package influxdb_v2

import (
	"bytes"
	"context"
	"crypto/tls"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"math"
	"net"
	"net/http"
	"net/url"
	"path"
	"strconv"
	"strings"
	"time"

	"golang.org/x/net/http2"

	"github.com/influxdata/telegraf"
	"github.com/influxdata/telegraf/config"
	"github.com/influxdata/telegraf/internal"
	"github.com/influxdata/telegraf/plugins/common/ratelimiter"
)

type APIError struct {
	Err        error
	StatusCode int
	Retryable  bool
}

func (e APIError) Error() string {
	return e.Err.Error()
}

func (e APIError) Unwrap() error {
	return e.Err
}

const (
	defaultMaxWaitSeconds           = 60
	defaultMaxWaitRetryAfterSeconds = 10 * 60
)

type httpClient struct {
	url              *url.URL
	localAddr        *net.TCPAddr
	token            config.Secret
	organization     string
	bucket           string
	bucketTag        string
	excludeBucketTag bool
	timeout          time.Duration
	headers          map[string]string
	proxy            *url.URL
	userAgent        string
	contentEncoding  string
	pingTimeout      config.Duration
	readIdleTimeout  config.Duration
	tlsConfig        *tls.Config
	encoder          internal.ContentEncoder
	serializer       ratelimiter.Serializer
	rateLimiter      *ratelimiter.RateLimiter
	client           *http.Client
	params           url.Values
	retryTime        time.Time
	retryCount       int
	log              telegraf.Logger
}

func (c *httpClient) Init() error {
	if c.headers == nil {
		c.headers = make(map[string]string, 1)
	}

	if _, ok := c.headers["User-Agent"]; !ok {
		c.headers["User-Agent"] = c.userAgent
	}

	var proxy func(*http.Request) (*url.URL, error)
	if c.proxy != nil {
		proxy = http.ProxyURL(c.proxy)
	} else {
		proxy = http.ProxyFromEnvironment
	}

	var transport *http.Transport
	switch c.url.Scheme {
	case "http", "https":
		var dialerFunc func(ctx context.Context, network, addr string) (net.Conn, error)
		if c.localAddr != nil {
			dialer := &net.Dialer{LocalAddr: c.localAddr}
			dialerFunc = dialer.DialContext
		}
		transport = &http.Transport{
			Proxy:           proxy,
			TLSClientConfig: c.tlsConfig,
			DialContext:     dialerFunc,
		}
		if c.readIdleTimeout != 0 || c.pingTimeout != 0 {
			http2Trans, err := http2.ConfigureTransports(transport)
			if err == nil {
				http2Trans.ReadIdleTimeout = time.Duration(c.readIdleTimeout)
				http2Trans.PingTimeout = time.Duration(c.pingTimeout)
			}
		}
	case "unix":
		transport = &http.Transport{
			Dial: func(_, _ string) (net.Conn, error) {
				return net.DialTimeout(
					c.url.Scheme,
					c.url.Path,
					c.timeout,
				)
			},
		}
	default:
		return fmt.Errorf("unsupported scheme %q", c.url.Scheme)
	}

	preppedURL, params, err := prepareWriteURL(*c.url, c.organization)
	if err != nil {
		return err
	}

	c.url = preppedURL
	c.client = &http.Client{
		Timeout:   c.timeout,
		Transport: transport,
	}
	c.params = params

	return nil
}

type genericRespError struct {
	Code      string
	Message   string
	Line      *int32
	MaxLength *int32
}

func (g genericRespError) Error() string {
	errString := fmt.Sprintf("%s: %s", g.Code, g.Message)
	if g.Line != nil {
		return fmt.Sprintf("%s - line[%d]", errString, g.Line)
	} else if g.MaxLength != nil {
		return fmt.Sprintf("%s - maxlen[%d]", errString, g.MaxLength)
	}
	return errString
}

func (c *httpClient) Write(ctx context.Context, metrics []telegraf.Metric) error {
	if c.retryTime.After(time.Now()) {
		return errors.New("retry time has not elapsed")
	}

	batches := make(map[string][]telegraf.Metric)
	batchIndices := make(map[string][]int)
	if c.bucketTag == "" {
		batches[c.bucket] = metrics
		batchIndices[c.bucket] = make([]int, len(metrics))
		for i := range metrics {
			batchIndices[c.bucket][i] = i
		}
	} else {
		for i, metric := range metrics {
			bucket, ok := metric.GetTag(c.bucketTag)
			if !ok {
				bucket = c.bucket
			} else if c.excludeBucketTag {
				// Avoid modifying the metric if we do remove the tag
				metric = metric.Copy()
				metric.Accept()
				metric.RemoveTag(c.bucketTag)
			}

			batches[bucket] = append(batches[bucket], metric)
			batchIndices[bucket] = append(batchIndices[bucket], i)
		}
	}

	var wErr internal.PartialWriteError
	for bucket, batch := range batches {
		err := c.writeBatch(ctx, bucket, batch)
		if err == nil {
			wErr.MetricsAccept = append(wErr.MetricsAccept, batchIndices[bucket]...)
			continue
		}

