// Copyright 2020 Google Inc.
//
// 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 attest

import "fmt"

type elWorkaround struct {
	id          string
	affectedPCR int
	apply       func(e *EventLog) error
}

// inject3 appends two new events into the event log.
func inject3(e *EventLog, pcr int, data1, data2, data3 string) error {
	if err := inject(e, pcr, data1); err != nil {
		return err
	}
	if err := inject(e, pcr, data2); err != nil {
		return err
	}
	return inject(e, pcr, data3)
}

// inject2 appends two new events into the event log.
func inject2(e *EventLog, pcr int, data1, data2 string) error {
	if err := inject(e, pcr, data1); err != nil {
		return err
	}
	return inject(e, pcr, data2)
}

// inject appends a new event into the event log.
func inject(e *EventLog, pcr int, data string) error {
	evt := rawEvent{
		data:     []byte(data),
		index:    pcr,
		sequence: e.rawEvents[len(e.rawEvents)-1].sequence + 1,
	}
	for _, alg := range e.Algs {
		hash, err := alg.cryptoHash()
		if err != nil {
			return fmt.Errorf("unknown algorithm ID %x: %v", alg, err)
		}
		h := hash.New()
		h.Write([]byte(data))
		evt.digests = append(evt.digests, digest{hash: hash, data: h.Sum(nil)})
	}
	e.rawEvents = append(e.rawEvents, evt)
	return nil
}

const (
	ebsInvocation = "Exit Boot Services Invocation"
	ebsSuccess    = "Exit Boot Services Returned with Success"
	ebsFailure    = "Exit Boot Services Returned with Failure"
)

var eventlogWorkarounds = []elWorkaround{
	{
		id:          "EBS Invocation + Success",
		affectedPCR: 5,
		apply: func(e *EventLog) error {
			return inject2(e, 5, ebsInvocation, ebsSuccess)
		},
	},
	{
		id:          "EBS Invocation + Failure",
		affectedPCR: 5,
		apply: func(e *EventLog) error {
			return inject2(e, 5, ebsInvocation, ebsFailure)
		},
	},
	{
		id:          "EBS Invocation + Failure + Success",
		affectedPCR: 5,
		apply: func(e *EventLog) error {
			return inject3(e, 5, ebsInvocation, ebsFailure, ebsSuccess)
		},
	},
}
