feat: limit the terminal width

Also add the possibility of configuring it.

README.md

@@ -10,6 +10,18 @@ Run:
 :OpenCodeToggle
 ```
 
-The command opens `opencode` in a right-side terminal window. Running the command
+The command opens `opencode` in a right-side terminal window sized to 40% of the
-again closes only the window; the terminal buffer and `opencode` session stay
+screen width. Running the command again closes only the window; the terminal
-alive. Run `:OpenCodeToggle` again to show the same session.
+buffer and `opencode` session stay alive. Run `:OpenCodeToggle` again to show the
+same session.
+
+## Configuration
+
+```lua
+require("opencode").setup({
+  width = 0.4,
+})
+```
+
+`width` is the fraction of the screen width used by the terminal window. The
+default is `0.4`.

lua/opencode.lua

@@ -6,6 +6,10 @@ local state = {
   job = nil,
 }
 
+local config = {
+  width = 0.4,
+}
+
 local function is_valid_window(win)
   return win and vim.api.nvim_win_is_valid(win)
 end
@@ -14,8 +18,18 @@ local function is_valid_buffer(buf)
   return buf and vim.api.nvim_buf_is_valid(buf)
 end
 
+local function terminal_width()
+  return math.max(1, math.floor(vim.o.columns * config.width))
+end
+
+local function resize_side_window()
+  if is_valid_window(state.win) then
+    vim.api.nvim_win_set_width(state.win, terminal_width())
+  end
+end
+
 local function open_side_window()
-  vim.cmd("botright vertical 80new")
+  vim.cmd("botright vertical " .. terminal_width() .. "new")
   state.win = vim.api.nvim_get_current_win()
 end
 
@@ -51,10 +65,27 @@ function M.toggle()
   vim.cmd("startinsert")
 end
 
-function M.setup()
+function M.setup(opts)
+  opts = opts or {}
+
+  if opts.width ~= nil then
+    assert(
+      type(opts.width) == "number" and opts.width > 0 and opts.width <= 1,
+      "opencode.nvim: width must be a number between 0 and 1"
+    )
+
+    config.width = opts.width
+    resize_side_window()
+  end
+
   vim.api.nvim_create_user_command("OpenCodeToggle", function()
     M.toggle()
-  end, {})
+  end, { force = true })
+
+  vim.api.nvim_create_autocmd("VimResized", {
+    group = vim.api.nvim_create_augroup("opencode_terminal_width", { clear = true }),
+    callback = resize_side_window,
+  })
 end
 
 return M