package mount

import (
	"context"
	"fmt"
	"syscall"

	"github.com/seaweedfs/go-fuse/v2/fuse"
	"github.com/seaweedfs/seaweedfs/weed/cluster/lock_manager"
	"github.com/seaweedfs/seaweedfs/weed/glog"
	"github.com/seaweedfs/seaweedfs/weed/pb/filer_pb"
	"github.com/seaweedfs/seaweedfs/weed/util"
)

// AcquireHandle returns the shared handle for inode plus this open's own fh
// value — the id handed to the kernel and seen again at RELEASE.
func (wfs *WFS) AcquireHandle(ctx context.Context, inode uint64, flags, uid, gid uint32) (fileHandle *FileHandle, openFh FileHandleId, status fuse.Status) {
	var path util.FullPath
	for {
		// If there is an in-flight async flush for this inode, wait for it to
		// complete before reopening.  Otherwise the new handle would be built
		// from pre-close filer metadata and its next flush could overwrite the
		// data that was just written asynchronously.
		if !wfs.waitForPendingAsyncFlush(ctx, inode) {
			return nil, 0, fuse.EINTR
		}

		var pathStatus fuse.Status
		path, pathStatus = wfs.inodeToPath.GetPath(inode)
		if pathStatus != fuse.OK {
			return nil, 0, pathStatus
		}

		// A fresh lookup returns the entry with the filer log position it
		// reflects; the handle takes that entry and version as one decision in
		// AcquireFileHandle, so a slower concurrent opener cannot
		// overwrite a newer install. An existing handle keeps its own entry and
		// version — they did not come from this lookup.
		var entry *filer_pb.Entry
		var entryVersionTsNs entryVersion
		freshLookup := false
		if existingFh, found := wfs.fhMap.FindFileHandle(inode); found {
			entry = existingFh.UpdateEntry(func(entry *filer_pb.Entry) {
				if entry != nil && existingFh.entry.Attributes == nil {
					entry.Attributes = &filer_pb.FuseAttributes{}
				}
			})
			entryVersionTsNs = entryVersion{tsNs: existingFh.entryVersionTsNs.Load(), signature: existingFh.entryVersionSignature.Load()}
		} else {
			entry, entryVersionTsNs, status = wfs.maybeLoadEntry(ctx, path)
			if status != fuse.OK {
				return nil, 0, status
			}
			freshLookup = true
		}
		if wormEnforced, _ := wfs.wormEnforcedForEntry(path, entry); wormEnforced && flags&fuse.O_ANYWRITE != 0 {
			return nil, 0, fuse.EPERM
		}
		// Check unix permission bits for the requested access mode. With
		// default_permissions the kernel already enforced them before this
		// open, so the check (and its supplementary-group lookup) is redundant.
		if !wfs.option.DefaultPermissions && entry != nil && entry.Attributes != nil {
			fileUid, fileGid := entry.Attributes.Uid, entry.Attributes.Gid
			if wfs.option.UidGidMapper != nil {
				fileUid, fileGid = wfs.option.UidGidMapper.FilerToLocal(fileUid, fileGid)
			}
			if mask := openFlagsToAccessMask(flags); mask != 0 && !hasAccess(uid, gid, fileUid, fileGid, entry.Attributes.FileMode, mask) {
				return nil, 0, fuse.EACCES
			}
		}
		// need to AcquireFileHandle again to ensure correct handle counter
		var existed, draining bool
		fileHandle, openFh, existed, draining = wfs.fhMap.AcquireFileHandle(wfs, inode, entry, entryVersionTsNs.tsNs, entryVersionTsNs.signature)
		if draining {
			// A RELEASE slipped between waitForPendingAsyncFlush and this
			// attach: the handle's last open closed and its deferred flush
			// is draining.  The pending-flush flag is registered under the
			// same mutex that dropped the counter, so the next iteration
			// blocks on the drain (or finds the handle already removed)
			// and rebuilds state from post-flush metadata.
			continue
		}
		fileHandle.RememberPath(path)
		if existed && freshLookup {
			// Another opener created the handle while our lookup was in flight;
			// install only state that provably improves on what it holds.
			fileHandle.installAckedEntry(entry, entryVersionTsNs.tsNs, entryVersionTsNs.signature)
		}
		break
	}

