nim-ffi/ffi/codegen/cpp.nim

## C++ binding generator for the nim-ffi framework.
## Generates a header-only C++ binding and CMakeLists.txt from compile-time FFI metadata.

import std/[os, strutils]
import ./meta

proc nimTypeToCpp*(typeName: string): string =
  case typeName
  of "string", "cstring": "std::string"
  of "int", "int64": "int64_t"
  of "int32": "int32_t"
  of "bool": "bool"
  of "float", "float64": "double"
  of "pointer": "void*"
  else: typeName

proc stripLibPrefixCpp(procName, libName: string): string =
  let prefix = libName & "_"
  if procName.startsWith(prefix):
    return procName[prefix.len .. ^1]
  return procName

proc generateCppHeader*(
    procs: seq[FFIProcMeta],
    types: seq[FFITypeMeta],
    libName: string,
): string =
  var lines: seq[string] = @[]

  lines.add("#pragma once")
  lines.add("#include <string>")
  lines.add("#include <cstdint>")
  lines.add("#include <stdexcept>")
  lines.add("#include <mutex>")
  lines.add("#include <condition_variable>")
  lines.add("#include <functional>")
  lines.add("#include <nlohmann/json.hpp>")
  lines.add("")

  # Types
  if types.len > 0:
    lines.add("// ============================================================")
    lines.add("// Types")
    lines.add("// ============================================================")
    lines.add("")
    for t in types:
      lines.add("struct $1 {" % [t.name])
      for f in t.fields:
        let cppType = nimTypeToCpp(f.typeName)
        lines.add("    $1 $2;" % [cppType, f.name])
      lines.add("};")
      var fieldNames: seq[string] = @[]
      for f in t.fields:
        fieldNames.add(f.name)
      lines.add("NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE($1, $2)" % [t.name, fieldNames.join(", ")])
      lines.add("")

  # C extern declarations
  lines.add("// ============================================================")
  lines.add("// C FFI declarations")
  lines.add("// ============================================================")
  lines.add("")
  lines.add("extern \"C\" {")
  lines.add("typedef void (*FfiCallback)(int ret, const char* msg, size_t len, void* user_data);")
  lines.add("")

  for p in procs:
    var params: seq[string] = @[]
    if p.kind == ffiFfiKind:
      params.add("void* ctx")
      params.add("FfiCallback callback")
      params.add("void* user_data")
      for ep in p.extraParams:
        params.add("const char* $1_json" % [ep.name])
    else: # ffiCtorKind
      for ep in p.extraParams:
        params.add("const char* $1_json" % [ep.name])
      params.add("FfiCallback callback")
      params.add("void* user_data")
    lines.add("int $1($2);" % [p.procName, params.join(", ")])

  lines.add("} // extern \"C\"")
  lines.add("")

  # Anonymous namespace with synchronous call helper
  lines.add("// ============================================================")
  lines.add("// Synchronous call helper (anonymous namespace, header-only)")
  lines.add("// ============================================================")
  lines.add("")
  lines.add("namespace {")
  lines.add("")
  lines.add("struct FfiCallState_ {")
  lines.add("    std::mutex              mtx;")
  lines.add("    std::condition_variable cv;")
  lines.add("    bool                    done{false};")
  lines.add("    bool                    ok{false};")
  lines.add("    std::string             msg;")
  lines.add("};")
  lines.add("")
  lines.add("inline void ffi_cb_(int ret, const char* msg, size_t /*len*/, void* ud) {")
  lines.add("    auto* s = static_cast<FfiCallState_*>(ud);")
  lines.add("    std::lock_guard<std::mutex> lock(s->mtx);")
  lines.add("    s->ok   = (ret == 0);")
  lines.add("    s->msg  = msg ? std::string(msg) : std::string{};")
  lines.add("    s->done = true;")
  lines.add("    s->cv.notify_one();")
  lines.add("}")
  lines.add("")
  lines.add("inline std::string ffi_call_(std::function<int(FfiCallback, void*)> f) {")
  lines.add("    FfiCallState_ state;")
  lines.add("    const int ret = f(ffi_cb_, &state);")
  lines.add("    if (ret == 2)")
  lines.add("        throw std::runtime_error(\"RET_MISSING_CALLBACK (internal error)\");")
  lines.add("    std::unique_lock<std::mutex> lock(state.mtx);")
  lines.add("    state.cv.wait(lock, [&state]{ return state.done; });")
  lines.add("    if (!state.ok)")
  lines.add("        throw std::runtime_error(state.msg);")
  lines.add("    return state.msg;")
  lines.add("}")
  lines.add("")
  lines.add("} // anonymous namespace")
  lines.add("")

