// Routines: tasks a bot repeats on a schedule. The schedule has the same shape as the original's
// (index.eager-app @1508626, `Prt` / `Irt`): frequency daily|weekly|monthly|yearly, an interval,
// weekdays MO..SU (`yA`), a day of the month or "the Nth weekday", a month, a time "HH:MM" and a
// time zone. Descriptions use the original's zh-TW wording (ids UdWx3W, orHQyz, W+dYrs, Y8bJts,
// kToBIG, kfbKQI, h3xQKP, ni0dzI, 1HiPWu, hlCyZb, kGmiCr, GGSF1N, gjpnJh, jjNxA6).

use chrono::{DateTime, Datelike, Duration, NaiveDate, NaiveTime, TimeZone, Utc, Weekday};
use chrono_tz::Tz;
use serde::{Deserialize, Serialize};

/// The original's weekday order (`yA=["MO","TU","WE","TH","FR","SA","SU"]`).
pub const WEEKDAYS: [&str; 7] = ["MO", "TU", "WE", "TH", "FR", "SA", "SU"];
pub const WORKWEEK: [&str; 5] = ["MO", "TU", "WE", "TH", "FR"];
const WEEKDAY_ZH: [&str; 7] = ["週一", "週二", "週三", "週四", "週五", "週六", "週日"];
const WEEKDAY_ZH_LONG: [&str; 7] = ["星期一", "星期二", "星期三", "星期四", "星期五", "星期六", "星期日"];
/// How far ahead to look for the next run (estimated).
const SEARCH_DAYS: i64 = 366 * 5;

#[derive(Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Debug)]
#[serde(rename_all = "lowercase")]
pub enum Frequency {
    /// 每 N 分鐘 (counted from when it was made).
    Minutely,
    /// 每小時 / 每 N 小時, at the minute of `time`.
    Hourly,
    Daily,
    Weekly,
    Monthly,
    Yearly,
}

#[derive(Clone, Serialize, Deserialize, Debug, PartialEq)]
pub struct WeekdayOfMonth {
    /// 1..=4, or -1 for the last one.
    pub week: i32,
    pub day: String,
}

#[derive(Clone, Serialize, Deserialize, Debug, PartialEq)]
pub struct Schedule {
    pub frequency: Frequency,
    #[serde(default = "one")]
    pub interval: u32,
    #[serde(default, rename = "daysOfWeek", skip_serializing_if = "Vec::is_empty")]
    pub days_of_week: Vec<String>,
    #[serde(default, rename = "monthDay", skip_serializing_if = "Option::is_none")]
    pub month_day: Option<u32>,
    #[serde(default, rename = "weekdayOfMonth", skip_serializing_if = "Option::is_none")]
    pub weekday_of_month: Option<WeekdayOfMonth>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub month: Option<u32>,
    /// "HH:MM", 24-hour.
    pub time: String,
    pub timezone: String,
    /// 僅一次: runs once, then stops.
    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
    pub once: bool,
    /// 「左右」: a flexible time, anywhere in ±FLEX_MINUTES (the original's flexible mode).
    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
    pub flexible: bool,
}

/// How far a flexible ("左右") time may move either way (estimated; the original has a window).
pub const FLEX_MINUTES: i64 = 15;
/// Shortest repeat for 每 N 分鐘 (estimated).
pub const MIN_MINUTES: u32 = 5;

fn one() -> u32 {
    1
}

#[derive(Clone, Serialize, Deserialize, Debug)]
pub struct Routine {
    pub id: u64,
    pub title: String,
    /// What the bot is asked to do each time.
    pub prompt: String,
    pub schedule: Schedule,
    #[serde(default)]
    pub paused: bool,
    /// Seconds since 1970 (UTC).
    #[serde(default)]
    pub created_at: i64,
    #[serde(default)]
    pub last_run: Option<i64>,
    #[serde(default)]
    pub next_run: Option<i64>,
    /// Which computer to work on ("" = the bot's default).
    #[serde(default)]
    pub computer: String,
    /// Run when something happens instead of on the schedule.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub trigger: Option<crate::triggers::Trigger>,
}

