// Copyright (C) The Arvados Authors. All rights reserved.
//
// SPDX-License-Identifier: Apache-2.0

// Package keepclient provides low-level Get/Put primitives for accessing
// Arvados Keep blocks.
package keepclient

import (
	"bytes"
	"context"
	"crypto/md5"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"net"
	"net/http"
	"regexp"
	"strconv"
	"strings"
	"sync"
	"time"

	"git.arvados.org/arvados.git/sdk/go/arvados"
	"git.arvados.org/arvados.git/sdk/go/arvadosclient"
	"git.arvados.org/arvados.git/sdk/go/httpserver"
)

// BLOCKSIZE defines the length of a Keep "block", which is 64MB.
const BLOCKSIZE = 64 * 1024 * 1024

var (
	DefaultRequestTimeout      = 20 * time.Second
	DefaultConnectTimeout      = 2 * time.Second
	DefaultTLSHandshakeTimeout = 4 * time.Second
	DefaultKeepAlive           = 180 * time.Second

	DefaultProxyRequestTimeout      = 300 * time.Second
	DefaultProxyConnectTimeout      = 30 * time.Second
	DefaultProxyTLSHandshakeTimeout = 10 * time.Second
	DefaultProxyKeepAlive           = 120 * time.Second
)

// Error interface with an error and boolean indicating whether the error is temporary
type Error interface {
	error
	Temporary() bool
}

// multipleResponseError is of type Error
type multipleResponseError struct {
	error
	isTemp bool
}

func (e *multipleResponseError) Temporary() bool {
	return e.isTemp
}

// BlockNotFound is a multipleResponseError where isTemp is false
var BlockNotFound = &ErrNotFound{multipleResponseError{
	error:  errors.New("Block not found"),
	isTemp: false,
}}

// ErrNotFound is a multipleResponseError where isTemp can be true or false
type ErrNotFound struct {
	multipleResponseError
}

type InsufficientReplicasError struct{ error }

type OversizeBlockError struct{ error }

var ErrOversizeBlock = OversizeBlockError{error: errors.New("Exceeded maximum block size (" + strconv.Itoa(BLOCKSIZE) + ")")}
var MissingArvadosApiHost = errors.New("Missing required environment variable ARVADOS_API_HOST")
var MissingArvadosApiToken = errors.New("Missing required environment variable ARVADOS_API_TOKEN")
var InvalidLocatorError = errors.New("Invalid locator")

// ErrNoSuchKeepServer is returned when GetIndex is invoked with a UUID with no matching keep server
var ErrNoSuchKeepServer = errors.New("No keep server matching the given UUID is found")

// ErrIncompleteIndex is returned when the Index response does not end with a new empty line
var ErrIncompleteIndex = errors.New("Got incomplete index")

const (
	XKeepDesiredReplicas         = "X-Keep-Desired-Replicas"
	XKeepReplicasStored          = "X-Keep-Replicas-Stored"
	XKeepStorageClasses          = "X-Keep-Storage-Classes"
	XKeepStorageClassesConfirmed = "X-Keep-Storage-Classes-Confirmed"
)

type HTTPClient interface {
	Do(*http.Request) (*http.Response, error)
}

// KeepClient holds information about Arvados and Keep servers.
type KeepClient struct {
	Arvados               *arvadosclient.ArvadosClient
	Want_replicas         int
	localRoots            map[string]string
	writableLocalRoots    map[string]string
	gatewayRoots          map[string]string
	lock                  sync.RWMutex
	HTTPClient            HTTPClient
	Retries               int
	BlockCache            *BlockCache
	RequestID             string
	StorageClasses        []string
	DefaultStorageClasses []string // Set by cluster's exported config

	// set to 1 if all writable services are of disk type, otherwise 0
	replicasPerService int

	// Any non-disk typed services found in the list of keepservers?
	foundNonDiskSvc bool

	// Disable automatic discovery of keep services
	disableDiscovery bool
}

func (kc *KeepClient) loadDefaultClasses() error {
	scData, err := kc.Arvados.ClusterConfig("StorageClasses")
	if err != nil {
		return err
	}
	classes := scData.(map[string]interface{})
	for scName := range classes {
		scConf, _ := classes[scName].(map[string]interface{})
		isDefault, ok := scConf["Default"].(bool)
		if ok && isDefault {
			kc.DefaultStorageClasses = append(kc.DefaultStorageClasses, scName)
		}
	}
	return nil
}

