From f4afc91c0785cb112bc507b0450f86278ad1cc2a Mon Sep 17 00:00:00 2001
From: Ekaitz Zarraga <ekaitz@elenq.tech>
Date: Thu, 28 May 2020 16:10:52 +0200
Subject: ToC filter

---
 filters/toc.lua | 128 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 128 insertions(+)
 create mode 100644 filters/toc.lua

(limited to 'filters')

diff --git a/filters/toc.lua b/filters/toc.lua
new file mode 100644
index 0000000..479b082
--- /dev/null
+++ b/filters/toc.lua
@@ -0,0 +1,128 @@
+--[[
+--  This filter creates the ToC from the headings so if it's applied before
+--  heading transformations, transformations do not appear in the ToC.
+--
+--  It's useful for HTML output where the anchors are added in an extra filter.
+--  Default ToC included the anchor. Using this filter anchor is not included.
+--
+--  It supports toc-depth metadata field.
+--]]
+pandoc.utils = require 'pandoc.utils'
+list_of_headers = {}
+
+
+if FORMAT:match 'html' then
+
+    -- TODO: ReMOVE THIS
+    function headers2links_level(headers)
+        local links = {}
+        for i, v in ipairs(headers) do
+            local l = pandoc.Link( pandoc.utils.stringify(v), "#"..v.identifier )
+            table.insert(links,{ v.level, pandoc.Plain( l ) })
+        end
+        return links
+    end
+
+    function create_ol(headers, toc_depth)
+        if #headers == 0 then
+            return pandoc.Null()
+        end
+        local links = headers2links_level(headers)
+
+        -- min_level doesn't have to be 1, it could be larger
+        local min_level = -1
+        for i, v in ipairs(links) do
+            if min_level == -1 or v[1] < min_level then min_level = v[1] end
+        end
+
+        -- max level needed for grouping
+        local max_level = 0
+        if toc_depth >= 1 then
+            -- toc_depth is set, so remove elements with larger level than
+            -- max_level
+            max_level = min_level + toc_depth - 1
+            local i = 1
+            while i <= #links do
+                if links[i][1] > max_level then
+                    table.remove(links, i)
+                    i = i - 1
+                end
+                i = i + 1
+            end
+        else 
+            -- toc_depth not set so get the max_level from the contents
+            for i, v in ipairs(links) do
+                if v[1] > max_level then max_level = v[1] end
+            end
+        end
+
+        -- Iterate trough valid levels
+        while max_level > min_level do
+            local i = 1
+            local tmp = {}
+            while i <= #links do
+                local level = links[i][1]  -- Element's level 
+                if level == max_level then -- Found group
+                    -- If group is found, it usually has a parent
+                    local parent = links[i-1]
+                    if parent[1] == level - 1 then
+                        -- It's the direct parent, add it's contents
+                        parent = parent[2]
+                    else
+                        -- Not direct parent, warn and discard
+                        io.stderr:write("[WARNING] Element of level ")
+                        io.stderr:write(tostring(parent[1]))
+                        io.stderr:write(" has no direct children: ")
+                        io.stderr:write(pandoc.utils.stringify(parent[2]))
+                        io.stderr:write("\n")
+                        parent = pandoc.Null()
+                    end
+
+                    while i <= #links and links[i][1] == level do
+                        -- Capture the group
+                        table.insert(tmp, table.remove(links, i)[2])
+                    end
+
+                    if #tmp ~= 0 then
+                        -- There was a group, convert it to
+                        -- {parent, OrderedList(group)}
+                        local children = pandoc.OrderedList(tmp)
+                        local pos = i
+                        if parent.t ~= "Null" then
+                            -- There was a parent: extract it from links
+                            table.remove(links, i-1)
+                            pos = i - 1
+                        end
+                        table.insert(links, pos, {level-1, {parent, children}})
+                        tmp = {}
+                    end
+                end
+                i = i + 1
+            end
+            max_level = max_level - 1
+        end
+
+        local lis = {}
+        for i,v in pairs(links) do
+            _,lis[i] = table.unpack(v)
+        end
+        return pandoc.OrderedList(lis)
+
+    end
+
+    function Meta(m)
+        local toc_depth 
+        if m["toc-depth"] ~= nil then
+            toc_depth = tonumber(m["toc-depth"][1]["c"])
+        else
+            toc_depth = -1
+        end
+        m["table-of-contents"] = pandoc.MetaBlocks({create_ol(list_of_headers, toc_depth)})
+        return m
+    end
+
+    function Header(el)
+        table.insert(list_of_headers, el)
+        return el
+    end
+end
-- 
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