Hello World Maze

local debug = (select(2,...))=='debug';
local termW, termH = term.getSize();
local w, h = math.floor(termW/2), math.floor(termH/2-1)
--w, h = tonumber(w) or 9, tonumber(h) or 9;
--[[local]] text = ((...) or 'Hello_World!'):gsub('%s', '_'):sub(1,16);

local movePos = function(pos, dir)
    local newpos = {pos[1], pos[2]}
    newpos[2-dir%2] = newpos[2-dir%2] + dir-dir%2-1;
    return newpos;
end

local getWallPos = function(pos, wall)
    pos = {2*pos[2],2*pos[1]};
    --[
    local dir = wall%2+1;
    wall = wall-dir
    pos[dir]=pos[dir]+wall
    --]]
    --pos = movePos(pos, wall);
    return pos[2], pos[1];
end

checkWalls = function(pos, count, _maze)
    if debug then term.setCursorPos(21,9); term.clearLine(); term.write('checkWalls called'); end
    if pos[1] < 1 or pos[2] < 1 or pos[1] > w or pos[2] > h then return false end
    local walls = 4;
    for i = 0,3 do
        local charX, charY = getWallPos(pos, i);
        if _maze[charX][charY]==' ' then
            if debug then term.setCursorPos(21,10); term.clearLine(); term.write('Missing walls at {'..table.concat(pos,', ')..', '..i..'}'); end
            if count then walls = walls - 1 else return false; end
        end
    end
    if debug then term.setCursorPos(21,10); term.clearLine(); term.write('All walls at {'..table.concat(pos, ', ')..'}'); end
    return count and walls or true;
end

local removeWall = function(pos, wall, _maze)
    local charX, charY = getWallPos(pos, wall);
    _maze[charX][charY] = ' '
end


local centerText = function(y, text)
    term.setCursorPos((termW-#text)/2,y)
    term.write(text);
end

local MAZECHARS = {'+', '-', '|', ' '};

function generateMaze(--[[w,h]])
    local maze = {};
    for x = 0, 2*w do
        local col = {};
        for y = 0, 2*h do
            col[y+1] = MAZECHARS[x%2 + (y%2)*2 + 1];
        end
        maze[x+1]=col;
    end



    local cells = {}; --LIFO stack containing visited cells
    local total = w*h; --Total number of cells to visit
    local visited = 1;
    local currentCell = {math.random(1,w), math.random(1,h)};
    while visited < total do
        if debug and currentCell then term.setCursorPos(24, 2); term.clearLine(); term.write('{'..table.concat(currentCell, ', ')..'}') end
        local adjacentCells = {};
        for j = 0, 3 do
            --[
            cell = {currentCell[1], currentCell[2]};
            cell[2-j%2] = cell[2-j%2] + j-j%2-1;
            --]]
            --local cell = movePos(currentCell, j)
            if debug then term.clear(); term.setCursorPos(1,1); term.write(tostring(visited)..'/{'..table.concat(cell, ', ')..'}'); end
            if checkWalls(cell, false, maze) then
                cell[3] = j;
                adjacentCells[#adjacentCells+1] = cell;
                if debug then term.setCursorPos(24+j, 19); term.clearLine(); term.write(tostring(j+1)); end
            end

            if debug then term.setCursorPos(24, 13+j); term.clearLine(); term.write('{'..table.concat(cell, ', ')..'}') end
        end
        if #adjacentCells >= 1 then
            local cell = adjacentCells[math.random(1,#adjacentCells)];
            removeWall(currentCell, cell[3], maze);
            cells[#cells+1]=currentCell;
            currentCell = cell;
            visited = visited + 1;
        else
            currentCell = cells[#cells];
            cells[#cells]=nil;
        end
        if debug then --[[draw(true);]] term.write(visited..' '); for k=1,4 do local zcf = adjacentCells[k]; term.setCursorPos(24,2+k); term.clearLine(); term.write(not zcf and '---' or '{'..table.concat(zcf, ', ')..'}') end term.setCursorPos(24,7); term.clearLine(); term.write(#adjacentCells); term.setCursorPos(1,1) end
    end
    return maze
end

local maze;
local deadEnds = {};
local letters = {};
local playerPos;
local collectedText = '';
local completed = false;
local easterEgg = false;