pub fn local_timezone() -> String {
    iana_time_zone::get_timezone().unwrap_or_else(|_| "Asia/Taipei".into())
}

fn tz_of(name: &str) -> Tz {
    name.parse::<Tz>().or_else(|_| local_timezone().parse::<Tz>()).unwrap_or(chrono_tz::Asia::Taipei)
}

fn weekday_code(w: Weekday) -> &'static str {
    WEEKDAYS[w.num_days_from_monday() as usize]
}

fn weekday_index(code: &str) -> Option<usize> {
    WEEKDAYS.iter().position(|w| w.eq_ignore_ascii_case(code))
}

pub fn parse_time(s: &str) -> Option<NaiveTime> {
    NaiveTime::parse_from_str(s.trim(), "%H:%M").ok()
}

/// Check a schedule a model wrote, and tidy it.
pub fn validate(mut s: Schedule) -> Result<Schedule, String> {
    if s.interval == 0 {
        s.interval = 1;
    }
    if parse_time(&s.time).is_none() {
        return Err(format!("時間「{}」看不懂，請用 24 小時制的 HH:MM，例如 09:00", s.time));
    }
    if s.timezone.trim().is_empty() || s.timezone.parse::<Tz>().is_err() {
        s.timezone = local_timezone();
    }
    s.days_of_week = s.days_of_week.iter().filter_map(|d| weekday_index(d).map(|i| WEEKDAYS[i].to_string())).collect();
    s.days_of_week.sort_by_key(|d| weekday_index(d));
    s.days_of_week.dedup();
    if s.frequency == Frequency::Minutely && s.interval < MIN_MINUTES {
        return Err(format!("每 N 分鐘最少 {MIN_MINUTES} 分鐘"));
    }
    match s.frequency {
        Frequency::Weekly if s.days_of_week.is_empty() => return Err("每週的例行任務要指定星期幾（daysOfWeek，例如 [\"MO\",\"WE\"]）".into()),
        Frequency::Monthly if s.month_day.is_none() && s.weekday_of_month.is_none() => s.month_day = Some(1),
        Frequency::Yearly if s.month.is_none() => s.month = Some(1),
        _ => {}
    }
    if let Some(d) = s.month_day {
        if !(1..=31).contains(&d) {
            return Err("每月的日期要在 1 到 31 之間".into());
        }
    }
    Ok(s)
}

/// "每週的週一、週三 09:00" in the original's wording.
pub fn describe(s: &Schedule) -> String {
    let n = s.interval.max(1);
    if s.frequency == Frequency::Minutely {
        return format!("每 {n} 分鐘{}", if s.once { "（僅一次）" } else { "" });
    }
    if s.frequency == Frequency::Hourly {
        let minute = parse_time(&s.time).map(|t| chrono::Timelike::minute(&t)).unwrap_or(0);
        let base = if n > 1 { format!("每 {n} 小時") } else { "每小時".into() };
        return format!("{base}的 {minute:02} 分{}{}", if s.flexible { "左右" } else { "" }, if s.once { "（僅一次）" } else { "" });
    }
    let unit = match s.frequency {
        Frequency::Minutely | Frequency::Hourly => unreachable!(),
        Frequency::Daily => "天",
        Frequency::Weekly => "週",
        Frequency::Monthly => "個月",
        Frequency::Yearly => "年",
    };
    let duration = format!("{n} {unit}");
    let repeats = match s.frequency {
        Frequency::Minutely | Frequency::Hourly => unreachable!(),
        Frequency::Daily => if n > 1 { format!("每{duration}") } else { "每天".into() },
        Frequency::Weekly => {
            let all_work = s.days_of_week.len() == WORKWEEK.len() && WORKWEEK.iter().all(|w| s.days_of_week.iter().any(|d| d == w));
            if n == 1 && all_work {
                "每個工作日".into()
            } else {
                let names: Vec<&str> = s.days_of_week.iter().filter_map(|d| weekday_index(d)).map(|i| WEEKDAY_ZH[i]).collect();
                let names = names.join("、");
                if n > 1 { format!("每{duration}的{names}") } else { format!("每週的{names}") }
            }
        }
        Frequency::Monthly => match &s.weekday_of_month {
            None => {
                let d = s.month_day.unwrap_or(1);
                if n > 1 { format!("每{duration}的{d}日") } else { format!("每月{d}日") }
            }
            Some(w) => {
                let week = if w.week < 0 { "最後一個".to_string() } else { format!("第{}個", w.week) };
                let day = weekday_index(&w.day).map(|i| WEEKDAY_ZH_LONG[i]).unwrap_or("");
                if n > 1 { format!("每{duration}的{week}{day}") } else { format!("每月的{week}{day}") }
            }
        },
        Frequency::Yearly => {
            let date = format!("{}月{}日", s.month.unwrap_or(1), s.month_day.unwrap_or(1));
            if n > 1 { format!("每{duration}的{date}") } else { format!("每年{date}") }
        }
    };
    let sentence = format!("{}{repeats} {}{}", if s.once { "僅一次：" } else { "" }, s.time, if s.flexible { "左右" } else { "" });
    if s.timezone == local_timezone() { sentence } else { format!("{sentence}（{}）", s.timezone) }
}

