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package chord
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import (
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	"encoding/json"
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	"net/http"
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	"strconv"
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	"time"
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	"go.miragespace.co/specter/spec/protocol"
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)
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type overviewIdentity struct {
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	ID      string `json:"id"`
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	Address string `json:"address"`
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}
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type overviewVNode struct {
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	Identity             overviewIdentity   `json:"identity"`
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	Root                 bool               `json:"root"`
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	State                string             `json:"state"`
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	LastStabilized       *time.Time         `json:"last_stabilized"`
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	ChordRequests        uint64             `json:"chord_requests"`
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	KVRequests           uint64             `json:"kv_requests"`
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	RPCErrors            uint64             `json:"rpc_errors"`
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	KVStale              uint64             `json:"kv_stale"`
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	PredecessorAvailable bool               `json:"predecessor_available"`
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	Predecessor          *overviewIdentity  `json:"predecessor"`
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	SuccessorsAvailable  bool               `json:"successors_available"`
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	Successors           []overviewIdentity `json:"successors"`
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}
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type localOverview struct {
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	ObservedAt time.Time        `json:"observed_at"`
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	Identity   overviewIdentity `json:"identity"`
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	Provider   string           `json:"provider"`
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	VNodes     []overviewVNode  `json:"vnodes"`
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}
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func overviewNodeIdentity(node *protocol.Node) overviewIdentity {
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	return overviewIdentity{
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		ID:      strconv.FormatUint(node.GetId(), 10),
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		Address: node.GetAddress(),
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	}
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}
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// snapshotOverview samples local counters and membership references independently.
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// It never consults storage or calls peers. Membership changes can hold locks
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// across network requests, so a busy reference is reported as unavailable.
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func snapshotOverview(rootNode *LocalNode, virtualNodes []*LocalNode, provider string) localOverview {
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	info := localOverview{
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		ObservedAt: time.Now().UTC(),
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		Identity:   overviewNodeIdentity(rootNode.Identity()),
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		Provider:   provider,
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		VNodes:     make([]overviewVNode, 0, len(virtualNodes)),
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	}
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	for _, node := range virtualNodes {
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		vnode := overviewVNode{
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			Identity:      overviewNodeIdentity(node.Identity()),
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			Root:          node == rootNode,
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			State:         node.state.Get().String(),
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			ChordRequests: node.chordRate.Total(),
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			KVRequests:    node.kvRate.Total(),
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			RPCErrors:     node.rpcErrorCount.Load(),
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			KVStale:       node.kvStaleCount.Load(),
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			Successors:    make([]overviewIdentity, 0),
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		}
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		if stabilized := node.lastStabilized.Load(); !stabilized.IsZero() {
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			vnode.LastStabilized = &stabilized
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		}
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		if node.predecessorMu.TryRLock() {
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			vnode.PredecessorAvailable = true
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			if node.predecessor != nil {
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				predecessor := overviewNodeIdentity(node.predecessor.Identity())
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				vnode.Predecessor = &predecessor
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			}
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			node.predecessorMu.RUnlock()
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		}
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		if node.successorsMu.TryRLock() {
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			vnode.SuccessorsAvailable = true
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			for _, successor := range node.successors {
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				if successor != nil {
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					vnode.Successors = append(vnode.Successors, overviewNodeIdentity(successor.Identity()))
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				}
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			}
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			node.successorsMu.RUnlock()
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		}
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		info.VNodes = append(info.VNodes, vnode)
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	}
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	return info
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}
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// OverviewHandler serves a bounded local JSON overview. The composition layer supplies
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// the effective provider name; the diagnostic snapshot does not identify storage
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// implementations or inspect their data directories.
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//
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// Mount this behind the same authentication as the other operator handlers at
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// /_internal/overview.json.
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func OverviewHandler(rootNode *LocalNode, virtualNodes []*LocalNode, provider string) http.Handler {
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	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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		info := snapshotOverview(rootNode, virtualNodes, provider)
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		w.Header().Set("Cache-Control", "no-store")
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		w.Header().Set("Content-Type", "application/json; charset=utf-8")
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		json.NewEncoder(w).Encode(info)
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	})
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}