feat: add simple contract

__crypto/simple_contract/src/credit.rs

@@ -0,0 +1,77 @@
+use std::{collections::HashMap, fs, fs::File};
+use serde::{Serialize, Deserialize};
+use crate::{tx::Transaction, util::{SimpleError, XResult}};
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct CreditContract {
+    pub credit_limit: u32,
+    pub issue_amount: u32,
+    pub admin: String,
+    pub credit: HashMap<String, u32>,
+}
+
+impl CreditContract {
+    pub fn new(tx: &Transaction, name: &str, credit_limit: u32) -> XResult<Self> {
+        let c = Self {
+            credit_limit,
+            issue_amount: 0,
+            admin: tx.sender.clone().unwrap(),
+            credit: HashMap::new(),
+        };
+        Self::save(name, &c)?;
+        Ok(c)
+    }
+
+    pub fn issue(&mut self, tx: &Transaction, receiver: &str, credit: u32) -> XResult<()> {
+        if &self.admin != tx.sender.as_ref().ok_or_else(|| SimpleError::new("Sender is not provided".into()))? {
+            return Err(SimpleError::new(format!("Current user is not admin, {} vs {:?}", self.admin, tx.sender)).into())
+        }
+        if self.issue_amount + credit > self.credit_limit {
+            return Err(SimpleError::new(format!("Issue too much credit, current: {}, issue: {}, limit: {}", self.issue_amount, credit, self.credit_limit)).into());
+        }
+        match self.credit.get_mut(receiver) {
+            None => { self.credit.insert(receiver.to_owned(), credit); },
+            Some(cr) => *cr += credit,
+        }
+        self.issue_amount += credit;
+        Ok(())
+    }
+
+    pub fn transfer(&mut self, tx: &Transaction, receiver: &str, credit: u32) -> XResult<()> {
+        match self.credit.get_mut(tx.sender.as_ref().ok_or_else(|| SimpleError::new("Sender is not provided".into()))?) {
+            None => return Err(SimpleError::new(format!("Have not enough credit: {:?}", tx.sender)).into()),
+            Some(cr) => {
+                if *cr >= credit {
+                    *cr -= credit;
+                    match self.credit.get_mut(receiver) {
+                        None => { self.credit.insert(receiver.to_owned(), credit); },
+                        Some(receiver_credit) => *receiver_credit += credit,
+                    }
+                } else {
+                    return Err(SimpleError::new(format!("Have not enough credit: {:?}", tx.sender)).into());
+                }
+            },
+        }
+        Ok(())
+    }
+
+    pub fn get(&self, _tx: &Transaction, account: &str) -> u32 {
+        match self.credit.get(account) {
+            None => 0,
+            Some(receiver_credit) => *receiver_credit,
+        }
+    }
+
+    pub fn load(name: &str) -> XResult<Self> {
+        let json = fs::read_to_string(name)?;
+        serde_json::from_str(&json).map_err(|e| e.into())
+    }
+
+    pub fn save(name: &str, c: &CreditContract) -> XResult<()> {
+        if let Ok(_) = File::open(name) {
+            return Err(SimpleError::new(format!("File exists: {}", name)).into());
+        }
+        fs::write(name, serde_json::to_string(c)?.as_bytes())?;
+        Ok(())
+    }
+}