LUA Lag Compensation Version 0.4

--LUA Lag Compensation version 0.4 by FlooD
--thx to Jermuk for his custom server, which first encouraged me to make lag compensation.
--thx to lasthope and def3ct for initial testing.
--thx to 3rr0r for ideas and suggestions for refining the code.

BUFFER_SIZE = 25
frame = 0

buffer = {}
buffer[1] = {} --x buffer
buffer[2] = {} --y buffer

function clearbuffer(id)
    buffer[1][id] = {}
    buffer[2][id] = {}
end

for i = 1, 32 do
    clearbuffer(i)
end

addhook("leave", "clearbuffer")
addhook("die", "clearbuffer")

addhook("always", "updatebuffer")
function updatebuffer()
    frame = frame + 1
    for i = 1, 32 do
        buffer[1][i][frame], buffer[2][i][frame] = player(i, "x"), player(i, "y")
        buffer[1][i][frame - BUFFER_SIZE], buffer[2][i][frame - BUFFER_SIZE] = nil, nil
    end
end

addhook("hit", "onhit")
function onhit(v,id,wpn)
    if wpn ~= 51 then
        return 1
    end
end

addhook("attack", "onattack")
function onattack(id)
    local wpn = player(id, "weapon")
    if wpn == 51 then
        return
    end
    simulate_attack(id, wpn)
end

addhook("attack2", "onattack2")
function onattack2(id, mode)
    local wpn = player(id, "weapon")
    if wpn == 50 then
        simulate_attack(id, wpn, itemtype(wpn, "dmg_z1") * game("mp_damagefactor"))
    end
end

--[[simulates the shooting of a bullet of damage (dmg) from (wpn) by (id) with
angle (rot). it has two parts. part 1 finds bullet's path before hitting
a wall; part 2 calculates hits on other players (with lag compensation).]]
function simulate_attack(id, wpn, dmg, rot, range)
    if not wpn then wpn = player(id, "weapon") end
    if not dmg then dmg = itemtype(wpn, "dmg") * game("mp_damagefactor") end
    if not rot then rot = player(id, "rot") end
    if not range then range = itemtype(wpn, "range") end

    local start_x = player(id, "x")
    local start_y = player(id, "y")
    local end_x = start_x + (3 * range) * math.sin(math.rad(rot))
    local end_y = start_y - (3 * range) * math.cos(math.rad(rot))
    local tile_x = math.floor(start_x / 32)
    local tile_y = math.floor(start_y / 32)

    --part 1 - find the intersection of the bullet with the first wall it hits.
    local inc_x, inc_y

    if rot < 0 then
        inc_x = -1
    elseif rot > 0 and rot ~= 180 then
        inc_x = 1
    end

    if math.abs(rot) > 90 then
        inc_y = 1
    elseif math.abs(rot) < 90 then
        inc_y = -1
    end

    while not tile(tile_x, tile_y, "wall") do
        local temp_x, temp_y = tile_x, tile_y
        if inc_x and intersect(start_x, start_y, end_x, end_y, topixel(temp_x + inc_x), topixel(temp_y), 32) then
            tile_x = temp_x + inc_x
        end
        if inc_y and intersect(start_x, start_y, end_x, end_y, topixel(temp_x), topixel(temp_y + inc_y), 32) then
            tile_y = temp_y + inc_y
        end
        if tile_x == temp_x and tile_y == temp_y then
            break
        end
    end

    end_x, end_y = intersect(start_x, start_y, end_x, end_y, topixel(tile_x), topixel(tile_y), 32)
    --part 2 - detect hits
    local frames = math.floor(player(id, "ping") / 20)
    if frames > (BUFFER_SIZE - 1) then
        frames = (BUFFER_SIZE - 1)
    end

    local alive = player(0, "tableliving")
    for _, v in ipairs(alive) do
        if ((game("sv_friendlyfire") == 1) or (player(v, "team") ~= player(id, "team"))) and (v ~= id) and intersect(start_x, start_y, end_x, end_y, buffer[1][v][frame - frames], buffer[2][v][frame - frames], 24) then
            local newarmor = player(v, "armor") - dmg
            if newarmor < 0 then
                newarmor = 0
            end
            local newhealth = player(v, "health") - (dmg - math.floor(game("mp_kevlar") * (player(v, "armor") - newarmor)))
            if newhealth > 0 then
                parse("sethealth "..v.." "..newhealth)
                parse("setarmor "..v.." "..newarmor)
            else
                parse("customkill "..id.." "..itemtype(wpn, "name").." "..v)
            end
        end
    end
end

--the following three functions are used in simulate_attack.

--converts a tile number to the tile's center pixel.
function topixel(tile)
    return (tile * 32) + 16
end

--quick test to see if i is in between s and e. used in intersect().
function isinorder(s, i, e)
    return (e >= i and i >= s) or (e <= i and i <= s)
end

--[[returns the first point of intersection between a box centered at (bx, by) with
side length (bl) and a line segment starting from (sx, sy) and ending at (ex, ey).
if the line segment is enclosed by the box, (ex, ey) is returned.]]
function intersect(sx, sy, ex, ey, bx, by, bl)
    bl = bl / 2

    if math.abs(sx - bx) <= bl and math.abs(sy - by) <= bl then
        if math.abs(ex - bx) <= bl and math.abs(ey - by) <= bl then
            return ex, ey
        else
            return intersect(ex, ey, sx, sy, bx, by, bl)
        end
    end

    local i_x, i_y

    if ey > sy then
        i_y = by - bl
    elseif ey < sy then
        i_y = by + bl
    end
    if i_y and isinorder(sy, i_y, ey) then
        i_x = ((ex - sx) * i_y + (sx * ey - sy * ex)) / (ey - sy)
        if math.abs(i_x - bx) <= bl and isinorder(sx, i_x, ex) then
            return i_x, i_y
        end
    end

    if ex > sx then
        i_x = bx - bl
    elseif ex < sx then
        i_x = bx + bl
    end
    if i_x and isinorder(sx, i_x, ex) then
        i_y = ((ey - sy) * i_x + (sy * ex - sx * ey)) / (ex - sx)
        if math.abs(i_y - by) <= bl and isinorder(sy, i_y, ey) then
            return i_x, i_y
        end
    end
end