feat: Terminal buffer keymap help (#64)

This sets up a base where the keymap g? shows a help buffer displaying the normal mode keymaps available.

lua/jj/ui/terminal.lua

@@ -50,6 +50,78 @@ function M.setup(user_opts)
 	opts = vim.tbl_deep_extend("force", opts, user_opts or {})
 end
 
+--- Help for terminal buffer
+function M.keymap_help()
+    -- get the normal mode keys defined for the current buffer
+    local keys = vim.api.nvim_buf_get_keymap(0, "n")
+
+    -- sort the keys table by desc
+    table.sort(keys, function(a, b) return (a.desc or "") < (b.desc or "") end)
+
+    -- Figure out the width of the longest key for later formatting
+    -- Ignore keys for entries without a desc
+    local max_key_width = 0
+    for _, mapping in ipairs(keys) do
+      local desc = mapping["desc"]
+      if desc ~= nil then
+        local key = mapping["lhs"]
+        local key_width = vim.api.nvim_strwidth(key)
+        if key_width > max_key_width then
+          max_key_width = key_width
+        end
+      end
+    end
+
+    -- create a buffer and floating window to show the key mappings
+    local buf, win = buffer.create_float({
+        title = " Key mappings ",
+        title_pos = "left",
+		enter = true,
+		bufhidden = "hide",
+		win_options = {
+			wrap = true,
+			number = false,
+			relativenumber = false,
+			cursorline = false,
+			signcolumn = "no",
+		},
+    })
+
+    -- helper function to pad a given key with spaces if necessary such that
+    -- its size will match max_key_width calculated above.
+    local function space_pad(key)
+      local key_width = vim.api.nvim_strwidth(key)
+      local delta = max_key_width - key_width
+      if delta > 0 then
+        return key .. string.rep(" ", delta)
+      end
+      return key
+    end
+
+    -- create formated entries for items with a non-nil desc
+    local lines = {}
+    for _, entry in ipairs(keys) do
+      if entry["desc"] ~= nil then
+        local line = string.format("  %s   %s",
+                                   space_pad(entry["lhs"]),
+                                   entry["desc"])
+        table.insert(lines, line)
+      end
+
+    end
+
+    -- add some helper text at the end
+    table.insert(lines, "")
+    table.insert(lines, '   Use "q" or ESC to close this window')
+
+    -- add the formatted lines to the buffer
+    vim.api.nvim_buf_set_lines(buf, 3, -1, false, lines)
+
+    -- Use q or ESC to close the buffer
+    vim.keymap.set("n", "q", "<cmd>close<CR>", { buffer = buf })
+    vim.keymap.set("n", "<Esc>", "<cmd>close<CR>", { buffer = buf })
+end
+
 --- Close the current terminal buffer if it exists
 function M.close_terminal_buffer()
 	buffer.close(state.buf)
@@ -338,6 +410,7 @@ function M.run(cmd, keymaps)
 	-- Set base keymaps only if they haven't been set for this buffer yet
 	if not vim.b[state.buf].jj_keymaps_set then
 		buffer.set_keymaps(state.buf, {
+            { modes = { "n" }, lhs = "g?", rhs = M.keymap_help },
 			-- Disable insert, command and append modes
 			{ modes = { "n", "v" }, lhs = "i", rhs = function() end },
 			{ modes = { "n", "v" }, lhs = "c", rhs = function() end },