package checker

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"html/template"
	"net/http"
	"time"

	sdk "git.happydns.org/checker-sdk-go/checker"
)

const otxEndpoint = "https://otx.alienvault.com/api/v1/indicators/domain/"

func init() { Register(&otxSource{endpoint: otxEndpoint}) }

type otxSource struct{ endpoint string }

func (*otxSource) ID() string   { return "otx" }
func (*otxSource) Name() string { return "AlienVault OTX" }

func (*otxSource) Options() SourceOptions {
	return SourceOptions{
		Admin: []sdk.CheckerOptionField{
			{
				Id:          "otx_api_key",
				Type:        "string",
				Label:       "AlienVault OTX API key",
				Description: "Free OTX API key from otx.alienvault.com. Leave empty to skip OTX lookups.",
				Secret:      true,
			},
		},
	}
}

type otxDetails struct {
	PulseCount int        `json:"pulse_count"`
	Reputation int        `json:"reputation"`
	Pulses     []otxPulse `json:"pulses"`
}

type otxPulse struct {
	Name            string   `json:"name"`
	Tags            []string `json:"tags,omitempty"`
	MalwareFamilies []string `json:"malware_families,omitempty"`
	Adversary       string   `json:"adversary,omitempty"`
	Created         string   `json:"created,omitempty"`
}

func (s *otxSource) Query(ctx context.Context, domain, registered string, opts sdk.CheckerOptions) []SourceResult {
	apiKey := stringOpt(opts, "otx_api_key")
	if apiKey == "" {
		return []SourceResult{{SourceID: s.ID(), SourceName: s.Name(), Enabled: false}}
	}
	if registered == "" {
		return []SourceResult{{SourceID: s.ID(), SourceName: s.Name(), Enabled: true}}
	}

	res := SourceResult{
		SourceID:  s.ID(),
		SourceName: s.Name(),
		Enabled:   true,
		Reference: "https://otx.alienvault.com/indicator/domain/" + registered,
	}

	reqCtx, cancel := context.WithTimeout(ctx, 15*time.Second)
	defer cancel()

	req, err := http.NewRequestWithContext(reqCtx, http.MethodGet, s.endpoint+registered+"/general", nil)
	if err != nil {
		res.Error = err.Error()
		return []SourceResult{res}
	}
	req.Header.Set("X-OTX-API-KEY", apiKey)
	req.Header.Set("Accept", "application/json")

	body, status, err := httpDo(req, 4<<20)
	if err != nil {
		res.Error = err.Error()
		return []SourceResult{res}
	}
	if status == http.StatusNotFound {
		return []SourceResult{res}
	}
	if status != http.StatusOK {
		res.Error = fmt.Sprintf("HTTP %d: %s", status, truncate(string(body), 200))
		return []SourceResult{res}
	}

	var parsed struct {
		Reputation int `json:"reputation"`
		PulseInfo  struct {
			Count  int `json:"count"`
			Pulses []struct {
				Name            string   `json:"name"`
				Tags            []string `json:"tags"`
				MalwareFamilies []struct {
					DisplayName string `json:"display_name"`
				} `json:"malware_families"`
				Adversary string `json:"adversary"`
				Created   string `json:"created"`
			} `json:"pulses"`
		} `json:"pulse_info"`
	}
	if err := json.Unmarshal(body, &parsed); err != nil {
		res.Error = "decode: " + err.Error()
		return []SourceResult{res}
	}

	d := otxDetails{
		PulseCount: parsed.PulseInfo.Count,
		Reputation: parsed.Reputation,
	}

	seenReason := map[string]bool{}
	for _, p := range parsed.PulseInfo.Pulses {
		pulse := otxPulse{
			Name:      p.Name,
			Tags:      p.Tags,
			Adversary: p.Adversary,
			Created:   p.Created,
		}
		for _, mf := range p.MalwareFamilies {
			pulse.MalwareFamilies = append(pulse.MalwareFamilies, mf.DisplayName)
			if !seenReason[mf.DisplayName] {
				seenReason[mf.DisplayName] = true
				res.Reasons = append(res.Reasons, mf.DisplayName)
			}
		}
		if p.Adversary != "" && !seenReason[p.Adversary] {
			seenReason[p.Adversary] = true
			res.Reasons = append(res.Reasons, p.Adversary)
		}
		d.Pulses = append(d.Pulses, pulse)
		res.Evidence = append(res.Evidence, Evidence{
			Label:  "Pulse",
			Value:  p.Name,
			Status: "threat",
		})
	}
	res.Details = mustJSON(d)
	return []SourceResult{res}
}

func (*otxSource) Evaluate(r SourceResult) (bool, string) {
	if !r.Enabled || r.Error != "" || len(r.Evidence) == 0 {
		return false, ""
	}
	var d otxDetails
	_ = json.Unmarshal(r.Details, &d)
	if d.Reputation < -1 {
		return true, SeverityCrit
	}
	return true, SeverityWarn
}

func (*otxSource) Diagnose(res SourceResult) Diagnosis {
	var d otxDetails
	_ = json.Unmarshal(res.Details, &d)
	detail := fmt.Sprintf(
		"%d threat pulse(s) reference this domain (OTX reputation score: %d). Indicators: %s. "+
			"Review the pulse details on AlienVault OTX to understand the threat context and take corrective action.",
		d.PulseCount, d.Reputation, joinNonEmpty(res.Reasons, ", "),
	)
	sev := SeverityWarn
	if d.Reputation < -1 {
		sev = SeverityCrit
	}
	return Diagnosis{
		Severity: sev,
		Title:    "Listed in AlienVault OTX threat pulses",
		Detail:   detail,
		Fix:      res.Reference,
		FixIsURL: res.Reference != "",
	}
}

func (*otxSource) RenderDetail(res SourceResult) (template.HTML, error) {
	var d otxDetails
	if len(res.Details) > 0 {
		if err := json.Unmarshal(res.Details, &d); err != nil {
			return "", fmt.Errorf("otx: decode details: %w", err)
		}
	}
	if len(d.Pulses) == 0 {
		return "", nil
	}
	var b bytes.Buffer
	if err := otxDetailTpl.Execute(&b, d); err != nil {
		return "", err
	}
	return template.HTML(b.String()), nil
}

var otxDetailTpl = template.Must(template.New("otx_detail").Parse(`
<p>OTX reputation score: <strong>{{.Reputation}}</strong>. Pulse count: <strong>{{.PulseCount}}</strong>.</p>
<table>
<thead><tr><th>Pulse</th><th>Malware families</th><th>Adversary</th><th>Tags</th><th>Created</th></tr></thead>
<tbody>{{range .Pulses}}<tr class="row-crit">
<td>{{.Name}}</td>
<td>{{range .MalwareFamilies}}<span>{{.}} </span>{{end}}</td>
<td>{{.Adversary}}</td>
<td>{{range .Tags}}<span>{{.}} </span>{{end}}</td>
<td><small>{{.Created}}</small></td>
</tr>{{end}}</tbody>
</table>`))