// 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/gtk/v4"

	"krino/gui/internal/model"
	"krino/internal/engine"
	"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
}

// 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 {
		w.plan.closeTab()
		w.plan.closePreview()
		w.history.closeTab()
		return false
	})
	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
}

// 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
}

// rowLabel is the middle cell of a row: what would happen to the file and
// where it would land, or - when nothing would - why not. Destinations
// inside root are shown relative to it, as the plan's own output does.
func rowLabel(r model.Row, root string) string {
	if len(r.Steps) == 0 {
		return strings.Join(r.Warnings, "; ")
	}
	var parts []string
	for _, s := range r.Steps {
		switch {
		case s.Skip != "":
			parts = append(parts, s.Kind.String()+" skipped: "+s.Skip)
		case s.Dst == "":
			parts = append(parts, s.Kind.String())
		default:
			parts = append(parts, s.Kind.String()+" "+shorten(s.Dst, root))
		}
	}
	return strings.Join(parts, ", ")
}

// 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)
}