package weed_server

import (
	"path"
	"sync"

	"github.com/seaweedfs/seaweedfs/weed/pb/filer_pb"
	"github.com/seaweedfs/seaweedfs/weed/util"
)

// mutateJobKind classifies a streamed mutation for conflict detection. This is
// the same taxonomy MetadataProcessor uses in weed/command/filer_sync_jobs.go:
// separate a "barrier" directory event (create/delete/rename) from an in-place
// attribute-only directory update so that mtime/xattr bumps do not serialize
// every file operation in the subtree.
type mutateJobKind int

const (
	// kindMutateFile: a regular file event. Conflicts with any in-flight job
	// on the same path and with any barrier directory on the same path or on
	// an ancestor.
	kindMutateFile mutateJobKind = iota
	// kindMutateBarrierDir: a directory create, a directory rename, or a
	// delete (target type unknown on the wire). Acts as a subtree barrier:
	// must drain every active descendant, and blocks every new job under it
	// until it completes.
	kindMutateBarrierDir
	// kindMutateNonBarrierDir: an in-place directory attribute update
	// (mode / xattr / mtime with unchanged name). Conflicts with any other
	// in-flight job at the same path, but never with descendants.
	kindMutateNonBarrierDir
)

// mutateScheduler serializes mutations by path while allowing cross-path work
// to run in parallel. The conflict taxonomy mirrors filer.sync's
// MetadataProcessor (weed/command/filer_sync_jobs.go); admission adds
// per-path FIFO ordering so two requests arriving on the same stream on the
// same path are always processed in arrival order, even when a Cond broadcast
// would otherwise race them.
//
// Invariants:
//   - pathQueue[p] contains every waiter (pending + admitted) that is
//     interested in path p, in arrival order. admit dequeues nothing; Done
//     dequeues the head.
//   - A waiter is admissible iff it is the head of every path queue it
//     joined (primary and secondary), pathConflictsLocked passes for each
//     path against *active* state, and totalActive < concurrencyLimit.
type mutateScheduler struct {
	concurrencyLimit int

	mu sync.Mutex

	totalActive              int
	activeFilePaths          map[util.FullPath]int
	activeBarrierDirPaths    map[util.FullPath]int
	activeNonBarrierDirPaths map[util.FullPath]int
	descendantCount          map[util.FullPath]int

	// pathQueue maps each path to the FIFO list of waiters (pending or
	// admitted) interested in it. Entries are removed by Done.
	pathQueue map[util.FullPath][]*mutateWaiter
}

// mutateWaiter is one outstanding Admit call. admitted flips under mu when
// the waiter moves from pending to active; ready is closed at the same time
// so the Admit caller unblocks.
type mutateWaiter struct {
	primary, secondary util.FullPath
	kind               mutateJobKind
	admitted           bool
	ready              chan struct{}
}

func newMutateScheduler(concurrency int) *mutateScheduler {
	return &mutateScheduler{
		concurrencyLimit:         concurrency,
		activeFilePaths:          make(map[util.FullPath]int),
		activeBarrierDirPaths:    make(map[util.FullPath]int),
		activeNonBarrierDirPaths: make(map[util.FullPath]int),
		descendantCount:          make(map[util.FullPath]int),
		pathQueue:                make(map[util.FullPath][]*mutateWaiter),
	}
}

// Admit blocks until this (primary, secondary, kind) tuple can be admitted
// without violating the conflict rules and without exceeding concurrencyLimit,
// and until every earlier waiter on any of its paths has itself been admitted.
// On return the job is registered in the indexes; the caller must call Done
// with the same arguments when the work is finished.
//
// For single-path operations (create / update / delete) pass secondary="".
// For rename, pass old path as primary and new path as secondary; kind is
// kindMutateBarrierDir.
func (s *mutateScheduler) Admit(primary, secondary util.FullPath, kind mutateJobKind) {
	w := &mutateWaiter{
		primary:   primary,
		secondary: secondary,
		kind:      kind,
		ready:     make(chan struct{}),
	}

	s.mu.Lock()
	s.pathQueue[primary] = append(s.pathQueue[primary], w)
	if secondary != "" && secondary != primary {
		s.pathQueue[secondary] = append(s.pathQueue[secondary], w)
	}
	s.tryPromoteLocked()
	s.mu.Unlock()

