sscsm/minify.lua

--
-- A primitive code minifier
--
-- © 2019 by luk3yx
--

-- Find multiple patterns
local function find_multiple(text, ...)
    local n = select('#', ...)
    local s, e, pattern
    for i = 1, n do
        local p = select(i, ...)
        local s2, e2 = text:find(p)
        if s2 and (not s or s2 < s) then
            s, e, pattern = s2, e2 or s2, p
        end
    end
    return s, e, pattern
end

-- Matches
-- These take 2-3 arguments (code, res, char) and should return code and res.
local matches = {
    -- Handle multi-line strings
    ['%[=*%['] = function(code, res, char)
        res = res .. char
        char = char:sub(2, -2)
        local s, e = code:find(']' .. char .. ']', nil, true)
        if not s or not e then return code, res end
        return code:sub(e + 1), res .. code:sub(1, e)
    end,

    -- Handle regular comments
    ['--'] = function(code, res, char)
        local s, e = code:find('\n', nil, true)
        if not s or not e then return code, res end

        -- Shift trailing spaces back
        local spaces = res:match('(%s*)$') or ''
        return spaces .. code:sub(e), res:sub(1, #res - #spaces)
    end,

    -- Handle multi-line comments
    ['%-%-%[=*%['] = function(code, res, char)
        char = char:sub(4, -2)
        local s, e = code:find(']' .. char .. ']', nil, true)
        if not s or not e then return code, res end

        -- Shift trailing spaces back
        local spaces = res:match('(%s*)$') or ''
        return spaces .. code:sub(e + 1), res:sub(1, #res - #spaces)
    end,

    -- Handle quoted text
    ['"'] = function(code, res, char)
        res = res .. char

        -- Handle backslashes
        repeat
            local s, e, pattern = find_multiple(code, '\\', char)
            if pattern == char then
                res = res .. code:sub(1, e)
                code = code:sub(e + 1)
            elseif pattern then
                res = res .. code:sub(1, e + 1)
                code = code:sub(e + 2)
            end
        until not pattern or pattern == char

        return code, res
    end,

    ['%s*[\r\n]%s*'] = function(code, res, char)
        return code, res .. '\n'
    end,

    ['[ \t]+'] = function(code, res, char)
        return code, res .. ' '
    end,
}

-- Give the functions alternate names
matches["'"] = matches['"']

-- The actual transpiler
return function(code)
    assert(type(code) == 'string')

    local res = ''

    -- Split the code by "tokens"
    while true do
        -- Search for special characters
        local s, e, pattern = find_multiple(code, '[\'"\\]', '%-%-%[=*%[',
            '%-%-', '%[=*%[', '%s*[\r\n]%s*', '[ \t]+')
        if not s then break end

        -- Add non-matching characters
        res = res .. code:sub(1, math.max(s - 1, 0))

        -- Call the correct function
        local char = code:sub(s, e)
        local func = matches[char] or matches[pattern]
        assert(func, 'No function found for pattern!')
        code, res = func(code:sub(e + 1), res, char)
    end

    return (res .. code):trim()
end