Merge pull request 'making-readme-more-tutorial-like' (#1) from making-readme-more-tutorial-like into main

Reviewed-on: #1

README.md

@@ -3,12 +3,17 @@
 A simple example of how to implement the state pattern in c. check [`main.c`](src/main.c) for the implementation.
 
 the state pattern is a pattern that aims to get rid of the mess that a state machine causes within your code. So i propose a problem for you, you are trying to write an state machine for a phone, sounds easy your phone only has 3 inputs that change the current state of the phone.
+
+#### inputs:
 - power button
 - lock button
 - string enter button
+
 the power button does what it says either turns the phone off or on, the lock button too does what it says on the tin locks the phone, lastly the string enter button enters what every string is in the phones buffer this is used for entering things like passwords to unlock the phone.
 
-using these buttons you determin you need 4 states for your phone these are:
+using these buttons you determine you need 4 states for your phone these are:
+
+#### states:
 - off
 - unlock
 - locked
@@ -47,10 +52,18 @@ str=x : string enter button press with string x
 ----------- \ state diagram -----------
 ```
 
-now you may read these requirements for the device and think ill just implement this with a state machine how bad can it be. Well your tech lead tells you that this systems needs to scaled to over 100 different states as they make the system more complex. you ask him "why do we need this" they reply back with managment said so. And so between the idea of getting fired from throwing a brick at the managment team and implementing this state diagram you decide you need this job and to implement state pattern.
+now you may read these requirements for the device and think ill just implement this with a state machine how bad can it be. Well your tech lead tells you that this systems needs to scaled to over 100 different states as they make the system more complex. you ask him "why do we need this" they reply back with management said so. And so between the idea of getting fired from throwing a brick at the management team and implementing this state diagram you decide you need this job and to implement state pattern.
-this pattern allows for greater flexablity when creating new states since you dont have to add to an ever growning state machine (lets do some simple math if we assume that you end up with 100 states in the end and each state takes up 20 odd line that would be a 2k line state machine and a nightmare to debug (i should know ive seen them in the wild))
+this pattern allows for greater flexibility when creating new states, since you dont have to add to an ever gowning state machine. we do some simple math to see how out of hand this can get, 
+if we assume that you end up with 100 states in the end and each state takes up 20 odd line 
+$$
+100_{\text{states}} \times 20_{\text{loc}} = 2000_{\text{loc}}
+$$
+that would be a 2k line state machine and a nightmare to debug (i should know ive seen them in the wild)
 
-so to start implement this pattern we first draw up a uml diagram of how it should go togeather. we can see we have the device itself and which is composed of a device state that has the pointer to the device that it is in
+so to start implement this pattern we first draw up a uml diagram of how it should go together. we can see we have the device itself and which is composed of a device state, and the entered string. 
+
+
+This "class" also has 3 methods pressPwrButton, pressStrInputButton, and pressLockButton. these methods are used to create an abstraction from the device state so the underlying state can change while using the same input functions.
 