		// Check if the request was too large and split it
		var apiErr *APIError
		if errors.As(err, &apiErr) {
			if apiErr.StatusCode == http.StatusRequestEntityTooLarge {
				// TODO: Need a testcase to verify rejected metrics are not retried...
				return c.splitAndWriteBatch(ctx, c.bucket, metrics)
			}
			wErr.Err = err
			if !apiErr.Retryable {
				wErr.MetricsReject = append(wErr.MetricsReject, batchIndices[bucket]...)
			}
			// TODO: Clarify if we should continue here to try the remaining buckets?
			return &wErr
		}

		// Check if we got a write error and if so, translate the returned
		// metric indices to return the original indices in case of bucketing
		var writeErr *internal.PartialWriteError
		if errors.As(err, &writeErr) {
			wErr.Err = writeErr.Err
			for _, idx := range writeErr.MetricsAccept {
				wErr.MetricsAccept = append(wErr.MetricsAccept, batchIndices[bucket][idx])
			}
			for _, idx := range writeErr.MetricsReject {
				wErr.MetricsReject = append(wErr.MetricsReject, batchIndices[bucket][idx])
			}
			if !errors.Is(writeErr.Err, internal.ErrSizeLimitReached) {
				continue
			}
			return &wErr
		}

		// Return the error without special treatment
		wErr.Err = err
		return &wErr
	}
	return nil
}

func (c *httpClient) splitAndWriteBatch(ctx context.Context, bucket string, metrics []telegraf.Metric) error {
	c.log.Warnf("Retrying write after splitting metric payload in half to reduce batch size")
	midpoint := len(metrics) / 2

	if err := c.writeBatch(ctx, bucket, metrics[:midpoint]); err != nil {
		return err
	}

	return c.writeBatch(ctx, bucket, metrics[midpoint:])
}

func (c *httpClient) writeBatch(ctx context.Context, bucket string, metrics []telegraf.Metric) error {
	// Get the current limit for the outbound data
	ratets := time.Now()
	limit := c.rateLimiter.Remaining(ratets)

	// Serialize the metrics with the remaining limit, exit early if nothing was serialized
	body, werr := c.serializer.SerializeBatch(metrics, limit)
	if werr != nil && !errors.Is(werr, internal.ErrSizeLimitReached) || len(body) == 0 {
		return werr
	}
	used := int64(len(body))

	// Encode the content if requested
	if c.encoder != nil {
		var err error
		if body, err = c.encoder.Encode(body); err != nil {
			return fmt.Errorf("encoding failed: %w", err)
		}
	}

	// Setup the request
	address := makeWriteURL(*c.url, c.params, bucket)
	req, err := http.NewRequest("POST", address, io.NopCloser(bytes.NewBuffer(body)))
	if err != nil {
		return fmt.Errorf("creating request failed: %w", err)
	}
	if c.encoder != nil {
		req.Header.Set("Content-Encoding", c.contentEncoding)
	}
	req.Header.Set("Content-Type", "text/plain; charset=utf-8")

	// Set authorization
	token, err := c.token.Get()
	if err != nil {
		return fmt.Errorf("getting token failed: %w", err)
	}
	req.Header.Set("Authorization", "Token "+token.String())
	token.Destroy()

	c.addHeaders(req)

	// Execute the request
	c.rateLimiter.Accept(ratets, used)
	resp, err := c.client.Do(req.WithContext(ctx))
	if err != nil {
		internal.OnClientError(c.client, err)
		return err
	}
	defer resp.Body.Close()

	// Check for success
	switch resp.StatusCode {
	case
		// this is the expected response:
		http.StatusNoContent,
		// but if we get these we should still accept it as delivered:
		http.StatusOK,
		http.StatusCreated,
		http.StatusAccepted,
		http.StatusPartialContent,
		http.StatusMultiStatus,
		http.StatusAlreadyReported:
		c.retryCount = 0
		return werr
	}

