--[[
    Math HW helper thingy.  Features:
        -distance formula (1D or 2D)
        -pythagorean theorem
        -midpoint formula

    MODES:
        1 : P. Theorem
        2 : Distance Formula
        3 : Midpoint Formula
]]

local maxMode = 3
local mode = 0

function comma(amount)
    local formatted = tostring(amount)
    while true do
        formatted, k = string.gsub(formatted, "^(-?%d+)(%d%d%d)", '%1,%2')
        if k == 0 then
            break
        end
    end
    return formatted
end

function round(number)
    return tostring(number):find("%.") and tostring(number):sub(1, tostring(number):find("%.") + 3) or tostring(number)
end

function promptReturn()
    io.write("return to menu? YES/NO -> ")
    local reply = io.read()
    if reply:lower():find("yes") then
        io.write("\n")
        mode = 0
    end
end

function unpackPar(par)
    local isolate = {}
    local row = ""
    local lastChar;
    par = par:gsub("%s+", "")
    for char = 1, par:len() do
        if lastChar then
            if tonumber(par:sub(char, char)) then
                row = row .. par:sub(char, char)
            elseif row:len() > 0 then
                table.insert(isolate, row)
                row = ""
            end
        end
        lastChar = par:sub(char, char)
    end
    return unpack(isolate)
end

function handleMath(mode, input)
    return (
        mode == 1 and
            function()
                local a, b, c;
                io.write("a -> ") a = io.read()
                io.write("b -> ") b = io.read()
                io.write("c -> ") c = io.read()
                print (
                    a == "?" and
                        "\na = " .. comma(round(math.sqrt((c ^ 2) - (b ^ 2)))) .. " || root( " .. comma((c ^ 2) - (b ^ 2)) .. " )"
                    or b == "?" and
                        "\nb = " .. comma(round(math.sqrt((c ^ 2) - (a ^ 2)))) .. " || root( " .. comma((c ^ 2) - (a ^ 2)) .. " )"
                    or c == "?" and
                        "\nc = " .. comma(round(math.sqrt((a ^ 2) + (b ^ 2)))) .. " || root( " .. comma((a ^ 2) + (b ^ 2)) .. " )"
                    or "\n---> syntax error <---"
                )
                promptReturn()
            end
        or mode == 2 and
            function()
                local coord1, coord2, answer, x1, y1, x2, y2;
                io.write("point 1 -> ") coord1 = io.read()
                io.write("point 2 -> ") coord2 = io.read()
                x1, y1 = unpackPar(coord1)
                x2, y2 = unpackPar(coord2)
                answer = ((x2 - x1) ^ 2) + ((y2 - y1) ^ 2)
                print (
                    not (x1 and y1 and x2 and y2) and
                        "\n---> syntax error <---"
                    or
                        "\ndistance = " .. comma(round(math.sqrt(answer))) .. " || root( " .. comma(answer) .. " ) "
                )
                promptReturn()
            end
        or mode == 3 and
            function()
                local coord1, coord2, answer, type, x1, y1, x2, y2;
                io.write("Type of midpoint? (1D or 2D) -> ") type = io.read()
                if type:lower():find("1d") then
                    io.write("position 1 -> ") coord1 = io.read()
                    io.write("position 2 -> ") coord2 = io.read()
                    print (
                        not (tonumber(coord1) and tonumber(coord2)) and
                            "\n---> syntax error <---"
                        or
                            "\nmidpoint = " .. comma(round(0.5 * (tonumber(coord1) + tonumber(coord2))))
                    )
                    promptReturn()
                else
                    io.write("point 1 -> ") coord1 = io.read()
                    io.write("point 2 -> ") coord2 = io.read()
                    x1, y1 = unpackPar(coord1)
                    x2, y2 = unpackPar(coord2)
                    print (
                        not (x1 and y1 and x2 and y2) and
                            "\n---> syntax error <---"
                        or
                            "\nmidpoint = (" .. comma(round((x1 + x2) / 2)) .. ", " .. comma(round((y1 + y2) / 2)) .. ")"
                    )
                    promptReturn()
                end
            end
    )()
end

function changeMode(mode)
    return (tonumber(mode) > -1 and tonumber(mode) <= maxMode) and tonumber(mode) or 0
end

while true do
    if mode == 0 then
        print(
            "Math HW Helper by David.  Choose a mode:\n" ..
            "\t1) Pythagorean Theorem\n" ..
            "\t2) Distance Formula\n" ..
            "\t3) Midpoint Formula\n"
        )
        mode = changeMode(io.read())
    else
        handleMath(mode)
    end
end