// MakeKeepClient creates a new KeepClient, loads default storage classes, calls
// DiscoverKeepServices(), and returns when the client is ready to
// use.
func MakeKeepClient(arv *arvadosclient.ArvadosClient) (*KeepClient, error) {
	kc := New(arv)
	return kc, kc.discoverServices()
}

// New creates a new KeepClient. Service discovery will occur on the
// next read/write operation.
func New(arv *arvadosclient.ArvadosClient) *KeepClient {
	defaultReplicationLevel := 2
	value, err := arv.Discovery("defaultCollectionReplication")
	if err == nil {
		v, ok := value.(float64)
		if ok && v > 0 {
			defaultReplicationLevel = int(v)
		}
	}
	kc := &KeepClient{
		Arvados:       arv,
		Want_replicas: defaultReplicationLevel,
		Retries:       2,
	}
	err = kc.loadDefaultClasses()
	if err != nil {
		DebugPrintf("DEBUG: Unable to load the default storage classes cluster config")
	}
	return kc
}

// PutHR puts a block given the block hash, a reader, and the number of bytes
// to read from the reader (which must be between 0 and BLOCKSIZE).
//
// Returns the locator for the written block, the number of replicas
// written, and an error.
//
// Returns an InsufficientReplicasError if 0 <= replicas <
// kc.Wants_replicas.
func (kc *KeepClient) PutHR(hash string, r io.Reader, dataBytes int64) (string, int, error) {
	resp, err := kc.BlockWrite(context.Background(), arvados.BlockWriteOptions{
		Hash:     hash,
		Reader:   r,
		DataSize: int(dataBytes),
	})
	return resp.Locator, resp.Replicas, err
}

// PutHB writes a block to Keep. The hash of the bytes is given in
// hash, and the data is given in buf.
//
// Return values are the same as for PutHR.
func (kc *KeepClient) PutHB(hash string, buf []byte) (string, int, error) {
	resp, err := kc.BlockWrite(context.Background(), arvados.BlockWriteOptions{
		Hash: hash,
		Data: buf,
	})
	return resp.Locator, resp.Replicas, err
}

// PutB writes a block to Keep. It computes the hash itself.
//
// Return values are the same as for PutHR.
func (kc *KeepClient) PutB(buffer []byte) (string, int, error) {
	resp, err := kc.BlockWrite(context.Background(), arvados.BlockWriteOptions{
		Data: buffer,
	})
	return resp.Locator, resp.Replicas, err
}

// PutR writes a block to Keep. It first reads all data from r into a buffer
// in order to compute the hash.
//
// Return values are the same as for PutHR.
//
// If the block hash and data size are known, PutHR is more efficient.
func (kc *KeepClient) PutR(r io.Reader) (locator string, replicas int, err error) {
	buffer, err := ioutil.ReadAll(r)
	if err != nil {
		return "", 0, err
	}
	return kc.PutB(buffer)
}

func (kc *KeepClient) getOrHead(method string, locator string, header http.Header) (io.ReadCloser, int64, string, http.Header, error) {
	if strings.HasPrefix(locator, "d41d8cd98f00b204e9800998ecf8427e+0") {
		return ioutil.NopCloser(bytes.NewReader(nil)), 0, "", nil, nil
	}

	reqid := kc.getRequestID()

	var expectLength int64
	if parts := strings.SplitN(locator, "+", 3); len(parts) < 2 {
		expectLength = -1
	} else if n, err := strconv.ParseInt(parts[1], 10, 64); err != nil {
		expectLength = -1
	} else {
		expectLength = n
	}

	var errs []string

	triesRemaining := 1 + kc.Retries

	serversToTry := kc.getSortedRoots(locator)

