global.player_spawns = {} -- player_index to spawn_name
global.spawns = {} -- spawn_name to x, y, player_online_count

function add_spawn(name, x, y)
    if type(name) ~= "string" then
        game.print("name must be a string")
        return
    end

    if type(x) ~= "number" then
        game.print("x must be a number")
        return
    end

    if type(y) ~= "number" then
        game.print("y must be a number")
        return
    end
    
    global.spawns[name] = { x = x, y = y, count = 0}
end

local function get_min_count_spawn_name()
    local min = 1000000
    local min_spawn = nil

    for name, t in pairs(global.spawns) do
        local count = t.count
        if min > count then
            min = count
            min_spawn = name            
        end
    end

    return min_spawn
end

local function player_joined_game(event)
    local index = event.player_index
    local spawn_name = global.player_spawns[index] 
    
    -- player already has a spawn.
    if spawn_name then
        local spawn = global.spawns[spawn_name]
        local count = spawn.count
        spawn.count = count + 1
        return
    end
    
    spawn_name = get_min_count_spawn_name()    

    if not spawn_name then                
        return
    end   

    local spawn = global.spawns[spawn_name]
    global.player_spawns[index] = spawn_name
    game.players[index].teleport(spawn)  
    
    local count = spawn.count
    spawn.count = count + 1
end

local function player_left_game(event)
    local index = event.player_index
    local spawn_name = global.player_spawns[index]
    local spawn = global.spawns[spawn_name]

    if not spawn then
        return
    end

    local count = spawn.count
    spawn.count = count - 1
end

local function player_respawned(event)
    local index = event.player_index
    local spawn_name = global.player_spawns[index]
    local spawn = global.spawns[spawn_name]    

    if not spawn then        
        return
    end
    
    game.players[index].teleport(spawn)   
end

local function tp_spawn(player_name, spawn_name)
    local player = game.players[player_name]
    if not player then
        player_name = player_name or ""
        game.player.print("player " .. player_name .. " does not exist.")
        return
    end

    local spawn = global.spawns[spawn_name]
    if not spawn then
        spawn_name = spawn_name or ""
        game.player.print("spawn " .. spawn_name .. " does not exist.")
        return
    end    
    
    player.teleport(spawn)
end

local function change_spawn(player_name, spawn_name)
    local new_spawn = global.spawns[spawn_name]

    if not new_spawn then
        spawn_name = spawn_name or ""
        game.player.print("spawn " .. spawn_name .. " does not exist.")
        return
    end

    local player = game.players[player_name]

    if not player then
        player_name = player_name or ""
        game.player.print("player " .. player_name .. " does not exist.")
        return
    end

    local index = player.index
    local old_spawn_name = global.player_spawns[index]
    local old_spawn = global.spawns[old_spawn_name]

    if old_spawn then
        local count = old_spawn.count
        old_spawn.count = count - 1
    end

    local count = new_spawn.count
    new_spawn.count = count + 1

    global.player_spawns[index] = spawn_name

    game.player.print(player_name .. " spawn moved to " .. spawn_name)
end

local function print_spawns()
    local str = ""
    for name, spawn in pairs(global.spawns) do
        str = str .. name .. ": (" .. spawn.x .. ", " .. spawn.y .. "), player count = " .. spawn.count .. "\n\r"
    end

    game.player.print(str)
end

local function print_players_for_spawn(target_spawn_name)
    if not global.spawns[target_spawn_name] then
        target_spawn_name = target_spawn_name or ""
        game.player.print("spawn " .. target_spawn_name .. " does not exist.")
        return
    end

    str = ""
    for index, spawn_name in pairs(global.player_spawns) do
        if target_spawn_name == spawn_name then
            local player = game.players[index]
            if player.connected then
                str = str .. player.name .. ", "
            end
        end
    end

    if str == "" then
        str = "no players"
    end
    game.player.print(str)
end

local function tp_spawn_command(cmd)
    if not game.player.admin then
      cant_run(cmd.name)
      return
    end

    local params = cmd.parameter
    if type(params) ~= "string" then
        game.player.print("Command failed. Usage: /tpspawn <player>, <spawn_name>")
        return
    end

    local ps ={}
    for p in params:gmatch("%S+") do
        table.insert( ps,p )
    end

    if #ps == 1 then
        tp_spawn(game.player.name, ps[1])
    else
        tp_spawn(ps[1], ps[2])    
    end
end

function change_spawn_command(cmd)
    if not game.player.admin then
      cant_run(cmd.name)
      return
    end

    local params = cmd.parameter
    if type(params) ~= "string" then
        game.player.print("Command failed. Usage: /changespawn <player>, <spawn_name>")
        return
    end

    local ps ={}
    for p in params:gmatch("%S+") do
        table.insert( ps,p )
    end

    change_spawn(ps[1], ps[2]) 
end

local function print_spawns_command(cmd)
    if not game.player.admin then
      cant_run(cmd.name)
      return
    end

    print_spawns()
end

local function print_players_for_spawn_command(cmd)
    if not game.player.admin then
      cant_run(cmd.name)
      return
    end

    local params = cmd.parameter
    if type(params) ~= "string" then
        game.player.print("Command failed. Usage: /playersforspawn <spawn_name>")
        return
    end

    local ps ={}
    for p in params:gmatch("%S+") do
        table.insert( ps,p )
    end

    print_players_for_spawn(ps[1])
end

Event.register(defines.events.on_player_joined_game, player_joined_game)
Event.register(defines.events.on_player_left_game, player_left_game)
Event.register(defines.events.on_player_respawned, player_respawned)

commands.add_command("tpspawn", "<player> <spawn_name> teleports a player to the spawn point (Admins only)", tp_spawn_command)
commands.add_command("changespawn", "<player> <spawn_name> changes the spawn point for a player (Admins only)", change_spawn_command)
commands.add_command("printspawns", "prints info on all spawn points (Admins only)", print_spawns_command)
commands.add_command("printplayersforspawn", "<spawn_name> prints all the connected players for a spawn (Admins only)", print_players_for_spawn_command)