 ```mermaid
 classDiagram
@@ -74,56 +87,121 @@ classDiagram
         +DeviceInterface_s methods
     }
     Device_t *-- DeviceState_t
-    %% DeviceInterface_s --o Device_t
     Device_t o-- DeviceInterface_s
-
     DeviceInterface_s --o DeviceState_t
 
 ```
 (note not real uml diagram because no one knows how to read them)
 
+1. so to implement this we will first start off with the [device struct](/src/device.h#L64) 
+    ```c
+    // device.h
+    typedef struct Device_s{
+        DeviceState_t state,
+        char* entered_string,
+    } Device_t;
+    ```
+
+2. Next we will implement the [methods](/src/device.h#L34) which in this case will be an [interface](https://en.wikipedia.org/wiki/Interface_(object-oriented_programming)). These methods are all the changes that can be made to the device i.e. your [inputs](#inputs).
+
+    ```c
+    // device.h
+    typedef struct DeviceInterface_s{
+        void (*pressPwr)(Device_t*);
+        void (*pressStrInput)(Device_t*);
+        void (*pressLock)(Device_t*);
+    } DeviceInterface_t;
+    ```
 
 
-so to implement this we will first create a struct for the device well call this [Device_t](/src/device.h#L67) this device holds its current state ([DeviceState_s](/src/device.h#L52)) and the string that was entered. The [DeviceState_s](/src/device.h#L52) actually holds all the [functions](/src/device.h#L34) or [methods](/src/device.h#L34) that this device uses, with the pressPwrButton, pressStrInputButton, and pressLockButton methods just being alias to these methods as can be seen in [device.c](/src/device.c). these method are defined within the [DeviceInterface_t](/src/device.h#L34) struct which really just acts as a [vtable](https://en.wikipedia.org/wiki/Virtual_method_table) for the given inputs (power button, lock button, string enter button) that will effect the device.
+3. and finally we will implement the [struct to hold the actual state](/src/device.h#L52) of the device. (note there is some funkiness in c with implementing this since you will need forward decls)
-This whole interface allows for the underlying state to change with out having to use differnt function calls depending on the current state.
+    ```c
+    // device.h
+    typedef struct DeviceState_s{
+        const char* state_name;    
+        DeviceInterface_t methods;
+    }DeviceState_t;
+    ```
+4. now we need to implement the 3 functions for device inputs, ive implemented one here as the rest are very [similar](/src/device.c#L14). So this function takes the given device and then uses the methods defined within the device state to change the current state of the device. 
+    ```c
+    // device.c
+    void pressPwrButton(Device_t *device) {
+        device->state.methods.pressPwr(device);
+    }
+    ```
+5. now we will create a new header file called state, this file will contain the functions that sets the state of the given device to a new state. so we will implement a function per out defined [states](#states).
+    ```c
+    //state.h
+    void setDeviceStateToUnlock(Device_t *device);
+    void setDeviceStateToDebug(Device_t *device);
+    void setDeviceStateToLock(Device_t *device);
+    void setDeviceStateToOff(Device_t *device);
+    ```
+6. now we can implement one of these states as the rest of them should be fairly self explanatory. the state we will be implementing is the [lock state](/src/states/lock_state.c) as this should show off most of the different transitions. we will first start out with implementing the set state function. this function takes the given device and sets that devices state to this new state.
+    ```c
+    // lock_state.h
+    void setDeviceStateToLock(Device_t *device) {
+        device->state = (DeviceState_t){
+            .state_name = lock_state_name,
+            .methods = (DeviceInterface_t){
+                .pressPwr = &pressPwrMethod,
+                .pressStrInput = &pressStrInputMethod,
+                .pressLock = &pressLockMethod,
+            },
+        };
+    }
+    ```
+7. now that we have the function for setting this state we can now implement the functions for what this functions does depending on the inputs we will first start with the power button function. This is one of the simplest when the power button is press i.e. when the function is called we set the devices state to off.
+    ```c
+    // lock_state.c
+    static void pressPwrMethod(Device_t *device) {
+        printf("turning off device\n");
+        setDeviceStateToOff(device);
+    }
 