	numServers := len(serversToTry)
	count404 := 0

	var retryList []string

	for triesRemaining > 0 {
		triesRemaining--
		retryList = nil

		for _, host := range serversToTry {
			url := host + "/" + locator

			req, err := http.NewRequest(method, url, nil)
			if err != nil {
				errs = append(errs, fmt.Sprintf("%s: %v", url, err))
				continue
			}
			for k, v := range header {
				req.Header[k] = append([]string(nil), v...)
			}
			if req.Header.Get("Authorization") == "" {
				req.Header.Set("Authorization", "OAuth2 "+kc.Arvados.ApiToken)
			}
			if req.Header.Get("X-Request-Id") == "" {
				req.Header.Set("X-Request-Id", reqid)
			}
			resp, err := kc.httpClient().Do(req)
			if err != nil {
				// Probably a network error, may be transient,
				// can try again.
				errs = append(errs, fmt.Sprintf("%s: %v", url, err))
				retryList = append(retryList, host)
				continue
			}
			if resp.StatusCode != http.StatusOK {
				var respbody []byte
				respbody, _ = ioutil.ReadAll(&io.LimitedReader{R: resp.Body, N: 4096})
				resp.Body.Close()
				errs = append(errs, fmt.Sprintf("%s: HTTP %d %q",
					url, resp.StatusCode, bytes.TrimSpace(respbody)))

				if resp.StatusCode == 408 ||
					resp.StatusCode == 429 ||
					resp.StatusCode >= 500 {
					// Timeout, too many requests, or other
					// server side failure, transient
					// error, can try again.
					retryList = append(retryList, host)
				} else if resp.StatusCode == 404 {
					count404++
				}
				continue
			}
			if expectLength < 0 {
				if resp.ContentLength < 0 {
					resp.Body.Close()
					return nil, 0, "", nil, fmt.Errorf("error reading %q: no size hint, no Content-Length header in response", locator)
				}
				expectLength = resp.ContentLength
			} else if resp.ContentLength >= 0 && expectLength != resp.ContentLength {
				resp.Body.Close()
				return nil, 0, "", nil, fmt.Errorf("error reading %q: size hint %d != Content-Length %d", locator, expectLength, resp.ContentLength)
			}
			// Success
			if method == "GET" {
				return HashCheckingReader{
					Reader: resp.Body,
					Hash:   md5.New(),
					Check:  locator[0:32],
				}, expectLength, url, resp.Header, nil
			}
			resp.Body.Close()
			return nil, expectLength, url, resp.Header, nil
		}
		serversToTry = retryList
	}
	DebugPrintf("DEBUG: %s %s failed: %v", method, locator, errs)

	var err error
	if count404 == numServers {
		err = BlockNotFound
	} else {
		err = &ErrNotFound{multipleResponseError{
			error:  fmt.Errorf("%s %s failed: %v", method, locator, errs),
			isTemp: len(serversToTry) > 0,
		}}
	}
	return nil, 0, "", nil, err
}

// LocalLocator returns a locator equivalent to the one supplied, but
// with a valid signature from the local cluster. If the given locator
// already has a local signature, it is returned unchanged.
func (kc *KeepClient) LocalLocator(locator string) (string, error) {
	if !strings.Contains(locator, "+R") {
		// Either it has +A, or it's unsigned and we assume
		// it's a local locator on a site with signatures
		// disabled.
		return locator, nil
	}
	sighdr := fmt.Sprintf("local, time=%s", time.Now().UTC().Format(time.RFC3339))
	_, _, url, hdr, err := kc.getOrHead("HEAD", locator, http.Header{"X-Keep-Signature": []string{sighdr}})
	if err != nil {
		return "", err
	}
	loc := hdr.Get("X-Keep-Locator")
	if loc == "" {
		return "", fmt.Errorf("missing X-Keep-Locator header in HEAD response from %s", url)
	}
	return loc, nil
}

// Get retrieves a block, given a locator. Returns a reader, the
// expected data length, the URL the block is being fetched from, and
// an error.
//
// If the block checksum does not match, the final Read() on the
// reader returned by this method will return a BadChecksum error
// instead of EOF.
func (kc *KeepClient) Get(locator string) (io.ReadCloser, int64, string, error) {
	rdr, size, url, _, err := kc.getOrHead("GET", locator, nil)
	return rdr, size, url, err
}

// ReadAt retrieves a portion of block from the cache if it's
// present, otherwise from the network.
func (kc *KeepClient) ReadAt(locator string, p []byte, off int) (int, error) {
	return kc.cache().ReadAt(kc, locator, p, off)
}

// Ask verifies that a block with the given hash is available and
// readable, according to at least one Keep service. Unlike Get, it
// does not retrieve the data or verify that the data content matches
// the hash specified by the locator.
//
// Returns the data size (content length) reported by the Keep service
// and the URI reporting the data size.
func (kc *KeepClient) Ask(locator string) (int64, string, error) {
	_, size, url, _, err := kc.getOrHead("HEAD", locator, nil)
	return size, url, err
}

