Diff Program

-- Diff
-- By KillaVanilla

local args = {...}

local function get_diff(f1, f2)
     -- Do trimming:
    local start = 1
    local f1_end = #f1
    local f2_end = #f2
    while (start <= #f1) and (start <= #f2) do
        if not (f1[start] == f2[start]) then
            start = start-1
            break
        else
            start = start+1
        end
    end
    while (f1_end >= start) and (f2_end >= start) do
       if not (f1[f1_end] == f2[f2_end]) then
            f1_end = f1_end+1
            f2_end = f2_end+1
            break
        else
            f1_end = f1_end-1
            f2_end = f2_end-1
        end
    end
    local c = {}
    for i=0, #f1 do
        c[i] = {}
        c[i][0] = 0
    end
    for i=0, #f2 do
        c[0][i] = 0
    end
    for i=1, #f1 do
        for j=1, #f2 do
            if f1[i] == f2[j] then
                c[i][j] = c[i-1][j-1]+1
            else
                c[i][j] = math.max(c[i][j-1], c[i-1][j])
            end
        end
    end

    local d = {}
    local function recurser(i, j)
        if (i>0) and (j>0) and (f1[i] == f2[j]) then
            recurser(i-1, j-1)
            table.insert(d, {0, f1[i]})
            --print(" "..f1[i])
        elseif (j>0) and ((i==0) or (c[i][j-1] >= c[i-1][j])) then
            recurser(i, j-1)
            table.insert(d, {1, f2[j], i, j})
            --print(j..">"..f2[j])
        elseif (i>0) and ((j==0) or (c[i][j-1] < c[i-1][j])) then
            recurser(i-1, j)
            table.insert(d, {2, f1[i], i, j})
            --print(i.."<"..f1[i])
        end
    end
    recurser(#f1, #f2)
    return d
end

if #args < 3 then
    print("diff - Get differences between files")
    print(string.rep("=", term.getSize()))
    print("USAGE: diff <file1> <file2> <output file>")
else
    assert(fs.exists(args[1]), args[1].." does not exist!")
    assert(fs.exists(args[2]), args[2].." does not exist!")
    local lines_1 = {}
    local lines_2 = {}
    local last_pause = os.clock()
    local f1 = fs.open(args[1], "r")
    while true do
        local line = f1.readLine()
        if line then
            table.insert(lines_1, line)
        else
            break
        end
        if (os.clock() - last_pause) >= 2.8 then
            os.queueEvent("")
            os.pullEvent("")
            last_pause = os.clock()
        end
    end
    f1.close()
    local f2 = fs.open(args[2], "r")
    while true do
        local line = f2.readLine()
        if line then
            table.insert(lines_2, line)
        else
            break
        end
        if (os.clock() - last_pause) >= 2.8 then
            os.queueEvent("")
            os.pullEvent("")
            last_pause = os.clock()
        end
    end
    f2.close()
    local diff = get_diff(lines_1, lines_2)
    local f3 = fs.open(args[3], "w")
    for i=1, #diff do
        if diff[i][1] == 1 then
            f3.writeLine(diff[i][4]..">"..diff[i][2])
        elseif diff[i][1] == 2 then
            f3.writeLine(diff[i][4].."<"..diff[i][2])
        end
    end
    --f3.writeLine(textutils.serialize(diff))
    f3.close()
end