people/actions/buy_and_sell.lua

local dbg
if moddebug then dbg=moddebug.dbg("people") else dbg={v1=function() end,v2=function() end,v3=function() end} end

-- Find a shop in range of the given position that's dealing in the
-- item specified. If 'buy' is true, we want to buy, otherwise we
-- want to sell. Returns shopinfo. (or nil)
local function near_shop(pos, item, buy)
    local range = {x=4, y=2, z=4}
    local minp = vector.subtract(pos, range)
    local maxp = vector.add(pos, range)
    local shops = minetest.find_nodes_in_area(minp, maxp, {"barrel:shop_barrel"})
    for _, p in pairs(shops) do
        local shopinfo = barrel.get_shopinfo(p)
        if shopinfo and shopinfo.item == item then
            if buy then
                if shopinfo.saleunit > 0 and
                    shopinfo.price > 0 and
                    shopinfo.stock >= shopinfo.saleunit then
                    return shopinfo
                end
            else
                if shopinfo.saleunit > 0 and
                    shopinfo.buyprice > 0 then
                    return shopinfo
                end
            end
        end
    end
    return nil

end

local function move_all(srcinv, srclist, destinv, destlist, item)
    local moved_all = true
    local moved_num = 0
    for i=1,srcinv:get_size(srclist) do
        local stk = srcinv:get_stack(srclist, i)
        if not item or stk:get_name() == item then
            if destinv:room_for_item(destlist, stk) then
                moved_num = moved_num + stk:get_count()
                srcinv:set_stack(srclist, i, nil)
                destinv:add_item(destlist, stk)
            else
                moved_all = false
            end
        end
    end
    return moved_all, moved_num
end


people.actions.buy = function(state)
    if not (state.action.item or state.action.num) then
        dbg.v1(state.ent.name.." has invalid buy action")
        return true, false
    end

    local shopinfo = near_shop(state.pos, state.action.item, true)
    if not shopinfo then
        dbg.v1(state.ent.name.." is not near an appropriate shop")
        return true, false
    end

    local yaw = vector.get_yaw(state.pos, shopinfo.pos)
    -- Need to be fuzzy about comparing this, because of the
    -- lua double/minetest float issue
    if math.abs(yaw - state.yaw) > 0.2 then
        dbg.v3(state.ent.name.." turning to face shop")
        state.action = {"face", yaw=yaw, prevaction=state.action}
        return false
    end

    local shopinv = shopinfo.meta:get_inventory()
    local repeats = math.ceil(state.action.num / shopinfo.saleunit)
    local cashneeded = repeats * shopinfo.price

    dbg.v3(state.ent.name.." trying to put $"..cashneeded.." into shop")
    if not currency.remove_from_inv(state.ent.inventory, "main", cashneeded) then
        dbg.v1(state.ent.name.." doesn't have enough money to buy")
        return true, false
    end
    -- TODO - the following just assumes there's room for it - really need
    --        to check and roll back, as we do for getting money
    currency.put_to_inv(shopinv, "exchange", cashneeded)

    local bought = 0
    while repeats > 0 do
        local success, msg = barrel.do_buy(shopinfo.pos)
        if not success then
            dbg.v3(state.ent.name.." failed during buy loop - shop said: "..msg)
            break
        end
        bought = bought + shopinfo.saleunit
        repeats = repeats - 1
    end

    if not move_all(shopinv, "exchange", state.ent.inventory, "main", nil) then
        dbg.v1(state.ent.name.." couldn't retrieve everything from shop inventory")
    end

    dbg.v1(state.ent.name.." finished buy action - bought "..bought.." "..state.action.item)
    return true, true
end

people.actions.sell = function(state)
    if not state.action.item then
        dbg.v1(state.ent.name.." has invalid sell action")
        return true, false
    end

    local shopinfo = near_shop(state.pos, state.action.item, false)
    if not shopinfo then
        dbg.v1(state.ent.name.." is not near an appropriate shop")
        return true, false
    end

    local yaw = vector.get_yaw(state.pos, shopinfo.pos)
    -- Need to be fuzzy about comparing this, because of the
    -- lua double/minetest float issue
    if math.abs(yaw - state.yaw) > 0.2 then
        dbg.v3(state.ent.name.." turning to face shop")
        state.action = {"face", yaw=yaw, prevaction=state.action}
        return false
    end

    local shopinv = shopinfo.meta:get_inventory()
    local moved_all, num = move_all(state.ent.inventory, "main",
        shopinv, "exchange", state.action.item)
    if num == 0 then
        dbg.v1(state.ent.name.." failed to put any "..state.action.item.." for sale into the shop")
        return true, false
    end
    local repeats = math.floor(num / shopinfo.saleunit)

    while repeats > 0 do
        if not barrel.do_sell(shopinfo.pos) then break end
        repeats = repeats - 1
    end

    if not move_all(shopinv, "exchange", state.ent.inventory, "main") then
        dbg.v1(state.ent.name.." couldn't retrieve everything from shop inventory")
    end

    dbg.v1(state.ent.name.." finished sell action")
    return true, true
end