// Package "performance" provides a tracker to observer CPU performance during
// execution.
package plugins

import (
	"os"
	"path/filepath"
	"runtime/pprof"

	"git.maximhutz.com/max/lambda/internal/engine"
)

// Observes a reduction process, and publishes a CPU performance profile on
// completion.
type Performance struct {
	File        string
	filePointer *os.File
	Error       error
}

// Create a performance tracker that outputs a profile to "file".
func NewPerformance(file string, process *engine.Engine) *Performance {
	plugin := &Performance{File: file}
	process.On(engine.StartEvent, plugin.Start)
	process.On(engine.StopEvent, plugin.Stop)

	return plugin
}

// Begin profiling.
func (t *Performance) Start() {
	var absPath string

	absPath, t.Error = filepath.Abs(t.File)
	if t.Error != nil {
		return
	}

	t.Error = os.MkdirAll(filepath.Dir(absPath), 0777)
	if t.Error != nil {
		return
	}

	t.filePointer, t.Error = os.Create(absPath)
	if t.Error != nil {
		return
	}

	t.Error = pprof.StartCPUProfile(t.filePointer)
	if t.Error != nil {
		return
	}
}

// Stop profiling.
func (t *Performance) Stop() {
	pprof.StopCPUProfile()
	t.filePointer.Close()
}