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package app

import (
	"strings"

	"github.com/gdamore/tcell/v2"

	"codeberg.org/turbo-editors/turbo-core/lsp"
	"codeberg.org/turbo-editors/turbo-core/theme"
	"codeberg.org/turbo-editors/turbo-core/ui"
)

// Completion popup geometry. It is deliberately small: a list that covers half
// the file hides the very code the completion is about.
const (
	completionMaxRows  = 8
	completionMinWidth = 24
	completionMaxWidth = 60
)

// CompletionBox is the list of suggestions that pops up under the cursor.
//
// It filters as the user types, so the language server is asked once and the
// narrowing that follows costs nothing.
type CompletionBox struct {
	ui.Box
	items    []lsp.CompletionItem
	matches  []int // indexes into items, in the order they are shown
	selected int
	top      int
	prefix   string
	visible  bool

	// OnAccept is called with the chosen item.
	OnAccept func(lsp.CompletionItem)
}

// Visible reports whether the popup is showing.
func (c *CompletionBox) Visible() bool { return c.visible }

// Show opens the popup with a set of suggestions, filtered by prefix, anchored
// so that its top-left corner is just below the cursor.
//
// It closes again straight away if nothing matches, because a popup showing
// nothing is worse than no popup.
func (c *CompletionBox) Show(items []lsp.CompletionItem, prefix string, cursorX, cursorY int, screen ui.Rect) {
	c.items = items
	c.prefix = prefix
	c.selected = 0
	c.top = 0
	c.refilter()

	if len(c.matches) == 0 {
		c.Hide()
		return
	}
	c.visible = true
	c.SetBounds(c.placeUnder(cursorX, cursorY, screen))
}

// Hide closes the popup.
func (c *CompletionBox) Hide() {
	c.visible = false
	c.items = nil
	c.matches = nil
	c.prefix = ""
}

// SetPrefix narrows the list as the user keeps typing, and closes it once
// nothing matches any more.
func (c *CompletionBox) SetPrefix(prefix string) {
	if !c.visible {
		return
	}
	c.prefix = prefix
	c.selected = 0
	c.top = 0
	c.refilter()

	if len(c.matches) == 0 {
		c.Hide()
	}
}

// refilter recomputes which items match the prefix.
//
// Matching is case-insensitive on the prefix, which is what makes typing
// "prin" find "Println" without having to guess the case first.
func (c *CompletionBox) refilter() {
	c.matches = c.matches[:0]
	wanted := strings.ToLower(c.prefix)

	for i, item := range c.items {
		if strings.HasPrefix(strings.ToLower(item.Label), wanted) {
			c.matches = append(c.matches, i)
		}
	}
}

// placeUnder returns where the popup should sit: under the cursor if it fits,
// above it if it does not, and always inside the screen.
func (c *CompletionBox) placeUnder(cursorX, cursorY int, screen ui.Rect) ui.Rect {
	height := min(len(c.matches), completionMaxRows) + 2
	width := min(max(c.widestEntry()+4, completionMinWidth), completionMaxWidth)

	bounds := ui.Rect{X: cursorX - 1, Y: cursorY + 1, W: width, H: height}
	if bounds.Bottom() > screen.Bottom() {
		bounds.Y = cursorY - height
	}
	return bounds.ClampInto(screen)
}

// widestEntry returns the width of the longest line the popup will show.
func (c *CompletionBox) widestEntry() int {
	widest := 0
	for _, index := range c.matches {
		widest = max(widest, len([]rune(c.entryText(c.items[index]))))
	}
	return widest
}

// entryText is one line of the popup: the label, then its kind.
func (c *CompletionBox) entryText(item lsp.CompletionItem) string {
	if item.Kind == 0 {
		return item.Label
	}
	return item.Label + "  " + item.Kind.String()
}

// Selected returns the highlighted item and whether there is one.
func (c *CompletionBox) Selected() (lsp.CompletionItem, bool) {
	if !c.visible || c.selected >= len(c.matches) {
		return lsp.CompletionItem{}, false
	}
	return c.items[c.matches[c.selected]], true
}

