// SPDX-License-Identifier: GPL-3.0-or-later

package ui

import (
	"context"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/diamondburned/gotk4/pkg/gdk/v4"
	"github.com/diamondburned/gotk4/pkg/pango"

	"github.com/diamondburned/gotk4/pkg/gtk/v4"

	"krino/gui/internal/model"
	"krino/internal/engine"
	"krino/internal/plan"
	"krino/internal/xdg"
)

// planView is the Plan tab: a directory picker and Scan, the plan as a list
// with a checkbox per file, the selected file's explanation beside it, and
// Apply (GUI design §3).
type planView struct {
	w    *Window
	root *gtk.Box

	dirs    *gtk.DropDown
	path    *gtk.Label
	scan    *gtk.Button
	apply   *gtk.Button
	cancel  *gtk.Button
	selAll  *gtk.Button
	selNone *gtk.Button
	checked *gtk.MenuButton

	groups     [8]*gtk.SizeGroup
	listScroll *gtk.ScrolledWindow
	filter     *gtk.SearchEntry
	shown      []int
	list       *gtk.ListBox
	headerBox  *gtk.Box
	details    *gtk.Box

	previewNote   *gtk.Label
	picture       *gtk.Picture
	previewText   *gtk.TextView
	previewScroll *gtk.ScrolledWindow
	previewTmp    string
	previewFor    string
	detailPane    *gtk.Paned
	arrangement   *gtk.Paned
	listSide      *gtk.Box
	detailScroll  *gtk.ScrolledWindow
	previewBox    *gtk.Box
	layout        string
	renderedDir   string
	previewHeight int
	previewOff    bool
	startSelected bool
	menu          *gtk.Popover
	menuRow       int

	tab      *model.PlanTab
	cancelOp context.CancelFunc
}

func newPlanView(w *Window) *planView {
	p := &planView{w: w}
	p.root = gtk.NewBox(gtk.OrientationVertical, 0)

	// The picker holds names only: a long path in it would widen the
	// window past the screen, so the path goes in a label that ellipsizes.
	names := make([]string, len(w.engine.Dirs))
	for i, d := range w.engine.Dirs {
		names[i] = d.Name
	}
	if len(names) == 0 {
		names = []string{"none"}
	}
	p.dirs = gtk.NewDropDownFromStrings(names)
	p.path = gtk.NewLabel("")
	p.path.SetXAlign(0)
	p.path.SetHExpand(true)
	p.path.SetEllipsize(pango.EllipsizeMiddle)
	p.path.SetMaxWidthChars(20)
	p.dirs.Connect("notify::selected", p.showPath)
	p.scan = gtk.NewButtonWithLabel("Scan")
	p.selAll = gtk.NewButtonWithLabel("Select all")
	p.selNone = gtk.NewButtonWithLabel("None")
	p.apply = gtk.NewButtonWithLabel("Apply")
	p.apply.AddCSSClass("suggested-action")
	p.cancel = gtk.NewButtonWithLabel("Cancel")
	p.cancel.SetSensitive(false)

	bar := gtk.NewBox(gtk.OrientationHorizontal, 6)
	bar.SetMarginTop(6)
	bar.SetMarginStart(6)
	bar.SetMarginEnd(6)
	bar.SetMarginBottom(6)
	bar.Append(gtk.NewLabel("Directory"))
	bar.Append(p.dirs)
	bar.Append(p.scan)
	// A filter over the plan: type a few letters of a name, as fzf does,
	// and act on what is left. It sits by the Scan button, where the eye
	// starts (his request, 2026-09-17).
	p.filter = gtk.NewSearchEntry()
	p.filter.SetPlaceholderText("filter")
	p.filter.SetTooltipText("show only the files whose name or rule has these letters, in order; Select all then checks those")
	p.filter.SetSizeRequest(200, -1)
	bar.Append(p.filter)

	bar.Append(p.path)
	bar.Append(p.selAll)
	bar.Append(p.selNone)
	bar.Append(p.checkedMenu())
	bar.Append(p.cancel)
	bar.Append(p.apply)

	p.list = gtk.NewListBox()
	p.list.SetSelectionMode(gtk.SelectionSingle)
	listScroll := gtk.NewScrolledWindow()
	listScroll.SetChild(p.list)
	listScroll.SetHExpand(true)
	listScroll.SetVExpand(true)
	p.listScroll = listScroll
	for i := range p.groups {
		p.groups[i] = gtk.NewSizeGroup(gtk.SizeGroupHorizontal)
	}
	p.headerBox = gtk.NewBox(gtk.OrientationHorizontal, 8)
	p.headerBox.SetMarginTop(4)
	p.headerBox.SetMarginBottom(4)
	listSide := gtk.NewBox(gtk.OrientationVertical, 0)
	listSide.Append(p.headerBox)
	listSide.Append(gtk.NewSeparator(gtk.OrientationHorizontal))
	listSide.Append(listScroll)

