//go:generate ../../../tools/readme_config_includer/generator
package http_listener_v2

import (
	"compress/gzip"
	"crypto/subtle"
	"crypto/tls"
	_ "embed"
	"errors"
	"io"
	"net"
	"net/http"
	"net/url"
	"strings"
	"sync"
	"time"

	"github.com/golang/snappy"

	"github.com/influxdata/telegraf"
	"github.com/influxdata/telegraf/config"
	"github.com/influxdata/telegraf/internal/choice"
	tlsint "github.com/influxdata/telegraf/plugins/common/tls"
	"github.com/influxdata/telegraf/plugins/inputs"
	"github.com/influxdata/telegraf/plugins/parsers"
)

//go:embed sample.conf
var sampleConfig string

// defaultMaxBodySize is the default maximum request body size, in bytes.
// if the request body is over this size, we will return an HTTP 413 error.
// 500 MB
const defaultMaxBodySize = 500 * 1024 * 1024

const (
	body    = "body"
	query   = "query"
	pathTag = "http_listener_v2_path"
)

// TimeFunc provides a timestamp for the metrics
type TimeFunc func() time.Time

// HTTPListenerV2 is an input plugin that collects external metrics sent via HTTP
type HTTPListenerV2 struct {
	ServiceAddress string            `toml:"service_address"`
	Path           string            `toml:"path" deprecated:"1.20.0;use 'paths' instead"`
	Paths          []string          `toml:"paths"`
	PathTag        bool              `toml:"path_tag"`
	Methods        []string          `toml:"methods"`
	HTTPHeaders    map[string]string `toml:"http_headers"`
	DataSource     string            `toml:"data_source"`
	ReadTimeout    config.Duration   `toml:"read_timeout"`
	WriteTimeout   config.Duration   `toml:"write_timeout"`
	MaxBodySize    config.Size       `toml:"max_body_size"`
	Port           int               `toml:"port"`
	BasicUsername  string            `toml:"basic_username"`
	BasicPassword  string            `toml:"basic_password"`
	HTTPHeaderTags map[string]string `toml:"http_header_tags"`

	tlsint.ServerConfig
	tlsConf *tls.Config

	TimeFunc
	Log telegraf.Logger

	wg    sync.WaitGroup
	close chan struct{}

	listener net.Listener

	parsers.Parser
	acc telegraf.Accumulator
}

func (*HTTPListenerV2) SampleConfig() string {
	return sampleConfig
}

func (h *HTTPListenerV2) Gather(_ telegraf.Accumulator) error {
	return nil
}

func (h *HTTPListenerV2) SetParser(parser parsers.Parser) {
	h.Parser = parser
}

// Start starts the http listener service.
func (h *HTTPListenerV2) Start(acc telegraf.Accumulator) error {
	if h.MaxBodySize == 0 {
		h.MaxBodySize = config.Size(defaultMaxBodySize)
	}

	if h.ReadTimeout < config.Duration(time.Second) {
		h.ReadTimeout = config.Duration(time.Second * 10)
	}
	if h.WriteTimeout < config.Duration(time.Second) {
		h.WriteTimeout = config.Duration(time.Second * 10)
	}

	// Append h.Path to h.Paths
	if h.Path != "" && !choice.Contains(h.Path, h.Paths) {
		h.Paths = append(h.Paths, h.Path)
	}

	h.acc = acc

	server := h.createHTTPServer()

	h.wg.Add(1)
	go func() {
		defer h.wg.Done()
		if err := server.Serve(h.listener); err != nil {
			if !errors.Is(err, net.ErrClosed) {
				h.Log.Errorf("Serve failed: %v", err)
			}
			close(h.close)
		}
	}()

	h.Log.Infof("Listening on %s", h.listener.Addr().String())

	return nil
}

func (h *HTTPListenerV2) createHTTPServer() *http.Server {
	return &http.Server{
		Addr:         h.ServiceAddress,
		Handler:      h,
		ReadTimeout:  time.Duration(h.ReadTimeout),
		WriteTimeout: time.Duration(h.WriteTimeout),
		TLSConfig:    h.tlsConf,
	}
}

// Stop cleans up all resources
func (h *HTTPListenerV2) Stop() {
	if h.listener != nil {
		h.listener.Close() //nolint:revive // ignore the returned error as we cannot do anything about it anyway
	}
	h.wg.Wait()
}

func (h *HTTPListenerV2) Init() error {
	tlsConf, err := h.ServerConfig.TLSConfig()
	if err != nil {
		return err
	}

	var listener net.Listener
	if tlsConf != nil {
		listener, err = tls.Listen("tcp", h.ServiceAddress, tlsConf)
	} else {
		listener, err = net.Listen("tcp", h.ServiceAddress)
	}
	if err != nil {
		return err
	}
	h.tlsConf = tlsConf
	h.listener = listener
	h.Port = listener.Addr().(*net.TCPAddr).Port

	return nil
}

func (h *HTTPListenerV2) ServeHTTP(res http.ResponseWriter, req *http.Request) {
	handler := h.serveWrite

	if !choice.Contains(req.URL.Path, h.Paths) {
		handler = http.NotFound
	}

	for key, value := range h.HTTPHeaders {
		res.Header().Set(key, value)
	}

	h.authenticateIfSet(handler, res, req)
}

func (h *HTTPListenerV2) serveWrite(res http.ResponseWriter, req *http.Request) {
	select {
	case <-h.close:
		res.WriteHeader(http.StatusGone)
		return
	default:
	}