	// Acquire distributed lock for write opens. The lock is held with
	// auto-renewal until the file handle is released (close).
	// Use the filer path as the lock key since inode numbers are
	// assigned per-mount and differ across mount instances.
	if wfs.lockClient != nil && flags&fuse.O_ANYWRITE != 0 && fileHandle.dlmLock == nil {
		owner := fmt.Sprintf("mount-%d", wfs.signature)
		fileHandle.dlmLock = wfs.lockClient.NewBlockingLongLivedLock(
			string(path), owner, lock_manager.LiveLockTTL,
		)
		if fileHandle.dlmLock == nil {
			// No lock server is reachable: proceeding would silently drop
			// cross-mount write serialization, so fail the open instead.
			wfs.ReleaseHandle(openFh)
			return nil, 0, fuse.Status(syscall.EAGAIN)
		}
		glog.V(1).Infof("DLM lock acquired for %s", path)
		// The previous holder's flush may not have reached the local cache,
		// and the lock orders this writer after it: take the filer's entry.
		if entry, version, err := wfs.lookupFilerEntry(ctx, path); err == nil {
			fileHandle.installAckedEntry(entry, version.tsNs, version.signature)
		}
	}
	return fileHandle, openFh, fuse.OK
}

// lookupFilerEntry reads path from the filer, bypassing the local cache, in
// local ids and with the log position the answer reflects.
func (wfs *WFS) lookupFilerEntry(ctx context.Context, path util.FullPath) (*filer_pb.Entry, entryVersion, error) {
	entry, version, err := wfs.lookupOwnerEntry(ctx, path)
	if err != nil {
		return nil, entryVersion{}, err
	}
	if entry.Attributes == nil {
		entry.Attributes = &filer_pb.FuseAttributes{}
	}
	wfs.mapPbIdFromFilerToLocal(entry)
	return entry, version, nil
}

// lookupOwnerEntry reads path in filer ids from the filer that checks path's
// write conditions, since another filer may lag it.
func (wfs *WFS) lookupOwnerEntry(ctx context.Context, path util.FullPath) (*filer_pb.Entry, entryVersion, error) {
	dir, name := path.DirAndName()
	var entry *filer_pb.Entry
	var version entryVersion
	lookup := func(ctx context.Context, client filer_pb.SeaweedFilerClient) error {
		resp, err := filer_pb.LookupEntry(ctx, client, &filer_pb.LookupDirectoryEntryRequest{Directory: dir, Name: name})
		if err != nil {
			return err
		}
		entry, version = resp.Entry, entryVersion{tsNs: resp.LogTsNs, signature: resp.LogSignature}
		return nil
	}
	var err error
	if owner := wfs.entryWriteOwner(path); owner != "" {
		err = wfs.callFiler(ctx, false, wfs.filerRPCWait(), owner.ToGrpcAddress(), lookup)
	} else {
		err = wfs.withFilerClient(ctx, false, wfs.filerRPCWait(), lookup)
	}
	if err != nil {
		return nil, entryVersion{}, err
	}
	return entry, version, nil
}

// ReleaseHandle is called from FUSE Release.  For handles with a pending
// async flush, the map removal and the pendingAsyncFlush registration are
// done under a single lock hold so that a concurrent AcquireHandle cannot
// slip through the gap between the two (P1-1 TOCTOU fix).
//
// The handle intentionally stays in fhMap during the drain so that rename
// and unlink can still find it via FindFileHandle (P1-2 fix).  It is
// removed from fhMap only after the drain completes (RemoveFileHandle).
func (wfs *WFS) ReleaseHandle(handleId FileHandleId) {
	// Hold pendingAsyncFlushMu across the counter decrement and the
	// pending-flush registration.  Lock ordering: pendingAsyncFlushMu → fhMap.
	wfs.pendingAsyncFlushMu.Lock()
	fhToRelease := wfs.fhMap.ReleaseByHandle(handleId)
	if fhToRelease != nil && fhToRelease.asyncFlushPending {
		done := make(chan struct{})
		wfs.pendingAsyncFlush[fhToRelease.inode] = done
		// Add(1) while holding the mutex so WaitForAsyncFlush cannot
		// observe a zero counter and close the channel before we send.
		wfs.asyncFlushWg.Add(1)
		wfs.pendingAsyncFlushMu.Unlock()

		// Send after unlock to avoid deadlock — workers acquire the
		// same mutex during cleanup.
		wfs.asyncFlushCh <- &asyncFlushItem{fh: fhToRelease, done: done}
		return
	}
	wfs.pendingAsyncFlushMu.Unlock()

	if fhToRelease != nil {
		fhToRelease.ReleaseHandle()
	}
}

// waitForPendingAsyncFlush blocks until any in-flight async flush for
// the given inode completes.  Called from AcquireHandle before building
// new handle state, so the filer metadata reflects the flushed data.
func (wfs *WFS) waitForPendingAsyncFlush(ctx context.Context, inode uint64) bool {
	wfs.pendingAsyncFlushMu.Lock()
	done, found := wfs.pendingAsyncFlush[inode]
	wfs.pendingAsyncFlushMu.Unlock()

	if !found {
		return true
	}
	glog.V(3).Infof("waitForPendingAsyncFlush: waiting for inode %d", inode)
	select {
	case <-done:
		return true
	case <-ctx.Done():
		return false
	}
}

func (wfs *WFS) GetHandle(handleId FileHandleId) *FileHandle {
	return wfs.fhMap.GetFileHandle(handleId)
}