package fs

import (
	"fmt"
	"io/ioutil"
	"os"
	"path/filepath"
	"regexp"
	"strings"
	"sync"

	"github.com/git-lfs/git-lfs/tools"
)

var oidRE = regexp.MustCompile(`\A[[:alnum:]]{64}`)

// Object represents a locally stored LFS object.
type Object struct {
	Oid  string
	Size int64
}

type Filesystem struct {
	GitStorageDir string // parent of objects/lfs (may be same as GitDir but may not)
	LFSStorageDir string // parent of lfs objects and tmp dirs. Default: ".git/lfs"
	ReferenceDir  string // alternative local media dir (relative to clone reference repo)
	lfsobjdir     string
	tmpdir        string
	logdir        string
	mu            sync.Mutex
}

func (f *Filesystem) EachObject(fn func(Object) error) error {
	var eachErr error
	tools.FastWalkGitRepo(f.LFSObjectDir(), func(parentDir string, info os.FileInfo, err error) {
		if err != nil {
			eachErr = err
			return
		}
		if eachErr != nil || info.IsDir() {
			return
		}
		if oidRE.MatchString(info.Name()) {
			fn(Object{Oid: info.Name(), Size: info.Size()})
		}
	})
	return eachErr
}

func (f *Filesystem) ObjectExists(oid string, size int64) bool {
	return tools.FileExistsOfSize(f.ObjectPathname(oid), size)
}

func (f *Filesystem) ObjectPath(oid string) (string, error) {
	dir := f.localObjectDir(oid)
	if err := os.MkdirAll(dir, 0755); err != nil {
		return "", fmt.Errorf("Error trying to create local storage directory in %q: %s", dir, err)
	}
	return filepath.Join(dir, oid), nil
}

func (f *Filesystem) ObjectPathname(oid string) string {
	return filepath.Join(f.localObjectDir(oid), oid)
}

func (f *Filesystem) localObjectDir(oid string) string {
	return filepath.Join(f.LFSObjectDir(), oid[0:2], oid[2:4])
}

func (f *Filesystem) ObjectReferencePath(oid string) string {
	if len(f.ReferenceDir) == 0 {
		return f.ReferenceDir
	}

	return filepath.Join(f.ReferenceDir, oid[0:2], oid[2:4], oid)
}

func (f *Filesystem) LFSObjectDir() string {
	f.mu.Lock()
	defer f.mu.Unlock()

	if len(f.lfsobjdir) == 0 {
		f.lfsobjdir = filepath.Join(f.LFSStorageDir, "objects")
		os.MkdirAll(f.lfsobjdir, 0755)
	}

	return f.lfsobjdir
}

func (f *Filesystem) LogDir() string {
	f.mu.Lock()
	defer f.mu.Unlock()

	if len(f.logdir) == 0 {
		f.logdir = filepath.Join(f.LFSStorageDir, "logs")
		os.MkdirAll(f.logdir, 0755)
	}

	return f.logdir
}

func (f *Filesystem) TempDir() string {
	f.mu.Lock()
	defer f.mu.Unlock()

	if len(f.tmpdir) == 0 {
		f.tmpdir = filepath.Join(f.LFSStorageDir, "tmp")
		os.MkdirAll(f.tmpdir, 0755)
	}

	return f.tmpdir
}

func (f *Filesystem) Cleanup() error {
	if f == nil {
		return nil
	}
	return f.cleanupTmp()
}

// New initializes a new *Filesystem with the given directories. gitdir is the
// path to the bare repo, workdir is the path to the repository working
// directory, and lfsdir is the optional path to the `.git/lfs` directory.
func New(gitdir, workdir, lfsdir string) *Filesystem {
	fs := &Filesystem{
		GitStorageDir: resolveGitStorageDir(gitdir),
	}

	fs.ReferenceDir = resolveReferenceDir(fs.GitStorageDir)

	if len(lfsdir) == 0 {
		lfsdir = "lfs"
	}

	if filepath.IsAbs(lfsdir) {
		fs.LFSStorageDir = lfsdir
	} else {
		fs.LFSStorageDir = filepath.Join(fs.GitStorageDir, lfsdir)
	}

	return fs
}

func resolveReferenceDir(gitStorageDir string) string {
	cloneReferencePath := filepath.Join(gitStorageDir, "objects", "info", "alternates")
	if tools.FileExists(cloneReferencePath) {
		buffer, err := ioutil.ReadFile(cloneReferencePath)
		if err == nil {
			path := strings.TrimSpace(string(buffer[:]))
			referenceLfsStoragePath := filepath.Join(filepath.Dir(path), "lfs", "objects")
			if tools.DirExists(referenceLfsStoragePath) {
				return referenceLfsStoragePath
			}
		}
	}
	return ""
}

// From a git dir, get the location that objects are to be stored (we will store lfs alongside)
// Sometimes there is an additional level of redirect on the .git folder by way of a commondir file
// before you find object storage, e.g. 'git worktree' uses this. It redirects to gitdir either by GIT_DIR
// (during setup) or .git/git-dir: (during use), but this only contains the index etc, the objects
// are found in another git dir via 'commondir'.
func resolveGitStorageDir(gitDir string) string {
	commondirpath := filepath.Join(gitDir, "commondir")
	if tools.FileExists(commondirpath) && !tools.DirExists(filepath.Join(gitDir, "objects")) {
		// no git-dir: prefix in commondir
		storage, err := processGitRedirectFile(commondirpath, "")
		if err == nil {
			return storage
		}
	}
	return gitDir
}

func processGitRedirectFile(file, prefix string) (string, error) {
	data, err := ioutil.ReadFile(file)
	if err != nil {
		return "", err
	}

	contents := string(data)
	var dir string
	if len(prefix) > 0 {
		if !strings.HasPrefix(contents, prefix) {
			// Prefix required & not found
			return "", nil
		}
		dir = strings.TrimSpace(contents[len(prefix):])
	} else {
		dir = strings.TrimSpace(contents)
	}

	if !filepath.IsAbs(dir) {
		// The .git file contains a relative path.
		// Create an absolute path based on the directory the .git file is located in.
		dir = filepath.Join(filepath.Dir(file), dir)
	}

	return dir, nil
}