-module(i3_client_trees).
-moduledoc """
Functions for processing i3 layout trees.

All functions assume they receive the whole tree, as returned by
`i3_client:get_tree/1,2`.
""".

-export([table/1, table/2]).

-include_lib("stdlib/include/qlc.hrl").

-doc """
Equivalent to [`table(Tree, dfs)`](`table/2`).
""".
-spec table(Table) -> QueryHandle when
    Table :: map(),
    QueryHandle :: qlc:query_handle().
table(Tree) ->
    table(Tree, dfs).

-doc """

Returns a Query List Comprehension (QLC) query handle.

The `m:qlc` module provides a query language, very similar to list
comprehensions, which allows iterator style traversal of data
structures. Calling `table/1,2` is the means to make the i3 tree
`Tree` usable to QLC.

The `Algo` argument can be either `dfs` or `bfs` which stand for
depth-first and breadth-first traversal respectively. Usually,
depth-first traversal is preferred so it's the default when calling
`table/1`.

_Examples:_

An example query for the focused node:

```erlang
0> {ok, Pid} = i3_client:start_link([]),
1> {ok, Tree} = i3_client:get_tree(Pid),
2> QH = qlc:q([Node || #{~"focused" := true} = Node <- i3_client_trees:table(Tree)]).
3> [#{~"focused" := true}] = qlc:eval(QH)
```

> #### Info {: .info } 
> It is necessary to add the following line to the source code:
> ```
> -include_lib("stdlib/include/qlc.hrl").
> ```
""".
-spec table(Table, Algo) -> QueryHandle when
    Table :: map(),
    Algo :: dfs | bfs,
    QueryHandle :: qlc:query_handle().
table(Tree, Algo) when (Algo =:= dfs) or (Algo =:= bfs) ->
    TraverseFun = fun() -> next([[Tree]], Algo) end,
    qlc:table(TraverseFun, []).

next([], _) ->
    [];
next([[] | Rest], Algo) ->
    next(Rest, Algo);
next([[Node | Siblings] | Rest], dfs = Algo) ->
    #{~"nodes" := Nodes, ~"floating_nodes" := FloatingNodes} = Node,
    [Node | fun() -> next([Nodes, FloatingNodes, Siblings | Rest], Algo) end];
next([[Node | Siblings] | Rest], bfs = Algo) ->
    #{~"nodes" := Nodes, ~"floating_nodes" := FloatingNodes} = Node,
    [Node | fun() -> next([Siblings, Nodes, FloatingNodes | Rest], Algo) end].