/*
 *
 * Copyright 2020 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 rls

import (
	"bytes"
	"encoding/json"
	"fmt"
	"time"

	"github.com/golang/protobuf/jsonpb"
	"github.com/golang/protobuf/ptypes"
	durationpb "github.com/golang/protobuf/ptypes/duration"
	"google.golang.org/grpc/balancer"
	"google.golang.org/grpc/balancer/rls/internal/keys"
	rlspb "google.golang.org/grpc/balancer/rls/internal/proto/grpc_lookup_v1"
	"google.golang.org/grpc/internal/grpcutil"
	"google.golang.org/grpc/resolver"
	"google.golang.org/grpc/serviceconfig"
)

const (
	// This is max duration that we are willing to cache RLS responses. If the
	// service config doesn't specify a value for max_age or if it specified a
	// value greater that this, we will use this value instead.
	maxMaxAge = 5 * time.Minute
	// If lookup_service_timeout is not specified in the service config, we use
	// a default of 10 seconds.
	defaultLookupServiceTimeout = 10 * time.Second
	// This is set to the targetNameField in the child policy config during
	// service config validation.
	dummyChildPolicyTarget = "target_name_to_be_filled_in_later"
)

// lbConfig contains the parsed and validated contents of the
// loadBalancingConfig section of the service config. The RLS LB policy will
// use this to directly access config data instead of ploughing through proto
// fields.
type lbConfig struct {
	serviceconfig.LoadBalancingConfig

	kbMap                keys.BuilderMap
	lookupService        string
	lookupServiceTimeout time.Duration
	maxAge               time.Duration
	staleAge             time.Duration
	cacheSizeBytes       int64
	defaultTarget        string
	cpName               string
	cpTargetField        string
	cpConfig             map[string]json.RawMessage
}

func (lbCfg *lbConfig) Equal(other *lbConfig) bool {
	return lbCfg.kbMap.Equal(other.kbMap) &&
		lbCfg.lookupService == other.lookupService &&
		lbCfg.lookupServiceTimeout == other.lookupServiceTimeout &&
		lbCfg.maxAge == other.maxAge &&
		lbCfg.staleAge == other.staleAge &&
		lbCfg.cacheSizeBytes == other.cacheSizeBytes &&
		lbCfg.defaultTarget == other.defaultTarget &&
		lbCfg.cpName == other.cpName &&
		lbCfg.cpTargetField == other.cpTargetField &&
		cpConfigEqual(lbCfg.cpConfig, other.cpConfig)
}

func cpConfigEqual(am, bm map[string]json.RawMessage) bool {
	if (bm == nil) != (am == nil) {
		return false
	}
	if len(bm) != len(am) {
		return false
	}

	for k, jsonA := range am {
		jsonB, ok := bm[k]
		if !ok {
			return false
		}
		if !bytes.Equal(jsonA, jsonB) {
			return false
		}
	}
	return true
}

// This struct resembles the JSON respresentation of the loadBalancing config
// and makes it easier to unmarshal.
type lbConfigJSON struct {
	RouteLookupConfig                json.RawMessage
	ChildPolicy                      []*loadBalancingConfig
	ChildPolicyConfigTargetFieldName string
}

// loadBalancingConfig represents a single load balancing config,
// stored in JSON format.
//
// TODO(easwars): This code seems to be repeated in a few places
// (service_config.go and in the xds code as well). Refactor and re-use.
type loadBalancingConfig struct {
	Name   string
	Config json.RawMessage
}

// MarshalJSON returns a JSON encoding of l.
func (l *loadBalancingConfig) MarshalJSON() ([]byte, error) {
	return nil, fmt.Errorf("rls: loadBalancingConfig.MarshalJSON() is unimplemented")
}

// UnmarshalJSON parses the JSON-encoded byte slice in data and stores it in l.
func (l *loadBalancingConfig) UnmarshalJSON(data []byte) error {
	var cfg map[string]json.RawMessage
	if err := json.Unmarshal(data, &cfg); err != nil {
		return err
	}
	for name, config := range cfg {
		l.Name = name
		l.Config = config
	}
	return nil
}

