package scanner

import (
	"context"
	"io/fs"
	"maps"
	"path"
	"path/filepath"
	"slices"
	"sort"
	"strings"

	"github.com/navidrome/navidrome/conf"
	"github.com/navidrome/navidrome/core/storage"
	"github.com/navidrome/navidrome/log"
	"github.com/navidrome/navidrome/model"
	"github.com/navidrome/navidrome/utils"
)

// walkDirTree recursively walks the directory tree starting from the given targetFolders.
// If no targetFolders are provided, it starts from the root folder (".").
// It returns a channel of folderEntry pointers representing each folder found.
func walkDirTree(ctx context.Context, job *scanJob, targetFolders ...string) (<-chan *folderEntry, error) {
	results := make(chan *folderEntry)
	folders := targetFolders
	if len(targetFolders) == 0 {
		// No specific folders provided, scan the root folder
		folders = []string{"."}
	}
	go func() {
		defer close(results)
		for _, folderPath := range folders {
			if utils.IsCtxDone(ctx) {
				return
			}

			// Check if target folder exists before walking it
			// If it doesn't exist (e.g., deleted between watcher detection and scan execution),
			// skip it so it remains in job.lastUpdates and gets handled in following steps
			_, err := fs.Stat(job.fs, folderPath)
			if err != nil {
				log.Warn(ctx, "Scanner: Target folder does not exist.", "path", folderPath, err)
				continue
			}

			// Create checker and push patterns from root to this folder
			checker := newIgnoreChecker(job.fs)
			err = checker.PushAllParents(ctx, folderPath)
			if err != nil {
				log.Error(ctx, "Scanner: Error pushing ignore patterns for target folder", "path", folderPath, err)
				continue
			}

			// Recursively walk this folder and all its children
			err = walkFolder(ctx, job, folderPath, checker, results)
			if err != nil {
				log.Error(ctx, "Scanner: Error walking target folder", "path", folderPath, err)
				continue
			}
		}
		log.Debug(ctx, "Scanner: Finished reading target folders", "lib", job.lib.Name, "path", job.lib.Path, "numFolders", job.numFolders.Load())
	}()
	return results, nil
}

func walkFolder(ctx context.Context, job *scanJob, currentFolder string, checker *IgnoreChecker, results chan<- *folderEntry) error {
	// Push patterns for this folder onto the stack
	_ = checker.Push(ctx, currentFolder)
	defer checker.Pop() // Pop patterns when leaving this folder

	folder, children, err := loadDir(ctx, job, currentFolder, checker)
	if err != nil {
		log.Warn(ctx, "Scanner: Error loading dir. Skipping", "path", currentFolder, err)
		return nil
	}
	for _, c := range children {
		err := walkFolder(ctx, job, c, checker, results)
		if err != nil {
			return err
		}
	}

	dir := path.Clean(currentFolder)
	log.Trace(ctx, "Scanner: Found directory", " path", dir, "audioFiles", maps.Keys(folder.audioFiles),
		"images", maps.Keys(folder.imageFiles), "playlists", folder.numPlaylists, "imagesUpdatedAt", folder.imagesUpdatedAt,
		"updTime", folder.updTime, "modTime", folder.modTime, "numChildren", len(children))
	folder.path = dir
	folder.elapsed.Start()

	results <- folder

	return nil
}

func loadDir(ctx context.Context, job *scanJob, dirPath string, checker *IgnoreChecker) (folder *folderEntry, children []string, err error) {
	// Check if directory exists before creating the folder entry
	// This is important to avoid removing the folder from lastUpdates if it doesn't exist
	dirInfo, err := fs.Stat(job.fs, dirPath)
	if err != nil {
		log.Warn(ctx, "Scanner: Error stating dir", "path", dirPath, err)
		return nil, nil, err
	}

