// 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 namespace

import (
	"io"
	"strings"
	"sync"

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

	"v.io/v23"
	"v.io/v23/context"
	"v.io/v23/naming"
	"v.io/v23/rpc"
	"v.io/v23/verror"
	"v.io/x/lib/vlog"
)

type tracks struct {
	m      sync.Mutex
	places map[string]struct{}
}

func (tr *tracks) beenThereDoneThat(servers []string, pstr string) bool {
	tr.m.Lock()
	defer tr.m.Unlock()
	found := false
	for _, s := range servers {
		x := s + "!" + pstr
		if _, ok := tr.places[x]; ok {
			found = true
		}
		tr.places[x] = struct{}{}
	}
	return found
}

// task is a sub-glob that has to be performed against a mount table.  Tasks are
// done in parrallel to speed up the glob.
type task struct {
	pattern *glob.Glob         // pattern to match
	er      *naming.GlobError  // error for that particular point in the name space
	me      *naming.MountEntry // server to match at
	error   error              // any error performing this task
	depth   int                // number of mount tables traversed recursively
}

// globAtServer performs a Glob on the servers at a mount point.  It cycles through the set of
// servers until it finds one that replies.
func (ns *namespace) globAtServer(ctx *context.T, t *task, replies chan *task, tr *tracks, opts []rpc.CallOpt) {
	defer func() {
		if t.error == nil {
			replies <- nil
		} else {
			replies <- t
		}
	}()
	client := v23.GetClient(ctx)
	pstr := t.pattern.String()
	vlog.VI(2).Infof("globAtServer(%v, %v)", *t.me, pstr)

	servers := []string{}
	for _, s := range t.me.Servers {
		servers = append(servers, naming.JoinAddressName(s.Server, ""))
	}

	// If there are no servers to call, this isn't a mount point.  No sense
	// trying to call servers that aren't there.
	if len(servers) == 0 {
		t.error = nil
		return
	}

	// If we've been there before with the same request, give up.
	if tr.beenThereDoneThat(servers, pstr) {
		t.error = nil
		return
	}

	call, err := ns.parallelStartCall(ctx, client, servers, rpc.GlobMethod, []interface{}{pstr}, opts)
	if err != nil {
		t.error = err
		return
	}

	// At this point we're commited to the server that answered the call
	// first. Cycle through all replies from that server.
	for {
		// If the mount table returns an error, we're done.  Send the task to the channel
		// including the error.  This terminates the task.
		var gr naming.GlobReply
		err := call.Recv(&gr)
		if err == io.EOF {
			break
		}
		if err != nil {
			t.error = err
			return
		}

		var x *task
		switch v := gr.(type) {
		case naming.GlobReplyEntry:
			// Convert to the ever so slightly different name.MountTable version of a MountEntry
			// and add it to the list.
			x = &task{
				me: &naming.MountEntry{
					Name:             naming.Join(t.me.Name, v.Value.Name),
					Servers:          v.Value.Servers,
					ServesMountTable: v.Value.ServesMountTable,
					IsLeaf:           v.Value.IsLeaf,
				},
				depth: t.depth + 1,
			}
		case naming.GlobReplyError:
			// Pass on the error.
			x = &task{
				er:    &v.Value,
				depth: t.depth + 1,
			}
		}

		// x.depth is the number of servers we've walked through since we've gone
		// recursive (i.e. with pattern length of 0).  Limit the depth of globs.
		// TODO(p): return an error?
		if t.pattern.Len() == 0 {
			if x.depth > ns.maxRecursiveGlobDepth {
				continue
			}
		}
		replies <- x
	}
	t.error = call.Finish()
	return
}

// depth returns the directory depth of a given name.  It is used to pick off the unsatisfied part of the pattern.
func depth(name string) int {
	name = strings.Trim(naming.Clean(name), "/")
	if name == "" {
		return 0
	}
	return strings.Count(name, "/") + 1
}

// globLoop fires off a go routine for each server and read backs replies.
func (ns *namespace) globLoop(ctx *context.T, e *naming.MountEntry, prefix string, pattern *glob.Glob, reply chan naming.GlobReply, tr *tracks, opts []rpc.CallOpt) {
	defer close(reply)

	// Provide enough buffers to avoid too much switching between the readers and the writers.
	// This size is just a guess.
	replies := make(chan *task, 100)
	defer close(replies)

	// Push the first task into the channel to start the ball rolling.  This task has the
	// root of the search and the full pattern.  It will be the first task fired off in the for
	// loop that follows.
	replies <- &task{me: e, pattern: pattern}
	inFlight := 0

	// Perform a parallel search of the name graph.  Each task will send what it learns
	// on the replies channel.  If the reply is a mount point and the pattern is not completely
	// fulfilled, a new task will be fired off to handle it.
	for {
		select {
		case t := <-replies:
			// A nil reply represents a successfully terminated task.
			// If no tasks are running, return.
			if t == nil {
				if inFlight--; inFlight <= 0 {
					return
				}
				continue
			}

			// We want to output this entry if there was a real error other than
			// "not a mount table".
			//
			// An error reply is also a terminated task.
			// If no tasks are running, return.
			if t.error != nil {
				if !notAnMT(t.error) {
					reply <- naming.GlobReplyError{naming.GlobError{Name: naming.Join(prefix, t.me.Name), Error: t.error}}
				}
				if inFlight--; inFlight <= 0 {
					return
				}
				continue
			}

			// If this is just an error from the mount table, pass it on.
			if t.er != nil {
				x := *t.er
				x.Name = naming.Join(prefix, x.Name)
				reply <- &naming.GlobReplyError{x}
				continue
			}

			// Get the pattern elements below the current path.
			suffix := pattern.Split(depth(t.me.Name))

			// If we've satisfied the request and this isn't the root,
			// reply to the caller.
			if suffix.Len() == 0 && t.depth != 0 {
				x := *t.me
				x.Name = naming.Join(prefix, x.Name)
				reply <- &naming.GlobReplyEntry{x}
			}

			// If the pattern is finished (so we're only querying about the root on the
			// remote server) and the server is not another MT, then we needn't send the
			// query on since we know the server will not supply a new address for the
			// current name.
			if suffix.Finished() {
				if !t.me.ServesMountTable {
					continue
				}
			}

			// If this is restricted recursive and not a mount table, don't descend into it.
			if suffix.Restricted() && suffix.Len() == 0 && !t.me.ServesMountTable {
				continue
			}

			// Perform a glob at the next server.
			inFlight++
			t.pattern = suffix
			go ns.globAtServer(ctx, t, replies, tr, opts)
		}
	}
}

// Glob implements naming.MountTable.Glob.
func (ns *namespace) Glob(ctx *context.T, pattern string, opts ...naming.NamespaceOpt) (chan naming.GlobReply, error) {
	defer vlog.LogCall()()
	// Root the pattern.  If we have no servers to query, give up.
	e, patternWasRooted := ns.rootMountEntry(pattern)
	if len(e.Servers) == 0 {
		return nil, verror.New(naming.ErrNoMountTable, ctx)
	}

	// If the name doesn't parse, give up.
	g, err := glob.Parse(e.Name)
	if err != nil {
		return nil, err
	}

	tr := &tracks{places: make(map[string]struct{})}

	// If pattern was already rooted, make sure we tack that root
	// onto all returned names.  Otherwise, just return the relative
	// name.
	var prefix string
	if patternWasRooted {
		prefix = e.Servers[0].Server
	}
	e.Name = ""
	reply := make(chan naming.GlobReply, 100)
	go ns.globLoop(ctx, e, prefix, g, reply, tr, getCallOpts(opts))
	return reply, nil
}