local ffi = require "ffi"

ffi.cdef "int curwin_col_off(void);"

local M = {
    config = {
        char = "┃",
    },
}

M.clear_buf = function(bufnr)
    if M.namespace then
        vim.api.nvim_buf_clear_namespace(bufnr, M.namespace, 0, -1)
    end
end

M.setup = function(config)
    M.config = vim.tbl_deep_extend("force", M.config, config or {})
    M.namespace = vim.api.nvim_create_namespace "virt-column"

    vim.cmd [[command! VirtColumnRefresh lua require("virt-column").refresh()]]
    vim.cmd [[highlight link VirtColumn Whitespace]]
    vim.cmd [[highlight clear ColorColumn]]

    vim.cmd [[
        augroup VirtColumnAutogroup
            autocmd!
            autocmd FileChangedShellPost,TextChanged,TextChangedI,CompleteChanged,BufWinEnter,WinScrolled * VirtColumnRefresh
            autocmd OptionSet colorcolumn VirtColumnRefresh
        augroup END
    ]]
end

M.refresh = function()
    local bufnr = 0
    local win_start = vim.fn.line "w0"
    local win_end = vim.fn.line "w$"
    local offset = math.max(win_start - 11, 0)
    local range = math.min(win_end + 11, vim.api.nvim_buf_line_count(bufnr))
    local lines = vim.api.nvim_buf_get_lines(bufnr, offset, range, false)
    local width = vim.api.nvim_win_get_width(0) - ffi.C.curwin_col_off()
    local textwidth = vim.opt.textwidth:get()
    local colorcolumn = vim.opt.colorcolumn:get()

    for i, c in ipairs(colorcolumn) do
        if vim.startswith(c, "+") then
            colorcolumn[i] = textwidth + tonumber(c:sub(2))
        elseif vim.startswith(c, "-") then
            colorcolumn[i] = textwidth - tonumber(c:sub(2))
        else
            colorcolumn[i] = tonumber(c)
        end
    end

    table.sort(colorcolumn, function(a, b)
        return a > b
    end)

    M.clear_buf()

    for i = 1, #lines, 1 do
        local current_offset = 0
        local virt_text = {}
        for _, column in ipairs(colorcolumn) do
            local line = lines[i]:gsub("\t", string.rep(" ", vim.opt.tabstop:get()))
            if width > column and vim.api.nvim_strwidth(line) < column then
                table.insert(virt_text, 1, { string.rep(" ", width - column - current_offset) })
                table.insert(virt_text, 1, { M.config.char, "VirtColumn" })
                current_offset = width - column + 1
            end
        end
        if #virt_text > 0 then
            vim.api.nvim_buf_set_extmark(bufnr, M.namespace, i - 1 + offset, 0, {
                virt_text = virt_text,
                virt_text_pos = "right_align",
                hl_mode = "combine",
            })
        end
    end
end

return M