package store

import (
	"crypto/subtle"
	"database/sql"
	"encoding/base64"
	"time"
)

// genDeletionToken returns a 32-char url-safe random token
func genDeletionToken() string {
	b := make([]byte, 24)
	cryptoRead(b)
	return base64.RawURLEncoding.EncodeToString(b)
}

// TimeNow is overridable in tests to inject the clock.
var TimeNow = time.Now

// registerRead applies the burn-after-read budget for one view (#49).
// For pastes with reads_limit set: the viewer's paste_views row is checked;
// a view within the burn viewer window of the viewer's last view is deduped
// (count=false). Otherwise reads_used is incremented, and the paste is
// soft-deleted (burned) once reads_used reaches reads_limit. Viewers without
// a cookie (plain API clients) count as their own viewer id "".
// For legacy plain burn_after_read pastes (no reads_limit), any read burns.
// Returns the number of reads remaining (0 when burned), or nil when no
// budget is set. view_count is tracked separately and unaffected.
func (s *Store) RegisterRead(row *PasteRow, viewerID string, burnWindowMinutes int) (remaining *int, count bool) {
	if !row.ReadsLimit.Valid {
		if row.BurnAfterRead {
			s.SoftDelete(row.ID)
			r := 0
			return &r, true
		}
		return nil, false
	}
	now := TimeNow().Unix()
	var last sql.NullInt64
	s.db.QueryRow(`SELECT last_viewed FROM paste_views WHERE paste_id=? AND viewer_id=?`,
		row.ID, viewerID).Scan(&last)
	if last.Valid && now-last.Int64 < int64(burnWindowMinutes)*60 {
		r := int(row.ReadsLimit.Int64) - row.ReadsUsed
		if r < 0 {
			r = 0
		}
		return &r, false
	}
	s.db.Exec(`INSERT INTO paste_views (paste_id, viewer_id, last_viewed) VALUES (?,?,?)
		ON CONFLICT(paste_id, viewer_id) DO UPDATE SET last_viewed = excluded.last_viewed`,
		row.ID, viewerID, now)
	used := row.ReadsUsed + 1
	s.db.Exec(`UPDATE pastes SET reads_used=? WHERE id=?`, used, row.ID)
	if int64(used) >= row.ReadsLimit.Int64 {
		s.SoftDelete(row.ID)
	}
	r := int(row.ReadsLimit.Int64) - int(used)
	if r < 0 {
		r = 0
	}
	return &r, true
}

// Burned reports whether a read-limited paste has exhausted its budget.
func (row *PasteRow) Burned() bool {
	return row.ReadsLimit.Valid && int64(row.ReadsUsed) >= row.ReadsLimit.Int64
}

func DeletionTokenEqual(stored, given string) bool {
	return subtle.ConstantTimeCompare([]byte(stored), []byte(given)) == 1
}