#![forbid(unsafe_code)]
#![deny(missing_docs)]
#![warn(clippy::nursery, clippy::pedantic)]

//! Bunbun is a pure-Rust implementation of bunny1 that provides a customizable
//! search engine and quick-jump tool in one small binary. For information on
//! usage, please take a look at the readme.

use crate::config::{get_config_data, load_custom_file, load_file, FileData, Route, RouteGroup};
use anyhow::Result;
use arc_swap::ArcSwap;
use axum::routing::get;
use axum::{Extension, Router};
use clap::Parser;
use error::BunBunError;
use handlebars::Handlebars;
use hotwatch::{Event, Hotwatch};
use std::collections::HashMap;
use std::sync::Arc;
use std::time::Duration;
use tracing::{debug, info, trace, warn};
use tracing_subscriber::layer::SubscriberExt;
use tracing_subscriber::util::SubscriberInitExt;

mod cli;
mod config;
#[cfg(not(tarpaulin_include))]
mod error;
mod routes;
#[cfg(not(tarpaulin_include))]
mod template_args;

/// Dynamic variables that either need to be present at runtime, or can be
/// changed during runtime.
pub struct State {
    public_address: String,
    default_route: Option<String>,
    groups: Vec<RouteGroup>,
    /// Cached, flattened mapping of all routes and their destinations.
    routes: HashMap<String, Route>,
}

#[tokio::main]
#[cfg(not(tarpaulin_include))]
async fn main() -> Result<()> {
    use tracing_subscriber::EnvFilter;

    let opts = cli::Opts::parse();

    let mut env_filter = EnvFilter::from_default_env();
    for directive in opts.log {
        env_filter = env_filter.add_directive(directive);
    }

    tracing_subscriber::registry()
        .with(tracing_subscriber::fmt::layer())
        .with(env_filter)
        .init();

    let conf_data = opts.config.map_or_else(get_config_data, load_custom_file)?;

    let conf = load_file(conf_data.file.try_clone()?, opts.large_config)?;
    let state = Arc::from(ArcSwap::from_pointee(State {
        public_address: conf.public_address,
        default_route: conf.default_route,
        routes: cache_routes(conf.groups.clone()),
        groups: conf.groups,
    }));

    // Cannot be named _ or Rust will immediately drop it.
    let _watch = start_watch(Arc::clone(&state), conf_data, opts.large_config);

    let app = Router::new()
        .route("/", get(routes::index))
        .route("/bunbunsearch.xml", get(routes::opensearch))
        .route("/ls", get(routes::list))
        .route("/hop", get(routes::hop))
        .layer(Extension(compile_templates()?))
        .layer(Extension(state));

    let bind_addr = conf.bind_address.parse()?;

    info!("Starting server at {bind_addr}");

    axum::Server::bind(&bind_addr)
        .serve(app.into_make_service())
        .await?;

    Ok(())
}

/// Generates a hashmap of routes from the data structure created by the config
/// file. This should improve runtime performance and is a better solution than
/// just iterating over the config object for every hop resolution.
fn cache_routes(groups: Vec<RouteGroup>) -> HashMap<String, Route> {
    let mut mapping = HashMap::new();
    for group in groups {
        for (kw, dest) in group.routes {
            // This function isn't called often enough to not be a performance issue.
            if let Some(old_value) = mapping.insert(kw.clone(), dest.clone()) {
                trace!("Overriding {kw} route from {old_value} to {dest}.");
            } else {
                trace!("Inserting {kw} into mapping.");
            }
        }
    }
    mapping
}

/// Returns an instance with all pre-generated templates included into the
/// binary. This allows for users to have a portable binary without needed the
/// templates at runtime.
fn compile_templates() -> Result<Handlebars<'static>> {
    let mut handlebars = Handlebars::new();
    handlebars.set_strict_mode(true);
    handlebars.register_partial("bunbun_version", env!("CARGO_PKG_VERSION"))?;
    handlebars.register_partial("bunbun_src", env!("CARGO_PKG_REPOSITORY"))?;
    macro_rules! register_template {
    [ $( $template:expr ),* ] => {
      $(
        handlebars
          .register_template_string(
            $template,
            String::from_utf8_lossy(
              include_bytes!(concat!("templates/", $template, ".hbs")))
          )?;
        debug!("Loaded {} template.", $template);
      )*
    };
  }
    register_template!["index", "list", "opensearch"];
    Ok(handlebars)
}

