use std::borrow::Cow;
use std::sync::atomic::{AtomicU64, AtomicU8, Ordering};
use std::sync::Arc;
use std::time::{Duration, Instant};
use std::{fmt, io};

use crate::draw_target::ProgressDrawTarget;
use crate::style::ProgressStyle;

pub(crate) struct BarState {
    pub(crate) draw_target: ProgressDrawTarget,
    pub(crate) on_finish: ProgressFinish,
    pub(crate) style: ProgressStyle,
    pub(crate) state: ProgressState,
    pub(crate) tab_width: usize,
}

impl BarState {
    pub(crate) fn new(
        len: Option<u64>,
        draw_target: ProgressDrawTarget,
        pos: Arc<AtomicPosition>,
    ) -> Self {
        Self {
            draw_target,
            on_finish: ProgressFinish::default(),
            style: ProgressStyle::default_bar(),
            state: ProgressState::new(len, pos),
            tab_width: DEFAULT_TAB_WIDTH,
        }
    }

    /// Finishes the progress bar using the [`ProgressFinish`] behavior stored
    /// in the [`ProgressStyle`].
    pub(crate) fn finish_using_style(&mut self, now: Instant, finish: ProgressFinish) {
        self.state.status = Status::DoneVisible;
        match finish {
            ProgressFinish::AndLeave => {
                if let Some(len) = self.state.len {
                    self.state.pos.set(len);
                }
            }
            ProgressFinish::WithMessage(msg) => {
                if let Some(len) = self.state.len {
                    self.state.pos.set(len);
                }
                self.state.message = TabExpandedString::new(msg, self.tab_width);
            }
            ProgressFinish::AndClear => {
                if let Some(len) = self.state.len {
                    self.state.pos.set(len);
                }
                self.state.status = Status::DoneHidden;
            }
            ProgressFinish::Abandon => {}
            ProgressFinish::AbandonWithMessage(msg) => {
                self.state.message = TabExpandedString::new(msg, self.tab_width)
            }
        }

        // There's no need to update the estimate here; once the `status` is no longer
        // `InProgress`, we will use the length and elapsed time to estimate.
        let _ = self.draw(true, now);
    }

    pub(crate) fn reset(&mut self, now: Instant, mode: Reset) {
        if let Reset::Eta | Reset::All = mode {
            self.state.est.reset(now);
        }

        if let Reset::Elapsed | Reset::All = mode {
            self.state.started = now;
        }

        if let Reset::All = mode {
            self.state.pos.reset(now);
            self.state.status = Status::InProgress;

            for (_, tracker) in self.style.format_map.iter_mut() {
                tracker.reset(&self.state, now);
            }

            let _ = self.draw(false, now);
        }
    }

    pub(crate) fn update(&mut self, now: Instant, f: impl FnOnce(&mut ProgressState)) {
        f(&mut self.state);
        self.tick(now);
    }

    pub(crate) fn set_length(&mut self, now: Instant, len: u64) {
        self.state.len = Some(len);
        self.update_estimate_and_draw(now);
    }

    pub(crate) fn inc_length(&mut self, now: Instant, delta: u64) {
        if let Some(len) = self.state.len {
            self.state.len = Some(len.saturating_add(delta));
        }
        self.update_estimate_and_draw(now);
    }

    pub(crate) fn set_tab_width(&mut self, tab_width: usize) {
        self.tab_width = tab_width;
        self.state.message.set_tab_width(tab_width);
        self.state.prefix.set_tab_width(tab_width);
        self.style.set_tab_width(tab_width);
    }

    pub(crate) fn set_style(&mut self, style: ProgressStyle) {
        self.style = style;
        self.style.set_tab_width(self.tab_width);
    }

    pub(crate) fn tick(&mut self, now: Instant) {
        self.state.tick = self.state.tick.saturating_add(1);
        self.update_estimate_and_draw(now);
    }

    pub(crate) fn update_estimate_and_draw(&mut self, now: Instant) {
        let pos = self.state.pos.pos.load(Ordering::Relaxed);
        self.state.est.record(pos, now);
        let _ = self.draw(false, now);

        for (_, tracker) in self.style.format_map.iter_mut() {
            tracker.tick(&self.state, now);
        }
    }

    pub(crate) fn println(&mut self, now: Instant, msg: &str) {
        let width = self.draw_target.width();
        let mut drawable = match self.draw_target.drawable(true, now) {
            Some(drawable) => drawable,
            None => return,
        };

        let mut draw_state = drawable.state();
        draw_state.lines.extend(msg.lines().map(Into::into));
        draw_state.orphan_lines = draw_state.lines.len();
        if !matches!(self.state.status, Status::DoneHidden) {
            self.style
                .format_state(&self.state, &mut draw_state.lines, width);
        }

        drop(draw_state);
        let _ = drawable.draw();
    }

    pub(crate) fn suspend<F: FnOnce() -> R, R>(&mut self, now: Instant, f: F) -> R {
        if let Some(drawable) = self.draw_target.drawable(true, now) {
            let _ = drawable.clear();
        }

        let ret = f();
        let _ = self.draw(true, Instant::now());
        ret
    }

    pub(crate) fn draw(&mut self, mut force_draw: bool, now: Instant) -> io::Result<()> {
        let width = self.draw_target.width();
        force_draw |= self.state.is_finished();
        let mut drawable = match self.draw_target.drawable(force_draw, now) {
            Some(drawable) => drawable,
            None => return Ok(()),
        };

