use anyhow::{Context, Result};
use chrono::{DateTime, Duration, Local, Utc};
use clap::{arg, command, Parser};
use log::{debug, trace};
use megalodon::{
    entities::{Account, Status, StatusVisibility},
    generator,
    megalodon::{GetAccountStatusesInputOptions, GetLocalTimelineInputOptions},
    response::Response,
    Megalodon,
};
use tokio::fs::try_exists;
use tokio_stream::{iter, StreamExt};

use std::{env, fs::File, io::prelude::*};

use self::{
    format::format_status,
    page::{bounds_from, Page},
    range::try_create_range,
    range::Range,
};

mod format;
mod page;
mod range;

#[derive(Debug, Parser)]
#[command()]
struct Config {
    #[arg(short, long, env = "MASTODON_URL", required = true)]
    url: String,
    #[arg(short, long, env = "MASTODON_ACCESS_TOKEN", required = true)]
    access_token: String,
    #[arg(short, long)]
    output_dir: Option<String>,
    #[arg(required = true)]
    date: String,
    #[arg(short, long, action = clap::ArgAction::Count)]
    verbose: u8,
}

#[tokio::main]
async fn main() -> Result<()> {
    let Config {
        date,
        verbose,
        url,
        access_token,
        output_dir,
    } = Config::parse();

    let level = match verbose {
        0 => "off",
        1 => "debug",
        _ => "trace",
    };
    env::set_var("RUST_LOG", format!("{}={}", module_path!(), level));
    env_logger::init();

    let day = try_create_range(date.clone())?;

    let client = create_client(url, access_token)?;
    let Response { json: account, .. } = client.verify_account_credentials().await?;

    debug!("Fetching posts for date, {}.", day.end.format("%Y-%m-%d"));

    // the server only provides a page of results at a time, keep the oldest status from any page
    // to request the next older page of statuses
    let mut last_id_on_page: Option<String> = None;
    // store the formatted posts in server order, reversed chronologically, to reverse at the end
    // for regular chronological ordering
    let mut reversed = Vec::new();
    loop {
        let statuses = fetch_page(&client, &last_id_on_page).await?;
        if statuses.is_empty() {
            debug!("No more posts in range.");
            break;
        }
        let page = bounds_from(&statuses);

        trace!("Page bounds {:?}", page);

        let (last_id, next_iter, mut formatted) =
            process_page(&client, &account, &statuses, &last_id_on_page, &day, 1).await?;
        reversed.append(&mut formatted);
        if let Some(NextIter::Stop) = next_iter {
            break;
        }
        if let Some(last_id) = last_id {
            last_id_on_page.replace(last_id);
        }
        if let Some(NextIter::Skip) = next_iter {
            continue;
        }
    }
    last_id_on_page = None;
    loop {
        let statuses = fetch_dm_page(&client, &account, &last_id_on_page).await?;
        if statuses.is_empty() {
            debug!("No more DMs in range.");
            break;
        }
        let page = bounds_from(&statuses);

        trace!("Page bounds {:?}", page);

        let (last_id, next_iter, mut formatted) =
            process_page(&client, &account, &statuses, &last_id_on_page, &day, 0).await?;
        reversed.append(&mut formatted);
        if let Some(NextIter::Stop) = next_iter {
            break;
        }
        if let Some(last_id) = last_id {
            last_id_on_page.replace(last_id);
        }
        if let Some(NextIter::Skip) = next_iter {
            continue;
        }
    }

    reversed.reverse();

    if let Some(output_dir) = output_dir {
        let output = format!("{}/{}.md", output_dir.trim_end_matches("/"), date);
        let mut f = match try_exists(&output).await {
            Ok(exists) if exists => {
                debug!("Appending {}", output);
                let mut file = File::options().append(true).open(&output)?;
                file.write("\n\n".as_bytes())?;
                file
            }
            _ => {
                debug!("Writing {}", output);
                let mut file = File::options()
                    .create(true)
                    .append(true)
                    .open(&output)
                    .with_context(|| format!("Failed to create {}", output))?;
                file.write(format!("# {}\n\n", day.end.format("%Y-%m-%d")).as_bytes())?;

                // TODO move to separate function
                file.write(create_back_link(&day.end, "[One week ago](diary:{})\n", 7).as_bytes())?;
                file.write(
                    create_back_link(&day.end, "[One month ago](diary:{})\n", 30).as_bytes(),
                )?;
                file.write(
                    create_back_link(&day.end, "[Six months ago](diary:{})\n", 6 * 30).as_bytes(),
                )?;
                file.write(
                    create_back_link(&day.end, "[One year ago](diary:{})\n", 365).as_bytes(),
                )?;
                file.write(
                    create_back_link(&day.end, "[Two years ago](diary:{})\n", 365 * 2).as_bytes(),
                )?;
                file.write(
                    create_back_link(&day.end, "[Three years ago](diary:{})\n", 365 * 3).as_bytes(),
                )?;
                file
            }
        };
        f.write_all(&reversed.join("\n\n").as_bytes())
            .with_context(|| format!("Failed to write all to {}", output))?;
        println!("Appended matching posts to {}.", output);
    } else {
        println!("{}", reversed.join("\n\n"));
    }
    Ok(())
}

