package acl

import (
	"context"
	"errors"
	"fmt"
	"time"

	"github.com/google/uuid"
	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgconn"
)

var ErrSelfShare = errors.New("cannot share with yourself")

// Entry ist eine Freigabe, wie sie der Eigentümer im Dialog sieht.
type Entry struct {
	ID          uuid.UUID  `json:"id"`
	SubjectType string     `json:"subject_type"` // "user" | "group"
	SubjectID   uuid.UUID  `json:"subject_id"`
	SubjectName string     `json:"subject_name"`
	Permission  Permission `json:"permission"`
	CreatedAt   time.Time  `json:"created_at"`
}

// SharedResource ist ein Eintrag in „Geteilt mit mir".
type SharedResource struct {
	Type       string     `json:"type"` // "folder" | "file"
	ID         uuid.UUID  `json:"id"`
	Name       string     `json:"name"`
	OwnerID    uuid.UUID  `json:"owner_id"`
	OwnerName  string     `json:"owner_name"`
	Permission Permission `json:"permission"`
	Size       int64      `json:"size"`
	MimeType   string     `json:"mime_type"`
	SharedAt   time.Time  `json:"shared_at"`
	// ViaGroup nennt die Gruppe, über die der Zugriff kommt – sonst wundert
	// man sich, wo die Freigabe herkommt, die man nie persönlich bekommen hat.
	ViaGroup string `json:"via_group"`
}

// ── Freigaben verwalten ──────────────────────────────────────────────────────

// GrantFolder gibt einen Ordner frei. subjectIsGroup entscheidet, ob subjectID
// ein Nutzer oder eine Gruppe ist.
func (s *Store) GrantFolder(ctx context.Context, folderID, subjectID uuid.UUID, subjectIsGroup bool, perm Permission, grantedBy uuid.UUID) (*Entry, error) {
	return s.grant(ctx, &folderID, nil, subjectID, subjectIsGroup, perm, grantedBy)
}

func (s *Store) GrantFile(ctx context.Context, fileID, subjectID uuid.UUID, subjectIsGroup bool, perm Permission, grantedBy uuid.UUID) (*Entry, error) {
	return s.grant(ctx, nil, &fileID, subjectID, subjectIsGroup, perm, grantedBy)
}

func (s *Store) grant(ctx context.Context, folderID, fileID *uuid.UUID, subjectID uuid.UUID, subjectIsGroup bool, perm Permission, grantedBy uuid.UUID) (*Entry, error) {
	if !perm.valid() {
		return nil, fmt.Errorf("invalid permission %q", perm)
	}
	// Sich selbst freigeben ist sinnlos und würde in „Geteilt mit mir" die
	// eigenen Ordner doppelt anzeigen.
	if !subjectIsGroup && subjectID == grantedBy {
		return nil, ErrSelfShare
	}

	var subjUser, subjGroup *uuid.UUID
	if subjectIsGroup {
		subjGroup = &subjectID
	} else {
		subjUser = &subjectID
	}

	var e Entry
	err := s.db.QueryRow(ctx,
		`INSERT INTO acl_entries
		   (subject_user_id, subject_group_id, resource_folder_id, resource_file_id, permission, granted_by)
		 VALUES ($1, $2, $3, $4, $5, $6)
		 RETURNING id, permission, created_at`,
		subjUser, subjGroup, folderID, fileID, perm, grantedBy,
	).Scan(&e.ID, &e.Permission, &e.CreatedAt)

	// Eine zweite Freigabe an denselben Empfänger ist keine neue, sondern eine
	// Änderung des Rechts – sonst müsste man erst widerrufen, um von „lesen"
	// auf „schreiben" zu wechseln. Die vier partiellen Unique-Indizes lassen
	// sich nicht in einer einzigen ON-CONFLICT-Klausel abdecken, deshalb hier
	// über den Fehlercode.
	var pgErr *pgconn.PgError
	if errors.As(err, &pgErr) && pgErr.Code == "23505" {
		return s.updateExisting(ctx, folderID, fileID, subjUser, subjGroup, perm)
	}
	if err != nil {
		return nil, fmt.Errorf("grant access: %w", err)
	}