// GetIndex retrieves a list of blocks stored on the given server whose hashes
// begin with the given prefix. The returned reader will return an error (other
// than EOF) if the complete index cannot be retrieved.
//
// This is meant to be used only by system components and admin tools.
// It will return an error unless the client is using a "data manager token"
// recognized by the Keep services.
func (kc *KeepClient) GetIndex(keepServiceUUID, prefix string) (io.Reader, error) {
	url := kc.LocalRoots()[keepServiceUUID]
	if url == "" {
		return nil, ErrNoSuchKeepServer
	}

	url += "/index"
	if prefix != "" {
		url += "/" + prefix
	}

	req, err := http.NewRequest("GET", url, nil)
	if err != nil {
		return nil, err
	}

	req.Header.Add("Authorization", "OAuth2 "+kc.Arvados.ApiToken)
	req.Header.Set("X-Request-Id", kc.getRequestID())
	resp, err := kc.httpClient().Do(req)
	if err != nil {
		return nil, err
	}

	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("Got http status code: %d", resp.StatusCode)
	}

	var respBody []byte
	respBody, err = ioutil.ReadAll(resp.Body)
	if err != nil {
		return nil, err
	}

	// Got index; verify that it is complete
	// The response should be "\n" if no locators matched the prefix
	// Else, it should be a list of locators followed by a blank line
	if !bytes.Equal(respBody, []byte("\n")) && !bytes.HasSuffix(respBody, []byte("\n\n")) {
		return nil, ErrIncompleteIndex
	}

	// Got complete index; strip the trailing newline and send
	return bytes.NewReader(respBody[0 : len(respBody)-1]), nil
}

// LocalRoots returns the map of local (i.e., disk and proxy) Keep
// services: uuid -> baseURI.
func (kc *KeepClient) LocalRoots() map[string]string {
	kc.discoverServices()
	kc.lock.RLock()
	defer kc.lock.RUnlock()
	return kc.localRoots
}

// GatewayRoots returns the map of Keep remote gateway services:
// uuid -> baseURI.
func (kc *KeepClient) GatewayRoots() map[string]string {
	kc.discoverServices()
	kc.lock.RLock()
	defer kc.lock.RUnlock()
	return kc.gatewayRoots
}

// WritableLocalRoots returns the map of writable local Keep services:
// uuid -> baseURI.
func (kc *KeepClient) WritableLocalRoots() map[string]string {
	kc.discoverServices()
	kc.lock.RLock()
	defer kc.lock.RUnlock()
	return kc.writableLocalRoots
}

// SetServiceRoots disables service discovery and updates the
// localRoots and gatewayRoots maps, without disrupting operations
// that are already in progress.
//
// The supplied maps must not be modified after calling
// SetServiceRoots.
func (kc *KeepClient) SetServiceRoots(locals, writables, gateways map[string]string) {
	kc.disableDiscovery = true
	kc.setServiceRoots(locals, writables, gateways)
}

func (kc *KeepClient) setServiceRoots(locals, writables, gateways map[string]string) {
	kc.lock.Lock()
	defer kc.lock.Unlock()
	kc.localRoots = locals
	kc.writableLocalRoots = writables
	kc.gatewayRoots = gateways
}

// getSortedRoots returns a list of base URIs of Keep services, in the
// order they should be attempted in order to retrieve content for the
// given locator.
func (kc *KeepClient) getSortedRoots(locator string) []string {
	var found []string
	for _, hint := range strings.Split(locator, "+") {
		if len(hint) < 7 || hint[0:2] != "K@" {
			// Not a service hint.
			continue
		}
		if len(hint) == 7 {
			// +K@abcde means fetch from proxy at
			// keep.abcde.arvadosapi.com
			found = append(found, "https://keep."+hint[2:]+".arvadosapi.com")
		} else if len(hint) == 29 {
			// +K@abcde-abcde-abcdeabcdeabcde means fetch
			// from gateway with given uuid
			if gwURI, ok := kc.GatewayRoots()[hint[2:]]; ok {
				found = append(found, gwURI)
			}
			// else this hint is no use to us; carry on.
		}
	}
	// After trying all usable service hints, fall back to local roots.
	found = append(found, NewRootSorter(kc.LocalRoots(), locator[0:32]).GetSortedRoots()...)
	return found
}

