ballistic/tools/generate_ffi.lua

--[[
    C-to-LuaJIT FFI Bindings Generator

    Usage: luajit generate_ffi.lua <header.h> <output.lua>
]]



local ffi = require("ffi")

local args = { ... }

if #args < 2 then
    io.stderr:write("Usage: luajit generate_ffi.lua <header.h> <output.lua>\n")
    os.exit(1)
end

local header_path = args[1]
local output_path = args[2]
local file = assert(io.open(header_path, "r"), "Failed to open header: " .. header_path)
local header_content = file:read("*a")
file:close()

local defines = {}

for name, value in header_content:gmatch("#define%s+([%w_]+)%s+([%w_]+)") do
    if tonumber(value) or defines[value] then
        defines[name] = value
    end
end

-- Resolve nested defines.
local changed = true

while changed do
    changed = false

    for k, v in pairs(defines) do
        if not tonumber(v) and defines[v] then
            defines[k] = defines[v]
            changed = true
        end
    end
end

local function clean_for_ffi(str)
    for name, value in pairs(defines) do
        str = str:gsub("%f[%w_]" .. name .. "%f[^%w_]", value)
    end

    str = str:gsub("BAL_ALIGNED%s*%b()", "")
    str = str:gsub("BAL_EXPORT", "")
    str = str:gsub("BAL_RESTRICT", "")
    str = str:gsub("BAL_HOT", "")
    str = str:gsub("BAL_COLD", "")
    str = str:gsub("static_assert%s*%b();?", "")
    str = str:gsub("_Static_assert%s*%b();?", "")
    str = str:gsub("%s+", " ")
    str = str:gsub("^%s+", ""):gsub("%s+$", "")
    return str
end

local exported_functions = {}

for function_declaration in header_content:gmatch("BAL_EXPORT%s+([^;]+;)") do
    table.insert(exported_functions, clean_for_ffi(function_declaration))
end

local clean_header = header_content
clean_header = clean_header:gsub("BAL_ALIGNED%s*%b()", "")
clean_header = clean_header:gsub("static_assert%s*%b();?", "")
clean_header = clean_header:gsub("_Static_assert%s*%b();?", "")

local struct_definitions = {}

for struct_block in clean_header:gmatch("(typedef%s+struct[%s%w_]*%b{}[%s%w_]*;)") do
    table.insert(struct_definitions, clean_for_ffi(struct_block))
end

local validation_buffer = {}

for _, struct in ipairs(struct_definitions) do
    table.insert(validation_buffer, struct)
end

for _, fn in ipairs(exported_functions) do
    table.insert(validation_buffer, fn)
end

local validation_string = table.concat(validation_buffer, "\n")

if validation_string == "" then
    io.stderr:write("Warning: No structs or functions extracted from " .. header_path .. "\n")
end

local ok, err = pcall(ffi.cdef, validation_string)
if not ok then
    io.stderr:write("FFI validation failed for " .. header_path .. ": " .. tostring(err) .. "\n")
    io.stderr:write("--- Generated C Definitions ---\n")
    io.stderr:write(tostring(validation_string) .. "\n")
    io.stderr:write("-------------------------------\n")
    os.exit(1)
end

local out = assert(io.open(output_path, "w"), "Failed to open output: " .. output_path)
out:write("-- Auto-generated FFI bindings. DO NOT EDIT.\n")
out:write("-- Source: " .. header_path .. "\n")
out:write("-- Generated by tools/generate_ffi.lua\n\n")
out:write("local ffi = require('ffi')\n\n")
out:write("ffi.cdef [[\n")

for _, struct in ipairs(struct_definitions) do
    out:write(struct .. "\n\n")
end

for _, fn in ipairs(exported_functions) do
    out:write(fn .. "\n")
end

out:write("]]\n\n")
out:write("local M = {}\n")
out:write("local C = ffi.C\n\n")

for _, struct in ipairs(struct_definitions) do
    local type_name = struct:match("}%s*([%w_]+)%s*;")

    if type_name then
        out:write(string.format("local %s_mt = { __index = {} }\n", type_name))
        out:write(string.format("%s_mt.__index.__type = '%s'\n", type_name, type_name))
        out:write(string.format("ffi.metatype('%s', %s_mt)\n\n", type_name, type_name))
    end
end

for _, fn in ipairs(exported_functions) do
    local return_type, function_name, parameters = fn:match("^(%S+)%s+([%w_]+)%s*%((.*)%)%s*;")

    if function_name then
        local namespace = function_name:match("^([%w_]-)_[%w_]+$") or "Global"
        local pascal_namespace = namespace:gsub("_(%w)", string.upper):gsub("^(%w)", string.upper)
        out:write(string.format("M.%s = M.%s or {}\n", pascal_namespace, pascal_namespace))
        out:write(string.format("function M.%s.%s(", pascal_namespace, function_name))

        local parameter_names = {}

        if parameters and parameters ~= "void" and parameters ~= "" then
            for parameter in parameters:gmatch("[^,]+") do
                local name = parameter:match("([%w_]+)%s*$") or parameter:match("%*([%w_]+)")

                if name then
                    table.insert(parameter_names, name)
                end
            end
        end

        out:write(table.concat(parameter_names, ", ") .. ")\n")
        out:write(string.format("    return C.%s(%s)\n", function_name, table.concat(parameter_names, ", ")))
        out:write("end\n\n")
    end
end

out:write("return M\n")
out:close()

io.stdout:write(string.format("[generate_ffi] Generated %d structs, %d functions -> %s\n", #struct_definitions,
        #exported_functions, output_path))