feat: add health check module for validating presets and options

- Introduced `health.lua` to validate the preset table and options.
- Added `validatePreset` function to ensure presets have required fields.
- Implemented `validate_opts_table` to check the validity of options.
- Created `check_dependencies` to verify the presence of `ai.nvim`.
- Defined `M.check` to run health checks via `:checkhealth` command.

lua/dante/health.lua

@@ -0,0 +1,85 @@
+local M = {}
+
+---Validate the preset table
+---@param preset Preset
+---@return boolean: Whether the preset is valid
+---@return string?: Error message
+local function validatePreset(preset)
+  -- Check if the preset has the required fields
+  if not preset.client or not preset.request then
+    return false, "Preset must contain 'client' and 'request' fields."
+  end
+
+  -- Validate client options
+  if type(preset.client) ~= "table" or not preset.client.base_url then
+    return false, "Client options must be a table with 'base_url' (required) and 'api_key' (optional)."
+  end
+
+  -- Validate request object
+  local request = preset.request
+  if type(request) ~= "table" or not request.model or not request.messages then
+    return false, "Request must be a table with 'model' and 'messages'."
+  end
+
+  if type(request.messages) ~= "table" or #request.messages == 0 then
+    return false, "Messages must be a non-empty table."
+  end
+
+  -- Check that all messages have the required fields
+  for _, message in ipairs(request.messages) do
+    if type(message) ~= "table" or not message.role or not message.content then
+      return false, "Each message must be a table with 'role' and 'content'."
+    end
+  end
+
+  return true
+end
+
+
+---Validate the options table obtained from merging defaults and user options
+local function validate_opts_table()
+  local opts = require("dante.config").options
+
+  for preset_key, preset in pairs(opts.presets) do
+    local ok, err = validatePreset(preset)
+    if not ok then
+      vim.health.error("Invalid preset `" .. preset_key .. "`: " .. err)
+    else
+      vim.health.ok("Preset `" .. preset_key .. "` is valid")
+    end
+  end
+
+  if type(opts.verbose) ~= "boolean" then
+    vim.health.error("Verbose option must be a boolean")
+  else
+    vim.health.ok("Verbose option is valid")
+  end
+
+  if vim.tbl_contains({ "right", "left", "above", "below" }, opts.layout) then
+    vim.health.ok("Layout option is valid")
+  else
+    vim.health.error("Layout option must be 'right', 'left', 'above', or 'below'")
+  end
+end
+
+
+local function check_dependencies()
+  local ok, _ = pcall(function() require("ai") end)
+  if not ok then
+    vim.health.error("ai.nvim is not installed")
+  else
+    vim.health.ok("ai.nvim is installed")
+  end
+end
+
+
+---This function is used to check the health of the plugin
+---It's called by `:checkhealth` command
+M.check = function()
+  vim.health.start("dante.nvim health check")
+  check_dependencies()
+  validate_opts_table()
+end
+
+
+return M