// Package progress contains progress bar widget functionality.
// Use progress.New to create a new progress widget container.
// That widget should be added to a context using progress.NewContext,
// and retrieved via progress.FromContext. Invoke one of the Progress.NewX
// methods to create a new progress.Bar. Invoke Bar.Incr to increment
// the bar's progress, and invoke Bar.Stop to stop the bar. Be sure
// to invoke Progress.Stop when the progress widget is no longer needed.
//
// You can use the progress.NewReader and progress.NewWriter functions
// to wrap an io.Reader or io.Writer, respectively, with a progress bar.
// Both functions expect the supplied ctx arg to contain a *progress.Progress.
// Note also that both wrappers are context-aware; that is, they will stop
// the reading/writing process when the context is canceled. Be sure to
// call Close on the wrappers when done.
package progress

import (
	"context"
	"io"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"github.com/samber/lo"
	mpb "github.com/vbauerster/mpb/v8"
	"github.com/vbauerster/mpb/v8/decor"

	"github.com/neilotoole/sq/libsq/core/lg"
	"github.com/neilotoole/sq/libsq/core/options"
	"github.com/neilotoole/sq/libsq/core/stringz"
)

type progCtxKey struct{}

// NewContext returns ctx with p added as a value.
func NewContext(ctx context.Context, p *Progress) context.Context {
	if ctx == nil {
		ctx = context.Background()
	}

	return context.WithValue(ctx, progCtxKey{}, p)
}

// FromContext returns the Progress added to ctx via NewContext,
// or returns nil. Note that it is safe to invoke the methods
// of a nil Progress.
func FromContext(ctx context.Context) *Progress {
	if ctx == nil {
		return nil
	}

	val := ctx.Value(progCtxKey{})
	if val == nil {
		return nil
	}

	if p, ok := val.(*Progress); ok {
		return p
	}

	return nil
}

type barCtxKey struct{}

// NewBarContext returns ctx with bar added as a value. This context can
// be used in conjunction with progress.Incr to increment the progress bar.
func NewBarContext(ctx context.Context, bar *Bar) context.Context {
	if ctx == nil {
		ctx = context.Background()
	}

	return context.WithValue(ctx, barCtxKey{}, bar)
}

// Incr increments the progress of the outermost bar (if any) in ctx
// by amount n. Use in conjunction with a context returned from NewBarContext.
// It safe to invoke Incr on a nil context or a context that doesn't
// contain a Bar.
//
// NOTE: This context-based incrementing is a bit of an experiment. I'm
// a bit hesitant in going even further with context-based logic, as it's not
// clear to me that it's a good idea to lean on context so much.
// So, it's possible this mechanism may be removed in the future.
func Incr(ctx context.Context, n int) {
	if ctx == nil {
		return
	}

	val := ctx.Value(barCtxKey{})
	if val == nil {
		return
	}

	if b, ok := val.(*Bar); ok {
		b.Incr(n)
	}
}

// New returns a new Progress instance, which is a container for progress bars.
// The returned Progress instance is safe for concurrent use, and all of its
// public methods can be safely invoked on a nil Progress. The caller is
// responsible for calling Progress.Stop on the returned Progress.
// Arg delay specifies a duration to wait before rendering the progress bar.
// The Progress is lazily initialized, and thus the delay clock doesn't
// start ticking until the first call to one of the Progress.NewX methods.
func New(ctx context.Context, out io.Writer, delay time.Duration, colors *Colors) *Progress {
	log := lg.FromContext(ctx)

	if colors == nil {
		colors = DefaultColors()
	}

	p := &Progress{
		mu:        &sync.Mutex{},
		colors:    colors,
		bars:      make([]*Bar, 0),
		delay:     delay,
		stoppedCh: make(chan struct{}),
		stopOnce:  &sync.Once{},
	}

	// Note that p.ctx is not the same as the arg ctx. This is a bit of a hack
	// to ensure that p.Stop gets called when ctx is cancelled, but before
	// the p.pc learns that its context is cancelled. This was done in an attempt
	// to clean up the progress bars before the main context is cancelled (i.e.
	// to remove bars when the user hits Ctrl-C).
	p.ctx, p.cancelFn = context.WithCancel(lg.NewContext(context.Background(), log))

	opts := []mpb.ContainerOption{
		mpb.WithOutput(out),
		mpb.WithWidth(boxWidth),
		mpb.WithAutoRefresh(), // Needed for color in Windows, apparently
	}

	p.pc = mpb.NewWithContext(ctx, opts...)
	return p
}

// Progress represents a container that renders one or more progress bars.
// The caller is responsible for calling Progress.Stop to indicate
// completion.
type Progress struct {
	// The implementation here may seem a bit convoluted. When a new bar is
	// created from this Progress, the Bar.bar is initialized only after the
	// bar's own render delay has expired. The details are ugly.
	//
	// Why not just use the mpb package directly? There are three main reasons:
	//
	// 1. At the time of creating this package, the mpb package didn't correctly
	//    honor the render delay. See: https://github.com/vbauerster/mpb/issues/136
	//    That bug has since been fixed, but...
	// 2. The delayed initialization of the Bar.bar is useful for our purposes.
	//    In particular, we can set the render delay on a per-bar basis, which is
	//    not possible with the mpb package (its render delay is per Progress, not
	//    per Bar).
	// 3. Having this wrapper around the mpb package allows us greater
	//    flexibility, e.g. if we ever want to swap out the mpb package for
	//    something else.

