#[macro_use]
extern crate anyhow;
#[macro_use]
extern crate log;

mod github;
mod types;

use std::{
    collections::{btree_map::Entry, BTreeMap},
    env,
    fs::File,
    io::{BufReader, BufWriter},
    path::{Path, PathBuf},
};

use anyhow::{Context, Result};
use chrono::{Duration, Utc};
use clap::{Args, Parser, Subcommand};
use github::Github;
use rss::{Channel, ChannelBuilder, Guid, Item, ItemBuilder};
use serde_json::{from_reader, to_writer};
use tempfile::NamedTempFile;
use types::{DateTime, IssueAction, PullAction, State, STATE_VERSION};

#[derive(Parser)]
#[clap(version)]
/// Poll github issues and PRs by label and generate RSS feeds.
struct App {
    #[clap(subcommand)]
    command: Command,
}

#[derive(Subcommand)]
#[clap(about)]
enum Command {
    /// Initialize a tracker state.
    ///
    /// Each tracker state applies to only one repository and only one label.
    Init {
        /// Path of the newly created state.
        state_file: PathBuf,
        /// Owner of the repository to query.
        owner: String,
        /// Name of the repository.
        repo: String,
        /// Name of the label to track.
        label: String,
    },
    /// Sync issues on a state.
    SyncIssues(SyncArgs),
    /// Sync pull requests on a state.
    SyncPrs(SyncArgs),
    /// Emit an RSS feed for issue changes.
    EmitIssues(EmitArgs),
    /// Emit an RSS feed for PR changes.
    EmitPrs(EmitArgs),
}

#[derive(Args)]
struct SyncArgs {
    /// State to sync.
    state_file: PathBuf,
}

#[derive(Args)]
struct EmitArgs {
    /// State to read.
    state_file: PathBuf,

    #[clap(short, long = "max-age")]
    /// How far to look back in history, in hours.
    age_hours: u32,

    #[clap(short, long)]
    /// Target file for the generated feed. Defaults to stdout.
    out: Option<PathBuf>,
}

fn with_state<F>(state_file: PathBuf, f: F) -> Result<()>
where
    F: FnOnce(State) -> Result<Option<State>>,
{
    let old_state: State = from_reader(BufReader::new(File::open(&state_file)?))?;
    if old_state.version != STATE_VERSION {
        bail!(
            "expected state version {}, got {}",
            STATE_VERSION,
            old_state.version
        );
    }

    let new_state = f(old_state)?;

    if let Some(state) = new_state {
        let new_state_file = NamedTempFile::new_in(
            state_file
                .ancestors()
                .nth(1)
                .unwrap_or_else(|| Path::new(".")),
        )?;

        to_writer(BufWriter::new(&new_state_file), &state)?;
        new_state_file.persist(state_file)?;
    }

    Ok(())
}

fn with_state_and_github<F>(state_file: PathBuf, f: F) -> Result<()>
where
    F: FnOnce(State, &Github) -> Result<Option<State>>,
{
    let github_api_token =
        env::var("GITHUB_API_TOKEN").context("failed to load GITHUB_API_TOKEN")?;

    with_state(state_file, |old_state| {
        let client = github::Github::new(
            &github_api_token,
            &old_state.owner,
            &old_state.repo,
            &old_state.label,
        )?;

        f(old_state, &client)
    })
}

fn sync_issues(mut state: State, github: &github::Github) -> Result<Option<State>> {
    let issues = github.query_issues(state.issues_updated)?;

    let mut new_history = vec![];

    for updated in issues {
        let issue_state = |is_new| match (updated.is_open, is_new) {
            (true, _) => IssueAction::New,
            (false, true) => IssueAction::NewClosed,
            (false, false) => IssueAction::Closed,
        };
        match state.issues.entry(updated.id.clone()) {
            Entry::Occupied(mut e) => {
                let stored = e.get_mut();
                if stored.is_open != updated.is_open {
                    new_history.push((updated.last_update, updated.id.clone(), issue_state(false)));
                }
                *stored = updated;
            }
            Entry::Vacant(e) => {
                new_history.push((updated.last_update, updated.id.clone(), issue_state(true)));
                e.insert(updated);
            }
        }
    }

    new_history.sort_by(|a, b| (a.0, &a.1).cmp(&(b.0, &b.1)));
    if let Some(&(at, _, _)) = new_history.last() {
        state.issues_updated = Some(at);
    }
    state.issue_history.append(&mut new_history);

