feat(chat): added chat interface and connection to ollama (#10)

Co-authored-by: Sharang Parnerkar <parnerkarsharang@gmail.com>
Reviewed-on: #10

src/infrastructure/provider_client.rs

@@ -0,0 +1,148 @@
+//! Unified LLM provider dispatch.
+//!
+//! Routes chat completion requests to Ollama, OpenAI, Anthropic, or
+//! HuggingFace based on the session's provider setting. All providers
+//! except Anthropic use the OpenAI-compatible chat completions format.
+
+use reqwest::Client;
+use serde::{Deserialize, Serialize};
+
+use super::server_state::ServerState;
+
+/// OpenAI-compatible chat message used for request bodies.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ProviderMessage {
+    pub role: String,
+    pub content: String,
+}
+
+/// Send a chat completion request to the configured provider.
+///
+/// # Arguments
+///
+/// * `state` - Server state (for default Ollama URL/model)
+/// * `provider` - Provider name (`"ollama"`, `"openai"`, `"anthropic"`, `"huggingface"`)
+/// * `model` - Model ID
+/// * `messages` - Conversation history
+/// * `api_key` - API key (required for non-Ollama providers)
+/// * `stream` - Whether to request streaming
+///
+/// # Returns
+///
+/// The raw `reqwest::Response` for the caller to consume (streaming or not).
+///
+/// # Errors
+///
+/// Returns an error if the HTTP request fails.
+pub async fn send_chat_request(
+    state: &ServerState,
+    provider: &str,
+    model: &str,
+    messages: &[ProviderMessage],
+    api_key: Option<&str>,
+    stream: bool,
+) -> Result<reqwest::Response, reqwest::Error> {
+    let client = Client::new();
+
+    match provider {
+        "openai" => {
+            let body = serde_json::json!({
+                "model": model,
+                "messages": messages,
+                "stream": stream,
+            });
+            client
+                .post("https://api.openai.com/v1/chat/completions")
+                .header("content-type", "application/json")
+                .header(
+                    "Authorization",
+                    format!("Bearer {}", api_key.unwrap_or_default()),
+                )
+                .json(&body)
+                .send()
+                .await
+        }
+        "anthropic" => {
+            // Anthropic uses a different API format -- translate.
+            // Extract system message separately, convert roles.
+            let system_msg: String = messages
+                .iter()
+                .filter(|m| m.role == "system")
+                .map(|m| m.content.clone())
+                .collect::<Vec<_>>()
+                .join("\n");
+
+            let anthropic_msgs: Vec<serde_json::Value> = messages
+                .iter()
+                .filter(|m| m.role != "system")
+                .map(|m| {
+                    serde_json::json!({
+                        "role": m.role,
+                        "content": m.content,
+                    })
+                })
+                .collect();
+
+            let mut body = serde_json::json!({
+                "model": model,
+                "messages": anthropic_msgs,
+                "max_tokens": 4096,
+                "stream": stream,
+            });
+            if !system_msg.is_empty() {
+                body["system"] = serde_json::Value::String(system_msg);
+            }
+
+            client
+                .post("https://api.anthropic.com/v1/messages")
+                .header("content-type", "application/json")
+                .header("x-api-key", api_key.unwrap_or_default())
+                .header("anthropic-version", "2023-06-01")
+                .json(&body)
+                .send()
+                .await
+        }
+        "huggingface" => {
+            let url = format!(
+                "https://api-inference.huggingface.co/models/{}/v1/chat/completions",
+                model
+            );
+            let body = serde_json::json!({
+                "model": model,
+                "messages": messages,
+                "stream": stream,
+            });
+            client
+                .post(&url)
+                .header("content-type", "application/json")
+                .header(
+                    "Authorization",
+                    format!("Bearer {}", api_key.unwrap_or_default()),
+                )
+                .json(&body)
+                .send()
+                .await
+        }
+        // Default: Ollama (OpenAI-compatible endpoint)
+        _ => {
+            let base_url = &state.services.ollama_url;
+            let resolved_model = if model.is_empty() {
+                &state.services.ollama_model
+            } else {
+                model
+            };
+            let url = format!("{}/v1/chat/completions", base_url.trim_end_matches('/'));
+            let body = serde_json::json!({
+                "model": resolved_model,
+                "messages": messages,
+                "stream": stream,
+            });
+            client
+                .post(&url)
+                .header("content-type", "application/json")
+                .json(&body)
+                .send()
+                .await
+        }
+    }
+}