/// Starts the watch on a file, if possible. This will only return an Error if
/// the notify library (used by Hotwatch) fails to initialize, which is
/// considered to be a more serve error as it may be indicative of a low-level
/// problem. If a watch was unsuccessfully obtained (the most common is due to
/// the file not existing), then this will simply warn before returning a watch
/// object.
///
/// This watch object should be kept in scope as dropping it releases all
/// watches.
#[cfg(not(tarpaulin_include))]
fn start_watch(
    state: Arc<ArcSwap<State>>,
    config_data: FileData,
    large_config: bool,
) -> Result<Hotwatch> {
    let mut watch = Hotwatch::new_with_custom_delay(Duration::from_millis(500))?;
    let FileData { path, mut file } = config_data;
    let watch_result = watch.watch(&path, move |e: Event| {
        if let Event::Create(ref path) = e {
            file = load_custom_file(path).expect("file to exist at path").file;
            trace!("Getting new file handler as file was recreated.");
        }

        match e {
            Event::Write(_) | Event::Create(_) => {
                trace!("Grabbing writer lock on state...");
                trace!("Obtained writer lock on state!");
                match load_file(
                    file.try_clone().expect("Failed to clone file handle"),
                    large_config,
                ) {
                    Ok(conf) => {
                        state.store(Arc::new(State {
                            public_address: conf.public_address,
                            default_route: conf.default_route,
                            routes: cache_routes(conf.groups.clone()),
                            groups: conf.groups,
                        }));
                        info!("Successfully updated active state");
                    }
                    Err(e) => warn!("Failed to update config file: {e}"),
                }
            }
            _ => debug!("Saw event {e:#?} but ignored it"),
        }
    });

    match watch_result {
        Ok(_) => info!("Watcher is now watching {path:?}"),
        Err(e) => {
            warn!("Couldn't watch {path:?}: {e}. Changes to this file won't be seen!");
        }
    }

    Ok(watch)
}

#[cfg(test)]
mod cache_routes {
    use super::*;
    use std::iter::FromIterator;

    fn generate_external_routes(routes: &[(&'static str, &'static str)]) -> HashMap<String, Route> {
        HashMap::from_iter(
            routes
                .into_iter()
                .map(|(key, value)| ((*key).to_owned(), Route::from(*value))),
        )
    }

    #[test]
    fn empty_groups_yield_empty_routes() {
        assert_eq!(cache_routes(Vec::new()), HashMap::new());
    }

    #[test]
    fn disjoint_groups_yield_summed_routes() {
        let group1 = RouteGroup {
            name: String::from("x"),
            description: Some(String::from("y")),
            routes: generate_external_routes(&[("a", "b"), ("c", "d")]),
            hidden: false,
        };

        let group2 = RouteGroup {
            name: String::from("5"),
            description: Some(String::from("6")),
            routes: generate_external_routes(&[("1", "2"), ("3", "4")]),
            hidden: false,
        };

        assert_eq!(
            cache_routes(vec![group1, group2]),
            generate_external_routes(&[("a", "b"), ("c", "d"), ("1", "2"), ("3", "4")])
        );
    }

    #[test]
    fn overlapping_groups_use_latter_routes() {
        let group1 = RouteGroup {
            name: String::from("x"),
            description: Some(String::from("y")),
            routes: generate_external_routes(&[("a", "b"), ("c", "d")]),
            hidden: false,
        };

        let group2 = RouteGroup {
            name: String::from("5"),
            description: Some(String::from("6")),
            routes: generate_external_routes(&[("a", "1"), ("c", "2")]),
            hidden: false,
        };

        assert_eq!(
            cache_routes(vec![group1.clone(), group2]),
            generate_external_routes(&[("a", "1"), ("c", "2")])
        );

        let group3 = RouteGroup {
            name: String::from("5"),
            description: Some(String::from("6")),
            routes: generate_external_routes(&[("a", "1"), ("b", "2")]),
            hidden: false,
        };

        assert_eq!(
            cache_routes(vec![group1, group3]),
            generate_external_routes(&[("a", "1"), ("b", "2"), ("c", "d")])
        );
    }
}

#[cfg(test)]
mod compile_templates {
    use super::compile_templates;

    /// Successful compilation of the binary guarantees that the templates will be
    /// present to be registered to. Thus, we only really need to see that
    /// compilation of the templates don't panic, which is just making sure that
    /// the function can be successfully called.
    #[test]
    fn templates_compile() {
        let _ = compile_templates();
    }
}