// Copyright 2015 The Vanadium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package rpc

import (
	"strings"

	"v.io/v23/context"
	"v.io/v23/naming"
	"v.io/v23/rpc"
	"v.io/v23/rpc/reserved"
	"v.io/v23/security"
	"v.io/v23/security/access"
	"v.io/v23/vdl"
	"v.io/v23/vdlroot/signature"
	"v.io/v23/verror"
	"v.io/x/lib/vlog"

	"v.io/x/ref/lib/glob"
)

// reservedInvoker returns a special invoker for reserved methods.  This invoker
// has access to the internal dispatchers, which allows it to perform special
// handling for methods like Glob and Signature.
func reservedInvoker(dispNormal, dispReserved rpc.Dispatcher) rpc.Invoker {
	methods := &reservedMethods{dispNormal: dispNormal, dispReserved: dispReserved}
	invoker := rpc.ReflectInvokerOrDie(methods)
	methods.selfInvoker = invoker
	return invoker
}

// reservedMethods is a regular server implementation object, which is passed to
// the regular ReflectInvoker in order to implement reserved methods.  The
// leading reserved "__" prefix is stripped before any methods are called.
//
// To add a new reserved method, simply add a method below, along with a
// description of the method.
type reservedMethods struct {
	dispNormal   rpc.Dispatcher
	dispReserved rpc.Dispatcher
	selfInvoker  rpc.Invoker
}

func (r *reservedMethods) Describe__() []rpc.InterfaceDesc {
	return []rpc.InterfaceDesc{{
		Name: "__Reserved",
		Doc:  `Reserved methods implemented by the RPC framework.  Each method name is prefixed with a double underscore "__".`,
		Methods: []rpc.MethodDesc{
			{
				Name:      "Glob",
				Doc:       "Glob returns all entries matching the pattern.",
				InArgs:    []rpc.ArgDesc{{Name: "pattern", Doc: ""}},
				OutStream: rpc.ArgDesc{Doc: "Streams matching entries back to the client."},
			},
			{
				Name: "MethodSignature",
				Doc:  "MethodSignature returns the signature for the given method.",
				InArgs: []rpc.ArgDesc{{
					Name: "method",
					Doc:  "Method name whose signature will be returned.",
				}},
				OutArgs: []rpc.ArgDesc{{
					Doc: "Method signature for the given method.",
				}},
			},
			{
				Name: "Signature",
				Doc:  "Signature returns all interface signatures implemented by the object.",
				OutArgs: []rpc.ArgDesc{{
					Doc: "All interface signatures implemented by the object.",
				}},
			},
		},
	}}
}

func (r *reservedMethods) Signature(call rpc.ServerCall) ([]signature.Interface, error) {
	ctx, suffix := call.Context(), call.Suffix()
	disp := r.dispNormal
	if naming.IsReserved(suffix) {
		disp = r.dispReserved
	}
	if disp == nil {
		return nil, rpc.NewErrUnknownSuffix(ctx, suffix)
	}
	obj, _, err := disp.Lookup(suffix)
	switch {
	case err != nil:
		return nil, err
	case obj == nil:
		return nil, rpc.NewErrUnknownSuffix(ctx, suffix)
	}
	invoker, err := objectToInvoker(obj)
	if err != nil {
		return nil, err
	}
	sig, err := invoker.Signature(call)
	if err != nil {
		return nil, err
	}
	// Append the reserved methods.  We wait until now to add the "__" prefix to
	// each method, so that we can use the regular ReflectInvoker.Signature logic.
	rsig, err := r.selfInvoker.Signature(call)
	if err != nil {
		return nil, err
	}
	for i := range rsig {
		for j := range rsig[i].Methods {
			rsig[i].Methods[j].Name = "__" + rsig[i].Methods[j].Name
		}
	}
	return signature.CleanInterfaces(append(sig, rsig...)), nil
}

func (r *reservedMethods) MethodSignature(call rpc.ServerCall, method string) (signature.Method, error) {
	// Reserved methods use our self invoker, to describe our own methods,
	if naming.IsReserved(method) {
		return r.selfInvoker.MethodSignature(call, naming.StripReserved(method))
	}

	ctx, suffix := call.Context(), call.Suffix()
	disp := r.dispNormal
	if naming.IsReserved(suffix) {
		disp = r.dispReserved
	}
	if disp == nil {
		return signature.Method{}, rpc.NewErrUnknownMethod(ctx, "__MethodSignature")
	}
	obj, _, err := disp.Lookup(suffix)
	switch {
	case err != nil:
		return signature.Method{}, err
	case obj == nil:
		return signature.Method{}, rpc.NewErrUnknownMethod(ctx, "__MethodSignature")
	}
	invoker, err := objectToInvoker(obj)
	if err != nil {
		return signature.Method{}, err
	}
	// TODO(toddw): Decide if we should hide the method signature if the
	// caller doesn't have access to call it.
	return invoker.MethodSignature(call, method)
}

func (r *reservedMethods) Glob(call rpc.StreamServerCall, pattern string) error {
	// Copy the original call to shield ourselves from changes the flowServer makes.
	glob := globInternal{r.dispNormal, r.dispReserved, call.Suffix()}
	return glob.Glob(call, pattern)
}