	// The explanation is laid out rather than printed: the file's name, then
	// a line per step with the action in its own colour, centred in the
	// pane so the eye lands on it (his request, 2026-09-17).
	p.details = gtk.NewBox(gtk.OrientationVertical, 6)
	p.details.SetHAlign(gtk.AlignCenter)
	p.details.SetVAlign(gtk.AlignStart)
	p.details.SetMarginTop(16)
	p.details.SetMarginBottom(12)
	p.details.SetMarginStart(12)
	p.details.SetMarginEnd(12)
	p.detailsHint("Select a file to see what would happen to it, and why.")
	detailScroll := gtk.NewScrolledWindow()
	detailScroll.SetChild(p.details)
	detailScroll.SetVExpand(true)
	detailScroll.SetSizeRequest(-1, 200)

	// Under the explanation, a look at the file itself: a picture for an
	// image, the first page for a PDF, the first lines for anything that is
	// text (his request, 2026-09-16).
	p.previewNote = gtk.NewLabel("")
	p.previewNote.SetXAlign(0)
	p.previewNote.SetMarginStart(8)
	p.previewNote.SetMarginEnd(8)
	p.previewNote.SetEllipsize(pango.EllipsizeEnd)
	p.previewNote.SetMaxWidthChars(20)
	p.previewNote.AddCSSClass("dim-label")
	// The picture fills whatever the divider leaves it. Inside a scrolled
	// window it would be given its smallest size instead, which is what
	// made the page a stamp (his report, 2026-09-17).
	p.picture = gtk.NewPicture()
	p.picture.SetCanShrink(true)
	p.picture.SetContentFit(gtk.ContentFitContain)
	p.picture.SetVisible(false)
	p.picture.SetVExpand(true)
	p.picture.SetHExpand(true)
	p.previewText = gtk.NewTextView()
	p.previewText.SetEditable(false)
	p.previewText.SetMonospace(true)
	p.previewText.SetLeftMargin(8)
	p.previewText.SetRightMargin(8)
	p.previewText.SetTopMargin(6)
	previewScroll := gtk.NewScrolledWindow()
	previewScroll.SetChild(p.previewText)
	previewScroll.SetVisible(false)
	previewScroll.SetVExpand(true)
	p.previewScroll = previewScroll

	previewBox := gtk.NewBox(gtk.OrientationVertical, 0)
	previewBox.Append(p.previewNote)
	previewBox.Append(p.picture)
	previewBox.Append(previewScroll)

	p.listSide = listSide
	p.detailScroll = detailScroll
	p.previewBox = previewBox

	p.root.Append(bar)
	p.root.Append(gtk.NewSeparator(gtk.OrientationHorizontal))
	p.setLayout(model.LayoutSide)

	p.scan.ConnectClicked(p.onScan)
	p.apply.ConnectClicked(p.onApply)
	p.cancel.ConnectClicked(func() {
		if p.cancelOp != nil {
			p.cancelOp()
		}
	})
	p.filter.ConnectSearchChanged(func() { p.fillList() })
	p.selAll.ConnectClicked(func() { p.selectAll(true) })
	p.selNone.ConnectClicked(func() { p.selectAll(false) })
	p.list.ConnectRowSelected(func(row *gtk.ListBoxRow) {
		if row != nil {
			p.showDetails(p.planIndex(row.Index()))
		}
	})
	// The right button on a row offers the two overrides the terminal
	// review has on t and d (GUI design §3).
	p.menu = p.newMenu()
	click := gtk.NewGestureClick()
	click.SetButton(3)
	click.ConnectPressed(func(_ int, x, y float64) { p.onRightClick(x, y) })
	p.list.AddController(click)

	p.showPath()
	p.setBusy(false)
	return p
}

// checkedMenu is "With checked": the same two overrides the row menu has,
// for every file that is checked at once (his request, 2026-09-17).
func (p *planView) checkedMenu() *gtk.MenuButton {
	box := gtk.NewBox(gtk.OrientationVertical, 0)
	trash := gtk.NewButtonWithLabel("Trash them instead")
	perm := gtk.NewButtonWithLabel("Delete them permanently instead...")
	for _, b := range []*gtk.Button{trash, perm} {
		b.SetHasFrame(false)
		b.SetHAlign(gtk.AlignFill)
		box.Append(b)
	}
	pop := gtk.NewPopover()
	pop.SetChild(box)
	button := gtk.NewMenuButton()
	button.SetLabel("With checked")
	button.SetPopover(pop)
	button.SetTooltipText("choose what happens to every checked file instead of what the rules decided")
	trash.ConnectClicked(func() {
		pop.Popdown()
		p.replaceChecked(plan.Trash)
	})
	perm.ConnectClicked(func() {
		pop.Popdown()
		p.confirmDeleteChecked()
	})
	p.checked = button
	return button
}