    Ok(Some(state))
}

fn sync_prs(mut state: State, github: &github::Github) -> Result<Option<State>> {
    let prs = github.query_pulls(state.pull_requests_updated)?;

    let mut new_history = vec![];

    for updated in prs {
        let pr_state = |is_new| match (updated.is_open, updated.is_merged, is_new) {
            (false, false, true) => PullAction::NewClosed,
            (false, false, false) => PullAction::Closed,
            (true, false, _) => PullAction::New,
            (_, true, true) => PullAction::NewMerged,
            (_, true, false) => PullAction::Merged,
        };
        match state.pull_requests.entry(updated.id.clone()) {
            Entry::Occupied(mut e) => {
                let stored = e.get_mut();
                if (stored.is_open, stored.is_merged) != (updated.is_open, updated.is_merged) {
                    new_history.push((updated.last_update, updated.id.clone(), pr_state(false)));
                }
                *stored = updated;
            }
            Entry::Vacant(e) => {
                new_history.push((updated.last_update, updated.id.clone(), pr_state(true)));
                e.insert(updated);
            }
        }
    }

    new_history.sort_by(|a, b| (a.0, &a.1).cmp(&(b.0, &b.1)));
    if let Some(&(at, _, _)) = new_history.last() {
        state.pull_requests_updated = Some(at);
    }
    state.pull_history.append(&mut new_history);

    Ok(Some(state))
}

fn format_history<V, A: Copy, F: Fn(&V, DateTime, A) -> Item>(
    items: &BTreeMap<String, V>,
    history: &[(DateTime, String, A)],
    age_hours: u32,
    format_entry: F,
) -> Result<Vec<Item>> {
    let since = Utc::now() - Duration::hours(age_hours as i64);

    history
        .iter()
        .rev()
        .take_while(|(changed, _, _)| changed >= &since)
        .map(|(changed, id, how)| {
            let entry = match items.get(id.as_str()) {
                Some(i) => i,
                None => bail!("database is corrupted (dangling key {})", id),
            };
            Ok(Item {
                guid: Some(Guid {
                    value: format!("{}/{}", changed.to_rfc3339(), id),
                    permalink: false,
                }),
                ..format_entry(entry, *changed, *how)
            })
        })
        .collect::<Result<Vec<_>, _>>()
}

fn new_rss_item(tag: &str, title: &str, url: &str, changed: DateTime, body: &str) -> Item {
    ItemBuilder::default()
        .title(Some(format!("{} {}", tag, title)))
        .link(Some(url.to_string()))
        .pub_date(Some(changed.to_rfc2822()))
        .content(Some(body.to_string()))
        .build()
}

fn emit_issues(state: &State, age_hours: u32) -> Result<Channel> {
    let entries = format_history(
        &state.issues,
        &state.issue_history,
        age_hours,
        |issue, changed, how| {
            let tag = match how {
                IssueAction::New => "[NEW]",
                IssueAction::Closed => "[CLOSED]",
                IssueAction::NewClosed => "[NEW][CLOSED]",
            };
            new_rss_item(tag, &issue.title, &issue.url, changed, &issue.body)
        },
    )?;

    let channel = ChannelBuilder::default()
        .title(format!(
            "Issues labeled `{}' in {}/{}",
            state.label, state.owner, state.repo
        ))
        .items(entries)
        .build();

    Ok(channel)
}

fn emit_prs(state: &State, age_hours: u32) -> Result<Channel> {
    let entries = format_history(
        &state.pull_requests,
        &state.pull_history,
        age_hours,
        |pr, changed, how| {
            let tag = match how {
                PullAction::New => "[NEW]",
                PullAction::NewMerged => "[NEW][MERGED]",
                PullAction::Closed => "[CLOSED]",
                PullAction::NewClosed => "[NEW][CLOSED]",
                PullAction::Merged => "[MERGED]",
            };
            let info = format!("{}({})", tag, pr.base_ref);
            new_rss_item(&info, &pr.title, &pr.url, changed, &pr.body)
        },
    )?;

    let channel = ChannelBuilder::default()
        .title(format!(
            "Pull requests labeled `{}' in {}/{}",
            state.label, state.owner, state.repo
        ))
        .items(entries)
        .build();

    Ok(channel)
}

fn write_feed(to: Option<PathBuf>, channel: Channel) -> Result<Option<State>> {
    match to {
        Some(to) => {
            let new_file =
                NamedTempFile::new_in(to.ancestors().nth(1).unwrap_or_else(|| Path::new(".")))?;

            channel.write_to(BufWriter::new(&new_file))?;
            new_file.persist(to)?;
        }
        None => println!("{}", channel.to_string()),
    }
    Ok(None)
}

fn main() -> Result<()> {
    pretty_env_logger::init();

    match App::parse().command {
        Command::Init {
            state_file,
            owner,
            repo,
            label,
        } => {
            let state = State {
                version: STATE_VERSION,
                owner,
                repo,
                label,
                ..State::default()
            };

            let file = File::options()
                .create_new(true)
                .write(true)
                .open(state_file)?;
            to_writer(file, &state)?;
        }
        Command::SyncIssues(cmd) => {
            with_state_and_github(cmd.state_file, sync_issues)?;
        }
        Command::SyncPrs(cmd) => {
            with_state_and_github(cmd.state_file, sync_prs)?;
        }
        Command::EmitIssues(cmd) => {
            with_state(cmd.state_file, |s| {
                write_feed(cmd.out, emit_issues(&s, cmd.age_hours)?)
            })?;
        }
        Command::EmitPrs(cmd) => {
            with_state(cmd.state_file, |s| {
                write_feed(cmd.out, emit_prs(&s, cmd.age_hours)?)
            })?;
        }
    };

    Ok(())
}