// Package main — observer analytics helpers.
//
// #1828 Phase A: extracted from cmd/server/routes.go handleObserverAnalytics
// (routes.go:2819-2953). Split the 5 aggregate builders into standalone
// functions for readability + isolated tests. No behavior change relative to
// the pre-#1828 handler; JSON output is byte-identical.
//
// The `filtered` argument is the time-window-filtered, timestamp-desc sorted
// slice of *StoreObs produced by the handler after snapshotting under RLock
// (see #1481 P0-2). Helpers do NOT touch store.mu — the handler owns lock
// scoping.
//
// Concurrency note (#1839 MINOR): the RLock snapshot only covers the
// *StoreObs pointer slice; reads of store.byTxID inside buildPacketTypes /
// buildNodesTimeline are unsynchronized concurrent-map reads (pre-existing
// behavior — enrichObs did the same). Not introduced by this refactor.
//
// Perf note (#1839 MINOR): dropping enrichObs on the histogram / nodes-
// timeline paths also eliminates N fetchResolvedPathForObs SQL calls per
// /analytics request (store.go:fetchResolvedPathForObs), not just the alloc/
// boxing win — /analytics SQL-load drops materially.
package main

import (
	"encoding/json"
	"fmt"
	"sort"
	"strconv"
	"time"
)

// observerAnalyticsBucketDur returns the timeline bucket size for a given day
// range. Mirrors the constant table in the legacy handler.
func observerAnalyticsBucketDur(days int) time.Duration {
	bucketDur := 24 * time.Hour
	if days <= 1 {
		bucketDur = time.Hour
	} else if days <= 7 {
		bucketDur = 4 * time.Hour
	}
	return bucketDur
}

// observerAnalyticsFormatLabel returns a closure that formats a bucket time
// as a human-readable label appropriate for the day range.
func observerAnalyticsFormatLabel(days int) func(time.Time) string {
	return func(t time.Time) string {
		if days <= 1 {
			return t.UTC().Format("15:04")
		}
		if days <= 7 {
			return t.UTC().Format("Mon 15:04")
		}
		return t.UTC().Format("Jan 02")
	}
}

// buildTimelineBuckets is the shared kernel used by both buildTimeline and
// buildNodesTimeline. Sorts the count map by bucket-key and returns
// TimeBucket entries with labels formatted per days.
func buildTimelineBuckets(counts map[int64]int, days int) []TimeBucket {
	formatLabel := observerAnalyticsFormatLabel(days)
	keys := make([]int64, 0, len(counts))
	for k := range counts {
		keys = append(keys, k)
	}
	sort.Slice(keys, func(i, j int) bool { return keys[i] < keys[j] })
	out := make([]TimeBucket, 0, len(keys))
	for _, k := range keys {
		lbl := formatLabel(time.Unix(k, 0))
		out = append(out, TimeBucket{Label: &lbl, Count: counts[k]})
	}
	return out
}

// buildTimeline builds the packet-timeline aggregate for /analytics.
func buildTimeline(filtered []*StoreObs, days int) []TimeBucket {
	bucketDur := observerAnalyticsBucketDur(days)
	counts := map[int64]int{}
	for _, obs := range filtered {
		ts, ok := obs.ParsedTime()
		if !ok {
			continue
		}
		bucketStart := ts.UTC().Truncate(bucketDur).Unix()
		counts[bucketStart]++
	}
	return buildTimelineBuckets(counts, days)
}

// buildPacketTypes builds the payload-type histogram. Uses a direct
// store.byTxID read (see #1828 triage) rather than enrichObs — the loop only
// needs payload_type, which is a single indirection off the transmission.
// This avoids one map allocation + several interface-boxing conversions per
// observation (routes.go:2886 hot path pre-#1828).
func buildPacketTypes(store *PacketStore, filtered []*StoreObs) map[string]int {
	out := map[string]int{}
	for _, obs := range filtered {
		tx := store.byTxID[obs.TransmissionID]
		if tx == nil || tx.PayloadType == nil {
			continue
		}
		out[strconv.Itoa(*tx.PayloadType)]++
	}
	return out
}

