// Copyright (C) 2019 Nicola Murino
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published
// by the Free Software Foundation, version 3.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.

package dataprovider

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"hash/fnv"
	"io"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/lestrrat-go/jwx/v2/jwa"
	"github.com/lestrrat-go/jwx/v2/jwt"
	"github.com/rs/xid"

	"github.com/drakkan/sftpgo/v2/internal/httpclient"
	"github.com/drakkan/sftpgo/v2/internal/kms"
	"github.com/drakkan/sftpgo/v2/internal/logger"
	"github.com/drakkan/sftpgo/v2/internal/util"
)

// Supported protocols for connecting to other nodes
const (
	NodeProtoHTTP  = "http"
	NodeProtoHTTPS = "https"
)

const (
	// NodeTokenHeader defines the header to use for the node auth token
	NodeTokenHeader = "X-SFTPGO-Node"
)

var (
	// current node
	currentNode        *Node
	errNoClusterNodes  = errors.New("no cluster node defined")
	activeNodeTimeDiff = -2 * time.Minute
	nodeReqTimeout     = 8 * time.Second
)

// NodeConfig defines the node configuration
type NodeConfig struct {
	Host  string `json:"host" mapstructure:"host"`
	Port  int    `json:"port" mapstructure:"port"`
	Proto string `json:"proto" mapstructure:"proto"`
}

func (n *NodeConfig) validate() error {
	currentNode = nil
	if config.IsShared != 1 {
		return nil
	}
	if n.Host == "" {
		return nil
	}
	currentNode = &Node{
		Data: NodeData{
			Host:  n.Host,
			Port:  n.Port,
			Proto: n.Proto,
		},
	}
	return provider.addNode()
}

// NodeData defines the details to connect to a cluster node
type NodeData struct {
	Host  string      `json:"host"`
	Port  int         `json:"port"`
	Proto string      `json:"proto"`
	Key   *kms.Secret `json:"api_key"`
}

func (n *NodeData) validate() error {
	if n.Host == "" {
		return util.NewValidationError("node host is mandatory")
	}
	if n.Port < 0 || n.Port > 65535 {
		return util.NewValidationError(fmt.Sprintf("invalid node port: %d", n.Port))
	}
	if n.Proto != NodeProtoHTTP && n.Proto != NodeProtoHTTPS {
		return util.NewValidationError(fmt.Sprintf("invalid node proto: %s", n.Proto))
	}
	n.Key = kms.NewPlainSecret(string(util.GenerateRandomBytes(32)))
	n.Key.SetAdditionalData(n.Host)
	if err := n.Key.Encrypt(); err != nil {
		return fmt.Errorf("unable to encrypt node key: %w", err)
	}
	return nil
}

func (n *NodeData) getNodeName() string {
	h := fnv.New64a()
	var b bytes.Buffer

	b.WriteString(fmt.Sprintf("%s:%d", n.Host, n.Port))
	h.Write(b.Bytes())
	return strconv.FormatUint(h.Sum64(), 10)
}

// Node defines a cluster node
type Node struct {
	Name      string   `json:"name"`
	Data      NodeData `json:"data"`
	CreatedAt int64    `json:"created_at"`
	UpdatedAt int64    `json:"updated_at"`
}

func (n *Node) validate() error {
	if n.Name == "" {
		n.Name = n.Data.getNodeName()
	}
	return n.Data.validate()
}

func (n *Node) authenticate(token string) (string, string, error) {
	if err := n.Data.Key.TryDecrypt(); err != nil {
		providerLog(logger.LevelError, "unable to decrypt node key: %v", err)
		return "", "", err
	}
	if token == "" {
		return "", "", ErrInvalidCredentials
	}
	t, err := jwt.Parse([]byte(token), jwt.WithKey(jwa.HS256, []byte(n.Data.Key.GetPayload())), jwt.WithValidate(true))
	if err != nil {
		return "", "", fmt.Errorf("unable to parse and validate token: %v", err)
	}
	var adminUsername, role string
	if admin, ok := t.Get("admin"); ok {
		if val, ok := admin.(string); ok && val != "" {
			adminUsername = val
		}
	}
	if adminUsername == "" {
		return "", "", errors.New("no admin username associated with node token")
	}
	if r, ok := t.Get("role"); ok {
		if val, ok := r.(string); ok && val != "" {
			role = val
		}
	}
	return adminUsername, role, nil
}

