#![forbid(unsafe_code)]

use clap::{crate_authors, crate_version, App, AppSettings, Arg};
use crossbeam::crossbeam_channel::unbounded;
use json5::from_str;
use notify::{RecommendedWatcher, RecursiveMode, Watcher};
use serde_json::Value;
use std::env;
use std::error::Error;
use std::fs::{create_dir_all, read_dir, read_to_string, write};
use std::process;
use tera::{Context, Error as TeraError, Tera};

const DEFAULT_TEMPLATE_DIR: &str = "templates";
const DEFAULT_OUTPUT_DIR: &str = "output";

fn main() -> Result<(), Box<dyn Error>> {
    process::exit(match run() {
        Ok(_) => 0,
        Err(e) => {
            eprintln!("{}", e);
            1
        }
    })
}

fn env_or_default(env_name: &str, default: &str) -> String {
    env::var(env_name).unwrap_or_else(|_| String::from(default))
}

fn run() -> Result<(), Box<dyn Error>> {
    let config: Value = from_str(&read_to_string("config.json5")?)?;
    let template_dir = env_or_default("PANRES_TEMPLATE_DIR", DEFAULT_TEMPLATE_DIR);
    let output_dir = env_or_default("PANRES_OUTPUT_DIR", DEFAULT_OUTPUT_DIR);

    let matches = get_args();

    let tera = Tera::new(&format!("{}/**/*", template_dir))?;
    let mut context = Context::new();
    context.insert("config", &config);
    let outputs: Vec<String> = matches
        .values_of("output-format")
        .unwrap_or_default()
        .map(String::from)
        .collect();

    output(&tera, &context, &output_dir, &outputs, &template_dir)?;

    if matches.is_present("watch") {
        watch_mode(tera, context, output_dir, outputs, template_dir)?;
    }

    Ok(())
}

/// Returns the args passed by the user.
fn get_args() -> clap::ArgMatches<'static> {
    App::new("panres")
        .version(crate_version!())
        .author(crate_authors!())
        .about("Universal resume formatter")
        .arg(Arg::with_name("watch").short("w").help("Watch for changes"))
        .arg(
            Arg::with_name("output-format")
                .help("Specifies which output format you want")
                .required(true)
                .multiple(true),
        )
        .settings(&[AppSettings::ArgRequiredElseHelp])
        .get_matches()
}

/// Usually never returns, unless there was an error initializing the watcher.
/// Handles watching for file changes, and reloads tera if there's a change.
fn watch_mode<'a>(
    mut engine: Tera,
    context: Context,
    dir: String,
    outputs: Vec<String>,
    template_dir: String,
) -> Result<(), Box<dyn Error>> {
    let (tx, rx) = unbounded();
    let mut watcher: RecommendedWatcher = Watcher::new_immediate(move |res| tx.send(res).unwrap())?;
    watcher.watch(&template_dir, RecursiveMode::Recursive)?;

    for res in rx {
        match res {
            Err(e) => println!("{}", e),
            Ok(event) => {
                println!("got event {:?}", event);
                engine.full_reload().expect("Failed to perform full reload");
                output(&engine, &context, &dir, &outputs, &template_dir)
                    .expect("Failed to call output");
            }
        }
    }

    Ok(())
}

/// Parses the output values and generates a file for each format specified or
/// found, if told to generate all outputs.
fn output<'a>(
    engine: &Tera,
    context: &Context,
    dir: &str,
    outputs: &[String],
    template_dir: &'a str,
) -> Result<(), Box<dyn Error>> {
    if outputs.contains(&String::from("all")) {
        for output in read_dir(template_dir)? {
            write_file(engine, context, dir, &output?.file_name().to_str().unwrap())?;
        }
    } else {
        for output in outputs {
            write_file(engine, context, dir, &output)?;
        }
    }

    Ok(())
}

/// Write out the post-template file to the output dir.
fn write_file(engine: &Tera, context: &Context, dir: &str, format: &str) -> Result<(), TeraError> {
    create_dir_all(dir).expect("Could not create output dir");
    write(
        format!("{}/{}", dir, format),
        engine.render(format, context)?,
    )
    .expect("to be able to write to output folder");
    Ok(())
}