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

// Package ui is krino-gui's GTK4 layer: it renders what package model
// holds and forwards what the user does back to it. It makes no decisions
// of its own (GUI design §1.2).
package ui

import (
	"context"
	"fmt"
	"os"
	"strings"

	"github.com/diamondburned/gotk4/pkg/glib/v2"
	"github.com/diamondburned/gotk4/pkg/gtk/v4"

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

// Window is krino-gui's one window: three tabs, and a status bar.
type Window struct {
	app *gtk.Application
	win *gtk.ApplicationWindow

	engine *engine.Engine

	plan      *planView
	history   *historyView
	rules     *rulesView
	status    *gtk.Label
	prefs     model.Prefs
	leaving   bool
	saveTimer glib.SourceHandle
}

// NewWindow builds the window for e. Each plan and each undo is its own
// run of krino, with its own run id in the log, so the window itself holds
// no session.
func NewWindow(app *gtk.Application, e *engine.Engine) *Window {
	w := &Window{app: app, engine: e, prefs: model.LoadPrefs()}
	w.win = gtk.NewApplicationWindow(app)
	w.win.SetTitle("krino")
	w.win.SetDefaultSize(1200, 720)

	notebook := gtk.NewNotebook()
	w.plan = newPlanView(w)
	notebook.AppendPage(w.plan.root, gtk.NewLabel("Plan"))
	w.history = newHistoryView(w)
	notebook.AppendPage(w.history.root, gtk.NewLabel("History & undo"))
	w.rules = newRulesView(w)
	notebook.AppendPage(w.rules.root, gtk.NewLabel("Rules"))
	// The log is read when the tab is first opened, not at start-up: a
	// window that only sorts never reads it.
	loaded := false
	notebook.ConnectSwitchPage(func(_ gtk.Widgetter, page uint) {
		if page == 1 && !loaded {
			loaded = true
			w.history.loadRuns()
		}
	})

	// Settings sits at the end of the tab strip - the window's top right -
	// with a gear beside the word (his request, 2026-09-17).
	settings := gtk.NewButton()
	settingsBox := gtk.NewBox(gtk.OrientationHorizontal, 6)
	settingsBox.Append(gtk.NewImageFromIconName("emblem-system-symbolic"))
	settingsBox.Append(gtk.NewLabel("Settings"))
	settings.SetChild(settingsBox)
	settings.SetHasFrame(false)
	settings.SetTooltipText("krino's defaults, and how this window behaves")
	settings.SetMarginEnd(6)
	settings.ConnectClicked(func() { w.showSettings() })
	notebook.SetActionWidget(settings, gtk.PackEnd)

	w.status = gtk.NewLabel("")
	w.status.SetXAlign(0)
	w.status.SetMarginStart(8)
	w.status.SetMarginEnd(8)
	w.status.SetMarginTop(4)
	w.status.SetMarginBottom(4)

	statusRow := gtk.NewBox(gtk.OrientationHorizontal, 6)
	w.status.SetHExpand(true)
	statusRow.Append(w.status)

	box := gtk.NewBox(gtk.OrientationVertical, 0)
	notebook.SetVExpand(true)
	box.Append(notebook)
	box.Append(gtk.NewSeparator(gtk.OrientationHorizontal))
	box.Append(statusRow)
	w.win.SetChild(box)
	// Closing the window releases whatever directory lock the open plan
	// holds, rather than leaving a lock file for the next run to find.
	w.win.ConnectCloseRequest(func() bool {
		// A plan is only a plan until Apply: leaving with one open throws
		// it away, which is worth saying out loud (his report, 2026-09-17).
		if w.plan.hasUnapplied() && !w.leaving {
			w.confirmLeaving()
			return true
		}
		w.plan.closeTab()
		w.plan.closePreview()
		w.history.closeTab()
		return false
	})
	themeColours(w.win)
	w.applyPrefs(w.prefs)
	return w
}

