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% lsp_metta_formater.pl
%
% Purpose:
%
% A Prolog implementation of a documentFormattingProvider for Lisp code.
%
% This module formats Lisp code by ensuring consistent indentation and removing
% unnecessary whitespace. The formatting rules account for Lisp's syntax, including
% proper indentation for nested expressions and balanced parentheses.
%
% How It Works:
% - Reads the document text from the provided URI.
% - Splits the document into lines.
% - Applies MeTTa-specific formatting rules, such as:
%   - Consistent indentation for nested parentheses.
%   - Removing unnecessary trailing whitespace.
%   - Ensuring consistent line breaks between nested forms.
% - Returns a list of text edits to apply to the document.
%
% Author: Douglas Miles
% Date: 10-21-2024
%
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    :- include(lsp_metta_include).

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% Handle the 'textDocument/formatting' Request and Format the Lisp Document
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lsp_hooks:handle_msg_hook("textDocument/formatting", Msg, _{id: Id, result: Edits}) :-
    _{id: Id, params: Params} :< Msg,
    _{textDocument: _{uri: Uri}} :< Params,
    format_lisp_document(Uri, Edits).  % Perform the document formatting

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% Helper: Format the Lisp Document by Applying Formatting Rules
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format_lisp_document(Uri, Edits) :-
    source_file_text(Uri, Text),      % Retrieve the document text
    split_string(Text, "\n", "", Lines),  % Split the text into lines
    format_lisp_lines(Lines, 0, 0, FormattedLines),  % Format each line, starting with indent level 0 and open parentheses 0
    create_edit_list(Lines, FormattedLines, Edits).  % Create a list of edits based on the differences

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% Format Each Line According to Lisp Syntax and Indentation Rules
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format_lisp_lines([], _, _, []).  % Base case: no more lines
format_lisp_lines([Line | Rest], IndentLevel, OpenParens, [FormattedLine | FormattedRest]) :-
    trim_line(Line, TrimmedLine),  % Remove trailing whitespace from the current line
    calculate_new_indent(TrimmedLine, IndentLevel, OpenParens, NewIndentLevel, NewOpenParens),  % Determine the new indent level and open parentheses count
    indent_line(TrimmedLine, NewIndentLevel, FormattedLine),  % Indent the line based on the new indent level
    format_lisp_lines(Rest, NewIndentLevel, NewOpenParens, FormattedRest).  % Format the rest of the lines

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% Helper: Trim Leading and Trailing Whitespace from a Line
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trim_line(Line, TrimmedLine) :-
    strip_leading_whitespace(Line, TempLine),
    remove_trailing_whitespace(TempLine, TrimmedLine).

strip_leading_whitespace(Line, Trimmed) :-
    split_string(Line, " \t", "", Words),  % Split the line by whitespace
    atomic_list_concat(Words, " ", Trimmed).  % Join them back together

remove_trailing_whitespace(Line, CleanLine) :-
    split_string(Line, "\n", "", Lines),
    maplist(strip_line_trailing_spaces, Lines, CleanLines),
    atomic_list_concat(CleanLines, "\n", CleanLine).

strip_line_trailing_spaces(Line, CleanLine) :-
    reverse(Line, Reversed),
    drop_leading_whitespace(Reversed, CleanReversed),
    reverse(CleanReversed, CleanLine).

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% drop_leading_whitespace(+Codes, -CleanCodes)
%
% Removes leading whitespace (spaces and tabs) from the input list of character codes.
%
% Codes: A list of character codes (representing a string).
% CleanCodes: The resulting list of character codes with leading whitespace removed.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

drop_leading_whitespace([], []).  % Base case: empty list
drop_leading_whitespace([32 | Rest], CleanCodes) :-  % If the first character is a space (ASCII 32)
    drop_leading_whitespace(Rest, CleanCodes).
drop_leading_whitespace([9 | Rest], CleanCodes) :-  % If the first character is a tab (ASCII 9)
    drop_leading_whitespace(Rest, CleanCodes).
drop_leading_whitespace(Codes, Codes).  % If no leading whitespace, return the list as is

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% Calculate New Indentation Level and Open Parentheses Count
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calculate_new_indent(Line, IndentLevel, OpenParens, NewIndentLevel, NewOpenParens) :-
    count_open_close_parens(Line, Opens, Closes),  % Count open and close parentheses
    NewOpenParens is OpenParens + Opens - Closes,  % Update the number of open parentheses
    (NewOpenParens > OpenParens -> NewIndentLevel is IndentLevel + 2 ; NewIndentLevel is IndentLevel).

% Helper to count open and close parentheses in a line
count_open_close_parens(Line, Opens, Closes) :-
    sub_atom_count(Line, '(', Opens),
    sub_atom_count(Line, ')', Closes).

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% Helper: Indent a Line Based on the Current Indentation Level
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indent_line(Line, IndentLevel, IndentedLine) :-
    IndentSpaces is IndentLevel,  % Indentation level determines the number of spaces
    generate_spaces(IndentSpaces, Spaces),  % Create the indent string
    atom_concat(Spaces, Line, IndentedLine).  % Prepend the spaces to the line

generate_spaces(0, "").
generate_spaces(N, Spaces) :-
    N > 0,
    N1 is N - 1,
    generate_spaces(N1, SubSpaces),
    atom_concat(' ', SubSpaces, Spaces).

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% Create a List of Edits from the Original and Formatted Lines
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create_edit_list([], [], []).
create_edit_list([OrigLine | OrigRest], [FormattedLine | FormattedRest], [Edit | EditRest]) :-
    (   OrigLine \= FormattedLine  % Only create an edit if the line has changed
    ->  Edit = _{
            range: _{
                start: _{line: LineNum, character: 0},
                end: _{line: LineNum, character: _}
            },
            newText: FormattedLine
        }
    ;   Edit = []
    ),
    create_edit_list(OrigRest, FormattedRest, EditRest).

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% Helper to count the number of specific characters (e.g., '(' or ')')
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sub_atom_count(Line, Char, Count) :-
    atom_chars(Line, Chars),
    include(=(Char), Chars, CharList),
    length(CharList, Count).