fn create_back_link(day_end: &DateTime<Local>, anchor_text: &str, ago: i64) -> String {
    let prior_date = *day_end - Duration::days(ago);
    // TODO check if the file exists
    format!(
        "[{}](diary:{})\n",
        anchor_text,
        prior_date.format("%Y-%m-%d")
    )
}

enum NextIter {
    Skip,
    Stop,
}

async fn process_page(
    client: &Box<dyn Megalodon + Send + Sync + 'static>,
    account: &Account,
    statuses: &Vec<Status>,
    last_id_on_page: &Option<String>,
    day: &Range,
    depth: usize,
) -> Result<(Option<String>, Option<NextIter>, Vec<String>)> {
    let page = bounds_from(&statuses);

    trace!("Page bounds {:?}", page);

    // this age comparison only applies after the first page is fetched; the rest of the loop
    // body handles if the requested date is newer than any statuses on the first page
    if last_id_on_page.is_some() && page_start_older_than(&page, day) {
        return Ok((None, Some(NextIter::Stop), Vec::new()));
    }

    // fetching returns 20 at a time, in reverse chronological order so may require skipping
    // pages after the requested date
    if let Some(oldest_id) = page_newer_than(&page, &day) {
        return Ok((Some(oldest_id), Some(NextIter::Skip), Vec::new()));
    }

    // mapping the vector runs into thorny ownership issues and only produces futures, not
    // resolved values; a for in loop works with await but also runs into thorny ownership
    // issues; a stream resolves both because the stream takes ownership of the statuses and
    // can be iterated in a simple way that allows the use of await in the body
    let mut stream = iter(filter_statuses(account, &day, &statuses));
    let mut formatted = Vec::new();
    while let Some(status) = stream.next().await {
        formatted.push(format_status(client, depth, &account, status).await?);
    }

    if page_end_older_than(&page, &day) {
        debug!("No more posts in range.");
        return Ok((None, Some(NextIter::Stop), formatted));
    }

    if let Some(id) = page.oldest_id {
        return Ok((Some(id.clone()), None, formatted));
    } else {
        return Ok((None, None, formatted));
    }
}

// Only ones authored by the user, on the date requested, that aren't a reply to any other status
fn filter_statuses<'a>(account: &Account, day: &Range, json: &'a Vec<Status>) -> Vec<&'a Status> {
    json.iter()
        .filter(|status| {
            status.account.id == account.id
                && status.in_reply_to_id.is_none()
                && day.start <= status.created_at
                && status.created_at <= day.end
        })
        .collect::<Vec<&Status>>()
}

fn create_client(url: String, token: String) -> Result<Box<dyn Megalodon + Send + Sync>> {
    Ok(generator(megalodon::SNS::Mastodon, url, Some(token), None))
}

async fn fetch_page(
    client: &Box<dyn Megalodon + Send + Sync>,
    last_id_on_page: &Option<String>,
) -> Result<Vec<Status>> {
    trace!("Fetching page of local timeline");
    let Response { json, .. } = if let Some(max_id) = last_id_on_page.as_ref() {
        trace!("Fetching next page");
        client
            .get_local_timeline(Some(&GetLocalTimelineInputOptions {
                max_id: Some(max_id.clone()),
                ..GetLocalTimelineInputOptions::default()
            }))
            .await?
    } else {
        trace!("Fetching first page");
        client.get_local_timeline(None).await?
    };
    Ok(json)
}

async fn fetch_dm_page(
    client: &Box<dyn Megalodon + Send + Sync>,
    account: &Account,
    last_id_on_page: &Option<String>,
) -> Result<Vec<Status>> {
    trace!("Fetching page of DMs");
    let Response { json, .. } = if let Some(max_id) = last_id_on_page.as_ref() {
        trace!("Fetching next page");
        client
            .get_account_statuses(
                account.id.clone(),
                Some(&GetAccountStatusesInputOptions {
                    max_id: Some(max_id.clone()),
                    ..GetAccountStatusesInputOptions::default()
                }),
            )
            .await?
    } else {
        trace!("Fetching first page");
        client
            .get_account_statuses(account.id.clone(), None)
            .await?
    };
    let json: Vec<Status> = json
        .into_iter()
        .filter(|s| {
            if let StatusVisibility::Direct = s.visibility {
                (s.in_reply_to_account_id.is_none()
                    || s.in_reply_to_account_id
                        .as_ref()
                        .map(|r| r == &account.id)
                        .unwrap_or_default())
                    && s.mentions.is_empty()
            } else {
                false
            }
        })
        .collect();
    Ok(json)
}

fn page_newer_than(page: &Page, range: &Range) -> Option<String> {
    page.oldest
        .filter(|oldest| *oldest > &range.end)
        .and_then(|_| page.oldest_id.clone())
}

fn page_end_older_than(page: &Page, range: &Range) -> bool {
    status_older_than(&page.oldest, &range.start)
}

fn page_start_older_than(page: &Page, range: &Range) -> bool {
    status_older_than(&page.newest, &range.start)
}

fn status_older_than(status: &Option<&DateTime<Utc>>, dt: &DateTime<Local>) -> bool {
    status.map(|status| status < dt).unwrap_or_default()
}