/******************************************************************************
 * Copyright 2021 TypeFox GmbH
 * This program and the accompanying materials are made available under the
 * terms of the MIT License, which is available in the project root.
 ******************************************************************************/

import type { DocumentSymbol, DocumentSymbolParams } from 'vscode-languageserver';
import type { CancellationToken } from '../utils/cancellation.js';
import type { NameProvider } from '../references/name-provider.js';
import type { LangiumServices } from './lsp-services.js';
import type { AstNode } from '../syntax-tree.js';
import { streamContents } from '../utils/ast-utils.js';
import type { MaybePromise } from '../utils/promise-utils.js';
import type { LangiumDocument } from '../workspace/documents.js';
import type { NodeKindProvider } from './node-kind-provider.js';

/**
 * Language-specific service for handling document symbols requests.
 */
export interface DocumentSymbolProvider {
    /**
     * Handle a document symbols request.
     *
     * @param document The document in the workspace.
     * @param params The parameters of the request.
     * @param cancelToken A cancellation token that migh be used to cancel the request.
     * @returns The symbols for the given document.
     *
     * @throws `OperationCancelled` if cancellation is detected during execution
     * @throws `ResponseError` if an error is detected that should be sent as response to the client
     */
    getSymbols(document: LangiumDocument, params: DocumentSymbolParams, cancelToken?: CancellationToken): MaybePromise<DocumentSymbol[]>;
}

export class DefaultDocumentSymbolProvider implements DocumentSymbolProvider {

    protected readonly nameProvider: NameProvider;
    protected readonly nodeKindProvider: NodeKindProvider;

    constructor(services: LangiumServices) {
        this.nameProvider = services.references.NameProvider;
        this.nodeKindProvider = services.shared.lsp.NodeKindProvider;
    }

    getSymbols(document: LangiumDocument, _params: DocumentSymbolParams, _cancelToken?: CancellationToken): MaybePromise<DocumentSymbol[]> {
        return this.getSymbol(document, document.parseResult.value);
    }

    protected getSymbol(document: LangiumDocument, astNode: AstNode): DocumentSymbol[] {
        const node = astNode.$cstNode;
        const nameNode = this.nameProvider.getNameNode(astNode);
        if (nameNode && node) {
            const name = this.nameProvider.getName(astNode);
            return [{
                kind: this.nodeKindProvider.getSymbolKind(astNode),
                name: name || nameNode.text,
                range: node.range,
                selectionRange: nameNode.range,
                children: this.getChildSymbols(document, astNode)
            }];
        } else {
            return this.getChildSymbols(document, astNode) || [];
        }
    }

    protected getChildSymbols(document: LangiumDocument, astNode: AstNode): DocumentSymbol[] | undefined {
        const children: DocumentSymbol[] = [];

        for (const child of streamContents(astNode)) {
            const result = this.getSymbol(document, child);
            children.push(...result);
        }
        if (children.length > 0) {
            return children;
        }
        return undefined;
    }
}