digTShape

local t = turtle

function detectGravel()
    while t.detect() == true do
        t.dig()
    end
end

-- Assumes starting on bottom
function digThreeByH(height, alreadyInside)
    if alreadyInside == false then
        t.dig()
        detectGravel()
        t.forward()
    end
    t.turnLeft()
    for i=1, height do
        t.dig()
        if i < height then
            t.digUp()
            t.up()
        end
    end
    t.turnRight()
    t.turnRight()
    t.dig()
    for i=1, height-1 do
        t.down()
        t.dig()
    end
    detectGravel()
    t.turnLeft()
    t.turnLeft()
    detectGravel()
    t.turnRight()
end

function digTunnel(len, height, alreadyInside)
    for i=1, len do
        if alreadyInside == true and i == 1 then
            digThreeByH(height, true)
        else
            digThreeByH(height, false)
        end
    end
end

function digTShape(baseLen, baseHeight, armLen, armHeight, alreadyInside)
    digTunnel(baseLen, baseHeight, alreadyInside)
    for i=1, 2 do
        t.dig()
        detectGravel()
        t.forward()
    end
    t.turnRight()
    for i=1, math.floor(armLen/2) do
        t.dig()
        detectGravel()
        t.forward()
    end
    t.turnLeft()
    t.turnLeft()
    digTunnel(armLen, armHeight, true)
    t.turnLeft()
    t.turnLeft()
    for i=1, math.floor(armLen/2) do
        t.forward()
    end
    t.turnRight()
    for i=1, baseLen+1 do
        t.forward()
    end
end

digTShape(9,3,15,4, true)