// Package node — /api/well-known-version endpoint.
//
// Clients hit this to feature-detect the node they're talking to, without
// hardcoding "node >= 0.5 supports channels" into every screen. The response
// lists three coordinates a client cares about:
//
//   - node_version     — human-readable build tag (ldflags-injectable)
//   - protocol_version — integer bumped only on wire-protocol breaking changes
//   - features         — stable string tags for "this binary implements X"
//
// Feature tags are ADDITIVE — once a tag ships in a release, it keeps being
// returned forever (even if the implementation moves around internally). The
// client uses them as "is this feature here or not?", not "what version is
// this feature at?". Versioning a feature is done by shipping a new tag
// (e.g. "channels_v2" alongside "channels_v1" for a deprecation window).
//
// Response shape:
//
//	{
//	  "node_version":     "0.5.0-dev",
//	  "protocol_version": 1,
//	  "features": [
//	    "channels_v1",
//	    "fan_out",
//	    "native_username_registry",
//	    "ws_submit_tx",
//	    "access_token"
//	  ],
//	  "chain_id": "dchain-ddb9a7e37fc8"
//	}
package node

import (
	"fmt"
	"net/http"
	"sort"

	"go-blockchain/node/version"
)

// ProtocolVersion is bumped only when the wire-protocol changes in a way
// that a client compiled against version N cannot talk to a node at
// version N+1 (or vice versa) without updating. Adding new optional fields,
// new EventTypes, new WS ops, new HTTP endpoints — none of those bump this.
//
// Bumping this means a coordinated release: every client and every node
// operator must update before the old version stops working.
const ProtocolVersion = 1

// nodeFeatures is the baked-in list of feature tags this binary implements.
// Append-only. When you add a new tag, add it here AND document what it means
// so clients can feature-detect reliably.
//
// Naming convention: snake_case, versioned suffix for anything that might get
// a breaking successor (e.g. `channels_v1`, not `channels`).
var nodeFeatures = []string{
	"access_token",              // DCHAIN_API_TOKEN gating on writes (+ optional reads)
	"channels_v1",               // /api/channels/:id + /members with X25519 enrichment
	"chain_id",                  // /api/network-info returns chain_id
	"contract_logs",             // /api/contract/:id/logs endpoint
	"fan_out",                   // client-side per-recipient envelope sealing
	"identity_registry",         // /api/identity/:pub returns X25519 pub + relay hints
	"native_username_registry",  // native:username_registry contract
	"onboarding_api",            // /api/network-info for joiner bootstrap
	"payment_channels",          // off-chain payment channel open/close
	"relay_mailbox",             // /relay/send + /relay/inbox
	"ws_submit_tx",              // WebSocket submit_tx op
}

func registerWellKnownVersionAPI(mux *http.ServeMux, q ExplorerQuery) {
	mux.HandleFunc("/api/well-known-version", func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodGet {
			jsonErr(w, fmt.Errorf("method not allowed"), 405)
			return
		}
		// Return a copy so callers can't mutate the shared slice.
		feats := make([]string, len(nodeFeatures))
		copy(feats, nodeFeatures)
		sort.Strings(feats)

		resp := map[string]any{
			"node_version":     version.Tag,
			"build":            version.Info(),
			"protocol_version": ProtocolVersion,
			"features":         feats,
		}
		// Include chain_id if the node exposes it (same helper as network-info).
		if q.ChainID != nil {
			resp["chain_id"] = q.ChainID()
		}
		jsonOK(w, resp)
	})
}