package main

// Port of lib/access.js: subscription client identity, active-client and
// observed-IP windows, and access-log pruning.
//
// JS Date.parse failures yield NaN and every comparison against NaN is
// false; ParseISOMs reports those as ok=false and the filters below exclude
// such records, preserving the JS semantics.

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"net/http"
	"strings"
	"time"
)

// Window constants from lib/access.js, in milliseconds.
const (
	ClientWindowMs = int64(24 * 60 * 60 * 1000)
	LogRetentionMs = int64(30 * 24 * 60 * 60 * 1000)
)

// ClientIdentityResult is the JS clientIdentity return shape
// { userAgent, kind, key }.
type ClientIdentityResult struct {
	UserAgent string `json:"userAgent"`
	Kind      string `json:"kind"`
	Key       string `json:"key"`
}

// truncRunes truncates to at most n characters. JS slice() counts UTF-16
// code units; counting runes matches for all BMP text.
func truncRunes(s string, n int) string {
	runes := []rune(s)
	if len(runes) > n {
		runes = runes[:n]
	}
	return string(runes)
}

// ClientIdentity mirrors JS clientIdentity(headers, secret): the declared
// identity is x-device-id, falling back to x-client-id, trimmed and cut to
// 128 chars; the user agent is trimmed and cut to 200 chars; kind is
// "header" when a declared identity exists, else "user-agent" when a user
// agent exists, else "unknown". Key is HMAC-SHA256(secret, "kind:identity")
// as hex.
func ClientIdentity(headers http.Header, secret string) ClientIdentityResult {
	declared := headers.Get("X-Device-Id")
	if declared == "" {
		declared = headers.Get("X-Client-Id")
	}
	declared = truncRunes(strings.TrimSpace(declared), 128)
	userAgent := truncRunes(strings.TrimSpace(headers.Get("User-Agent")), 200)
	kind := "unknown"
	if declared != "" {
		kind = "header"
	} else if userAgent != "" {
		kind = "user-agent"
	}
	identity := declared
	if identity == "" {
		identity = userAgent
	}
	if identity == "" {
		identity = "unknown"
	}
	mac := hmac.New(sha256.New, []byte(secret))
	mac.Write([]byte(kind + ":" + identity))
	return ClientIdentityResult{
		UserAgent: userAgent,
		Kind:      kind,
		Key:       hex.EncodeToString(mac.Sum(nil)),
	}
}

func observationTtlMinutes(d *Data) float64 {
	ttl := d.Settings.ObservationTtlMinutes
	if ttl == 0 {
		// JS: settings.observationTtlMinutes || 10 — 0 (and NaN) fall back.
		ttl = 10
	}
	return ttl
}

// ActiveClients returns the clientKeys of the customer's subscription
// clients seen within the last 24h, in stored order.
func ActiveClients(d *Data, customerID string, now time.Time) []string {
	cutoff := now.UnixMilli() - ClientWindowMs
	out := []string{}
	for _, item := range d.SubscriptionClients {
		if item.CustomerID != customerID {
			continue
		}
		ms, ok := ParseISOMs(item.LastSeenAt)
		if ok && ms > cutoff {
			out = append(out, item.ClientKey)
		}
	}
	return out
}

// ObservedIPs returns the customer's observations fresher than the
// configured observation TTL (settings.observationTtlMinutes || 10).
func ObservedIPs(d *Data, customerID string, now time.Time) []*Observation {
	cutoff := now.UnixMilli() - int64(observationTtlMinutes(d)*60000)
	out := []*Observation{}
	for _, item := range d.Observations {
		if item.CustomerID != customerID {
			continue
		}
		ms, ok := ParseISOMs(item.LastSeenAt)
		if ok && ms > cutoff {
			out = append(out, item)
		}
	}
	return out
}

// PruneAccess mirrors JS pruneAccess: subscriptionAccess keeps the last
// 10000 entries fresher than 30 days, subscriptionClients keeps entries
// fresher than 24h, observations keep entries fresher than the TTL.
func PruneAccess(d *Data, now time.Time) {
	nowMs := now.UnixMilli()

	retentionCutoff := nowMs - LogRetentionMs
	access := []*SubscriptionAccess{}
	for _, item := range d.SubscriptionAccess {
		if ms, ok := ParseISOMs(item.At); ok && ms > retentionCutoff {
			access = append(access, item)
		}
	}
	if len(access) > 10000 { // JS: .slice(-10000)
		access = access[len(access)-10000:]
	}
	d.SubscriptionAccess = access

	clientCutoff := nowMs - ClientWindowMs
	clients := []*SubscriptionClient{}
	for _, item := range d.SubscriptionClients {
		if ms, ok := ParseISOMs(item.LastSeenAt); ok && ms > clientCutoff {
			clients = append(clients, item)
		}
	}
	d.SubscriptionClients = clients

	observationCutoff := nowMs - int64(observationTtlMinutes(d)*60000)
	observations := []*Observation{}
	for _, item := range d.Observations {
		if ms, ok := ParseISOMs(item.LastSeenAt); ok && ms > observationCutoff {
			observations = append(observations, item)
		}
	}
	d.Observations = observations
}