parameter_cache.h

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#pragma once
 
#include <cstdint>
#include <expected>
#include <filesystem>
#include <nlohmann/json_fwd.hpp>
#include <optional>
#include <string>
#include <string_view>
#include <vector>
 
#include "node/device_parameter.h"
#include "node/synapticon.h"  // kSynapticonVendorId
 
namespace mm::node {
 
// The cache is enabled by default only for @c kSynapticonVendorId: for this vendor the CoE object
// dictionary is uniquely determined by @c (productCode, revisionNumber) — Synapticon bumps the
// revision whenever the dictionary changes, so an on-disk cache keyed on identity alone can never
// serve definitions that do not match the device. That guarantee does not hold for arbitrary
// third-party vendors (see @c ParameterCacheConfig::cacheAllVendors).
 
struct ParameterCacheConfig {
  bool cacheAllVendors =
      false;              
  std::string directory;  
  bool enabled = true;    
};
 
class ParameterCache {
 public:
  static constexpr int kFormatVersion = 2;
 
  ParameterCache() = default;
  explicit ParameterCache(ParameterCacheConfig config);
 
  void configure(ParameterCacheConfig config);
 
  bool enabledForVendor(uint32_t vendorId) const;
 
  std::optional<std::vector<DeviceParameter>> load(uint32_t vendorId, uint32_t productCode,
                                                   uint32_t revisionNumber) const;
 
  void store(uint32_t vendorId, uint32_t productCode, uint32_t revisionNumber,
             const std::vector<DeviceParameter>& parameters) const;
 
  struct CacheEntry {
    std::string id;                
    uint32_t vendorId = 0;         
    uint32_t productCode = 0;      
    uint32_t revisionNumber = 0;   
    uint32_t parameterCount = 0;   
    std::uintmax_t sizeBytes = 0;  
  };
 
  static std::string makeId(uint32_t vendorId, uint32_t productCode, uint32_t revisionNumber);
 
  std::vector<CacheEntry> list() const;
 
  std::expected<std::vector<uint8_t>, std::string> readRaw(std::string_view id) const;
 
  std::expected<void, std::string> remove(std::string_view id) const;
 
 private:
  std::filesystem::path resolveDir() const;
 
  std::filesystem::path pathFor(uint32_t vendorId, uint32_t productCode,
                                uint32_t revisionNumber) const;
 
  ParameterCacheConfig config_;
};
 
void to_json(nlohmann::json& j, const ParameterCache::CacheEntry& e);
 
}  // namespace mm::node