// ParseConfig parses and validates the JSON representation of the service
// config and returns the loadBalancingConfig to be used by the RLS LB policy.
//
// Helps implement the balancer.ConfigParser interface.
//
// The following validation checks are performed:
// * routeLookupConfig:
//   ** grpc_keybuilders field:
//      - must have at least one entry
//      - must not have two entries with the same Name
//      - must not have any entry with a Name with the service field unset or
//        empty
//      - must not have any entries without a Name
//      - must not have a headers entry that has required_match set
//      - must not have two headers entries with the same key within one entry
//   ** lookup_service field:
//      - must be set and non-empty and must parse as a target URI
//   ** max_age field:
//      - if not specified or is greater than maxMaxAge, it will be reset to
//        maxMaxAge
//   ** stale_age field:
//      - if the value is greater than or equal to max_age, it is ignored
//      - if set, then max_age must also be set
//   ** valid_targets field:
//      - will be ignored
//   ** cache_size_bytes field:
//      - must be greater than zero
//      - TODO(easwars): Define a minimum value for this field, to be used when
//        left unspecified
// * childPolicy field:
//  - must find a valid child policy with a valid config (the child policy must
//    be able to parse the provided config successfully when we pass it a dummy
//    target name in the target_field provided by the
//    childPolicyConfigTargetFieldName field)
// * childPolicyConfigTargetFieldName field:
//   - must be set and non-empty
func (*rlsBB) ParseConfig(c json.RawMessage) (serviceconfig.LoadBalancingConfig, error) {
	cfgJSON := &lbConfigJSON{}
	if err := json.Unmarshal(c, cfgJSON); err != nil {
		return nil, fmt.Errorf("rls: json unmarshal failed for service config {%+v}: %v", string(c), err)
	}

	m := jsonpb.Unmarshaler{AllowUnknownFields: true}
	rlsProto := &rlspb.RouteLookupConfig{}
	if err := m.Unmarshal(bytes.NewReader(cfgJSON.RouteLookupConfig), rlsProto); err != nil {
		return nil, fmt.Errorf("rls: bad RouteLookupConfig proto {%+v}: %v", string(cfgJSON.RouteLookupConfig), err)
	}

	var childPolicy *loadBalancingConfig
	for _, lbcfg := range cfgJSON.ChildPolicy {
		if balancer.Get(lbcfg.Name) != nil {
			childPolicy = lbcfg
			break
		}
	}

	kbMap, err := keys.MakeBuilderMap(rlsProto)
	if err != nil {
		return nil, err
	}

	lookupService := rlsProto.GetLookupService()
	if lookupService == "" {
		return nil, fmt.Errorf("rls: empty lookup_service in service config {%+v}", string(c))
	}
	parsedTarget := grpcutil.ParseTarget(lookupService)
	if parsedTarget.Scheme == "" {
		parsedTarget.Scheme = resolver.GetDefaultScheme()
	}
	if resolver.Get(parsedTarget.Scheme) == nil {
		return nil, fmt.Errorf("rls: invalid target URI in lookup_service {%s}", lookupService)
	}

	lookupServiceTimeout, err := convertDuration(rlsProto.GetLookupServiceTimeout())
	if err != nil {
		return nil, fmt.Errorf("rls: failed to parse lookup_service_timeout in service config {%+v}: %v", string(c), err)
	}
	if lookupServiceTimeout == 0 {
		lookupServiceTimeout = defaultLookupServiceTimeout
	}
	maxAge, err := convertDuration(rlsProto.GetMaxAge())
	if err != nil {
		return nil, fmt.Errorf("rls: failed to parse max_age in service config {%+v}: %v", string(c), err)
	}
	staleAge, err := convertDuration(rlsProto.GetStaleAge())
	if err != nil {
		return nil, fmt.Errorf("rls: failed to parse staleAge in service config {%+v}: %v", string(c), err)
	}
	if staleAge != 0 && maxAge == 0 {
		return nil, fmt.Errorf("rls: stale_age is set, but max_age is not in service config {%+v}", string(c))
	}
	if staleAge >= maxAge {
		logger.Info("rls: stale_age {%v} is greater than max_age {%v}, ignoring it", staleAge, maxAge)
		staleAge = 0
	}
	if maxAge == 0 || maxAge > maxMaxAge {
		logger.Infof("rls: max_age in service config is %v, using %v", maxAge, maxMaxAge)
		maxAge = maxMaxAge
	}
	cacheSizeBytes := rlsProto.GetCacheSizeBytes()
	if cacheSizeBytes <= 0 {
		return nil, fmt.Errorf("rls: cache_size_bytes must be greater than 0 in service config {%+v}", string(c))
	}
	if childPolicy == nil {
		return nil, fmt.Errorf("rls: childPolicy is invalid in service config {%+v}", string(c))
	}
	if cfgJSON.ChildPolicyConfigTargetFieldName == "" {
		return nil, fmt.Errorf("rls: childPolicyConfigTargetFieldName field is not set in service config {%+v}", string(c))
	}
	// TODO(easwars): When we start instantiating the child policy from the
	// parent RLS LB policy, we could make this function a method on the
	// lbConfig object and share the code. We would be parsing the child policy
	// config again during that time. The only difference betweeen now and then
	// would be that we would be using real targetField name instead of the
	// dummy. So, we could make the targetName field a parameter to this
	// function during the refactor.
	cpCfg, err := validateChildPolicyConfig(childPolicy, cfgJSON.ChildPolicyConfigTargetFieldName)
	if err != nil {
		return nil, err
	}

