// Cthulhu screen reader.
// Copyright (c) 2026 Storm Dragon
// Authors: Storm Dragon, Angus Kola
//
// This program is free software: you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by the Free
// Software Foundation, either version 3 of the License, or (at your option)
// any later version.
//
// This program is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
// more details.
//
// You should have received a copy of the GNU General Public License along with
// this program. If not, see <https://www.gnu.org/licenses/gpl-3.0.html>.

package atspi

import (
	"context"
	"errors"
)

var ErrNotInDocument = errors.New("accessible is outside web document content")

// DocumentContext identifies both the innermost document and the outermost
// document containing an object. Ancestors run from the object to the tree
// root. All data is copied under one tree lock; no native references escape.
type DocumentContext struct {
	Document  ObjectReference
	TopLevel  ObjectReference
	Ancestors []Snapshot
}

// IsWebDocumentRole follows the shared Python web script's document roles.
// Generic text/spreadsheet documents must not enable browser key handling.
func IsWebDocumentRole(role string) bool {
	return role == "document web" || role == "document frame" || role == "embedded"
}

func (tree *AccessibleTree) DocumentContext(reference ObjectReference) (DocumentContext, error) {
	tree.mu.RLock()
	defer tree.mu.RUnlock()
	return tree.documentContextLocked(reference)
}

func (tree *AccessibleTree) documentContextLocked(reference ObjectReference) (DocumentContext, error) {
	entry, err := tree.resolveLocked(reference)
	if err != nil {
		return DocumentContext{}, err
	}
	var result DocumentContext
	for {
		if entry.snapshotInvalid {
			return DocumentContext{}, ErrStaleSnapshot
		}
		result.Ancestors = append(result.Ancestors, entry.snapshot)
		if IsWebDocumentRole(entry.snapshot.Role) {
			if !result.Document.Valid() {
				result.Document = reference
			}
			result.TopLevel = reference
		}
		if !entry.hasParent {
			break
		}
		id := entry.parent
		entry = tree.nodes[id]
		reference = newObjectReference(id, entry)
	}
	if !result.Document.Valid() {
		return DocumentContext{}, ErrNotInDocument
	}
	return result, nil
}

// DocumentNode is one owned semantic object in document tree order. Visible
// does not mean on-screen: document navigation must include offscreen content.
type DocumentNode struct {
	Reference ObjectReference
	Parent    ObjectID
	Snapshot  Snapshot
	Geometry  Geometry
	Text      VisibleText
	Hidden    bool
	// ParentEditable is captured with the node so entry matching stays
	// constant-time instead of rescanning the complete document per candidate.
	ParentEditable bool
	Children       []ObjectID
}

type DocumentSnapshot struct {
	Context DocumentContext
	Nodes   []DocumentNode
	data    *documentData
}

// Document copies the top-level document, including embedded documents but
// excluding browser chrome and other tabs. A stale/incomplete capture fails
// atomically. It does not use flat review's viewport-limited text ranges.
func (tree *AccessibleTree) Document(ctx context.Context, reference ObjectReference) (DocumentSnapshot, error) {
	view, err := tree.DocumentView(ctx, reference)
	if err != nil {
		return DocumentSnapshot{}, err
	}
	view.Nodes = append([]DocumentNode(nil), view.Nodes...)
	view.data = nil
	return view, nil
}

// DocumentView validates the complete document atomically and shares its
// immutable data. Like NavigationDocument, the returned Nodes are read-only.
func (tree *AccessibleTree) DocumentView(ctx context.Context, reference ObjectReference) (DocumentSnapshot, error) {
	tree.mu.Lock()
	defer tree.mu.Unlock()
	view, err := tree.navigation_document_locked(ctx, reference)
	if err != nil {
		return DocumentSnapshot{}, err
	}
	if err := tree.validate_document_range_locked(ctx, view, 0, len(view.Nodes)-1); err != nil {
		return DocumentSnapshot{}, err
	}
	return view, nil
}

// NavigationDocument shares immutable document data until Replace or removal
// changes the tree. Callers must not modify Nodes or their nested slices. Dirty
// entries remain in the view: navigation validates the path it actually uses
// with ValidateDocumentRange rather than recapturing unrelated page updates.
func (tree *AccessibleTree) NavigationDocument(ctx context.Context, reference ObjectReference) (DocumentSnapshot, error) {
	tree.mu.Lock()
	defer tree.mu.Unlock()
	return tree.navigation_document_locked(ctx, reference)
}

func (tree *AccessibleTree) navigation_document_locked(ctx context.Context, reference ObjectReference) (DocumentSnapshot, error) {
	if err := ctx.Err(); err != nil {
		return DocumentSnapshot{}, err
	}
	owner, err := tree.documentContextLocked(reference)
	if err != nil {
		return DocumentSnapshot{}, err
	}
	if data := tree.documents[owner.TopLevel.ID()]; data != nil {
		return DocumentSnapshot{Context: owner, Nodes: data.nodes, data: data}, nil
	}
	capacity := 128
	if owner.TopLevel.ID() == tree.root {
		capacity = len(tree.nodes)
	}
	result := DocumentSnapshot{Context: owner, Nodes: make([]DocumentNode, 0, capacity)}
	type pendingNode struct {
		id     ObjectID
		hidden bool
	}
	pending := []pendingNode{{id: owner.TopLevel.ID()}}
	for len(pending) > 0 {
		if err := ctx.Err(); err != nil {
			return DocumentSnapshot{}, err
		}
		last := len(pending) - 1
		next := pending[last]
		pending = pending[:last]
		entry, present := tree.nodes[next.id]
		if !present {
			return DocumentSnapshot{}, ErrIncompleteTree
		}
		hidden := next.hidden || entry.geometry.VisibilityKnown && !entry.geometry.Visible
		parentEditable := false
		if entry.hasParent {
			parentEditable = tree.nodes[entry.parent].snapshot.Editable
		}
		result.Nodes = append(result.Nodes, DocumentNode{
			Parent:         entry.parent,
			Reference:      newObjectReference(next.id, entry),
			Snapshot:       entry.snapshot,
			Geometry:       entry.geometry,
			Text:           entry.text,
			Hidden:         hidden,
			ParentEditable: parentEditable,
			Children:       entry.children,
		})
		for i := len(entry.children) - 1; i >= 0; i-- {
			pending = append(pending, pendingNode{entry.children[i], hidden})
		}
	}
	result.data = new_document_data(result.Nodes)
	populate_document_rows(&result)
	if tree.documents == nil {
		tree.documents = make(map[ObjectID]*documentData)
	}
	tree.documents[owner.TopLevel.ID()] = result.data
	return result, nil
}