#ifndef CACHE_ENGINE_H
#define CACHE_ENGINE_H

struct cache_engine {
    /*
     * Allocate a `struct cache`-compatible struct and return it via cache_ptr.
     */
    int (*fn_init) (struct cache_engine *, struct cache **);
    
    /*
     * Allocate a `struct cache_op`-compatible struct and return it via cache_ptr.
     *
     * Begin the index lookup.
     */
    int (*fn_op_start) (struct cache *, struct cache_op **, struct cache_key *);
    
    /*
     * Return some information about the available data.
     */
    int (*fn_op_available) (struct cache_op *op, size_t *size, size_t *offset);

    /*
     * Prepare to write and possibly read this cache entry.
     *
     * size_hint, if nonzero, provides a guess at the size of the cache entry that can be used to optimize stuff
     */
    int (*fn_op_begin_write) (struct cache_op *, size_t size_hint);
    
    /*
     * Read some data from the given fd into this cache entry. Size may contain a non-zero value to hint at how many
     * bytes should be read, or zero to just read a suitable amount. Should be updated to how many bytes were actually
     * written (may be zero if writes are currently paused).
     */
    int (*fn_op_push) (struct cache_op *op, int fd, size_t *size);

    /*
     * No more calls to fn_op_push will take place. The cache entry now contains the complete data.
     */
    int (*fn_op_done) (struct cache_op *op);

    /*
     * The op is not needed for any operations anymore. Free any resources and memory associated with this op,
     * including the op itself.
     */
    int (*fn_op_close) (struct cache_op *op);
};

#endif /* CACHE_ENGINE_H */