Neovim, complex replacement in lua

complex_replace.lua

-- GOAL: replace placeholders with values
--
-- FIELDS EXAMPLE:
-- title,text,link
-- hello,world,something.com
-- good,morning,example.com
-- another,line,asdf.com
-- last,line,asdf.com
--
-- PATTERN EXAMPLE:
-- (placeholders and headers must match. example: title, text, link)
-- <h1>title</h1> <p>text</p> <a href="link">read more</a>
--
-- OUTPUT EXAMPLE:
-- <h1>hello</h1> <p>world</p> <a href="something.com">read more</a>
-- <h1>good</h1> <p>morning</p> <a href="example.com">read more</a>
-- <h1>another</h1> <p>line</p> <a href="asdf.com">read more</a>
-- <h1>last</h1> <p>line</p> <a href="asdf.com">read more</a>

-- subsitutes multiple strings
local function multiple_substitution(layout, searches, replacements)
  local outputString = layout
  for i, v in ipairs(searches) do
    outputString = string.gsub(outputString, v, replacements[i])
  end
  return outputString
end

-- splits a string into a table by a separator
local function split_string(inputstr, separator)
  separator = separator or "%s" -- default
  local t = {}
  for str in string.gmatch(inputstr, "([^" .. separator .. "]+)") do
    table.insert(t, str)
  end
  return t
end

-- performs complex replacement, first line in fields are headers, and must match the placerholders in pattern
local function complex_replace(fields, pattern)
  local headers
  local body = {}

  -- step 1: get headers and body in fields
  -- Iterate over non-empty lines in the string using string.gmatch
  for line in fields:gmatch("[^\r\n]+") do
    -- non empty lines
    if line:match("%S") then
      -- fist is headers, else is body
      if headers == nil then
        headers = split_string(line, ",")
      else
        body[#body + 1] = split_string(line, ",")
      end
    end
  end

  -- perform substitution on pattern on each row in body
  for i, replacements in ipairs(body) do
    body[i] = multiple_substitution(pattern, headers, replacements)
  end

  return body
end

local fields = [[
title,text,link
hello,world,something.com
good,morning,example.com
another,line,asdf.com
last,line,asdf.com
]]

local pattern = '<h1>title</h1> <p>text</p> <a href="link">read more</a>'

local result = complex_replace(fields, pattern)

for _, v in ipairs(result) do
  print(v)
end