// replaceChecked gives every checked file the same action.
func (p *planView) replaceChecked(kind plan.Kind) {
	if p.tab == nil {
		return
	}
	n, err := p.tab.ReplaceSelected(kind)
	if err != nil {
		p.w.setStatus("%v", err)
		return
	}
	if n == 0 {
		p.w.setStatus("no file is checked")
		return
	}
	p.fillList()
	p.w.setStatus("%d file(s) set to %s - press Apply to carry it out; nothing has moved yet", n, kind)
}

// confirmDeleteChecked asks before the one action nothing can undo, saying
// how many files it would be.
func (p *planView) confirmDeleteChecked() {
	if p.tab == nil {
		return
	}
	n := p.tab.SelectedCount()
	if n == 0 {
		p.w.setStatus("no file is checked")
		return
	}
	d := gtk.NewMessageDialog(&p.w.win.Window, gtk.DialogModal|gtk.DialogDestroyWithParent,
		gtk.MessageWarning, gtk.ButtonsNone)
	d.SetObjectProperty("text", fmt.Sprintf("Delete %d checked file(s) permanently?", n))
	d.SetObjectProperty("secondary-text",
		"They are not moved to the Trash and undo cannot bring them back. Nothing happens until you press Apply.")
	d.AddButton("Cancel", int(gtk.ResponseCancel))
	del := d.AddButton("Delete permanently", int(gtk.ResponseAccept))
	if b, ok := del.(*gtk.Button); ok {
		b.AddCSSClass("destructive-action")
	}
	d.ConnectResponse(func(response int) {
		d.Destroy()
		if response == int(gtk.ResponseAccept) {
			p.replaceChecked(plan.DeletePermanent)
		}
	})
	d.Show()
}

// newMenu builds the row menu: what to do with a file instead of what the
// rules decided.
func (p *planView) newMenu() *gtk.Popover {
	box := gtk.NewBox(gtk.OrientationVertical, 0)
	trash := gtk.NewButtonWithLabel("Trash instead")
	perm := gtk.NewButtonWithLabel("Delete permanently instead...")
	for _, b := range []*gtk.Button{trash, perm} {
		b.SetHasFrame(false)
		b.SetHAlign(gtk.AlignFill)
		box.Append(b)
	}
	pop := gtk.NewPopover()
	pop.SetChild(box)
	pop.SetParent(p.list)
	pop.SetHasArrow(false)
	trash.ConnectClicked(func() {
		pop.Popdown()
		p.replace(plan.Trash)
	})
	perm.ConnectClicked(func() {
		pop.Popdown()
		p.confirmDeletePermanent()
	})
	return pop
}

// planIndex is the plan row a list row stands for: with a filter on, the
// two are not the same.
func (p *planView) planIndex(listRow int) int {
	if listRow < 0 || listRow >= len(p.shown) {
		return -1
	}
	return p.shown[listRow]
}

// onRightClick opens the menu on the row under the pointer. A plan that has
// been applied is history and cannot be changed.
func (p *planView) onRightClick(x, y float64) {
	if p.tab == nil || p.tab.Applied {
		return
	}
	row := p.list.RowAtY(int(y))
	if row == nil {
		return
	}
	p.list.SelectRow(row)
	p.menuRow = p.planIndex(row.Index())
	if p.menuRow < 0 {
		return
	}
	at := gdk.NewRectangle(int(x), int(y), 1, 1)
	p.menu.SetPointingTo(&at)
	p.menu.Popup()
}

// replace swaps the menu row's steps for the one the user chose.
func (p *planView) replace(kind plan.Kind) {
	if p.tab == nil {
		return
	}
	if err := p.tab.Replace(p.menuRow, kind); err != nil {
		p.w.setStatus("%v", err)
		return
	}
	rel := p.tab.Rows[p.menuRow].Rel
	p.fillList()
	p.showDetails(p.menuRow)
	p.w.setStatus("%s: %s instead - press Apply to carry it out; nothing has moved yet",
		escape(rel), kind)
}

// confirmDeletePermanent asks before a step nothing can undo, naming the
// file (GUI design §3).
func (p *planView) confirmDeletePermanent() {
	if p.tab == nil || p.menuRow < 0 || p.menuRow >= len(p.tab.Rows) {
		return
	}
	rel := p.tab.Rows[p.menuRow].Rel
	d := gtk.NewMessageDialog(&p.w.win.Window, gtk.DialogModal|gtk.DialogDestroyWithParent,
		gtk.MessageWarning, gtk.ButtonsNone)
	d.SetObjectProperty("text", "Delete "+escape(rel)+" permanently?")
	d.SetObjectProperty("secondary-text",
		"It is not moved to the Trash and undo cannot bring it back.")
	d.AddButton("Cancel", int(gtk.ResponseCancel))
	del := d.AddButton("Delete permanently", int(gtk.ResponseAccept))
	if b, ok := del.(*gtk.Button); ok {
		b.AddCSSClass("destructive-action")
	}
	d.ConnectResponse(func(response int) {
		d.Destroy()
		if response == int(gtk.ResponseAccept) {
			p.replace(plan.DeletePermanent)
		}
	})
	d.Show()
}

