// Copyright (C) 2018 Storj Labs, Inc.
// See LICENSE for copying information.

package telemetry

import (
	"context"
	"net"
	"os"
	"time"

	"github.com/zeebo/admission/admmonkit"
	"github.com/zeebo/admission/admproto"
	"go.uber.org/zap"
	monkit "gopkg.in/spacemonkeygo/monkit.v2"
)

const (
	DefaultInterval = time.Hour

	// MTUs are often 1500, though a good argument could be made for 512
	DefaultPacketSize = 1000
)

// ClientOpts allows you to set Client Options
type ClientOpts struct {
	// Interval is how frequently stats from the provided Registry will be
	// sent up. Note that this interval is "jittered", so the actual interval
	// is taken from a normal distribution with a mean of Interval and a
	// variance of Interval/4. Defaults to DefaultInterval
	Interval time.Duration

	// Application is the application name, usually prepended to metric names.
	// By default it will be os.Args[0]
	Application string

	// Instance is a string that identifies this particular server. Could be a
	// node id, but defaults to the first non-nil MAC address
	Instance string

	// PacketSize controls how we fragment the data as it goes out in UDP
	// packets. Defaults to DefaultPacketSize
	PacketSize int

	// Registry is where to get stats from. Defaults to monkit.Default
	Registry *monkit.Registry

	// FloatEncoding is how floats should be encoded on the wire.
	// Default is float16.
	FloatEncoding admproto.FloatEncoding
}

// Client is a telemetry client for sending UDP packets at a regular interval
// from a monkit.Registry
type Client struct {
	interval time.Duration
	opts     admmonkit.Options
}

// NewClient constructs a telemetry client that sends packets to remote_addr
// over UDP.
func NewClient(remote_addr string, opts ClientOpts) (rv *Client, err error) {
	if opts.Interval == 0 {
		opts.Interval = DefaultInterval
	}
	if opts.Application == "" {
		if len(os.Args) > 0 {
			opts.Application = os.Args[0]
		} else {
			// what the actual heck
			opts.Application = "unknown"
		}
	}
	if opts.Instance == "" {
		// instance by default is the first non-nil mac address
		ifaces, err := net.Interfaces()
		if err != nil {
			return nil, err
		}
		for _, iface := range ifaces {
			if iface.HardwareAddr != nil {
				opts.Instance = iface.HardwareAddr.String()
				break
			}
		}
		if opts.Instance == "" {
			opts.Instance = "unknown"
		}
	}
	if opts.Registry == nil {
		opts.Registry = monkit.Default
	}
	if opts.PacketSize == 0 {
		opts.PacketSize = DefaultPacketSize
	}

	return &Client{
		interval: opts.Interval,
		opts: admmonkit.Options{
			Application: opts.Application,
			InstanceId:  []byte(opts.Instance),
			Address:     remote_addr,
			PacketSize:  opts.PacketSize,
			Registry:    opts.Registry,
			ProtoOpts:   admproto.Options{FloatEncoding: opts.FloatEncoding},
		},
	}, nil
}

// Run calls Report roughly every Interval
func (c *Client) Run(ctx context.Context) {
	for {
		time.Sleep(jitter(c.interval))
		if ctx.Err() != nil {
			return
		}
		err := c.Report(ctx)
		if err != nil {
			zap.S().Errorf("failed sending telemetry report: %v", err)
		}
	}
}

// Report bundles up all the current stats and writes them out as UDP packets
func (c *Client) Report(ctx context.Context) error {
	return admmonkit.Send(ctx, c.opts)
}