	// Check that the content length is not too large for us to handle.
	if req.ContentLength > int64(h.MaxBodySize) {
		if err := tooLarge(res); err != nil {
			h.Log.Debugf("error in too-large: %v", err)
		}
		return
	}

	// Check if the requested HTTP method was specified in config.
	isAcceptedMethod := false
	for _, method := range h.Methods {
		if req.Method == method {
			isAcceptedMethod = true
			break
		}
	}
	if !isAcceptedMethod {
		if err := methodNotAllowed(res); err != nil {
			h.Log.Debugf("error in method-not-allowed: %v", err)
		}
		return
	}

	var bytes []byte
	var ok bool

	switch strings.ToLower(h.DataSource) {
	case query:
		bytes, ok = h.collectQuery(res, req)
	default:
		bytes, ok = h.collectBody(res, req)
	}

	if !ok {
		return
	}

	metrics, err := h.Parse(bytes)
	if err != nil {
		h.Log.Debugf("Parse error: %s", err.Error())
		if err := badRequest(res); err != nil {
			h.Log.Debugf("error in bad-request: %v", err)
		}
		return
	}

	for _, m := range metrics {
		for headerName, measurementName := range h.HTTPHeaderTags {
			headerValues := req.Header.Get(headerName)
			if len(headerValues) > 0 {
				m.AddTag(measurementName, headerValues)
			}
		}

		if h.PathTag {
			m.AddTag(pathTag, req.URL.Path)
		}

		h.acc.AddMetric(m)
	}

	res.WriteHeader(http.StatusNoContent)
}

func (h *HTTPListenerV2) collectBody(res http.ResponseWriter, req *http.Request) ([]byte, bool) {
	encoding := req.Header.Get("Content-Encoding")

	switch encoding {
	case "gzip":
		r, err := gzip.NewReader(req.Body)
		if err != nil {
			h.Log.Debug(err.Error())
			if err := badRequest(res); err != nil {
				h.Log.Debugf("error in bad-request: %v", err)
			}
			return nil, false
		}
		defer r.Close()
		maxReader := http.MaxBytesReader(res, r, int64(h.MaxBodySize))
		bytes, err := io.ReadAll(maxReader)
		if err != nil {
			if err := tooLarge(res); err != nil {
				h.Log.Debugf("error in too-large: %v", err)
			}
			return nil, false
		}
		return bytes, true
	case "snappy":
		defer req.Body.Close()
		bytes, err := io.ReadAll(req.Body)
		if err != nil {
			h.Log.Debug(err.Error())
			if err := badRequest(res); err != nil {
				h.Log.Debugf("error in bad-request: %v", err)
			}
			return nil, false
		}
		// snappy block format is only supported by decode/encode not snappy reader/writer
		bytes, err = snappy.Decode(nil, bytes)
		if err != nil {
			h.Log.Debug(err.Error())
			if err := badRequest(res); err != nil {
				h.Log.Debugf("error in bad-request: %v", err)
			}
			return nil, false
		}
		return bytes, true
	default:
		defer req.Body.Close()
		bytes, err := io.ReadAll(req.Body)
		if err != nil {
			h.Log.Debug(err.Error())
			if err := badRequest(res); err != nil {
				h.Log.Debugf("error in bad-request: %v", err)
			}
			return nil, false
		}
		return bytes, true
	}
}

func (h *HTTPListenerV2) collectQuery(res http.ResponseWriter, req *http.Request) ([]byte, bool) {
	rawQuery := req.URL.RawQuery

	query, err := url.QueryUnescape(rawQuery)
	if err != nil {
		h.Log.Debugf("Error parsing query: %s", err.Error())
		if err := badRequest(res); err != nil {
			h.Log.Debugf("error in bad-request: %v", err)
		}
		return nil, false
	}

	return []byte(query), true
}

func tooLarge(res http.ResponseWriter) error {
	res.Header().Set("Content-Type", "application/json")
	res.WriteHeader(http.StatusRequestEntityTooLarge)
	_, err := res.Write([]byte(`{"error":"http: request body too large"}`))
	return err
}

func methodNotAllowed(res http.ResponseWriter) error {
	res.Header().Set("Content-Type", "application/json")
	res.WriteHeader(http.StatusMethodNotAllowed)
	_, err := res.Write([]byte(`{"error":"http: method not allowed"}`))
	return err
}

func badRequest(res http.ResponseWriter) error {
	res.Header().Set("Content-Type", "application/json")
	res.WriteHeader(http.StatusBadRequest)
	_, err := res.Write([]byte(`{"error":"http: bad request"}`))
	return err
}

func (h *HTTPListenerV2) authenticateIfSet(handler http.HandlerFunc, res http.ResponseWriter, req *http.Request) {
	if h.BasicUsername != "" && h.BasicPassword != "" {
		reqUsername, reqPassword, ok := req.BasicAuth()
		if !ok ||
			subtle.ConstantTimeCompare([]byte(reqUsername), []byte(h.BasicUsername)) != 1 ||
			subtle.ConstantTimeCompare([]byte(reqPassword), []byte(h.BasicPassword)) != 1 {
			http.Error(res, "Unauthorized.", http.StatusUnauthorized)
			return
		}
		handler(res, req)
	} else {
		handler(res, req)
	}
}

func init() {
	inputs.Add("http_listener_v2", func() telegraf.Input {
		return &HTTPListenerV2{
			ServiceAddress: ":8080",
			TimeFunc:       time.Now,
			Paths:          []string{"/telegraf"},
			Methods:        []string{"POST", "PUT"},
			DataSource:     body,
			close:          make(chan struct{}),
		}
	})
}
