Modules in Lua

-- mymodule.lua
local mymodule = {}

function mymodule.hello(name)
    return "Hello, " .. name .. "!"
end

function mymodule.add(a, b)
    return a + b
end

return mymodule

-- calculator.lua
local calculator = {}

-- Private variables (local to the module)
local version = "1.0"

-- Public functions
function calculator.add(a, b)
    return a + b
end

function calculator.subtract(a, b)
    return a - b
end

function calculator.multiply(a, b)
    return a * b
end

function calculator.divide(a, b)
    if b == 0 then
        error("Division by zero!")
    end
    return a / b
end

-- Function to access private data
function calculator.get_version()
    return version
end

return calculator

-- main.lua
local calc = require("calculator")

local sum = calc.add(10, 5)
print("Sum:", sum)  -- Sum: 15

local product = calc.multiply(4, 7)
print("Product:", product)  -- Product: 28

print("Calculator version:", calc.get_version())  -- Calculator version: 1.0

-- View the current module search path
print(package.path)

-- Typical paths might include:
-- ./?.lua
-- /usr/share/lua/5.4/?.lua
-- /usr/local/share/lua/5.4/?.lua

-- Different ways to require the same module
local utils = require("utils")           -- utils.lua
local math_lib = require("math_lib")     -- math_lib.lua
local http = require("socket.http")      -- socket/http.lua

-- counter.lua
local counter = {
    count = 0,
    history = {}
}

function counter.increment(inc)
    inc = inc or 1
    counter.count = counter.count + inc
    table.insert(counter.history, counter.count)
    return counter.count
end

function counter.reset()
    counter.count = 0
    counter.history = {}
end

function counter.get_count()
    return counter.count
end

function counter.get_history()
    return counter.history
end

return counter

-- database.lua
local database = {
    config = {
        host = "localhost",
        port = 5432,
        name = "myapp",
        timeout = 30
    },
    connection = nil
}

function database.set_config(new_config)
    for key, value in pairs(new_config) do
        database.config[key] = value
    end
end

function database.connect()
    -- Simulated connection
    database.connection = {
        connected = true,
        config = database.config
    }
    print("Connected to database:", database.config.name)
end

function database.query(sql)
    if not database.connection then
        database.connect()
    end
    print("Executing query:", sql)
    return "Query result"
end

return database

-- user_manager.lua
local json = require("json")  -- Assuming a json module exists
local utils = require("utils")

local user_manager = {
    users = {}
}

function user_manager.add_user(user_data)
    -- Validate using utils module
    if not utils.validate_email(user_data.email) then
        error("Invalid email address")
    end
    
    local user = {
        id = #user_manager.users + 1,
        name = user_data.name,
        email = user_data.email,
        created_at = os.time()
    }
    
    table.insert(user_manager.users, user)
    return user
end

function user_manager.get_user(id)
    for _, user in ipairs(user_manager.users) do
        if user.id == id then
            return user
        end
    end
    return nil
end

function user_manager.export_to_json()
    return json.encode(user_manager.users)
end

return user_manager

-- good_module.lua
local M = {}  -- Public module table

-- Private helper function
local function validate_input(input)
    return type(input) == "string" and #input > 0
end

-- Public function that uses private helper
function M.process_string(input)
    if not validate_input(input) then
        error("Invalid input")
    end
    return string.upper(input)
end

-- Private variable
local internal_counter = 0

-- Public function using private variable
function M.get_next_id()
    internal_counter = internal_counter + 1
    return internal_counter
end

return M

-- config.lua
local M = {}

-- Module initialization function
function M.init(user_config)
    M.config = {
        debug = false,
        timeout = 30,
        retries = 3
    }
    
    -- Merge with user config
    if user_config then
        for key, value in pairs(user_config) do
            M.config[key] = value
        end
    end
end

function M.get_config(key)
    return M.config[key]
end

-- Auto-initialize if not already done
local initialized = false
local function ensure_initialized()
    if not initialized then
        M.init()
        initialized = true
    end
end

function M.debug(message)
    ensure_initialized()
    if M.config.debug then
        print("[DEBUG]", message)
    end
end

return M

-- math_utils.lua
local M = {}

-- Calculate factorial
function M.factorial(n)
    if n <= 1 then
        return 1
    end
    return n * M.factorial(n - 1)
end

-- Generate Fibonacci sequence
function M.fibonacci(n)
    if n <= 0 then return 0 end
    if n == 1 then return 1 end
    
    local a, b = 0, 1
    for i = 2, n do
        a, b = b, a + b
    end
    return b
end

-- Calculate greatest common divisor
function M.gcd(a, b)
    while b ~= 0 do
        a, b = b, a % b
    end
    return a
end

-- Check if number is prime
function M.is_prime(n)
    if n <= 1 then return false end
    if n <= 3 then return true end
    if n % 2 == 0 or n % 3 == 0 then return false end
    
    local i = 5
    while i * i <= n do
        if n % i == 0 or n % (i + 2) == 0 then
            return false
        end
        i = i + 6
    end
    return true
end

return M

-- file_ops.lua
local M = {}

function M.read_file(path)
    local file = io.open(path, "r")
    if not file then
        error("Cannot open file: " .. path)
    end
    
    local content = file:read("*all")
    file:close()
    return content
end

function M.write_file(path, content)
    local file = io.open(path, "w")
    if not file then
        error("Cannot open file for writing: " .. path)
    end
    
    file:write(content)
    file:close()
end

function M.file_exists(path)
    local file = io.open(path, "r")
    if file then
        file:close()
        return true
    end
    return false
end

function M.get_file_lines(path)
    local lines = {}
    local file = io.open(path, "r")
    if not file then
        return lines
    end
    
    for line in file:lines() do
        table.insert(lines, line)
    end
    
    file:close()
    return lines
end

return M

-- main_app.lua
local math_utils = require("math_utils")
local file_ops = require("file_ops")
local config = require("config")

-- Initialize configuration
config.init({debug = true, timeout = 60})

-- Process some data
local numbers = {5, 10, 15, 20}
local results = {}

for i, num in ipairs(numbers) do
    table.insert(results, {
        original = num,
        factorial = math_utils.factorial(num),
        is_prime = math_utils.is_prime(num)
    })
    
    config.debug("Processed " .. num)
end

-- Save results to file
local json_data = require("json").encode(results)
file_ops.write_file("results.json", json_data)

print("Processing complete. Results saved to results.json")