package hub

import (
	"sort"

	"github.com/shcizo/package-updater/internal/master/model"
	"github.com/shcizo/package-updater/internal/protocol"
)

// candidate is a connection that has finished its hello and may get jobs.
type candidate struct {
	agentID int64
	connID  uint64
	hello   protocol.Hello
}

// Route picks the connection a job for svc goes to, among agents that speak
// at least protocol version minProtocol. It returns model.ErrAgentOffline or
// model.ErrAgentTooOld (model.ErrAgentTooOldForSelfUpdate when minProtocol
// asks for self-update, model.ErrAgentTooOldForPinned when it asks for a
// pinned ref) when there is none.
func (h *Hub) Route(svc model.Service, minProtocol int) (model.Route, error) {
	h.mu.Lock()
	conns := make([]candidate, 0, len(h.conns))
	for id, c := range h.conns {
		if c.hello != nil {
			conns = append(conns, candidate{agentID: id, connID: c.id, hello: *c.hello})
		}
	}
	h.mu.Unlock()
	return route(svc, conns, minProtocol)
}

// route picks the connection a job for svc goes to. Compose services and
// containers can only run on the agent that reported them. Swarm services
// run on the reporting agent if it qualifies, else on any other connected
// manager of the same cluster (lowest agent ID first). Too-old wins over
// offline only when a connection would otherwise have qualified.
func route(svc model.Service, conns []candidate, minProtocol int) (model.Route, error) {
	sort.Slice(conns, func(a, b int) bool { return conns[a].agentID < conns[b].agentID })
	tooOld := false
	try := func(c candidate) bool {
		if svc.Kind == protocol.KindSwarm {
			if !c.hello.SwarmManager || c.hello.SwarmClusterID == "" || c.hello.SwarmClusterID != svc.SwarmClusterID {
				return false
			}
		}
		if c.hello.ProtocolVersion < minProtocol {
			tooOld = true
			return false
		}
		return true
	}
	if svc.AgentID != nil {
		for _, c := range conns {
			if c.agentID == *svc.AgentID && try(c) {
				return model.Route{AgentID: c.agentID, ConnID: c.connID}, nil
			}
		}
	}
	if svc.Kind == protocol.KindSwarm {
		for _, c := range conns {
			if try(c) {
				return model.Route{AgentID: c.agentID, ConnID: c.connID}, nil
			}
		}
	}
	if tooOld {
		if minProtocol >= protocol.MinSelfUpdateVersion {
			return model.Route{}, model.ErrAgentTooOldForSelfUpdate
		}
		if minProtocol >= protocol.MinPinnedRefVersion {
			return model.Route{}, model.ErrAgentTooOldForPinned
		}
		return model.Route{}, model.ErrAgentTooOld
	}
	return model.Route{}, model.ErrAgentOffline
}