My attempt at implementing your idea in PR #79

lua/headlines/class.lua

@@ -0,0 +1,80 @@
+local Headline = {}
+Headline.__index = Headline
+
+local renderer = require('headlines.renderer')
+local config_manager = require('headlines.config')
+
+---@class Headline
+---@field config HeadlineConfig
+---@field namespace number
+---@field buffer buffer
+---@field autocmds table<number>
+---@field attach fun(self: Headline, buffer: buffer): Headline
+---@field delete fun(self: Headline)
+---@field refresh fun(self: Headline)
+
+---Create a new Headline
+---@param config? HeadlineConfig
+---@return Headline
+function Headline.new(config)
+    return setmetatable({
+        config = config,
+        namespace = '',
+        buffer = 0,
+        autocmds = {}
+    }, Headline)
+end
+
+---Attach headline to buffer
+---@param buffer buffer
+---@return Headline
+function Headline:attach(buffer)
+    local refresh_autocmd = vim.api.nvim_create_autocmd({
+        'FileChangedShellPost',
+        'Syntax',
+        'TextChanged',
+        'InsertLeave',
+        'WinScrolled',
+    }, {
+        group = 'Headlines',
+        buffer = buffer,
+        desc = 'Refresh buffer local headline',
+        callback = function()
+            self:refresh()
+        end,
+    })
+    local delete_autocmd = vim.api.nvim_create_autocmd({
+        'BufDelete',
+    }, {
+        group = 'Headlines',
+        buffer = buffer,
+        desc = 'Delete buffer local headline',
+        callback = function()
+            self:delete()
+        end,
+    })
+
+    local filetype = vim.api.nvim_buf_get_option(buffer, 'filetype')
+    self.config = config_manager.merge(self.config, config_manager.filetype_defaults(filetype))
+    self.namespace = vim.api.nvim_create_namespace('headline_namespace_' .. buffer)
+    self.buffer = buffer
+    self.autocmds = {
+        refresh = refresh_autocmd,
+        delete = delete_autocmd
+    }
+
+    self:refresh()
+
+    return self
+end
+
+function Headline:delete()
+    vim.api.nvim_del_autocmd(self.autocmds.refresh)
+    vim.api.nvim_del_autocmd(self.autocmds.delete)
+end
+
+function Headline:refresh()
+    renderer.render(self)
+end
+
+return Headline

