initial support for #36 : pickers can now show the number of links and

backlinks if opts.show_link_counts is set. Which it is for the 'link
search' following the tag selection.

lua/taglinks/linkutils.lua

@@ -0,0 +1,135 @@
+-- local async = require("plenary.async")
+local scan = require("plenary.scandir")
+
+local M = {}
+
+local function file_exists(fn, file_list)
+    return file_list[fn] ~= nil
+end
+
+local function resolve_link(title, file_list, subdir_list, opts)
+    local fexists = false
+    local filename = title .. opts.extension
+    filename = filename:gsub("^%./", "") -- strip potential leading ./
+
+    if
+        opts.weeklies
+        and file_exists(opts.weeklies .. "/" .. filename, file_list)
+    then
+        filename = opts.weeklies .. "/" .. filename
+        fexists = true
+    end
+    if
+        opts.dailies and file_exists(opts.dailies .. "/" .. filename, file_list)
+    then
+        filename = opts.dailies .. "/" .. filename
+        fexists = true
+    end
+    if file_exists(opts.home .. "/" .. filename, file_list) then
+        filename = opts.home .. "/" .. filename
+        fexists = true
+    end
+
+    if fexists == false then
+        -- now search for it in all subdirs
+        local tempfn
+        for _, folder in pairs(subdir_list) do
+            tempfn = folder .. "/" .. filename
+            -- [[testnote]]
+            if file_exists(tempfn, file_list) then
+                filename = tempfn
+                fexists = true
+                -- print("Found: " .. filename)
+                break
+            end
+        end
+    end
+
+    if fexists == false then
+        -- default fn for creation
+        filename = opts.home .. "/" .. filename
+    end
+    return fexists, filename
+end
+
+-- TODO: cache mtimes and only update if changed
+
+-- The reason we go over all notes in one go, is: backlinks
+-- We generate 2 maps: one containing the number of links within a note
+--    and a second one containing the number of backlinks to a note
+-- Since we're parsing all notes anyway, we can mark linked notes as backlinked from the currently parsed note
+M.generate_backlink_map = function(opts)
+    assert(opts ~= nil, "opts must not be nil")
+    -- TODO: check for code blocks
+    -- local in_fenced_code_block = false
+    -- also watch out for \t tabbed code blocks or ones with leading spaces that don't end up in a - or * list
+
+    -- first, find all notes
+    assert(opts.extension ~= nil, "Error: need extension in opts!")
+    assert(opts.home ~= nil, "Error: need home dir in opts!")
+
+    -- async seems to have lost await and we don't want to enter callback hell, hence we go sync here
+    local subdir_list = scan.scan_dir(opts.home, { only_dirs = true })
+    local file_list = {}
+    -- transform the file list
+    local _x = scan.scan_dir(opts.home, {
+        search_pattern = function(entry)
+            return entry:sub(-#opts.extension) == opts.extension
+        end,
+    })
+    for _, v in pairs(_x) do
+        file_list[v] = true
+    end
+
+    -- now process all the notes
+    local link_counts = {}
+    local backlink_counts = {}
+    for note_fn, _ in pairs(file_list) do
+        -- print("processing " .. note_fn .. "...")
+        -- go over file line by line
+        for line in io.lines(note_fn) do
+            for linktitle in line:gmatch("%[%[(.-)%]%]") do
+                -- strip # from title
+                linktitle = linktitle:gsub("#.*$", "")
+
+                -- now: inc our link count
+                link_counts[note_fn] = link_counts[note_fn] or 0
+                link_counts[note_fn] = link_counts[note_fn] + 1
+
+                -- and: inc the backlinks of the linked note
+                local fexists, backlinked_file = resolve_link(
+                    linktitle,
+                    file_list,
+                    subdir_list,
+                    opts
+                )
+                -- print(
+                --     "note for link `"
+                --         .. linktitle
+                --         .. "` = "
+                --         .. backlinked_file
+                --         .. " (exists: "
+                --         .. tostring(fexists)
+                --         .. ')'
+                -- )
+                if fexists and (note_fn ~= backlinked_file) then
+                    backlink_counts[backlinked_file] = backlink_counts[backlinked_file]
+                        or 0
+                    backlink_counts[backlinked_file] = backlink_counts[backlinked_file]
+                        + 1
+                end
+            end
+        end
+
+        -- check if in comments block
+        -- find all links in the note and count them
+        -- add 1 (this note) as back-link to linked note
+    end
+    local ret = {
+        link_counts = link_counts,
+        backlink_counts = backlink_counts,
+    }
+    return ret
+end
+
+return M