// Package store provides the shared ring-buffer, label-encoding and query
// helpers used by both the collector and the aggregator.
package store

import (
	"container/heap"
	"fmt"
	"time"

	pb "git.ipng.ch/ipng/nginx-logtail/proto/logtailpb"
)

// Ring-buffer dimensions — shared between collector and aggregator.
const (
	FineRingSize   = 60      // 60 × 1-min buckets  → 1 hour
	CoarseRingSize = 288     // 288 × 5-min buckets → 24 hours
	FineTopK       = 50_000  // entries kept per fine snapshot
	CoarseTopK     = 5_000   // entries kept per coarse snapshot
	CoarseEvery    = 5       // fine ticks between coarse writes
)

// Tuple4 is the four-dimensional aggregation key.
type Tuple4 struct {
	Website string
	Prefix  string
	URI     string
	Status  string
}

// Entry is a labelled count used in snapshots and query results.
type Entry struct {
	Label string
	Count int64
}

// Snapshot is one sorted (desc) slice of top-K entries for a time bucket.
type Snapshot struct {
	Timestamp time.Time
	Entries   []Entry
}

// TrendPoint is a (timestamp, total-count) pair for sparkline queries.
type TrendPoint struct {
	Timestamp time.Time
	Count     int64
}

// RingView is a read-only snapshot of a ring buffer for iteration.
type RingView struct {
	Ring []Snapshot
	Head int // index of next write slot (one past the latest entry)
	Size int
}

// BucketsForWindow returns the RingView and number of buckets to sum for window.
func BucketsForWindow(window pb.Window, fine, coarse RingView, fineFilled, coarseFilled int) (RingView, int) {
	switch window {
	case pb.Window_W1M:
		return fine, min(1, fineFilled)
	case pb.Window_W5M:
		return fine, min(5, fineFilled)
	case pb.Window_W15M:
		return fine, min(15, fineFilled)
	case pb.Window_W60M:
		return fine, min(60, fineFilled)
	case pb.Window_W6H:
		return coarse, min(72, coarseFilled) // 72 × 5-min = 6 h
	case pb.Window_W24H:
		return coarse, min(288, coarseFilled)
	default:
		return fine, min(5, fineFilled)
	}
}

// --- label encoding: "website\x00prefix\x00uri\x00status" ---

// EncodeTuple encodes a Tuple4 as a NUL-separated string suitable for use
// as a map key in snapshots.
func EncodeTuple(t Tuple4) string {
	return t.Website + "\x00" + t.Prefix + "\x00" + t.URI + "\x00" + t.Status
}

// LabelTuple decodes a NUL-separated snapshot label back into a Tuple4.
func LabelTuple(label string) Tuple4 {
	parts := splitN(label, '\x00', 4)
	if len(parts) != 4 {
		return Tuple4{}
	}
	return Tuple4{parts[0], parts[1], parts[2], parts[3]}
}

func splitN(s string, sep byte, n int) []string {
	result := make([]string, 0, n)
	for len(result) < n-1 {
		i := indexOf(s, sep)
		if i < 0 {
			break
		}
		result = append(result, s[:i])
		s = s[i+1:]
	}
	return append(result, s)
}

func indexOf(s string, b byte) int {
	for i := 0; i < len(s); i++ {
		if s[i] == b {
			return i
		}
	}
	return -1
}

// --- filtering and grouping ---

// MatchesFilter returns true if t satisfies all constraints in f.
// A nil filter matches everything.
func MatchesFilter(t Tuple4, f *pb.Filter) bool {
	if f == nil {
		return true
	}
	if f.Website != nil && t.Website != f.GetWebsite() {
		return false
	}
	if f.ClientPrefix != nil && t.Prefix != f.GetClientPrefix() {
		return false
	}
	if f.HttpRequestUri != nil && t.URI != f.GetHttpRequestUri() {
		return false
	}
	if f.HttpResponse != nil && t.Status != fmt.Sprint(f.GetHttpResponse()) {
		return false
	}
	return true
}

// DimensionLabel returns the string value of t for the given group-by dimension.
func DimensionLabel(t Tuple4, g pb.GroupBy) string {
	switch g {
	case pb.GroupBy_WEBSITE:
		return t.Website
	case pb.GroupBy_CLIENT_PREFIX:
		return t.Prefix
	case pb.GroupBy_REQUEST_URI:
		return t.URI
	case pb.GroupBy_HTTP_RESPONSE:
		return t.Status
	default:
		return t.Website
	}
}

// --- heap-based top-K selection ---

type entryHeap []Entry

func (h entryHeap) Len() int            { return len(h) }
func (h entryHeap) Less(i, j int) bool  { return h[i].Count < h[j].Count } // min-heap
func (h entryHeap) Swap(i, j int)       { h[i], h[j] = h[j], h[i] }
func (h *entryHeap) Push(x interface{}) { *h = append(*h, x.(Entry)) }
func (h *entryHeap) Pop() interface{} {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[:n-1]
	return x
}

// TopKFromMap selects the top-k entries from a label→count map, sorted desc.
func TopKFromMap(m map[string]int64, k int) []Entry {
	if k <= 0 {
		return nil
	}
	h := make(entryHeap, 0, k+1)
	for label, count := range m {
		heap.Push(&h, Entry{Label: label, Count: count})
		if h.Len() > k {
			heap.Pop(&h)
		}
	}
	result := make([]Entry, h.Len())
	for i := len(result) - 1; i >= 0; i-- {
		result[i] = heap.Pop(&h).(Entry)
	}
	return result
}

// TopKFromTupleMap encodes a Tuple4 map and returns the top-k as a Snapshot.
// Used by the collector to snapshot its live map.
func TopKFromTupleMap(m map[Tuple4]int64, k int, ts time.Time) Snapshot {
	flat := make(map[string]int64, len(m))
	for t, c := range m {
		flat[EncodeTuple(t)] = c
	}
	return Snapshot{Timestamp: ts, Entries: TopKFromMap(flat, k)}
}