diff --git a/flow b/flow
new file mode 100755
index 0000000..886223c
--- /dev/null
+++ b/flow
@@ -0,0 +1,153 @@
+#!/usr/bin/python3
+
+import os
+import hashlib
+from subprocess import run
+
+build_files_src = {}
+build_files_level = {}
+build_files_toBuild = {}
+
+def check_if_file(filename, build_file_name):
+    """ Checks it the given file exists, else print error and exit """
+    if os.path.isfile(filename):
+        return True
+    else:
+        print("In " + build_file_name + " : " +  filename + " is not a file")
+        exit(1)
+
+def getmd5(filename):
+    """ Takes Path to a file and get it's md5sum """
+    with open(filename, 'rb') as file_to_check:
+        data = file_to_check.read()
+        md5_returned = hashlib.md5(data).hexdigest()
+    return md5_returned
+
+def get_meta_file(filename):
+    """ Takes src file name in build file and converts it to entry in .flow folder filename """
+    fname = ""
+    for letter in filename:
+        if letter == "." or letter == "\\" or letter == "/":
+            pass
+        else:
+            fname += letter
+    return fname
+
+def update_md5(filename):
+    """ Takes the filename in .flow as var fname and updates it's md5sum value according to contents of var filename """
+    fname = get_meta_file(filename)
+    with open(".flow/" + fname, "w") as f:
+        f.write(getmd5(filename).strip())
+
+
+def getstoredmd5(filename):
+    """ get value of file's md5 from .flow folder, else create entry. return the (md5, createdEntry)"""
+    md5_returned = ""
+    fname = get_meta_file(filename)
+    if fname in os.listdir(".flow"):
+        with open(".flow/" + fname, "r") as f:
+            md5_returned = f.readline()
+    else:
+        print("INFO : md5sum entry not present for " + filename + " creating one.")
+        update_md5(filename)
+    return md5_returned
+
+def recieved_file(filename, level, rebuild):
+    if build_files_toBuild.get(filename, False) == False:
+        build_files_toBuild[filename] = rebuild
+    if build_files_level.get(filename, -1) < level:
+        build_files_level[filename] = level
+        pass
+    
+    start, mid, end = "", "", ""
+    with open(filename, "r") as f:
+        x = f.read().split(";!run!;")
+        start = x[0]
+        y = x[1].split(";!end!;")
+        mid = y[0]
+        end = y[1]
+
+    # start
+    src_files = []
+    for line in start.split():
+        entry = line.strip()
+        src_files.append(entry)
+
+    build_files_src[filename] = src_files
+    
+    if rebuild:
+        build_files_toBuild[filename] = True
+    else:
+        for line in start.split():
+            entry = line.strip()
+            check_if_file(entry, filename)
+            new_md5, old_md5 = "", ""
+            new_md5 = getmd5(entry)
+            old_md5 = getstoredmd5(entry)
+            
+            if old_md5 != new_md5:
+                print(entry + " was modified")
+                build_files_toBuild[filename] = True
+
+    # mid
+    if build_files_toBuild[filename]:
+        with open(filename + ".temp", "w") as f:
+            f.write(mid)
+
+    # end
+    for line in end.split():
+        entry = line.strip()
+        check_if_file(entry, filename)
+        recieved_file(entry, level + 1, build_files_toBuild[filename])
+        
+    
+
+def main():
+    with open("build.flow", "r") as main_build_file:
+        if not os.path.exists(".flow"):
+            os.makedirs(".flow")
+        for line in main_build_file:
+            entry = line.strip()
+            
+            if os.path.isfile(entry):
+                recieved_file(entry, 0, False)
+            else:
+                print("ERROR : " + entry + " is neither a file or a directory")
+                exit(1)
+
+    print(build_files_level)
+    print(build_files_src)
+    print(build_files_toBuild)
+    print()
+    print("┅ ┅ ┅ ┅ ┅ ┅ ┅ ┅ ┅ ┅ ┅ ┅ ┅ ┅ ┅ ┅ ┅ ┅ ┅ ┅ ")
+    print()
+
+    """ Build by using the data structures """
+    for f, x  in list(build_files_toBuild.items()):
+        if x == False:
+            del build_files_level[f]
+            del build_files_src[f]
+            del build_files_toBuild[f]
+
+    levels_list = []
+    for f,x in build_files_level.items():
+        levels_list.append((f,x))
+
+    n = len(levels_list)
+    for i in range(n):
+        for j in range(0, n-i-1):
+            if levels_list[j][1] > levels_list[j+1][1]:
+                levels_list[j], levels_list[j+1] = levels_list[j+1], levels_list[j]
+
+    for item in levels_list:
+        p = run([ "bash", item[0] + ".temp"  ])
+        if p.returncode != 0:
+            print(p)
+            exit(p.returncode)
+
+    for item in levels_list:
+        build_file_name = item[0]
+        for src_file in build_files_src[build_file_name]:
+            update_md5(src_file)
+        
+main()