local embed_create_ctx_mt = {}

function embed_create_ctx_mt:__index(key)
    -- rawget ensures we don't do recursion
    local form = rawget(self, "_flow_embed_parent_form")
    local prefix = rawget(self, "_flow_embed_prefix")
    return form[prefix .. key]
end

function embed_create_ctx_mt:__newindex(key, value)
    local form = rawget(self, "_flow_embed_parent_form")
    local prefix = rawget(self, "_flow_embed_prefix")
    form[prefix .. key] = value
end

local function embed_create_ctx(ctx, name, prefix)
    if not ctx[name] then
        ctx[name] = {}
    end
    if not ctx[name].form then
        ctx[name].form = {}
    end
    if getmetatable(ctx[name].form) ~= embed_create_ctx_mt then
        ctx[name].form._flow_embed_prefix = prefix
        ctx[name].form._flow_embed_parent_form = ctx.form
        ctx[name].form = setmetatable(ctx[name].form, embed_create_ctx_mt)
    end
    return ctx[name]
end

local function embed_wrap_callback_func(func, name, prefix)
    return function(player, ctx)
        return func(player, embed_create_ctx(ctx, name, prefix))
    end
end

local function embed_add_prefix(node, name, prefix)
    if node.type == "style" and node.selectors then
        -- Add prefix to style[] selectors
        for i, selector in ipairs(node.selectors) do
            node.selectors[i] = prefix .. selector
        end
    elseif node.type == "scroll_container" and node.scrollbar_name then
        node.scrollbar_name = prefix .. node.scrollbar_name
    elseif node.type == "tooltip" and node.gui_element_name then
        node.gui_element_name = prefix .. node.gui_element_name
    end

    -- Add prefix to all names
    if node.name then
        node.name = prefix .. node.name
    end

    -- Wrap callback functions
    if node.on_event then
        node.on_event = embed_wrap_callback_func(node.on_event, name, prefix)
    end
    if node.on_quit then
        node.on_quit = embed_wrap_callback_func(node.on_quit, name, prefix)
    end

    -- Recurse to child nodes
    for _, child in ipairs(node) do
        embed_add_prefix(child, name, prefix)
    end
end

-- TODO: Unit test this
local change_ctx = ...

return function(self, fields)
    local player = fields.player
    local name = fields.name
    -- TODO: It might be cool to somehow pass elements down (number-indexes
    -- of fields) into the child form, but I'm not sure how that would look
    -- on the form definition side.
    -- Perhaps passing it in via the context, or an extra arg to _build?
    local parent_ctx = flow.get_context()
    if name == nil then
        -- Don't prefix anything if name is unspecified
        return self._build(player, parent_ctx)
    end

    local prefix = "\2" .. name .. "\2"
    local child_ctx = embed_create_ctx(parent_ctx, name, prefix)
    change_ctx(child_ctx)
    local root_node = self._build(player, child_ctx)
    change_ctx(parent_ctx)

    embed_add_prefix(root_node, name, prefix)
    return root_node
end