MarkupReferenceResolver.swift

/*
 This source file is part of the Swift.org open source project

 Copyright (c) 2021-2022 Apple Inc. and the Swift project authors
 Licensed under Apache License v2.0 with Runtime Library Exception

 See https://swift.org/LICENSE.txt for license information
 See https://swift.org/CONTRIBUTORS.txt for Swift project authors
*/

import Foundation
import Markdown
import SymbolKit

fileprivate func invalidLinkDestinationProblem(destination: String, source: URL?, range: SourceRange?, severity: DiagnosticSeverity) -> Problem {
    let diagnostic = Diagnostic(source: source, severity: severity, range: range, identifier: "org.swift.docc.invalidLinkDestination", summary: "Link destination \(destination.singleQuoted) is not a valid URL")
    return Problem(diagnostic: diagnostic, possibleSolutions: [])
}

fileprivate func disabledLinkDestinationProblem(reference: ResolvedTopicReference, source: URL?, range: SourceRange?, severity: DiagnosticSeverity) -> Problem {
    return Problem(diagnostic: Diagnostic(source: source, severity: severity, range: range, identifier: "org.swift.docc.disabledLinkDestination", summary: "The topic \(reference.path.singleQuoted) cannot be linked to."), possibleSolutions: [])
}

fileprivate func unknownSnippetSliceProblem(snippetPath: String, slice: String, source: URL?, range: SourceRange?) -> Problem {
    let diagnostic = Diagnostic(source: source, severity: .warning, range: range, identifier: "org.swift.docc.unknownSnippetSlice", summary: "Snippet slice \(slice.singleQuoted) does not exist in snippet \(snippetPath.singleQuoted); this directive will be ignored")
    return Problem(diagnostic: diagnostic, possibleSolutions: [])
}

/**
 Rewrites a ``Markup`` tree to resolve ``UnresolvedTopicReference`s using a ``DocumentationContext``.
 */
struct MarkupReferenceResolver: MarkupRewriter {
    var context: DocumentationContext
    var bundle: DocumentationBundle
    var source: URL?
    var problems = [Problem]()
    var rootReference: ResolvedTopicReference
    
    init(context: DocumentationContext, bundle: DocumentationBundle, source: URL?, rootReference: ResolvedTopicReference) {
        self.context = context
        self.bundle = bundle
        self.source = source
        self.rootReference = rootReference
    }

    // If the property is set and returns a problem, that problem will be
    // emitted instead of the default "unresolved topic" problem.
    // This property offers a customization point for when we need to try
    // resolving links in other contexts than the current one to provide more
    // precise diagnostics.
    var problemForUnresolvedReference: ((_ unresolvedReference: UnresolvedTopicReference, _ source: URL?, _ range: SourceRange?, _ fromSymbolLink: Bool, _ underlyingErrorMessage: String) -> Problem?)? = nil

    private mutating func resolve(reference: TopicReference, range: SourceRange?, severity: DiagnosticSeverity, fromSymbolLink: Bool = false) -> ResolvedTopicReference? {
        switch context.resolve(reference, in: rootReference, fromSymbolLink: fromSymbolLink) {
        case .success(let resolved):
            // If the linked node is part of the topic graph,
            // verify that linking to it is enabled, else return `nil`.
            if let node = context.topicGraph.nodeWithReference(resolved) {
                guard context.topicGraph.isLinkable(node.reference) else {
                    problems.append(disabledLinkDestinationProblem(reference: resolved, source: source, range: range, severity: severity))
                    return nil
                }
            }
            return resolved
            
        case .failure(let unresolved, let errorMessage):
            if let callback = problemForUnresolvedReference,
                let problem = callback(unresolved, source, range, fromSymbolLink, errorMessage) {
                problems.append(problem)
                return nil
            }
            
            // FIXME: Provide near-miss suggestion here. The user is likely to make mistakes with capitalization because of character input (rdar://59660520).
            let uncuratedArticleMatch = context.uncuratedArticles[bundle.articlesDocumentationRootReference.appendingPathOfReference(unresolved)]?.source
            problems.append(unresolvedReferenceProblem(reference: reference, source: source, range: range, severity: severity, uncuratedArticleMatch: uncuratedArticleMatch, underlyingErrorMessage: errorMessage))
            return nil
        }
    }

    mutating func visitImage(_ image: Image) -> Markup? {
        if let reference = image.reference(in: bundle), !context.resourceExists(with: reference) {
            problems.append(unresolvedResourceProblem(resource: reference, source: source, range: image.range, severity: .warning))
        }

        var image = image
        let newChildren = image.children.compactMap {
            visit($0) as? InlineMarkup
        }
        image.replaceChildrenInRange(0..<image.childCount, with: newChildren)
        return image
    }
    
    mutating func visitInlineHTML(_ inlineHTML: InlineHTML) -> Markup? {
        return inlineHTML
    }
    
