// host_bandwidth_push.go — server → agent fan-out of host-wide
// bandwidth caps via config.update.
//
// Two entry points: pushBandwidthOnHello (called from onAgentHello,
// always pushes the current state so the agent picks up edits made
// while it was offline) and pushBandwidthToAgent (called after the
// PUT bandwidth handler succeeds, so an online agent re-arms within
// seconds).
//
// We always send pointer fields (zero-valued when uncapped) so the
// agent can distinguish "no change" (nil → field absent on the wire)
// from "explicitly cleared" (non-nil zero pointer). See
// api.ConfigUpdatePayload doc for the wire semantics.
package http

import (
	"context"
	"log/slog"
	"time"

	"gitea.dcglab.co.uk/steve/restic-manager/internal/api"
	"gitea.dcglab.co.uk/steve/restic-manager/internal/server/ws"
)

// pushBandwidthOnHello ships the host's current bandwidth caps as a
// config.update on the supplied conn. Silent no-op on lookup error.
func (s *Server) pushBandwidthOnHello(ctx context.Context, hostID string, conn *ws.Conn) {
	host, err := s.deps.Store.GetHost(ctx, hostID)
	if err != nil {
		slog.Warn("on-hello: load host for bandwidth", "host_id", hostID, "err", err)
		return
	}
	payload := bandwidthPayload(host.BandwidthUpKBps, host.BandwidthDownKBps)
	env, err := api.Marshal(api.MsgConfigUpdate, "", payload)
	if err != nil {
		slog.Error("on-hello: marshal bandwidth config.update", "host_id", hostID, "err", err)
		return
	}
	sendCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
	defer cancel()
	if err := conn.Send(sendCtx, env); err != nil {
		slog.Warn("on-hello: send bandwidth config.update", "host_id", hostID, "err", err)
	}
}

// pushBandwidthToAgent ships the supplied caps via the hub. Caller is
// expected to check Hub.Connected first when it matters.
func (s *Server) pushBandwidthToAgent(ctx context.Context, hostID string, up, down *int) error {
	env, err := api.Marshal(api.MsgConfigUpdate, "", bandwidthPayload(up, down))
	if err != nil {
		return err
	}
	sendCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
	defer cancel()
	return s.deps.Hub.Send(sendCtx, hostID, env)
}

// bandwidthPayload builds a ConfigUpdatePayload with only the
// bandwidth fields populated. Pointers are passed through verbatim;
// callers wanting to clear a cap should pass a non-nil pointer to 0.
// On the on-hello path we materialise zero-valued pointers when the
// host record has no cap set, so the agent's stored state is always
// in sync (rather than retaining whatever value it last received).
func bandwidthPayload(up, down *int) api.ConfigUpdatePayload {
	zero := 0
	upPtr := up
	if upPtr == nil {
		upPtr = &zero
	}
	downPtr := down
	if downPtr == nil {
		downPtr = &zero
	}
	return api.ConfigUpdatePayload{
		BandwidthUpKBps:   upPtr,
		BandwidthDownKBps: downPtr,
	}
}