// showPath writes the chosen directory's path beside the picker.
func (p *planView) showPath() {
	if d := p.currentDir(); d != nil {
		p.path.SetText(escape(xdg.Abbrev(d.Root)))
		return
	}
	p.path.SetText("no directory is included; add one with: krino new NAME PATH")
}

// currentDir is the directory the picker names.
func (p *planView) currentDir() *engine.Dir {
	i := int(p.dirs.Selected())
	if i < 0 || i >= len(p.w.engine.Dirs) {
		return nil
	}
	return p.w.engine.Dirs[i]
}

// onScan plans the chosen directory, off the main loop.
func (p *planView) onScan() {
	d := p.currentDir()
	if d == nil {
		p.w.setStatus("no directory is included; add one with: krino new NAME PATH")
		return
	}
	// One plan at a time: the open one holds its directory's lock, and
	// scanning again - the same directory or another - replaces it.
	p.closeTab()
	p.setBusy(true)
	p.w.setStatus("scanning %s...", escape(d.Name))
	var tab *model.PlanTab
	p.cancelOp = runInBackground(func(ctx context.Context) error {
		var err error
		tab, err = model.Plan(ctx, p.w.engine, d)
		return err
	}, func(err error) {
		p.setBusy(false)
		if err != nil {
			p.w.setStatus("%s: %v", escape(d.Name), err)
			return
		}
		p.tab = tab
		if !p.startSelected {
			tab.SelectNone()
		}
		p.fillList()
		c := tab.Counts
		p.w.setStatus("%d scanned, %d to act on, %d excluded, %d skipped, %d with warnings",
			c.Scanned, c.Acting, c.Excluded, c.Skipped, c.Warned)
	})
}

// onApply acts on the checked files, off the main loop.
func (p *planView) onApply() {
	if p.tab == nil {
		return
	}
	n := p.tab.SelectedCount()
	p.setBusy(true)
	p.w.setStatus("applying %d file(s)...", n)
	var res *engine.ApplyResult
	p.cancelOp = runInBackground(func(ctx context.Context) error {
		var err error
		res, err = p.tab.Apply(ctx)
		return err
	}, func(err error) {
		p.setBusy(false)
		p.apply.SetSensitive(false)
		p.fillList()
		if err != nil {
			p.w.setStatus("apply: %v", err)
			return
		}
		p.w.setStatus("%d applied, %d failed, %d declined - this plan is done; press Scan for a fresh one",
			res.Applied, res.Failed, res.Declined)
	})
}

// closeTab drops the open plan and releases the directory's lock.
func (p *planView) closeTab() {
	if p.tab == nil {
		return
	}
	if err := p.tab.Close(); err != nil {
		p.w.setStatus("%s: %v", escape(p.tab.Dir.Name), err)
	}
	p.tab = nil
	p.fillList()
}

// setBusy turns the buttons on or off around a background operation.
func (p *planView) setBusy(busy bool) {
	p.scan.SetSensitive(!busy)
	p.dirs.SetSensitive(!busy)
	done := p.tab != nil && p.tab.Applied
	p.selAll.SetSensitive(!busy && !done)
	p.selNone.SetSensitive(!busy && !done)
	if p.checked != nil {
		p.checked.SetSensitive(!busy && p.tab != nil && !p.tab.Applied)
	}
	p.apply.SetSensitive(!busy && p.tab != nil && !p.tab.Applied)
	p.cancel.SetSensitive(busy)
}

// selectAll checks or unchecks every file that can be applied - and, while
// a filter is on, only the files it leaves on screen, so what Apply acts on
// is what was in front of him.
func (p *planView) selectAll(on bool) {
	if p.tab == nil {
		return
	}
	switch {
	case !on:
		p.tab.SelectNone()
	case p.filter.Text() == "":
		p.tab.SelectAll()
	default:
		p.tab.SelectOnly(p.shown)
	}
	p.fillList()
}

// sayWhatIsShown keeps the status line honest about a filter: how much of
// the plan is on screen, and whether it is hiding something that is
// checked and would be applied.
func (p *planView) sayWhatIsShown() {
	if p.tab == nil {
		return
	}
	if p.tab.Applied {
		if p.filter.Text() != "" {
			p.w.setStatus("%d of %d files shown; this plan has been applied - press Scan for a fresh one",
				len(p.shown), len(p.tab.Rows))
		}
		return
	}
	if p.filter.Text() == "" {
		return
	}
	hidden := p.tab.HiddenSelected(p.shown)
	if hidden > 0 {
		p.w.setStatus("%d of %d files shown; %d checked file(s) are hidden and would still be applied",
			len(p.shown), len(p.tab.Rows), hidden)
		return
	}
	p.w.setStatus("%d of %d files shown", len(p.shown), len(p.tab.Rows))
}

