-- Test function definition (your calculateStringSimilarity function goes here)
local prefix_weight = 0.1
local threshold = 0.8

local function test(str1, str2)
    local similarity = calculateStringSimilarity(str1, str2)
    local result = string.format('Comparing "%s" with "%s": %.3f', str1, str2, similarity)
    
    if threshold then
        local passes = similarity >= threshold
        result = result .. string.format(' [Threshold %.2f: %s]', 
            threshold, 
            passes and "PASS" or "FAIL")
    end
    
    print(result)
    return similarity
end

function calculateStringSimilarity(str1, str2)
    str1, str2 = str1:lower(), str2:lower()
    if str1 == str2 then
        return 1.0
    end

    local len1, len2 = #str1, #str2
    local str1_matches, str2_matches = {}, {}

    local match_distance = math.floor(math.max(len1, len2) / 2) - 1
    local matches = 0

    -- Count the number of matching characters
    for i = 1, len1 do
        local start = math.max(1, i - match_distance)
        local ends = math.min(i + match_distance, len2)

        for j = start, ends do
            if str2:sub(j,j) == str1:sub(i,i) and not str2_matches[j] then
                str1_matches[i] = true
                str2_matches[j] = true
                matches = matches + 1
                break
            end
        end
    end
    
    if matches == 0 then
        return 0.0
    end

    -- Count how many characters needed to change str1 into str2
    local k = 1
    local transpositions = 0
    for i = 1, len1 do
        if str1_matches[i] then
            while not str2_matches[k] do
                k = k + 1
            end
            if str1:sub(i,i) ~= str2:sub(k,k) then
                transpositions = transpositions + 1
            end
            k = k + 1
        end
    end

    -- With those two numbers, calculate the similary
    -- score with Jaro string comparison formula
    local distance = (
        matches / len1 +
        matches / len2 +
        (matches - transpositions/2) / matches
    ) / 3

    -- Set up for adjusting the score by prefix weight
    local prefix_length = 0
    for i = 1, math.min(4, math.min(len1, len2)) do
        if str1:sub(i,i) == str2:sub(i,i) then
            prefix_length = prefix_length + 1
        else
            break
        end
    end

    return distance + (prefix_length * prefix_weight * (1 - distance))
end

-- Test here
test("Elephant", "elephant")
test("Elephant", "élephant")
test("Elephant", "olephant")
test("Elephant", "esephant")