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src/chunkers/Chunker.h

@@ -0,0 +1,74 @@
+//
+// Created by Stepan Usatiuk on 15.04.2023.
+//
+
+#ifndef SEMBACKUP_CHUNKER_H
+#define SEMBACKUP_CHUNKER_H
+
+#include <array>
+#include <optional>
+#include <streambuf>
+#include <vector>
+
+/// Abstract base class for a Chunker that takes a file and splits it into chunks to be backed up
+class Chunker {
+private:
+    /// Convenience iterator to allow using Chunker%s in range for loops
+    struct ChunkerIterator {
+        using value_type = std::pair<std::string, std::vector<char>>;
+
+        /// Creates a ChunkerIterator pointing to the first chunk or past-EOF
+        /// \param source Pointer to a Chunker, should be available during the entire iterator lifetime, or nullptr if this is pastEOF iterator
+        ChunkerIterator(Chunker *source);
+
+        /// Increments the iterator to the next chunk, or past-EOF
+        /// \throws Exception if iterator points past-EOF
+        ChunkerIterator &operator++();
+
+        /// Returns the current pointed-to chunk
+        /// \throws Exception if iterator points past-EOF
+        value_type operator*() const;
+
+        /// Returns true if both iterators are past-EOF
+        bool operator==(const ChunkerIterator &rhs) const;
+
+        /// Returns false if both iterators are past-EOF
+        bool operator!=(const ChunkerIterator &rhs) const;
+
+    private:
+        Chunker *const source;        ///< Pointer to the underlying Chunker
+        std::optional<value_type> buf;///< Currently pointed to chunk
+        bool pastEOF = false;         ///< Whether past EOF has been reached
+    };
+
+public:
+    /// Returns the next chunk of the file
+    /// Returns a single empty chunk if a file is empty
+    /// \return Pair consisting of chunk's bytes and its MD5 hash
+    /// \throws Exception if EOF was already reached
+    virtual std::pair<std::string, std::vector<char>> getNext() = 0;
+
+    /// Returns True if EOF was reached, False otherwise
+    bool getEof() const;
+
+    /// Default virtual destructor
+    virtual ~Chunker();
+
+    /// Returns a ChunkerIterator pointing to the first chunk in a file
+    ChunkerIterator begin();
+
+    /// Returns a past-EOF ChunkerIterator
+    static ChunkerIterator end();
+
+protected:
+    /// \param buf          Pointer to a std::streambuf, should be available during the entire lifetime of a Chunker
+    /// \param maxBytes     Maximal amount of bytes in returned chunks
+    Chunker(std::streambuf *buf, unsigned long long maxBytes);
+
+    std::streambuf *const buf;        ///< Constant pointer to the source std::streambuf
+    bool eof = false;                 ///< Indicates whether EOF has been reached
+    const unsigned long long maxBytes;///< Max number of bytes in returned chunks
+};
+
+
+#endif//SEMBACKUP_CHUNKER_H