package ui

import (
	"github.com/gdamore/tcell/v2"
	"github.com/rivo/tview"
)

// arrowNavigation lets a form be driven with the arrow keys:
//   - Up/Down move between the fields and buttons,
//   - Left/Right change the value of a closed dropdown without opening it
//     (and move between the buttons),
//
// Enter or Space still opens a dropdown list. While a list is open it gets all keys.
//
// With hooks, the highlighted entry of an open list is reported while the user
// moves through it, before anything is selected.
//
// cancel is called on Esc, except when Esc only closes an open dropdown list
// (tview would otherwise treat that as cancelling the whole form).
func arrowNavigation(f *tview.Form, cancel func(), hooks *browseHooks) {
	var b browser
	var closingList bool
	f.SetCancelFunc(func() {
		if closingList {
			closingList = false
			return
		}
		if cancel != nil {
			cancel()
		}
	})
	f.SetInputCapture(func(ev *tcell.EventKey) *tcell.EventKey {
		closingList = false
		item, button := f.GetFocusedItemIndex()
		if item < 0 && button < 0 {
			return ev
		}
		dd, _ := focusedDropDown(f, item)
		if dd != nil && dd.IsOpen() {
			closingList = ev.Key() == tcell.KeyEscape
			if hooks != nil {
				b.track(dd, ev, hooks)
			}
			return ev
		}
		b.dd = nil
		total := f.GetFormItemCount() + f.GetButtonCount()
		pos := item
		if button >= 0 {
			pos = f.GetFormItemCount() + button
		}
		switch ev.Key() {
		case tcell.KeyDown, tcell.KeyUp:
			dir := 1
			if ev.Key() == tcell.KeyUp {
				dir = -1
			}
			next := neighbour(f, pos, dir)
			if next == pos { // nothing further in this direction
				if hooks != nil && hooks.edge != nil && hooks.edge(dir > 0) {
					return nil
				}
				return nil
			}
			f.SetFocus(next)
		case tcell.KeyTab, tcell.KeyBacktab:
			dir := 1
			if ev.Key() == tcell.KeyBacktab {
				dir = -1
			}
			if hooks != nil && hooks.tab != nil && hooks.tab(dir) {
				return nil
			}
			return ev
		case tcell.KeyLeft, tcell.KeyRight:
			step := 1
			if ev.Key() == tcell.KeyLeft {
				step = -1
			}
			switch {
			case dd != nil:
				n := dd.GetOptionCount()
				cur, _ := dd.GetCurrentOption()
				dd.SetCurrentOption((cur + step + n) % n)
			case button >= 0:
				f.SetFocus(min(max(pos+step, f.GetFormItemCount()), total-1))
			default:
				return ev
			}
		default:
			return ev
		}
		return nil
	})
}

func focusedDropDown(f *tview.Form, item int) (*tview.DropDown, bool) {
	if item < 0 {
		return nil, false
	}
	dd, ok := f.GetFormItem(item).(*tview.DropDown)
	return dd, ok
}

// bindSearchNow keeps a "Search now" checkbox consistent with whether a search
// can find anything. While searchable() is false the box is unchecked, greyed
// out and cannot be ticked (blocked is called instead); it returns to the
// user's earlier choice afterwards. The returned function must be called
// whenever the answer of searchable() may have changed.
//
// tview's SetDisabled is avoided on purpose: on a form item it re-triggers
// the form's focus handling and leaves two fields highlighted.
func bindSearchNow(box *tview.Checkbox, searchable func() bool, blocked func()) (sync func()) {
	want := true
	box.SetChangedFunc(func(checked bool) {
		switch {
		case searchable():
			want = checked
		case checked:
			box.SetChecked(false)
			blocked()
		}
	})
	return func() {
		if searchable() {
			box.SetLabelColor(tview.Styles.SecondaryTextColor)
			box.SetChecked(want)
			return
		}
		box.SetLabelColor(named("gray"))
		box.SetChecked(false)
	}
}

// browseHooks lets a form follow the highlight of an open dropdown list.
type browseHooks struct {
	browse func(dd *tview.DropDown, index int) // the highlight moved to entry index
	abort  func()                              // the list was closed without selecting
	// edge is called when Down is pressed on the last field or Up on the first;
	// it returns true if it moved the focus elsewhere.
	edge func(down bool) bool
	// tab is called for Tab (dir 1) and Shift+Tab (dir -1); true if handled.
	tab func(dir int) bool
}

// browser mirrors the highlight of an open dropdown list, which tview does
// not expose: it starts at the current option and follows the navigation keys.
type browser struct {
	dd    *tview.DropDown
	idx   int
	known bool // false after keys that move the highlight in ways we do not track
}

func (b *browser) track(dd *tview.DropDown, ev *tcell.EventKey, h *browseHooks) {
	n := dd.GetOptionCount()
	if b.dd != dd {
		cur, _ := dd.GetCurrentOption()
		b.dd, b.idx, b.known = dd, max(cur, 0), true
	}
	move := func(to int) {
		b.idx = to
		if b.known && h.browse != nil {
			h.browse(dd, b.idx)
		}
	}
	switch ev.Key() {
	case tcell.KeyDown:
		move((b.idx + 1) % n)
	case tcell.KeyUp:
		move((b.idx - 1 + n) % n)
	case tcell.KeyHome:
		move(0)
	case tcell.KeyEnd:
		move(n - 1)
	case tcell.KeyEscape:
		b.dd = nil
		if h.abort != nil {
			h.abort()
		}
	case tcell.KeyEnter:
		b.dd = nil // the selection is reported by the dropdown itself
	default:
		b.known = false // paging, typed prefixes
	}
}

