Deterministic peer id from seed for alice

This includes the introduction of the --data-dir parameter instead of the --database.
Both the seed file and the database are stored in the data-dir, the database in sub-folder `database`.

swap/src/seed.rs

@@ -0,0 +1,58 @@
+use ::bitcoin::secp256k1::{self, constants::SECRET_KEY_SIZE, SecretKey};
+use rand::prelude::*;
+use std::fmt;
+
+pub const SEED_LENGTH: usize = 32;
+
+#[derive(Clone, Copy, Eq, PartialEq)]
+pub struct Seed([u8; SEED_LENGTH]);
+
+impl Seed {
+    pub fn random() -> Result<Self, Error> {
+        let mut bytes = [0u8; SECRET_KEY_SIZE];
+        rand::thread_rng().fill_bytes(&mut bytes);
+
+        // If it succeeds once, it'll always succeed
+        let _ = SecretKey::from_slice(&bytes)?;
+
+        Ok(Seed(bytes))
+    }
+
+    pub fn bytes(&self) -> [u8; SEED_LENGTH] {
+        self.0
+    }
+}
+
+impl fmt::Debug for Seed {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Seed([*****])")
+    }
+}
+
+impl fmt::Display for Seed {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{:?}", self)
+    }
+}
+
+impl From<[u8; SEED_LENGTH]> for Seed {
+    fn from(bytes: [u8; SEED_LENGTH]) -> Self {
+        Seed(bytes)
+    }
+}
+
+#[derive(Debug, Copy, Clone, thiserror::Error)]
+pub enum Error {
+    #[error("Secp256k1: ")]
+    Secp256k1(#[from] secp256k1::Error),
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn generate_random_seed() {
+        let _ = Seed::random().unwrap();
+    }
+}