// buildNodesTimeline builds the distinct-node-per-bucket timeline aggregate.
// Nodes = path-json hops ∪ decoded_json pubKey/srcHash/destHash.
func buildNodesTimeline(store *PacketStore, filtered []*StoreObs, days int) []TimeBucket {
	bucketDur := observerAnalyticsBucketDur(days)
	nodeBucketSets := map[int64]map[string]struct{}{}
	for _, obs := range filtered {
		ts, ok := obs.ParsedTime()
		if !ok {
			continue
		}
		bucketStart := ts.UTC().Truncate(bucketDur).Unix()
		if nodeBucketSets[bucketStart] == nil {
			nodeBucketSets[bucketStart] = map[string]struct{}{}
		}
		// Legacy handler read decoded_json via enrichObs (which pulls it off
		// tx.DecodedJSON). Read tx directly for parity + savings.
		if tx := store.byTxID[obs.TransmissionID]; tx != nil && tx.DecodedJSON != "" {
			var decoded map[string]interface{}
			if json.Unmarshal([]byte(tx.DecodedJSON), &decoded) == nil {
				for _, k := range []string{"pubKey", "srcHash", "destHash"} {
					if v, ok := decoded[k].(string); ok && v != "" {
						nodeBucketSets[bucketStart][v] = struct{}{}
					}
				}
			}
		}
		for _, hop := range parsePathJSON(obs.PathJSON) {
			if hop != "" {
				nodeBucketSets[bucketStart][hop] = struct{}{}
			}
		}
	}
	nodeCounts := make(map[int64]int, len(nodeBucketSets))
	for k, nodes := range nodeBucketSets {
		nodeCounts[k] = len(nodes)
	}
	return buildTimelineBuckets(nodeCounts, days)
}

// buildSnrDistribution builds the SNR histogram (2-unit buckets, floor).
func buildSnrDistribution(filtered []*StoreObs) []SnrDistributionEntry {
	snrBuckets := map[int]*SnrDistributionEntry{}
	for _, obs := range filtered {
		if obs.SNR == nil {
			continue
		}
		bucket := int(*obs.SNR) / 2 * 2
		if *obs.SNR < 0 && int(*obs.SNR) != bucket {
			bucket -= 2
		}
		if snrBuckets[bucket] == nil {
			snrBuckets[bucket] = &SnrDistributionEntry{Range: fmt.Sprintf("%d to %d", bucket, bucket+2)}
		}
		snrBuckets[bucket].Count++
	}
	keys := make([]int, 0, len(snrBuckets))
	for k := range snrBuckets {
		keys = append(keys, k)
	}
	sort.Ints(keys)
	out := make([]SnrDistributionEntry, 0, len(keys))
	for _, k := range keys {
		out = append(out, *snrBuckets[k])
	}
	return out
}

// buildRecentPackets builds the "first N enriched observations" list. This is
// the only aggregate that needs the full enrichObs map — recentPackets is a
// UI-facing payload and the extra fields matter here.
//
// Legacy parity (#1839): the pre-#1828 routes.go loop was
//
//	for i, obs := range filtered {
//	    if _, ok := obs.ParsedTime(); !ok { continue }
//	    ...
//	    if i < limit { recentPackets = append(..., enriched) }
//	}
//
// The `i` in the gate is the RAW slice index — a bad-ts obs at position k<limit
// consumed its slot (via `continue`) and could not be replaced by a later
// good-ts obs. Result can be <limit when bad-ts obs sit in the head of
// `filtered`. We reproduce that exact semantic here to keep output byte-
// identical.
func buildRecentPackets(store *PacketStore, filtered []*StoreObs, limit int) []map[string]interface{} {
	if limit <= 0 {
		return []map[string]interface{}{}
	}
	out := make([]map[string]interface{}, 0, limit)
	for i, obs := range filtered {
		if i >= limit {
			break
		}
		if _, ok := obs.ParsedTime(); !ok {
			continue
		}
		out = append(out, store.enrichObs(obs))
	}
	return out
}