Lua Session 02: Tables

-- Arrays are 1-indexed!
local hosts = {"kvm-01", "kvm-02", "vault-01"}

print(hosts[1])  -- kvm-01 (NOT hosts[0])
print(hosts[3])  -- vault-01
print(#hosts)    -- 3 (length)

local hosts = {"kvm-01", "kvm-02"}

-- Add to end
table.insert(hosts, "vault-01")

-- Add at position
table.insert(hosts, 1, "gateway")

-- Remove from position
table.remove(hosts, 1)

print(table.concat(hosts, ", "))

local hosts = {"kvm-01", "kvm-02", "vault-01"}

-- ipairs for arrays (ordered, numeric keys)
for i, host in ipairs(hosts) do
    print(i .. ": " .. host)
end

local server = {
    name = "kvm-01",
    ip = "10.50.1.110",
    port = 22,
    active = true
}

-- Dot access for string keys
print(server.name)
print(server.ip)

-- Bracket access (required for special keys)
print(server["port"])

local server = {}

-- Add keys dynamically
server.name = "kvm-01"
server["ip-address"] = "10.50.1.110"  -- Dash requires brackets

-- Variable as key
local key = "vlan"
server[key] = 10

print(server.vlan)  -- 10

local server = {
    name = "kvm-01",
    ip = "10.50.1.110",
    role = "hypervisor"
}

-- pairs for dictionaries (unordered)
for key, value in pairs(server) do
    print(key .. ": " .. tostring(value))
end

local t = {1, 2, nil, 4, 5}

print("ipairs (stops at nil):")
for i, v in ipairs(t) do
    print(i, v)  -- Only prints 1, 2
end

print("pairs (all non-nil):")
for k, v in pairs(t) do
    print(k, v)  -- Prints 1, 2, 4, 5
end

local mixed = {
    "first",           -- [1]
    "second",          -- [2]
    name = "kvm-01",   -- string key
    ip = "10.50.1.110" -- string key
}

print("Array part (ipairs):")
for i, v in ipairs(mixed) do
    print(i, v)  -- 1: first, 2: second
end

print("All keys (pairs):")
for k, v in pairs(mixed) do
    print(k, v)  -- All 4 entries
end

local hosts = {"kvm-01", "kvm-02", "vault-01"}

print(table.concat(hosts, ", "))
-- kvm-01, kvm-02, vault-01

print(table.concat(hosts, "\n"))
-- Each on new line

local numbers = {3, 1, 4, 1, 5, 9}
table.sort(numbers)
print(table.concat(numbers, ", "))  -- 1, 1, 3, 4, 5, 9

-- Custom sort
local hosts = {"vault-01", "kvm-02", "kvm-01"}
table.sort(hosts)
print(table.concat(hosts, ", "))  -- kvm-01, kvm-02, vault-01

-- Sort by field
local servers = {
    {name = "vault", cpu = 45},
    {name = "kvm-01", cpu = 85},
    {name = "kvm-02", cpu = 32}
}
table.sort(servers, function(a, b)
    return a.cpu > b.cpu  -- Descending
end)

-- Lua has no built-in "contains"
local function contains(t, value)
    for _, v in ipairs(t) do
        if v == value then return true end
    end
    return false
end

local hosts = {"kvm-01", "kvm-02"}
print(contains(hosts, "kvm-01"))  -- true
print(contains(hosts, "vault"))   -- false

-- Tables are passed by reference
local function copy(t)
    local new = {}
    for k, v in pairs(t) do
        new[k] = v
    end
    return new
end

local original = {name = "kvm-01", ip = "10.50.1.110"}
local copied = copy(original)
copied.name = "kvm-02"

print(original.name)  -- kvm-01 (unchanged)
print(copied.name)    -- kvm-02