package policy

import (
	"net/netip"
	"time"

	"github.com/juanfont/headscale/hscontrol/policy/matcher"
	policyv2 "github.com/juanfont/headscale/hscontrol/policy/v2"
	"github.com/juanfont/headscale/hscontrol/types"
	"tailscale.com/tailcfg"
	"tailscale.com/types/views"
)

type PolicyManager interface {
	// Filter returns the current filter rules for the entire tailnet and the associated matchers.
	Filter() ([]tailcfg.FilterRule, []matcher.Match)
	// FilterForNode returns filter rules for a specific node, handling autogroup:self
	FilterForNode(node types.NodeView) ([]tailcfg.FilterRule, error)
	// MatchersForNode returns matchers for peer relationship determination (unreduced)
	MatchersForNode(node types.NodeView) ([]matcher.Match, error)
	// BuildPeerMap constructs peer relationship maps for the given nodes
	BuildPeerMap(nodes views.Slice[types.NodeView]) map[types.NodeID][]types.NodeID
	SSHPolicy(baseURL string, node types.NodeView) (*tailcfg.SSHPolicy, error)
	// SSHCheckParams resolves the SSH check period for src logging in to
	// dst as localUser from the current policy, avoiding trust of
	// client-provided URL params.
	SSHCheckParams(srcNodeID, dstNodeID types.NodeID, localUser string) (time.Duration, bool)
	SetPolicy(pol []byte) (bool, error)
	// SetUsers replaces the user list. policyChanged reports whether clients
	// need a policy refresh; peerMapChanged reports whether user-derived peer
	// adjacency may have changed. Both are false when the list is unchanged.
	SetUsers(users []types.User) (policyChanged, peerMapChanged bool, err error)
	SetNodes(nodes views.Slice[types.NodeView]) (bool, error)
	// NodesGeneration counts SetNodes calls that reported a change; see
	// [policyv2.PolicyManager.NodesGeneration].
	NodesGeneration() uint64
	// NodeCanHaveTag reports whether the given node can have the given tag.
	NodeCanHaveTag(node types.NodeView, tag string) bool

	// UserCanHaveTag reports whether the given user owns the given tag, i.e.
	// is listed (directly or via a group) in the tag's tagOwners. This is the
	// user half of NodeCanHaveTag, used to authorise re-auth tag changes
	// against the authenticating user rather than the node's stale ownership.
	UserCanHaveTag(user types.UserView, tag string) bool

	// TagExists reports whether the given tag is defined in the policy.
	TagExists(tag string) bool

	// TagOwnedByTags reports whether a credential holding ownerTags may apply
	// tag: true if tag is one of ownerTags, or tag's tag-to-tag ownership chain
	// transitively includes one of ownerTags. Authorises the tags an OAuth
	// access token may set on the auth keys it mints.
	TagOwnedByTags(tag string, ownerTags []string) bool

	// NodeCanApproveRoute reports whether the given node can approve the given route.
	NodeCanApproveRoute(node types.NodeView, route netip.Prefix) bool

	// NodeNeedsPeerRecompute reports whether peers must recompute their
	// netmap when the node's online state changes. True for subnet
	// routers, relay targets (tailscale.com/cap/relay), and via targets;
	// false for ordinary nodes, which only need a lightweight online or
	// offline peer patch. [State.Connect] and [State.Disconnect] use it to
	// avoid a tailnet-wide recompute on every ordinary reconnect.
	NodeNeedsPeerRecompute(node types.NodeView) bool

	// ViaRoutesForPeer computes via grant effects for a viewer-peer pair.
	// It returns which routes should be included (peer is via-designated for viewer)
	// and excluded (steered to a different peer). When no via grants apply,
	// both fields are empty and the caller falls back to existing behavior.
	ViaRoutesForPeer(viewer, peer types.NodeView) types.ViaRouteResult

	// NodeCapMap returns compiled policy capabilities for the given node,
	// or nil when none target it. The map is a defensive clone; its values
	// are shared and read-only. It describes the node's own capabilities,
	// not a per-viewer view.
	NodeCapMap(id types.NodeID) tailcfg.NodeCapMap

	// NodeCapMaps snapshots every node's policy CapMap. The outer map is
	// caller-owned; inner maps are shared with the manager and read-only.
	// NodeCapMapsForPeers limits copying when fewer peers are requested.
	NodeCapMaps() map[types.NodeID]tailcfg.NodeCapMap

	// NodeCapMapsForPeers snapshots requested peer caps under one lock. It may
	// include unselected entries when copying the whole compiled table is less work.
	// The outer map is caller-owned; inner maps are shared and read-only.
	// Empty selections or no compiled policy capabilities return nil; missing IDs read nil.
	NodeCapMapsForPeers(peers views.Slice[types.NodeView]) map[types.NodeID]tailcfg.NodeCapMap

	// NodesWithChangedCapMap returns the IDs of nodes whose nodeAttrs
	// CapMap shifted during recent updateLocked calls. The buffer
	// drains on read; callers consume it once per update cycle to
	// decide which nodes need a self-targeted MapResponse.
	// refreshNodeAttrsLocked appends to the buffer rather than
	// overwriting, so a SetUsers/SetNodes between SetPolicy and the
	// drain cannot lose the policy-reload diff.
	NodesWithChangedCapMap() []types.NodeID

	Version() int
	DebugString() string
}

// NewPolicyManager returns a new [PolicyManager].
func NewPolicyManager(pol []byte, users []types.User, nodes views.Slice[types.NodeView]) (PolicyManager, error) {
	var (
		polMan PolicyManager
		err    error
	)

	polMan, err = policyv2.NewPolicyManager(pol, users, nodes)
	if err != nil {
		return nil, err
	}

	return polMan, err
}

// PolicyManagersForTest returns all available [PolicyManager] implementations to
// be used in tests to validate them in tests that try to determine that they
// behave the same.
func PolicyManagersForTest(pol []byte, users []types.User, nodes views.Slice[types.NodeView]) ([]PolicyManager, error) {
	var polMans []PolicyManager

	for _, pmf := range PolicyManagerFuncsForTest(pol) {
		pm, err := pmf(users, nodes)
		if err != nil {
			return nil, err
		}

		polMans = append(polMans, pm)
	}

	return polMans, nil
}

func PolicyManagerFuncsForTest(pol []byte) []func([]types.User, views.Slice[types.NodeView]) (PolicyManager, error) {
	polmanFuncs := make([]func([]types.User, views.Slice[types.NodeView]) (PolicyManager, error), 0, 1)

	polmanFuncs = append(polmanFuncs, func(u []types.User, n views.Slice[types.NodeView]) (PolicyManager, error) {
		return policyv2.NewPolicyManager(pol, u, n)
	})

	return polmanFuncs
}