garrysmod-coop/gamemode/maprotation.lua

local changeDelay = CreateConVar(
    "gc_mapchangedelay",
    "8",
    FCVAR_ARCHIVE,
    "Seconds between map completion and loading the next coop map"
)

local maxMapTime = CreateConVar(
    "gc_mapmaxtime",
    "3600",
    FCVAR_ARCHIVE,
    "Maximum map time in seconds before rotating; 0 disables the time limit"
)

local skipVoteRatio = CreateConVar(
    "gc_mapskipvoteratio",
    "0.6",
    FCVAR_ARCHIVE,
    "Fraction of connected human players required to skip the current map"
)

local nextMapVoteRatio = CreateConVar(
    "gc_nextmapvoteratio",
    "0.6",
    FCVAR_ARCHIVE,
    "Fraction of connected human players required to select the next map"
)

local skipChangeDelay = CreateConVar(
    "gc_mapskipchangedelay",
    "3",
    FCVAR_ARCHIVE,
    "Seconds between a successful player skip vote and changing map"
)

local changeQueued = false
local skipVotes = {}
local nextMapVotes = {}
local nextMapChoices = {}
local nextMapVoteFinished = false
local installedMaps

local function RefreshInstalledMaps()
    installedMaps = {}
    for _, fileName in ipairs(file.Find("maps/*.bsp", "GAME")) do
        installedMaps[string.lower(string.StripExtension(fileName))] = true
    end
end

local function MapExists(mapName)
    if not mapName or mapName == "" then return false end
    if not installedMaps then RefreshInstalledMaps() end
    return installedMaps[string.lower(string.StripExtension(mapName))] == true
end

local function SetFreshNextLevel()
    local nextLevel = GetConVar("nextlevel"):GetString()
    if nextLevel == "" or not MapExists(nextLevel) or string.lower(nextLevel) == string.lower(game.GetMap()) then
        nextLevel = NextRandomLevel()
    end
    return nextLevel
end

local function PlayerVoteID(ply)
    local steamID64 = ply:SteamID64()
    if steamID64 and steamID64 ~= "" then return steamID64 end
    return "user:" .. tostring(ply:UserID())
end

local function RequiredVotes(ratioConVar)
    local humanCount = #player.GetHumans()
    local ratio = math.Clamp(ratioConVar:GetFloat(), 0.1, 1)
    return math.max(math.ceil(humanCount * ratio), 1)
end

local function BuildNextMapChoices()
    local candidates = {}
    local currentMap = string.lower(game.GetMap())

    for _, mapName in ipairs(GetInstalledCoopLevels()) do
        if mapName ~= currentMap then
            candidates[#candidates + 1] = mapName
        end
    end

    for index = #candidates, 2, -1 do
        local other = math.random(index)
        candidates[index], candidates[other] = candidates[other], candidates[index]
    end

    nextMapChoices = {}
    local plannedMap = SetFreshNextLevel()
    if plannedMap then
        nextMapChoices[1] = string.lower(plannedMap)
    end

    for _, mapName in ipairs(candidates) do
        if #nextMapChoices >= 5 then break end
        if not table.HasValue(nextMapChoices, mapName) then
            nextMapChoices[#nextMapChoices + 1] = mapName
        end
    end
end

local function ShowNextMapChoices(ply)
    if #nextMapChoices == 0 then BuildNextMapChoices() end

    if #nextMapChoices == 0 then
        ply:ChatPrint("[CO-OP] No alternative installed co-op map is available.")
        return
    end

    ply:ChatPrint("[CO-OP] Vote for the map that should follow this one:")
    for index, mapName in ipairs(nextMapChoices) do
        ply:ChatPrint(string.format("[CO-OP] %d. %s", index, mapName))
    end
    ply:ChatPrint("[CO-OP] Type !votenext <number>. Type !skip if this map is stuck.")
end

local function ResolveNextMapChoice(requestedChoice)
    local choiceNumber = tonumber(requestedChoice)
    if choiceNumber then
        return nextMapChoices[math.floor(choiceNumber)]
    end

    local normalizedChoice = string.lower(string.Trim(requestedChoice or ""))
    for _, mapName in ipairs(nextMapChoices) do
        if normalizedChoice == mapName then return mapName end
    end
end

local function CastNextMapVote(ply, requestedChoice)
    if nextMapVoteFinished then
        ply:ChatPrint("[CO-OP] The next map has already been selected: " .. GetConVar("nextlevel"):GetString())
        return
    end

    local mapName = ResolveNextMapChoice(requestedChoice)
    if not mapName then
        ply:ChatPrint("[CO-OP] That is not one of the current choices.")
        ShowNextMapChoices(ply)
        return
    end

    nextMapVotes[PlayerVoteID(ply)] = mapName

    local votesForMap = 0
    for _, connectedPlayer in ipairs(player.GetHumans()) do
        if nextMapVotes[PlayerVoteID(connectedPlayer)] == mapName then
            votesForMap = votesForMap + 1
        end
    end

    local required = RequiredVotes(nextMapVoteRatio)
    PrintMessage(HUD_PRINTTALK, string.format(
        "%s voted for %s as the next map (%d/%d).",
        ply:Nick(), mapName, votesForMap, required
    ))

    if votesForMap < required then return end

    nextMapVoteFinished = true
    RunConsoleCommand("nextlevel", mapName)
    PrintMessage(HUD_PRINTTALK, "Next map selected: " .. mapName)
end

