use std::path::PathBuf;

use config::{Config, ConfigError, Environment};
use directories::ProjectDirs;
use serde::Deserialize;
use thiserror::Error;
use tracing::debug;

#[derive(Error, Debug)]
pub enum AppConfigError {
    #[error("No valid home directory found.")]
    HomePathError,
    #[error("Configuration error.")]
    ConfigError(#[from] ConfigError),
}

fn default_server_address() -> String {
    String::from("[::1]:3000")
}

fn default_feeds() -> Vec<String> {
    Vec::new()
}

#[derive(Clone, Debug, Default, Deserialize)]
pub struct PenguinConfig {
    #[serde(default = "default_server_address")]
    pub server_address: String,
    #[serde(default = "default_feeds")]
    pub feeds: Vec<String>,
}

impl PenguinConfig {
    /// Find the correct project directory for the respective operating system.
    fn get_project_dirs() -> Result<ProjectDirs, AppConfigError> {
        let project_dirs = ProjectDirs::from("ch", "vanwa", "findpenguins-feed")
            .ok_or(AppConfigError::HomePathError)?;

        Ok(project_dirs)
    }

    /// Find the correct configuration file for the respective operating system.
    /// - linux: `$XDG_CONFIG_HOME/stray/config.toml` or `$HOME/.config/stray/config.toml`
    /// - macOS: `$HOME/Library/Preferences/ch.fhnw.stray/config.toml`
    /// - windows: `{FOLDERID_RoamingAppData}/stray/config/config.toml`
    fn config_path() -> Result<PathBuf, AppConfigError> {
        let project_dirs = Self::get_project_dirs()?;
        let config_path = project_dirs.config_dir();
        let config_file = config_path.join("config.toml");

        Ok(config_file)
    }

    /// Read the server configuration.
    /// See [config_path](struct.AppConfig.html#method.config_path) for the different configuration file paths.
    /// Everything in the config file can be overridden at runtime by setting the respective ENV variables.
    /// Use `__` (double underscore) as a separator between hierarchies.
    /// For example `WOWEB__INITIAL_REMOTES="http://[::1]:3002,http://[::1]:3003"`
    /// This is necessary for configuration keys to have single underscores.
    pub fn read() -> Result<Self, AppConfigError> {
        let mut config_builder = Config::builder();
        if let Ok(config_path) = Self::config_path() {
            debug!("trying config file at {:#?}...", config_path);
            config_builder =
                config_builder.add_source(config::File::from(config_path).required(false));
        }

        debug!("merging settings from environment variables...");
        config_builder = config_builder.add_source(
            Environment::with_prefix("findpenguins_feed")
                .separator("__")
                .list_separator(",")
                .with_list_parse_key("feeds")
                .try_parsing(true),
        );

        Ok(config_builder.build()?.try_deserialize()?)
    }
}