// HTTP-transport (PAT) access checks.
//
// A PAT is an opaque credential. Only its sha256 hash is stored; the plaintext
// is returned once at creation. AccessByPAT takes the PAT string directly (the
// cmd layer parses it out of the Authorization header) and checks it against the
// repo's (or its namespace's) ACL -- the state-layer half of the IState.AccessByPAT
// contract.
//
// PATs are created via ACLUpsertPATOnNS/OnRepo (IStateMut); there is no separate
// CreatePAT and intentionally no list/management read surface.

package state

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"time"

	"simplegit/common"
)

const patPrefix = "sgp_" // plaintext token prefix

// AccessByPAT authorizes pat for perm on owner/name.
//
//   - public read is open to everyone, including anonymous (pat ignored);
//   - an empty pat is anonymous: allowed only by the public-read shortcut,
//     otherwise ErrDenied (the caller decides 401 vs 403 from pat presence);
//   - a present-but-unknown or expired pat yields ErrInvalidToken;
//   - an authenticated but insufficient grant yields ErrDenied;
//   - an unknown repo yields ErrDenied (existence never leaked).
//
// skip-auth allows all.
func (s *LocalState) AccessByPAT(ctx context.Context, pat, owner, name string, perm common.Perm) (bool, error) {
	r, err := s.findRepo(owner, name)
	if err != nil {
		if errors.Is(err, ErrRepoNotFound) {
			return false, ErrDenied
		}
		return false, err
	}
	// public read is open to everyone, including anonymous
	if perm == common.PermRead && !r.IsPrivate {
		return true, nil
	}
	if pat == "" {
		// anonymous, but this needs a grant (private read, or any write)
		return false, ErrDenied
	}
	p, err := s.lookupPAT(pat)
	if err != nil {
		return false, err // ErrInvalidToken
	}
	ok, err := s.hasAccess(CredTypePAT, p.ID, r.ID, r.NamespaceID, perm)
	if err != nil {
		return false, err
	}
	if !ok {
		return false, ErrDenied
	}
	return true, nil
}

// lookupPAT hashes the presented token and returns the matching PAT row, or
// ErrInvalidToken if unknown or expired. Best-effort last-used stamp.
func (s *LocalState) lookupPAT(token string) (*PAT, error) {
	sum := sha256.Sum256([]byte(token))
	var pat PAT
	has, err := s.engine.Where("token_hash = ?", hex.EncodeToString(sum[:])).Get(&pat)
	if err != nil {
		return nil, fmt.Errorf("lookup pat: %w", err)
	}
	if !has {
		return nil, ErrInvalidToken
	}
	if pat.ExpiresAt != nil && time.Now().After(*pat.ExpiresAt) {
		return nil, ErrInvalidToken
	}
	// best-effort last-used stamp; a failure here must not block access
	now := time.Now()
	if _, err := s.engine.ID(pat.ID).Cols("last_used_at").Update(&PAT{LastUsedAt: &now}); err == nil {
		pat.LastUsedAt = &now
	}
	return &pat, nil
}