	<-w.ready
}

// Done releases the slot reserved by Admit and promotes any waiters that
// became admissible as a result. Must be called exactly once per successful
// Admit with the same arguments.
func (s *mutateScheduler) Done(primary, secondary util.FullPath, kind mutateJobKind) {
	s.mu.Lock()
	defer s.mu.Unlock()

	s.removePathLocked(primary, kind)
	if secondary != "" {
		s.removePathLocked(secondary, kind)
	}
	s.totalActive--

	s.dequeueHeadLocked(primary)
	if secondary != "" && secondary != primary {
		s.dequeueHeadLocked(secondary)
	}

	s.tryPromoteLocked()
}

// dequeueHeadLocked removes the current head of path p and deletes the map
// entry when the queue becomes empty. Must be called under s.mu.
func (s *mutateScheduler) dequeueHeadLocked(p util.FullPath) {
	q := s.pathQueue[p]
	if len(q) == 0 {
		return
	}
	// Shift left without reallocating; drop the reference so the waiter can
	// be garbage-collected before the tail shrinks.
	q[0] = nil
	copy(q, q[1:])
	q = q[:len(q)-1]
	if len(q) == 0 {
		delete(s.pathQueue, p)
	} else {
		s.pathQueue[p] = q
	}
}

// tryPromoteLocked admits as many queue heads as possible while respecting
// path-FIFO order, the active-state conflict rules, and concurrencyLimit.
// The admitted set can grow in one call because admitting one waiter frees
// zero or more paths whose new heads may now pass the conflict check.
// Must be called under s.mu.
func (s *mutateScheduler) tryPromoteLocked() {
	for s.totalActive < s.concurrencyLimit {
		promoted := false
		// Walk distinct head waiters across all path queues. Map iteration
		// order is randomized, which is fine: path-FIFO is preserved by the
		// head-of-queue check inside admitIfHeadLocked, and cross-path order
		// is not constrained.
		for _, q := range s.pathQueue {
			if len(q) == 0 {
				continue
			}
			w := q[0]
			if w.admitted {
				continue
			}
			if s.admitIfHeadLocked(w) {
				promoted = true
				if s.totalActive >= s.concurrencyLimit {
					return
				}
			}
		}
		if !promoted {
			return
		}
	}
}

// admitIfHeadLocked admits w if w is the head of every path queue it joined
// and pathConflictsLocked passes. Returns true if admitted. Must be called
// under s.mu.
func (s *mutateScheduler) admitIfHeadLocked(w *mutateWaiter) bool {
	if s.pathQueue[w.primary][0] != w {
		return false
	}
	if w.secondary != "" && w.secondary != w.primary {
		q := s.pathQueue[w.secondary]
		if len(q) == 0 || q[0] != w {
			return false
		}
	}
	if s.pathConflictsLocked(w.primary, w.kind) {
		return false
	}
	if w.secondary != "" && s.pathConflictsLocked(w.secondary, w.kind) {
		return false
	}
	s.addPathLocked(w.primary, w.kind)
	if w.secondary != "" {
		s.addPathLocked(w.secondary, w.kind)
	}
	s.totalActive++
	w.admitted = true
	close(w.ready)
	return true
}

// pathConflictsLocked mirrors MetadataProcessor.pathConflicts exactly.
func (s *mutateScheduler) pathConflictsLocked(p util.FullPath, kind mutateJobKind) bool {
	if s.activeBarrierDirPaths[p] > 0 {
		return true
	}
	if kind == kindMutateBarrierDir && s.activeNonBarrierDirPaths[p] > 0 {
		return true
	}
	if s.activeFilePaths[p] > 0 && (kind == kindMutateFile || kind == kindMutateBarrierDir) {
		return true
	}
	if kind == kindMutateBarrierDir && s.descendantCount[p] > 0 {
		return true
	}
	for _, ancestor := range mutatePathAncestors(p) {
		if s.activeBarrierDirPaths[ancestor] > 0 {
			return true
		}
	}
	return false
}

func (s *mutateScheduler) addPathLocked(p util.FullPath, kind mutateJobKind) {
	switch kind {
	case kindMutateFile:
		s.activeFilePaths[p]++
	case kindMutateBarrierDir:
		s.activeBarrierDirPaths[p]++
	case kindMutateNonBarrierDir:
		s.activeNonBarrierDirPaths[p]++
	}
	for _, ancestor := range mutatePathAncestors(p) {
		s.descendantCount[ancestor]++
	}
}

