--- Style helpers for HTML parser: width calculation and attribute copying.
--- Uses global `tex` and `math` like the legacy code.
local M = {}

---@class HtmlStyles
---@field calculated_width number
---@field width string|number|nil
---@field height string|number|nil
---@field fontsize_sp number
---@field rootfontsize_sp number
---@field lineheight_sp number
---@field color string|nil

---Recompute styles.calculated_width based on CSS-like width and box extras.
---@param styles HtmlStyles
---@return nil
function M.set_calculated_width(styles)
    local sw = styles.width or "auto"
    local cw = styles.calculated_width

    if type(sw) == "string" and string.match(sw, "%%$") then
        local amount = string.match(sw, "(%d+)%%$")
        cw = math.round(cw * tonumber(amount) / 100, 0)
    elseif type(sw) == "string" and string.match(sw, "em$") then
        local amount = string.match(sw, "(%d+)em$")
        cw = math.round(styles.fontsize_sp * tonumber(amount), 0)
    elseif sw == "auto" then
        cw = styles.calculated_width

        if styles.height and styles.height ~= "auto" then
            styles.height = tex.sp(styles.height)
        else
            styles.height = nil
        end

        ---Subtract a TeX length field from cw if present.
        ---@param key string
        local function sub_len(key)
            local v = styles[key]
            if v then cw = cw - tex.sp(v) end
        end

        sub_len("padding-left"); sub_len("padding-right")
        sub_len("margin-left"); sub_len("margin-right")
        sub_len("border-left-width"); sub_len("border-right-width")
    elseif tonumber(sw) then
        cw = tex.sp(string.format("%spx", sw))
    elseif type(sw) == "string" and tex.sp(sw) then
        cw = tex.sp(sw)
    end

    styles.calculated_width = cw
end

---Copy (inline-)style attributes into styles table and post-process line-height & width.
---@param styles HtmlStyles
---@param attributes table<string, any>
---@param elementname string|nil
---@return nil
function M.copy_attributes(styles, attributes, elementname)

    local remember_currentcolor ---@type string[]
    remember_currentcolor = {}

    for k, v in pairs(attributes) do
        if k == "font-size" then
            if type(v) == "string" and string.match(v, "rem$") then
                local amount = string.gsub(v, "^(.*)rem$", "%1")
                styles.fontsize_sp = math.round(styles.rootfontsize_sp * amount)
            elseif type(v) == "string" and string.match(v, "em$") then
                local amount = string.gsub(v, "^(.*)em$", "%1")
                styles.fontsize_sp = math.round(styles.fontsize_sp * amount)
            elseif type(v) == "string" and string.match(v, "%d+%%$") then
                local amount = string.match(v, "(%d+)%%$")
                styles.fontsize_sp = math.round(styles.fontsize_sp * tonumber(amount) / 100, 0)
            elseif v == "small" then
                styles.fontsize_sp = math.round(styles.fontsize_sp * 0.8)
            else
                styles.fontsize_sp = tex.sp(v)
            end
        elseif k == "width" then
            styles.width = v
            M.set_calculated_width(styles)
        end

        if v == "currentcolor" then
            remember_currentcolor[#remember_currentcolor + 1] = k
        end

        styles[k] = v
    end

    -- Resolve "currentcolor" after color has possibly been set above.
    for i = 1, #remember_currentcolor do
        styles[remember_currentcolor[i]] = styles.color
    end

    -- line-height post-processing
    local lh = attributes["line-height"]
    if lh then
        if lh == "normal" then
            styles.lineheight_sp = 1.2 * styles.fontsize_sp
        elseif tonumber(lh) then
            styles.lineheight_sp = styles.fontsize_sp * tonumber(lh)
        else
            styles.lineheight_sp = tex.sp(lh)
        end
    end
end

return M
