package apm

import (
	"errors"
	"fmt"
	"net"
	"net/url"
	"strconv"
	"strings"
	"time"
)

type urlInfo struct {
	addrs   []string
	user    string
	pass    string
	db      string
	options map[string]string
}

func isOptSep(c rune) bool {
	return c == ';' || c == '&'
}

func extractURL(s string) (*urlInfo, error) {
	if strings.HasPrefix(s, "mongodb://") {
		s = s[10:]
	}
	info := &urlInfo{options: make(map[string]string)}
	if c := strings.Index(s, "?"); c != -1 {
		for _, pair := range strings.FieldsFunc(s[c+1:], isOptSep) {
			l := strings.SplitN(pair, "=", 2)
			if len(l) != 2 || l[0] == "" || l[1] == "" {
				return nil, errors.New("connection option must be key=value: " + pair)
			}
			info.options[l[0]] = l[1]
		}
		s = s[:c]
	}
	if c := strings.Index(s, "@"); c != -1 {
		pair := strings.SplitN(s[:c], ":", 2)
		if len(pair) > 2 || pair[0] == "" {
			return nil, errors.New("credentials must be provided as user:pass@host")
		}
		var err error
		info.user, err = url.QueryUnescape(pair[0])
		if err != nil {
			return nil, fmt.Errorf("cannot unescape username in URL: %q", pair[0])
		}
		if len(pair) > 1 {
			info.pass, err = url.QueryUnescape(pair[1])
			if err != nil {
				return nil, fmt.Errorf("cannot unescape password in URL")
			}
		}
		s = s[c+1:]
	}
	if c := strings.Index(s, "/"); c != -1 {
		info.db = s[c+1:]
		s = s[:c]
	}
	info.addrs = strings.Split(s, ",")
	return info, nil
}

func ParseMongoURL(url string) (scheme string, host string, path string) {
	dialInfo, err := doParseMongoURL(url)
	if err != nil {
		return "", "", ""
	}
	scheme = "mongodb"
	if dialInfo.Addrs == nil {
		host = ""
	} else {
		host = strings.Join(dialInfo.Addrs, ",")
	}
	path = dialInfo.Database
	return scheme, host, path
}

// ParseURL parses a MongoDB URL as accepted by the Dial function and returns
// a value suitable for providing into DialWithInfo.
//
// See Dial for more details on the format of url.
func doParseMongoURL(url string) (*DialInfo, error) {
	uinfo, err := extractURL(url)
	if err != nil {
		return nil, err
	}
	direct := false
	mechanism := ""
	service := ""
	source := ""
	setName := ""
	poolLimit := 0
	for k, v := range uinfo.options {
		switch k {
		case "authSource":
			source = v
		case "authMechanism":
			mechanism = v
		case "gssapiServiceName":
			service = v
		case "replicaSet":
			setName = v
		case "maxPoolSize":
			poolLimit, err = strconv.Atoi(v)
			if err != nil {
				return nil, errors.New("bad value for maxPoolSize: " + v)
			}
		case "connect":
			if v == "direct" {
				direct = true
				break
			}
			if v == "replicaSet" {
				break
			}
			fallthrough
		default:
			return nil, errors.New("unsupported connection URL option: " + k + "=" + v)
		}
	}
	info := DialInfo{
		Addrs:          uinfo.addrs,
		Direct:         direct,
		Database:       uinfo.db,
		Username:       uinfo.user,
		Password:       uinfo.pass,
		Mechanism:      mechanism,
		Service:        service,
		Source:         source,
		PoolLimit:      poolLimit,
		ReplicaSetName: setName,
	}
	return &info, nil
}

// DialInfo holds options for establishing a session with a MongoDB cluster.
// To use a URL, see the Dial function.
type DialInfo struct {
	// Addrs holds the addresses for the seed servers.
	Addrs []string

	// Direct informs whether to establish connections only with the
	// specified seed servers, or to obtain information for the whole
	// cluster and establish connections with further servers too.
	Direct bool

	// Timeout is the amount of time to wait for a server to respond when
	// first connecting and on follow up operations in the session. If
	// timeout is zero, the call may block forever waiting for a connection
	// to be established. Timeout does not affect logic in DialServer.
	Timeout time.Duration

	// FailFast will cause connection and query attempts to fail faster when
	// the server is unavailable, instead of retrying until the configured
	// timeout period. Note that an unavailable server may silently drop
	// packets instead of rejecting them, in which case it's impossible to
	// distinguish it from a slow server, so the timeout stays relevant.
	FailFast bool

	// Database is the default database name used when the Session.DB method
	// is called with an empty name, and is also used during the initial
	// authentication if Source is unset.
	Database string

	// ReplicaSetName, if specified, will prevent the obtained session from
	// communicating with any server which is not part of a replica set
	// with the given name. The default is to communicate with any server
	// specified or discovered via the servers contacted.
	ReplicaSetName string

	// Source is the database used to establish credentials and privileges
	// with a MongoDB server. Defaults to the value of Database, if that is
	// set, or "admin" otherwise.
	Source string

	// Service defines the service name to use when authenticating with the GSSAPI
	// mechanism. Defaults to "mongodb".
	Service string

	// ServiceHost defines which hostname to use when authenticating
	// with the GSSAPI mechanism. If not specified, defaults to the MongoDB
	// server's address.
	ServiceHost string

	// Mechanism defines the protocol for credential negotiation.
	// Defaults to "MONGODB-CR".
	Mechanism string

	// Username and Password inform the credentials for the initial authentication
	// done on the database defined by the Source field. See Session.Login.
	Username string
	Password string

	// PoolLimit defines the per-server socket pool limit. Defaults to 4096.
	// See Session.SetPoolLimit for details.
	PoolLimit int

	// DialServer optionally specifies the dial function for establishing
	// connections with the MongoDB servers.
	DialServer func(addr *ServerAddr) (net.Conn, error)

	// WARNING: This field is obsolete. See DialServer above.
	Dial func(addr net.Addr) (net.Conn, error)
}

// ServerAddr represents the address for establishing a connection to an
// individual MongoDB server.
type ServerAddr struct {
	str string
	tcp *net.TCPAddr
}