// Show puts the window on screen.
func (w *Window) Show() { w.win.Show() }

// reloadEngine re-reads the configuration, after the rules editor saves, so
// every tab works from the rules the user just wrote. An open plan came
// from the old ones, so it is closed and its lock released.
func (w *Window) reloadEngine() error {
	e, diags := engine.Load(w.engine.MainFile)
	if len(diags) > 0 {
		return diags[0]
	}
	e.CacheDir = w.engine.CacheDir
	w.plan.closeTab()
	w.history.closeTab()
	w.engine = e
	return nil
}

// confirmLeaving asks before a window with an unapplied plan closes.
func (w *Window) confirmLeaving() {
	n := w.plan.tab.SelectedCount()
	d := gtk.NewMessageDialog(&w.win.Window, gtk.DialogModal|gtk.DialogDestroyWithParent,
		gtk.MessageQuestion, gtk.ButtonsNone)
	d.SetObjectProperty("text", "Close without applying?")
	d.SetObjectProperty("secondary-text", fmt.Sprintf(
		"%d file(s) are checked but nothing has been moved: a plan lives in this window until Apply, and closing throws it away.", n))
	d.AddButton("Stay", int(gtk.ResponseCancel))
	d.AddButton("Close without applying", int(gtk.ResponseAccept))
	d.ConnectResponse(func(response int) {
		d.Destroy()
		if response == int(gtk.ResponseAccept) {
			w.leaving = true
			w.win.Close()
		}
	})
	d.Show()
}

// addDirectory asks for a name and a path and makes krino sort that
// directory too - the window had no way to do it (his report, 2026-09-17).
func (w *Window) addDirectory() {
	d := gtk.NewWindow()
	d.SetTitle("Add a directory")
	d.SetTransientFor(&w.win.Window)
	d.SetModal(true)
	d.SetDefaultSize(520, 200)

	name := gtk.NewEntry()
	name.SetPlaceholderText("papers")
	name.SetTooltipText("the name krino knows it by: letters, digits, '.', '_' and '-'; its rules go in dirs/NAME.conf")
	path := gtk.NewEntry()
	path.SetPlaceholderText("~/papers")
	path.SetHExpand(true)
	path.SetTooltipText("the directory to sort")

	note := gtk.NewLabel("")
	note.SetXAlign(0)
	note.SetWrap(true)

	box := gtk.NewBox(gtk.OrientationVertical, 8)
	box.SetMarginStart(12)
	box.SetMarginEnd(12)
	box.SetMarginTop(12)
	box.SetMarginBottom(12)
	box.Append(field("name", name))
	box.Append(field("path", path))
	box.Append(note)

	create := gtk.NewButtonWithLabel("Add")
	create.AddCSSClass("suggested-action")
	cancel := gtk.NewButtonWithLabel("Cancel")
	cancel.ConnectClicked(func() { d.Close() })
	buttons := gtk.NewBox(gtk.OrientationHorizontal, 6)
	buttons.SetHAlign(gtk.AlignEnd)
	buttons.Append(cancel)
	buttons.Append(create)
	box.Append(buttons)

	create.ConnectClicked(func() {
		file, err := model.AddDirectory(w.engine, strings.TrimSpace(name.Text()), strings.TrimSpace(path.Text()))
		if err != nil {
			note.SetText(escape(err.Error()))
			note.AddCSSClass("error")
			return
		}
		added := strings.TrimSpace(name.Text())
		if err := w.reloadEngine(); err != nil {
			note.SetText(escape(err.Error()))
			note.AddCSSClass("error")
			return
		}
		w.plan.refreshDirs(w.plan.currentName())
		w.rules.refreshDirs(added)
		w.setStatus("added %s; its rules are in %s", escape(added), escape(xdg.Abbrev(file)))
		d.Close()
	})
	d.SetChild(box)
	d.Show()
}

// savePrefsSoon writes the preferences a moment after the last change, so
// dragging a divider does not write the file on every pixel.
func (w *Window) savePrefsSoon() {
	if w.saveTimer != 0 {
		glib.SourceRemove(w.saveTimer)
	}
	w.saveTimer = glib.TimeoutAdd(500, func() bool {
		w.saveTimer = 0
		if err := w.prefs.Save(); err != nil {
			w.setStatus("settings: %v", err)
		}
		return false
	})
}

