From 3f9a15c967aa152f78c4c48524f8e68eae879b5e Mon Sep 17 00:00:00 2001
From: Omikhleia <didier.willis@gmail.com>
Date: Thu, 2 Jan 2025 19:08:40 +0100
Subject: [PATCH] feat(packages): Support page ranges in indexer

---
 packages/indexer/init.lua | 80 ++++++++++++++++++++++++++++++++++-----
 1 file changed, 71 insertions(+), 9 deletions(-)

diff --git a/packages/indexer/init.lua b/packages/indexer/init.lua
index 5a31ac33c..c3d63c2ab 100644
--- a/packages/indexer/init.lua
+++ b/packages/indexer/init.lua
@@ -3,9 +3,31 @@ local base = require("packages.base")
 local package = pl.class(base)
 package._name = "indexer"
 
-function package.buildIndex (class) -- Called from the class, not as a package method
+local function isNotSamePage (p1, p2)
+   if not p1 then
+      return true
+   end
+   return p1.display ~= p2.display or p1.value ~= p2.value
+end
+
+local function groupPageRanges(pages)
+   local ret = {}
+   for _, page in ipairs(pages) do
+      if #ret == 0
+         or ret[#ret][#ret[#ret]].display ~= page.display
+         or ret[#ret][#ret[#ret]].value + 1 ~= page.value
+      then
+         table.insert(ret, { page })
+      else
+         table.insert(ret[#ret], page)
+      end
+   end
+   return ret
+end
+
+function package.buildIndex ()
    local nodes = SILE.scratch.info.thispage.index
-   local thisPage = class.packages.counters:formatCounter(SILE.scratch.counters.folio)
+   local pageno = pl.tablex.copy(SILE.scratch.counters.folio)
    if not nodes then
       return
    end
@@ -13,18 +35,24 @@ function package.buildIndex (class) -- Called from the class, not as a package m
       if not SILE.scratch.index[node.index] then
          SILE.scratch.index[node.index] = {}
       end
-      local thisIndex = SILE.scratch.index[node.index]
-      if not thisIndex[node.label] then
-         thisIndex[node.label] = {}
+      local index = SILE.scratch.index[node.index]
+      if not index[node.label] then
+         index[node.label] = {}
       end
-      if not #thisIndex[node.label] or (thisIndex[node.label])[#thisIndex[node.label]] ~= thisPage then
-         table.insert(thisIndex[node.label], thisPage)
+      local pages = index[node.label]
+      if not #pages or isNotSamePage(pages[#pages], pageno) then
+         table.insert(pages, pageno)
       end
    end
 end
 
-function package:_init ()
+function package:_init (options)
    base._init(self)
+   self.config = pl.tablex.merge({
+      ["page-range-format"] = "expanded",
+      ["page-range-delimiter"] = "–",
+      ["page-delimiter"] = ", "
+   }, options, true)
    self:loadPackage("infonode")
    self.class:registerHook("endpage", self.buildIndex)
    if not SILE.scratch.index then
@@ -32,6 +60,31 @@ function package:_init ()
    end
 end
 
+function package:formatPageRanges (pages)
+   local ranges = {}
+   for _, range in ipairs(groupPageRanges(pages)) do
+      if #range == 1 then
+         table.insert(ranges, self.class.packages.counters:formatCounter(range[1]))
+      else
+         table.insert(ranges,
+            self.class.packages.counters:formatCounter(range[1])
+               .. self.config['page-range-delimiter']
+               .. self.class.packages.counters:formatCounter(range[#range]))
+      end
+   end
+   return table.concat(ranges, self.config['page-delimiter'])
+end
+
+function package:formatPages (pages)
+   if self.config['page-range-format'] ~= 'none' then
+      return self:formatPageRanges(pages)
+   end
+   local ret = pl.tablex.map(function (page)
+      return self.class.packages.counters:formatCounter(page)
+   end, pages)
+   return table.concat(ret, self.config['page-delimiter'])
+end
+
 function package:registerCommands ()
    self:registerCommand("indexentry", function (options, content)
       if not options.label then
@@ -64,7 +117,7 @@ function package:registerCommands ()
       SU.collatedSort(sortedIndex)
       SILE.call("bigskip")
       for _, k in ipairs(sortedIndex) do
-         local pageno = table.concat(index[k], ", ")
+         local pageno = self:formatPages(index[k])
          SILE.call("index:item", { pageno = pageno }, { k })
       end
    end)
@@ -85,6 +138,15 @@ end
 package.documentation = [[
 \begin{document}
 An index is essentially the same thing as a table of contents, but sorted.
+
+The package accepts several configuration options:
+\begin{itemize}
+\item{\autodoc:parameter{page-range-format}: The format of the page range.
+Possible values are \autodoc:parameter{expanded} (default), \autodoc:parameter{none}.}
+\item{\autodoc:parameter{page-range-delimiter}: The delimiter between the start and end of a page range.}
+\item{\autodoc:parameter{page-delimiter}: The delimiter between pages.}
+\end{itemize}
+
 This package provides the \autodoc:command{\indexentry} command, which can be called as either \autodoc:command{\indexentry[label=<text>]} or \autodoc:command{\indexentry{<text>}} (so that it can be called from a macro).
 Index entries are collated at the end of each page, and the command \autodoc:command{\printindex} will deposit them in a list.
 The entry can be styled using the \autodoc:command{\index:item} command.