//! JSON file–backed `ConversationRepository` implementation.
//!
//! Stores `Conversation` as pretty-printed JSON at `<session_dir>/conversation.json`.
//! Uses atomic write (temp file + rename + fsync) for crash safety.
//!
//! ## Data Flow
//! - `load()`: read file → deserialize JSON → return Conversation
//! - `save()`: serialize Conversation → atomic write to conversation.json

use std::path::Path;

use anyhow::{Context, Result};
use zesdex_utils::write_json_atomic;

use crate::domain::conversation::Conversation;
use crate::domain::repository::ConversationRepository;

/// File-based `ConversationRepository` that reads/writes `conversation.json`.
///
/// Zero-allocation: the struct is a unit type marker.
#[derive(Debug, Clone, Default)]
pub struct JsonConversationRepository;

impl JsonConversationRepository {
    /// Create a new repository instance.
    pub fn new() -> Self {
        Self
    }
}

impl ConversationRepository for JsonConversationRepository {
    /// Load a `Conversation` from `<session_dir>/conversation.json`.
    ///
    /// Flow: read file → parse JSON → return Conversation.
    fn load(&self, session_dir: &Path) -> Result<Conversation> {
        let path = session_dir.join("conversation.json");
        let data = std::fs::read_to_string(&path)
            .with_context(|| format!("failed to read conversation at '{}'", path.display()))?;
        let conv: Conversation = serde_json::from_str(&data)
            .with_context(|| format!("failed to parse conversation at '{}'", path.display()))?;
        Ok(conv)
    }

    /// Persist a `Conversation` to `<session_dir>/conversation.json`.
    ///
    /// Flow: create session dir → atomic JSON write → log success.
    fn save(&self, session_dir: &Path, conversation: &Conversation) -> Result<()> {
        tracing::debug!("saving conversation to {session_dir:?}");
        std::fs::create_dir_all(session_dir)
            .with_context(|| format!("failed to create session dir '{}'", session_dir.display()))?;
        let path = session_dir.join("conversation.json");
        write_json_atomic(&path, conversation, None)
            .with_context(|| "failed to save conversation")?;
        tracing::debug!("conversation saved to '{}'", path.display());
        Ok(())
    }
}