package mobius

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"github.com/jhalter/mobius/hotline"
)

// ResolveUserPath processes paths for the special `~` directory.
func ResolveUserPath(cc *hotline.ClientConn, requestedPath string) (string, error) {
	if !strings.HasPrefix(requestedPath, "~") {
		return requestedPath, nil
	}

	userFolder := filepath.Join("~", cc.Account.Login)
	actualUserFolder := filepath.Join(cc.FileRoot(), userFolder)
	if stat, err := os.Stat(actualUserFolder); err == nil && stat.IsDir() {
		return strings.Replace(requestedPath, "~", userFolder, 1), nil
	}

	return "", fmt.Errorf("user folder does not exist")
}

// updateTransactionPath updates the FieldFilePath in a transaction in-place.
func updateTransactionPath(t *hotline.Transaction, newPath string) {
	for i, field := range t.Fields {
		if field.Type == hotline.FieldFilePath {
			if encodedPath, err := txtEncoder.String(newPath); err == nil {
				if fpBytes, err := encodeFilePath(encodedPath); err == nil {
					t.Fields[i].Data = fpBytes
				}
			}
			return
		}
	}
}

// encodeFilePath encodes a string path into hotline.FilePath binary format.
func encodeFilePath(path string) ([]byte, error) {
	components := strings.Split(path, string(filepath.Separator))
	var fp hotline.FilePath
	binary.BigEndian.PutUint16(fp.ItemCount[:], uint16(len(components)))

	var buffer bytes.Buffer
	if err := binary.Write(&buffer, binary.BigEndian, fp.ItemCount); err != nil {
		return nil, err
	}

	for _, component := range components {
		if component == "" || len(component) > 255 {
			return nil, fmt.Errorf("invalid file path component")
		}
		encodedComponent, err := txtEncoder.String(component)
		if err != nil {
			return nil, err
		}
		buffer.Write([]byte{0x00, 0x00, byte(len(encodedComponent))})
		buffer.Write([]byte(encodedComponent))
	}

	return buffer.Bytes(), nil
}

// handleFileTransaction handles various file operations that require resolving `~`
func handleFileTransaction(cc *hotline.ClientConn, t *hotline.Transaction, handler func(*hotline.ClientConn, *hotline.Transaction) []hotline.Transaction, errMsg string) []hotline.Transaction {
	requestedPath, err := hotline.ReadPath(cc.FileRoot(), t.GetField(hotline.FieldFilePath).Data, nil)
	if err != nil {
		return nil
	}

	sliceLen := min(len(cc.FileRoot()) + 1, len(requestedPath))
	resolvedPath, err := ResolveUserPath(cc, requestedPath[sliceLen:])
	if err != nil {
		return cc.NewErrReply(t, errMsg)
	}

	updateTransactionPath(t, resolvedPath)
	return handler(cc, t)
}

// File operation handlers
func HandleUploadFileWithUserFolders(cc *hotline.ClientConn, t *hotline.Transaction) []hotline.Transaction {
	return handleFileTransaction(cc, t, HandleUploadFile, "Cannot upload to non-existent user folder.")
}

func HandleUploadFolderWithUserFolders(cc *hotline.ClientConn, t *hotline.Transaction) []hotline.Transaction {
	return handleFileTransaction(cc, t, HandleUploadFolder, "Cannot upload to non-existent user folder.")
}

func HandleDeleteFileWithUserFolders(cc *hotline.ClientConn, t *hotline.Transaction) []hotline.Transaction {
	return handleFileTransaction(cc, t, HandleDeleteFile, "Cannot delete non-existent file.")
}

func HandleDownloadFileWithUserFolders(cc *hotline.ClientConn, t *hotline.Transaction) []hotline.Transaction {
	return handleFileTransaction(cc, t, HandleDownloadFile, "Cannot download non-existent user file.")
}

func HandleDownloadFolderWithUserFolders(cc *hotline.ClientConn, t *hotline.Transaction) []hotline.Transaction {
	return handleFileTransaction(cc, t, HandleDownloadFolder, "Cannot download non-existent user folder.")
}

// HandleGetFileNameListWithUserFolders modifies the file listing behavior for `~`
func HandleGetFileNameListWithUserFolders(cc *hotline.ClientConn, t *hotline.Transaction) []hotline.Transaction {
	requestedPath, err := hotline.ReadPath(cc.FileRoot(), t.GetField(hotline.FieldFilePath).Data, nil)
	if err != nil {
		return nil
	}

	if requestedPath == cc.FileRoot() {
		fileNames, err := hotline.GetFileNameList(cc.FileRoot(), cc.Server.Config.IgnoreFiles)
		if err != nil {
			return nil
		}

		userFolder := filepath.Join(cc.FileRoot(), "~", cc.Account.Login)
		if stat, err := os.Stat(userFolder); err != nil || !stat.IsDir() {
			filteredFiles := make([]hotline.Field, 0, len(fileNames))
			for _, file := range fileNames {
				if !strings.Contains(string(file.Data), "~") {
					filteredFiles = append(filteredFiles, file)
				}
			}
			return []hotline.Transaction{cc.NewReply(t, filteredFiles...)}
		}
		return []hotline.Transaction{cc.NewReply(t, fileNames...)}
	}

	if strings.HasPrefix(requestedPath, filepath.Join(cc.FileRoot(), "~")) {
		resolvedPath, err := ResolveUserPath(cc, requestedPath[len(cc.FileRoot())+1:])
		if err != nil {
			return nil
		}
		updateTransactionPath(t, resolvedPath)
		return HandleGetFileNameList(cc, t)
	}

	return HandleGetFileNameList(cc, t)
}