fn months_between(a: NaiveDate, b: NaiveDate) -> i64 {
    (b.year() as i64 - a.year() as i64) * 12 + b.month() as i64 - a.month() as i64
}

fn nth_weekday_matches(d: NaiveDate, w: &WeekdayOfMonth) -> bool {
    let Some(i) = weekday_index(&w.day) else { return false };
    if d.weekday().num_days_from_monday() as usize != i {
        return false;
    }
    if w.week < 0 {
        (d + Duration::days(7)).month() != d.month()
    } else {
        ((d.day() - 1) / 7 + 1) as i32 == w.week
    }
}

fn day_matches(s: &Schedule, anchor: NaiveDate, d: NaiveDate) -> bool {
    let n = s.interval.max(1) as i64;
    match s.frequency {
        Frequency::Minutely | Frequency::Hourly => true,
        Frequency::Daily => (d - anchor).num_days().rem_euclid(n) == 0,
        Frequency::Weekly => {
            let week0 = anchor - Duration::days(anchor.weekday().num_days_from_monday() as i64);
            let weeks = (d - week0).num_days().div_euclid(7);
            weeks.rem_euclid(n) == 0 && s.days_of_week.iter().any(|w| w == weekday_code(d.weekday()))
        }
        Frequency::Monthly => {
            months_between(anchor, d).rem_euclid(n) == 0
                && match &s.weekday_of_month {
                    Some(w) => nth_weekday_matches(d, w),
                    // A day past the month's end runs on its last day.
                    None => {
                        let want = s.month_day.unwrap_or(1);
                        let last = (d + Duration::days(1)).month() != d.month();
                        d.day() == want || (last && d.day() < want)
                    }
                }
        }
        Frequency::Yearly => {
            (d.year() - anchor.year()) as i64 % n == 0 && d.month() == s.month.unwrap_or(1) && d.day() == s.month_day.unwrap_or(1)
        }
    }
}

/// The first run strictly after `after`, counting intervals from `created`. A flexible time moves
/// by a steady amount within ±FLEX_MINUTES; a one-time schedule has no run after its first.
pub fn next_run(s: &Schedule, created: i64, after: i64) -> Option<i64> {
    if s.once {
        let first = exact_next(s, created, created - 1)?;
        let first = flex(s, created, first);
        return (first > after).then_some(first);
    }
    // Look a little earlier so a time pulled forward by "左右" isn't skipped.
    let pad = if s.flexible { FLEX_MINUTES * 60 } else { 0 };
    let mut from = after - pad;
    for _ in 0..4 {
        let t = exact_next(s, created, from)?;
        let f = flex(s, created, t);
        if f > after {
            return Some(f);
        }
        from = t;
    }
    None
}

