local chupacabra = {}

-- Parse a string into a list of tokens
function chupacabra.tokenize(s)
    local tokens = {}
    local array = nil
    for token in s:gmatch("%S+") do
        if array then
            array = array .. " " .. token
            if token:find("]$") then
                table.insert(tokens, array)
                array = nil
            end
        elseif token:find("^%[") then
            array = token
        else
            table.insert(tokens, token)
        end
    end
    return tokens
end

function chupacabra.evaluate(tokens, context)
    local stack = {}

    for _, token in ipairs(tokens) do
        if tonumber(token) then
            table.insert(stack, tonumber(token))
        elseif token:match("^%b[]$") then -- If the token is an array
            local array = {}
            for number in token:sub(2, -2):gmatch("%S+") do
                table.insert(array, tonumber(number))
            end
            table.insert(stack, array)
        elseif token == "pop" then
            table.remove(stack) -- testing is fun
        elseif token == "+" then
            local b = table.remove(stack)
            local a = table.remove(stack)
            table.insert(stack, a + b)
        elseif token == "-" then
            local b = table.remove(stack)
            local a = table.remove(stack)
            table.insert(stack, a - b)
        elseif token == "*" then
            local b = table.remove(stack)
            local a = table.remove(stack)
            table.insert(stack, a * b)
        elseif token == "/" then
            local b = table.remove(stack)
            local a = table.remove(stack)
            table.insert(stack, a / b)
        elseif token == "map+" then -- FIXME: fix all map functions to either add 2 arrays or spread
            local a = table.remove(stack)
            for i, v in ipairs(a) do
                a[i] = v + 1
            end
            table.insert(stack, a)
        elseif token == "map*" then
            local a = table.remove(stack)
            for i, v in ipairs(a) do
                a[i] = v * 2
            end
            table.insert(stack, a)
        elseif token == "map-" then
            local a = table.remove(stack)
            for i, v in ipairs(a) do
                a[i] = v - 1
            end
            table.insert(stack, a)
        elseif token == "map/" then
            local a = table.remove(stack)
            for i, v in ipairs(a) do
                a[i] = v / 2
            end
            table.insert(stack, a)
        else
            error("invalid token: " .. token)
        end
    end

    return table.remove(stack)
end

function chupacabra.run(str, context)
    local tokens = chupacabra.tokenize(str)
    return chupacabra.evaluate(tokens, context)
end

return chupacabra