package common

import (
	"context"
	"encoding/json"
	"sort"
	"time"

	oclib "cloud.o-forge.io/core/oc-lib"
	"github.com/libp2p/go-libp2p/core/host"
	"github.com/libp2p/go-libp2p/core/network"
	pp "github.com/libp2p/go-libp2p/core/peer"
)

// ProtocolIndexerCandidates is opened by a node toward its remaining indexers
// to request candidate replacement indexers after an ejection event.
const ProtocolIndexerCandidates = "/opencloud/indexer/candidates/1.0"

// IndexerCandidatesRequest is sent by a node to one of its indexers.
// Count is how many candidates are needed.
type IndexerCandidatesRequest struct {
	Count int `json:"count"`
}

// IndexerCandidatesResponse carries a random sample of known indexers from
// the responding indexer's DHT cache.
type IndexerCandidatesResponse struct {
	Candidates []pp.AddrInfo `json:"candidates"`
}

// TriggerConsensus asks each remaining indexer for a random pool of candidates,
// scores them asynchronously via a one-shot probe heartbeat, and admits the
// best ones to StaticIndexers. Falls back to DHT replenishment for any gap.
//
// Must be called in a goroutine — it blocks until all probes have returned
// (or timed out), which can take up to ~10s.
func TriggerConsensus(h host.Host, remaining []pp.AddrInfo, need int) {
	if need <= 0 || len(remaining) == 0 {
		return
	}
	logger := oclib.GetLogger()
	logger.Info().Int("voters", len(remaining)).Int("need", need).
		Msg("[consensus] starting indexer candidate consensus")

	// Phase 1 — collect candidates from all remaining indexers in parallel.
	type collectResult struct{ candidates []pp.AddrInfo }
	collectCh := make(chan collectResult, len(remaining))
	for _, ai := range remaining {
		go func(ai pp.AddrInfo) {
			ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
			defer cancel()
			s, err := h.NewStream(ctx, ai.ID, ProtocolIndexerCandidates)
			if err != nil {
				collectCh <- collectResult{}
				return
			}
			defer s.Close()
			s.SetDeadline(time.Now().Add(5 * time.Second))
			if err := json.NewEncoder(s).Encode(IndexerCandidatesRequest{Count: need + 2}); err != nil {
				collectCh <- collectResult{}
				return
			}
			var resp IndexerCandidatesResponse
			if err := json.NewDecoder(s).Decode(&resp); err != nil {
				collectCh <- collectResult{}
				return
			}
			collectCh <- collectResult{candidates: resp.Candidates}
		}(ai)
	}

	// Merge and deduplicate, excluding indexers already in the pool.
	seen := map[pp.ID]struct{}{}
	for _, ai := range Indexers.GetAddrIDs() {
		seen[ai] = struct{}{}

	}
	var candidates []pp.AddrInfo
	for range remaining {
		r := <-collectCh
		for _, ai := range r.candidates {
			if _, dup := seen[ai.ID]; !dup {
				seen[ai.ID] = struct{}{}
				candidates = append(candidates, ai)
			}
		}
	}

	if len(candidates) == 0 {
		logger.Info().Msg("[consensus] no candidates from voters, falling back to DHT")
		replenishIndexersFromDHT(h, need)
		return
	}
	logger.Info().Int("candidates", len(candidates)).Msg("[consensus] scoring candidates")

	// Phase 2 — score all candidates in parallel via a one-shot probe heartbeat.
	type scoreResult struct {
		ai    pp.AddrInfo
		score float64
	}
	scoreCh := make(chan scoreResult, len(candidates))
	for _, ai := range candidates {
		go func(ai pp.AddrInfo) {
			resp, rtt, err := probeIndexer(h, ai)
			if err != nil {
				scoreCh <- scoreResult{ai: ai, score: 0}
				return
			}
			scoreCh <- scoreResult{ai: ai, score: quickScore(resp, rtt)}
		}(ai)
	}

	results := make([]scoreResult, 0, len(candidates))
	for range candidates {
		results = append(results, <-scoreCh)
	}

	// Sort descending by quick score, admit top `need` above the minimum bar.
	sort.Slice(results, func(i, j int) bool { return results[i].score > results[j].score })
	minQ := dynamicMinScore(0) // fresh peer: threshold starts at 20

	admitted := 0
	for _, res := range results {
		if admitted >= need {
			break
		}
		if res.score < minQ {
			break // sorted desc: everything after is worse
		}
		key := addrKey(res.ai)
		if Indexers.ExistsAddr(key) {
			continue // already in pool (race with heartbeat path)
		}
		cpy := res.ai
		Indexers.SetAddr(key, &cpy)
		admitted++
	}

	if admitted > 0 {
		logger.Info().Int("admitted", admitted).Msg("[consensus] candidates admitted to pool")
		Indexers.NudgeIt()
	}

	// Fill any remaining gap with DHT discovery.
	if gap := need - admitted; gap > 0 {
		logger.Info().Int("gap", gap).Msg("[consensus] gap after consensus, falling back to DHT")
		replenishIndexersFromDHT(h, gap)
	}
}

// probeIndexer dials the candidate, sends one lightweight heartbeat, and
// returns the HeartbeatResponse (nil if the indexer doesn't support it) and RTT.
func probeIndexer(h host.Host, ai pp.AddrInfo) (*HeartbeatResponse, time.Duration, error) {
	ctx, cancel := context.WithTimeout(context.Background(), 8*time.Second)
	defer cancel()
	if h.Network().Connectedness(ai.ID) != network.Connected {
		if err := h.Connect(ctx, ai); err != nil {
			return nil, 0, err
		}
	}
	s, err := h.NewStream(ctx, ai.ID, ProtocolHeartbeat)
	if err != nil {
		return nil, 0, err
	}
	defer s.Close()

	hb := Heartbeat{PeerID: h.ID().String(), Timestamp: time.Now().UTC().Unix()}
	s.SetWriteDeadline(time.Now().Add(3 * time.Second))
	if err := json.NewEncoder(s).Encode(hb); err != nil {
		return nil, 0, err
	}
	s.SetWriteDeadline(time.Time{})

	sentAt := time.Now()
	s.SetReadDeadline(time.Now().Add(5 * time.Second))
	var resp HeartbeatResponse
	if err := json.NewDecoder(s).Decode(&resp); err != nil {
		// Indexer connected but no response: connection itself is the signal.
		return nil, time.Since(sentAt), nil
	}
	return &resp, time.Since(sentAt), nil
}

// quickScore computes a lightweight score [0,100] from a probe result.
// Uses only fill rate (inverse) and latency — the two signals available
// without a full heartbeat history.
func quickScore(resp *HeartbeatResponse, rtt time.Duration) float64 {
	maxRTT := BaseRoundTrip * 10
	latencyScore := 1.0 - float64(rtt)/float64(maxRTT)
	if latencyScore < 0 {
		latencyScore = 0
	}
	if resp == nil {
		// Connection worked but no response (old indexer): moderate score.
		return latencyScore * 50
	}
	fillScore := 1.0 - resp.FillRate // prefer less-loaded indexers
	return (0.5*latencyScore + 0.5*fillScore) * 100
}