fn flex(s: &Schedule, created: i64, t: i64) -> i64 {
    if !s.flexible {
        return t;
    }
    // A steady shift per run (same routine + same slot → same moment).
    let h = (created as u64 ^ (t as u64).wrapping_mul(0x9E37_79B9_7F4A_7C15)).wrapping_mul(0xBF58_476D_1CE4_E5B9) >> 33;
    t + (h % (2 * FLEX_MINUTES as u64 * 60 + 1)) as i64 - FLEX_MINUTES * 60
}

fn exact_next(s: &Schedule, created: i64, after: i64) -> Option<i64> {
    let n = s.interval.max(1) as i64;
    if s.frequency == Frequency::Minutely {
        let step = n * 60;
        let k = ((after - created).div_euclid(step) + 1).max(1);
        return Some(created + k * step);
    }
    if s.frequency == Frequency::Hourly {
        let minute = parse_time(&s.time).map(|t| chrono::Timelike::minute(&t) as i64).unwrap_or(0);
        let hour0 = created.div_euclid(3600);
        let mut h = after.div_euclid(3600);
        for _ in 0..(n * 2 + 2) {
            let ts = h * 3600 + minute * 60;
            if ts > after && (h - hour0).rem_euclid(n) == 0 {
                return Some(ts);
            }
            h += 1;
        }
        return None;
    }
    let tz = tz_of(&s.timezone);
    let time = parse_time(&s.time)?;
    let anchor = Utc.timestamp_opt(created, 0).single()?.with_timezone(&tz).date_naive();
    let start = Utc.timestamp_opt(after, 0).single()?.with_timezone(&tz).date_naive();
    for i in 0..SEARCH_DAYS {
        let d = start + Duration::days(i);
        if !day_matches(s, anchor, d) {
            continue;
        }
        // Skipped or doubled clock times (summer time) take the earliest valid moment.
        let Some(at) = tz.from_local_datetime(&d.and_time(time)).earliest() else { continue };
        let ts = at.timestamp();
        if ts > after {
            return Some(ts);
        }
    }
    None
}

/// "今天 09:00", "明天 09:00" or "11月5日 09:00" in the routine's time zone.
pub fn describe_when(ts: i64, timezone: &str) -> String {
    let tz = tz_of(timezone);
    let Some(t) = Utc.timestamp_opt(ts, 0).single().map(|t| t.with_timezone(&tz)) else { return String::new() };
    let today = Utc::now().with_timezone(&tz).date_naive();
    let day = match (t.date_naive() - today).num_days() {
        0 => "今天".to_string(),
        1 => "明天".to_string(),
        _ => format!("{}月{}日", t.month(), t.day()),
    };
    format!("{day} {}", t.format("%H:%M"))
}

pub fn now() -> i64 {
    Utc::now().timestamp()
}

pub fn now_in(timezone: &str) -> DateTime<Tz> {
    Utc::now().with_timezone(&tz_of(timezone))
}

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

    fn ts(y: i32, m: u32, d: u32, h: u32, mi: u32) -> i64 {
        chrono_tz::Asia::Taipei.with_ymd_and_hms(y, m, d, h, mi, 0).unwrap().timestamp()
    }

    /// Drop the "（Asia/Taipei）" a computer in another timezone adds.
    fn here(s: String) -> String {
        s.trim_end_matches("（Asia/Taipei）").to_string()
    }

    fn sched(f: Frequency) -> Schedule {
        Schedule { frequency: f, interval: 1, days_of_week: vec![], month_day: None, weekday_of_month: None, month: None, time: "09:00".into(), timezone: "Asia/Taipei".into(), once: false, flexible: false }
    }