local function CountCurrentSkipVotes()
    local connectedPlayers = {}
    for _, ply in ipairs(player.GetHumans()) do
        connectedPlayers[PlayerVoteID(ply)] = true
    end

    local count = 0
    for voterID in pairs(skipVotes) do
        if connectedPlayers[voterID] then
            count = count + 1
        else
            skipVotes[voterID] = nil
        end
    end
    return count
end

local function CheckSkipVote()
    if changeQueued then return end

    local voteCount = CountCurrentSkipVotes()
    if voteCount >= RequiredVotes(skipVoteRatio) then
        QueueCoopMapChange("player skip vote")
    end
end

local function CastSkipVote(ply)
    if changeQueued then
        ply:ChatPrint("[CO-OP] A map change is already on its way.")
        return
    end

    local voterID = PlayerVoteID(ply)
    if skipVotes[voterID] then
        ply:ChatPrint("[CO-OP] You have already voted to skip this map.")
        return
    end

    skipVotes[voterID] = true
    local voteCount = CountCurrentSkipVotes()
    local required = RequiredVotes(skipVoteRatio)
    PrintMessage(HUD_PRINTTALK, string.format(
        "%s voted to skip this map (%d/%d). Type !skip to vote.",
        ply:Nick(), voteCount, required
    ))
    CheckSkipVote()
end

function QueueCoopMapChange(reason, requestedMap)
    if changeQueued then return end

    local destination = requestedMap and string.lower(requestedMap) or nil
    if not MapExists(destination) or destination == string.lower(game.GetMap()) then
        destination = SetFreshNextLevel()
    end

    if not destination then
        ErrorNoHalt("[custom_coop] Map completed, but no installed destination map is available\n")
        return
    end

    changeQueued = true
    local delay = reason == "player skip vote"
        and math.max(skipChangeDelay:GetFloat(), 0)
        or math.max(changeDelay:GetFloat(), 0)
    PrintMessage(HUD_PRINTTALK, "Loading " .. destination .. " in " .. math.ceil(delay) .. " seconds.")
    print("[custom_coop] Map change queued by " .. (reason or "unknown") .. ": " .. destination)

    timer.Create("CustomCoopChangeCompletedMap", delay, 1, function()
        RunConsoleCommand("changelevel", destination)
    end)
end

hook.Add("PlayerSay", "CustomCoopMapVoting", function(ply, text)
    local command = string.lower(string.Trim(text or ""))

    if command == "!skip" or command == "/skip" or command == "!skipmap" then
        CastSkipVote(ply)
        return ""
    end

    if command == "!nextmap" or command == "/nextmap"
        or command == "!votenext" or command == "/votenext" then
        ShowNextMapChoices(ply)
        return ""
    end

    local requestedChoice = string.match(command, "^[!/]votenext%s+(.+)$")
    if requestedChoice then
        CastNextMapVote(ply, requestedChoice)
        return ""
    end
end)

hook.Add("PlayerInitialSpawn", "CustomCoopExplainMapVoting", function(ply)
    timer.Simple(6, function()
        if not IsValid(ply) then return end
        ply:ChatPrint("[CO-OP] Type !nextmap to vote for what comes next, or !skip if the current map is stuck.")
    end)
end)

hook.Add("PlayerDisconnected", "CustomCoopRecountMapSkipVote", function()
    timer.Simple(0, CheckSkipVote)
end)

hook.Add("AcceptInput", "CustomCoopDetectMapCompletion", function(ent, inputName, _, _, value)
    if not IsValid(ent) then return end

    local className = string.lower(ent:GetClass())
    local input = string.lower(inputName or "")

    if className == "game_end" and input == "endgame" then
        QueueCoopMapChange("game_end")
        return true
    end

    if className ~= "point_servercommand" or input ~= "command" then return end

    local command = string.lower(string.Trim(tostring(value or "")))
    local requestedMap = string.match(command, "^changelevel%s+[%\"]?([%w_%-%[%]!]+)")
        or string.match(command, "^map%s+[%\"]?([%w_%-%[%]!]+)")

    if requestedMap and (not MapExists(requestedMap) or string.lower(requestedMap) == string.lower(game.GetMap())) then
        QueueCoopMapChange("point_servercommand", requestedMap)
        return true
    end
end)

-- Repair old trigger_changelevel/point_changelevel entities that refer to a map
-- which is not mounted. Valid campaign destinations remain untouched.
hook.Add("EntityKeyValue", "CustomCoopRepairChangelevelTargets", function(ent, key, value)
    local className = string.lower(ent:GetClass())
    if className ~= "trigger_changelevel" and className ~= "point_changelevel" then return end
    if string.lower(key or "") ~= "map" then return end
    if MapExists(value) and string.lower(value) ~= string.lower(game.GetMap()) then return end

    local replacement = GetRandomLevel()
    if replacement then
        print("[custom_coop] Replacing unavailable changelevel target '" .. tostring(value) .. "' with " .. replacement)
        return replacement
    end
end)

hook.Add("InitPostEntity", "CustomCoopStartMapTimeLimit", function()
    SetFreshNextLevel()
    BuildNextMapChoices()

    local limit = maxMapTime:GetFloat()
    if limit <= 0 then return end

    timer.Create("CustomCoopMapTimeLimit", limit, 1, function()
        QueueCoopMapChange("time limit")
    end)
end)