        // `|| self.is_finished()` should not be needed here, but we used to always for draw for
        // finished progress bar, so it's kept as to not cause compatibility issues in weird cases.
        let mut draw_state = drawable.state();

        if !matches!(self.state.status, Status::DoneHidden) {
            self.style
                .format_state(&self.state, &mut draw_state.lines, width);
        }

        drop(draw_state);
        drawable.draw()
    }
}

impl Drop for BarState {
    fn drop(&mut self) {
        // Progress bar is already finished.  Do not need to do anything.
        if self.state.is_finished() {
            return;
        }

        self.finish_using_style(Instant::now(), self.on_finish.clone());
    }
}

pub(crate) enum Reset {
    Eta,
    Elapsed,
    All,
}

/// The state of a progress bar at a moment in time.
#[non_exhaustive]
pub struct ProgressState {
    pos: Arc<AtomicPosition>,
    len: Option<u64>,
    pub(crate) tick: u64,
    pub(crate) started: Instant,
    status: Status,
    est: Estimator,
    pub(crate) message: TabExpandedString,
    pub(crate) prefix: TabExpandedString,
}

impl ProgressState {
    pub(crate) fn new(len: Option<u64>, pos: Arc<AtomicPosition>) -> Self {
        Self {
            pos,
            len,
            tick: 0,
            status: Status::InProgress,
            started: Instant::now(),
            est: Estimator::new(Instant::now()),
            message: TabExpandedString::NoTabs("".into()),
            prefix: TabExpandedString::NoTabs("".into()),
        }
    }

    /// Indicates that the progress bar finished.
    pub fn is_finished(&self) -> bool {
        match self.status {
            Status::InProgress => false,
            Status::DoneVisible => true,
            Status::DoneHidden => true,
        }
    }

    /// Returns the completion as a floating-point number between 0 and 1
    pub fn fraction(&self) -> f32 {
        let pos = self.pos.pos.load(Ordering::Relaxed);
        let pct = match (pos, self.len) {
            (_, None) => 1.0,
            (_, Some(0)) => 1.0,
            (0, _) => 0.0,
            (pos, Some(len)) => pos as f32 / len as f32,
        };
        pct.max(0.0).min(1.0)
    }

    /// The expected ETA
    pub fn eta(&self) -> Duration {
        if self.is_finished() {
            return Duration::new(0, 0);
        }

        let len = match self.len {
            Some(len) => len,
            None => return Duration::new(0, 0),
        };

        let pos = self.pos.pos.load(Ordering::Relaxed);
        let t = self.est.seconds_per_step();
        secs_to_duration(t * len.saturating_sub(pos) as f64)
    }

    /// The expected total duration (that is, elapsed time + expected ETA)
    pub fn duration(&self) -> Duration {
        if self.len.is_none() || self.is_finished() {
            return Duration::new(0, 0);
        }
        self.started.elapsed() + self.eta()
    }

    /// The number of steps per second
    pub fn per_sec(&self) -> f64 {
        match self.status {
            Status::InProgress => match 1.0 / self.est.seconds_per_step() {
                per_sec if per_sec.is_nan() => 0.0,
                per_sec => per_sec,
            },
            _ => {
                let len = self.len.unwrap_or_else(|| self.pos());
                len as f64 / self.started.elapsed().as_secs_f64()
            }
        }
    }

    pub fn elapsed(&self) -> Duration {
        self.started.elapsed()
    }

    pub fn pos(&self) -> u64 {
        self.pos.pos.load(Ordering::Relaxed)
    }

    pub fn set_pos(&mut self, pos: u64) {
        self.pos.set(pos);
    }

    #[allow(clippy::len_without_is_empty)]
    pub fn len(&self) -> Option<u64> {
        self.len
    }

    pub fn set_len(&mut self, len: u64) {
        self.len = Some(len);
    }
}

#[derive(Debug, PartialEq, Eq, Clone)]
pub(crate) enum TabExpandedString {
    NoTabs(Cow<'static, str>),
    WithTabs {
        original: Cow<'static, str>,
        expanded: String,
        tab_width: usize,
    },
}

