package querytracer

import (
	"bytes"
	"encoding/json"
	"flag"
	"fmt"
	"io"
	"strings"
	"time"
)

var denyQueryTracing = flag.Bool("denyQueryTracing", false, "Whether to disable the ability to trace queries. See https://docs.victoriametrics.com/#query-tracing")

// Tracer represents query tracer.
//
// It must be created via New call.
// Each created tracer must be finalized via Donef call.
//
// Tracer may contain sub-tracers (branches) in order to build tree-like execution order.
// Call Tracer.NewChild func for adding sub-tracer.
type Tracer struct {
	// startTime is the time when Tracer was created
	startTime time.Time
	// doneTime is the time when Donef was called
	doneTime time.Time
	// message is the message generated by Printf or Donef call.
	message string
	// children is a list of children Tracer objects
	children []*Tracer
	// span contains span for the given Tracer. It is added via Tracer.AddSpan().
	// If span is non-nil, then the remaining fields aren't used.
	span *span
}

// New creates a new instance of the tracer.
//
// If enabled isn't set, then all function calls to the returned object will be no-op.
//
// Donef must be called when the tracer should be finished.
func New(enabled bool) *Tracer {
	if *denyQueryTracing || !enabled {
		return nil
	}
	return &Tracer{
		startTime: time.Now(),
	}
}

// Enabled returns true if the t is enabled.
func (t *Tracer) Enabled() bool {
	return t != nil
}

// NewChild adds a new child Tracer to t.
//
// NewChild cannot be called from concurrent goroutines.
// Create children tracers from a single goroutine and then pass them
// to concurrent goroutines.
func (t *Tracer) NewChild() *Tracer {
	if t == nil {
		return nil
	}
	if t.message != "" {
		panic(fmt.Errorf("BUG: NewChild() cannot be called after Donef(%q) call", t.message))
	}
	child := &Tracer{
		startTime: time.Now(),
	}
	t.children = append(t.children, child)
	return child
}

// Donef finishes t.
//
// Donef cannot be called multiple times.
// Other Tracer functions cannot be called after Donef call.
func (t *Tracer) Donef(format string, args ...interface{}) {
	if t == nil {
		return
	}
	if t.message != "" {
		panic(fmt.Errorf("BUG: Donef() already called with message %q", t.message))
	}
	t.message = fmt.Sprintf(format, args...)
	t.doneTime = time.Now()
}

// Printf adds new message to t.
//
// Printf cannot be called from concurrent goroutines.
func (t *Tracer) Printf(format string, args ...interface{}) {
	if t == nil {
		return
	}
	if t.message != "" {
		panic(fmt.Errorf("BUG: Printf() cannot be called after Done(%q) call", t.message))
	}
	now := time.Now()
	child := &Tracer{
		startTime: now,
		doneTime:  now,
		message:   fmt.Sprintf(format, args...),
	}
	t.children = append(t.children, child)
}

// AddJSON adds a sub-trace to t.
//
// The jsonTrace must be encoded with ToJSON.
//
// AddJSON cannot be called from concurrent goroutines.
func (t *Tracer) AddJSON(jsonTrace []byte) error {
	if t == nil {
		return nil
	}
	if len(jsonTrace) == 0 {
		return nil
	}
	var s *span
	if err := json.Unmarshal(jsonTrace, &s); err != nil {
		return fmt.Errorf("cannot unmarshal json trace: %s", err)
	}
	child := &Tracer{
		span: s,
	}
	t.children = append(t.children, child)
	return nil
}

// String returns string representation of t.
//
// String must be called when t methods aren't called by other goroutines.
func (t *Tracer) String() string {
	if t == nil {
		return ""
	}
	s := t.toSpan()
	var bb bytes.Buffer
	s.writePlaintextWithIndent(&bb, 0)
	return bb.String()
}

// ToJSON returns JSON representation of t.
//
// ToJSON must be called when t methods aren't called by other goroutines.
func (t *Tracer) ToJSON() string {
	if t == nil {
		return ""
	}
	s := t.toSpan()
	data, err := json.Marshal(s)
	if err != nil {
		panic(fmt.Errorf("BUG: unexpected error from json.Marshal: %w", err))
	}
	return string(data)
}

func (t *Tracer) toSpan() *span {
	s, _ := t.toSpanInternal(time.Now())
	return s
}

func (t *Tracer) toSpanInternal(prevTime time.Time) (*span, time.Time) {
	if t.span != nil {
		return t.span, prevTime
	}
	if t.doneTime == t.startTime {
		// a single-line trace
		d := t.startTime.Sub(prevTime)
		s := &span{
			DurationMsec: float64(d.Microseconds()) / 1000,
			Message:      t.message,
		}
		return s, t.doneTime
	}
	// tracer with children
	msg := t.message
	doneTime := t.doneTime
	if msg == "" {
		msg = "missing Tracer.Donef() call"
		doneTime = t.getLastChildDoneTime(t.startTime)
	}
	d := doneTime.Sub(t.startTime)
	var children []*span
	var sChild *span
	prevChildTime := t.startTime
	for _, child := range t.children {
		sChild, prevChildTime = child.toSpanInternal(prevChildTime)
		children = append(children, sChild)
	}
	s := &span{
		DurationMsec: float64(d.Microseconds()) / 1000,
		Message:      msg,
		Children:     children,
	}
	return s, doneTime
}

func (t *Tracer) getLastChildDoneTime(defaultTime time.Time) time.Time {
	if len(t.children) == 0 {
		return defaultTime
	}
	lastChild := t.children[len(t.children)-1]
	return lastChild.getLastChildDoneTime(lastChild.startTime)
}

// span represents a single trace span
type span struct {
	// DurationMsec is the duration for the current trace span in microseconds.
	DurationMsec float64 `json:"duration_msec"`
	// Message is a trace message
	Message string `json:"message"`
	// Children contains children spans
	Children []*span `json:"children,omitempty"`
}

func (s *span) writePlaintextWithIndent(w io.Writer, indent int) {
	prefix := ""
	for i := 0; i < indent; i++ {
		prefix += "| "
	}
	prefix += "- "
	msg := s.messageWithPrefix(prefix)
	fmt.Fprintf(w, "%s%.03fms: %s\n", prefix, s.DurationMsec, msg)
	childIndent := indent + 1
	for _, sChild := range s.Children {
		sChild.writePlaintextWithIndent(w, childIndent)
	}
}

func (s *span) messageWithPrefix(prefix string) string {
	prefix = strings.Replace(prefix, "-", "|", 1)
	lines := strings.Split(s.Message, "\n")
	result := lines[:1]
	for i := range lines[1:] {
		ln := lines[i+1]
		if ln == "" {
			continue
		}
		ln = prefix + ln
		result = append(result, ln)
	}
	return strings.Join(result, "\n")
}