diff --git a/day2.cr b/day2.cr
index 5a5515a..4730600 100644
--- a/day2.cr
+++ b/day2.cr
@@ -1,25 +1,11 @@
+require "./intcode.cr"
 lines = File.read("day2.txt").lines.map(&.split(",").map(&.to_i32)).flatten
-def run(lines, noun, verb)
-  lines[1] = noun
-  lines[2] = verb
-  pos = 0
-  loop do
-    case lines[pos]
-    when 1
-      lines[lines[pos+3]] = lines[lines[pos+1]] + lines[lines[pos+2]]
-      pos += 4
-    when 2
-      lines[lines[pos+3]] = lines[lines[pos+1]] * lines[lines[pos+2]]
-      pos += 4
-    when 99
-      break
-    end
-  end
-  lines[0]
-end
 100.times do |noun|
   100.times do |verb|
-    if run(lines.dup, noun, verb) == 19690720
+    prog = lines.clone
+    prog[1] = noun
+    prog[2] = verb
+    if run(prog, [] of Int32)[1][0] == 19690720
       puts 100*noun + verb 
       break
     end
diff --git a/day5.cr b/day5.cr
index 7ec0c43..db464b4 100644
--- a/day5.cr
+++ b/day5.cr
@@ -1,49 +1,4 @@
+require "./intcode.cr"
 lines = File.read("day5.txt").chomp.split(",").map(&.to_i32)
-def run(lines, input)
-  output = [] of Int32
-  pos = 0
-  get = ->(x : Char, p : Int32) {
-    x == '0' ? lines[lines[pos+p]] : lines[pos+p]
-  }
-  loop do
-    str = "000" + lines[pos].to_s
-    case str
-    when .ends_with?("1")
-      lines[lines[pos+3]] = get.call(str[-3], 1) + get.call(str[-4], 2)
-      pos += 4
-    when .ends_with?("2")
-      lines[lines[pos+3]] = get.call(str[-3], 1) * get.call(str[-4], 2)
-      pos += 4
-    when .ends_with?("3")
-      lines[lines[pos+1]] = input.pop
-      pos += 2
-    when .ends_with?("4")
-      output << get.call(str[-3], 1)
-      pos += 2
-    when .ends_with?("5")
-      if get.call(str[-3], 1) != 0
-        pos = get.call(str[-4], 2) 
-      else
-        pos += 3
-      end
-    when .ends_with?("6")
-      if get.call(str[-3], 1) == 0
-        pos = get.call(str[-4], 2) 
-      else
-        pos += 3
-      end
-    when .ends_with?("7")
-      lines[lines[pos+3]] = (get.call(str[-3], 1) < get.call(str[-4], 2)) ? 1 : 0
-      pos += 4
-    when .ends_with?("8")
-      lines[lines[pos+3]] = (get.call(str[-3], 1) == get.call(str[-4], 2)) ? 1 : 0
-      pos += 4
-    when .ends_with?("99")
-      break
-    else
-      raise "aahhh #{str}"
-    end
-  end
-  {output, lines}
-end
-puts run(lines, [5])
+puts run(lines.clone, [1])
+puts run(lines.clone, [5])
diff --git a/day7.cr b/day7.cr
new file mode 100644
index 0000000..e8ed3b4
--- /dev/null
+++ b/day7.cr
@@ -0,0 +1,35 @@
+require "./intcode.cr"
+require "./intcode_fibers.cr"
+
+prog = File.read("day7.txt").chomp.split(",").map(&.to_i32)
+
+def chain_amplifiers(prog, perm, loop = false)
+  chans = perm.map { |f| new_interpreter(f, prog) }
+  chans.zip perm do |amp, freq|
+    amp[0].send freq
+  end
+
+  chans[0][0].send 0
+
+  i = 0
+  history = Array(Int32).new(chans.size, 0)
+  loop do
+    j = (i+1) % chans.size
+    break unless received = chans[i][1].receive
+    history[i] = received
+    chans[j][0].send received
+    i = j
+    break if i == 0 && !loop
