// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package debug

import (
	"context"
	"fmt"
	"html/template"
	"net/http"
	"sort"
	"sync"
	"time"

	"golang.org/x/tools/internal/lsp/debug/tag"
	"golang.org/x/tools/internal/telemetry/event"
	"golang.org/x/tools/internal/telemetry/export"
	"golang.org/x/tools/internal/telemetry/export/metric"
)

var rpcTmpl = template.Must(template.Must(baseTemplate.Clone()).Parse(`
{{define "title"}}RPC Information{{end}}
{{define "body"}}
	<H2>Inbound</H2>
	{{template "rpcSection" .Inbound}}
	<H2>Outbound</H2>
	{{template "rpcSection" .Outbound}}
{{end}}
{{define "rpcSection"}}
	{{range .}}<P>
		<b>{{.Method}}</b> {{.Started}} <a href="/trace/{{.Method}}">traces</a> ({{.InProgress}} in progress)
		<br>
		<i>Latency</i> {{with .Latency}}{{.Mean}} ({{.Min}}<{{.Max}}){{end}}
		<i>By bucket</i> 0s {{range .Latency.Values}}<b>{{.Count}}</b> {{.Limit}} {{end}}
		<br>
		<i>Received</i> {{with .Received}}{{.Mean}} ({{.Min}}<{{.Max}}){{end}}
		<i>Sent</i> {{with .Sent}}{{.Mean}} ({{.Min}}<{{.Max}}){{end}}
		<br>
		<i>Result codes</i> {{range .Codes}}{{.Key}}={{.Count}} {{end}}
		</P>
	{{end}}
{{end}}
`))

type rpcs struct {
	mu       sync.Mutex
	Inbound  []*rpcStats
	Outbound []*rpcStats
}

type rpcStats struct {
	Method     string
	Started    int64
	Completed  int64
	InProgress int64
	Latency    rpcTimeHistogram
	Received   rpcBytesHistogram
	Sent       rpcBytesHistogram
	Codes      []*rpcCodeBucket
}

type rpcTimeHistogram struct {
	Sum    timeUnits
	Count  int64
	Mean   timeUnits
	Min    timeUnits
	Max    timeUnits
	Values []rpcTimeBucket
}

type rpcTimeBucket struct {
	Limit timeUnits
	Count int64
}

type rpcBytesHistogram struct {
	Sum    byteUnits
	Count  int64
	Mean   byteUnits
	Min    byteUnits
	Max    byteUnits
	Values []rpcBytesBucket
}

type rpcBytesBucket struct {
	Limit byteUnits
	Count int64
}

type rpcCodeBucket struct {
	Key   string
	Count int64
}

func (r *rpcs) ProcessEvent(ctx context.Context, ev event.Event, tagMap event.TagMap) context.Context {
	switch {
	case ev.IsEndSpan():
		// calculate latency if this was an rpc span
		span := export.GetSpan(ctx)
		if span == nil {
			return ctx
		}
		// is this a finished rpc span, if so it will have a status code record
		for _, ev := range span.Events() {
			code := tag.StatusCode.Get(ev.Map())
			if code != "" {
				elapsedTime := span.Finish().At.Sub(span.Start().At)
				latencyMillis := float64(elapsedTime) / float64(time.Millisecond)
				statsCtx := event.Label1(ctx, tag.StatusCode.Of(code))
				event.Record1(statsCtx, tag.Latency.Of(latencyMillis))
			}
		}
		return ctx
	case ev.IsRecord():
		// fall through to the metrics handling logic
	default:
		// ignore all other event types
		return ctx
	}
	r.mu.Lock()
	defer r.mu.Unlock()
	//TODO(38168): we should just deal with the events here and not use metrics
	metrics := metric.Entries.Get(tagMap).([]metric.Data)
	for _, data := range metrics {
		for i, group := range data.Groups() {
			set := &r.Inbound
			groupTags := event.NewTagMap(group...)
			if tag.RPCDirection.Get(groupTags) == tag.Outbound {
				set = &r.Outbound
			}
			method := tag.Method.Get(groupTags)
			index := sort.Search(len(*set), func(i int) bool {
				return (*set)[i].Method >= method
			})
			if index >= len(*set) || (*set)[index].Method != method {
				old := *set
				*set = make([]*rpcStats, len(old)+1)
				copy(*set, old[:index])
				copy((*set)[index+1:], old[index:])
				(*set)[index] = &rpcStats{Method: method}
			}
			stats := (*set)[index]
			switch data.Handle() {
			case started.Name:
				stats.Started = data.(*metric.Int64Data).Rows[i]
			case completed.Name:
				status := tag.StatusCode.Get(groupTags)
				var b *rpcCodeBucket
				for c, entry := range stats.Codes {
					if entry.Key == status {
						b = stats.Codes[c]
						break
					}
				}
				if b == nil {
					b = &rpcCodeBucket{Key: status}
					stats.Codes = append(stats.Codes, b)
					sort.Slice(stats.Codes, func(i int, j int) bool {
						return stats.Codes[i].Key < stats.Codes[j].Key
					})
				}
				b.Count = data.(*metric.Int64Data).Rows[i]
			case latency.Name:
				data := data.(*metric.HistogramFloat64Data)
				row := data.Rows[i]
				stats.Latency.Count = row.Count
				stats.Latency.Sum = timeUnits(row.Sum)
				stats.Latency.Min = timeUnits(row.Min)
				stats.Latency.Max = timeUnits(row.Max)
				stats.Latency.Mean = timeUnits(row.Sum) / timeUnits(row.Count)
				stats.Latency.Values = make([]rpcTimeBucket, len(data.Info.Buckets))
				last := int64(0)
				for i, b := range data.Info.Buckets {
					stats.Latency.Values[i].Limit = timeUnits(b)
					stats.Latency.Values[i].Count = row.Values[i] - last
					last = row.Values[i]
				}
			case sentBytes.Name:
				data := data.(*metric.HistogramInt64Data)
				row := data.Rows[i]
				stats.Sent.Count = row.Count
				stats.Sent.Sum = byteUnits(row.Sum)
				stats.Sent.Min = byteUnits(row.Min)
				stats.Sent.Max = byteUnits(row.Max)
				stats.Sent.Mean = byteUnits(row.Sum) / byteUnits(row.Count)
			case receivedBytes.Name:
				data := data.(*metric.HistogramInt64Data)
				row := data.Rows[i]
				stats.Received.Count = row.Count
				stats.Received.Sum = byteUnits(row.Sum)
				stats.Sent.Min = byteUnits(row.Min)
				stats.Sent.Max = byteUnits(row.Max)
				stats.Received.Mean = byteUnits(row.Sum) / byteUnits(row.Count)
			}
		}
	}

	for _, set := range [][]*rpcStats{r.Inbound, r.Outbound} {
		for _, stats := range set {
			stats.Completed = 0
			for _, b := range stats.Codes {
				stats.Completed += b.Count
			}
			stats.InProgress = stats.Started - stats.Completed
		}
	}
	return ctx
}

func (r *rpcs) getData(req *http.Request) interface{} {
	return r
}

func units(v float64, suffixes []string) string {
	s := ""
	for _, s = range suffixes {
		n := v / 1000
		if n < 1 {
			break
		}
		v = n
	}
	return fmt.Sprintf("%.2f%s", v, s)
}

type timeUnits float64

func (v timeUnits) String() string {
	v = v * 1000 * 1000
	return units(float64(v), []string{"ns", "μs", "ms", "s"})
}

type byteUnits float64

func (v byteUnits) String() string {
	return units(float64(v), []string{"B", "KB", "MB", "GB", "TB"})
}