package libp2p

import (
	"fmt"

	"github.com/dustin/go-humanize"
	"github.com/ipfs/kubo/config"
	"github.com/ipfs/kubo/core/node/libp2p/fd"
	"github.com/libp2p/go-libp2p"
	rcmgr "github.com/libp2p/go-libp2p/p2p/host/resource-manager"
	"github.com/pbnjay/memory"
)

var infiniteResourceLimits = rcmgr.InfiniteLimits.ToPartialLimitConfig().System

// This file defines implicit limit defaults used when Swarm.ResourceMgr.Enabled

// createDefaultLimitConfig creates LimitConfig to pass to libp2p's resource manager.
// The defaults follow the documentation in docs/libp2p-resource-management.md.
// Any changes in the logic here should be reflected there.
func createDefaultLimitConfig(cfg config.SwarmConfig) (limitConfig rcmgr.ConcreteLimitConfig, logMessageForStartup string, err error) {
	maxMemoryDefault := uint64(memory.TotalMemory()) / 2
	maxMemory := cfg.ResourceMgr.MaxMemory.WithDefault(maxMemoryDefault)

	maxMemoryMB := maxMemory / (1024 * 1024)
	maxFD := int(cfg.ResourceMgr.MaxFileDescriptors.WithDefault(int64(fd.GetNumFDs()) / 2))

	// At least as of 2023-01-25, it's possible to open a connection that
	// doesn't ask for any memory usage with the libp2p Resource Manager/Accountant
	// (see https://github.com/libp2p/go-libp2p/issues/2010#issuecomment-1404280736).
	// As a result, we can't currently rely on Memory limits to full protect us.
	// Until https://github.com/libp2p/go-libp2p/issues/2010 is addressed,
	// we take a proxy now of restricting to 1 inbound connection per MB.
	// Note: this is more generous than go-libp2p's default autoscaled limits which do
	// 64 connections per 1GB
	// (see https://github.com/libp2p/go-libp2p/blob/master/p2p/host/resource-manager/limit_defaults.go#L357 ).
	systemConnsInbound := int(1 * maxMemoryMB)

	partialLimits := rcmgr.PartialLimitConfig{
		System: rcmgr.ResourceLimits{
			Memory: rcmgr.LimitVal64(maxMemory),
			FD:     rcmgr.LimitVal(maxFD),

			Conns:         rcmgr.Unlimited,
			ConnsInbound:  rcmgr.LimitVal(systemConnsInbound),
			ConnsOutbound: rcmgr.Unlimited,

			Streams:         rcmgr.Unlimited,
			StreamsOutbound: rcmgr.Unlimited,
			StreamsInbound:  rcmgr.Unlimited,
		},

		// Transient connections won't cause any memory to be accounted for by the resource manager/accountant.
		// Only established connections do.
		// As a result, we can't rely on System.Memory to protect us from a bunch of transient connection being opened.
		// We limit the same values as the System scope, but only allow the Transient scope to take 25% of what is allowed for the System scope.
		Transient: rcmgr.ResourceLimits{
			Memory: rcmgr.LimitVal64(maxMemory / 4),
			FD:     rcmgr.LimitVal(maxFD / 4),

			Conns:         rcmgr.Unlimited,
			ConnsInbound:  rcmgr.LimitVal(systemConnsInbound / 4),
			ConnsOutbound: rcmgr.Unlimited,

			Streams:         rcmgr.Unlimited,
			StreamsInbound:  rcmgr.Unlimited,
			StreamsOutbound: rcmgr.Unlimited,
		},

		// Lets get out of the way of the allow list functionality.
		// If someone specified "Swarm.ResourceMgr.Allowlist" we should let it go through.
		AllowlistedSystem: infiniteResourceLimits,

		AllowlistedTransient: infiniteResourceLimits,

		// Keep it simple by not having Service, ServicePeer, Protocol, ProtocolPeer, Conn, or Stream limits.
		ServiceDefault: infiniteResourceLimits,

		ServicePeerDefault: infiniteResourceLimits,

		ProtocolDefault: infiniteResourceLimits,

		ProtocolPeerDefault: infiniteResourceLimits,

		Conn: infiniteResourceLimits,

		Stream: infiniteResourceLimits,

		// Limit the resources consumed by a peer.
		// This doesn't protect us against intentional DoS attacks since an attacker can easily spin up multiple peers.
		// We specify this limit against unintentional DoS attacks (e.g., a peer has a bug and is sending too much traffic intentionally).
		// In that case we want to keep that peer's resource consumption contained.
		// To keep this simple, we only constrain inbound connections and streams.
		PeerDefault: rcmgr.ResourceLimits{
			Memory:          rcmgr.Unlimited64,
			FD:              rcmgr.Unlimited,
			Conns:           rcmgr.Unlimited,
			ConnsInbound:    rcmgr.DefaultLimit,
			ConnsOutbound:   rcmgr.Unlimited,
			Streams:         rcmgr.Unlimited,
			StreamsInbound:  rcmgr.DefaultLimit,
			StreamsOutbound: rcmgr.Unlimited,
		},
	}

	scalingLimitConfig := rcmgr.DefaultLimits
	libp2p.SetDefaultServiceLimits(&scalingLimitConfig)

	// Anything set above in partialLimits that had a value of rcmgr.DefaultLimit will be overridden.
	// Anything in scalingLimitConfig that wasn't defined in partialLimits above will be added (e.g., libp2p's default service limits).
	partialLimits = partialLimits.Build(scalingLimitConfig.Scale(int64(maxMemory), maxFD)).ToPartialLimitConfig()

	// Simple checks to override autoscaling ensuring limits make sense versus the connmgr values.
	// There are ways to break this, but this should catch most problems already.
	// We might improve this in the future.
	// See: https://github.com/ipfs/kubo/issues/9545
	if partialLimits.System.ConnsInbound > rcmgr.DefaultLimit && cfg.ConnMgr.Type.WithDefault(config.DefaultConnMgrType) != "none" {
		maxInboundConns := int64(partialLimits.System.ConnsInbound)
		if connmgrHighWaterTimesTwo := cfg.ConnMgr.HighWater.WithDefault(config.DefaultConnMgrHighWater) * 2; maxInboundConns < connmgrHighWaterTimesTwo {
			maxInboundConns = connmgrHighWaterTimesTwo
		}

		if maxInboundConns < config.DefaultResourceMgrMinInboundConns {
			maxInboundConns = config.DefaultResourceMgrMinInboundConns
		}

		// Scale System.StreamsInbound as well, but use the existing ratio of StreamsInbound to ConnsInbound
		if partialLimits.System.StreamsInbound > rcmgr.DefaultLimit {
			partialLimits.System.StreamsInbound = rcmgr.LimitVal(maxInboundConns * int64(partialLimits.System.StreamsInbound) / int64(partialLimits.System.ConnsInbound))
		}
		partialLimits.System.ConnsInbound = rcmgr.LimitVal(maxInboundConns)
	}

	msg := fmt.Sprintf(`
Computed default go-libp2p Resource Manager limits based on:
    - 'Swarm.ResourceMgr.MaxMemory': %q
    - 'Swarm.ResourceMgr.MaxFileDescriptors': %d

These can be inspected with 'ipfs swarm resources'.

`, humanize.Bytes(maxMemory), maxFD)

	// We already have a complete value thus pass in an empty ConcreteLimitConfig.
	return partialLimits.Build(rcmgr.ConcreteLimitConfig{}), msg, nil
}