refer to https://github.com/grpc/proposal/pull/346 for more details
// about audit logging.
type Logger interface {
	// Log performs audit logging for the provided audit event.
	//
	// This method is invoked in the RPC path and therefore implementations
	// must not block.
	Log(*Event)
}

// LoggerBuilder is the interface to be implemented by audit logger
// builders that are used at runtime to configure and instantiate audit loggers.
//
// Users who want to implement their own audit logging logic should
// implement this interface, along with the Logger interface, and register
// it by calling RegisterLoggerBuilder() at init time.
//
// TODO(lwge): Change the link to the merged gRFC once it's ready.
// Please refer to https://github.com/grpc/proposal/pull/346 for more details
// about audit logging.
type LoggerBuilder interface {
	// ParseLoggerConfig parses the given JSON bytes into a structured
	// logger config this builder can use to build an audit logger.
	ParseLoggerConfig(config json.RawMessage) (LoggerConfig, error)
	// Build builds an audit logger with the given logger config.
	// This will only be called with valid configs returned from
	// ParseLoggerConfig() and any runtime issues such as failing to
	// create a file should be handled by the logger implementation instead of
	// failing the logger instantiation. So implementers need to make sure it
	// can return a logger without error at this stage.
	Build(LoggerConfig) Logger
	// Name returns the name of logger built by this builder.
	// This is used to register and pick the builder.
	Name() string
}