package servewaf

// The heuristic header_limits. It reads no setting: its limits are fixed.

import (
	"context"
	"strings"
	"time"

	"sneak.berlin/go/smallwebwaf/internal/requestlog"
)

// The header limits: the most cookies and header fields a request may have
// when the checks reach the Core Rule Set. Real clients never reach them.
const (
	maxCookies      = 50
	maxHeaderFields = 100
)

// headerLimits refuses a request over the header limits, with 431. Its figures
// are the request's header fields and cookies, and the limit of each.
type headerLimits struct{}

func (headerLimits) name() string { return "header_limits" }

func (headerLimits) check(_ context.Context, rq *request, _ time.Time) *verdict {
	fields, cookies := rq.headerCounts()
	if fields <= maxHeaderFields && cookies <= maxCookies {
		return nil
	}

	return &verdict{
		action: requestlog.ActionTooLarge,
		figures: map[string]any{
			"fields": fields, "fields_limit": maxHeaderFields,
			"cookies": cookies, "cookies_limit": maxCookies,
		},
	}
}

// overHeaderLimits reports whether the request is over the header limits: it
// has more than maxHeaderFields fields or more than maxCookies cookies, as
// headerCounts counts them.
func (rq *request) overHeaderLimits() bool {
	fields, cookies := rq.headerCounts()

	return fields > maxHeaderFields || cookies > maxCookies
}

// headerCounts returns the request's header fields, each value of a header sent
// twice being one, and its cookies, each part of a Cookie header between
// semicolons being one unless it is empty or only spaces and tabs. The Core
// Rule Set runs each of its rules on each cookie, so that thousands of small
// cookies keep it busy for over a second. It trims only spaces and control
// characters, of which a header value can hold only tabs, so a part of Unicode
// spaces is a cookie to it.
func (rq *request) headerCounts() (int, int) {
	fields, cookies := 0, 0

	for _, values := range rq.in.Header {
		fields += len(values)
	}

	for _, value := range rq.in.Header.Values("Cookie") {
		for part := range strings.SplitSeq(value, ";") {
			if strings.Trim(part, " \t") != "" {
				cookies++
			}
		}
	}

	return fields, cookies
}