package store

import (
	"crypto/sha256"
	"database/sql"
	"errors"
	"fmt"
	"path/filepath"
	"strings"
	"time"
)

// #38: file attachments, one file per paste (iteration 1). A paste either
// has text content OR one attached file. Bytes live in the BlobStore; this
// table carries the metadata.

type Attachment struct {
	ID        string `json:"id"`
	PasteID   string `json:"paste_id"`
	Filename  string `json:"filename"`
	Mime      string `json:"mime"`
	Size      int64  `json:"size"`
	SHA256    string `json:"sha256"`
	CreatedAt int64  `json:"created_at"`

	SizeHuman string `json:"-"` // template-only: human-readable size
}

// MaxFilenameLen caps stored attachment filenames (bytes) to bound DB
// rows and Content-Disposition echoes. 128 keeps names readable while
// stopping filename-bloat abuse; longer names truncate.
const MaxFilenameLen = 128

// ErrFileTooLarge is returned when an attachment exceeds the per-file cap.
var ErrFileTooLarge = errors.New("file too large")

// SanitizeFilename cleans a user-supplied filename: strips directory
// components, control chars, and caps at 255 bytes. The extension is never
// trusted for mime decisions (mime is sniffed server-side).
func SanitizeFilename(name string) string {
	name = filepath.Base(strings.ReplaceAll(name, "\\", "/"))
	name = strings.TrimSpace(name)
	var b strings.Builder
	for _, r := range name {
		if r < 32 || r == 127 {
			continue
		}
		b.WriteRune(r)
	}
	name = b.String()
	if len(name) > MaxFilenameLen {
		runes := []rune(name)
		for len(string(runes)) > MaxFilenameLen {
			runes = runes[:len(runes)-1]
		}
		name = string(runes)
	}
	if name == "" || name == "." || name == ".." {
		name = "file"
	}
	return name
}

// CreateAttachment stores the file bytes and inserts the attachments row.
// The mime MUST already be sniffed server-side (http.DetectContentType by
// the caller); it is never taken from the client.
func (s *Store) CreateAttachment(a *Attachment, r interface{ Read([]byte) (int, error) }, blobs BlobStore) error {
	pasteID := a.PasteID
	sha, size, err := blobs.Put(pasteID+"/pending", r)
	if err != nil {
		return err
	}
	if a.Size > 0 && size > a.Size {
		// caller-provided pre-check limit; treat as too large
		blobs.Delete(pasteID + "/" + sha)
		return ErrFileTooLarge
	}
	a.SHA256 = sha
	a.Size = size
	now := time.Now().Unix()
	id := genSlug(20)
	_, err = s.db.Exec(`INSERT INTO attachments (id, paste_id, filename, mime, size, sha256, created_at)
		VALUES (?,?,?,?,?,?,?)`, id, pasteID, a.Filename, a.Mime, size, sha, now)
	if err != nil {
		blobs.Delete(pasteID + "/" + sha)
		return err
	}
	a.ID = id
	a.CreatedAt = now
	return nil
}

// GetAttachment returns the attachment row for a paste, or nil.
// One file per paste (iteration 1), so a single-row lookup keyed on paste.
func (s *Store) GetAttachmentForPaste(pasteID string) (*Attachment, error) {
	row := s.db.QueryRow(`SELECT id, paste_id, filename, mime, size, sha256, created_at
		FROM attachments WHERE paste_id = ? ORDER BY created_at ASC LIMIT 1`, pasteID)
	return scanAttachment(row)
}

func (s *Store) GetAttachment(id string) (*Attachment, error) {
	row := s.db.QueryRow(`SELECT id, paste_id, filename, mime, size, sha256, created_at
		FROM attachments WHERE id = ?`, id)
	return scanAttachment(row)
}

func scanAttachment(row *sql.Row) (*Attachment, error) {
	var a Attachment
	err := row.Scan(&a.ID, &a.PasteID, &a.Filename, &a.Mime, &a.Size, &a.SHA256, &a.CreatedAt)
	if err == sql.ErrNoRows {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	a.SizeHuman = humanBytes(a.Size)
	return &a, nil
}

// humanBytes formats a byte count for display (KB/MB).
func humanBytes(n int64) string {
	switch {
	case n >= 1<<20:
		return fmt.Sprintf("%.1f MB", float64(n)/(1<<20))
	case n >= 1<<10:
		return fmt.Sprintf("%.1f KB", float64(n)/(1<<10))
	default:
		return fmt.Sprintf("%d B", n)
	}
}

// DeleteAttachment removes the row and its blob.
func (s *Store) DeleteAttachment(a *Attachment, blobs BlobStore) error {
	blobs.Delete(a.PasteID + "/" + a.SHA256)
	_, err := s.db.Exec(`DELETE FROM attachments WHERE id = ?`, a.ID)
	return err
}

// HasAttachment reports whether a paste already carries a file (#38: one file per paste).
func (s *Store) HasAttachment(pasteID string) bool {
	var n int
	s.db.QueryRow(`SELECT COUNT(*) FROM attachments WHERE paste_id = ?`, pasteID).Scan(&n)
	return n > 0
}

// HashBytes is a small helper used by handlers to name/verify blobs.
func HashBytes(b []byte) string {
	h := sha256.Sum256(b)
	return string(h[:])
}