	// We got an error and now try to decode further
	var desc string
	writeResp := &genericRespError{}
	if json.NewDecoder(resp.Body).Decode(writeResp) == nil {
		desc = ": " + writeResp.Error()
	}

	switch resp.StatusCode {
	// request was too large, send back to try again
	case http.StatusRequestEntityTooLarge:
		c.log.Errorf("Failed to write metric to %s, request was too large (413)", bucket)
		return &APIError{
			Err:        fmt.Errorf("%s: %s", resp.Status, desc),
			StatusCode: resp.StatusCode,
		}
	case
		// request was malformed:
		http.StatusBadRequest,
		// request was received but server refused to process it due to a semantic problem with the request.
		// for example, submitting metrics outside the retention period.
		http.StatusUnprocessableEntity,
		http.StatusNotAcceptable:

		// Clients should *not* repeat the request and the metrics should be rejected.
		return &APIError{
			Err:        fmt.Errorf("failed to write metric to %s (will be dropped: %s)%s", bucket, resp.Status, desc),
			StatusCode: resp.StatusCode,
		}
	case http.StatusUnauthorized, http.StatusForbidden:
		return fmt.Errorf("failed to write metric to %s (%s)%s", bucket, resp.Status, desc)
	case http.StatusTooManyRequests,
		http.StatusServiceUnavailable,
		http.StatusBadGateway,
		http.StatusGatewayTimeout:
		// ^ these handle the cases where the server is likely overloaded, and may not be able to say so.
		c.retryCount++
		retryDuration := c.getRetryDuration(resp.Header)
		c.retryTime = time.Now().Add(retryDuration)
		c.log.Warnf("Failed to write to %s; will retry in %s. (%s)\n", bucket, retryDuration, resp.Status)
		return fmt.Errorf("waiting %s for server (%s) before sending metric again", retryDuration, bucket)
	}

	// if it's any other 4xx code, the client should not retry as it's the client's mistake.
	// retrying will not make the request magically work.
	if len(resp.Status) > 0 && resp.Status[0] == '4' {
		return &APIError{
			Err:        fmt.Errorf("failed to write metric to %s (will be dropped: %s)%s", bucket, resp.Status, desc),
			StatusCode: resp.StatusCode,
		}
	}

	// This is only until platform spec is fully implemented. As of the
	// time of writing, there is no error body returned.
	if xErr := resp.Header.Get("X-Influx-Error"); xErr != "" {
		desc = fmt.Sprintf(": %s; %s", desc, xErr)
	}

	return &APIError{
		Err:        fmt.Errorf("failed to write metric to bucket %q: %s%s", bucket, resp.Status, desc),
		StatusCode: resp.StatusCode,
		Retryable:  true,
	}
}

// retryDuration takes the longer of the Retry-After header and our own back-off calculation
func (c *httpClient) getRetryDuration(headers http.Header) time.Duration {
	// basic exponential backoff (x^2)/40 (denominator to widen the slope)
	// at 40 denominator, it'll take 49 retries to hit the max defaultMaxWait of 60s
	backoff := math.Pow(float64(c.retryCount), 2) / 40
	backoff = math.Min(backoff, defaultMaxWaitSeconds)

	// get any value from the header, if available
	retryAfterHeader := float64(0)
	retryAfterHeaderString := headers.Get("Retry-After")
	if len(retryAfterHeaderString) > 0 {
		var err error
		retryAfterHeader, err = strconv.ParseFloat(retryAfterHeaderString, 64)
		if err != nil {
			// there was a value but we couldn't parse it? guess minimum 10 sec
			retryAfterHeader = 10
		}
		// protect against excessively large retry-after
		retryAfterHeader = math.Min(retryAfterHeader, defaultMaxWaitRetryAfterSeconds)
	}
	// take the highest value of backoff and retry-after.
	retry := math.Max(backoff, retryAfterHeader)
	return time.Duration(retry*1000) * time.Millisecond
}

func (c *httpClient) addHeaders(req *http.Request) {
	for header, value := range c.headers {
		if strings.EqualFold(header, "host") {
			req.Host = value
		} else {
			req.Header.Set(header, value)
		}
	}
}

func makeWriteURL(loc url.URL, params url.Values, bucket string) string {
	params.Set("bucket", bucket)
	loc.RawQuery = params.Encode()
	return loc.String()
}

func prepareWriteURL(loc url.URL, org string) (*url.URL, url.Values, error) {
	switch loc.Scheme {
	case "unix":
		loc.Scheme = "http"
		loc.Host = "127.0.0.1"
		loc.Path = "/api/v2/write"
	case "http", "https":
		loc.Path = path.Join(loc.Path, "/api/v2/write")
	default:
		return nil, nil, fmt.Errorf("unsupported scheme: %q", loc.Scheme)
	}

	params := loc.Query()
	params.Set("org", org)

	return &loc, params, nil
}

func (c *httpClient) Close() {
	c.client.CloseIdleConnections()
}
