package storage

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"os"
	"path/filepath"

	"github.com/jackc/pgx/v5"
)

// tenantFilePath returns the per-tenant hardlink path for a mail (PROJ-65).
// It mirrors filePath's 2-char shard layout, nested under a tenant directory,
// so a `find store/tenant_<id>/` gives a physically browsable view of exactly
// what one tenant can see, without duplicating file content on disk.
func (s *Store) tenantFilePath(tenantID int64, id string) string {
	return filepath.Join(s.dir, "store", fmt.Sprintf("tenant_%d", tenantID), id[:2], id)
}

// linkTenantDir ensures a hardlink to mail id exists under tenantID's
// directory (PROJ-65). Best-effort: the canonical content-addressed file
// under store/<shard>/<id> remains the source of truth and the only thing
// DB-driven access (Load/Delete) ever touches; this hardlink is purely an
// additional, physically browsable view for defense-in-depth / manual
// filesystem audits. A failure here must never fail the caller's Save/import.
func (s *Store) linkTenantDir(id string, tenantID int64) {
	src := s.filePath(id)
	dst := s.tenantFilePath(tenantID, id)

	if _, err := os.Stat(dst); err == nil {
		return // already linked
	}
	if err := os.MkdirAll(filepath.Dir(dst), 0o700); err != nil {
		s.logLinkWarn("mkdir tenant dir", id, tenantID, err)
		return
	}
	if err := os.Link(src, dst); err != nil {
		if errors.Is(err, os.ErrExist) {
			return
		}
		s.logLinkWarn("hardlink", id, tenantID, err)
	}
}

// unlinkTenantDirs best-effort removes a mail's hardlinks from every tenant
// directory it was visible under (PROJ-65). Called from Delete() after the
// canonical file has already been removed, using the tenant set captured
// before the DB rows were deleted. A missing link is not an error.
func (s *Store) unlinkTenantDirs(id string, tenantIDs []int64) {
	for _, tid := range tenantIDs {
		dst := s.tenantFilePath(tid, id)
		if err := os.Remove(dst); err != nil && !errors.Is(err, os.ErrNotExist) {
			s.logLinkWarn("unlink", id, tid, err)
		}
	}
}

func (s *Store) logLinkWarn(op, id string, tenantID int64, err error) {
	slog.Default().Warn("storage: tenant dir link failed", "op", op, "id", id, "tenant_id", tenantID, "err", err)
}

// TenantsForMail returns every tenant ID a mail is currently visible under:
// its primary emails.tenant_id plus any additional email_refs entries
// (cross-tenant dedup, PROJ-32/PROJ-37). Used by Delete() to know which
// tenant hardlinks to clean up, and by the migrate-tenant-dirs backfill.
func (s *Store) TenantsForMail(ctx context.Context, id string) ([]int64, error) {
	if s.db == nil {
		return nil, nil
	}
	seen := map[int64]bool{}
	var primary *int64
	err := s.db.QueryRow(ctx, `SELECT tenant_id FROM emails WHERE id = $1`, id).Scan(&primary)
	if err != nil && !errors.Is(err, pgx.ErrNoRows) {
		return nil, fmt.Errorf("storage: tenants for mail: %w", err)
	}
	if primary != nil {
		seen[*primary] = true
	}

	rows, err := s.db.Query(ctx, `SELECT DISTINCT tenant_id FROM email_refs WHERE email_id = $1`, id)
	if err != nil {
		return nil, fmt.Errorf("storage: tenants for mail refs: %w", err)
	}
	defer rows.Close()
	for rows.Next() {
		var tid int64
		if err := rows.Scan(&tid); err == nil {
			seen[tid] = true
		}
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("storage: tenants for mail refs rows: %w", err)
	}

	out := make([]int64, 0, len(seen))
	for tid := range seen {
		out = append(out, tid)
	}
	return out, nil
}

// BackfillTenantDirs walks all existing mails and creates any missing
// per-tenant hardlinks (PROJ-65). Intended for the one-time
// `archivmail migrate-tenant-dirs` CLI backfill after upgrading to a version
// with tenant directories — mails saved before that point only exist under
// the root content-addressed path. Idempotent: re-running only fills gaps.
func (s *Store) BackfillTenantDirs(ctx context.Context) (linked int, errCount int, err error) {
	if s.db == nil {
		return 0, 0, nil
	}
	ids, err := s.GetAllIDs(ctx)
	if err != nil {
		return 0, 0, fmt.Errorf("storage: backfill tenant dirs: list ids: %w", err)
	}
	for _, id := range ids {
		tenantIDs, terr := s.TenantsForMail(ctx, id)
		if terr != nil {
			errCount++
			continue
		}
		for _, tid := range tenantIDs {
			dst := s.tenantFilePath(tid, id)
			if _, statErr := os.Stat(dst); statErr == nil {
				continue // already linked
			}
			s.linkTenantDir(id, tid)
			if _, statErr := os.Stat(dst); statErr == nil {
				linked++
			} else {
				errCount++
			}
		}
	}
	return linked, errCount, nil
}