package api

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strconv"
	"strings"

	"github.com/prometheus/client_golang/prometheus"

	"gitlab.com/gitlab-org/gitaly-proto/go/gitalypb"

	"gitlab.com/gitlab-org/gitlab-workhorse/internal/gitaly"
	"gitlab.com/gitlab-org/gitlab-workhorse/internal/helper"
	"gitlab.com/gitlab-org/gitlab-workhorse/internal/secret"
)

const (
	// Custom content type for API responses, to catch routing / programming mistakes
	ResponseContentType = "application/vnd.gitlab-workhorse+json"

	failureResponseLimit = 32768
)

type API struct {
	Client  *http.Client
	URL     *url.URL
	Version string
}

var (
	requestsCounter = prometheus.NewCounterVec(
		prometheus.CounterOpts{
			Name: "gitlab_workhorse_internal_api_requests",
			Help: "How many internal API requests have been completed by gitlab-workhorse, partitioned by status code and HTTP method.",
		},
		[]string{"code", "method"},
	)
	bytesTotal = prometheus.NewCounter(
		prometheus.CounterOpts{
			Name: "gitlab_workhorse_internal_api_failure_response_bytes",
			Help: "How many bytes have been returned by upstream GitLab in API failure/rejection response bodies.",
		},
	)
)

func init() {
	prometheus.MustRegister(requestsCounter)
	prometheus.MustRegister(bytesTotal)
}

func NewAPI(myURL *url.URL, version string, roundTripper http.RoundTripper) *API {
	return &API{
		Client:  &http.Client{Transport: roundTripper},
		URL:     myURL,
		Version: version,
	}
}

type HandleFunc func(http.ResponseWriter, *http.Request, *Response)

type MultipartUploadParams struct {
	// PartSize is the exact size of each uploaded part. Only the last one can be smaller
	PartSize int64
	// PartURLs contains the presigned URLs for each part
	PartURLs []string
	// CompleteURL is a presigned URL for CompleteMulipartUpload
	CompleteURL string
	// AbortURL is a presigned URL for AbortMultipartUpload
	AbortURL string
}

type RemoteObject struct {
	// GetURL is an S3 GetObject URL
	GetURL string
	// DeleteURL is a presigned S3 RemoveObject URL
	DeleteURL string
	// StoreURL is the temporary presigned S3 PutObject URL to which upload the first found file
	StoreURL string
	// Boolean to indicate whether to use headers included in PutHeaders
	CustomPutHeaders bool
	// PutHeaders are HTTP headers (e.g. Content-Type) to be sent with StoreURL
	PutHeaders map[string]string
	// ID is a unique identifier of object storage upload
	ID string
	// Timeout is a number that represents timeout in seconds for sending data to StoreURL
	Timeout int
	// MultipartUpload contains presigned URLs for S3 MultipartUpload
	MultipartUpload *MultipartUploadParams
}

type Response struct {
	// GL_ID is an environment variable used by gitlab-shell hooks during 'git
	// push' and 'git pull'
	GL_ID string

	// GL_USERNAME holds gitlab username of the user who is taking the action causing hooks to be invoked
	GL_USERNAME string

	// GL_REPOSITORY is an environment variable used by gitlab-shell hooks during
	// 'git push' and 'git pull'
	GL_REPOSITORY string
	// GitConfigOptions holds the custom options that we want to pass to the git command
	GitConfigOptions []string
	// StoreLFSPath is provided by the GitLab Rails application to mark where the tmp file should be placed.
	// This field is deprecated. GitLab will use TempPath instead
	StoreLFSPath string
	// LFS object id
	LfsOid string
	// LFS object size
	LfsSize int64
	// TmpPath is the path where we should store temporary files
	// This is set by authorization middleware
	TempPath string
	// RemoteObject is provided by the GitLab Rails application
	// and defines a way to store object on remote storage
	RemoteObject RemoteObject
	// Archive is the path where the artifacts archive is stored
	Archive string `json:"archive"`
	// Entry is a filename inside the archive point to file that needs to be extracted
	Entry string `json:"entry"`
	// Used to communicate terminal session details
	Terminal *TerminalSettings
	// GitalyServer specifies an address and authentication token for a gitaly server we should connect to.
	GitalyServer gitaly.Server
	// Repository object for making gRPC requests to Gitaly.
	Repository gitalypb.Repository
	// For git-http, does the requestor have the right to view all refs?
	ShowAllRefs bool
}

// singleJoiningSlash is taken from reverseproxy.go:NewSingleHostReverseProxy
func singleJoiningSlash(a, b string) string {
	aslash := strings.HasSuffix(a, "/")
	bslash := strings.HasPrefix(b, "/")
	switch {
	case aslash && bslash:
		return a + b[1:]
	case !aslash && !bslash:
		return a + "/" + b
	}
	return a + b
}

// rebaseUrl is taken from reverseproxy.go:NewSingleHostReverseProxy
func rebaseUrl(url *url.URL, onto *url.URL, suffix string) *url.URL {
	newUrl := *url
	newUrl.Scheme = onto.Scheme
	newUrl.Host = onto.Host
	if suffix != "" {
		newUrl.Path = singleJoiningSlash(url.Path, suffix)
	}
	if onto.RawQuery == "" || newUrl.RawQuery == "" {
		newUrl.RawQuery = onto.RawQuery + newUrl.RawQuery
	} else {
		newUrl.RawQuery = onto.RawQuery + "&" + newUrl.RawQuery
	}
	return &newUrl
}

func (api *API) newRequest(r *http.Request, suffix string) (*http.Request, error) {
	authReq := &http.Request{
		Method: r.Method,
		URL:    rebaseUrl(r.URL, api.URL, suffix),
		Header: helper.HeaderClone(r.Header),
	}