func (kc *KeepClient) cache() *BlockCache {
	if kc.BlockCache != nil {
		return kc.BlockCache
	}
	return DefaultBlockCache
}

func (kc *KeepClient) ClearBlockCache() {
	kc.cache().Clear()
}

func (kc *KeepClient) SetStorageClasses(sc []string) {
	// make a copy so the caller can't mess with it.
	kc.StorageClasses = append([]string{}, sc...)
}

var (
	// There are four global http.Client objects for the four
	// possible permutations of TLS behavior (verify/skip-verify)
	// and timeout settings (proxy/non-proxy).
	defaultClient = map[bool]map[bool]HTTPClient{
		// defaultClient[false] is used for verified TLS reqs
		false: {},
		// defaultClient[true] is used for unverified
		// (insecure) TLS reqs
		true: {},
	}
	defaultClientMtx sync.Mutex
)

// httpClient returns the HTTPClient field if it's not nil, otherwise
// whichever of the four global http.Client objects is suitable for
// the current environment (i.e., TLS verification on/off, keep
// services are/aren't proxies).
func (kc *KeepClient) httpClient() HTTPClient {
	if kc.HTTPClient != nil {
		return kc.HTTPClient
	}
	defaultClientMtx.Lock()
	defer defaultClientMtx.Unlock()
	if c, ok := defaultClient[kc.Arvados.ApiInsecure][kc.foundNonDiskSvc]; ok {
		return c
	}

	var requestTimeout, connectTimeout, keepAlive, tlsTimeout time.Duration
	if kc.foundNonDiskSvc {
		// Use longer timeouts when connecting to a proxy,
		// because this usually means the intervening network
		// is slower.
		requestTimeout = DefaultProxyRequestTimeout
		connectTimeout = DefaultProxyConnectTimeout
		tlsTimeout = DefaultProxyTLSHandshakeTimeout
		keepAlive = DefaultProxyKeepAlive
	} else {
		requestTimeout = DefaultRequestTimeout
		connectTimeout = DefaultConnectTimeout
		tlsTimeout = DefaultTLSHandshakeTimeout
		keepAlive = DefaultKeepAlive
	}

	c := &http.Client{
		Timeout: requestTimeout,
		// It's not safe to copy *http.DefaultTransport
		// because it has a mutex (which might be locked)
		// protecting a private map (which might not be nil).
		// So we build our own, using the Go 1.12 default
		// values, ignoring any changes the application has
		// made to http.DefaultTransport.
		Transport: &http.Transport{
			DialContext: (&net.Dialer{
				Timeout:   connectTimeout,
				KeepAlive: keepAlive,
				DualStack: true,
			}).DialContext,
			MaxIdleConns:          100,
			IdleConnTimeout:       90 * time.Second,
			TLSHandshakeTimeout:   tlsTimeout,
			ExpectContinueTimeout: 1 * time.Second,
			TLSClientConfig:       arvadosclient.MakeTLSConfig(kc.Arvados.ApiInsecure),
		},
	}
	defaultClient[kc.Arvados.ApiInsecure][kc.foundNonDiskSvc] = c
	return c
}

var reqIDGen = httpserver.IDGenerator{Prefix: "req-"}

func (kc *KeepClient) getRequestID() string {
	if kc.RequestID != "" {
		return kc.RequestID
	}
	return reqIDGen.Next()
}

type Locator struct {
	Hash  string
	Size  int      // -1 if data size is not known
	Hints []string // Including the size hint, if any
}

func (loc *Locator) String() string {
	s := loc.Hash
	if len(loc.Hints) > 0 {
		s = s + "+" + strings.Join(loc.Hints, "+")
	}
	return s
}

var locatorMatcher = regexp.MustCompile("^([0-9a-f]{32})([+](.*))?$")

func MakeLocator(path string) (*Locator, error) {
	sm := locatorMatcher.FindStringSubmatch(path)
	if sm == nil {
		return nil, InvalidLocatorError
	}
	loc := Locator{Hash: sm[1], Size: -1}
	if sm[2] != "" {
		loc.Hints = strings.Split(sm[3], "+")
	} else {
		loc.Hints = []string{}
	}
	if len(loc.Hints) > 0 {
		if size, err := strconv.Atoi(loc.Hints[0]); err == nil {
			loc.Size = size
		}
	}
	return &loc, nil
}