File Storage System

Inputs have the documented types: names/prefixes are strings; sizes, quota, timestamps, limits, and supplied TTLs are integers. Sizes are bytes; no unit parsing is required. Instances are independent. Every returned value record and list must be fresh. There is no overwrite, filesystem access, or historical rollback.

Prototype: implement FileCatalog() with upload() and get(). An empty upload name or negative size raises std::invalid_argument. Duplicate names return false and retain their size. Otherwise upload returns true. Zero-byte files are valid. Missing get returns nullopt. The prototype has no quota or expiration.

Final: implement FileStorage(quota):

• Negative quota raises std::invalid_argument; zero is valid. Start at logical time 0 with usage 0.
• advance_to(): require timestamp >= current time (and thus nonnegative), otherwise raise std::invalid_argument without changing state or time. Equal timestamps are allowed. Set time and remove every entry with expires_at <= timestamp, releasing its size exactly once. No other method advances time.
• upload(): empty name, negative size, or a supplied TTL below 1 raises std::invalid_argument before other checks. Omitted TTL means no expiration. Return false for an existing name or insufficient quota, unchanged. On success store expiry current_time + ttl or nullopt, charge size, and return true.
• get(): return exactly the fields declared in the value record below for an existing entry, otherwise nullopt.
• copy(): empty destination raises std::invalid_argument before other checks. Missing source, existing destination (including source == destination), or insufficient quota returns false unchanged. Success creates distinct metadata with the same size and absolute expiry as the source, charges the full size again, and returns true.
• erase(): return true and release the size if present; return false if absent. Repeated deletion must not release space twice.
• usage(): return the total sizes of all current entries.
• search(): match case-sensitive name.starts_with(prefix). Empty prefix matches all. Sort by size descending then name ascending, return at most limit snapshots. Negative limit raises std::invalid_argument without mutation; zero returns [].

Rejected calls leave all entries and quota accounting unchanged.

The public C++ API below is authoritative for field types and return values. erase is used where another language might use a method named delete, because delete is a C++ keyword. Returned records are value snapshots with the documented named fields; mutating a record or its nested vectors cannot affect the service.

struct File {std::string name;Int size;Opt<Int> expires_at;bool operator==(const File&)const=default;};
class FileCatalog { public:
 FileCatalog();
 bool upload(const std::string& name,Int size);
 Opt<Int> get(const std::string& name) const;
};
class FileStorage { public:
 explicit FileStorage(Int quota);
 void advance_to(Int ts);
 bool upload(const std::string& name,Int size,Opt<Int> ttl=std::nullopt);
 Opt<File> get(const std::string& name) const;
 bool copy(const std::string& source,const std::string& destination);
 bool erase(const std::string& name);
 Int usage() const;
 Vec<File> search(const std::string& prefix,Int limit=10) const;
};

Compile and run from this directory:

c++ -std=c++20 -O2 -Wall -Wextra -pedantic -pthread main.cpp -o practice
./practice --stage prototype
./practice --stage final

Edit exercise.hpp. Both stages start unfinished and must report failures until implemented. Keep main.cpp as the executable contract. The runner returns nonzero for a failed check, an unexpected exception, an invalid stage, or an empty suite. C++20 and only the standard library are required.