    #[test]
    fn hourly_minutes_once_and_flexible() {
        let mut h = sched(Frequency::Hourly);
        h.time = "00:15".into();
        assert_eq!(next_run(&h, ts(2026, 11, 3, 8, 0), ts(2026, 11, 3, 8, 20)), Some(ts(2026, 11, 3, 9, 15)));
        h.interval = 3;
        assert_eq!(next_run(&h, ts(2026, 11, 3, 8, 0), ts(2026, 11, 3, 8, 20)), Some(ts(2026, 11, 3, 11, 15)));
        assert_eq!(describe(&h), "每 3 小時的 15 分");
        let mut m = sched(Frequency::Minutely);
        m.interval = 30;
        assert_eq!(next_run(&m, ts(2026, 11, 3, 8, 0), ts(2026, 11, 3, 8, 31)), Some(ts(2026, 11, 3, 9, 0)));
        m.interval = 2;
        assert!(validate(m).is_err());
        let mut o = sched(Frequency::Daily);
        o.once = true;
        assert_eq!(next_run(&o, ts(2026, 11, 3, 8, 0), ts(2026, 11, 3, 8, 0)), Some(ts(2026, 11, 3, 9, 0)));
        assert_eq!(next_run(&o, ts(2026, 11, 3, 8, 0), ts(2026, 11, 3, 9, 0)), None);
        let mut f = sched(Frequency::Daily);
        f.flexible = true;
        let t = next_run(&f, ts(2026, 11, 3, 8, 0), ts(2026, 11, 3, 8, 0)).unwrap();
        assert!((t - ts(2026, 11, 3, 9, 0)).abs() <= FLEX_MINUTES * 60);
        assert_eq!(next_run(&f, ts(2026, 11, 3, 8, 0), ts(2026, 11, 3, 8, 0)), Some(t));
        assert!(here(describe(&f)).ends_with("09:00左右"));
        let t2 = next_run(&f, ts(2026, 11, 3, 8, 0), t).unwrap();
        assert!(t2 > t && (t2 - ts(2026, 11, 4, 9, 0)).abs() <= FLEX_MINUTES * 60);
    }

    #[test]
    fn daily_and_weekly() {
        let s = sched(Frequency::Daily);
        // 2026-11-03 is a Tuesday.
        assert_eq!(next_run(&s, ts(2026, 11, 3, 8, 0), ts(2026, 11, 3, 8, 0)), Some(ts(2026, 11, 3, 9, 0)));
        assert_eq!(next_run(&s, ts(2026, 11, 3, 8, 0), ts(2026, 11, 3, 9, 0)), Some(ts(2026, 11, 4, 9, 0)));
        let mut w = sched(Frequency::Weekly);
        w.days_of_week = vec!["MO".into(), "FR".into()];
        assert_eq!(next_run(&w, ts(2026, 11, 3, 8, 0), ts(2026, 11, 3, 8, 0)), Some(ts(2026, 11, 6, 9, 0)));
        w.interval = 2;
        assert_eq!(next_run(&w, ts(2026, 11, 3, 8, 0), ts(2026, 11, 7, 8, 0)), Some(ts(2026, 11, 16, 9, 0)));
        assert_eq!(here(describe(&w)), "每2 週的週一、週五 09:00");
        w.interval = 1;
        w.days_of_week = WORKWEEK.iter().map(|s| s.to_string()).collect();
        assert_eq!(here(describe(&w)), "每個工作日 09:00");
    }

    #[test]
    fn monthly_rules() {
        let mut m = sched(Frequency::Monthly);
        m.month_day = Some(31);
        // November has 30 days: runs on the 30th.
        assert_eq!(next_run(&m, ts(2026, 11, 3, 8, 0), ts(2026, 11, 3, 8, 0)), Some(ts(2026, 11, 30, 9, 0)));
        m.month_day = None;
        m.weekday_of_month = Some(WeekdayOfMonth { week: -1, day: "FR".into() });
        assert_eq!(next_run(&m, ts(2026, 11, 3, 8, 0), ts(2026, 11, 3, 8, 0)), Some(ts(2026, 11, 27, 9, 0)));
        assert_eq!(here(describe(&m)), "每月的最後一個星期五 09:00");
    }

    #[test]
    fn validation() {
        let mut w = sched(Frequency::Weekly);
        assert!(validate(w.clone()).is_err());
        w.days_of_week = vec!["fr".into(), "MO".into(), "MO".into()];
        w.time = "7:30".into();
        let v = validate(w).unwrap();
        assert_eq!(v.days_of_week, vec!["MO", "FR"]);
        let mut bad = sched(Frequency::Daily);
        bad.time = "noon".into();
        assert!(validate(bad).is_err());
    }
}