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

package review

import (
	"context"
	"strings"
	"unicode/utf8"

	"git.stormux.org/storm/cthulhu/internal/atspi"
)

// A range uses native text offsets, except for explicitly named links whose
// label offsets stay virtual. Hypertext containers can occur more than once,
// before and after their embedded children.
type caretRange struct{ index, start, end int }

func caretNodeRanges(nodes []atspi.DocumentNode) []caretRange {
	indices, _, expanded := caret_node_indices(nodes, atspi.ObjectReference{})
	eligible := make(map[int]bool, len(indices))
	byID := make(map[atspi.ObjectID]int, len(nodes))
	for _, index := range indices {
		eligible[index] = true
	}
	for index, node := range nodes {
		byID[node.Reference.ID()] = index
	}
	var result []caretRange
	var visit func(int)
	visit = func(index int) {
		node := nodes[index]
		if node.Hidden || node.Snapshot.Role == "password text" || passive_caret_tooltip(node.Snapshot) {
			return
		}
		children := node.Snapshot.TextChildren
		valid := len(children) > 0 && !node.Snapshot.Editable && !wholeCaretNode(node.Snapshot)
		previous := -1
		direct := make(map[atspi.ObjectID]bool, len(node.Children))
		for _, id := range node.Children {
			direct[id] = true
		}
		for _, child := range children {
			if child.Offset <= previous || child.Offset >= node.Snapshot.CharacterCount || !direct[child.Child] {
				valid = false
				break
			}
			previous = child.Offset
		}
		if valid {
			offset := 0
			for _, child := range children {
				if offset < child.Offset {
					result = append(result, caretRange{index, offset, child.Offset})
				}
				if childIndex, ok := byID[child.Child]; ok {
					visit(childIndex)
				}
				delete(direct, child.Child)
				offset = child.Offset + 1
			}
			if offset < node.Snapshot.CharacterCount {
				result = append(result, caretRange{index, offset, node.Snapshot.CharacterCount})
			}
			for _, id := range node.Children {
				if direct[id] {
					if child, ok := byID[id]; ok {
						visit(child)
					}
				}
			}
			return
		}
		if eligible[index] {
			result = append(result, caretRange{index, 0, caret_text_count(node.Snapshot)})
			if wholeCaretNode(node.Snapshot) && !expanded[node.Reference.ID()] {
				return
			}
		}
		for _, id := range node.Children {
			if child, ok := byID[id]; ok {
				visit(child)
			}
		}
	}
	if len(nodes) > 0 {
		visit(0)
	}
	return result
}

// Object-local range positions also handle a hypertext parent occurring on
// both sides of an embedded child. after preserves provider traversal order,
// which is not monotonically increasing in document node index.
type caretRangeLookup struct {
	objects [][]int
	after   []int
}

func new_caret_range_lookup(ranges []caretRange, nodeCount int) *caretRangeLookup {
	lookup := &caretRangeLookup{objects: make([][]int, nodeCount), after: make([]int, nodeCount)}
	for position, item := range ranges {
		lookup.objects[item.index] = append(lookup.objects[item.index], position)
	}
	following := len(ranges)
	for index := nodeCount - 1; index >= 0; index-- {
		lookup.after[index] = following
		if positions := lookup.objects[index]; len(positions) > 0 {
			following = min(following, positions[0])
		}
	}
	return lookup
}

func (lookup *caretRangeLookup) containing(ranges []caretRange, current, offset int) int {
	for _, position := range lookup.objects[current] {
		item := ranges[position]
		if offset >= item.start && offset < max(item.start+1, item.end) {
			return position
		}
	}
	return -1
}

func (lookup *caretRangeLookup) position(ranges []caretRange, current, offset int) (int, bool) {
	if position := lookup.containing(ranges, current, offset); position >= 0 {
		return position, true
	}
	// Word and Read All cursors may be just after the final character.
	for _, position := range lookup.objects[current] {
		if offset == ranges[position].end {
			return position, true
		}
	}
	return lookup.after[current], false
}

func readCaretRange(ctx context.Context, reader DocumentCaretReader, doc atspi.DocumentSnapshot, item caretRange, offset int, unit atspi.DocumentCaretUnit) (atspi.DocumentCaretText, error) {
	offset = max(item.start, min(offset, item.end-1))
	node := doc.Nodes[item.index]
	text, err := read_caret_text(ctx, reader, node, offset, unit)
	if err != nil || text.End <= text.Start {
		return text, err
	}
	if item.start == 0 && item.end == caret_text_count(node.Snapshot) {
		return text, nil
	}
	if text.Start < 0 || text.Start > offset || text.End <= offset || text.End > text.CharacterCount {
		return text, nil
	}
	start, end := max(text.Start, item.start), min(text.End, item.end)
	if start >= end {
		return atspi.DocumentCaretText{CharacterCount: item.end}, nil
	}
	if start != text.Start || end != text.End {
		raw := text.RawText
		if raw == "" {
			raw = text.Text
		}
		// Speech may be whitespace-normalized. Clip using the raw native text;
		// never treat offsets in a normalized string as native character offsets.
		runes := []rune(raw)
		if unit == atspi.DocumentCaretLineRemainder && len(runes) > text.End-text.Start {
			runes = runes[len(runes)-(text.End-text.Start):]
		}
		if len(runes) != text.End-text.Start {
			return atspi.DocumentCaretText{}, atspi.ErrNoDocumentCaret
		}
		raw = string(runes[start-text.Start : end-text.Start])
		if text.RawText != "" {
			text.RawText = raw
			text.Text = strings.Join(strings.Fields(raw), " ")
		} else {
			text.Text = raw
		}
		text.Start, text.End = start, end
	}
	// Range-local traversal must stop at the embedded object. The retained
	// snapshot still has the full native character count for routing/placement.
	text.CharacterCount = item.end
	if unit == atspi.DocumentCaretCharacter && utf8.RuneCountInString(text.Text) > 1 {
		return atspi.DocumentCaretText{}, atspi.ErrNoDocumentCaret
	}
	return text, nil
}