	e.SubjectID = subjectID
	e.SubjectType = subjectTypeName(subjectIsGroup)
	return &e, nil
}

func (s *Store) updateExisting(ctx context.Context, folderID, fileID, subjUser, subjGroup *uuid.UUID, perm Permission) (*Entry, error) {
	var e Entry
	err := s.db.QueryRow(ctx,
		`UPDATE acl_entries SET permission = $1
		  WHERE resource_folder_id IS NOT DISTINCT FROM $2
		    AND resource_file_id   IS NOT DISTINCT FROM $3
		    AND subject_user_id    IS NOT DISTINCT FROM $4
		    AND subject_group_id   IS NOT DISTINCT FROM $5
		 RETURNING id, permission, created_at`,
		perm, folderID, fileID, subjUser, subjGroup,
	).Scan(&e.ID, &e.Permission, &e.CreatedAt)
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, ErrNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("update access: %w", err)
	}
	if subjGroup != nil {
		e.SubjectID, e.SubjectType = *subjGroup, "group"
	} else if subjUser != nil {
		e.SubjectID, e.SubjectType = *subjUser, "user"
	}
	return &e, nil
}

// Revoke entfernt eine Freigabe. ownerID stellt sicher, dass nur der
// Eigentümer der Ressource widerrufen kann.
func (s *Store) Revoke(ctx context.Context, entryID, ownerID uuid.UUID) error {
	tag, err := s.db.Exec(ctx,
		`DELETE FROM acl_entries e
		  WHERE e.id = $1
		    AND ( EXISTS (SELECT 1 FROM folders f WHERE f.id = e.resource_folder_id AND f.owner_id = $2)
		       OR EXISTS (SELECT 1 FROM files   x WHERE x.id = e.resource_file_id   AND x.owner_id = $2) )`,
		entryID, ownerID)
	if err != nil {
		return fmt.Errorf("revoke access: %w", err)
	}
	if tag.RowsAffected() == 0 {
		return ErrNotFound
	}
	return nil
}

// ListForFolder / ListForFile zeigen dem Eigentümer, wer aktuell Zugriff hat.
func (s *Store) ListForFolder(ctx context.Context, folderID uuid.UUID) ([]Entry, error) {
	return s.list(ctx, `e.resource_folder_id = $1`, folderID)
}

func (s *Store) ListForFile(ctx context.Context, fileID uuid.UUID) ([]Entry, error) {
	return s.list(ctx, `e.resource_file_id = $1`, fileID)
}

func (s *Store) list(ctx context.Context, where string, resourceID uuid.UUID) ([]Entry, error) {
	rows, err := s.db.Query(ctx, `
		SELECT e.id,
		       CASE WHEN e.subject_group_id IS NOT NULL THEN 'group' ELSE 'user' END,
		       COALESCE(e.subject_group_id, e.subject_user_id),
		       COALESCE(g.name, NULLIF(u.display_name, ''), u.username, ''),
		       e.permission, e.created_at
		  FROM acl_entries e
		  LEFT JOIN users  u ON u.id = e.subject_user_id
		  LEFT JOIN groups g ON g.id = e.subject_group_id
		 WHERE `+where+`
		 ORDER BY e.created_at`, resourceID)
	if err != nil {
		return nil, fmt.Errorf("list access entries: %w", err)
	}
	defer rows.Close()

	out := []Entry{}
	for rows.Next() {
		var e Entry
		if err := rows.Scan(&e.ID, &e.SubjectType, &e.SubjectID, &e.SubjectName,
			&e.Permission, &e.CreatedAt); err != nil {
			return nil, fmt.Errorf("scan access entry: %w", err)
		}
		out = append(out, e)
	}
	return out, rows.Err()
}

