// Join helper: a newcomer POSTs its JoinInfo to a target node's join endpoint
// and adopts the returned ring state (leader preserved, newcomer inserted as
// the target's successor).
package cluster

import (
	"bytes"
	"context"
	"crypto/rand"
	"encoding/json"
	"fmt"
	"net/http"
	"time"
)

// GenerateNodeKey returns a random 16-byte hex string for use as a cluster
// admission key. Called on first startup when no key is persisted yet.
func GenerateNodeKey() string {
	b := make([]byte, 16)
	if _, err := rand.Read(b); err != nil {
		return fmt.Sprintf("%x", time.Now().UnixNano())
	}
	return fmt.Sprintf("%x", b)
}

// JoinRing asks target to add us to its ring and returns the adopted state.
func (e *Engine) JoinRing(ctx context.Context, targetAddr string, ji JoinInfo) error {
	url := fmt.Sprintf("http://%s/api/manager/cluster/join", targetAddr)
	body, err := json.Marshal(ji)
	if err != nil {
		return err
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(body))
	if err != nil {
		return err
	}
	req.Header.Set("Content-Type", "application/json")
	if e.User != "" || e.Pass != "" {
		req.SetBasicAuth(e.User, e.Pass)
	}
	cli := &http.Client{Timeout: 8 * time.Second}
	resp, err := cli.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("join %s -> HTTP %d", targetAddr, resp.StatusCode)
	}
	var out struct {
		State State `json:"state"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&out); err != nil {
		return err
	}
	e.AdoptState(out.State)
	return nil
}

// JoinRingAddr wraps JoinRing for HTTP handlers: it builds the newcomer's
// JoinInfo from this node's own id/addr/version/cache (so the caller doesn't
// touch the engine's unexported fields) and asks targetAddr to sponsor us
// into its ring. joinKey is the sponsor's nodeKey — the sponsor verifies it
// before admitting. This is the runtime "加入集群" path (vs. the startup
// bootstrap call in cmd/webui4frpc/main.go).
func (e *Engine) JoinRingAddr(ctx context.Context, targetAddr, joinKey string) error {
	ji := JoinInfo{ID: e.ID, Addr: e.myAddr, Version: e.Version, Cache: e.Cache, JoinKey: joinKey}
	return e.JoinRing(ctx, targetAddr, ji)
}