-now to actually create the meat of this device the logic that changes the state, to do this we will first create a [header file](/src/states/state.h) to store all the functions that change the state of the device. now we will implement and state so we will start [off state](/src/states/off_state.c) with the easest one the off state (no bother having the rest if the device cant turn on). to create this state we will implement the functions that are defined within the [interface](/src/device.h#L34) we created, this functions will define what happens to the current state based on the given input. so `pressPwrMethod` is what happens when the power button is pressed when its in the off state (to make the code [grep-able](https://morizbuesing.com/blog/greppability-code-metric/) these functions should probably be prefixed with the given state like `OffStatePressPwrMethod`). these function are prefix with the static keyword as they should only ever be used here and not exposed. the other methods should be self explanatory. lastly we must implement the function that actually changes the state of the device to this given state, so to change the state we just set the devices state to a new struct with the given methods that we defined within this file.
+    ```
+8. now we will implement the next function the lock button which in the lock state will do nothing.
+    ```c
+    // lock_state.c
+    static void pressLockMethod(Device_t *device) {
+        (void) device;
+        printf("nothing happens\n");
+    }
+    ```
     
-```c
+9. finally we create the function for handling the text input, this function will check the entered string to see if its either "dbg", or "pwd" and if it is enter debug or unlock respectively.
+    ```c
+    static void pressStrInputMethod(Device_t *device) {
+        if (strcmp(device->entered_string, "dbg") == 0) {
+            printf("entering debug state\n");
+            setDeviceStateToDebug(device);
+            return;
+        }
+        if (strcmp(device->entered_string, "pwd") == 0) {
+            printf("entering unlock state\n");
+            setDeviceStateToUnlock(device);
+            return;
+        }
+        printf("unknown string %s\n", device->entered_string);
+    }
+    ```
+10. now we just need to implement the other [states](#states) in the same way we implemented this first one.
+11. finally we need to test our device. firstly within main we create a new device and set its initial state to off.
+    ```c
+    Device_t device;
+    initDevice(&device);
+    setDeviceStateToOff(&device);
+    ```
+12. now we can test that the device correctly travels through each state, by pressing one of the buttons ([invoking the input method functions](/src/device.h#L34)) then checking that the `state_name` is equal to the set state name.
+    ```c
     
-static void pressPwrMethod(Device_t *device) {
+    // turn on the device
-    printf("turning on device\n");
+    pressPwrButton(&device);
-    setDeviceStateToLock(device);
+    if (strcmp(device.state.state_name, "lock_state.c") != 0) return 0;
-}
 
-static void pressStrInputMethod(Device_t *device) {
+    ```
-    // cast it to void since its unused
-    (void) device;
-    printf("nothing happens\n");
-}
 
-static void pressLockMethod(Device_t *device) {
+now that you have implement this basic state pattern your tech lead comes to you and tells you to implement one more state then they will let you throw a brick at management as a treat this state is:
-    // cast it to void since its unused
-    (void) device;
-    printf("nothing happens\n");
-}
-
-void setDeviceStateToOff(Device_t *device) {
-    device->state = (DeviceState_t){
-        .state_name = off_state_name,
-        .device = device,
-        .methods = (DeviceInterface_t){
-            .pressPwr = &pressPwrMethod,
-            .pressStrInput = &pressStrInputMethod,
-            .pressLock = &pressLockMethod,
-        },
-    };
-}
-
-```
-and finally we expose the set method in our [header file](/src/states/state.h) so the other states can set to this state. next we just implement the rest of the state Lock, Unlock, and Debug and can finally test our creation in [`main.c`](/src/main.c).
-
-now that you have implement this basic state pattern your tech lead comes to you and tells you to implement one more state then they will let you throw a brick at managment as a treat this state is:
 - A calling state where:
     - when the phone is unlocked you can type in a number in the the string input and it will call it
     - you can also turn off the phone from this state
@@ -131,6 +209,8 @@ now that you have implement this basic state pattern your tech lead comes to you
 
 so try implementing this yourself.
 
+other good resources for learning how this patterns works is [bob nystrom's game programming patterns book](https://gameprogrammingpatterns.com/state.html) as well as [refactoring Guru](https://refactoring.guru/design-patterns/state) however both of these implement this in the fun languages with object and interfaces.
+
 # how to build and run it
 
 this demo uses a simple build system called [nob](https://github.com/tsoding/nob.h) a header only build system for c projects.
@@ -148,4 +228,4 @@ to build run these command in the root of the project:
 > ./build/main 
 
 ```
-and if you have a differnt complier you want to use that is posix compliant just change the `CC` macro in the `nob.c` with your one.
+and if you have a different compiler you want to use that is posix compliant just change the `CC` macro in the `nob.c` with your one.