package servewaf

// The heuristic core_rule_set. It reads SWWAF_WAF_MODE, SWWAF_WAF_EXEMPT_PATHS
// and SWWAF_WAF_ANOMALY_THRESHOLD.

import (
	"context"
	"time"

	"sneak.berlin/go/smallwebwaf/internal/alerts"
	"sneak.berlin/go/smallwebwaf/internal/config"
	"sneak.berlin/go/smallwebwaf/internal/requestlog"
	"sneak.berlin/go/smallwebwaf/internal/waf"
)

// coreRuleSet inspects the request with the Core Rule Set, unless
// SWWAF_WAF_MODE is off or SWWAF_WAF_EXEMPT_PATHS exempts its path, as
// pathExempt decides, and notes the rules it matched and its score in the
// log line, and the rules in the metrics. A score at or over
// SWWAF_WAF_ANOMALY_THRESHOLD is a match: it raises the waf_block alert,
// and in block mode refuses the request with 403, which is an offence its
// client's history counts. Its figures are the score and the threshold.
type coreRuleSet struct{}

func (coreRuleSet) name() string { return "core_rule_set" }

func (coreRuleSet) check(_ context.Context, rq *request, _ time.Time) *verdict {
	cfg := rq.h.config
	if cfg.WAFMode == config.WAFModeOff || pathExempt(rq.in, cfg.WAFExemptPaths) {
		return nil
	}

	start := time.Now()

	// A question's body has been read into memory, so that reading it here
	// cannot fail.
	result, read, _ := rq.h.coreRuleSet.Inspect(rq.in, rq.client, rq.in.Body)
	rq.requestBytes = int64(len(read))

	rq.line.DurationWAF = new(requestlog.Milliseconds(time.Since(start)))
	rq.line.WAFRuleIDs = result.RuleIDs
	rq.line.WAFScore = &result.Score

	for _, id := range result.RuleIDs {
		rq.h.metrics.WAFMatched(cfg.WAFMode, id)
	}

	threshold := cfg.WAFAnomalyThreshold
	if threshold == 0 || result.Score < threshold {
		return nil
	}

	rq.alertWAFBlock(result)

	if cfg.WAFMode == config.WAFModeDetect {
		return nil
	}

	rq.wafBlocked = true

	return &verdict{
		action:  requestlog.ActionWAFBlocked,
		figures: map[string]any{figureScore: result.Score, "threshold": threshold},
	}
}

// alertWAFBlock raises the waf_block alert for the request, which the Core
// Rule Set scored at result, at or over SWWAF_WAF_ANOMALY_THRESHOLD. Its
// detail gives the rule ids, the score, the method and the path with the
// query, and, for a request that is not refused for it, the mode: detect,
// or observe in observe mode.
func (rq *request) alertWAFBlock(result waf.Result) {
	detail := map[string]any{
		"rule_ids": result.RuleIDs,
		"score":    result.Score,
		"method":   rq.in.Method,
		"path":     rq.in.URL.RequestURI(),
	}

	switch {
	case rq.h.config.WAFMode == config.WAFModeDetect:
		detail["mode"] = config.WAFModeDetect
	case rq.h.config.Observe:
		detail["mode"] = "observe"
	}

	rq.h.alerts.Raise(alerts.Alert{
		Event:    alerts.EventWAFBlock,
		Host:     rq.site,
		Client:   rq.client,
		Netblock: rq.h.clientGroup(rq.client),
		ASN:      rq.line.ASN,
		ASName:   rq.line.ASName,
		Country:  rq.line.Country,
		Reason:   "scored by the Core Rule Set at or over SWWAF_WAF_ANOMALY_THRESHOLD",
		Detail:   detail,
	})
}