// globInternal handles ALL the Glob requests received by a server and
// constructs a response from the state of internal server objects and the
// service objects.
//
// Internal objects exist only at the root of the server and have a name that
// starts with a double underscore ("__"). They are only visible in the Glob
// response if the double underscore is explicitly part of the pattern, e.g.
// "".Glob("__*/*"), or "".Glob("__debug/...").
//
// Service objects may choose to implement either AllGlobber or ChildrenGlobber.
// AllGlobber is more flexible, but ChildrenGlobber is simpler to implement and
// less prone to errors.
//
// If objects implement AllGlobber, it must be able to handle recursive pattern
// for the entire namespace below the receiver object, i.e. "a/b".Glob("...")
// must return the name of all the objects under "a/b".
//
// If they implement ChildrenGlobber, it provides a list of the receiver's
// immediate children names, or a non-nil error if the receiver doesn't exist.
//
// globInternal constructs the Glob response by internally accessing the
// AllGlobber or ChildrenGlobber interface of objects as many times as needed.
//
// Before accessing an object, globInternal ensures that the requester is
// authorized to access it. Internal objects require access.Debug. Service
// objects require access.Resolve.
type globInternal struct {
	dispNormal   rpc.Dispatcher
	dispReserved rpc.Dispatcher
	receiver     string
}

// The maximum depth of recursion in Glob. We only count recursion levels
// associated with a recursive glob pattern, e.g. a pattern like "..." will be
// allowed to recurse up to 10 levels, but "*/*/*/*/..." will go up to 14
// levels.
const maxRecursiveGlobDepth = 10

func (i *globInternal) Glob(call rpc.StreamServerCall, pattern string) error {
	vlog.VI(3).Infof("rpc Glob: Incoming request: %q.Glob(%q)", i.receiver, pattern)
	g, err := glob.Parse(pattern)
	if err != nil {
		return err
	}
	disp := i.dispNormal
	tags := []*vdl.Value{vdl.ValueOf(access.Resolve)}
	if naming.IsReserved(i.receiver) || (i.receiver == "" && naming.IsReserved(pattern)) {
		disp = i.dispReserved
		tags = []*vdl.Value{vdl.ValueOf(access.Debug)}
	}
	if disp == nil {
		return reserved.NewErrGlobNotImplemented(call.Context())
	}
	call = callWithMethodTags(call, tags)

	type gState struct {
		name  string
		glob  *glob.Glob
		depth int
	}
	queue := []gState{gState{glob: g}}

	someMatchesOmitted := false
	for len(queue) != 0 {
		select {
		case <-call.Context().Done():
			// RPC timed out or was canceled.
			return nil
		default:
		}
		state := queue[0]
		queue = queue[1:]

		subcall := callWithSuffix(call, naming.Join(i.receiver, state.name))
		ctx, suffix := subcall.Context(), subcall.Suffix()
		if state.depth > maxRecursiveGlobDepth {
			vlog.Errorf("rpc Glob: exceeded recursion limit (%d): %q", maxRecursiveGlobDepth, suffix)
			call.Send(naming.GlobReplyError{
				naming.GlobError{Name: state.name, Error: reserved.NewErrGlobMaxRecursionReached(ctx)},
			})
			continue
		}
		obj, auth, err := disp.Lookup(suffix)
		if err != nil {
			vlog.VI(3).Infof("rpc Glob: Lookup failed for %q: %v", suffix, err)
			call.Send(naming.GlobReplyError{
				naming.GlobError{Name: state.name, Error: verror.Convert(verror.ErrNoExist, ctx, err)},
			})
			continue
		}
		if obj == nil {
			vlog.VI(3).Infof("rpc Glob: object not found for %q", suffix)
			call.Send(naming.GlobReplyError{
				naming.GlobError{Name: state.name, Error: verror.New(verror.ErrNoExist, ctx, "nil object")},
			})
			continue
		}

		// Verify that that requester is authorized for the current object.
		if err := authorize(ctx, auth); err != nil {
			someMatchesOmitted = true
			vlog.VI(3).Infof("rpc Glob: client is not authorized for %q: %v", suffix, err)
			continue
		}