	ctx      context.Context
	cancelFn context.CancelFunc

	// mu guards ALL public methods.
	mu *sync.Mutex

	// stoppedCh is closed when the progress widget is stopped.
	// This somewhat duplicates <-p.ctx.Done()... maybe it can be removed?
	stoppedCh chan struct{}
	stopOnce  *sync.Once

	// pc is the underlying progress container. It is lazily initialized
	// by pcInitFn. Any method that accesses pc must be certain that
	// pcInitFn has been called.
	pc *mpb.Progress

	// colors contains the color scheme to use.
	colors *Colors

	// bars contains all bars that have been created on this Progress.
	bars []*Bar

	// delay is the duration to wait before rendering a progress bar.
	// Each newly-created bar gets its own render delay.
	delay time.Duration
}

// Stop waits for all bars to complete and finally shuts down the
// progress container. After this method has been called, there is
// no way to reuse the Progress instance.
func (p *Progress) Stop() {
	if p == nil {
		return
	}

	p.mu.Lock()
	p.doStop()
	<-p.stoppedCh
	p.mu.Unlock()
}

// doStop is probably needlessly complex, but at the time it was written,
// there was a bug in the mpb package (to do with delayed render and abort),
// and so was created an extra-paranoid workaround. It's still not clear
// if all of this works to remove the progress bars before content
// is written to stdout.
func (p *Progress) doStop() {
	p.stopOnce.Do(func() {
		if p.pc == nil {
			p.cancelFn()
			<-p.ctx.Done()
			close(p.stoppedCh)
			return
		}

		if len(p.bars) == 0 {
			p.cancelFn()
			<-p.ctx.Done()
			close(p.stoppedCh)
			return
		}

		for _, b := range p.bars {
			// We abort each of the bars here, before we call b.doStop() below.
			// In theory, this gives the bar abortion process a head start before
			// b.bar.Wait() is invoked by b.doStop(). This may be completely
			// unnecessary, but it doesn't seem to hurt.
			if b.bar != nil {
				b.bar.SetTotal(-1, true)
				b.bar.Abort(true)
			}
		}

		for _, b := range p.bars {
			b.doStop()
			<-b.barStoppedCh // Wait for bar to stop
		}

		// So, now we REALLY want to wait for the progress widget
		// to finish. Alas, the pc.Wait method doesn't seem to
		// always remove the bars from the terminal. So, we do
		// some probably useless extra steps to hopefully trigger
		// the terminal wipe before we return.
		p.pc.Wait()
		// Important: we must call cancelFn after pc.Wait() or the bars
		// may not be removed from the terminal.
		p.cancelFn()
		<-p.ctx.Done()
		// We shouldn't need this extra call to pc.Wait,
		// but it shouldn't hurt?
		p.pc.Wait()
		close(p.stoppedCh)
	})

	<-p.ctx.Done()
}

// Opt is a functional option for Bar creation.
type Opt interface {
	apply(*Progress, *barConfig)
}

// barConfig is passed to Progress.newBar.
type barConfig struct {
	style      mpb.BarFillerBuilder
	msg        string
	decorators []decor.Decorator
	total      int64
}

// newBar returns a new Bar. This function must only be called from
// inside the Progress mutex.
func (p *Progress) newBar(cfg *barConfig, opts []Opt) *Bar {
	if p == nil {
		return nil
	}

	cfg.decorators = lo.WithoutEmpty(cfg.decorators)

	select {
	case <-p.stoppedCh:
		return nil
	case <-p.ctx.Done():
		return nil
	default:
	}

	if cfg.total < 0 {
		cfg.total = 0
	}

	// We want the bar message to be a consistent width.
	switch {
	case len(cfg.msg) < msgLength:
		cfg.msg += strings.Repeat(" ", msgLength-len(cfg.msg))
	case len(cfg.msg) > msgLength:
		cfg.msg = stringz.Ellipsify(cfg.msg, msgLength)
	}

	b := &Bar{
		p:            p,
		incrStash:    &atomic.Int64{},
		barInitOnce:  &sync.Once{},
		barStopOnce:  &sync.Once{},
		barStoppedCh: make(chan struct{}),
	}
	b.barInitFn = func() {
		p.mu.Lock()
		defer p.mu.Unlock()