// fillList renders the rows: a checkbox, the file, what would happen, the
// rule, and the outcome once applied.
func (p *planView) fillList() {
	clearList(p.list)
	for i := range p.groups {
		p.groups[i] = gtk.NewSizeGroup(gtk.SizeGroupHorizontal)
	}
	if p.tab == nil {
		return
	}
	w := p.widths()
	p.header(w)
	p.shown = p.tab.Matching(p.filter.Text())
	for _, i := range p.shown {
		p.list.Append(p.rowWidget(i, p.tab.Rows[i], w))
	}
	p.apply.SetLabel(fmt.Sprintf("Apply %d selected", p.tab.SelectedCount()))
	p.apply.SetSensitive(!p.tab.Applied && p.tab.SelectedCount() > 0)
	// The plan arrives after setBusy has already run, so the menu over the
	// checked files is enabled here rather than there.
	p.checked.SetSensitive(!p.tab.Applied)
	p.selAll.SetSensitive(!p.tab.Applied)
	p.selNone.SetSensitive(!p.tab.Applied)
	p.sayWhatIsShown()
	// A fresh list starts at its left edge: without this the view can open
	// scrolled sideways, with the file names out of sight (his report,
	// 2026-09-17).
	if adj := p.listScroll.HAdjustment(); adj != nil {
		adj.SetValue(0)
	}
}

// widths is how wide each column has to be for this plan: enough for the
// longest value it holds, within limits, so a rule name or an outcome is
// shown whole rather than cut to an ellipsis. The list scrolls sideways
// when the total does not fit (his report, 2026-09-16).
func (p *planView) widths() [7]int {
	w := [7]int{16, 4, 3, 6, 16, 8, 6}
	root := p.dirRoot()
	now := time.Now()
	for _, r := range p.tab.Rows {
		action, _ := rowAction(r)
		w[colFile] = max(w[colFile], len([]rune(r.Rel)))
		w[colSize] = max(w[colSize], len([]rune(model.SizeText(r.Size))))
		w[colAge] = max(w[colAge], len([]rune(model.AgeText(r.ModTime, now))))
		w[colAction] = max(w[colAction], len([]rune(action)))
		w[colWhere] = max(w[colWhere], len([]rune(rowWhere(r, root))))
		w[colRule] = max(w[colRule], len([]rune(r.Rule)))
		w[colOutcome] = max(w[colOutcome], len([]rune(r.Outcome)))
	}
	// Past these a single long value would push every other column off the
	// window; the details pane holds the whole text either way.
	for i, cap := range [7]int{40, 7, 5, 16, 52, 34, 24} {
		w[i] = min(w[i], cap)
	}
	// A column is never narrower than its own heading, or the heading is
	// the thing that ends in an ellipsis (his report, 2026-09-17).
	for i, title := range columnTitles {
		w[i] = max(w[i], len([]rune(title)))
	}
	return w
}

// The columns of the plan, in the order they are shown.
const (
	colFile = iota
	colSize
	colAge
	colAction
	colWhere
	colRule
	colOutcome
)

// showColumn reports whether a column is shown: three of them are settings,
// and the outcome appears only once a plan has been applied.
func (p *planView) showColumn(i int) bool {
	switch i {
	case colSize:
		return p.w.prefs.ShowSize
	case colAge:
		return p.w.prefs.ShowAge
	case colRule:
		return p.w.prefs.ShowRule
	case colOutcome:
		return p.showOutcome()
	}
	return true
}

// showOutcome reports whether there is anything to put in the last column.
func (p *planView) showOutcome() bool {
	return p.tab != nil && p.tab.Applied
}

// headerFloors are how narrow each heading may become, matching the cells
// under it.
var headerFloors = [7]int{12, 4, 3, 6, 16, 10, 8}

// columnTitles name the columns of the plan.
var columnTitles = [7]string{"file", "size", "age", "action", "where it would go", "rule", "outcome"}

// header is the line above the list saying what each column is.
func (p *planView) header(w [7]int) {
	if child := p.headerBox.FirstChild(); child != nil {
		for child != nil {
			next := gtk.BaseWidget(child).NextSibling()
			p.headerBox.Remove(child)
			child = next
		}
	}
	p.headerBox.SetMarginStart(6)
	p.headerBox.SetMarginEnd(6)
	// The checkbox has no title, but its width has to be accounted for.
	spacer := gtk.NewLabel("")
	spacer.SetSizeRequest(24, -1)
	p.groups[0].AddWidget(spacer)
	p.headerBox.Append(spacer)
	for i, title := range columnTitles {
		if !p.showColumn(i) {
			continue
		}
		l := columnMin(title, w[i], headerFloors[i], i == colFile || i == colWhere)
		l.AddCSSClass("heading")
		l.SetTooltipText("")
		p.groups[i+1].AddWidget(l)
		p.headerBox.Append(l)
	}
}

