//! Account manager: loading, saving, migration, and resolution.
//!
//! Handles `accounts.toml` lifecycle and legacy `./tdlib_data/` migration
//! to XDG data directory.

use std::fs;
use std::path::PathBuf;

use super::profile::{account_db_path, validate_account_name, AccountsConfig};

/// Returns the path to `accounts.toml` in the config directory.
///
/// `~/.config/tele-tui/accounts.toml`
pub fn accounts_config_path() -> Option<PathBuf> {
    dirs::config_dir().map(|mut path| {
        path.push("tele-tui");
        path.push("accounts.toml");
        path
    })
}

/// Loads `accounts.toml` or creates it with default values.
///
/// On first run, also attempts to migrate legacy `./tdlib_data/` directory
/// to the XDG data location.
pub fn load_or_create() -> AccountsConfig {
    let config_path = match accounts_config_path() {
        Some(path) => path,
        None => {
            tracing::warn!("Could not determine config directory for accounts, using defaults");
            return AccountsConfig::default_single();
        }
    };

    if config_path.exists() {
        // Load existing config
        match fs::read_to_string(&config_path) {
            Ok(content) => match toml::from_str::<AccountsConfig>(&content) {
                Ok(config) => return config,
                Err(e) => {
                    tracing::warn!("Could not parse accounts.toml: {}", e);
                    return AccountsConfig::default_single();
                }
            },
            Err(e) => {
                tracing::warn!("Could not read accounts.toml: {}", e);
                return AccountsConfig::default_single();
            }
        }
    }

    // First run: migrate legacy data if present, then create default config
    migrate_legacy();

    let config = AccountsConfig::default_single();
    if let Err(e) = save(&config) {
        tracing::warn!("Could not save initial accounts.toml: {}", e);
    }
    config
}

/// Saves `AccountsConfig` to `accounts.toml`.
pub fn save(config: &AccountsConfig) -> Result<(), String> {
    let config_path =
        accounts_config_path().ok_or_else(|| "Could not determine config directory".to_string())?;

    // Ensure parent directory exists
    if let Some(parent) = config_path.parent() {
        fs::create_dir_all(parent)
            .map_err(|e| format!("Could not create config directory: {}", e))?;
    }

    let toml_string = toml::to_string_pretty(config)
        .map_err(|e| format!("Could not serialize accounts config: {}", e))?;

    fs::write(&config_path, toml_string)
        .map_err(|e| format!("Could not write accounts.toml: {}", e))?;

    Ok(())
}

/// Migrates legacy `./tdlib_data/` from CWD to XDG data dir.
///
/// If `./tdlib_data/` exists in the current working directory, moves it to
/// `~/.local/share/tele-tui/accounts/default/tdlib_data/`.
fn migrate_legacy() {
    let legacy_path = PathBuf::from("tdlib_data");
    if !legacy_path.exists() || !legacy_path.is_dir() {
        return;
    }

    let target = account_db_path("default");

    // Don't overwrite if target already exists
    if target.exists() {
        tracing::info!(
            "Legacy ./tdlib_data/ found but target already exists at {}, skipping migration",
            target.display()
        );
        return;
    }

    // Create parent directories
    if let Some(parent) = target.parent() {
        if let Err(e) = fs::create_dir_all(parent) {
            tracing::error!("Could not create target directory for migration: {}", e);
            return;
        }
    }

    // Move (rename) the directory
    match fs::rename(&legacy_path, &target) {
        Ok(()) => {
            tracing::info!("Migrated ./tdlib_data/ -> {}", target.display());
        }
        Err(e) => {
            tracing::error!("Could not migrate ./tdlib_data/ to {}: {}", target.display(), e);
        }
    }
}

/// Resolves which account to use from CLI arg or default.
///
/// # Arguments
///
/// * `config` - The loaded accounts configuration
/// * `account_arg` - Optional account name from `--account` CLI flag
///
/// # Returns
///
/// The resolved account name and its db_path.
///
/// # Errors
///
/// Returns an error if the specified account is not found or the name is invalid.
pub fn resolve_account(
    config: &AccountsConfig,
    account_arg: Option<&str>,
) -> Result<(String, PathBuf), String> {
    let account_name = account_arg.unwrap_or(&config.default_account);

    // Validate name
    validate_account_name(account_name)?;

    // Find account in config
    let _account = config.find_account(account_name).ok_or_else(|| {
        let available: Vec<&str> = config.accounts.iter().map(|a| a.name.as_str()).collect();
        format!(
            "Account '{}' not found. Available accounts: {}",
            account_name,
            available.join(", ")
        )
    })?;

    let db_path = account_db_path(account_name);
    Ok((account_name.to_string(), db_path))
}

/// Adds a new account to `accounts.toml` and creates its data directory.
///
/// Validates the name, checks for duplicates, adds the profile to config,
/// saves the config, and creates the data directory.
///
/// # Returns
///
/// The db_path for the new account.
///
/// # Errors
///
/// Returns an error if the name is invalid, already exists, or I/O fails.
pub fn add_account(name: &str, display_name: &str) -> Result<std::path::PathBuf, String> {
    validate_account_name(name)?;

    let mut config = load_or_create();

    // Check for duplicate
    if config.find_account(name).is_some() {
        return Err(format!("Account '{}' already exists", name));
    }

    // Add new profile
    config.accounts.push(super::profile::AccountProfile {
        name: name.to_string(),
        display_name: display_name.to_string(),
    });

    // Save config
    save(&config)?;

    // Create data directory
    ensure_account_dir(name)
}

/// Ensures the account data directory exists.
///
/// Creates `~/.local/share/tele-tui/accounts/{name}/tdlib_data/` if needed.
pub fn ensure_account_dir(account_name: &str) -> Result<PathBuf, String> {
    let db_path = account_db_path(account_name);
    fs::create_dir_all(&db_path)
        .map_err(|e| format!("Could not create account directory: {}", e))?;
    Ok(db_path)
}