local enable_crash = false
local crash_threshold = 6.5     -- ignored if enable_crash=false

------------------------------------------------------------------------------

local mobs_redo = false
if minetest.get_modpath("mobs") then
    if mobs.mod and mobs.mod == "redo" then
        mobs_redo = true
    end
end

--
-- Helper functions
--

--local function is_group(pos, group)
--  local nn = minetest.get_node(pos).name
--  return minetest.get_item_group(nn, group) ~= 0
--end

local function node_is(pos)
    local node = minetest.get_node(pos)
    if node.name == "air" then
        return "air"
    end
    if minetest.get_item_group(node.name, "liquid") ~= 0 then
        return "liquid"
    end
    if minetest.get_item_group(node.name, "walkable") ~= 0 then
        return "walkable"
    end
    return "other"
end

local function get_sign(i)
    i = i or 0
    if i == 0 then
        return 0
    else
        return i / math.abs(i)
    end
end

local function get_velocity(v, yaw, y)
    local x = -math.sin(yaw) * v
    local z =  math.cos(yaw) * v
    return {x = x, y = y, z = z}
end

local function get_v(v)
    return math.sqrt(v.x ^ 2 + v.z ^ 2)
end

local function force_detach(player)
    local attached_to = player:get_attach()
    if attached_to then
        local entity = attached_to:get_luaentity()
        if entity.driver and entity.driver == player then
            entity.driver = nil
        elseif entity.passenger and entity.passenger == player then
            entity.passenger = nil
        end
        player:set_detach()
        default.player_attached[player:get_player_name()] = false
        player:set_eye_offset({x=0, y=0, z=0}, {x=0, y=0, z=0})
    end
end

-------------------------------------------------------------------------------


minetest.register_on_leaveplayer(function(player)
    force_detach(player)
end)

minetest.register_on_shutdown(function()
    local players = minetest.get_connected_players()
    for i = 1,#players do
        force_detach(players[i])
    end
end)

minetest.register_on_dieplayer(function(player)
    force_detach(player)
    return true
end)

-------------------------------------------------------------------------------


lib_mount = {}

function lib_mount.attach(entity, player, is_passenger)
    local attach_at, eye_offset = {}, {}

    if not entity.player_rotation then
        entity.player_rotation = {x=0, y=0, z=0}
    end

    local rot_view = 0
    if entity.player_rotation.y == 90 then
        rot_view = math.pi/2
    end

    if is_passenger == true then
        if not entity.passenger_attach_at then
            entity.passenger_attach_at = {x=0, y=0, z=0}
        end
        if not entity.passenger_eye_offset then
            entity.passenger_eye_offset = {x=0, y=0, z=0}
        end
        attach_at = entity.passenger_attach_at
        eye_offset = entity.passenger_eye_offset
        entity.passenger = player
    else
        if not entity.driver_attach_at then
            entity.driver_attach_at = {x=0, y=0, z=0}
        end
        if not entity.driver_eye_offset then
            entity.driver_eye_offset = {x=0, y=0, z=0}
        end
        attach_at = entity.driver_attach_at
        eye_offset = entity.driver_eye_offset
        entity.driver = player
    end

    force_detach(player)

    player:set_attach(entity.object, "", attach_at, entity.player_rotation)
    default.player_attached[player:get_player_name()] = true
    player:set_eye_offset(eye_offset, {x=0, y=0, z=0})
    minetest.after(0.2, function()
        default.player_set_animation(player, "sit" , 30)
    end)
    player:set_look_yaw(entity.object:getyaw() - rot_view)
end

function lib_mount.detach(player, offset)
    force_detach(player)
    default.player_set_animation(player, "stand" , 30)
    local pos = player:getpos()
    local pname = player:get_player_name()
if pos == nil then
return
end

    pos = {x = pos.x + offset.x, y = pos.y + 0.2 + offset.y, z = pos.z + offset.z}
    minetest.after(0.1, function()
        player:setpos(pos)
    end)
end

local aux_timer = 0

function lib_mount.drive(entity, dtime, is_mob, moving_anim, stand_anim, jump_height, can_fly)
    aux_timer = aux_timer + dtime

    if can_fly and can_fly == true then
        jump_height = 0
    end

    local rot_steer, rot_view = math.pi/2, 0
    if entity.player_rotation.y == 90 then
        rot_steer, rot_view = 0, math.pi/2
    end

    local acce_y = 0

    local velo = entity.object:getvelocity()
    entity.v = get_v(velo) * get_sign(entity.v)

