---@class RequiredAmount
---@field defined_by "amount" | "belts" | "lanes"
---@field amount number
---@field belt_proto FPBeltPrototype

---@class FPItem
---@field proto FPItemPrototype
---@field amount number
---@field required_amount RequiredAmount
---@field satisfied_amount number
---@field top_level boolean
---@field valid boolean
---@field id integer
---@field gui_position integer
---@field parent FPSubfactory | FPLine
---@field class "Product" | "Byproduct" | "Ingredient"

-- 'Class' representing an item in the general sense
Item = {}
Product, Byproduct, Ingredient = Item, Item, Item  -- allows _G[class] to work for all items

-- Initialised by passing a prototype from the all_items global table
-- This is set up as a top-level item if a required_amount is given
function Item.init(proto, class, amount, required_amount)
    -- Special case for non-product top level items
    if required_amount == 0 then required_amount = {defined_by="amount", amount=0} end

    return {
        proto = proto,
        amount = amount or 0,  -- produced amount
        required_amount = required_amount,  -- is a table
        satisfied_amount = 0,  -- used with ingredient satisfaction
        top_level = (required_amount ~= nil),
        valid = true,
        id = nil,  -- set by collection
        gui_position = nil,  -- set by collection
        parent = nil,  -- set by parent
        class = class
    }
end


-- Returns the converted numeric required_amount for this (top level) item
function Item.required_amount(self)
    local req_amount = self.required_amount
    if req_amount.defined_by == "amount" then
        return req_amount.amount
    else  -- defined_by == "belts"/"lanes"
        -- If this is defined by lanes, only half of the throughput of a full belt needs to be considered
        local multiplier = (req_amount.defined_by == "belts") and 1 or 0.5
        local timescale = self.parent.timescale
        return req_amount.amount * (req_amount.belt_proto.throughput * multiplier) * timescale
    end
end


function Item.paste(self, object)  -- this is implicitly only called on top level items
    if object.class == "Product" or object.class == "Byproduct"
            or object.class == "Ingredient" or object.class == "Fuel" then
        local existing_item = Subfactory.get_by_name(self.parent, self.class, object.proto.name)
        -- Avoid duplicate items, but allow pasting over the same item proto
        if existing_item and existing_item.proto.name == object.proto.name
         and not (self.proto.name == object.proto.name) then
            return false, "already_exists"
        end

        -- Convert object into the appropriate top-level form if necessary
        if not (object.top_level and object.class == self.class) then
            local required_amount = {defined_by = "amount", amount = object.amount}
            object = Item.init(object.proto, self.class, 0, required_amount)
        end

        -- Detect when this is called on a fake item and add instead of replacing
        if not self.amount then Subfactory.add(self.parent, object)
        else Subfactory.replace(self.parent, self, object) end
        return true, nil

    elseif object.class == "Line" then
        local relevant_line = (object.subfloor) and object.subfloor.defining_line or object
        for _, product in pairs(Line.get_in_order(relevant_line, "Product")) do
            local fake_item = {proto={name=""}, parent=self.parent, class=self.class}
            Item.paste(fake_item, product)  -- avoid duplicating existing items
        end

        local top_floor = Subfactory.get(self.parent, "Floor", 1)  -- line count can be 0
        if object.subfloor then  -- if the line has a subfloor, paste its contents on the top floor
            local fake_line = {parent=top_floor, class="Line", gui_position=top_floor.Line.count}
            for _, line in pairs(Floor.get_in_order(object.subfloor, "Line")) do
                Line.paste(fake_line, line)
                fake_line.gui_position = fake_line.gui_position + 1
            end
        else  -- if the line has no subfloor, just straight paste it onto the top floor
            local fake_line = {parent=top_floor, class="Line", gui_position=top_floor.Line.count}
            Line.paste(fake_line, object)
        end
        return true, nil
    else
        return false, "incompatible_class"
    end
end


function Item.pack(self)
    return {
        proto = prototyper.util.simplify_prototype(self.proto, self.proto.type),
        amount = self.amount,  -- conserve for cloning non-product items
        required_amount = (self.top_level) and {
            defined_by = self.required_amount.defined_by,
            amount = self.required_amount.amount,
            belt_proto = (self.required_amount.defined_by ~= "amount")
                and prototyper.util.simplify_prototype(self.required_amount.belt_proto, nil)
        } or nil,
        top_level = self.top_level,
        class = self.class
    }
end

function Item.unpack(packed_self)
    return packed_self
end


-- Needs validation: proto, required_amount
function Item.validate(self)
    self.proto = prototyper.util.validate_prototype_object(self.proto, "type")
    self.valid = (not self.proto.simplified)

    -- Validate the belt_proto if the item proto is still valid, ie not simplified
    local req_amount = self.required_amount
    if req_amount and req_amount.defined_by ~= "amount" then
        local belt_throughput = req_amount.belt_proto.throughput
        req_amount.belt_proto = prototyper.util.validate_prototype_object(req_amount.belt_proto, nil)
        self.valid = (not req_amount.belt_proto.simplified) and self.valid

        -- If the proto has to be simplified, conserve the throughput, so repair can convert it to an amount-spec
        if req_amount.belt_proto.simplified then req_amount.belt_proto.throughput = belt_throughput end
    end

    return self.valid
end

-- Needs repair: required_amount
-- This will only be called on top level items, so they can be treated as such
function Item.repair(self, _)
    -- If the item-proto is still simplified, validate couldn't repair it, so it has to be removed
    if self.proto.simplified then return false end

    -- If the item is fine, the belt_proto has to be the things that is invalid. Thus, we will repair
    -- this item by converting it to be defined by amount, so it can be preserved in some form
    self.required_amount = {
        defined_by = "amount",
        amount = Item.required_amount(self)
    }
    self.valid = true

    return self.valid
end