lua/headlines/config.lua

@@ -0,0 +1,237 @@
+local Config = {}
+
+local utils = require('headlines.utils')
+
+---@class HeadlineConfig
+---@field query? Query
+---@field headline_highlights? table<string>
+---@field bullet_highlights? table<string>
+---@field bullets? table<string>
+---@field codeblock_highlight? string
+---@field dash_highlight? string
+---@field dash_string? string
+---@field doubledash_highlight? string
+---@field doubledash_string? string
+---@field quote_highlight? string
+---@field quote_string? string
+---@field fat_headlines? boolean
+---@field fat_headline_upper_string? string
+---@field fat_headline_lower_string? string
+---@field treesitter_language? string
+
+---Get headline config defaults
+---@return table<string, HeadlineConfig>
+function Config.defaults()
+    return {
+        markdown = {
+            query = utils.parse_query_save(
+                'markdown',
+                [[
+                    (atx_heading [
+                    (atx_h1_marker)
+                    (atx_h2_marker)
+                    (atx_h3_marker)
+                    (atx_h4_marker)
+                    (atx_h5_marker)
+                    (atx_h6_marker)
+                ] @headline)
+
+                (thematic_break) @dash
+
+                (fenced_code_block) @codeblock
+
+                (block_quote_marker) @quote
+                (block_quote (paragraph (inline (block_continuation) @quote)))
+                (block_quote (paragraph (block_continuation) @quote))
+                (block_quote (block_continuation) @quote)
+                ]]
+            ),
+            headline_highlights = { 'Headline' },
+            bullet_highlights = {
+                '@text.title.1.marker.markdown',
+                '@text.title.2.marker.markdown',
+                '@text.title.3.marker.markdown',
+                '@text.title.4.marker.markdown',
+                '@text.title.5.marker.markdown',
+                '@text.title.6.marker.markdown',
+            },
+            bullets = { '◉', '○', '✸', '✿' },
+            codeblock_highlight = 'CodeBlock',
+            dash_highlight = 'Dash',
+            dash_string = '-',
+            quote_highlight = 'Quote',
+            quote_string = '┃',
+            fat_headlines = true,
+            fat_headline_upper_string = '▃',
+            fat_headline_lower_string = '🬂',
+        },
+        rmd = {
+            query = utils.parse_query_save(
+                'markdown',
+                [[
+                    (atx_heading [
+                    (atx_h1_marker)
+                    (atx_h2_marker)
+                    (atx_h3_marker)
+                    (atx_h4_marker)
+                    (atx_h5_marker)
+                    (atx_h6_marker)
+                ] @headline)
+
+                (thematic_break) @dash
+
+                (fenced_code_block) @codeblock
+
+                (block_quote_marker) @quote
+                (block_quote (paragraph (inline (block_continuation) @quote)))
+                (block_quote (paragraph (block_continuation) @quote))
+                (block_quote (block_continuation) @quote)
+                ]]
+            ),
+            treesitter_language = 'markdown',
+            headline_highlights = { 'Headline' },
+            bullet_highlights = {
+                '@text.title.1.marker.markdown',
+                '@text.title.2.marker.markdown',
+                '@text.title.3.marker.markdown',
+                '@text.title.4.marker.markdown',
+                '@text.title.5.marker.markdown',
+                '@text.title.6.marker.markdown',
+            },
+            bullets = { '◉', '○', '✸', '✿' },
+            codeblock_highlight = 'CodeBlock',
+            dash_highlight = 'Dash',
+            dash_string = '-',
+            quote_highlight = 'Quote',
+            quote_string = '┃',
+            fat_headlines = true,
+            fat_headline_upper_string = '▃',
+            fat_headline_lower_string = '🬂',
+        },
+        norg = {
+            query = utils.parse_query_save(
+                'norg',
+                [[
+                    [
+                        (heading1_prefix)
+                        (heading2_prefix)
+                        (heading3_prefix)
+                        (heading4_prefix)
+                        (heading5_prefix)
+                        (heading6_prefix)
+                    ] @headline
+
+                    (weak_paragraph_delimiter) @dash
+                    (strong_paragraph_delimiter) @doubledash
+
+                    ([(ranged_tag
+                        name: (tag_name) @_name
+                        (#eq? @_name "code")
+                    )
+                    (ranged_verbatim_tag
+                        name: (tag_name) @_name
+                        (#eq? @_name "code")
+                    )] @codeblock (#offset! @codeblock 0 0 1 0))
+
+                    (quote1_prefix) @quote
+                ]]
+            ),
+            headline_highlights = { 'Headline' },
+            bullet_highlights = {
+                '@neorg.headings.1.prefix',
+                '@neorg.headings.2.prefix',
+                '@neorg.headings.3.prefix',
+                '@neorg.headings.4.prefix',
+                '@neorg.headings.5.prefix',
+                '@neorg.headings.6.prefix',
+            },
+            bullets = { '◉', '○', '✸', '✿' },
+            codeblock_highlight = 'CodeBlock',
+            dash_highlight = 'Dash',
+            dash_string = '-',
+            doubledash_highlight = 'DoubleDash',
+            doubledash_string = '=',
+            quote_highlight = 'Quote',
+            quote_string = '┃',
+            fat_headlines = true,
+            fat_headline_upper_string = '▃',
+            fat_headline_lower_string = '🬂',
+            treesitter_language = 'norg',
+        },
+        org = {
+            query = utils.parse_query_save(
+                'org',
+                [[
+                    (headline (stars) @headline)
+
+                    (
+                        (expr) @dash
+                        (#match? @dash "^-----+$")
+                    )
+
+                    (block
+                        name: (expr) @_name
+                        (#match? @_name "(SRC|src)")
+                    ) @codeblock
+
+                    (paragraph . (expr) @quote
+                        (#eq? @quote ">")
+                    )
+                ]]
+            ),
+            headline_highlights = { 'Headline' },
+            bullet_highlights = {
+                '@org.headline.level1',
+                '@org.headline.level2',
+                '@org.headline.level3',
+                '@org.headline.level4',
+                '@org.headline.level5',
+                '@org.headline.level6',
+                '@org.headline.level7',
+                '@org.headline.level8',
+            },
+            bullets = { '◉', '○', '✸', '✿' },
+            codeblock_highlight = 'CodeBlock',
+            dash_highlight = 'Dash',
+            dash_string = '-',
+            quote_highlight = 'Quote',
+            quote_string = '┃',
+            fat_headlines = true,
+            fat_headline_upper_string = '▃',
+            fat_headline_lower_string = '🬂',
+        },
+    }
+end
+
+---Get headline generic config defaults
+---@return HeadlineConfig
+function Config.generic_defaults()
+    return {}
+end
+
+---Get filetype specific headline config defaults.
+---If one is not found, then it returns a generic config
+---@param filetype string
+---@return HeadlineConfig
+function Config.filetype_defaults(filetype)
+    local defaults = Config.defaults()
+    return defaults[filetype] or Config.generic_defaults()
+end
+
+---Merge user config with default config.
+---Uses user config when applicable, otherwise uses default config
+---@param user_config HeadlineConfig
+---@param default_config HeadlineConfig
+---@return HeadlineConfig
+function Config.merge(user_config, default_config)
+    local merged = user_config and vim.tbl_deep_extend('force', default_config, user_config) or default_config
+
+    -- tbl_deep_extend does not handle metatables
+    if user_config.query then
+        merged.query = user_config.query
+    end
+
+    return merged
+end
+
+return Config