package checker

import (
	"bufio"
	"context"
	"fmt"
	"io"
	"net/http"
	"strings"
	"sync"
	"time"

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

const (
	botvrijFeedURL     = "https://www.botvrij.eu/data/ioclist.domain.simple"
	botvrijDefaultTTL  = 6 * time.Hour
	botvrijFailBackoff = 1 * time.Minute
)

func init() {
	Register(&botvrijSource{
		cache: newBotvrijCache(botvrijFeedURL),
	})
}

type botvrijSource struct {
	cache *botvrijCache
}

func (*botvrijSource) ID() string   { return "botvrij" }
func (*botvrijSource) Name() string { return "Botvrij.eu domain blocklist" }

func (*botvrijSource) Options() SourceOptions {
	return SourceOptions{
		User: []sdk.CheckerOptionField{
			{
				Id:          "enable_botvrij",
				Type:        "bool",
				Label:       "Use Botvrij.eu domain blocklist",
				Description: "Download the Botvrij.eu public domain blocklist (refreshed every 6h) and check the domain against it.",
				Default:     true,
			},
		},
	}
}

func (s *botvrijSource) Query(ctx context.Context, domain, registered string, opts sdk.CheckerOptions) []SourceResult {
	if !sdk.GetBoolOption(opts, "enable_botvrij", true) || registered == "" {
		return disabledResult(s.ID(), s.Name())
	}

	matched, size, fetched, err := s.cache.lookup(ctx, registered)
	res := SourceResult{
		SourceID: s.ID(), SourceName: s.Name(), Enabled: true,
		Reference: "https://botvrij.eu/",
		Details:   mustJSON(map[string]any{"feed_size": size, "fetched_at": fetched}),
	}
	if err != nil {
		res.Error = err.Error()
	}
	if len(matched) > 0 {
		res.Reasons = []string{"Malicious domain"}
		for _, d := range matched {
			res.Evidence = append(res.Evidence, Evidence{Label: "Domain", Value: d})
		}
	}
	return []SourceResult{res}
}

func (*botvrijSource) Evaluate(r SourceResult) (bool, string) {
	return evidenceEval(r, SeverityCrit)
}

func (*botvrijSource) Diagnose(res SourceResult) Diagnosis {
	domains := make([]string, 0, len(res.Evidence))
	for _, e := range res.Evidence {
		domains = append(domains, e.Value)
	}
	previewN := min(len(domains), 5)
	return Diagnosis{
		Severity: SeverityCrit,
		Title:    "Listed in the Botvrij.eu domain blocklist",
		Detail: fmt.Sprintf(
			"%d domain(s) matching this registered domain appear in the Botvrij.eu IOC list; examples: %s. Botvrij.eu tracks domains associated with malware C2, exploit kits, and other malicious infrastructure. Investigate recent DNS changes and hosted content.",
			len(domains), joinNonEmpty(domains[:previewN], ", "),
		),
		Fix:      "https://botvrij.eu/",
		FixIsURL: true,
	}
}

// ---------- cache ----------

type botvrijCache struct {
	mu            sync.Mutex
	domains       []string            // all domains in feed
	byDomain      map[string]struct{} // set for O(1) exact-match test
	fetchedAt     time.Time
	lastAttemptAt time.Time
	refreshing    bool
	ttl           time.Duration
	failBackoff   time.Duration
	feedURL       string
}

func newBotvrijCache(feedURL string) *botvrijCache {
	return &botvrijCache{
		ttl:         botvrijDefaultTTL,
		failBackoff: botvrijFailBackoff,
		feedURL:     feedURL,
	}
}

func (c *botvrijCache) lookup(ctx context.Context, registered string) (matched []string, size int, fetchedAt time.Time, err error) {
	registered = strings.ToLower(strings.TrimSuffix(registered, "."))

	c.mu.Lock()
	stale := c.byDomain == nil || time.Since(c.fetchedAt) > c.ttl
	doRefresh := stale && !c.refreshing && time.Since(c.lastAttemptAt) > c.failBackoff
	if doRefresh {
		c.refreshing = true
	}
	c.mu.Unlock()

	if doRefresh {
		newDomains, newByDomain, ferr := c.fetch(ctx)
		c.mu.Lock()
		c.refreshing = false
		c.lastAttemptAt = time.Now()
		if ferr == nil {
			c.domains = newDomains
			c.byDomain = newByDomain
			c.fetchedAt = c.lastAttemptAt
		} else {
			err = ferr
		}
		c.mu.Unlock()
	}

	c.mu.Lock()
	suffix := "." + registered
	for d := range c.byDomain {
		if d == registered || strings.HasSuffix(d, suffix) {
			matched = append(matched, d)
		}
	}
	size = len(c.domains)
	fetchedAt = c.fetchedAt
	c.mu.Unlock()
	return matched, size, fetchedAt, err
}

func (c *botvrijCache) fetch(ctx context.Context) ([]string, map[string]struct{}, error) {
	reqCtx, cancel := context.WithTimeout(ctx, 30*time.Second)
	defer cancel()

	req, err := http.NewRequestWithContext(reqCtx, http.MethodGet, c.feedURL, nil)
	if err != nil {
		return nil, nil, err
	}
	req.Header.Set("User-Agent", "happydomain-checker-blacklist/1.0")

	resp, err := sharedHTTPClient.Do(req)
	if err != nil {
		return nil, nil, err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return nil, nil, fmt.Errorf("botvrij HTTP %d", resp.StatusCode)
	}

	domains := make([]string, 0, 4096)
	byDomain := make(map[string]struct{}, 4096)
	scanner := bufio.NewScanner(io.LimitReader(resp.Body, 16<<20))
	for scanner.Scan() {
		line := strings.TrimSpace(scanner.Text())
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		d := strings.ToLower(line)
		domains = append(domains, d)
		byDomain[d] = struct{}{}
	}
	if err := scanner.Err(); err != nil {
		return nil, nil, err
	}
	return domains, byDomain, nil
}