// Copyright 2018 Google Inc. All Rights Reserved.
//
// 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 metrics

import (
	"os"
	"syscall"
	"time"

	"android/soong/ui/metrics/metrics_proto"
	"android/soong/ui/tracer"
	"github.com/golang/protobuf/proto"
)

// for testing purpose only
var _now = now

type event struct {
	desc string
	name string

	// the time that the event started to occur.
	start time.Time

	// The list of process resource information that was executed
	procResInfo []*soong_metrics_proto.ProcessResourceInfo
}

type EventTracer interface {
	Begin(name, desc string, thread tracer.Thread)
	End(thread tracer.Thread) soong_metrics_proto.PerfInfo
	AddProcResInfo(string, *os.ProcessState)
}

type eventTracerImpl struct {
	activeEvents []event
}

var _ EventTracer = &eventTracerImpl{}

func now() time.Time {
	return time.Now()
}

// AddProcResInfo adds information on an executed process such as max resident set memory
// and the number of voluntary context switches.
func (t *eventTracerImpl) AddProcResInfo(name string, state *os.ProcessState) {
	if len(t.activeEvents) < 1 {
		return
	}

	rusage := state.SysUsage().(*syscall.Rusage)
	// The implementation of the metrics system is a stacked based system. The steps of the
	// build system in the UI layer is sequential so the Begin function is invoked when a
	// function (or scoped code) is invoked. That is translated to a new event which is added
	// at the end of the activeEvents array. When the invoking function is completed, End is
	// invoked which is a pop operation from activeEvents.
	curEvent := &t.activeEvents[len(t.activeEvents)-1]
	curEvent.procResInfo = append(curEvent.procResInfo, &soong_metrics_proto.ProcessResourceInfo{
		Name:             proto.String(name),
		UserTimeMicros:   proto.Uint64(uint64(rusage.Utime.Usec)),
		SystemTimeMicros: proto.Uint64(uint64(rusage.Stime.Usec)),
		MinorPageFaults:  proto.Uint64(uint64(rusage.Minflt)),
		MajorPageFaults:  proto.Uint64(uint64(rusage.Majflt)),
		// ru_inblock and ru_oublock are measured in blocks of 512 bytes.
		IoInputKb:                  proto.Uint64(uint64(rusage.Inblock / 2)),
		IoOutputKb:                 proto.Uint64(uint64(rusage.Oublock / 2)),
		VoluntaryContextSwitches:   proto.Uint64(uint64(rusage.Nvcsw)),
		InvoluntaryContextSwitches: proto.Uint64(uint64(rusage.Nivcsw)),
	})
}

func (t *eventTracerImpl) Begin(name, desc string, _ tracer.Thread) {
	t.activeEvents = append(t.activeEvents, event{name: name, desc: desc, start: _now()})
}

func (t *eventTracerImpl) End(tracer.Thread) soong_metrics_proto.PerfInfo {
	if len(t.activeEvents) < 1 {
		panic("Internal error: No pending events for endAt to end!")
	}
	lastEvent := t.activeEvents[len(t.activeEvents)-1]
	t.activeEvents = t.activeEvents[:len(t.activeEvents)-1]
	realTime := uint64(_now().Sub(lastEvent.start).Nanoseconds())

	return soong_metrics_proto.PerfInfo{
		Desc:                  proto.String(lastEvent.desc),
		Name:                  proto.String(lastEvent.name),
		StartTime:             proto.Uint64(uint64(lastEvent.start.UnixNano())),
		RealTime:              proto.Uint64(realTime),
		ProcessesResourceInfo: lastEvent.procResInfo,
	}
}