impl TabExpandedString {
    pub(crate) fn new(s: Cow<'static, str>, tab_width: usize) -> Self {
        let expanded = s.replace('\t', &" ".repeat(tab_width));
        if s == expanded {
            Self::NoTabs(s)
        } else {
            Self::WithTabs {
                original: s,
                expanded,
                tab_width,
            }
        }
    }

    pub(crate) fn expanded(&self) -> &str {
        match &self {
            Self::NoTabs(s) => {
                debug_assert!(!s.contains('\t'));
                s
            }
            Self::WithTabs { expanded, .. } => expanded,
        }
    }

    pub(crate) fn set_tab_width(&mut self, new_tab_width: usize) {
        if let TabExpandedString::WithTabs {
            original,
            expanded,
            tab_width,
        } = self
        {
            if *tab_width != new_tab_width {
                *tab_width = new_tab_width;
                *expanded = original.replace('\t', &" ".repeat(new_tab_width));
            }
        }
    }
}

/// Estimate the number of seconds per step
///
/// Ring buffer with constant capacity. Used by `ProgressBar`s to display `{eta}`,
/// `{eta_precise}`, and `{*_per_sec}`.
pub(crate) struct Estimator {
    steps: [f64; 16],
    pos: u8,
    full: bool,
    prev: (u64, Instant),
}

impl Estimator {
    fn new(now: Instant) -> Self {
        Self {
            steps: [0.0; 16],
            pos: 0,
            full: false,
            prev: (0, now),
        }
    }

    fn record(&mut self, new: u64, now: Instant) {
        let delta = new.saturating_sub(self.prev.0);
        if delta == 0 || now < self.prev.1 {
            return;
        }

        let elapsed = now - self.prev.1;
        let divisor = delta as f64;
        let mut batch = 0.0;
        if divisor != 0.0 {
            batch = duration_to_secs(elapsed) / divisor;
        };

        self.steps[self.pos as usize] = batch;
        self.pos = (self.pos + 1) % 16;
        if !self.full && self.pos == 0 {
            self.full = true;
        }

        self.prev = (new, now);
    }

    pub(crate) fn reset(&mut self, now: Instant) {
        self.pos = 0;
        self.full = false;
        self.prev = (0, now);
    }

    /// Average time per step in seconds, using rolling buffer of last 15 steps
    fn seconds_per_step(&self) -> f64 {
        let len = self.len();
        self.steps[0..len].iter().sum::<f64>() / len as f64
    }

    fn len(&self) -> usize {
        match self.full {
            true => 16,
            false => self.pos as usize,
        }
    }
}

impl fmt::Debug for Estimator {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Estimate")
            .field("steps", &&self.steps[..self.len()])
            .field("prev", &self.prev)
            .finish()
    }
}

pub(crate) struct AtomicPosition {
    pub(crate) pos: AtomicU64,
    capacity: AtomicU8,
    prev: AtomicU64,
    start: Instant,
}

impl AtomicPosition {
    pub(crate) fn new() -> Self {
        Self {
            pos: AtomicU64::new(0),
            capacity: AtomicU8::new(MAX_BURST),
            prev: AtomicU64::new(0),
            start: Instant::now(),
        }
    }

    pub(crate) fn allow(&self, now: Instant) -> bool {
        if now < self.start {
            return false;
        }

        let mut capacity = self.capacity.load(Ordering::Acquire);
        // `prev` is the number of ms after `self.started` we last returned `true`, in ns
        let prev = self.prev.load(Ordering::Acquire);
        // `elapsed` is the number of ns since `self.started`
        let elapsed = (now - self.start).as_nanos() as u64;
        // `diff` is the number of ns since we last returned `true`
        let diff = elapsed.saturating_sub(prev);

        // If `capacity` is 0 and not enough time (1ms) has passed since `prev`
        // to add new capacity, return `false`. The goal of this method is to
        // make this decision as efficient as possible.
        if capacity == 0 && diff < INTERVAL {
            return false;
        }

        // We now calculate `new`, the number of ms, in ns, since we last returned `true`,
        // and `remainder`, which represents a number of ns less than 1ms which we cannot
        // convert into capacity now, so we're saving it for later. We do this by
        // substracting this from `elapsed` before storing it into `self.prev`.
        let (new, remainder) = ((diff / INTERVAL), (diff % INTERVAL));
        // We add `new` to `capacity`, subtract one for returning `true` from here,
        // then make sure it does not exceed a maximum of `MAX_BURST`.
        capacity = Ord::min(MAX_BURST as u128, (capacity as u128) + (new as u128) - 1) as u8;

