//go:build ((freebsd || openbsd || netbsd || dragonfly || illumos) && (386 || arm || amd64 || arm64 || riscv64 || ppc64le) && !(sqlite3_dotlk || sqlite3_nosys)) || sqlite3_flock

package vfs

import (
	"context"
	"io"
	"os"
	"sync"

	"github.com/tetratelabs/wazero/api"
	"golang.org/x/sys/unix"

	"github.com/ncruces/go-sqlite3/internal/util"
)

type vfsShmFile struct {
	*os.File
	info os.FileInfo

	refs int // +checklocks:vfsShmFilesMtx

	lock [_SHM_NLOCK]int16 // +checklocks:Mutex
	sync.Mutex
}

var (
	// +checklocks:vfsShmFilesMtx
	vfsShmFiles    []*vfsShmFile
	vfsShmFilesMtx sync.Mutex
)

type vfsShm struct {
	*vfsShmFile
	path    string
	lock    [_SHM_NLOCK]bool
	regions []*util.MappedRegion
}

func (s *vfsShm) Close() error {
	if s.vfsShmFile == nil {
		return nil
	}

	vfsShmFilesMtx.Lock()
	defer vfsShmFilesMtx.Unlock()

	// Unlock everything.
	s.shmLock(0, _SHM_NLOCK, _SHM_UNLOCK)

	// Decrease reference count.
	if s.vfsShmFile.refs > 0 {
		s.vfsShmFile.refs--
		s.vfsShmFile = nil
		return nil
	}

	err := s.File.Close()
	for i, g := range vfsShmFiles {
		if g == s.vfsShmFile {
			vfsShmFiles[i] = nil
			s.vfsShmFile = nil
			return err
		}
	}
	panic(util.AssertErr())
}

func (s *vfsShm) shmOpen() _ErrorCode {
	if s.vfsShmFile != nil {
		return _OK
	}

	// Always open file read-write, as it will be shared.
	f, err := os.OpenFile(s.path,
		unix.O_RDWR|unix.O_CREAT|unix.O_NOFOLLOW, 0666)
	if err != nil {
		return _CANTOPEN
	}
	// Closes file if it's not nil.
	defer func() { f.Close() }()

	fi, err := f.Stat()
	if err != nil {
		return _IOERR_FSTAT
	}

	vfsShmFilesMtx.Lock()
	defer vfsShmFilesMtx.Unlock()

	// Find a shared file, increase the reference count.
	for _, g := range vfsShmFiles {
		if g != nil && os.SameFile(fi, g.info) {
			s.vfsShmFile = g
			g.refs++
			return _OK
		}
	}

	// Lock and truncate the file.
	// The lock is only released by closing the file.
	if rc := osLock(f, unix.LOCK_EX|unix.LOCK_NB, _IOERR_LOCK); rc != _OK {
		return rc
	}
	if err := f.Truncate(0); err != nil {
		return _IOERR_SHMOPEN
	}

	// Add the new shared file.
	s.vfsShmFile = &vfsShmFile{
		File: f,
		info: fi,
	}
	f = nil // Don't close the file.
	for i, g := range vfsShmFiles {
		if g == nil {
			vfsShmFiles[i] = s.vfsShmFile
			return _OK
		}
	}
	vfsShmFiles = append(vfsShmFiles, s.vfsShmFile)
	return _OK
}

func (s *vfsShm) shmMap(ctx context.Context, mod api.Module, id, size int32, extend bool) (uint32, _ErrorCode) {
	// Ensure size is a multiple of the OS page size.
	if int(size)&(unix.Getpagesize()-1) != 0 {
		return 0, _IOERR_SHMMAP
	}

	if rc := s.shmOpen(); rc != _OK {
		return 0, rc
	}

	// Check if file is big enough.
	o, err := s.Seek(0, io.SeekEnd)
	if err != nil {
		return 0, _IOERR_SHMSIZE
	}
	if n := (int64(id) + 1) * int64(size); n > o {
		if !extend {
			return 0, _OK
		}
		if osAllocate(s.File, n) != nil {
			return 0, _IOERR_SHMSIZE
		}
	}

	r, err := util.MapRegion(ctx, mod, s.File, int64(id)*int64(size), size, false)
	if err != nil {
		return 0, _IOERR_SHMMAP
	}
	s.regions = append(s.regions, r)
	return r.Ptr, _OK
}

func (s *vfsShm) shmLock(offset, n int32, flags _ShmFlag) _ErrorCode {
	s.Lock()
	defer s.Unlock()

	switch {
	case flags&_SHM_UNLOCK != 0:
		for i := offset; i < offset+n; i++ {
			if s.lock[i] {
				if s.vfsShmFile.lock[i] == 0 {
					panic(util.AssertErr())
				}
				if s.vfsShmFile.lock[i] <= 0 {
					s.vfsShmFile.lock[i] = 0
				} else {
					s.vfsShmFile.lock[i]--
				}
				s.lock[i] = false
			}
		}
	case flags&_SHM_SHARED != 0:
		for i := offset; i < offset+n; i++ {
			if s.lock[i] {
				panic(util.AssertErr())
			}
			if s.vfsShmFile.lock[i]+1 <= 0 {
				return _BUSY
			}
		}
		for i := offset; i < offset+n; i++ {
			s.vfsShmFile.lock[i]++
			s.lock[i] = true
		}
	case flags&_SHM_EXCLUSIVE != 0:
		for i := offset; i < offset+n; i++ {
			if s.lock[i] {
				panic(util.AssertErr())
			}
			if s.vfsShmFile.lock[i] != 0 {
				return _BUSY
			}
		}
		for i := offset; i < offset+n; i++ {
			s.vfsShmFile.lock[i] = -1
			s.lock[i] = true
		}
	default:
		panic(util.AssertErr())
	}

	return _OK
}

func (s *vfsShm) shmUnmap(delete bool) {
	if s.vfsShmFile == nil {
		return
	}

	// Unmap regions.
	for _, r := range s.regions {
		r.Unmap()
	}
	s.regions = nil

	// Close the file.
	if delete {
		os.Remove(s.path)
	}
	s.Close()
}

func (s *vfsShm) shmBarrier() {
	s.Lock()
	//lint:ignore SA2001 memory barrier.
	s.Unlock()
}