// rowWidget is one line of the list.
func (p *planView) rowWidget(i int, r model.Row, w [7]int) *gtk.ListBoxRow {
	box := gtk.NewBox(gtk.OrientationHorizontal, 8)
	box.SetMarginStart(6)
	box.SetMarginEnd(6)
	box.SetMarginTop(2)
	box.SetMarginBottom(2)

	check := gtk.NewCheckButton()
	check.SetActive(r.Selected)
	check.SetSensitive(r.Actable && (p.tab == nil || !p.tab.Applied))
	check.ConnectToggled(func() {
		if p.tab != nil && p.tab.Rows[i].Selected != check.Active() {
			p.tab.Toggle(i)
			p.apply.SetLabel(fmt.Sprintf("Apply %d selected", p.tab.SelectedCount()))
			p.apply.SetSensitive(!p.tab.Applied && p.tab.SelectedCount() > 0)
		}
	})
	p.groups[0].AddWidget(check)
	box.Append(check)

	// The name and destination columns share whatever space is left and
	// shrink first; the action and the rule keep their width, so neither is
	// ever the column cut to an ellipsis.
	action, colour := rowAction(r)
	// Every column can shrink: a pane narrower than their natural widths
	// used to push the whole row out of view to the left (his report,
	// 2026-09-17).
	cells := [7]gtk.Widgetter{
		colFile:    columnMin(escape(r.Rel), w[colFile], 12, true),
		colSize:    columnMin(model.SizeText(r.Size), w[colSize], 4, false),
		colAge:     columnMin(model.AgeText(r.ModTime, time.Now()), w[colAge], 3, false),
		colAction:  colouredColumn(action, w[colAction], colour),
		colWhere:   columnMin(escape(rowWhere(r, p.dirRoot())), w[colWhere], 16, true),
		colRule:    columnMin(escape(r.Rule), w[colRule], 10, false),
		colOutcome: columnMin(escape(r.Outcome), w[colOutcome], 8, false),
	}
	for i, cell := range cells {
		if !p.showColumn(i) {
			continue
		}
		p.groups[i+1].AddWidget(cell)
		box.Append(cell)
	}
	row := gtk.NewListBoxRow()
	row.SetChild(box)
	return row
}

// dirRoot is the directory the list belongs to, for shortening destinations.
func (p *planView) dirRoot() string {
	if p.tab != nil {
		return p.tab.Dir.Root
	}
	return ""
}

// column is one cell of a row: left-aligned, and ellipsized to chars so
// that a long name or warning cannot widen the window past the screen. The
// whole text is in the details pane beside the list.
//
// The expanding column - the file's name - may shrink to yieldChars when
// the window is too narrow for every column, so it is the one that gives
// way and the columns beside it (what would happen, and which rule decided)
// stay readable. A fixed column keeps its width and the list scrolls.
func column(text string, chars int, expand bool) *gtk.Label {
	return columnMin(text, chars, yieldChars, expand)
}

// columnMin is column with the width it may shrink to given explicitly.
func columnMin(text string, chars, floor int, expand bool) *gtk.Label {
	l := gtk.NewLabel(text)
	l.SetXAlign(0)
	l.SetEllipsize(pango.EllipsizeEnd)
	if expand {
		l.SetWidthChars(min(chars, floor))
	} else {
		l.SetWidthChars(chars)
	}
	l.SetMaxWidthChars(chars)
	l.SetHExpand(expand)
	l.SetTooltipText(text)
	return l
}

// colouredColumn is a fixed column carrying the CSS classes that colour an
// action, so that a MOVE and a DELETE do not read alike - and so that a
// selected row can take the colour back for readability.
func colouredColumn(text string, chars int, class string) *gtk.Label {
	l := column(escape(text), chars, false)
	if class == "" || text == "" {
		return l
	}
	l.AddCSSClass("krino-action")
	l.AddCSSClass(class)
	return l
}

// yieldChars is how narrow an expanding column may become.
const yieldChars = 14

// detailsHint empties the explanation and leaves one dim line in it.
func (p *planView) detailsHint(text string) {
	p.clearDetails()
	l := gtk.NewLabel(text)
	l.SetWrap(true)
	l.SetJustify(gtk.JustifyCenter)
	l.AddCSSClass("dim-label")
	p.details.Append(l)
}

// clearDetails takes the last explanation out of the pane.
func (p *planView) clearDetails() {
	for child := p.details.FirstChild(); child != nil; child = p.details.FirstChild() {
		p.details.Remove(child)
	}
}

// detailLine is one centred line of the explanation.
func detailLine(text string, classes ...string) *gtk.Label {
	l := gtk.NewLabel(text)
	l.SetWrap(true)
	l.SetJustify(gtk.JustifyCenter)
	l.SetMaxWidthChars(60)
	l.SetSelectable(true)
	for _, c := range classes {
		l.AddCSSClass(c)
	}
	return l
}