		// If the object implements both AllGlobber and ChildrenGlobber, we'll
		// use AllGlobber.
		invoker, err := objectToInvoker(obj)
		if err != nil {
			vlog.VI(3).Infof("rpc Glob: object for %q cannot be converted to invoker: %v", suffix, err)
			call.Send(naming.GlobReplyError{
				naming.GlobError{Name: state.name, Error: verror.Convert(verror.ErrInternal, ctx, err)},
			})
			continue
		}
		gs := invoker.Globber()
		if gs == nil || (gs.AllGlobber == nil && gs.ChildrenGlobber == nil) {
			if state.glob.Len() == 0 {
				subcall.Send(naming.GlobReplyEntry{naming.MountEntry{Name: state.name, IsLeaf: true}})
			} else {
				subcall.Send(naming.GlobReplyError{
					naming.GlobError{Name: state.name, Error: reserved.NewErrGlobNotImplemented(ctx)},
				})
			}
			continue
		}
		if gs.AllGlobber != nil {
			vlog.VI(3).Infof("rpc Glob: %q implements AllGlobber", suffix)
			ch, err := gs.AllGlobber.Glob__(subcall, state.glob.String())
			if err != nil {
				vlog.VI(3).Infof("rpc Glob: %q.Glob(%q) failed: %v", suffix, state.glob, err)
				subcall.Send(naming.GlobReplyError{naming.GlobError{Name: state.name, Error: verror.Convert(verror.ErrInternal, ctx, err)}})
				continue
			}
			if ch == nil {
				continue
			}
			for gr := range ch {
				switch v := gr.(type) {
				case naming.GlobReplyEntry:
					v.Value.Name = naming.Join(state.name, v.Value.Name)
					subcall.Send(v)
				case naming.GlobReplyError:
					v.Value.Name = naming.Join(state.name, v.Value.Name)
					subcall.Send(v)
				}
			}
			continue
		}
		vlog.VI(3).Infof("rpc Glob: %q implements ChildrenGlobber", suffix)
		children, err := gs.ChildrenGlobber.GlobChildren__(subcall)
		// The requested object doesn't exist.
		if err != nil {
			subcall.Send(naming.GlobReplyError{naming.GlobError{Name: state.name, Error: verror.Convert(verror.ErrInternal, ctx, err)}})
			continue
		}
		// The glob pattern matches the current object.
		if state.glob.Len() == 0 {
			subcall.Send(naming.GlobReplyEntry{naming.MountEntry{Name: state.name}})
		}
		// The current object has no children.
		if children == nil {
			continue
		}
		depth := state.depth
		// This is a recursive pattern. Make sure we don't recurse forever.
		if state.glob.Len() == 0 {
			depth++
		}
		for child := range children {
			if len(child) == 0 || strings.Contains(child, "/") {
				vlog.Errorf("rpc Glob: %q.GlobChildren__() sent an invalid child name: %q", suffix, child)
				continue
			}
			if ok, _, left := state.glob.MatchInitialSegment(child); ok {
				next := naming.Join(state.name, child)
				queue = append(queue, gState{next, left, depth})
			}
		}
	}
	if someMatchesOmitted {
		call.Send(naming.GlobReplyError{naming.GlobError{Error: reserved.NewErrGlobMatchesOmitted(call.Context())}})
	}
	return nil
}

// derivedServerCall allows us to derive calls with slightly different properties,
// useful for our various special-cased reserved methods.
type derivedServerCall struct {
	rpc.StreamServerCall
	ctx    *context.T
	suffix string
}

func callWithSuffix(src rpc.StreamServerCall, suffix string) rpc.StreamServerCall {
	ctx := src.Context()
	secCall := security.GetCall(ctx)
	ctx = security.SetCall(ctx, &derivedSecurityCall{
		Call:       secCall,
		suffix:     suffix,
		methodTags: secCall.MethodTags(),
	})
	return &derivedServerCall{src, ctx, suffix}
}

func callWithMethodTags(src rpc.StreamServerCall, tags []*vdl.Value) rpc.StreamServerCall {
	ctx, suffix := src.Context(), src.Suffix()
	ctx = security.SetCall(ctx, &derivedSecurityCall{
		Call:       security.GetCall(ctx),
		suffix:     suffix,
		methodTags: tags,
	})
	return &derivedServerCall{src, ctx, suffix}
}

func (c *derivedServerCall) Context() *context.T { return c.ctx }
func (c *derivedServerCall) Suffix() string      { return c.suffix }

type derivedSecurityCall struct {
	security.Call
	suffix     string
	methodTags []*vdl.Value
}

func (c *derivedSecurityCall) Suffix() string           { return c.suffix }
func (c *derivedSecurityCall) MethodTags() []*vdl.Value { return c.methodTags }