local l = require("pandoc.logging")
local read = pandoc.read

assert(#arg == 2, "\n" ..
  "[ERROR] usage: pandoc lua collect_deps.lua <index file> <output file")

local index_file, output_file = table.unpack(arg)

local f = assert(io.open(index_file), "\n" ..
  "[ERROR] could not open " .. index_file .. " for reading.")
local data = f:read("a")
f:close()


local visited = {}
local lines = {}
local all_target = "all: "
local all_prereqs = {}
local sitemap_target = "public_html/sitemap.html.part: "
local sitemap_prereqs = {}

local function collect (fp)
  local f = assert(io.open(fp), "\n" ..
    "[ERROR] could not open " .. fp .. " for reading.")
  visited[fp] = true
  local target = fp:gsub("(.+)%.md", "public_html/%1.html")
  table.insert(all_prereqs, target)
  table.insert(sitemap_prereqs, fp)
  local prereqs = { fp }
  local data = f:read("a")
  f:close()
  read(data):walk({ Link = function (link)
    if not link.target:find(".%.md$") then return end
    local f = io.open(link.target)
    if f == nil then return else f:close() end
    if visited[link.target] then return end
    local prereq = link.target:gsub("(.+)%.md", "public_html/%1.html.part")
    table.insert(prereqs, prereq)
    collect(link.target)
  end })
  table.insert(prereqs, "public_html/sitemap.html.part")
  target = ("%s: "):format(target)
  table.insert(lines, table.concat({ target, table.concat(prereqs, " ") }))
end

collect(arg[1])
table.insert(lines, 1, table.concat({ all_target, table.concat(all_prereqs, " ") }))
table.insert(lines, table.concat({ sitemap_target, table.concat(sitemap_prereqs, " ") }))

local f = assert(io.open(output_file, "w"), "\n" ..
  "[ERROR] could not open " .. output_file .. " for writing.")
f:write(table.concat(lines, "\n"))
f:close()