	// Now that we know the folder exists, create the entry (which removes it from lastUpdates)
	folder = job.createFolderEntry(dirPath)
	folder.modTime = dirInfo.ModTime()

	dir, err := job.fs.Open(dirPath)
	if err != nil {
		log.Warn(ctx, "Scanner: Error in Opening directory", "path", dirPath, err)
		return folder, children, err
	}
	defer dir.Close()
	dirFile, ok := dir.(fs.ReadDirFile)
	if !ok {
		log.Error(ctx, "Not a directory", "path", dirPath)
		return folder, children, err
	}

	entries := fullReadDir(ctx, dirFile)
	children = make([]string, 0, len(entries))
	for _, entry := range entries {
		entryPath := path.Join(dirPath, entry.Name())
		if checker.ShouldIgnore(ctx, entryPath) {
			log.Trace(ctx, "Scanner: Ignoring entry", "path", entryPath)
			continue
		}
		if ctx.Err() != nil {
			return folder, children, ctx.Err()
		}
		isDir, err := isDirOrSymlinkToDir(job.fs, dirPath, entry)
		// Skip invalid symlinks
		if err != nil {
			log.Warn(ctx, "Scanner: Invalid symlink", "dir", entryPath, err)
			continue
		}
		if isIgnoredEntry(entry.Name(), isDir) {
			continue
		}
		if isDir && isDirReadable(ctx, job.fs, entryPath) {
			children = append(children, entryPath)
			folder.numSubFolders++
		} else {
			fileInfo, err := entry.Info()
			if err != nil {
				log.Warn(ctx, "Scanner: Error getting fileInfo", "name", entry.Name(), err)
				return folder, children, err
			}
			if fileInfo.ModTime().After(folder.modTime) {
				folder.modTime = fileInfo.ModTime()
			}
			name, ok := resolveEntryName(ctx, job.fs, dirPath, entry)
			if !ok {
				continue
			}
			switch {
			case model.IsAudioFile(name):
				folder.audioFiles[entry.Name()] = entry
			case model.IsValidPlaylist(name):
				folder.numPlaylists++
			case model.IsImageFile(name):
				folder.imageFiles[entry.Name()] = entry
				folder.imagesUpdatedAt = utils.TimeNewest(folder.imagesUpdatedAt, fileInfo.ModTime(), folder.modTime)
			}
		}
	}
	return folder, children, nil
}

// fullReadDir reads all files in the folder, skipping the ones with errors.
// It also detects when it is "stuck" with an error in the same directory over and over.
// In this case, it stops and returns whatever it was able to read until it got stuck.
// See discussion here: https://github.com/navidrome/navidrome/issues/1164#issuecomment-881922850
func fullReadDir(ctx context.Context, dir fs.ReadDirFile) []fs.DirEntry {
	var allEntries []fs.DirEntry
	var prevErrStr = ""
	for {
		if ctx.Err() != nil {
			return nil
		}
		entries, err := dir.ReadDir(-1)
		allEntries = append(allEntries, entries...)
		if err == nil {
			break
		}
		log.Warn(ctx, "Skipping DirEntry", err)
		if prevErrStr == err.Error() {
			log.Error(ctx, "Scanner: Duplicate DirEntry failure, bailing", err)
			break
		}
		prevErrStr = err.Error()
	}
	sort.Slice(allEntries, func(i, j int) bool { return allEntries[i].Name() < allEntries[j].Name() })
	return allEntries
}

// isDirOrSymlinkToDir returns true if and only if the dirEnt represents a file
// system directory, or a symbolic link to a directory. Note that if the dirEnt
// is not a directory but is a symbolic link, this method will resolve by
// sending a request to the operating system to follow the symbolic link.
// originally copied from github.com/karrick/godirwalk, modified to use dirEntry for
// efficiency for go 1.16 and beyond
func isDirOrSymlinkToDir(fsys fs.FS, baseDir string, dirEnt fs.DirEntry) (bool, error) {
	if dirEnt.IsDir() {
		return true, nil
	}
	if dirEnt.Type()&fs.ModeSymlink == 0 {
		return false, nil
	}
	// If symlinks are disabled, return false for symlinks
	if !conf.Server.Scanner.FollowSymlinks {
		return false, nil
	}
	// Does this symlink point to a directory?
	fileInfo, err := fs.Stat(fsys, path.Join(baseDir, dirEnt.Name()))
	if err != nil {
		return false, err
	}
	return fileInfo.IsDir(), nil
}

