package tusd

import (
	"sync"
	"sync/atomic"
)

// Metrics provides numbers about the usage of the tusd handler. Since these may
// be accessed from multiple goroutines, it is necessary to read and modify them
// atomically using the functions exposed in the sync/atomic package, such as
// atomic.LoadUint64. In addition the maps must not be modified to prevent data
// races.
type Metrics struct {
	// RequestTotal counts the number of incoming requests per method
	RequestsTotal map[string]*uint64
	// ErrorsTotal counts the number of returned errors by their message
	ErrorsTotal       ErrorsTotalMap
	BytesReceived     *uint64
	UploadsFinished   *uint64
	UploadsCreated    *uint64
	UploadsTerminated *uint64
}

// incRequestsTotal increases the counter for this request method atomically by
// one. The method must be one of GET, HEAD, POST, PATCH, DELETE.
func (m *Metrics) incRequestsTotal(method string) {
	if ptr, ok := m.RequestsTotal[method]; ok {
		atomic.AddUint64(ptr, 1)
	}
}

// incErrorsTotal increases the counter for this error atomically by one.
func (m *Metrics) incErrorsTotal(err HTTPError) {
	m.ErrorsTotal.incError(err)
}

// incBytesReceived increases the number of received bytes atomically be the
// specified number.
func (m *Metrics) incBytesReceived(delta uint64) {
	atomic.AddUint64(m.BytesReceived, delta)
}

// incUploadsFinished increases the counter for finished uploads atomically by one.
func (m *Metrics) incUploadsFinished() {
	atomic.AddUint64(m.UploadsFinished, 1)
}

// incUploadsCreated increases the counter for completed uploads atomically by one.
func (m *Metrics) incUploadsCreated() {
	atomic.AddUint64(m.UploadsCreated, 1)
}

// incUploadsTerminated increases the counter for completed uploads atomically by one.
func (m *Metrics) incUploadsTerminated() {
	atomic.AddUint64(m.UploadsTerminated, 1)
}

func newMetrics() Metrics {
	return Metrics{
		RequestsTotal: map[string]*uint64{
			"GET":     new(uint64),
			"HEAD":    new(uint64),
			"POST":    new(uint64),
			"PATCH":   new(uint64),
			"DELETE":  new(uint64),
			"OPTIONS": new(uint64),
		},
		ErrorsTotal:       newErrorsTotalMap(),
		BytesReceived:     new(uint64),
		UploadsFinished:   new(uint64),
		UploadsCreated:    new(uint64),
		UploadsTerminated: new(uint64),
	}
}

// ErrorsTotalMap stores the counter for the different http errors.
type ErrorsTotalMap struct {
	sync.RWMutex
	m map[HTTPError]*uint64
}

func newErrorsTotalMap() ErrorsTotalMap {
	m := make(map[HTTPError]*uint64, 20)
	return ErrorsTotalMap{
		m: m,
	}
}

// incErrorsTotal increases the counter for this error atomically by one.
func (e *ErrorsTotalMap) incError(err HTTPError) {
	// The goal is to have a valid ptr to the counter for this err
	e.RLock()
	ptr, ok := e.m[err]
	e.RUnlock()
	if !ok {
		// The ptr does not seem to exist for this err
		// Hence we create it (using a write lock)
		e.Lock()
		// We ensure that the ptr wasn't created in the meantime
		if ptr, ok = e.m[err]; !ok {
			ptr = new(uint64)
			e.m[err] = ptr
		}
		e.Unlock()
	}
	// We can then increase the counter
	atomic.AddUint64(ptr, 1)
}

// Load retrieves the map of the counter pointers atomically
func (e *ErrorsTotalMap) Load() (m map[HTTPError]*uint64) {
	m = make(map[HTTPError]*uint64, len(e.m))
	e.RLock()
	for err, ptr := range e.m {
		m[err] = ptr
	}
	e.RUnlock()
	return
}