// Shared utilities

use crate::store;

use serde::de::DeserializeOwned;
use serde::Serialize;

use std::fs;
use std::io::Write;
use std::path::{Path, PathBuf};

/// Ensure a subdirectory of the memory dir exists and return its path.
pub fn memory_subdir(name: &str) -> Result<PathBuf, String> {
    let dir = store::memory_dir().join(name);
    fs::create_dir_all(&dir)
        .map_err(|e| format!("create {}: {}", dir.display(), e))?;
    Ok(dir)
}

/// Truncate text to `max_len` bytes at a char boundary, appending `suffix`.
/// Returns the original string if it's already short enough.
pub fn truncate(text: &str, max_len: usize, suffix: &str) -> String {
    if text.len() <= max_len {
        text.to_string()
    } else {
        let end = text.floor_char_boundary(max_len);
        format!("{}{}", &text[..end], suffix)
    }
}

/// Take the first `n` chars from a string.
pub fn first_n_chars(s: &str, n: usize) -> String {
    s.chars().take(n).collect()
}

// ── JSONL helpers ───────────────────────────────────────────────────

/// Read a JSONL file, deserializing each line. Silently skips bad lines.
pub fn jsonl_load<T: DeserializeOwned>(path: &Path) -> Vec<T> {
    let content = match fs::read_to_string(path) {
        Ok(c) => c,
        Err(_) => return Vec::new(),
    };
    content.lines()
        .filter_map(|line| serde_json::from_str(line).ok())
        .collect()
}

/// Append one record as a JSON line to a file (create if missing).
pub fn jsonl_append<T: Serialize>(path: &Path, item: &T) -> Result<(), String> {
    let json = serde_json::to_string(item)
        .map_err(|e| format!("serialize: {}", e))?;
    let mut f = fs::OpenOptions::new()
        .create(true).append(true).open(path)
        .map_err(|e| format!("open {}: {}", path.display(), e))?;
    writeln!(f, "{}", json)
        .map_err(|e| format!("write {}: {}", path.display(), e))
}