+  end
+
+  history[4]
+end
+
+max_single = [0,1,2,3,4].permutations.max_of do |perm|
+  chain_amplifiers(prog.clone, perm)
+end
+puts max_single
+max_cycled = [5,6,7,8,9].permutations.max_of do |perm|
+  chain_amplifiers(prog.clone, perm, loop=true)
+end
+puts max_cycled
diff --git a/intcode.cr b/intcode.cr
new file mode 100644
index 0000000..483dd2d
--- /dev/null
+++ b/intcode.cr
@@ -0,0 +1,47 @@
+def run(lines, input)
+  output = [] of Int32
+  pos = 0
+  get = ->(x : Char, p : Int32) {
+    x == '0' ? lines[lines[pos+p]] : lines[pos+p]
+  }
+  loop do
+    str = "000" + lines[pos].to_s
+    case str
+    when .ends_with?("1")
+      lines[lines[pos+3]] = get.call(str[-3], 1) + get.call(str[-4], 2)
+      pos += 4
+    when .ends_with?("2")
+      lines[lines[pos+3]] = get.call(str[-3], 1) * get.call(str[-4], 2)
+      pos += 4
+    when .ends_with?("3")
+      lines[lines[pos+1]] = input.pop
+      pos += 2
+    when .ends_with?("4")
+      output << get.call(str[-3], 1)
+      pos += 2
+    when .ends_with?("5")
+      if get.call(str[-3], 1) != 0
+        pos = get.call(str[-4], 2) 
+      else
+        pos += 3
+      end
+    when .ends_with?("6")
+      if get.call(str[-3], 1) == 0
+        pos = get.call(str[-4], 2) 
+      else
+        pos += 3
+      end
+    when .ends_with?("7")
+      lines[lines[pos+3]] = (get.call(str[-3], 1) < get.call(str[-4], 2)) ? 1 : 0
+      pos += 4
+    when .ends_with?("8")
+      lines[lines[pos+3]] = (get.call(str[-3], 1) == get.call(str[-4], 2)) ? 1 : 0
+      pos += 4
+    when .ends_with?("99")
+      break
+    else
+      raise "Invalid instruction"
+    end
+  end
+  {output, lines}
+end
diff --git a/intcode_fibers.cr b/intcode_fibers.cr
new file mode 100644
index 0000000..18ee2e1
--- /dev/null
+++ b/intcode_fibers.cr
@@ -0,0 +1,42 @@
+def new_interpreter(f, prog)
+  prog = prog.clone
+  input = Channel(Int32).new
+  output = Channel(Int32?).new
+  spawn do
+    op = ""
+    pc = 0
+    arg = ->(i : Int32) { op[-(3+i)] == '0' ? prog[prog[pc+1+i]] : prog[pc+1+i] }
+    loop do
+      op = "0000" + prog[pc].to_s
+      case op
+      when .ends_with? "1"
+        prog[prog[pc+3]] = arg.call(0) + arg.call(1)
+        pc += 4
+      when .ends_with? "2"
+        prog[prog[pc+3]] = arg.call(0) * arg.call(1)
+        pc += 4
+      when .ends_with? "3"
+        prog[prog[pc+1]] = input.receive
+        pc += 2
+      when .ends_with? "4"
+        output.send(arg.call(0))
+        pc += 2
+      when .ends_with? "5"
+        pc = arg.call(0) != 0 ? arg.call(1) : pc + 3
+      when .ends_with? "6"
+        pc = arg.call(0) == 0 ? arg.call(1) : pc + 3
+      when .ends_with? "7"
+        prog[prog[pc+3]] = arg.call(0) < arg.call(1) ? 1 : 0
+        pc += 4
+      when .ends_with? "8"
+        prog[prog[pc+3]] = arg.call(0) ==  arg.call(1) ? 1 : 0
+        pc += 4
+      when .ends_with? "99"
+        input.receive
+        output.send(nil)
+        break
+      end
+    end
+  end
+  {input, output}
+end