// showDetails lays out the selected file's steps and warnings.
func (p *planView) showDetails(i int) {
	if p.tab == nil || i < 0 || i >= len(p.tab.Rows) {
		return
	}
	r := p.tab.Rows[i]
	p.clearDetails()

	title := detailLine(escape(r.Rel), "krino-title")
	p.details.Append(title)
	if what := describeFile(r); what != "" {
		p.details.Append(detailLine(what, "dim-label"))
	}

	for _, s := range r.Steps {
		row := gtk.NewBox(gtk.OrientationHorizontal, 8)
		row.SetHAlign(gtk.AlignCenter)
		row.SetMarginTop(6)
		action := gtk.NewLabel(strings.ToUpper(s.Kind.String()))
		action.AddCSSClass("krino-action")
		if class, ok := actionClasses[s.Kind]; ok {
			action.AddCSSClass(class)
		}
		row.Append(action)
		switch {
		case s.Skip != "":
			row.Append(detailLine("skipped: "+escape(s.Skip), "dim-label"))
		case s.Kind == plan.Trash:
			row.Append(detailLine("to the Trash"))
		case s.Kind == plan.DeletePermanent:
			row.Append(detailLine("gone for good", "krino-warn"))
		default:
			row.Append(detailLine("→ " + escape(shorten(s.Dst, p.dirRoot()))))
		}
		p.details.Append(row)
		if s.Rule != "" {
			p.details.Append(detailLine("rule "+escape(s.Rule), "dim-label"))
		}
		if s.Reason != "" {
			p.details.Append(detailLine("because "+escape(s.Reason), "dim-label"))
		}
	}
	for _, warn := range r.Warnings {
		p.details.Append(detailLine(escape(warn), "krino-warn"))
	}
	if r.Outcome != "" {
		p.details.Append(detailLine(escape(r.Outcome), "krino-title"))
	}
	if adj := p.detailScroll.VAdjustment(); adj != nil {
		adj.SetValue(0)
	}
	p.showPreview(r.Rel)
}

// describeFile is the line under the name: how big the file is and how long
// it has been sitting there.
func describeFile(r model.Row) string {
	var parts []string
	if r.Size > 0 {
		parts = append(parts, model.SizeText(r.Size))
	}
	if age := model.AgeText(r.ModTime, time.Now()); age != "" {
		parts = append(parts, "last written "+age+" ago")
	}
	return strings.Join(parts, ", ")
}

// showPreview looks at the file behind row rel, off the main loop: reading
// it, and rendering a PDF page, takes long enough to stutter the window.
func (p *planView) showPreview(rel string) {
	if p.tab == nil || p.previewOff {
		return
	}
	path := filepath.Join(p.tab.Dir.Root, filepath.FromSlash(rel))
	if p.previewFor == path {
		return
	}
	p.previewFor = path
	p.picture.SetVisible(false)
	p.previewScroll.SetVisible(false)
	p.previewNote.SetText("looking at " + escape(rel) + "...")
	if p.previewTmp == "" {
		dir, err := os.MkdirTemp("", "krino-preview-")
		if err != nil {
			p.previewNote.SetText(escape(err.Error()))
			return
		}
		p.previewTmp = dir
	}
	var pv model.Preview
	runInBackground(func(ctx context.Context) error {
		pv = model.MakePreview(ctx, path, p.previewTmp, p.previewHeight)
		return nil
	}, func(error) {
		if p.previewFor != path {
			return // another row was chosen while this one was read
		}
		p.previewNote.SetText(escape(pv.Note))
		switch pv.Kind {
		case model.PreviewImage:
			p.picture.SetFilename(pv.Image)
			p.picture.SetVisible(true)
			// The picture is loaded, so the page rendered for the row
			// before it can go.
			p.dropRendered()
			p.renderedDir = pv.Dir
		case model.PreviewText:
			p.previewText.Buffer().SetText(escapeText(pv.Text))
			p.previewScroll.SetVisible(true)
			p.dropRendered()
		default:
			p.dropRendered()
		}
	})
}

// setLayout arranges the tab the way the settings ask: the file list beside
// the explanation, or above it with the preview to its side (his sketch,
// 2026-09-17). The widgets are the same either way; only the panes holding
// them change.
func (p *planView) setLayout(which string) {
	if p.layout == which && p.arrangement != nil {
		return
	}
	p.layout = which
	if p.arrangement != nil {
		p.detailPane.SetStartChild(nil)
		p.detailPane.SetEndChild(nil)
		p.arrangement.SetStartChild(nil)
		p.arrangement.SetEndChild(nil)
		p.root.Remove(p.arrangement)
	}

