#ifndef MERCURY_KERNEL_STORAGE_HPP
#define MERCURY_KERNEL_STORAGE_HPP

#include <mercury/kernel/utility.hpp>
#include <cstdint>

namespace mercury::kernel::storage {

  typedef uint64_t node_id_t;
  typedef uint64_t directory_iter_t;

  enum file_type {
    regular_file,
    directory,
    symlink
  };

  enum io_result {
    success,
    mount_point_already_used,
    not_a_directory,
    not_supported,
    out_of_bounds,
    device_error,
    fs_corrupt,
    not_found,
    bad_path,
  };

  class file_system_instance {

  public:
    virtual ~file_system_instance() {}

    virtual io_result get_root_node(node_id_t &out) = 0;

    //get_first_child sets iter_out to a "directory iterator" representing the
    //first child of this node. get_next_child gets the child after the child
    //represented by the value of iter passed in, and changes iter to represent
    //that next child. for an empty directory node, get_first_child returns
    //io_result::not_found. when iter represents the last child of a node,
    //get_next_child also returns io_result::not_found.
    virtual io_result get_first_child(node_id_t node, node_id_t &out, directory_iter_t &iter_out) = 0;
    virtual io_result get_next_child(node_id_t node, node_id_t &out, directory_iter_t &iter) = 0;
    virtual io_result get_child(node_id_t node, node_id_t &out, const char *name, unsigned name_len) = 0;

    virtual io_result get_name_length(node_id_t node, unsigned &length_out) = 0;
    //buffer is assumed to be long enough - call get_name_length first.
    virtual io_result get_name(node_id_t node, char *buffer, unsigned &length_out) = 0;
    virtual io_result get_file_length(node_id_t node, uint64_t &length_out) = 0;
    virtual io_result get_file_type(node_id_t node, file_type &out) = 0;

    virtual io_result resize_file(node_id_t node, uint64_t new_length) = 0;
    virtual io_result read_bytes_from_file(node_id_t node, uint64_t start, uint64_t count, void *into) = 0;
    virtual io_result write_bytes_into_file(node_id_t node, uint64_t start, uint64_t count, const void *from) = 0;

  };

  class block_device {

  private:
    uint8_t *block_cache;
    uint64_t block_cache_i;
    bool block_cache_dirty;

    io_result load_cache_block(uint64_t i);

  protected:
    //implemented in driver, bounds not checked
    virtual io_result read_blocks_no_cache(uint64_t start, uint64_t count, void *into) = 0;
    virtual io_result write_blocks_no_cache(uint64_t start, uint64_t count, const void *from) = 0;

    //it is assumed that this is only called once, by the driver, after
    //block_size and block_count have been set, and before read_bytes or
    //write_bytes can be called (e.g. in the derived class's constructor)
    void allocate_block_cache();

  public:
    //set by storage component
    file_system_instance *mounted_as;
    utility::uuid id;

    //set by driver
    uint64_t block_size;
    uint64_t block_count;

    virtual ~block_device() {
      if (block_cache)
        delete block_cache;
    }

    io_result read_bytes(uint64_t start, uint64_t count, void *into);
    io_result write_bytes(uint64_t start, uint64_t count, const void *from);

  };

  typedef io_result (*file_system_mounter)(block_device *bd, file_system_instance *&fs_out);

  extern utility::list<block_device *> *block_devices;

  void init_storage();

  //a canon path contains no . or empty directory names, and
  //contains no .. except for at the start of a relative path.
  struct canon_path {

    bool absolute;
    unsigned parent_count;
    utility::vector<utility::string> segments;

    void parent();
    void rel(const canon_path &r);

    utility::string to_string(bool trailing_slash) const;

  };

  void canonize_path(const char *str, unsigned len, canon_path &out);

  //path must be absolute.
  io_result mount_device(block_device *bd, const canon_path &path, file_system_mounter mounter);

  //path must be absolute. symlinks are always resolved on nodes other than the
  //final one. they are resolved on the final node if and only if resolve final
  //node is set to true. mount points are always traversed, including on the
  //final node. this assumes that the path is under some mount point, and the
  //same for any symlinks traversed (e.g. / is mounted).
  io_result look_up_absolute_path(const canon_path &path, block_device *&bd_out,
    node_id_t &node_out, bool resolve_final_node, canon_path &path_without_symlinks_out);

}

#endif