    mutating func visitLineBreak(_ lineBreak: LineBreak) -> Markup? {
        return lineBreak
    }

    mutating func visitLink(_ link: Link) -> Markup? {
        guard let destination = link.destination else {
            return link
        }
        guard let url = ValidatedURL(parsingAuthoredLink: destination) else {
            problems.append(invalidLinkDestinationProblem(destination: destination, source: source, range: link.range, severity: .warning))
            return link
        }
        guard url.components.scheme == ResolvedTopicReference.urlScheme else {
            return link // Create a non-topic link
        }
        let unresolved = TopicReference.unresolved(.init(topicURL: url))
        guard let resolvedURL = resolve(reference: unresolved, range: link.range, severity: .warning) else {
            return link
        }
        var link = link
        link.destination = resolvedURL.absoluteString
        return link
    }

    mutating func resolveAbsoluteSymbolLink(unresolvedDestination: String, elementRange range: SourceRange?) -> ResolvedTopicReference? {
        if let cached = context.documentationCacheBasedLinkResolver.referenceFor(absoluteSymbolPath: unresolvedDestination, parent: rootReference) {
            guard context.topicGraph.isLinkable(cached) == true else {
                problems.append(disabledLinkDestinationProblem(reference: cached, source: source, range: range, severity: .warning))
                return nil
            }
            return cached
        }

        // We don't require a scheme here as the link can be a relative one, e.g. ``SwiftUI/View``.
        let url = ValidatedURL(parsingExact: unresolvedDestination)?.requiring(scheme: ResolvedTopicReference.urlScheme) ?? ValidatedURL(symbolPath: unresolvedDestination)
        return resolve(reference: .unresolved(.init(topicURL: url)), range: range, severity: .warning, fromSymbolLink: true)
    }
    
    mutating func visitSymbolLink(_ symbolLink: SymbolLink) -> Markup? {
        guard let destination = symbolLink.destination else {
            return symbolLink
        }
        
        var symbolLink = symbolLink
        if let resolved = resolveAbsoluteSymbolLink(unresolvedDestination: destination, elementRange: symbolLink.range) {
            symbolLink.destination = resolved.absoluteString
        }
        
        return symbolLink
    }

    mutating func visitBlockDirective(_ blockDirective: BlockDirective) -> Markup? {
        switch blockDirective.name {
        case Snippet.directiveName:
            var problems = [Problem]()
            guard let snippet = Snippet(from: blockDirective, source: source, for: bundle, in: context, problems: &problems) else {
                return blockDirective
            }
            
            if let resolved = resolveAbsoluteSymbolLink(unresolvedDestination: snippet.path, elementRange: blockDirective.range) {
                var argumentText = "path: \"\(resolved.absoluteString)\""
                if let requestedSlice = snippet.slice,
                   let snippetMixin = try? context.entity(with: resolved).symbol?
                    .mixins[SymbolGraph.Symbol.Snippet.mixinKey] as? SymbolGraph.Symbol.Snippet {
                    guard snippetMixin.slices[requestedSlice] != nil else {
                        problems.append(unknownSnippetSliceProblem(snippetPath: snippet.path, slice: requestedSlice, source: blockDirective.nameLocation?.source, range: blockDirective.nameRange))
                        return blockDirective
                    }
                    argumentText.append(", slice: \"\(requestedSlice)\"")
                }
                return BlockDirective(name: Snippet.directiveName, argumentText: argumentText, children: [])
            } else {
                return blockDirective
            }
        case ImageMedia.directiveName:
            guard let imageMedia = ImageMedia(from: blockDirective, source: source, for: bundle, in: context) else {
                return blockDirective
            }
            
            if !context.resourceExists(with: imageMedia.source, ofType: .image) {
                problems.append(
                    unresolvedResourceProblem(
                        resource: imageMedia.source,
                        expectedType: .image,
                        source: source,
                        range: imageMedia.originalMarkup.range,
                        severity: .warning
                    )
                )
            }
            
            return blockDirective
        case VideoMedia.directiveName:
            guard let videoMedia = VideoMedia(from: blockDirective, source: source, for: bundle, in: context) else {
                return blockDirective
            }
            
            if !context.resourceExists(with: videoMedia.source, ofType: .video) {
                problems.append(
                    unresolvedResourceProblem(
                        resource: videoMedia.source,
                        expectedType: .video,
                        source: source,
                        range: videoMedia.originalMarkup.range,
                        severity: .warning
                    )
                )
            }
            
            if let posterReference = videoMedia.poster,
                !context.resourceExists(with: posterReference, ofType: .image)
            {
                problems.append(
                    unresolvedResourceProblem(
                        resource: posterReference,
                        expectedType: .image,
                        source: source,
                        range: videoMedia.originalMarkup.range,
                        severity: .warning
                    )
                )
            }
            
            return blockDirective
        case Comment.directiveName:
            return blockDirective
        default:
            return defaultVisit(blockDirective)
        }
    }
}