	// The divider between the explanation and the preview is the size
	// control: drag it, and the preview stays that big.
	detailOrientation, outerOrientation := gtk.OrientationVertical, gtk.OrientationHorizontal
	if which == model.LayoutStacked {
		detailOrientation, outerOrientation = gtk.OrientationHorizontal, gtk.OrientationVertical
	}
	p.detailPane = gtk.NewPaned(detailOrientation)
	p.detailPane.SetStartChild(p.detailScroll)
	p.detailPane.SetEndChild(p.previewBox)
	p.detailPane.SetResizeStartChild(true)
	p.detailPane.SetResizeEndChild(false)
	p.detailPane.SetShrinkEndChild(false)
	p.detailPane.SetVExpand(true)
	p.detailPane.Connect("notify::position", p.rememberPreviewHeight)

	p.arrangement = gtk.NewPaned(outerOrientation)
	p.arrangement.SetStartChild(p.listSide)
	p.arrangement.SetEndChild(p.detailPane)
	p.arrangement.SetResizeStartChild(true)
	p.arrangement.SetResizeEndChild(false)
	p.arrangement.SetShrinkEndChild(false)
	p.arrangement.SetVExpand(true)
	prefs := p.w.prefs
	if which == model.LayoutSide {
		p.detailPane.SetSizeRequest(340, -1)
		p.arrangement.SetPosition(orDefault(prefs.ListWidth, model.DefaultListWidth))
		p.previewHeight = orDefault(prefs.PreviewHeight, model.DefaultPreviewHeight)
	} else {
		p.detailPane.SetSizeRequest(-1, 240)
		p.arrangement.SetPosition(orDefault(prefs.ListHeight, model.DefaultListHeight))
		p.previewHeight = orDefault(prefs.PreviewWidth, model.DefaultPreviewWidth)
	}
	p.arrangement.Connect("notify::position", p.rememberListSize)
	p.root.Append(p.arrangement)
	p.setPreviewHeight(p.previewHeight)
}

// orDefault is n, or the default when nothing has been chosen yet.
func orDefault(n, def int) int {
	if n < 80 {
		return def
	}
	return n
}

// rememberListSize keeps where the divider between the file list and the
// explanation was left, for this layout.
func (p *planView) rememberListSize() {
	at := p.arrangement.Position()
	if at < 80 {
		return
	}
	prefs := p.w.prefs
	if p.layout == model.LayoutStacked {
		if prefs.ListHeight == at {
			return
		}
		prefs.ListHeight = at
	} else {
		if prefs.ListWidth == at {
			return
		}
		prefs.ListWidth = at
	}
	p.w.prefs = prefs
	p.w.savePrefsSoon()
}

// rememberPreviewHeight keeps what a drag of the divider chose, so the next
// window opens the same way.
func (p *planView) rememberPreviewHeight() {
	total := p.detailPane.Height()
	if p.layout == model.LayoutStacked {
		total = p.detailPane.Width()
	}
	height := total - p.detailPane.Position()
	if height < 80 || height == p.previewHeight {
		return
	}
	p.previewHeight = height
	prefs := p.w.prefs
	if p.layout == model.LayoutStacked {
		prefs.PreviewWidth = height
	} else {
		prefs.PreviewHeight = height
	}
	p.w.prefs = prefs
	p.w.savePrefsSoon()
}

// setPreviewHeight puts the divider where a height asks for.
func (p *planView) setPreviewHeight(height int) {
	if height < 80 {
		height = model.DefaultPreviewHeight
	}
	p.previewHeight = height
	total := p.detailPane.Height()
	if p.layout == model.LayoutStacked {
		total = p.detailPane.Width()
	}
	if total > height+80 {
		p.detailPane.SetPosition(total - height)
		return
	}
	// Before the window is drawn there is no height to subtract from, so
	// the end child's own request puts the divider in the right place.
	if child := p.detailPane.EndChild(); child != nil {
		if p.layout == model.LayoutStacked {
			gtk.BaseWidget(child).SetSizeRequest(height, -1)
		} else {
			gtk.BaseWidget(child).SetSizeRequest(-1, height)
		}
	}
}

// applyPrefs turns the file preview on or off, sets how tall it is, and
// says how a fresh plan starts.
func (p *planView) applyPrefs(prefs model.Prefs) {
	p.previewOff = !prefs.Preview
	p.startSelected = prefs.SelectAll
	p.setLayout(prefs.Layout)
	if p.tab != nil {
		p.fillList()
	}
	if prefs.Layout == model.LayoutStacked {
		p.setPreviewHeight(orDefault(prefs.PreviewWidth, model.DefaultPreviewWidth))
	} else {
		p.setPreviewHeight(orDefault(prefs.PreviewHeight, model.DefaultPreviewHeight))
	}
	if p.previewOff {
		p.previewFor = ""
		p.picture.SetVisible(false)
		p.previewScroll.SetVisible(false)
		p.previewNote.SetText("")
	}
}

// dropRendered removes the page rendered for the previous row.
func (p *planView) dropRendered() {
	if p.renderedDir != "" {
		os.RemoveAll(p.renderedDir)
		p.renderedDir = ""
	}
}

// hasUnapplied reports whether a plan is open with files checked and
// nothing done about them yet.
func (p *planView) hasUnapplied() bool {
	return p.tab != nil && !p.tab.Applied && p.tab.SelectedCount() > 0
}

// closePreview removes what the previews left behind.
func (p *planView) closePreview() {
	p.dropRendered()
	if p.previewTmp != "" {
		os.RemoveAll(p.previewTmp)
		p.previewTmp = ""
	}
}