From b95a41520cf3fbd5de98578f26b9a61f6f7c8c6c Mon Sep 17 00:00:00 2001
From: Colby <colby@taplaboratories.com.au>
Date: Tue, 9 Aug 2016 20:54:51 +1000
Subject: [PATCH] implement mbc3 functionality

---
 lib/waterfoul/mbc/mbc3.rb | 47 ++++++++++++++++++++++++++++++++++-----
 1 file changed, 42 insertions(+), 5 deletions(-)

diff --git a/lib/waterfoul/mbc/mbc3.rb b/lib/waterfoul/mbc/mbc3.rb
index 5b845f1..b04131b 100644
--- a/lib/waterfoul/mbc/mbc3.rb
+++ b/lib/waterfoul/mbc/mbc3.rb
@@ -1,14 +1,51 @@
 module Waterfoul
   module MBC
     class MBC3
-      def self.[](i)
-        fail
+      def initialize(program)
+        @game_program = program
+        @ram_bank = 0
+        @rom_bank = 0
+        @ram_enable = false
       end
 
-      def self.[]=(i,v)
-        fail
+      def [](i)
+        case i
+        when 0x0...0x4000 # ROM Bank 0
+          @game_program[i]
+        when 0x4000...0x8000 # ROM Bank n
+          addr = i - 0x4000
+          offset = @rom_bank * 0x4000
+          @game_program[offset + addr]
+        when 0xA000...0xC000
+          if @ram_enabled
+            addr = i - 0xA000
+            if @ram_bank == 0
+              @ram[addr]
+            else
+              offset = @ram_bank * 0x8000
+              @ram[offset + addr]
+            end
+          else
+            0xFF
+          end
+        end
+      end
+
+      def []=(i,v)
+        case i
+        when 0x0...0x2000
+          @ram_enable = (v & 0xA == 0xA ? true : false)
+        when 0x2000...0x4000
+          @rom_bank = (v & 0x7F)
+          @rom_bank += 1 if @rom_bank == 0
+        when 0x4000...0x6000
+          if v <= 0x3
+            @ram_bank = (v & 0x3)
+          #elsif (0x8..0xC) === v
+          end
+        when 0x6000...0x8000
+        end
       end
     end
   end
 end
-