func (s *mutateScheduler) removePathLocked(p util.FullPath, kind mutateJobKind) {
	switch kind {
	case kindMutateFile:
		if s.activeFilePaths[p] <= 1 {
			delete(s.activeFilePaths, p)
		} else {
			s.activeFilePaths[p]--
		}
	case kindMutateBarrierDir:
		if s.activeBarrierDirPaths[p] <= 1 {
			delete(s.activeBarrierDirPaths, p)
		} else {
			s.activeBarrierDirPaths[p]--
		}
	case kindMutateNonBarrierDir:
		if s.activeNonBarrierDirPaths[p] <= 1 {
			delete(s.activeNonBarrierDirPaths, p)
		} else {
			s.activeNonBarrierDirPaths[p]--
		}
	}
	for _, ancestor := range mutatePathAncestors(p) {
		if s.descendantCount[ancestor] <= 1 {
			delete(s.descendantCount, ancestor)
		} else {
			s.descendantCount[ancestor]--
		}
	}
}

// mutatePathAncestors mirrors filer_sync_jobs.go:pathAncestors — returns the
// proper ancestor directories of p. For "/a/b/c", returns ["/a/b", "/a", "/"].
func mutatePathAncestors(p util.FullPath) []util.FullPath {
	var ancestors []util.FullPath
	s := string(p)
	for {
		parent := path.Dir(s)
		if parent == s {
			break
		}
		ancestors = append(ancestors, util.FullPath(parent))
		s = parent
	}
	return ancestors
}

// classifyMutation extracts the admission key(s) and kind for a mutation
// request. It returns primary, secondary (empty unless rename), and kind.
//
// Malformed requests (missing oneof payload, nil Entry, missing rename fields)
// are routed to a barrier at "/" so admission still runs under the full stream
// lock; the handler will then send EINVAL to the client. This keeps the
// scheduler and Recv loop crash-free regardless of client-side validation.
//
// Deletes are always classified as kindMutateBarrierDir because a
// DeleteEntryRequest can target a directory (empty or, with IsRecursive, with
// contents) but does not carry IsDirectory on the wire. Treating every delete
// as a barrier at its target path makes it conflict with an in-flight
// non-barrier directory update on the same path (e.g. chmod), which a
// kindMutateFile classification would miss.
func classifyMutation(req *filer_pb.StreamMutateEntryRequest) (primary, secondary util.FullPath, kind mutateJobKind) {
	// Default fallback for any shape we cannot classify safely.
	primary = util.FullPath("/")
	kind = kindMutateBarrierDir

	switch r := req.Request.(type) {

	case *filer_pb.StreamMutateEntryRequest_CreateRequest:
		cr := r.CreateRequest
		if cr == nil || cr.Entry == nil {
			return
		}
		primary = util.FullPath(cr.Directory).Child(cr.Entry.Name)
		kind = classifyEntry(cr.Entry.IsDirectory, false)
		return

	case *filer_pb.StreamMutateEntryRequest_UpdateRequest:
		ur := r.UpdateRequest
		if ur == nil || ur.Entry == nil {
			return
		}
		primary = util.FullPath(ur.Directory).Child(ur.Entry.Name)
		// UpdateEntry never changes the name, so directory updates are always
		// in-place attribute updates. File updates (chunk manifests, xattrs)
		// are kindMutateFile and thus serialize against same-path file ops.
		kind = classifyEntry(ur.Entry.IsDirectory, true)
		return

	case *filer_pb.StreamMutateEntryRequest_DeleteRequest:
		dr := r.DeleteRequest
		if dr == nil {
			return
		}
		primary = util.FullPath(dr.Directory).Child(dr.Name)
		// Barrier regardless of IsRecursive: the request does not carry the
		// target's IsDirectory, and barrier classification correctly blocks
		// concurrent non-barrier dir updates at the same path. Descendant
		// wait for a non-recursive delete of a non-empty dir is wasted but
		// not wrong — that call fails at the store anyway.
		kind = kindMutateBarrierDir
		return

	case *filer_pb.StreamMutateEntryRequest_RenameRequest:
		rr := r.RenameRequest
		if rr == nil {
			return
		}
		primary = util.FullPath(rr.OldDirectory).Child(rr.OldName)
		secondary = util.FullPath(rr.NewDirectory).Child(rr.NewName)
		// Renames reshape the namespace on both sides; conservatively treat as
		// a subtree barrier so any in-flight descendant drains before the move
		// and no new descendant is admitted until it completes.
		kind = kindMutateBarrierDir
		return

	default:
		return
	}
}

func classifyEntry(isDirectory, isAttributeUpdate bool) mutateJobKind {
	if !isDirectory {
		return kindMutateFile
	}
	if isAttributeUpdate {
		return kindMutateNonBarrierDir
	}
	return kindMutateBarrierDir
}