        // Then, we just store `capacity` and `prev` atomically for the next iteration
        self.capacity.store(capacity, Ordering::Release);
        self.prev.store(elapsed - remainder, Ordering::Release);
        true
    }

    fn reset(&self, now: Instant) {
        self.set(0);
        let elapsed = (now.saturating_duration_since(self.start)).as_millis() as u64;
        self.prev.store(elapsed, Ordering::Release);
    }

    pub(crate) fn inc(&self, delta: u64) {
        self.pos.fetch_add(delta, Ordering::SeqCst);
    }

    pub(crate) fn set(&self, pos: u64) {
        self.pos.store(pos, Ordering::Release);
    }
}

const INTERVAL: u64 = 1_000_000;
const MAX_BURST: u8 = 10;

/// Behavior of a progress bar when it is finished
///
/// This is invoked when a [`ProgressBar`] or [`ProgressBarIter`] completes and
/// [`ProgressBar::is_finished`] is false.
///
/// [`ProgressBar`]: crate::ProgressBar
/// [`ProgressBarIter`]: crate::ProgressBarIter
/// [`ProgressBar::is_finished`]: crate::ProgressBar::is_finished
#[derive(Clone, Debug)]
pub enum ProgressFinish {
    /// Finishes the progress bar and leaves the current message
    ///
    /// Same behavior as calling [`ProgressBar::finish()`](crate::ProgressBar::finish).
    AndLeave,
    /// Finishes the progress bar and sets a message
    ///
    /// Same behavior as calling [`ProgressBar::finish_with_message()`](crate::ProgressBar::finish_with_message).
    WithMessage(Cow<'static, str>),
    /// Finishes the progress bar and completely clears it (this is the default)
    ///
    /// Same behavior as calling [`ProgressBar::finish_and_clear()`](crate::ProgressBar::finish_and_clear).
    AndClear,
    /// Finishes the progress bar and leaves the current message and progress
    ///
    /// Same behavior as calling [`ProgressBar::abandon()`](crate::ProgressBar::abandon).
    Abandon,
    /// Finishes the progress bar and sets a message, and leaves the current progress
    ///
    /// Same behavior as calling [`ProgressBar::abandon_with_message()`](crate::ProgressBar::abandon_with_message).
    AbandonWithMessage(Cow<'static, str>),
}

impl Default for ProgressFinish {
    fn default() -> Self {
        Self::AndClear
    }
}

fn duration_to_secs(d: Duration) -> f64 {
    d.as_secs() as f64 + f64::from(d.subsec_nanos()) / 1_000_000_000f64
}

fn secs_to_duration(s: f64) -> Duration {
    let secs = s.trunc() as u64;
    let nanos = (s.fract() * 1_000_000_000f64) as u32;
    Duration::new(secs, nanos)
}

#[derive(Debug)]
pub(crate) enum Status {
    InProgress,
    DoneVisible,
    DoneHidden,
}

pub(crate) const DEFAULT_TAB_WIDTH: usize = 8;

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

    #[test]
    fn test_time_per_step() {
        let test_rate = |items_per_second| {
            let mut now = Instant::now();
            let mut est = Estimator::new(now);
            let mut pos = 0;

            for _ in 0..est.steps.len() {
                pos += items_per_second;
                now += Duration::from_secs(1);
                est.record(pos, now);
            }
            let avg_seconds_per_step = est.seconds_per_step();

            assert!(avg_seconds_per_step > 0.0);
            assert!(avg_seconds_per_step.is_finite());

            let expected_rate = 1.0 / items_per_second as f64;
            let absolute_error = (avg_seconds_per_step - expected_rate).abs();
            assert!(
                absolute_error < f64::EPSILON,
                "Expected rate: {}, actual: {}, absolute error: {}",
                expected_rate,
                avg_seconds_per_step,
                absolute_error
            );
        };

        test_rate(1);
        test_rate(1_000);
        test_rate(1_000_000);
        test_rate(1_000_000_000);
        test_rate(1_000_000_001);
        test_rate(100_000_000_000);
        test_rate(1_000_000_000_000);
        test_rate(100_000_000_000_000);
        test_rate(1_000_000_000_000_000);
    }

    #[test]
    fn test_duration_stuff() {
        let duration = Duration::new(42, 100_000_000);
        let secs = duration_to_secs(duration);
        assert_eq!(secs_to_duration(secs), duration);
    }

    #[test]
    fn test_estimator_rewind_position() {
        let now = Instant::now();
        let mut est = Estimator::new(now);
        est.record(0, now);
        est.record(1, now);
        // Should not panic.
        est.record(0, now);

        let pb = ProgressBar::hidden();
        pb.set_length(10);
        pb.set_position(1);
        pb.tick();
        // Should not panic.
        pb.set_position(0);
    }

    #[test]
    fn test_atomic_position_large_time_difference() {
        let atomic_position = AtomicPosition::new();
        let later = atomic_position.start + Duration::from_nanos(INTERVAL * u64::from(u8::MAX));
        // Should not panic.
        atomic_position.allow(later);
    }
}