#include <mercury/kernel/storage.hpp>

#define RETURN_IF_NOT_SUCCESS(expr) \
  { \
    io_result _result = expr; \
    if (_result != io_result::success) \
      return _result; \
  }

namespace mercury::kernel::storage {

  io_result block_device::load_cache_block(uint64_t i) {

    if (block_cache_i == i)
      return io_result::success;

    if (block_cache_dirty) {
      RETURN_IF_NOT_SUCCESS(
        write_blocks_no_cache(block_cache_i, 1, block_cache))
      block_cache_dirty = false;
    }

    io_result result = read_blocks_no_cache(i, 1, block_cache);

    if (result != io_result::success) {
      block_cache_i = block_count;
      return result;
    }

    block_cache_i = i;
    return io_result::success;

  }

  io_result block_device::read_bytes(
    uint64_t start, uint64_t count, void *into
  ) {

    if (start + count > block_size * block_count)
      return io_result::out_of_bounds;

    uint8_t *into_u8 = (uint8_t *)into;

    if (start % block_size != 0) {
      uint64_t prefix_len = block_size - start % block_size;
      RETURN_IF_NOT_SUCCESS(load_cache_block(start / block_size))
      for (uint64_t i = 0; i < prefix_len; ++i)
        into_u8[i] = block_cache[start % block_size + i];
      into_u8 += prefix_len;
      start += prefix_len;
      count -= prefix_len;
    }

    uint64_t postfix_start = ((start + count) / block_size) * block_size;

    if (postfix_start != start) {
      RETURN_IF_NOT_SUCCESS(read_blocks_no_cache(
        start / block_size, (postfix_start - start) / block_size, into_u8))
      count -= postfix_start - start;
      into_u8 += postfix_start - start;
      start = postfix_start;
    }

    if (count != 0) {
      RETURN_IF_NOT_SUCCESS(load_cache_block(start / block_size))
      for (uint64_t i = 0; i < count; ++i)
        into_u8[i] = block_cache[i];
    }

    return io_result::success;

  }

  utility::list<block_device *> *block_devices;

  static utility::trie<utility::string, block_device *> *mounted_devices;

  void init_storage() {
    block_devices = new utility::list<block_device *>();
    mounted_devices = new utility::trie<utility::string, block_device *>();
  }

  void canon_path::parent() {
    if (segments.count != 0)
      --segments.count;
    else if (!absolute)
      ++parent_count;
  }

  void canon_path::rel(const canon_path &r) {
    if (r.absolute) {
      segments.count = 0;
      absolute = true;
      parent_count = 0;
    }
    for (unsigned i = 0; i < r.parent_count; ++i)
      parent();
    for (unsigned i = 0; i < r.segments.count; ++i)
      segments.add_end(r.segments.buffer[i]);
  }

  void canonize_path(const char *str, size_t len, canon_path &out) {

    out.absolute = false;
    out.parent_count = 0;
    out.segments.count = 0;

    if (len == 0)
      return;

    if (len == 1 && str[0] == '/') {
      out.absolute = true;
      return;
    }

    if (str[0] == '/') {
      out.absolute = true;
      ++str;
      --len;
    }

    while (len != 0) {

      size_t segment_len = utility::find(str, len, '/');
      size_t to_skip = segment_len == len ? segment_len : segment_len + 1;

      if (segment_len == 0)
        ;

      else if (segment_len == 1 && str[0] == '.')
        ;

      else if (segment_len == 2 && str[0] == '.' && str[1] == '.')
        out.parent();

      else {
        utility::string segment(str, segment_len);
        out.segments.add_end(std::move(segment));
      }

      str += to_skip;
      len -= to_skip;

    }

  }

  io_result mount_device(
    block_device *bd, const canon_path &path, file_system_mounter mounter
  ) {

    if (!path.absolute)
      return io_result::bad_path;

    if (mounted_devices->has_key(path.segments))
      return io_result::mount_point_already_used;

    file_system_instance *fs;
    RETURN_IF_NOT_SUCCESS(mounter(bd, fs));
    bd->mounted_as = fs;
    mounted_devices->try_insert(path.segments, bd);
    return io_result::success;

  }

  static io_result symlink_contents(
    block_device *bd, node_id_t node, canon_path &out
  ) {
    //TODO
    while (1)
      ;
  }

  static io_result resolve_symlinks(
    block_device *&bd, node_id_t &node, canon_path &path
  ) {

    file_type ft;
    RETURN_IF_NOT_SUCCESS(bd->mounted_as->get_file_type(node, ft))

    if (ft != file_type::symlink)
      return io_result::success;

    canon_path contents;
    RETURN_IF_NOT_SUCCESS(symlink_contents(bd, node, contents))
    path.parent();
    path.rel(contents);

    return look_up_absolute_path(path, bd, node, true, path);

  }

  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
  ) {

    if (!path.absolute)
      return io_result::bad_path;

    unsigned prefix_length;
    bd_out =
      *mounted_devices->longest_prefix_with_value(path.segments, prefix_length)
        .value_here;
    RETURN_IF_NOT_SUCCESS(bd_out->mounted_as->get_root_node(node_out))

    path_without_symlinks_out.absolute = true;
    path_without_symlinks_out.parent_count = 0;
    path_without_symlinks_out.segments.count = 0;

    for (unsigned i = 0; i < prefix_length; ++i)
      path_without_symlinks_out.segments.add_end(path.segments.buffer[i]);

    if (path.segments.count == 0)
      goto on_final_node;

    for (unsigned i = prefix_length; i < path.segments.count - 1; ++i) {

      path_without_symlinks_out.segments.add_end(path.segments.buffer[i]);

      RETURN_IF_NOT_SUCCESS(bd_out->mounted_as->get_child(node_out, node_out,
        path.segments.buffer[i].buffer, path.segments.buffer[i].count))
      RETURN_IF_NOT_SUCCESS(resolve_symlinks(
        bd_out, node_out, path_without_symlinks_out))

      file_type ft;
      RETURN_IF_NOT_SUCCESS(bd_out->mounted_as->get_file_type(node_out, ft))

      if (ft != file_type::directory)
        return io_result::not_a_directory;

    }

    {
      //in a block so that compiler sees last_segment
      //isn't needed after this and allows the goto above.
      const utility::string &last_segment =
        path.segments.buffer[path.segments.count - 1];
      path_without_symlinks_out.segments.add_end(last_segment);
      RETURN_IF_NOT_SUCCESS(bd_out->mounted_as->get_child(
        node_out, node_out, last_segment.buffer, last_segment.count))
    }

  on_final_node:
    if (resolve_final_node)
      RETURN_IF_NOT_SUCCESS(resolve_symlinks(
        bd_out, node_out, path_without_symlinks_out))

    return io_result::success;

  }

}