local zzlib = require('arti-pack.vendor.zzlib')

local M = {}

local function le(n, bytes)
  local out = {}
  for _ = 1, bytes do
    table.insert(out, string.char(n % 256))
    n = math.floor(n / 256)
  end
  return table.concat(out)
end

-- A stored-entry zip built here rather than shelled out to the zip binary, so
-- tests that need a real archive run wherever nvim does.
function M.bytes(entries)
  local locals, central, offset = {}, {}, 0
  for _, e in ipairs(entries) do
    local data = e.data or ''
    local crc = zzlib.crc32(data)
    local head = 'PK\3\4'
      .. le(20, 2)
      .. le(0, 2)
      .. le(0, 2)
      .. le(0, 4)
      .. le(crc, 4)
      .. le(#data, 4)
      .. le(#data, 4)
      .. le(#e.name, 2)
      .. le(0, 2)
      .. e.name
    table.insert(locals, head .. data)
    table.insert(
      central,
      'PK\1\2'
        .. le(3 * 256 + 20, 2)
        .. le(20, 2)
        .. le(0, 2)
        .. le(0, 2)
        .. le(0, 4)
        .. le(crc, 4)
        .. le(#data, 4)
        .. le(#data, 4)
        .. le(#e.name, 2)
        .. le(0, 2)
        .. le(0, 2)
        .. le(0, 2)
        .. le(0, 2)
        .. le(0, 4)
        .. le(offset, 4)
        .. e.name
    )
    offset = offset + #head + #data
  end
  local body = table.concat(locals)
  local cd = table.concat(central)
  local eocd = 'PK\5\6'
    .. le(0, 2)
    .. le(0, 2)
    .. le(#entries, 2)
    .. le(#entries, 2)
    .. le(#cd, 4)
    .. le(#body, 4)
    .. le(0, 2)
  return body .. cd .. eocd
end

-- Mirrors an upstream source archive: everything under one "<repo>-<ref>" root.
function M.write(path, root, marker)
  local fd = assert(io.open(path, 'wb'))
  fd:write(M.bytes({ { name = root .. '/lua/marker.lua', data = 'return "' .. marker .. '"' } }))
  fd:close()
  return path
end

return M