More docs (Readme#Adding-Languages)

docs/advanced-integration.md

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+# Advanced Integration
+
+## Configuration file
+
+The configuration file for a language is in `lua/configurations/{lang}.lua`. 
+
+_Note: Be aware that Neogen uses Treesitter to operate. You can install [TSPlayground](https://github.com/nvim-treesitter/playground) to check the AST._
+
+Below is a commented sample of the configuration file for `lua`.
+
+```lua
+-- Search for these nodes
+parent = { "function", "local_function", "local_variable_declaration", "field", "variable_declaration" },
+                                                                                                          
+-- Traverse down these nodes and extract the information as necessary
+data = {
+    -- If function or local_function is found as a parent
+    ["function|local_function"] = {
+        -- Get second child from the parent node
+        ["2"] = {
+            -- This second child has to be of type "parameters", otherwise does nothing
+            match = "parameters",
+                                                                                       
+	    -- Extractor function that returns a set of TSname = values with values being of type string[]
+            extract = function(node)
+                local regular_params = neogen.utilities.extractors:extract_children_text("identifier")(node)
+                local varargs = neogen.utilities.extractors:extract_children_text("spread")(node)
+                                                                                                          
+                return {
+                    parameters = regular_params,
+                    vararg = varargs,
+                }
+            end,
+        },
+    },
+},
+                                                                                                          
+-- Custom lua locator that escapes from comments (More on locators below)
+-- Passing nil will use the default locator
+locator = require("neogen.locators.lua"),
+                                                                                                          
+-- Use default granulator and generator (More on them below)
+granulator = nil,
+generator = nil,
+                                                            
+-- Template to use with the generator. (More on this below)
+template = {
+    -- Which annotation convention to use
+    annotation_convention = "emmylua",
+    emmylua = {
+        { nil, "- " },
+        { "parameters", "- @param %s any" },
+        { "vararg", "- @vararg any" },
+        { "return_statement", "- @return any" }
+    }
+},
+```
+
+The Neogen code is then divided in 3 major concepts:
+
+## Locators
+
+A locator tries to find (from the cursor node) one of the nodes from `parents` field specified in configuration.
+
+This is the signature of the function:
+
+```lua
+function(node_info, nodes_to_match)
+    return node
+end
+```
+
+- With `node_info` being a table with 2 fields:
+
+```lua
+{
+    root = root_node -- <TSnode>
+    current = current_node -- <TSnode>
+}
+```
+
+- `nodes_to_match` is the field from `parents` in language configuration.
+
+_Default: The default locator (in `lua/locators/default.lua`) just go back to the parent node of the current one and sees if it's one of the requested parents._
+
+## Granulators
+
+Now that a parent node is found (with locators) from the cursor location, it's time to use this node to find all requested fields.
+
+The function signature is this:
+
+```lua
+function(parent_node, node_data)
+    return result
+end
+```
+
+- `parent_node` being the node returned from the locator
+- `result` is a table containing a set of `type = values` with values from type `string[]`, and type being a TS node name.
+- `node_data` being the field `data` from configuration file. For example, if the `data` field is this one:
+
+```lua
+data = {
+    ["function|local_function"] = {
+        -- get second child from the parent node
+        ["2"] = {
+            -- it has to be of type "parameters"
+            match = "parameters",
+
+            extract = function(node)
+                local tree = {
+                    { retrieve = "all", node_type = "identifier", extract = true },
+                    { retrieve = "all", node_type = "spread", extract = true }
+                }
+                local nodes = neogen.utilities.nodes:matching_nodes_from(node, tree)
+                local res = neogen.utilities.extractors:extract_from_matched(nodes)
+
+                return {
+                    parameters = res.identifier,
+                    vararg = res.spread,
+                }
+            end,
+        },
+    },
+}
+```
+
+Notes:
+
+- If you create your own granulator, you can add any kind of parameters in the `data` field from configuration file as long as the function signature is the same provided. 
+- Utilities are provided. You can check out their documentation in `lua/utilities/`.
+
+## Generators
+
+A generator takes in the results from the granulator and tries to generate the template according to the language's configuration.
+
+This is the function signature for a generator:
+
+```lua
+function(parent, data, template)
+    return start_row, start_col, generated_template
+end
+```
+
+- `parent` is the parent node found with the locator
+- `data` is the result from the granulator
+- `template` being the `template` field from the language configuration file.
+- `start_row` is the row in which we will append `generated_template` 
+- `start_col` is the col in which the `generated_template` will start
+- `generated_template` is the output we will append on the specified locations.