local attempts = 0;
repeat
    deadEnds = {};
    maze = generateMaze(--[[w,h]])
    for x = 1, w do
        for y = 1, h do
            if checkWalls({x,y}, true, maze) == 3 then
                deadEnds[#deadEnds+1] = {x, y};
            end
        end
    end
    attempts = attempts+1;
until #deadEnds >= #text+1 or attempts>=16;

if attempts>=16 then
    term.clear()
    term.setCursorPos(1,1)
    print('Failed to generate a maze with at least ',#text+1,' dead ends within 16 attempts. Try again with a larger screen size.')
    return
end

--[[repeat]] playerPos = {math.random(1,w), math.random(1,h)}
--until not letters[playerPos[1]*w+playerPos[2]];

local assignToDeadEnd = function(letter)
    local num = math.random(1,#deadEnds)
    if (playerPos[1] == deadEnds[num][1] and playerPos[2] == deadEnds[num][2]) then
        num = num % #deadEnds + 1
    end
    local deadEnd = table.remove(deadEnds, num);
    letters[deadEnd[1]-1+(deadEnd[2]-1)*w]=letter;
end

for i = 1, #text do
    assignToDeadEnd(text:sub(i,i));
end


local checkForLetter = function()
    --if playerPos[1]%2 ==1 or playerPos[2]%2 ==1 then return end
    local pos = playerPos[1]-1+(playerPos[2]-1)*w;
    local letter = letters[pos];
    if letter then
        collectedText = collectedText .. letter;
        letters[pos] = nil;
        deadEnds[#deadEnds+1]={playerPos[1],playerPos[2]};
        if collectedText == text then completed = true; return end
        if collectedText == text:reverse() then completed = true; easterEgg = true; return end
    end
end

local returnLetter = function()
    if #collectedText < 1 then return end
    assignToDeadEnd(collectedText:sub(-1,-1));
    collectedText=collectedText:sub(1,-2);
end

local movePlayer = function(dir)
    local wallX, wallY = getWallPos(playerPos, dir)
    if maze[wallX][wallY] ~= ' ' then return end
    playerPos = movePos(playerPos, dir)
    checkForLetter();
end

local draw = function()
    term.clear();
    local w1, h1 = math.min(2*w+1,(term.getSize())), math.min(2*h+1, (select(2,term.getSize())));
    for x = 1, w1 do
        for y = 1, h1 do
            term.setCursorPos(x, y);
            term.write(maze[x][y]);
        end
    end
    for i, v in pairs(letters) do
        local x = i%w+1;
        local y = (i-x+1)/w+1;
        term.setCursorPos(2*x, 2*y);
        term.write(v)
    end
    term.setCursorPos(playerPos[1]*2, playerPos[2]*2);
    term.write('#');
    term.setCursorPos(1,termH);
    centerText(termH,collectedText);
    term.setCursorPos(1,1);
end

local controls = {
    [keys.up] = function() movePlayer(0) end,
    [keys.left] = function() movePlayer(1) end,
    [keys.down] = function() movePlayer(2) end,
    [keys.right] = function() movePlayer(3) end,
    [keys.space] = returnLetter
}

term.clear()
centerText(3, 'Instructions')
centerText(math.floor(termH/2)-2, 'Arrow keys to move')
centerText(math.floor(termH/2)-1, 'SPACE to return letter to maze')
centerText(math.floor(termH/2), '_ is a space')
centerText(math.floor(termH/2)+1, 'You control the #')
centerText(termH-2, 'Press ENTER to continue')
for evt, key in os.pullEvent do if evt=='key' and key==keys.enter then break end end

draw();
while not completed do
    local evt, key = os.pullEvent('key');
    if controls[key] then
        controls[key]();
        draw()
    end
end

for i = 1, termH-1 do
    term.setCursorPos(1,i);
    term.clearLine();
    sleep(0.1);
end
for i = 1,5 do
    centerText(math.floor(termH/2), not easterEgg and text or ({'!oot', 'sdrawkcab', 'etirw', 'nac', 'I'})[i])
    sleep(0.6)
    term.clearLine()
    sleep(0.4)
end
term.setCursorPos(1,1)