	return &lbConfig{
		kbMap:                kbMap,
		lookupService:        lookupService,
		lookupServiceTimeout: lookupServiceTimeout,
		maxAge:               maxAge,
		staleAge:             staleAge,
		cacheSizeBytes:       cacheSizeBytes,
		defaultTarget:        rlsProto.GetDefaultTarget(),
		// TODO(easwars): Once we refactor validateChildPolicyConfig and make
		// it a method on the lbConfig object, we could directly store the
		// balancer.Builder and/or balancer.ConfigParser here instead of the
		// Name. That would mean that we would have to create the lbConfig
		// object here first before validating the childPolicy config, but
		// that's a minor detail.
		cpName:        childPolicy.Name,
		cpTargetField: cfgJSON.ChildPolicyConfigTargetFieldName,
		cpConfig:      cpCfg,
	}, nil
}

// validateChildPolicyConfig validates the child policy config received in the
// service config. This makes it possible for us to reject service configs
// which contain invalid child policy configs which we know will fail for sure.
//
// It does the following:
// * Unmarshals the provided child policy config into a map of string to
//   json.RawMessage. This allows us to add an entry to the map corresponding
//   to the targetFieldName that we received in the service config.
// * Marshals the map back into JSON, finds the config parser associated with
//   the child policy and asks it to validate the config.
// * If the validation succeeded, removes the dummy entry from the map and
//   returns it. If any of the above steps failed, it returns an error.
func validateChildPolicyConfig(cp *loadBalancingConfig, cpTargetField string) (map[string]json.RawMessage, error) {
	var childConfig map[string]json.RawMessage
	if err := json.Unmarshal(cp.Config, &childConfig); err != nil {
		return nil, fmt.Errorf("rls: json unmarshal failed for child policy config {%+v}: %v", cp.Config, err)
	}
	childConfig[cpTargetField], _ = json.Marshal(dummyChildPolicyTarget)

	jsonCfg, err := json.Marshal(childConfig)
	if err != nil {
		return nil, fmt.Errorf("rls: json marshal failed for child policy config {%+v}: %v", childConfig, err)
	}
	builder := balancer.Get(cp.Name)
	if builder == nil {
		// This should never happen since we already made sure that the child
		// policy name mentioned in the service config is a valid one.
		return nil, fmt.Errorf("rls: balancer builder not found for child_policy %v", cp.Name)
	}
	parser, ok := builder.(balancer.ConfigParser)
	if !ok {
		return nil, fmt.Errorf("rls: balancer builder for child_policy does not implement balancer.ConfigParser: %v", cp.Name)
	}
	_, err = parser.ParseConfig(jsonCfg)
	if err != nil {
		return nil, fmt.Errorf("rls: childPolicy config validation failed: %v", err)
	}
	delete(childConfig, cpTargetField)
	return childConfig, nil
}

func convertDuration(d *durationpb.Duration) (time.Duration, error) {
	if d == nil {
		return 0, nil
	}
	return ptypes.Duration(d)
}