  # Derive context type name and separate ctors / methods
  var ctors: seq[FFIProcMeta] = @[]
  var methods: seq[FFIProcMeta] = @[]
  for p in procs:
    if p.kind == ffiCtorKind: ctors.add(p)
    else: methods.add(p)

  let libTypeName =
    if ctors.len > 0: ctors[0].libTypeName
    else: libName[0 .. 0].toUpperAscii() & libName[1 .. ^1]

  let ctxTypeName = libTypeName & "Ctx"

  lines.add("// ============================================================")
  lines.add("// High-level C++ context class")
  lines.add("// ============================================================")
  lines.add("")
  lines.add("class $1 {" % [ctxTypeName])
  lines.add("public:")

  # Static create() factory
  for ctor in ctors:
    var ctorParams: seq[string] = @[]
    for ep in ctor.extraParams:
      let cppType = nimTypeToCpp(ep.typeName)
      ctorParams.add("const $1& $2" % [cppType, ep.name])

    lines.add("    static $1 create($2) {" % [ctxTypeName, ctorParams.join(", ")])
    for ep in ctor.extraParams:
      lines.add("        const auto $1_json = nlohmann::json($1).dump();" % [ep.name])

    var callArgs: seq[string] = @[]
    for ep in ctor.extraParams:
      callArgs.add("$1_json.c_str()" % [ep.name])
    callArgs.add("cb")
    callArgs.add("ud")

    lines.add("        const auto raw = ffi_call_([&](FfiCallback cb, void* ud) {")
    lines.add("            return $1($2);" % [ctor.procName, callArgs.join(", ")])
    lines.add("        });")
    lines.add("        // ctor returns the context address as a plain decimal string")
    lines.add("        const auto addr = std::stoull(raw);")
    lines.add("        return $1(reinterpret_cast<void*>(static_cast<uintptr_t>(addr)));" % [ctxTypeName])
    lines.add("    }")
    lines.add("")

  # Instance methods
  for m in methods:
    let methodName = stripLibPrefixCpp(m.procName, libName)
    let retCppType = nimTypeToCpp(m.returnTypeName)

    var methParams: seq[string] = @[]
    for ep in m.extraParams:
      let cppType = nimTypeToCpp(ep.typeName)
      methParams.add("const $1& $2" % [cppType, ep.name])
    let methParamsStr = methParams.join(", ")

    lines.add("    $1 $2($3) const {" % [retCppType, methodName, methParamsStr])
    for ep in m.extraParams:
      lines.add("        const auto $1_json = nlohmann::json($1).dump();" % [ep.name])

    var callArgs = @["ptr_", "cb", "ud"]
    for ep in m.extraParams:
      callArgs.add("$1_json.c_str()" % [ep.name])

    lines.add("        const auto raw = ffi_call_([&](FfiCallback cb, void* ud) {")
    lines.add("            return $1($2);" % [m.procName, callArgs.join(", ")])
    lines.add("        });")

    if retCppType == "std::string":
      lines.add("        return nlohmann::json::parse(raw).get<std::string>();")
    else:
      lines.add("        return nlohmann::json::parse(raw).get<$1>();" % [retCppType])
    lines.add("    }")
    lines.add("")

  lines.add("private:")
  lines.add("    void* ptr_;")
  lines.add("    explicit $1(void* p) : ptr_(p) {}" % [ctxTypeName])
  lines.add("};")
  lines.add("")

  result = lines.join("\n")