// applyPrefs takes a change from the settings window: the font of the
// editor, whether the configuration is coloured, and whether the file
// behind a row is shown. What is already on screen changes at once.
func (w *Window) applyPrefs(p model.Prefs) {
	w.prefs = p
	w.rules.applyPrefs(p)
	w.plan.applyPrefs(p)
}

// dirRoot is the path of the configured directory called name, or "" if
// the configuration no longer has one - a log entry can outlive its
// directory.
func (w *Window) dirRoot(name string) string {
	for _, d := range w.engine.Dirs {
		if d.Name == name {
			return d.Root
		}
	}
	return ""
}

// setStatus writes the line at the bottom of the window.
func (w *Window) setStatus(format string, args ...any) {
	w.status.SetText(fmt.Sprintf(format, args...))
}

// placeholder is the page of a tab that is not built yet.
func placeholder(text string) gtk.Widgetter {
	l := gtk.NewLabel(text)
	l.SetVExpand(true)
	return l
}

// escape returns text as it is safe to show: control, bidirectional and
// separator characters are written as escapes, the way the terminal
// front end does it (spec §15.1), so a hostile file name cannot reorder or
// restyle the window. GTK labels are set as plain text, never as markup.
func escape(s string) string {
	var b strings.Builder
	for _, r := range s {
		switch {
		case r == '\t':
			b.WriteString("\\t")
		case r < 0x20, r == 0x7f, r >= 0x80 && r <= 0x9f,
			r == 0x061c, r >= 0x200e && r <= 0x200f, r >= 0x202a && r <= 0x202e,
			r >= 0x2066 && r <= 0x2069, r == 0x2028, r == 0x2029:
			fmt.Fprintf(&b, "\\u%04x", r)
		default:
			b.WriteRune(r)
		}
	}
	return b.String()
}

// escapeText is escape for text shown in a pane rather than on one line:
// line breaks are the layout, so they are kept, and every other control or
// bidirectional character is still written as an escape.
func escapeText(s string) string {
	var b strings.Builder
	for _, line := range strings.Split(s, "\n") {
		b.WriteString(escape(line))
		b.WriteString("\n")
	}
	return strings.TrimSuffix(b.String(), "\n")
}

// runInBackground runs work off the main loop and hands its result back to
// the GTK thread with done. GTK may only be touched from the main loop.
func runInBackground(work func(context.Context) error, done func(error)) context.CancelFunc {
	ctx, cancel := context.WithCancel(context.Background())
	go func() {
		err := work(ctx)
		idleAdd(func() { done(err) })
	}()
	return cancel
}

// actionColours are what each action is painted in, so the eye finds the
// deletions without reading: they are the ones that cannot be undone from
// the window. They are the fallbacks; themeColours replaces them with the
// running theme's own, so the window looks like the rest of the desktop
// rather than like GNOME's palette (his request, 2026-09-17).
var actionColours = map[plan.Kind]string{
	plan.Copy:            "#2a9d8f",
	plan.Move:            "#3584e4",
	plan.Rename:          "#9141ac",
	plan.Trash:           "#c06014",
	plan.DeletePermanent: "#c01c28",
}

// actionClasses name the CSS class each action's cell carries. The colour
// is applied by a style sheet rather than by painting the text, so that a
// selected row - which draws its own background - can take the colour back
// and stay readable: his green accent on his green selection was not (his
// report, 2026-09-17).
var actionClasses = map[plan.Kind]string{
	plan.Copy:            "krino-copy",
	plan.Move:            "krino-move",
	plan.Rename:          "krino-rename",
	plan.Trash:           "krino-trash",
	plan.DeletePermanent: "krino-delete",
}

