package gateway

import (
	"context"
)

// wsReplayLimit is the number of most-recent messages replayed to a connecting
// client. It is intentionally small so a reconnect is cheap; the frontend pulls
// the full active-session history via REST (design/16 §4.1) and the replay is
// only there to give a brand-new connection immediate context.
const wsReplayLimit = 50

// replayHistory sends the most recent messages for sessionID to a single,
// freshly-registered connection as a ws "history" event.
//
// The replay carries the main session's message bodies, so it is owner/admin only
// (design/11 §7.2 A, decided by the owner on 2026-10-03). ownerAdminClaims is the
// same predicate the proactive push uses, so 「who may be handed the owner's
// conversation unasked」 is answered in one place instead of per caller. A viewer
// connection completes the handshake with no replay at all: its read-only window
// is the REST monitoring surface (design/11 §7.1 「语义澄清」), not a push.
//
// The gate lives here rather than at the register/replay call site in
// ws_hub_conn.go on purpose: this is the only function that emits the replay, so
// no future caller can reach it without the check. A role the owner later wants
// to serve the replay to has to be registered in design/11 §7.2 first, exactly
// like an inbound frame (see ws_route.go).
//
// It is best-effort: a nil store or a read error skips the replay silently.
// Thinking is NOT included (design/16 §6), so the frame never leaks
// chain-of-thought even to owner/admin.
func (h *hub) replayHistory(c *wsConn, sessionID string) {
	if !ownerAdminClaims(c.claims) {
		return
	}
	if h.history == nil {
		return
	}
	msgs, err := h.history.Recent(context.Background(), sessionID, wsReplayLimit)
	if err != nil {
		h.log.Warn("history replay", "err", err, "session", sessionID)
		return
	}
	out := make([]historyMessage, 0, len(msgs))
	for _, m := range msgs {
		wire := toHistoryMessage(m)
		wire.Thinking = ""
		out = append(out, wire)
	}
	c.enqueueJSON(wsEvent{Type: "history", SessionID: sessionID, Data: map[string]any{"messages": out}})
}