		select {
		case <-p.ctx.Done():
			return
		case <-p.stoppedCh:
			return
		case <-b.barStoppedCh:
			return
		default:
		}

		for _, opt := range opts {
			if opt != nil {
				opt.apply(p, cfg)
			}
		}

		// REVISIT: It shouldn't be the case that it's possible that the
		// progress has already been stopped. If it is stopped, the call
		// below will panic. Maybe consider wrapping the call in a recover?
		b.bar = p.pc.New(cfg.total,
			cfg.style,
			mpb.BarWidth(barWidth),
			mpb.PrependDecorators(
				colorize(decor.Name(cfg.msg, decor.WCSyncWidthR), p.colors.Message),
			),
			mpb.AppendDecorators(cfg.decorators...),
			mpb.BarRemoveOnComplete(),
		)

		b.bar.IncrBy(int(b.incrStash.Load()))
		b.incrStash = nil
	}

	b.delayCh = barRenderDelay(b, p.delay)
	p.bars = append(p.bars, b)

	return b
}

// Bar represents a single progress bar. The caller should invoke
// Bar.Incr as necessary to increment the bar's progress. When
// the bar is complete, the caller should invoke Bar.Stop. All
// methods are safe to call on a nil Bar.
type Bar struct {
	// bar is nil until barInitOnce.Do(barInitFn) is called
	bar *mpb.Bar
	// p is never nil
	p *Progress

	// There's a bug in the mpb package, wherein it doesn't fully
	// respect the render delay.
	//
	// https://github.com/vbauerster/mpb/issues/136
	//
	// Until that bug is fixed, the Bar is lazily initialized
	// after the render delay expires. In fact, even when the
	// bug is fixed, we may just stick with the lazy initialization
	// mechanism, as it allows us to set the render delay on a
	// per-bar basis, which is not possible with the mpb package.

	barInitOnce *sync.Once
	barInitFn   func()

	barStopOnce  *sync.Once
	barStoppedCh chan struct{}

	delayCh <-chan struct{}

	// incrStash holds the increment count until the
	// bar is fully initialized.
	incrStash *atomic.Int64
}

// Incr increments progress by amount n. It is safe to
// call IncrBy on a nil Bar.
func (b *Bar) Incr(n int) {
	if b == nil {
		return
	}

	b.p.mu.Lock()
	defer b.p.mu.Unlock()

	select {
	case <-b.p.stoppedCh:
		return
	case <-b.barStoppedCh:
		return
	case <-b.p.ctx.Done():
		return
	case <-b.delayCh:
		b.barInitOnce.Do(b.barInitFn)
		if b.bar != nil {
			b.bar.IncrBy(n)
		}
		return
	default:
		// The bar hasn't been initialized yet, so we stash
		// the increment count for later use.
		b.incrStash.Add(int64(n))
	}
}

// Stop stops and removes the bar. It is safe to call Stop on a nil Bar,
// or to call Stop multiple times.
func (b *Bar) Stop() {
	if b == nil {
		return
	}

	b.p.mu.Lock()
	defer b.p.mu.Unlock()

	b.doStop()
	<-b.barStoppedCh
}

func (b *Bar) doStop() {
	if b == nil {
		return
	}

	b.barStopOnce.Do(func() {
		if b.bar == nil {
			close(b.barStoppedCh)
			return
		}

		// We *probably* only need to call b.bar.Abort() here?
		b.bar.SetTotal(-1, true)
		b.bar.Abort(true)
		b.bar.Wait()
		close(b.barStoppedCh)
	})
}

// barRenderDelay returns a channel that will be closed after d,
// at which point b will be initialized.
func barRenderDelay(b *Bar, d time.Duration) <-chan struct{} {
	delayCh := make(chan struct{})
	t := time.NewTimer(d)
	go func() {
		defer close(delayCh)
		defer t.Stop()

		<-t.C
		b.barInitOnce.Do(b.barInitFn)
	}()
	return delayCh
}

// OptDebugSleep configures DebugSleep. It should be removed when the
// progress impl is stable.
var OptDebugSleep = options.NewDuration(
	"debug.progress.sleep",
	"",
	0,
	0,
	"DEBUG: Sleep during operations to facilitate testing progress bars",
	`DEBUG: Sleep during operations to facilitate testing progress bars.`,
)

// DebugSleep sleeps for a period of time to facilitate testing the
// progress impl. It uses the value from OptDebugSleep. This function
// (and OptDebugSleep) should be removed when the progress impl is
// stable.
func DebugSleep(ctx context.Context) {
	sleep := OptDebugSleep.Get(options.FromContext(ctx))
	if sleep > 0 {
		time.Sleep(sleep)
	}
}