// Package geolocate implements IP lookup, resolver lookup, and geolocation.
package geolocate

import (
	"context"
	"fmt"

	"github.com/ooni/probe-cli/v3/internal/engine/netx"
	"github.com/ooni/probe-cli/v3/internal/model"
	"github.com/ooni/probe-cli/v3/internal/version"
)

const (
	// DefaultProbeASN is the default probe ASN as a number.
	DefaultProbeASN uint = 0

	// DefaultProbeCC is the default probe CC.
	DefaultProbeCC = "ZZ"

	// DefaultProbeIP is the default probe IP.
	DefaultProbeIP = model.DefaultProbeIP

	// DefaultProbeNetworkName is the default probe network name.
	DefaultProbeNetworkName = ""

	// DefaultResolverASN is the default resolver ASN.
	DefaultResolverASN uint = 0

	// DefaultResolverIP is the default resolver IP.
	DefaultResolverIP = "127.0.0.2"

	// DefaultResolverNetworkName is the default resolver network name.
	DefaultResolverNetworkName = ""
)

var (
	// DefaultProbeASNString is the default probe ASN as a string.
	DefaultProbeASNString = fmt.Sprintf("AS%d", DefaultProbeASN)

	// DefaultResolverASNString is the default resolver ASN as a string.
	DefaultResolverASNString = fmt.Sprintf("AS%d", DefaultResolverASN)
)

// Results contains geolocate results.
type Results struct {
	// ASN is the autonomous system number.
	ASN uint

	// CountryCode is the country code.
	CountryCode string

	// didResolverLookup indicates whether we did a resolver lookup.
	didResolverLookup bool

	// NetworkName is the network name.
	NetworkName string

	// IP is the probe IP.
	ProbeIP string

	// ResolverASN is the resolver ASN.
	ResolverASN uint

	// ResolverIP is the resolver IP.
	ResolverIP string

	// ResolverNetworkName is the resolver network name.
	ResolverNetworkName string
}

// ASNString returns the ASN as a string.
func (r *Results) ASNString() string {
	return fmt.Sprintf("AS%d", r.ASN)
}

type probeIPLookupper interface {
	LookupProbeIP(ctx context.Context) (addr string, err error)
}

type asnLookupper interface {
	LookupASN(ip string) (asn uint, network string, err error)
}

type countryLookupper interface {
	LookupCC(ip string) (cc string, err error)
}

type resolverIPLookupper interface {
	LookupResolverIP(ctx context.Context) (addr string, err error)
}

// Resolver is a DNS resolver.
type Resolver interface {
	LookupHost(ctx context.Context, domain string) ([]string, error)
	Network() string
	Address() string
}

// Config contains configuration for a geolocate Task.
type Config struct {
	// Resolver is the resolver we should use when
	// making requests for discovering the IP. When
	// this field is not set, we use the stdlib.
	Resolver Resolver

	// Logger is the logger to use. If not set, then we will
	// use a logger that discards all messages.
	Logger model.Logger

	// UserAgent is the user agent to use. If not set, then
	// we will use a default user agent.
	UserAgent string
}

// NewTask creates a new instance of Task from config.
func NewTask(config Config) *Task {
	if config.Logger == nil {
		config.Logger = model.DiscardLogger
	}
	if config.UserAgent == "" {
		config.UserAgent = fmt.Sprintf("ooniprobe-engine/%s", version.Version)
	}
	if config.Resolver == nil {
		config.Resolver = netx.NewResolver(
			netx.Config{Logger: config.Logger})
	}
	return &Task{
		countryLookupper:     mmdbLookupper{},
		probeIPLookupper:     ipLookupClient(config),
		probeASNLookupper:    mmdbLookupper{},
		resolverASNLookupper: mmdbLookupper{},
		resolverIPLookupper:  resolverLookupClient{},
	}
}

// Task performs a geolocation. You must create a new
// instance of Task using the NewTask factory.
type Task struct {
	countryLookupper     countryLookupper
	probeIPLookupper     probeIPLookupper
	probeASNLookupper    asnLookupper
	resolverASNLookupper asnLookupper
	resolverIPLookupper  resolverIPLookupper
}

// Run runs the task.
func (op Task) Run(ctx context.Context) (*Results, error) {
	var err error
	out := &Results{
		ASN:                 DefaultProbeASN,
		CountryCode:         DefaultProbeCC,
		NetworkName:         DefaultProbeNetworkName,
		ProbeIP:             DefaultProbeIP,
		ResolverASN:         DefaultResolverASN,
		ResolverIP:          DefaultResolverIP,
		ResolverNetworkName: DefaultResolverNetworkName,
	}
	ip, err := op.probeIPLookupper.LookupProbeIP(ctx)
	if err != nil {
		return out, fmt.Errorf("lookupProbeIP failed: %w", err)
	}
	out.ProbeIP = ip
	asn, networkName, err := op.probeASNLookupper.LookupASN(out.ProbeIP)
	if err != nil {
		return out, fmt.Errorf("lookupASN failed: %w", err)
	}
	out.ASN = asn
	out.NetworkName = networkName
	cc, err := op.countryLookupper.LookupCC(out.ProbeIP)
	if err != nil {
		return out, fmt.Errorf("lookupProbeCC failed: %w", err)
	}
	out.CountryCode = cc
	out.didResolverLookup = true
	// Note: ignoring the result of lookupResolverIP and lookupASN
	// here is intentional. We don't want this (~minor) failure
	// to influence the result of the overall lookup. Another design
	// here could be that of retrying the operation N times?
	resolverIP, err := op.resolverIPLookupper.LookupResolverIP(ctx)
	if err != nil {
		return out, nil // intentional
	}
	out.ResolverIP = resolverIP
	resolverASN, resolverNetworkName, err := op.resolverASNLookupper.LookupASN(
		out.ResolverIP,
	)
	if err != nil {
		return out, nil // intentional
	}
	out.ResolverASN = resolverASN
	out.ResolverNetworkName = resolverNetworkName
	return out, nil
}