	// Clean some headers when issuing a new request without body
	authReq.Header.Del("Content-Type")
	authReq.Header.Del("Content-Encoding")
	authReq.Header.Del("Content-Length")
	authReq.Header.Del("Content-Disposition")
	authReq.Header.Del("Accept-Encoding")

	// Hop-by-hop headers. These are removed when sent to the backend.
	// http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html
	authReq.Header.Del("Transfer-Encoding")
	authReq.Header.Del("Connection")
	authReq.Header.Del("Keep-Alive")
	authReq.Header.Del("Proxy-Authenticate")
	authReq.Header.Del("Proxy-Authorization")
	authReq.Header.Del("Te")
	authReq.Header.Del("Trailers")
	authReq.Header.Del("Upgrade")

	// Also forward the Host header, which is excluded from the Header map by the http libary.
	// This allows the Host header received by the backend to be consistent with other
	// requests not going through gitlab-workhorse.
	authReq.Host = r.Host

	return authReq, nil
}

// PreAuthorize performs a pre-authorization check against the API for the given HTTP request
//
// If `outErr` is set, the other fields will be nil and it should be treated as
// a 500 error.
//
// If httpResponse is present, the caller is responsible for closing its body
//
// authResponse will only be present if the authorization check was successful
func (api *API) PreAuthorize(suffix string, r *http.Request) (httpResponse *http.Response, authResponse *Response, outErr error) {
	authReq, err := api.newRequest(r, suffix)
	if err != nil {
		return nil, nil, fmt.Errorf("preAuthorizeHandler newUpstreamRequest: %v", err)
	}

	httpResponse, err = api.doRequestWithoutRedirects(authReq)
	if err != nil {
		return nil, nil, fmt.Errorf("preAuthorizeHandler: do request: %v", err)
	}
	defer func() {
		if outErr != nil {
			httpResponse.Body.Close()
			httpResponse = nil
		}
	}()
	requestsCounter.WithLabelValues(strconv.Itoa(httpResponse.StatusCode), authReq.Method).Inc()

	// This may be a false positive, e.g. for .../info/refs, rather than a
	// failure, so pass the response back
	if httpResponse.StatusCode != http.StatusOK || !validResponseContentType(httpResponse) {
		return httpResponse, nil, nil
	}

	authResponse = &Response{}
	// The auth backend validated the client request and told us additional
	// request metadata. We must extract this information from the auth
	// response body.
	if err := json.NewDecoder(httpResponse.Body).Decode(authResponse); err != nil {
		return httpResponse, nil, fmt.Errorf("preAuthorizeHandler: decode authorization response: %v", err)
	}

	return httpResponse, authResponse, nil
}

func (api *API) PreAuthorizeHandler(next HandleFunc, suffix string) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		httpResponse, authResponse, err := api.PreAuthorize(suffix, r)
		if httpResponse != nil {
			defer httpResponse.Body.Close()
		}

		if err != nil {
			helper.Fail500(w, r, err)
			return
		}

		// The response couldn't be interpreted as a valid auth response, so
		// pass it back (mostly) unmodified
		if httpResponse != nil && authResponse == nil {
			passResponseBack(httpResponse, w, r)
			return
		}

		httpResponse.Body.Close() // Free up the Unicorn worker

		copyAuthHeader(httpResponse, w)

		next(w, r, authResponse)
	})
}

func (api *API) doRequestWithoutRedirects(authReq *http.Request) (*http.Response, error) {
	signingTripper := secret.NewRoundTripper(api.Client.Transport, api.Version)

	return signingTripper.RoundTrip(authReq)
}

func copyAuthHeader(httpResponse *http.Response, w http.ResponseWriter) {
	// Negotiate authentication (Kerberos) may need to return a WWW-Authenticate
	// header to the client even in case of success as per RFC4559.
	for k, v := range httpResponse.Header {
		// Case-insensitive comparison as per RFC7230
		if strings.EqualFold(k, "WWW-Authenticate") {
			w.Header()[k] = v
		}
	}
}

func passResponseBack(httpResponse *http.Response, w http.ResponseWriter, r *http.Request) {
	// NGINX response buffering is disabled on this path (with
	// X-Accel-Buffering: no) but we still want to free up the Unicorn worker
	// that generated httpResponse as fast as possible. To do this we buffer
	// the entire response body in memory before sending it on.
	responseBody, err := bufferResponse(httpResponse.Body)
	if err != nil {
		helper.Fail500(w, r, err)
		return
	}
	httpResponse.Body.Close() // Free up the Unicorn worker
	bytesTotal.Add(float64(responseBody.Len()))

	for k, v := range httpResponse.Header {
		// Accomodate broken clients that do case-sensitive header lookup
		if k == "Www-Authenticate" {
			w.Header()["WWW-Authenticate"] = v
		} else {
			w.Header()[k] = v
		}
	}
	w.WriteHeader(httpResponse.StatusCode)
	if _, err := io.Copy(w, responseBody); err != nil {
		helper.LogError(r, err)
	}
}

func bufferResponse(r io.Reader) (*bytes.Buffer, error) {
	responseBody := &bytes.Buffer{}
	n, err := io.Copy(responseBody, io.LimitReader(r, failureResponseLimit))
	if err != nil {
		return nil, err
	}

	if n == failureResponseLimit {
		return nil, fmt.Errorf("response body exceeded maximum buffer size (%d bytes)", failureResponseLimit)
	}

	return responseBody, nil
}

func validResponseContentType(resp *http.Response) bool {
	return helper.IsContentType(ResponseContentType, resp.Header.Get("Content-Type"))
}