// Count returns how many suggestions are currently shown.
func (c *CompletionBox) Count() int { return len(c.matches) }

// Matches returns the suggestions currently shown, in the order they appear.
func (c *CompletionBox) Matches() []lsp.CompletionItem {
	items := make([]lsp.CompletionItem, 0, len(c.matches))
	for _, index := range c.matches {
		items = append(items, c.items[index])
	}
	return items
}

// Accept chooses the highlighted item and closes the popup.
func (c *CompletionBox) Accept() {
	item, ok := c.Selected()
	c.Hide()
	if ok && c.OnAccept != nil {
		c.OnAccept(item)
	}
}

// move walks the list, clamping at either end rather than wrapping: a list
// that wraps makes it easy to sail past the entry you wanted.
func (c *CompletionBox) move(by int) {
	if len(c.matches) == 0 {
		return
	}
	c.selected = min(max(c.selected+by, 0), len(c.matches)-1)

	rows := min(len(c.matches), completionMaxRows)
	c.top = min(c.top, c.selected)
	if c.selected >= c.top+rows {
		c.top = c.selected - rows + 1
	}
}

// Draw paints the popup, framed and shadowed like every other floating thing.
func (c *CompletionBox) Draw(p *ui.Painter, th *theme.Theme) {
	if !c.visible {
		return
	}

	bounds := c.Bounds()
	ui.DrawShadow(p, bounds, th.Style(theme.KeyShadow))

	panel := p.Sub(bounds)
	panel.Clear(th.Style(theme.KeyCompletionItem))
	ui.DrawFrame(panel, panel.Size(), ui.FrameSingle, th.Style(theme.KeyCompletionFrame))

	rows := min(panel.Size().H-2, len(c.matches)-c.top)
	for row := range rows {
		c.drawEntry(panel, th, row)
	}
}

// drawEntry paints one line of the popup.
func (c *CompletionBox) drawEntry(p *ui.Painter, th *theme.Theme, row int) {
	index := c.matches[c.top+row]
	item := c.items[index]
	width := p.Size().W - 2

	style := th.Style(theme.KeyCompletionItem)
	if c.top+row == c.selected {
		style = th.Style(theme.KeyCompletionSelected)
	}

	p.HLine(1, row+1, width, ' ', style)
	end := p.TextLimited(1, row+1, width, item.Label, style)

	if item.Kind != 0 {
		tag := " " + item.Kind.String()
		x := p.Size().W - 1 - len([]rune(tag))
		if x > end {
			p.Text(x, row+1, tag, th.Style(theme.KeyCompletionDetail))
		}
	}
}

// HandleKey works the popup and reports whether it consumed the key.
//
// Anything it does not use — a printable character, most notably — falls
// through to the editor, which is what lets the user keep typing while the
// list narrows itself.
func (c *CompletionBox) HandleKey(ev *tcell.EventKey) bool {
	if !c.visible {
		return false
	}

	switch ev.Key() {
	case tcell.KeyUp:
		c.move(-1)
	case tcell.KeyDown:
		c.move(+1)
	case tcell.KeyPgUp:
		c.move(-completionMaxRows)
	case tcell.KeyPgDn:
		c.move(+completionMaxRows)
	case tcell.KeyEnter, tcell.KeyTab:
		c.Accept()
	case tcell.KeyEscape:
		c.Hide()
	default:
		return false
	}
	return true
}

// HandleMouse selects and accepts entries with the pointer.
func (c *CompletionBox) HandleMouse(ev *tcell.EventMouse) bool {
	if !c.visible {
		return false
	}

	x, y := ev.Position()
	if !c.Bounds().Contains(x, y) {
		if ev.Buttons() == tcell.Button1 {
			c.Hide() // a click elsewhere puts the list away
		}
		return false
	}

	index := c.top + y - c.Bounds().Y - 1
	if index < 0 || index >= len(c.matches) {
		return true
	}
	c.selected = index
	if ev.Buttons() == tcell.Button1 {
		c.Accept()
	}
	return true
}