// skipsFocus marks form items that only decorate (section headings): the
// arrow keys pass over them.
type skipsFocus interface{ skipFocus() bool }

// neighbour returns the position of the next focusable item or button after
// pos in the given direction, or pos itself if there is none.
func neighbour(f *tview.Form, pos, dir int) int {
	total := f.GetFormItemCount() + f.GetButtonCount()
	for i := pos + dir; i >= 0 && i < total; i += dir {
		if i < f.GetFormItemCount() {
			if s, ok := f.GetFormItem(i).(skipsFocus); ok && s.skipFocus() {
				continue
			}
		}
		return i
	}
	return pos
}

// firstFocusable returns the position of the first item or button that can
// take the focus.
func firstFocusable(f *tview.Form) int {
	if f.GetFormItemCount() == 0 {
		return 0 // a form of buttons only
	}
	if s, ok := f.GetFormItem(0).(skipsFocus); ok && s.skipFocus() {
		return neighbour(f, 0, 1)
	}
	return 0
}

// formHeading is a section heading inside a form: a bold title above the next
// group of fields. It never takes the focus.
type formHeading struct {
	*tview.Box
	title    string
	finished func(tcell.Key)
}

func newFormHeading(title string) *formHeading {
	return &formHeading{Box: tview.NewBox(), title: title}
}

func (h *formHeading) skipFocus() bool { return true }

func (h *formHeading) GetLabel() string { return "" }

func (h *formHeading) SetFormAttributes(int, tcell.Color, tcell.Color, tcell.Color, tcell.Color) tview.FormItem {
	return h
}

func (h *formHeading) GetFieldWidth() int { return 0 }

// GetFieldHeight is 2: an empty line above the title separates the sections.
func (h *formHeading) GetFieldHeight() int { return 2 }

func (h *formHeading) SetFinishedFunc(handler func(key tcell.Key)) tview.FormItem {
	h.finished = handler
	return h
}

func (h *formHeading) SetDisabled(bool) tview.FormItem { return h }

// Focus passes the focus on, like a disabled input field does, so tview's own
// Tab handling skips the heading too.
func (h *formHeading) Focus(delegate func(p tview.Primitive)) {
	if h.finished != nil {
		h.finished(-1)
		return
	}
	h.Box.Focus(delegate)
}

func (h *formHeading) Draw(screen tcell.Screen) {
	h.Box.DrawForSubclass(screen, h)
	x, y, w, _ := h.GetInnerRect()
	tview.Print(screen, "[::b]"+tview.Escape(h.title)+"[::-]", x, y+1, w, tview.AlignLeft, named("yellow"))
}

// formAction is a button inside a form's list of fields, so it can sit between
// sections instead of at the end. Enter or Space presses it.
type formAction struct {
	*tview.Button
	labelWidth int
	finished   func(tcell.Key)
}

func newFormAction(label string, pressed func()) *formAction {
	a := &formAction{Button: tview.NewButton(label)}
	a.SetSelectedFunc(pressed)
	return a
}

func (a *formAction) GetLabel() string { return "" } // the button text is its own label

func (a *formAction) SetFormAttributes(labelWidth int, _, _, _, _ tcell.Color) tview.FormItem {
	a.labelWidth = labelWidth
	return a
}

func (a *formAction) GetFieldWidth() int { return tview.TaggedStringWidth(a.GetLabel()) + 4 }

// GetFieldHeight is 2: an empty line above the button.
func (a *formAction) GetFieldHeight() int { return 2 }

func (a *formAction) SetFinishedFunc(handler func(key tcell.Key)) tview.FormItem {
	a.SetExitFunc(handler) // Tab, Shift+Tab and Esc
	a.finished = handler
	return a
}

func (a *formAction) SetDisabled(disabled bool) tview.FormItem {
	a.Button.SetDisabled(disabled)
	return a
}

// SetRect places the button under the field column, one line down, as wide as its text.
func (a *formAction) SetRect(x, y, width, height int) {
	w := min(max(width-a.labelWidth, 0), tview.TaggedStringWidth(a.Button.GetLabel())+4)
	a.Button.SetRect(x+a.labelWidth, y+1, w, 1)
}

func (a *formAction) InputHandler() func(event *tcell.EventKey, setFocus func(p tview.Primitive)) {
	inner := a.Button.InputHandler()
	return func(event *tcell.EventKey, setFocus func(p tview.Primitive)) {
		if event.Key() == tcell.KeyRune && event.Rune() == ' ' {
			event = tcell.NewEventKey(tcell.KeyEnter, 0, 0)
		}
		inner(event, setFocus)
	}
}