diff --git a/Cargo.lock b/Cargo.lock
index 6b446b9..446f1aa 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -110,6 +110,18 @@ version = "1.70.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a6cb138bb79a146c1bd460005623e142ef0181e3d0219cb493e02f7d08a35695"
 
+[[package]]
+name = "itoa"
+version = "1.0.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "92ecc6618181def0457392ccd0ee51198e065e016d1d527a7ac1b6dc7c1f09d2"
+
+[[package]]
+name = "memchr"
+version = "2.7.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f52b00d39961fc5b2736ea853c9cc86238e165017a493d1d5c8eac6bdc4cc273"
+
 [[package]]
 name = "once_cell_polyfill"
 version = "1.70.2"
@@ -122,6 +134,7 @@ version = "0.1.0"
 dependencies = [
  "clap",
  "serde",
+ "serde_json",
 ]
 
 [[package]]
@@ -172,6 +185,19 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "serde_json"
+version = "1.0.149"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "83fc039473c5595ace860d8c4fafa220ff474b3fc6bfdb4293327f1a37e94d86"
+dependencies = [
+ "itoa",
+ "memchr",
+ "serde",
+ "serde_core",
+ "zmij",
+]
+
 [[package]]
 name = "strsim"
 version = "0.11.1"
@@ -215,3 +241,9 @@ checksum = "ae137229bcbd6cdf0f7b80a31df61766145077ddf49416a728b02cb3921ff3fc"
 dependencies = [
  "windows-link",
 ]
+
+[[package]]
+name = "zmij"
+version = "1.0.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1966f8ac2c1f76987d69a74d0e0f929241c10e78136434e3be70ff7f58f64214"
diff --git a/Cargo.toml b/Cargo.toml
index 8c31b46..b507dca 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,3 +6,4 @@ edition = "2024"
 [dependencies]
 clap = { version = "4.5.54", features = ["derive"] }
 serde = { version = "1.0.228", features = ["derive"] }
+serde_json = "1.0.149"
diff --git a/src/logic.rs b/src/logic.rs
index 3311f2b..889c291 100644
--- a/src/logic.rs
+++ b/src/logic.rs
@@ -2,6 +2,8 @@
 
 use serde::{Deserialize, Serialize};
 use std::fmt;
+use std::fs;
+use std::error::Error;
 
 #[derive(Default, Serialize, Deserialize, PartialEq)]
 enum Stav {
@@ -66,7 +68,39 @@ struct Kniznica {
 }
 
 impl Kniznica {
-    // fn pridaj_knihu
-    // fn odstran_knihu
-    // fn daj_knihu_podla_isbn
+    // Asociovana funkcia
+    fn nacitaj_zo_suboru(cesta: &std::path::PathBuf) -> Option<Self>{
+        let obsah = match std::fs::read_to_string(cesta) {
+            Ok(text) => text,
+            Err(_) => return None,
+        };
+        let kniznica = match serde_json::from_str(obsah.as_str()) {
+            Ok(k) => k,
+            Err(_) => return None,
+        };
+        Some(kniznica)
+    }
+    // Metoda
+    fn uloz_do_suboru(&self, cesta: &std::path::PathBuf) -> bool {
+        let converted = match serde_json::to_string(&self) {
+            Ok(k) => k,
+            Err(_) => return false,
+        };
+        match std::fs::write(cesta, converted) {
+            Ok(_) => return true,
+            Err(_) => return false,
+        };
+    }
+
+    fn pridaj_knihu(&mut self, nova_kniha: Kniha) -> Result<(), ()> {
+        if (&self.knihy).len() > 0 {
+            for x in &self.knihy {
+                if x.isbn == nova_kniha.isbn {
+                    return Err(());
+                }
+            }
+        }
+        self.knihy.push(nova_kniha);
+        Ok(())
+    }
 }