feat: support rst experimentally (#4)

* feat: support rst experimentally

* fix: these vars should have been used

README.md

@@ -10,9 +10,10 @@ An extension for [telescope.nvim](https://github.com/nvim-telescope/telescope.nv
 
 ## Supported File Type
 
-- Markdown (headings from `h1` to `h6`)
+- Markdown
 - AsciiDoc (experimental)
 - OrgMode (experimental)
+- ReStructuredText (experimental)
 
 ## Setup
 

fixtures/README.md

@@ -0,0 +1,6 @@
+The format examples are referenced from:
+
+- Markdown Example: <https://github.com/crispgm/crispgm.com/blob/master/site/_drafts/test-for-styles.md>
+- AsciiDoc Example: <https://asciidoctor.org/docs/asciidoc-article/>
+- OrgMode Example: <https://writequit.org/denver-emacs/presentations/files/example.org.html>
+- ReStructuredText Example: <https://fangohr.github.io/computing/rst/rst.txt>

fixtures/example.rst

@@ -0,0 +1,87 @@
+=========================================
+ReStructuredText (rst): plain text markup
+=========================================
+
+.. sectnum::
+
+.. contents:: The tiny table of contents
+
+What is reStructuredText?
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+An easy-to-read, what-you-see-is-what-you-get plaintext markup syntax
+and parser system, abbreviated *rst*. In other words, using a simple
+text editor, documents can be created which
+
+- are easy to read in text editor and
+- can be *automatically* converted to
+
+  - html and
+  - latex (and therefore pdf)
+
+What is it good for?
+~~~~~~~~~~~~~~~~~~~~
+
+reStructuredText can be used, for example, to
+
+- write technical documentation (so that it can easily be offered as a
+  pdf file or a web page)
+
+- create html webpages without knowing html
+
+- to document source code
+
+Show me some formatting examples
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+You can highlight text in *italics* or, to provide even more emphasis
+in **bold**. Often, when describing computer code, we like to use a
+``fixed space font`` to quote code snippets.
+
+We can also include footnotes [1]_. We could include source code files
+(by specifying their name) which is useful when documenting code. We
+can also copy source code verbatim (i.e. include it in the rst
+document) like this::
+
+  int main ( int argc, char *argv[] ) {
+      printf("Hello World\n");
+      return 0;
+  }
+
+We have already seen at itemised list in section `What is it good
+for?`_. Enumerated list and descriptive lists are supported as
+well. It provides very good support for including html-links in a
+variety of ways. Any section and subsections defined can be linked to,
+as well.
+
+
+Where can I learn more?
+~~~~~~~~~~~~~~~~~~~~~~~
+
+reStructuredText is described at
+http://docutils.sourceforge.net/rst.html. We provide some geeky small
+print in this footnote [2]_.
+
+
+Show me some more stuff, please
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+We can also include figures:
+
+.. figure:: image.png
+   :width: 300pt
+
+
+   The magnetisation in a small ferromagnetic disk. The diametre is of the order of 120 nanometers and the material is Ni20Fe80. Png is a file format that is both acceptable for html pages as well as for (pdf)latex.
+
+---------------------------------------------------------------------------
+
+.. [1] although there isn't much point of using a footnote here.
+
+.. [2] Random facts:
+
+  - Emacs provides an rst mode
+  - when converting rst to html, a style sheet can be provided (there is a similar feature for latex)
+  - rst can also be converted into XML
+  - the recommended file extension for rst is ``.txt``
+

lua/telescope/_extensions/heading/format/rst.lua

@@ -0,0 +1,91 @@
+local ReStructuredText = {}
+
+local function is_heading(line, char)
+    for i = 1, #line do
+        local c = line:sub(i, i)
+        if c ~= char then
+            return false
+        end
+    end
+
+    return true
+end
+
+function ReStructuredText.get_headings(filepath, start, total)
+    local headings = {}
+    local index = start
+    -- not all, but all recommended
+    local sectionChars = {
+        '=',
+        '-',
+        '`',
+        ':',
+        '.',
+        "'",
+        '"',
+        '~',
+        '^',
+        '_',
+        '*',
+        '+',
+        '#',
+    }
+    local last_line = ''
+    local line_mode = 0 -- 1: overline, 2: underline
+    -- luacheck: no unused
+    local line_top = 0 -- for underline, there is no line_top, only line_bottom
+    local line_title = 0
+    local line_bottom = 0
+    local heading = ''
+    while index <= total do
+        local line = vim.fn.getline(index)
+        for _, char in pairs(sectionChars) do
+            if is_heading(line, char) then
+                if last_line == '' then -- overline start
+                    line_mode = 1
+                    line_top = string.len(line)
+                else
+                    if line_mode == 1 then -- overline end
+                        line_title = string.len(last_line)
+                        line_bottom = string.len(line)
+                        if
+                            line_top
+                                == line_title
+                            and line_title
+                                == line_bottom
+                        then
+                            heading = last_line
+                        end
+                    else -- underline
+                        line_title = string.len(last_line)
+                        line_bottom = string.len(line)
+                        if line_title == line_bottom then
+                            heading = last_line
+                            line_mode = 2
+                        end
+                    end
+                end
+                if #heading > 0 then
+                    table.insert(headings, {
+                        heading = vim.trim(heading),
+                        line = index,
+                        path = filepath,
+                    })
+                    -- reset
+                    heading = ''
+                    line_mode = 0
+                    line_top, line_bottom, line_title = 0, 0, 0
+                end
+
+                break
+            end
+        end
+
+        last_line = line
+        index = index + 1
+    end
+
+    return headings
+end
+
+return ReStructuredText