use std::collections::HashMap;
use std::path::Path;

/// Name of the file (inside the workspace) that stores the manual ordering.
/// It is committed to git so the order syncs across machines.
pub const ORDER_FILE: &str = "order.json";

/// Name of the file that stores per-file chapter title overrides
/// (a JSON object mapping `file name` -> `chapter title`). Also committed to git.
pub const TITLES_FILE: &str = "titles.json";

/// Read the chapter-title overrides. Missing/invalid -> empty map.
pub fn read_titles(workspace: &Path) -> HashMap<String, String> {
    let path = workspace.join(TITLES_FILE);
    match std::fs::read_to_string(&path) {
        Ok(text) => serde_json::from_str(&text).unwrap_or_default(),
        Err(_) => HashMap::new(),
    }
}

/// Persist the chapter-title overrides as JSON into the workspace.
pub fn write_titles(workspace: &Path, titles: &HashMap<String, String>) -> std::io::Result<()> {
    let path = workspace.join(TITLES_FILE);
    let text = serde_json::to_string_pretty(titles).unwrap_or_else(|_| "{}".to_string());
    std::fs::write(path, text)
}

/// Read the saved order (a JSON array of file names). Missing/invalid -> empty.
fn read_saved_order(workspace: &Path) -> Vec<String> {
    let path = workspace.join(ORDER_FILE);
    match std::fs::read_to_string(&path) {
        Ok(text) => serde_json::from_str(&text).unwrap_or_default(),
        Err(_) => Vec::new(),
    }
}

/// Persist the given order as JSON into the workspace.
pub fn write_order(workspace: &Path, order: &[String]) -> std::io::Result<()> {
    let path = workspace.join(ORDER_FILE);
    let text = serde_json::to_string_pretty(order).unwrap_or_else(|_| "[]".to_string());
    std::fs::write(path, text)
}

/// List all `*.md` files currently present in the workspace (file names only).
fn list_markdown_files(workspace: &Path) -> Vec<String> {
    let mut files = Vec::new();
    if let Ok(entries) = std::fs::read_dir(workspace) {
        for entry in entries.flatten() {
            let path = entry.path();
            if path.is_file() {
                if let Some(ext) = path.extension() {
                    if ext.eq_ignore_ascii_case("md") {
                        if let Some(name) = path.file_name().and_then(|n| n.to_str()) {
                            files.push(name.to_string());
                        }
                    }
                }
            }
        }
    }
    files
}

/// Produce the effective ordered list of markdown files:
///   1. saved-order entries that still exist on disk, in saved order
///   2. any new `.md` files not yet in the saved order, appended alphabetically
pub fn resolve_order(workspace: &Path) -> Vec<String> {
    let saved = read_saved_order(workspace);
    let mut present = list_markdown_files(workspace);
    present.sort_by(|a, b| a.to_lowercase().cmp(&b.to_lowercase()));

    let mut result: Vec<String> = Vec::new();
    for name in &saved {
        if present.contains(name) && !result.contains(name) {
            result.push(name.clone());
        }
    }
    for name in present {
        if !result.contains(&name) {
            result.push(name);
        }
    }
    result
}