package attachment

import (
	"io"
	"os"
	"path/filepath"
)

// ErrInvalidAttachmentID is returned when attachmentID contains unsafe characters
var ErrInvalidAttachmentID = os.ErrInvalid

type AttachmentManager struct {
	attachmentsDir string
}

const maxUploadSize = 50 * 1024 * 1024 // 50MB

func NewAttachmentManager() *AttachmentManager {
	return &AttachmentManager{
		attachmentsDir: filepath.Join(os.Getenv("HOME"), ".config", "pop", "attachments"),
	}
}

// isAttachmentIDSafe validates that attachmentID contains only safe characters
// to prevent path traversal attacks
func isAttachmentIDSafe(id string) bool {
	if id == "" {
		return false
	}
	// Only allow alphanumeric, hyphen, and underscore
	for _, r := range id {
		if !((r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') ||
			(r >= '0' && r <= '9') || r == '-' || r == '_') {
			return false
		}
	}
	return true
}

// sanitizeAttachmentID ensures the attachmentID is safe and the resolved path
// is within the attachments directory
func sanitizeAttachmentID(id string) (string, error) {
	if !isAttachmentIDSafe(id) {
		return "", ErrInvalidAttachmentID
	}
	// Use filepath.Clean to resolve any .. or . components
	cleanID := filepath.Clean(id)
	if cleanID != id {
		return "", ErrInvalidAttachmentID
	}
	return cleanID, nil
}

func (m *AttachmentManager) Download(attachmentID, name, destPath string) error {
	// Sanitize attachmentID to prevent path traversal
	if sanitizedID, err := sanitizeAttachmentID(attachmentID); err != nil {
		return err
	} else {
		attachmentID = sanitizedID
	}

	if err := os.MkdirAll(m.attachmentsDir, 0700); err != nil {
		return err
	}

	srcPath := filepath.Join(m.attachmentsDir, attachmentID)
	dest := filepath.Join(destPath, name)

	if err := os.MkdirAll(filepath.Dir(dest), 0755); err != nil {
		return err
	}

	data, err := os.ReadFile(srcPath)
	if err != nil {
		return err
	}

	return os.WriteFile(dest, data, 0600)
}

func (m *AttachmentManager) Upload(attachmentID, name string, reader io.Reader) error {
	// Sanitize attachmentID to prevent path traversal
	if sanitizedID, err := sanitizeAttachmentID(attachmentID); err != nil {
		return err
	} else {
		attachmentID = sanitizedID
	}

	if err := os.MkdirAll(m.attachmentsDir, 0700); err != nil {
		return err
	}

	// Limit reader to maxUploadSize to prevent DoS
	limitedReader := io.LimitReader(reader, maxUploadSize)
	data, err := io.ReadAll(limitedReader)
	if err != nil {
		return err
	}

	return os.WriteFile(filepath.Join(m.attachmentsDir, attachmentID), data, 0600)
}

func (m *AttachmentManager) Get(attachmentID string) ([]byte, error) {
	// Sanitize attachmentID to prevent path traversal
	if sanitizedID, err := sanitizeAttachmentID(attachmentID); err != nil {
		return nil, err
	} else {
		attachmentID = sanitizedID
	}
	path := filepath.Join(m.attachmentsDir, attachmentID)
	return os.ReadFile(path)
}

func (m *AttachmentManager) Delete(attachmentID string) error {
	// Sanitize attachmentID to prevent path traversal
	if sanitizedID, err := sanitizeAttachmentID(attachmentID); err != nil {
		return err
	} else {
		attachmentID = sanitizedID
	}
	path := filepath.Join(m.attachmentsDir, attachmentID)
	return os.Remove(path)
}

func (m *AttachmentManager) List() ([]string, error) {
	entries, err := os.ReadDir(m.attachmentsDir)
	if err != nil {
		if os.IsNotExist(err) {
			return []string{}, nil
		}
		return nil, err
	}

	ids := make([]string, len(entries))
	for i, entry := range entries {
		ids[i] = entry.Name()
	}
	return ids, nil
}