package security

// This file provides an implementation of security.Authorizer.
//
// Definitions
// * Self-RPC: An RPC request is said to be a "self-RPC" if the identities
// at the local and remote ends are identical.

import (
	"errors"
	"os"
	"reflect"

	"veyron.io/veyron/veyron2/security"
)

var (
	errACL          = errors.New("no matching ACL entry found")
	errInvalidLabel = errors.New("label is invalid")
)

// aclAuthorizer implements Authorizer.
type aclAuthorizer security.ACL

// Authorize verifies a request iff the identity at the remote end has a name authorized by
// the aclAuthorizer's ACL for the request's label, or the request corresponds to a self-RPC.
func (a aclAuthorizer) Authorize(ctx security.Context) error {
	// Test if the request corresponds to a self-RPC.
	if ctx.LocalBlessings() != nil && ctx.RemoteBlessings() != nil && reflect.DeepEqual(ctx.LocalBlessings().PublicKey(), ctx.RemoteBlessings().PublicKey()) {
		return nil
	}
	if ctx.LocalID() != nil && ctx.RemoteID() != nil && reflect.DeepEqual(ctx.LocalID(), ctx.RemoteID()) {
		return nil
	}
	var blessings []string
	if ctx.RemoteBlessings() != nil {
		blessings = ctx.RemoteBlessings().ForContext(ctx)
	} else if ctx.RemoteID() != nil {
		blessings = ctx.RemoteID().Names()
	}
	return matchesACL(blessings, ctx.Label(), security.ACL(a))
}

// NewACLAuthorizer creates an authorizer from the provided ACL. The
// authorizer authorizes a request iff the identity at the remote end has a name
// authorized by the provided ACL for the request's label, or the request
// corresponds to a self-RPC.
func NewACLAuthorizer(acl security.ACL) security.Authorizer { return aclAuthorizer(acl) }

// fileACLAuthorizer implements Authorizer.
type fileACLAuthorizer string

// Authorize reads and decodes the fileACLAuthorizer's ACL file into a ACL and
// then verifies the request according to an aclAuthorizer based on the ACL. If
// reading or decoding the file fails then no requests are authorized.
func (a fileACLAuthorizer) Authorize(ctx security.Context) error {
	acl, err := loadACLFromFile(string(a))
	if err != nil {
		return err
	}
	return aclAuthorizer(acl).Authorize(ctx)
}

// NewFileACLAuthorizer creates an authorizer from the provided path to a file
// containing a JSON-encoded ACL. Each call to "Authorize" involves reading and
// decoding a ACL from the file and then authorizing the request according to the
// ACL. The authorizer monitors the file so out of band changes to the contents of
// the file are reflected in the ACL. If reading or decoding the file fails then
// no requests are authorized.
//
// The JSON-encoding of a ACL is essentially a JSON object describing a map from
// BlessingPatterns to encoded LabelSets (see LabelSet.MarshalJSON).
// Examples:
// * `{"In": {"..." : "RW"}}` encodes an ACL that allows all principals to access all methods with
//   ReadLabel or WriteLabel.
// * `{"In":{"veyron/alice": "RW", "veyron/bob/...": "R"}}` encodes an ACL that allows all principals
//   matched by "veyron/alice" to access methods with ReadLabel or WriteLabel, and all
//   principals matched by "veyron/bob/..." to access methods with ReadLabel.
// * `{"In": {"...": "RW"}, "NotIn": {"veyron/alice": "W"}}` encodes an ACL that allows all principals
//   access to all ReadLabel or WriteLabel methods, EXCEPT that methods with a WriteLabel are not
//   accessible to veyron/alice and her delegates.
// (Also see BlessingPattern.MatchedBy)
//
// TODO(ataly, ashankar): Instead of reading the file on each call we should use the "inotify"
// mechanism to watch the file. Eventually we should also support ACLs stored in the Veyron
// store.
func NewFileACLAuthorizer(filePath string) security.Authorizer { return fileACLAuthorizer(filePath) }

func matchesACL(blessings []string, label security.Label, acl security.ACL) error {
	if len(blessings) == 0 && acl.CanAccess("", label) {
		// No blessings, check if that satisfies the ACL (it will be if AllPrincipals appears in the ACL).
		return nil
	}
	for _, b := range blessings {
		if acl.CanAccess(b, label) {
			return nil
		}
	}
	return errACL
}

func loadACLFromFile(filePath string) (security.ACL, error) {
	f, err := os.Open(filePath)
	if err != nil {
		return nullACL, err
	}
	defer f.Close()
	return LoadACL(f)
}