//! A terminal tool for pointing Runway's own stack at a real CalDAV server.
//!
//! Deliberately thin: it holds no logic of its own, so what it prints is what
//! `runway-caldav` fetched and what `runway-core` expanded. When a calendar
//! looks wrong in the browser, this is how to find out whether the problem is
//! in the view or underneath it — a question the previous iteration could only
//! answer by adding `println!`s to the backend and redeploying.

use chrono::{DateTime, NaiveDate, TimeZone, Utc};
use chrono_tz::Tz;
use clap::{Parser, Subcommand};
use runway_caldav::{CalDavClient, Credentials};
use runway_core::model::Occurrence;
use runway_core::recurrence::{Window, Zones, expand, unresolved_zones};
use std::process::ExitCode;

#[derive(Parser)]
#[command(
    name = "runway",
    about = "Talk to a CalDAV server the way Runway does."
)]
struct Cli {
    /// The DAV root, e.g. https://example.com/dav.php/
    #[arg(long, env = "RUNWAY_CALDAV_URL")]
    server: String,

    #[arg(long, env = "RUNWAY_CALDAV_USER")]
    user: String,

    /// Read from the environment rather than the command line, so it does not
    /// end up in shell history or in the process list.
    #[arg(long, env = "RUNWAY_CALDAV_PASSWORD", hide_env_values = true)]
    password: String,

    /// The zone to show times in, and to read floating times as.
    ///
    /// Defaults to whatever the machine is set to. Baking in a zone would be
    /// the same mistake in miniature that this project exists to correct: the
    /// right zone is a property of the reader, and readers move.
    #[arg(long, default_value_t = local_timezone())]
    timezone: Tz,

    #[command(subcommand)]
    command: Command,
}

/// The system's own IANA zone, falling back to UTC when it cannot be read.
///
/// UTC rather than a guess at somewhere populated: a wrong zone that looks
/// plausible is worse than an obviously neutral one, because nobody checks it.
fn local_timezone() -> Tz {
    iana_time_zone::get_timezone()
        .ok()
        .and_then(|name| name.parse().ok())
        .unwrap_or(Tz::UTC)
}

#[derive(Subcommand)]
enum Command {
    /// List the calendars the server offers.
    Calendars,

    /// List occurrences in a date range, expanded.
    ListEvents {
        /// Inclusive start date, YYYY-MM-DD.
        #[arg(long)]
        from: NaiveDate,
        /// Exclusive end date, YYYY-MM-DD.
        #[arg(long)]
        to: NaiveDate,
        /// Only this calendar, matched on href or display name. Repeatable.
        #[arg(long = "calendar")]
        calendars: Vec<String>,
    },

    /// Print the raw iCalendar for one resource, as the server stores it.
    Show {
        /// The href of the resource.
        href: String,
    },
}

#[tokio::main]
async fn main() -> ExitCode {
    tracing_subscriber::fmt()
        .with_env_filter(
            tracing_subscriber::EnvFilter::try_from_default_env()
                .unwrap_or_else(|_| "runway_cli=info,runway_caldav=info".into()),
        )
        .with_target(false)
        .init();

    let cli = Cli::parse();
    match run(cli).await {
        Ok(()) => ExitCode::SUCCESS,
        Err(error) => {
            eprintln!("error: {error}");
            ExitCode::FAILURE
        }
    }
}

async fn run(cli: Cli) -> Result<(), Box<dyn std::error::Error>> {
    let client = CalDavClient::new(&cli.server, Credentials::new(&cli.user, cli.password))?;

    match cli.command {
        Command::Calendars => list_calendars(&client).await,
        Command::ListEvents {
            from,
            to,
            calendars,
        } => list_events(&client, from, to, &calendars, cli.timezone).await,
        Command::Show { href } => show(&client, &href).await,
    }
}

