// Copyright (c) 2026 Storm Dragon
// Authors: Storm Dragon, Angus Kola
// SPDX-License-Identifier: GPL-3.0-or-later

package interaction

import (
	"errors"
	"fmt"
	"strings"
	"unicode"
	"unicode/utf8"
)

// GridTab holds one category. Filtering and selection belong to each session.
type GridTab struct {
	ID, Label string
	Items     []Item
}
type gridPage struct {
	GridTab
	query    string
	selected int
}
type gridSession struct {
	pages               []gridPage
	tab, focus, columns int // focus: 0 tab strip, 1 grid, 2 checkbox
	checkbox            Element
	closed              bool
}

// NewGridSession is a core tabbed grid with a shared checkbox. External forms
// keep their existing protocol and limits. Navigation follows Fenrir's picker.
func NewGridSession(title string, tabs []GridTab, columns int, checkbox Element) (*Session, error) {
	if title == "" || len(tabs) == 0 || columns < 1 || columns > 64 || checkbox.Kind != CheckBox || checkbox.ID == "" || checkbox.Label == "" {
		return nil, errors.New("invalid tabbed grid")
	}
	grid := &gridSession{columns: columns, checkbox: checkbox}
	ids := map[string]bool{}
	for _, tab := range tabs {
		if tab.ID == "" || tab.Label == "" || ids[tab.ID] {
			return nil, errors.New("invalid grid tab")
		}
		ids[tab.ID] = true
		items := map[string]bool{}
		for _, item := range tab.Items {
			if item.ID == "" || item.Label == "" || items[item.ID] {
				return nil, errors.New("invalid grid item")
			}
			items[item.ID] = true
		}
		tab.Items = append([]Item(nil), tab.Items...)
		page := gridPage{GridTab: tab}
		page.filter()
		grid.pages = append(grid.pages, page)
	}
	return &Session{title: title, grid: grid}, nil
}
func (page *gridPage) matches() []int {
	var result []int
	for index, item := range page.Items {
		if !item.Disabled && strings.HasPrefix(strings.ToLower(item.Label), strings.ToLower(page.query)) {
			result = append(result, index)
		}
	}
	return result
}
func (page *gridPage) filter() {
	page.selected = -1
	if matches := page.matches(); len(matches) > 0 {
		page.selected = matches[0]
	}
}
func (grid *gridSession) values() map[string]Value {
	page := &grid.pages[grid.tab]
	values := map[string]Value{grid.checkbox.ID: {Checked: grid.checkbox.Checked}}
	if grid.focus == 1 && page.selected >= 0 {
		values["grid"] = Value{Selected: page.Items[page.selected].ID, Text: page.Items[page.selected].Label}
	}
	return values
}
func (grid *gridSession) presentation() Presentation {
	if grid.closed {
		return Presentation{}
	}
	page := &grid.pages[grid.tab]
	text := page.Label + " tab"
	switch grid.focus {
	case 1:
		text = "No matches"
		for position, index := range page.matches() {
			if index == page.selected {
				text = fmt.Sprintf("%s. row %d, column %d. %d of %d", page.Items[index].Label, position/grid.columns+1, position%grid.columns+1, position+1, len(page.matches()))
				break
			}
		}
	case 2:
		text = grid.checkbox.Label + ", unchecked"
		if grid.checkbox.Checked {
			text = grid.checkbox.Label + ", checked"
		}
	}
	return Presentation{Speech: text, Braille: text, Cursor: -1}
}
func (grid *gridSession) handle(event Event) Effect {
	if grid.closed {
		return Effect{}
	}
	if event.Key == Escape {
		grid.closed = true
		return Effect{Cancelled: true}
	}
	if event.Alt {
		return Effect{}
	}
	if event.Key == Tab && !event.Control {
		delta := 1
		if event.Shift {
			delta = -1
		}
		grid.focus = (grid.focus + delta + 3) % 3
		return Effect{Presentation: grid.presentation()}
	}
	page := &grid.pages[grid.tab]
	if grid.focus == 0 {
		if event.Control {
			return Effect{}
		}
		switch event.Key {
		case Up, Left:
			grid.tab = (grid.tab + len(grid.pages) - 1) % len(grid.pages)
		case Down, Right:
			grid.tab = (grid.tab + 1) % len(grid.pages)
		case Enter:
			grid.focus = 1
		case Text:
			if event.Text != " " {
				return Effect{}
			}
			grid.focus = 1
		default:
			return Effect{}
		}
		return Effect{Presentation: grid.presentation()}
	}
	if grid.focus == 2 {
		if !event.Control && (event.Key == Enter || event.Key == Text && event.Text == " ") {
			grid.checkbox.Checked = !grid.checkbox.Checked
			return Effect{Presentation: grid.presentation()}
		}
		return Effect{}
	}
	if event.Control && event.Key != Backspace {
		return Effect{}
	}
	if event.Key == Backspace || event.Key == Text && event.Text != "" {
		query := []rune(page.query)
		if event.Key == Backspace {
			if event.Control {
				query = nil
			} else if len(query) > 0 {
				query = query[:len(query)-1]
			}
		} else {
			if !utf8.ValidString(event.Text) || len(query)+len([]rune(event.Text)) > 4096 {
				return Effect{}
			}
			for _, character := range event.Text {
				if !unicode.IsPrint(character) {
					return Effect{}
				}
			}
			query = append(query, []rune(event.Text)...)
		}
		page.query = string(query)
		page.filter()
		output := grid.presentation()
		prefix := "Search cleared"
		if page.query != "" {
			prefix = "Search " + page.query
		}
		output.Speech = prefix + ". " + output.Speech
		return Effect{Presentation: output}
	}
	matches := page.matches()
	if len(matches) == 0 {
		return Effect{Presentation: grid.presentation()}
	}
	position := 0
	for current, index := range matches {
		if index == page.selected {
			position = current
			break
		}
	}
	switch event.Key {
	case Left:
		position = max(0, position-1)
	case Right:
		position = min(len(matches)-1, position+1)
	case Up:
		if position >= grid.columns {
			position -= grid.columns
		}
	case Down:
		if position/grid.columns < (len(matches)-1)/grid.columns {
			position = min(len(matches)-1, position+grid.columns)
		}
	case Home:
		position = 0
	case End:
		position = len(matches) - 1
	case PageUp:
		position = max(0, position-grid.columns*5)
	case PageDown:
		position = min(len(matches)-1, position+grid.columns*5)
	case Enter:
		return Effect{Activated: "select-grid-item"}
	default:
		return Effect{}
	}
	page.selected = matches[position]
	return Effect{Presentation: grid.presentation()}
}