    -- process controls
    if entity.driver then
        local ctrl = entity.driver:get_player_control()
        if ctrl.aux1 then
            if aux_timer >= 0.2 then
                entity.mouselook = not entity.mouselook
                aux_timer = 0
            end
        end
        if ctrl.up then
            if get_sign(entity.v) >= 0 then
                entity.v = entity.v + entity.accel/10
            else
                entity.v = entity.v + entity.braking/10
            end
        elseif ctrl.down then
            if entity.max_speed_reverse == 0 and entity.v == 0 then return end
            if get_sign(entity.v) < 0 then
                entity.v = entity.v - entity.accel/10
            else
                entity.v = entity.v - entity.braking/10
            end
        end
        if entity.mouselook then
            if ctrl.left then
                entity.object:setyaw(entity.object:getyaw()+get_sign(entity.v)*math.rad(1+dtime)*entity.turn_spd)
            elseif ctrl.right then
                entity.object:setyaw(entity.object:getyaw()-get_sign(entity.v)*math.rad(1+dtime)*entity.turn_spd)
            end
        else
            entity.object:setyaw(entity.driver:get_look_yaw() - rot_steer)
        end
        if ctrl.jump then
            if jump_height > 0 and velo.y == 0 then
                velo.y = velo.y + (jump_height * 3) + 1
                acce_y = acce_y + (acce_y * 3) + 1
            end
            if can_fly and can_fly == true then
                velo.y = velo.y + 1
                acce_y = acce_y + 1
            end
        end
        if ctrl.sneak then
            if can_fly and can_fly == true then
                velo.y = velo.y - 1
                acce_y = acce_y - 1
            end
        end
    end

    -- if not moving then set animation and return
    if entity.v == 0 and velo.x == 0 and velo.y == 0 and velo.z == 0 then
        if is_mob and mobs_redo == true then
            if stand_anim and stand_anim ~= nil then
                set_animation(entity, stand_anim)
            end
        end
        return
    end

    -- set animation
    if is_mob and mobs_redo == true then
        if moving_anim and moving_anim ~= nil then
            set_animation(entity, moving_anim)
        end
    end

    -- Stop!
    local s = get_sign(entity.v)
    entity.v = entity.v - 0.02 * s
    if s ~= get_sign(entity.v) then
        entity.object:setvelocity({x=0, y=0, z=0})
        entity.v = 0
        return
    end

    -- enforce speed limit forward and reverse
    local max_spd = entity.max_speed_reverse
    if get_sign(entity.v) >= 0 then
        max_spd = entity.max_speed_forward
    end
    if math.abs(entity.v) > max_spd then
        entity.v = entity.v - get_sign(entity.v)
    end

    -- Set position, velocity and acceleration
    local p = entity.object:getpos()
    local new_velo = {x=0, y=0, z=0}
    local new_acce = {x=0, y=-9.8, z=0}

    p.y = p.y - 0.5
    local ni = node_is(p)
    local v = entity.v
    if ni == "air" then
        if can_fly == true then
            new_acce.y = 0
        end
    elseif ni == "liquid" then
        if entity.terrain_type == 2 or entity.terrain_type == 3 then
            new_acce.y = 0
            p.y = p.y + 1
            if node_is(p) == "liquid" then
                if velo.y >= 5 then
                    velo.y = 5
                elseif velo.y < 0 then
                    new_acce.y = 20
                else
                    new_acce.y = 5
                end
            else
                if math.abs(velo.y) < 1 then
                    local pos = entity.object:getpos()
                    pos.y = math.floor(pos.y) + 0.5
                    entity.object:setpos(pos)
                    velo.y = 0
                end
            end
        else
            v = v*0.25
        end
--  elseif ni == "walkable" then
--      v = 0
--      new_acce.y = 1
    end

    new_velo = get_velocity(v, entity.object:getyaw() - rot_view, velo.y)
    new_acce.y = new_acce.y + acce_y

    entity.object:setvelocity(new_velo)
    entity.object:setacceleration(new_acce)

    -- CRASH!
    if enable_crash then
        local intensity = entity.v2 - v
        if intensity >= crash_threshold then
            if is_mob then
                entity.object:set_hp(entity.object:get_hp() - intensity)
            else
                if entity.driver then
                    local drvr = entity.driver
                    lib_mount.detach(drvr, {x=0, y=0, z=0})
                    drvr:setvelocity(new_velo)
                    drvr:set_hp(drvr:get_hp() - intensity)
                end
                if entity.passenger then
                    local pass = entity.passenger
                    lib_mount.detach(pass, {x=0, y=0, z=0})
                    pass:setvelocity(new_velo)
                    pass:set_hp(pass:get_hp() - intensity)
                end
                local pos = entity.object:getpos()
                minetest.add_item(pos, entity.drop_on_destroy)
                entity.removed = true
                -- delay remove to ensure player is detached
                minetest.after(0.1, function()
                    entity.object:remove()
                end)
            end
        end
    end

    entity.v2 = v
end