async fn list_calendars(client: &CalDavClient) -> Result<(), Box<dyn std::error::Error>> {
    let calendars = client.discover().await?;
    if calendars.is_empty() {
        println!("no calendars on this server");
        return Ok(());
    }
    for calendar in &calendars {
        let colour = calendar.color.as_deref().unwrap_or("—");
        println!("{:<28} {:<9} {}", calendar.name(), colour, calendar.href);
        if !calendar.supports_events() {
            println!("{:<28} (holds no events)", "");
        }
    }
    Ok(())
}

async fn list_events(
    client: &CalDavClient,
    from: NaiveDate,
    to: NaiveDate,
    wanted: &[String],
    timezone: Tz,
) -> Result<(), Box<dyn std::error::Error>> {
    let zones = Zones::new(timezone);
    let window = Window::new(midnight(timezone, from), midnight(timezone, to));

    let calendars: Vec<_> = client
        .discover()
        .await?
        .into_iter()
        .filter(|c| c.supports_events())
        .filter(|c| wanted.is_empty() || wanted.iter().any(|w| matches(c, w)))
        .collect();

    if calendars.is_empty() {
        return Err("no calendar matched".into());
    }

    let mut rows: Vec<(String, Occurrence)> = Vec::new();
    for calendar in &calendars {
        let objects = client
            .events_in_range(&calendar.href, window.from, window.to)
            .await?;

        for object in &objects {
            // Reported, not swallowed: a zone we could not identify means the
            // times below may be wrong by hours.
            for zone in unresolved_zones(&object.calendar, zones) {
                eprintln!("warning: {} names an unknown time zone {zone}", object.href);
            }
            for occurrence in expand(&object.calendar, window, zones)? {
                rows.push((calendar.name().to_owned(), occurrence));
            }
        }
    }

    rows.sort_by_key(|(_, occurrence)| occurrence.start_utc);

    println!(
        "{} occurrence(s) between {from} and {to}, shown in {timezone}",
        rows.len(),
    );
    for (calendar, occurrence) in &rows {
        println!(
            "{:<10}  {:<13}  {:<16}  {}",
            occurrence.start.date(),
            span(occurrence, timezone),
            truncate(calendar, 16),
            label(occurrence),
        );
    }
    Ok(())
}

async fn show(client: &CalDavClient, href: &str) -> Result<(), Box<dyn std::error::Error>> {
    let calendar_path = href.rsplit_once('/').map(|(dir, _)| dir).unwrap_or("");
    let object = client
        .get_object(&format!("{calendar_path}/"), href)
        .await?;
    if let Some(etag) = &object.etag {
        eprintln!("etag: {etag}");
    }
    print!("{}", runway_core::ical::write(&object.calendar));
    Ok(())
}

fn matches(calendar: &runway_caldav::Calendar, wanted: &str) -> bool {
    calendar.href.contains(wanted) || calendar.name().eq_ignore_ascii_case(wanted)
}

fn midnight(tz: Tz, date: NaiveDate) -> DateTime<Utc> {
    let local = date.and_hms_opt(0, 0, 0).unwrap_or_default();
    runway_core::recurrence::instant_in(tz, local)
}

/// The time column: a clock range, or the fact that there is not one.
fn span(occurrence: &Occurrence, tz: Tz) -> String {
    if occurrence.is_all_day() {
        return "all-day".to_owned();
    }
    let clock = |instant: DateTime<Utc>| {
        tz.from_utc_datetime(&instant.naive_utc())
            .format("%H:%M")
            .to_string()
    };
    format!(
        "{}-{}",
        clock(occurrence.start_utc),
        clock(occurrence.end_utc)
    )
}

fn label(occurrence: &Occurrence) -> String {
    let title = occurrence.title().unwrap_or("(untitled)");
    if occurrence.is_override {
        format!("{title}  [moved]")
    } else if occurrence.recurrence_id.is_some() {
        format!("{title}  [recurring]")
    } else {
        title.to_owned()
    }
}

fn truncate(text: &str, width: usize) -> String {
    if text.chars().count() <= width {
        return text.to_owned();
    }
    text.chars()
        .take(width.saturating_sub(1))
        .collect::<String>()
        + "…"
}