// getBaseURL returns the base URL for this node
func (n *Node) getBaseURL() string {
	var sb strings.Builder
	sb.WriteString(n.Data.Proto)
	sb.WriteString("://")
	sb.WriteString(n.Data.Host)
	if n.Data.Port > 0 {
		sb.WriteString(":")
		sb.WriteString(strconv.Itoa(n.Data.Port))
	}
	return sb.String()
}

// generateAuthToken generates a new auth token
func (n *Node) generateAuthToken(username, role string) (string, error) {
	if err := n.Data.Key.TryDecrypt(); err != nil {
		return "", fmt.Errorf("unable to decrypt node key: %w", err)
	}
	now := time.Now().UTC()

	t := jwt.New()
	t.Set("admin", username)                          //nolint:errcheck
	t.Set("role", role)                               //nolint:errcheck
	t.Set(jwt.JwtIDKey, xid.New().String())           //nolint:errcheck
	t.Set(jwt.NotBeforeKey, now.Add(-30*time.Second)) //nolint:errcheck
	t.Set(jwt.ExpirationKey, now.Add(1*time.Minute))  //nolint:errcheck

	payload, err := jwt.Sign(t, jwt.WithKey(jwa.HS256, []byte(n.Data.Key.GetPayload())))
	if err != nil {
		return "", fmt.Errorf("unable to sign authentication token: %w", err)
	}
	return string(payload), nil
}

func (n *Node) prepareRequest(ctx context.Context, username, role, relativeURL, method string,
	body io.Reader,
) (*http.Request, error) {
	url := fmt.Sprintf("%s%s", n.getBaseURL(), relativeURL)
	req, err := http.NewRequestWithContext(ctx, method, url, body)
	if err != nil {
		return nil, err
	}
	token, err := n.generateAuthToken(username, role)
	if err != nil {
		return nil, err
	}
	req.Header.Set(NodeTokenHeader, fmt.Sprintf("Bearer %s", token))
	return req, nil
}

// SendGetRequest sends an HTTP GET request to this node.
// The responseHolder must be a pointer
func (n *Node) SendGetRequest(username, role, relativeURL string, responseHolder any) error {
	ctx, cancel := context.WithTimeout(context.Background(), nodeReqTimeout)
	defer cancel()

	req, err := n.prepareRequest(ctx, username, role, relativeURL, http.MethodGet, nil)
	if err != nil {
		return err
	}
	client := httpclient.GetHTTPClient()
	defer client.CloseIdleConnections()

	resp, err := client.Do(req)
	if err != nil {
		return fmt.Errorf("unable to send HTTP GET to node %s: %w", n.Name, err)
	}
	defer resp.Body.Close()

	if resp.StatusCode < http.StatusOK || resp.StatusCode > http.StatusNoContent {
		return fmt.Errorf("unexpected status code: %d", resp.StatusCode)
	}
	respBody, err := io.ReadAll(io.LimitReader(resp.Body, 10485760))
	if err != nil {
		return fmt.Errorf("unable to read response body: %w", err)
	}
	err = json.Unmarshal(respBody, responseHolder)
	if err != nil {
		return errors.New("unable to decode response as json")
	}
	return nil
}

// SendDeleteRequest sends an HTTP DELETE request to this node
func (n *Node) SendDeleteRequest(username, role, relativeURL string) error {
	ctx, cancel := context.WithTimeout(context.Background(), nodeReqTimeout)
	defer cancel()

	req, err := n.prepareRequest(ctx, username, role, relativeURL, http.MethodDelete, nil)
	if err != nil {
		return err
	}
	client := httpclient.GetHTTPClient()
	defer client.CloseIdleConnections()

	resp, err := client.Do(req)
	if err != nil {
		return fmt.Errorf("unable to send HTTP DELETE to node %s: %w", n.Name, err)
	}
	defer resp.Body.Close()

	if resp.StatusCode < http.StatusOK || resp.StatusCode > http.StatusNoContent {
		return fmt.Errorf("unexpected status code: %d", resp.StatusCode)
	}
	return nil
}

// AuthenticateNodeToken check the validity of the provided token
func AuthenticateNodeToken(token string) (string, string, error) {
	if currentNode == nil {
		return "", "", errNoClusterNodes
	}
	return currentNode.authenticate(token)
}

// GetNodeName returns the node name or an empty string
func GetNodeName() string {
	if currentNode == nil {
		return ""
	}
	return currentNode.Name
}