#!/bin/env lua
-- Basic mass file renamer using osx and
-- standard Lua gsub().
--
-- SYNOPSIS:
-- rename.lua <pattern> <replacement> [directory]
--
-- Renames every file inside a directory (defaults to current directory).
-- Trimmed down but functional and useful variant of util-linux rename(1).
--
-- Example uses:
-- lua rename.lua 'something' 'something_else'
-- lua rename.lua '(%w+).lua' '%1.lua.bk' src
--
-- Author: Lorenzo Cogotti, The DoubleFourteen Code Forge

local io = require 'io'
local osx = require 'osx'
local write = io.write
local dir = osx.dir
local sep = osx.sep

local ENOENT = 2  -- errno value for No such file or directory

-- Read command line arguments
local pattern = assert(select(1, ...), "Missing filename pattern argument")
local repl = assert(select(2, ...), "Missing filename replacement argument")
local path = select(3, ...) or "."

-- Rename en-masse
for filename in dir(path) do
    local newfilename = filename:gsub(pattern, repl, 1)

    if filename ~= newfilename then
        local from = path..sep..filename
        local to = path..sep..newfilename

        -- Refuse to overwrite files
        local buf, err, code = osx.stat(to)
        if buf then
            error(filename..": File '"..to.."' exists, refusing to overwrite.")
        end
        if code ~= ENOENT then
            -- Anything but "file does not exist" is dangerous, so bail out
            error(err)
        end

        -- Print a nice message and rename things
        write(from, ' -> ', to, '\n')
        assert(osx.rename(from, to))
    end
end