// ListSharedWith liefert alles, was userID freigegeben bekommen hat – direkt
// oder über eine Gruppe. Das ist der Inhalt von „Geteilt mit mir".
//
// Nur die obersten freigegebenen Knoten erscheinen: Wer einen Ordner und darin
// eine Datei freigegeben bekommt, soll den Ordner sehen und die Datei darin,
// nicht beides nebeneinander.
func (s *Store) ListSharedWith(ctx context.Context, userID uuid.UUID) ([]SharedResource, error) {
	const q = `
		SELECT 'folder', f.id, f.name, f.owner_id,
		       COALESCE(NULLIF(o.display_name, ''), o.username),
		       e.permission, 0::bigint, '', e.created_at,
		       COALESCE(g.name, '')
		  FROM acl_entries e
		  JOIN folders f ON f.id = e.resource_folder_id
		  JOIN users   o ON o.id = f.owner_id
		  LEFT JOIN groups g ON g.id = e.subject_group_id
		 WHERE (e.subject_user_id = $1
		        OR e.subject_group_id IN (SELECT group_id FROM group_members WHERE user_id = $1))
		   -- Ordner weglassen, deren Elternteil ohnehin schon freigegeben ist.
		   AND NOT EXISTS (
		       SELECT 1
		         FROM acl_entries pe
		         JOIN folders pf ON pf.id = pe.resource_folder_id
		        WHERE pf.id = f.parent_id
		          AND (pe.subject_user_id = $1
		               OR pe.subject_group_id IN (SELECT group_id FROM group_members WHERE user_id = $1))
		   )

		UNION ALL

		SELECT 'file', x.id, x.name, x.owner_id,
		       COALESCE(NULLIF(o.display_name, ''), o.username),
		       e.permission, x.size, x.mime_type, e.created_at,
		       COALESCE(g.name, '')
		  FROM acl_entries e
		  JOIN files x ON x.id = e.resource_file_id
		  JOIN users o ON o.id = x.owner_id
		  LEFT JOIN groups g ON g.id = e.subject_group_id
		 WHERE x.is_deleted = false
		   AND (e.subject_user_id = $1
		        OR e.subject_group_id IN (SELECT group_id FROM group_members WHERE user_id = $1))
		   -- Datei weglassen, wenn ihr Ordner bereits freigegeben ist.
		   AND NOT EXISTS (
		       SELECT 1
		         FROM acl_entries fe
		        WHERE fe.resource_folder_id = x.folder_id
		          AND (fe.subject_user_id = $1
		               OR fe.subject_group_id IN (SELECT group_id FROM group_members WHERE user_id = $1))
		   )

		ORDER BY 1, 3`

	rows, err := s.db.Query(ctx, q, userID)
	if err != nil {
		return nil, fmt.Errorf("list shared resources: %w", err)
	}
	defer rows.Close()

	out := []SharedResource{}
	for rows.Next() {
		var r SharedResource
		if err := rows.Scan(&r.Type, &r.ID, &r.Name, &r.OwnerID, &r.OwnerName,
			&r.Permission, &r.Size, &r.MimeType, &r.SharedAt, &r.ViaGroup); err != nil {
			return nil, fmt.Errorf("scan shared resource: %w", err)
		}
		out = append(out, r)
	}
	return out, rows.Err()
}

// ── Verzeichnis für den Freigabedialog ───────────────────────────────────────

type Recipient struct {
	ID   uuid.UUID `json:"id"`
	Name string    `json:"name"`
	Type string    `json:"type"` // "user" | "group"
}

// Recipients listet mögliche Empfänger. Bewusst nur ID, Anzeigename und Art –
// Quota, Admin-Status und E-Mail gehen einen normalen Nutzer nichts an, auch
// wenn er teilen darf.
func (s *Store) Recipients(ctx context.Context, exclude uuid.UUID) ([]Recipient, error) {
	rows, err := s.db.Query(ctx, `
		SELECT id, COALESCE(NULLIF(display_name, ''), username), 'user'
		  FROM users WHERE id <> $1
		UNION ALL
		SELECT id, name, 'group' FROM groups
		 ORDER BY 3 DESC, 2`, exclude)
	if err != nil {
		return nil, fmt.Errorf("list recipients: %w", err)
	}
	defer rows.Close()

	out := []Recipient{}
	for rows.Next() {
		var r Recipient
		if err := rows.Scan(&r.ID, &r.Name, &r.Type); err != nil {
			return nil, fmt.Errorf("scan recipient: %w", err)
		}
		out = append(out, r)
	}
	return out, rows.Err()
}

func subjectTypeName(isGroup bool) string {
	if isGroup {
		return "group"
	}
	return "user"
}