const maxSymlinkHops = 40

// resolveEntryName returns the name to classify the entry by, and whether to
// consider it at all. Symlinks are resolved to their final target so the caller
// classifies by the target's extension, not the link's name. Returns ok=false
// when symlinks are disabled or the target can't be resolved.
func resolveEntryName(ctx context.Context, fsys fs.FS, dirPath string, entry fs.DirEntry) (string, bool) {
	if entry.Type()&fs.ModeSymlink == 0 {
		return entry.Name(), true
	}
	linkPath := path.Join(dirPath, entry.Name())
	if !conf.Server.Scanner.FollowSymlinks {
		log.Trace(ctx, "Scanner: Skipping symlink, following is disabled", "path", linkPath)
		return "", false
	}
	// OS-backed filesystems can resolve the whole chain, even when it leaves the FS root
	// (e.g. a link into another folder/drive), so the final target is always what gets
	// classified. The fs.ReadLink loop below can't see past the root: it classifies by the
	// last in-chain name it can reach.
	if resolver, ok := fsys.(storage.SymlinkResolverFS); ok {
		target, err := resolver.ResolveSymlink(linkPath)
		if err != nil {
			log.Trace(ctx, "Scanner: Skipping symlink, cannot resolve target", "path", linkPath, err)
			return "", false
		}
		resolved := filepath.Base(target)
		log.Trace(ctx, "Scanner: Resolved symlink", "path", linkPath, "target", target, "name", resolved)
		return resolved, true
	}
	cur := linkPath
	for hop := 0; hop < maxSymlinkHops; hop++ {
		target, err := fs.ReadLink(fsys, cur)
		if err != nil {
			if hop == 0 {
				log.Trace(ctx, "Scanner: Skipping symlink, cannot resolve target", "path", linkPath, err)
				return "", false
			}
			resolved := path.Base(cur)
			log.Trace(ctx, "Scanner: Resolved symlink", "path", linkPath, "target", cur, "name", resolved)
			return resolved, true
		}
		if path.IsAbs(target) {
			// Absolute targets are not valid fs.FS paths, so the next ReadLink fails and
			// resolution stops here, leaving cur as the target to classify by name.
			cur = target
		} else {
			cur = path.Join(path.Dir(cur), target)
		}
	}
	log.Trace(ctx, "Scanner: Skipping symlink, too many hops (possible loop)", "path", linkPath)
	return "", false
}

// isDirReadable returns true if the directory represented by dirEnt is readable
func isDirReadable(ctx context.Context, fsys fs.FS, dirPath string) bool {
	dir, err := fsys.Open(dirPath)
	if err != nil {
		log.Warn("Scanner: Skipping unreadable directory", "path", dirPath, err)
		return false
	}
	err = dir.Close()
	if err != nil {
		log.Warn(ctx, "Scanner: Error closing directory", "path", dirPath, err)
	}
	return true
}

// List of special directories to ignore
var ignoredDirs = []string{
	"$RECYCLE.BIN",
	"#snapshot",
	"@Recycle",
	"@Recently-Snapshot",
	".git",
	".streams",
	"lost+found",
}

// isIgnoredEntry returns true if a directory entry with the given name should be
// skipped during scanning. It centralizes all name- and type-based ignore policy:
//   - special system directories in ignoredDirs are always ignored;
//   - dot-prefixed files are always ignored;
//   - dot-prefixed folders are ignored unless Scanner.IgnoreDotFolders is disabled,
//     allowing albums like ".Hack Sign" to be scanned when the option is off.
func isIgnoredEntry(name string, isDir bool) bool {
	if isDir && isDirIgnored(name) {
		return true
	}
	return isDotEntry(name) && (!isDir || conf.Server.Scanner.IgnoreDotFolders)
}

// isDirIgnored returns true if the directory name is in the explicit ignoredDirs
// blocklist. Used both while walking the tree and by the file watcher.
func isDirIgnored(name string) bool {
	return slices.ContainsFunc(ignoredDirs, func(s string) bool { return strings.EqualFold(s, name) })
}

// isDotEntry returns true only for names with exactly one leading dot (the
// convention for hidden entries), e.g. ".hidden". Names with two or more leading
// dots are not considered hidden: "." and ".." are the special self/parent
// references, and anything like "..foo" or "...Album" is a regular name (album
// folders sometimes start with ellipses), so all of these return false.
func isDotEntry(name string) bool {
	return name != "." && strings.HasPrefix(name, ".") && !strings.HasPrefix(name, "..")
}
