Compiler_Module_Resolver.H

/*
                          Aleph_w

  Data structures & Algorithms
  version 2.0.0b
  https://github.com/lrleon/Aleph-w

  This file is part of Aleph-w library

  Copyright (c) 2002-2026 Leandro Rabindranath Leon

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*/

/** @file Compiler_Module_Resolver.H
 *  @brief Reusable source-name module dependency resolution helpers.
 *
 *  This header provides a deliberately small dependency resolver for frontends
 *  whose imports are identified by exact source names. It computes one stable
 *  merge order, reports missing dependencies and cycles structurally, and can
 *  render the resulting order as a deterministic text artifact.
 *
 *  @ingroup Utilities
 */

#ifndef COMPILER_MODULE_RESOLVER_H
#define COMPILER_MODULE_RESOLVER_H

#include <sstream>
#include <string>

#include <ah-source.H>
#include <tpl_dynArray.H>

namespace Aleph {
/** @brief One source-name dependency edge originating from one module. */
struct Compiler_Module_Dependency
{
  std::string module_name;  ///< Exact imported source name.
  Source_Span span;         ///< Source location where the import was declared.
};

/** @brief One module descriptor consumed by the reusable resolver. */
struct Compiler_Module_Descriptor
{
  std::string name;                              ///< Stable module/source name.
  DynArray<Compiler_Module_Dependency> imports;  ///< Ordered dependency list.
};

/** @brief Structural issue kinds produced by module dependency resolution. */
enum class Compiler_Module_Resolution_Issue_Kind
{
  Missing_Dependency,
  Cyclic_Dependency
};

/** @brief One structured issue emitted by the reusable module resolver. */
struct Compiler_Module_Resolution_Issue
{
  Compiler_Module_Resolution_Issue_Kind kind
    = Compiler_Module_Resolution_Issue_Kind::Missing_Dependency;
  size_t module_index = 0;                            ///< Module whose import triggered the issue.
  size_t dependency_index = static_cast<size_t>(-1);  ///< Known dependency index when available.
  std::string module_name;                            ///< Stable importer name.
  std::string dependency_name;                        ///< Missing or cyclic dependency name.
  Source_Span span;  ///< Source location of the problematic import.
};

/** @brief Resolution result for one set of source-name module descriptors. */
struct Compiler_Module_Resolution_Result
{
  bool valid = true;       ///< `true` when no missing dependencies or cycles were found.
  DynArray<size_t> order;  ///< Stable dependency-first module order.
  DynArray<Compiler_Module_Resolution_Issue> issues;  ///< Structured issues, if any.
};

/** @brief Returns the stable debug name of one module-resolution issue kind. */
inline const char *compiler_module_resolution_issue_name(
  const Compiler_Module_Resolution_Issue_Kind kind) noexcept
{
  switch (kind)
    {
    case Compiler_Module_Resolution_Issue_Kind::Missing_Dependency:
      return "Missing_Dependency";
    case Compiler_Module_Resolution_Issue_Kind::Cyclic_Dependency:
      return "Cyclic_Dependency";
    }

  return "Unknown";
}

/** @brief Renders one deterministic text artifact for a module order. */
inline std::string compiler_render_module_order(const DynArray<size_t> &order,
                                                const DynArray<Compiler_Module_Descriptor> &modules)
{
  std::ostringstream out;
  out << "ImportOrder\n";
  for (size_t i = 0; i < order.size(); ++i)
    {
      const auto index = order.access(i);
      const auto name = index < modules.size() ? modules.access(index).name : "<invalid-module>";
      out << "  [" << i << "] " << name << '\n';
    }
  return out.str();
}

namespace Compiler_Module_Resolver_Detail {
inline size_t find_module_index(const DynArray<Compiler_Module_Descriptor> &modules,
                                const std::string &name) noexcept
{
  for (size_t i = 0; i < modules.size(); ++i)
    if (modules.access(i).name == name)
      return i;
  return static_cast<size_t>(-1);
}

inline bool resolve_visit(const DynArray<Compiler_Module_Descriptor> &modules,
                          const size_t index,
                          DynArray<unsigned char> &states,
                          Compiler_Module_Resolution_Result &result)
{
  const auto state = states.access(index);
  if (state == 2)
    return true;
  if (state == 1 or state == 3)
    return false;

  states.access(index) = 1;
  const auto &module = modules.access(index);
  for (size_t i = 0; i < module.imports.size(); ++i)
    {
      const auto &dep = module.imports.access(i);
      const auto dep_index = find_module_index(modules, dep.module_name);
      if (dep_index == static_cast<size_t>(-1))
        {
          result.valid = false;
          result.issues.append({Compiler_Module_Resolution_Issue_Kind::Missing_Dependency,
                                index,
                                static_cast<size_t>(-1),
                                module.name,
                                dep.module_name,
                                dep.span});
          continue;
        }

      if (dep_index == index)
        {
          result.valid = false;
          result.issues.append({Compiler_Module_Resolution_Issue_Kind::Cyclic_Dependency,
                                index,
                                dep_index,
                                module.name,
                                dep.module_name,
                                dep.span});
          continue;
        }

      if (states.access(dep_index) == 1)
        {
          result.valid = false;
          result.issues.append({Compiler_Module_Resolution_Issue_Kind::Cyclic_Dependency,
                                index,
                                dep_index,
                                module.name,
                                dep.module_name,
                                dep.span});
          states.access(index) = 3;
          return false;
        }

      if (states.access(dep_index) == 0 and not resolve_visit(modules, dep_index, states, result))
        {
          states.access(index) = 3;
          return false;
        }
    }

  states.access(index) = 2;
  result.order.append(index);
  return true;
}
}  // namespace Compiler_Module_Resolver_Detail

/** @brief Resolves one dependency-first order for exact-name module imports.
 *
 *  Missing dependencies are reported and skipped so the caller can still get
 *  a best-effort order. Cycles stop DFS along the offending path because no
 *  valid dependency-first ordering exists for that strongly connected region.
 */
inline Compiler_Module_Resolution_Result compiler_resolve_module_order(
  const DynArray<Compiler_Module_Descriptor> &modules)
{
  Compiler_Module_Resolution_Result result;
  DynArray<unsigned char> states;
  for (size_t i = 0; i < modules.size(); ++i)
    states.append(0);

  for (size_t i = 0; i < modules.size(); ++i)
    if (states.access(i) == 0)
      Compiler_Module_Resolver_Detail::resolve_visit(modules, i, states, result);

  return result;
}
}  // namespace Aleph

#endif