#include "kernel/filesystem/mount_table.hpp"

#include "kernel/filesystem/dentry.hpp"
#include "kernel/filesystem/mount.hpp"

#include <kstd/memory>
#include <kstd/vector>

#include <algorithm>
#include <cstddef>
#include <ranges>
#include <string_view>

namespace kernel::filesystem
{
  namespace
  {
    auto is_descendant_of(kstd::shared_ptr<mount> const & candidate, kstd::shared_ptr<mount> const & ancestor) -> bool
    {
      for (auto current = candidate; current; current = current->get_parent_mount())
      {
        if (current == ancestor)
        {
          return true;
        }
      }

      return false;
    }

    auto is_strict_prefix(std::string_view prefix, std::string_view path) -> bool
    {
      return prefix != "/" && path.starts_with(prefix) && path.size() > prefix.size() && path[prefix.size()] == '/';
    }

    auto is_visible_mount(kstd::shared_ptr<mount> const & candidate,
                          kstd::vector<kstd::shared_ptr<mount>> const & mounts) -> bool
    {
      return std::ranges::none_of(mounts, [&](auto const & other) {
        return other != candidate && is_strict_prefix(other->get_mount_path(), candidate->get_mount_path()) &&
               !is_descendant_of(candidate, other);
      });
    }
  }  // namespace

  auto mount_table::has_child_mounts(kstd::shared_ptr<mount> const & parent_mount) const -> bool
  {
    return std::ranges::any_of(
        m_mounts, [&parent_mount](auto const & mount) { return mount->get_parent_mount() == parent_mount; });
  }

  void mount_table::add_mount(kstd::shared_ptr<mount> const & mount)
  {
    m_mounts.push_back(mount);
    if (auto mount_dentry = mount->get_mount_dentry())
    {
      mount_dentry->set_flag(dentry::dentry_flags::dcache_mounted);
    }
  }

  auto mount_table::remove_mount(std::string_view path) -> operation_result
  {
    auto mount_it = std::ranges::find_if(std::ranges::reverse_view(m_mounts), [&](auto const & mount) {
      return mount->get_mount_path() == path && is_visible_mount(mount, m_mounts);
    });

    if (mount_it == std::ranges::reverse_view(m_mounts).end())
    {
      return operation_result::mount_not_found;
    }

    auto const & mount = *mount_it;
    if (has_child_mounts(mount))
    {
      return operation_result::has_child_mounts;
    }

    mount->get_mount_dentry()->unset_flag(dentry::dentry_flags::dcache_mounted);
    m_mounts.erase(std::ranges::find(m_mounts, mount));
    return operation_result::removed;
  }

  auto mount_table::find_longest_prefix_mount(std::string_view path) const -> kstd::shared_ptr<mount>
  {
    kstd::shared_ptr<mount> mount_with_longest_prefix = nullptr;
    std::size_t best_len = 0;

    for (auto const & mount : m_mounts)
    {
      auto mp = mount->get_mount_path();

      // /a/b/c should match /a/b but not /a/bb or /a/b/c/d, / should match everything
      bool is_prefix = path.starts_with(mp) && (mp == "/" || path.size() == mp.size() || path[mp.size()] == '/');
      bool visible = is_visible_mount(mount, m_mounts);

      if (is_prefix && visible && mp.size() >= best_len)
      {
        mount_with_longest_prefix = mount;
        best_len = mp.size();
      }
    }

    return mount_with_longest_prefix;
  }
}  // namespace kernel::filesystem