feat(provider): add mailgun provider (#6)

Changelog
* Add mailgun provider struct
* Add provider error enum
* Add email notification struct
* Add thiserror dependancy to cargo.toml

Cargo.toml

@@ -4,6 +4,9 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
+# Error handling
+thiserror = "2.0.1"
+
 # API
 axum = "0.7.7"
 hyper = { version = "1.5.0", features = ["full"] }

src/main.rs

@@ -1,5 +1,6 @@
 mod config;
 mod templates;
+mod providers;
 
 use axum:: Router;
 use crate::config::Config;

src/providers/errors.rs

@@ -0,0 +1,42 @@
+use std::fmt;
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum ProviderError {
+    #[error("Network error: {0}")]
+    NetworkError(String),
+
+    #[error("Invalid configuration: {0}")]
+    InvalidConfig(String),
+
+    #[error("Template error: {0}")]
+    TemplateError(String),
+
+    #[error("Unexpected error: {0}")]
+    UnexpectedError(String),
+
+    #[error["Api error: {0}"]]
+    ApiError(String)
+}
+
+impl ProviderError {
+    pub fn network_error(details: impl Into<String>) -> Self {
+        ProviderError::NetworkError(details.into())
+    }
+
+    pub fn invalid_config(details: impl Into<String>) -> Self {
+        ProviderError::InvalidConfig(details.into())
+    }
+
+    pub fn template_error(details: impl Into<String>) -> Self {
+        ProviderError::TemplateError(details.into())
+    }
+
+    pub fn unexpected_error(details: impl Into<String>) -> Self {
+        ProviderError::UnexpectedError(details.into())
+    }
+
+    pub fn api_error(details: impl Into<String>) -> Self {
+        ProviderError::ApiError(details.into())
+    }
+}

src/providers/mailgun.rs

@@ -0,0 +1,60 @@
+use reqwest::Client;
+use serde::Deserialize;
+
+use crate::providers::EmailNotification;
+use crate::providers::errors::ProviderError;
+
+#[derive(Debug, Deserialize, Clone)]
+pub struct MailgunConfig {
+    pub domain: String,
+    pub api_key: String,
+    pub base_url: Option<String>,
+}
+
+pub struct MailgunProvider {
+    config: MailgunConfig,
+    client: Client,
+}
+
+impl MailgunProvider {
+    pub fn new(config: MailgunConfig) -> Self {
+        let client = Client::new();
+        Self { config, client }
+    }
+
+    // Send notification to Mailgun API
+    async fn send_email(&self, notification: &EmailNotification) -> Result<(), ProviderError> {
+        let url = format!(
+            "{}/v3/{}/messages",
+            self.config.base_url.clone().unwrap_or_else(|| "https://api.mailgun.net".to_string()),
+            self.config.domain
+        );
+
+        let params = [
+            ("from", &notification.from),
+            ("to", &notification.to),
+            ("subject", &notification.subject),
+            ("text", &notification.body),
+        ];
+
+        let response = self
+            .client
+            .post(&url)
+            .basic_auth("api", Some(&self.config.api_key))
+            .form(&params)
+            .send()
+            .await
+            .map_err(|e| ProviderError::NetworkError(e.to_string()))?;
+
+        if response.status().is_success() {
+            Ok(())
+        } else {
+            let status = response.status();
+            let text = response.text().await.unwrap_or_default();
+            Err(ProviderError::ApiError(format!(
+                "Mailgun API error: {} - {}",
+                status, text
+            )))
+        }
+    }
+}

src/providers/mod.rs

@@ -0,0 +1,9 @@
+use serde:: {Serialize, Deserialize};
+
+#[derive(Debug, Serialize, Deserialize, Clone)]
+pub struct EmailNotification {
+    pub from: String,
+    pub to: String,
+    pub subject: String,
+    pub body: String,
+}