local l = require("pandoc.logging")
assert(#arg > 0, "\n" ..
  "[ERROR] usage: pandoc lua dependencies.lua <input-file>")

for i, v in ipairs(arg) do
  local f = assert(io.open(v), "\n" ..
    "[ERROR] could not open " .. v .. " for reading.")
  local data = f:read("a")
  f:close()

  local visited = {}
  pandoc.read(data):walk({ Link = function(link)
    -- early return for external links
    if link.target:find("^https?%:%/%/") then return end
    if link.target:find("^mailto%:") then return end

    local fp, anchor = link.target:match("^(.+%.md)#?(.*)$")
    -- early return for non markdown files
    if not fp then return end

    local f = io.open(fp)
    if f == nil then 
      print("Broken internal link: " .. v .. " -> " .. fp)
      return 
    end

    if anchor == "" then f:close(); return end

    local data = f:read("a"); f:close()

    local found = false
    pandoc.read(data):walk({ Div = function(div)
      if not div.attr then return end
      if div.attr.identifier == anchor then found = true end
    end }):walk({ Span = function(span) 
      if not span.attr then return end
      if span.attr.identifier == anchor then found = true end
    end }):walk({ Header = function(header) 
      if not header.attr then return end
      if header.attr.identifier == anchor then found = true end
    end }):walk({ CodeBlock = function(codeblock) 
      if not codeblock.attr then return end
      if codeblock.attr.identifier == anchor then found = true end
    end }):walk({ Code = function(code) 
      if not code.attr then return end
      if code.attr.identifier == anchor then found = true end
    end })

    if not found then print("Broken link: " .. v .. " -> " .. link.target) end
  end })
end