-- feed.lua — Atom feed (RFC 4287) for published blog posts.

local db     = require "db"
local md     = require "md"
local config = require "config"

local M = {}

local XML_ESC = {
  ["&"] = "&amp;", ["<"] = "&lt;", [">"] = "&gt;",
  ['"'] = "&quot;", ["'"] = "&apos;",
}
local function xesc(s)
  return (tostring(s or ""):gsub("[&<>\"']", XML_ESC))
end

M.FEED_LIMIT = 20

--- Build the Atom feed document.  Returns the XML string.
function M.atom()
  local base   = config.base_url()
  local title  = config.get("site_title")
  local author = config.get("site_author")
  local posts  = db.list_published_page("blog", M.FEED_LIMIT, 0)

  -- Feed-level updated: newest updated_at, or "now" for an empty feed.
  local feed_updated = os.date("!%Y-%m-%dT%H:%M:%SZ")
  if posts[1] then
    feed_updated = posts[1].updated_at
    for _, p in ipairs(posts) do
      if p.updated_at > feed_updated then feed_updated = p.updated_at end
    end
  end

  local out = {
    '<?xml version="1.0" encoding="utf-8"?>',
    '<feed xmlns="http://www.w3.org/2005/Atom">',
    "<title>" .. xesc(title) .. "</title>",
    '<link href="' .. xesc(base) .. '/"/>',
    '<link rel="self" type="application/atom+xml" href="' .. xesc(base) .. '/atom.xml"/>',
    "<id>" .. xesc(base) .. "/</id>",
    "<updated>" .. xesc(feed_updated) .. "</updated>",
  }
  if author ~= "" then
    out[#out + 1] = "<author><name>" .. xesc(author) .. "</name></author>"
  end
  local tagline = config.get("site_tagline")
  if tagline ~= "" then
    out[#out + 1] = "<subtitle>" .. xesc(tagline) .. "</subtitle>"
  end

  for _, p in ipairs(posts) do
    local url = base .. "/blog/" .. EscapePath(p.slug)
    out[#out + 1] = "<entry>"
      .. "<title>" .. xesc(p.title) .. "</title>"
      .. '<link href="' .. xesc(url) .. '"/>'
      .. "<id>" .. xesc(url) .. "</id>"
      .. "<published>" .. xesc(p.created_at) .. "</published>"
      .. "<updated>" .. xesc(p.updated_at) .. "</updated>"
      .. (p.summary ~= ""
          and ("<summary>" .. xesc(p.summary) .. "</summary>") or "")
      .. '<content type="html">' .. xesc(md.render(p.body)) .. "</content>"
      .. "</entry>"
  end

  out[#out + 1] = "</feed>"
  return table.concat(out, "\n")
end

return M