// themeColours takes what it can from the GTK theme - the accent for a
// move, the selection blue for a rename, the theme's own success, warning
// and error for the rest - and installs the style sheet that paints the
// action cells. A theme that names none of them leaves the fallbacks above.
func themeColours(w gtk.Widgetter) {
	widget := gtk.BaseWidget(w)
	ctx := widget.StyleContext()
	pick := func(names ...string) string {
		for _, name := range names {
			if rgba, ok := ctx.LookupColor(name); ok {
				return fmt.Sprintf("#%02x%02x%02x",
					int(rgba.Red()*255), int(rgba.Green()*255), int(rgba.Blue()*255))
			}
		}
		return ""
	}
	set := func(kind plan.Kind, colour string) {
		if colour != "" {
			actionColours[kind] = colour
		}
	}
	set(plan.Move, pick("accent_color", "theme_selected_bg_color", "accent_bg_color"))
	set(plan.Copy, pick("success_color", "success_bg_color"))
	set(plan.Rename, pick("theme_selected_bg_color", "accent_bg_color"))
	set(plan.Trash, pick("warning_color", "warning_bg_color"))
	set(plan.DeletePermanent, pick("error_color", "destructive_color", "error_bg_color"))

	var css strings.Builder
	css.WriteString(".krino-action { font-weight: bold; }\n")
	for kind, class := range actionClasses {
		fmt.Fprintf(&css, ".%s { color: %s; }\n", class, actionColours[kind])
	}
	// A selected row paints its own background; the action takes that row's
	// foreground so it never sits on a colour of its own.
	fmt.Fprintf(&css, ".krino-warn { color: %s; }\n", actionColours[plan.Trash])
	css.WriteString(".krino-title { font-weight: bold; font-size: 115%; }\n")
	css.WriteString("row:selected .krino-action { color: @theme_selected_fg_color; }\n")
	css.WriteString("row:selected .krino-action { color: @accent_fg_color; }\n")
	provider := gtk.NewCSSProvider()
	provider.LoadFromData(css.String())
	if display := widget.Display(); display != nil {
		gtk.StyleContextAddProviderForDisplay(display, provider, 700)
	}
}

// actionRank decides which action gives a row its colour when a file gets
// several: the one that matters most to the reader.
var actionRank = map[plan.Kind]int{
	plan.Rename: 1, plan.Copy: 2, plan.Move: 3, plan.Trash: 4, plan.DeletePermanent: 5,
}

// rowAction is a row's actions in capitals - "MOVE", "RENAME+MOVE" - and
// the CSS class they are painted with. A row that would do nothing has
// neither.
func rowAction(r model.Row) (text, class string) {
	if len(r.Steps) == 0 {
		return "", ""
	}
	var parts []string
	var worst plan.Kind
	rank := -1
	skipped := 0
	for _, s := range r.Steps {
		if s.Skip != "" {
			skipped++
			continue
		}
		parts = append(parts, strings.ToUpper(s.Kind.String()))
		if actionRank[s.Kind] > rank {
			rank, worst = actionRank[s.Kind], s.Kind
		}
	}
	if len(parts) == 0 {
		return "SKIPPED", ""
	}
	return strings.Join(parts, "+"), actionClasses[worst]
}

// rowWhere is where a row's file would end up - the last place its steps
// put it - or, when nothing would happen, why not. Destinations inside root
// are shown relative to it, as the plan's own output does.
func rowWhere(r model.Row, root string) string {
	if len(r.Steps) == 0 {
		return strings.Join(r.Warnings, "; ")
	}
	where := ""
	var notes []string
	for _, s := range r.Steps {
		switch {
		case s.Skip != "":
			notes = append(notes, strings.ToLower(s.Kind.String())+" skipped: "+s.Skip)
		case s.Kind == plan.Trash:
			where = "the Trash"
		case s.Kind == plan.DeletePermanent:
			where = "gone for good"
		case s.Dst != "":
			where = shorten(s.Dst, root)
		}
	}
	if where == "" {
		return strings.Join(notes, "; ")
	}
	if len(notes) > 0 {
		return where + "  (" + strings.Join(notes, "; ") + ")"
	}
	return where
}

// dimColour is for text that is not an action: a skip, a warning.
const dimColour = "#8b8b8b"

// shorten writes a destination inside root relative to it, and any other
// with ~ for the home directory.
func shorten(dst, root string) string {
	if root != "" && strings.HasPrefix(dst, root+string(os.PathSeparator)) {
		return dst[len(root)+1:]
	}
	return xdg.Abbrev(dst)
}