proc generateCppCMakeLists*(libName: string, nimSrcRelPath: string): string =
  ## Generates CMakeLists.txt for the C++ bindings directory.
  ## CMake uses ${...} which would clash with Nim's % format operator,
  ## so we build the file line by line using string concatenation.
  let src = nimSrcRelPath.replace("\\", "/")
  let cv  = "${CMAKE_CURRENT_SOURCE_DIR}"  # CMake variable shorthand
  let rv  = "${REPO_ROOT}"
  let lf  = "${NIM_LIB_FILE}"
  let nm  = "${NIM_EXECUTABLE}"
  let ns  = "${NIM_SRC}"
  let sd  = "${_search_dir}"
  var L: seq[string] = @[]
  L.add("cmake_minimum_required(VERSION 3.14)")
  L.add("project(" & libName & "_cpp_bindings CXX)")
  L.add("")
  L.add("set(CMAKE_CXX_STANDARD 17)")
  L.add("set(CMAKE_CXX_STANDARD_REQUIRED ON)")
  L.add("")
  L.add("# ── nlohmann/json ─────────────────────────────────────────────────────────────")
  L.add("include(FetchContent)")
  L.add("FetchContent_Declare(")
  L.add("    nlohmann_json")
  L.add("    GIT_REPOSITORY https://github.com/nlohmann/json.git")
  L.add("    GIT_TAG        v3.11.3")
  L.add("    GIT_SHALLOW    TRUE")
  L.add(")")
  L.add("FetchContent_MakeAvailable(nlohmann_json)")
  L.add("")
  L.add("# ── Locate the repository root (contains ffi.nimble) ─────────────────────────")
  L.add("set(_search_dir \"" & cv & "\")")
  L.add("set(REPO_ROOT \"\")")
  L.add("foreach(_i RANGE 10)")
  L.add("    if(EXISTS \"" & sd & "/ffi.nimble\")")
  L.add("        set(REPO_ROOT \"" & sd & "\")")
  L.add("        break()")
  L.add("    endif()")
  L.add("    get_filename_component(_search_dir \"" & sd & "\" DIRECTORY)")
  L.add("endforeach()")
  L.add("if(\"${REPO_ROOT}\" STREQUAL \"\")")
  L.add("    message(FATAL_ERROR \"Cannot find repo root (no ffi.nimble in any ancestor)\")")
  L.add("endif()")
  L.add("")
  L.add("# ── Nim source path ───────────────────────────────────────────────────────────")
  L.add("get_filename_component(NIM_SRC")
  L.add("    \"" & cv & "/" & src & "\"")
  L.add("    ABSOLUTE)")
  L.add("")
  L.add("# ── Compile the Nim shared library ───────────────────────────────────────────")
  L.add("find_program(NIM_EXECUTABLE nim REQUIRED)")
  L.add("")
  L.add("if(CMAKE_SYSTEM_NAME STREQUAL \"Darwin\")")
  L.add("    set(NIM_LIB_FILE \"" & rv & "/lib" & libName & ".dylib\")")
  L.add("elseif(CMAKE_SYSTEM_NAME STREQUAL \"Windows\")")
  L.add("    set(NIM_LIB_FILE \"" & rv & "/" & libName & ".dll\")")
  L.add("else()")
  L.add("    set(NIM_LIB_FILE \"" & rv & "/lib" & libName & ".so\")")
  L.add("endif()")
  L.add("")
  L.add("add_custom_command(")
  L.add("    OUTPUT  \"" & lf & "\"")
  L.add("    COMMAND \"" & nm & "\" c")
  L.add("                --mm:orc")
  L.add("                -d:chronicles_log_level=WARN")
  L.add("                --app:lib")
  L.add("                --noMain")
  L.add("                \"--nimMainPrefix:lib" & libName & "\"")
  L.add("                \"-o:" & lf & "\"")
  L.add("                \"" & ns & "\"")
  L.add("    WORKING_DIRECTORY \"" & rv & "\"")
  L.add("    DEPENDS \"" & ns & "\"")
  L.add("    COMMENT \"Compiling Nim library lib" & libName & "\"")
  L.add("    VERBATIM")
  L.add(")")
  L.add("add_custom_target(nim_lib ALL DEPENDS \"" & lf & "\")")
  L.add("")
  L.add("add_library(" & libName & " SHARED IMPORTED GLOBAL)")
  L.add("set_target_properties(" & libName & " PROPERTIES IMPORTED_LOCATION \"" & lf & "\")")
  L.add("add_dependencies(" & libName & " nim_lib)")
  L.add("")
  L.add("# ── Interface target exposing the generated header ────────────────────────────")
  L.add("add_library(" & libName & "_headers INTERFACE)")
  L.add("target_include_directories(" & libName & "_headers INTERFACE \"" & cv & "\")")
  L.add("target_link_libraries(" & libName & "_headers INTERFACE " & libName & " nlohmann_json::nlohmann_json)")
  L.add("")
  L.add("# ── Optional example executable ───────────────────────────────────────────────")
  L.add("if(EXISTS \"" & cv & "/main.cpp\")")
  L.add("    add_executable(example main.cpp)")
  L.add("    target_link_libraries(example PRIVATE " & libName & "_headers)")
  L.add("    add_dependencies(example nim_lib)")
  L.add("endif()")
  L.add("")
  result = L.join("\n")

proc generateCppBindings*(
    procs: seq[FFIProcMeta],
    types: seq[FFITypeMeta],
    libName: string,
    outputDir: string,
    nimSrcRelPath: string,
) =
  createDir(outputDir)
  writeFile(outputDir / (libName & ".hpp"), generateCppHeader(procs, types, libName))
  writeFile(outputDir / "CMakeLists.txt", generateCppCMakeLists(libName, nimSrcRelPath))