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

package review

import (
	"context"
	"errors"
	"strings"

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

// move_caret_line handles line and document boundaries under the cursor lock
// held by MoveCaret. Text-unit movement has its separate traversal helper.
func move_caret_object_line(ctx context.Context, reader DocumentCaretReader, doc atspi.DocumentSnapshot, place *documentPlace, indices []caretRange, current int, command DocumentCaretCommand) (DocumentCaretMove, error) {
	unit := atspi.DocumentCaretLine
	if command == CaretReadLine {
		unit = atspi.DocumentCaretLineRemainder
	}
	position, same := caretRangePosition(indices, current, place.offset)
	backwards := command == CaretPreviousLine || command == CaretDocumentEnd
	if command == CaretDocumentStart {
		position = 0
	} else if command == CaretDocumentEnd {
		position = len(indices) - 1
	}
	offset := place.offset
	if !same || command == CaretDocumentStart {
		offset = 0
	}
	if command == CaretDocumentEnd {
		offset = indices[position].end - 1
	}
	if backwards && command != CaretDocumentEnd && !same {
		position--
		if position < 0 {
			return DocumentCaretMove{Position: documentPosition(doc, *place)}, nil
		}
		offset = indices[position].end - 1
	}
	initialPosition := position
	for attempts := 0; attempts < len(indices)+1; attempts++ {
		if position < 0 || position >= len(indices) {
			return DocumentCaretMove{Position: documentPosition(doc, *place)}, nil
		}
		node := doc.Nodes[indices[position].index]
		if node.Snapshot.CharacterCount == 0 || wholeCaretNode(node.Snapshot) {
			if (command == CaretNextLine || command == CaretPreviousLine) && node.Reference == place.object {
				if backwards {
					position--
					if position >= 0 {
						offset = indices[position].end - 1
					}
				} else {
					position++
					offset = 0
				}
				continue
			}
			place.object, place.offset, place.origin = node.Reference, 0, CaretNavigation
			return DocumentCaretMove{Position: documentPosition(doc, *place), Moved: true}, nil
		}
		if offset < indices[position].start {
			offset = indices[position].start
		}
		if command == CaretReadLine && offset >= indices[position].end {
			position++
			offset = 0
			continue
		}
		if offset >= indices[position].end {
			offset = indices[position].end - 1
		}
		piece, readErr := readCaretRange(ctx, reader, doc, indices[position], offset, unit)
		if readErr != nil && !errors.Is(readErr, atspi.ErrNoDocumentCaret) {
			return DocumentCaretMove{}, readErr
		}
		if readErr == nil && piece.End > piece.Start && strings.TrimSpace(piece.Text) != "\ufffc" {
			nextOffset := offset
			sameCurrent := position == initialPosition && same ||
				place.origin == StructuralNavigation && position == initialPosition && indices[position].index >= current
			switch command {
			case CaretNextLine:
				if sameCurrent {
					nextOffset = piece.End
					if nextOffset < piece.CharacterCount {
						piece, readErr = readCaretRange(ctx, reader, doc, indices[position], nextOffset, unit)
						if readErr != nil {
							return DocumentCaretMove{}, readErr
						}
					} else {
						position++
						if position >= len(indices) {
							return DocumentCaretMove{Position: documentPosition(doc, *place)}, nil
						}
						offset = 0
						continue
					}
				}
				nextOffset = piece.Start
			case CaretPreviousLine:
				if sameCurrent {
					if piece.Start > indices[position].start {
						piece, readErr = readCaretRange(ctx, reader, doc, indices[position], piece.Start-1, unit)
						if readErr != nil {
							return DocumentCaretMove{}, readErr
						}
					} else {
						position--
						if position < 0 {
							return DocumentCaretMove{Position: documentPosition(doc, *place)}, nil
						}
						offset = indices[position].end - 1
						continue
					}
				}
				nextOffset = piece.Start
			case CaretLineStart:
				nextOffset = piece.Start
			case CaretLineEnd, CaretDocumentEnd:
				nextOffset = max(piece.Start, piece.End-1)
			case CaretDocumentStart:
				nextOffset = piece.Start
			}
			if piece.End <= piece.Start || strings.TrimSpace(piece.Text) == "\ufffc" {
				// An embedded-object placeholder is a container, not spoken text.
				if backwards {
					position--
					if position >= 0 {
						offset = indices[position].end - 1
					}
				} else {
					position++
					offset = 0
				}
				continue
			}
			spoken := piece.Text
			if command == CaretLineStart || command == CaretLineEnd {
				character, charErr := readCaretRange(ctx, reader, doc, indices[position], nextOffset, atspi.DocumentCaretCharacter)
				if charErr != nil {
					return DocumentCaretMove{}, charErr
				}
				spoken = character.Text
			}
			place.object = node.Reference
			place.offset = nextOffset
			place.origin = CaretNavigation
			return DocumentCaretMove{Position: documentPosition(doc, *place), Text: spoken, RawText: piece.RawText, Misspelled: piece.Misspelled, Moved: true, Start: piece.Start, End: piece.End}, nil
		}
		if backwards {
			position--
			if position >= 0 {
				offset = indices[position].end - 1
			}
		} else {
			position++
			offset = 0
		}
	}
	return DocumentCaretMove{Position: documentPosition(doc, *place)}, nil
}