WikiLinkService.swift

//
//  WikiLinkService.swift
//  MarkdownEngine
//
//  Created by Luca Chen on 16.03.26.
//
//  Generic wiki-link transformer used by the editor engine.
//
//  Wiki-links live in two forms:
//    Storage form    [[Name|<opaque-id>]]
//    Display form    [[Name]]
//
//  This service converts between the two and maintains a metadata map
//  that lets callers look up the storage range and identifier for any
//  display occurrence. The identifier is opaque to the engine — it can
//  be a UUID, a slug, a database key, anything an embedder hands out
//  via the ``WikiLinkResolver`` protocol.
//

import AppKit
import Foundation
import os

/// Bidirectional transform between the storage and display forms of wiki-links.
public enum WikiLinkService {

    /// Hashable wrapper around `NSRange` so we can use it as a dictionary key.
    public struct RangeKey: Hashable, Sendable {
        public let location: Int
        public let length: Int

        public init(_ range: NSRange) {
            self.location = range.location
            self.length = range.length
        }
    }

    /// Identifier and storage-side range associated with a display occurrence.
    public struct LinkMetadata: Sendable {
        public let id: String?
        public let storageRange: NSRange

        public init(id: String?, storageRange: NSRange) {
            self.id = id
            self.storageRange = storageRange
        }
    }

    /// Regex pattern matching the storage form `[[Name|optional-id]]`.
    public static let storagePattern = #"!?\[\[([^\|\]\r\n]*)(?:\|([^\]\r\n]+))?\]\]"#
    /// Regex pattern matching the display form `[[Name]]` (no `|`).
    public static let displayPattern = #"(?<!!)\[\[([^\]\r\n]*)\]\]"#

    private static let storageLinkRegex = try! NSRegularExpression(pattern: storagePattern)
    private static let displayLinkRegex = try! NSRegularExpression(pattern: displayPattern)
    private static let logger = Logger(subsystem: "com.markdownengine.wikilinks", category: "WikiLink")

    /// Convert storage form `[[Name|<id>]]` to display `[[Name]]`, returning a display-range metadata map.
    ///
    /// When `nameForID` is supplied, each matched link's stored label is replaced in the
    /// DISPLAY text by the target's current name looked up via the opaque suffix's uuid
    /// (the suffix itself — uuid for links, uuid|width for images — is preserved unchanged
    /// in the metadata). Unknown/empty/unsafe live names fall back to the stored label.
    public static func makeDisplayState(
        from storageText: String,
        nameForID: ((String) -> String?)? = nil
    ) -> (display: String, metadata: [RangeKey: LinkMetadata]) {
        let nsStorage = storageText as NSString
        let fullRange = NSRange(location: 0, length: nsStorage.length)
        var result = ""
        result.reserveCapacity(storageText.count)
        var metadata: [RangeKey: LinkMetadata] = [:]
        var cursor = 0
        var displayLength = 0

        for match in storageLinkRegex.matches(in: storageText, options: [], range: fullRange) {
            let prefixLength = match.range.location - cursor
            if prefixLength > 0 {
                let prefixRange = NSRange(location: cursor, length: prefixLength)
                let prefix = nsStorage.substring(with: prefixRange)
                result.append(prefix)
                displayLength += prefix.utf16.count
                cursor += prefixLength
            }

            let nameRange = match.range(at: 1)
            let name = nsStorage.substring(with: nameRange)
            let isImage = nsStorage.character(at: match.range.location) == 0x21 // '!'

            var linkID: String? = nil
            if match.numberOfRanges > 2 {
                let idRange = match.range(at: 2)
                if idRange.location != NSNotFound && idRange.length > 0 {
                    linkID = nsStorage.substring(with: idRange)
                }
            }

            // Auto-sync the DISPLAY label to the target's current name (looked up by the
            // uuid carried in the suffix). The suffix in metadata.id stays untouched.
            var displayName = name
            if let linkID, let nameForID {
                let bareID = linkID.split(separator: "|", maxSplits: 1).first.map(String.init) ?? linkID
                if let live = nameForID(bareID), !live.isEmpty,
                   live.rangeOfCharacter(from: CharacterSet(charactersIn: "|]\n\r")) == nil {
                    displayName = live
                }
            }

            let displayFragment = isImage ? "![[\(displayName)]]" : "[[\(displayName)]]"
            let displayRange = NSRange(location: displayLength, length: displayFragment.utf16.count)
            result.append(displayFragment)
            displayLength += displayFragment.utf16.count

            metadata[RangeKey(displayRange)] = LinkMetadata(id: linkID, storageRange: match.range)
            cursor = match.range.location + match.range.length
        }

        if cursor < nsStorage.length {
            let suffixRange = NSRange(location: cursor, length: nsStorage.length - cursor)
            result.append(nsStorage.substring(with: suffixRange))
        }

        return (result, metadata)
    }

    /// Convert display `[[Name]]` back to storage `[[Name|<id>]]`, preferring the `.wikiLinkID` attribute.
    public static func makeStorageState(
        from displayText: String,
        existingMetadata: [RangeKey: LinkMetadata],
        textStorage: NSTextStorage?
    ) -> (storage: String, metadata: [RangeKey: LinkMetadata]) {
        let nsDisplay = displayText as NSString
        // No `[[` anywhere → storage == display; skip the O(document) rebuild.
        if nsDisplay.range(of: "[[").location == NSNotFound {
            return (displayText, [:])
        }
        var storage = ""
        storage.reserveCapacity(nsDisplay.length)   // was displayText.count (O(doc) grapheme count)
        var metadata: [RangeKey: LinkMetadata] = [:]
        var cursor = 0
        var storageLength = 0

        for (matchRange, isImage) in displayLinkRanges(nsDisplay) {
            let prefixLength = matchRange.location - cursor
            if prefixLength > 0 {
                let prefixRange = NSRange(location: cursor, length: prefixLength)
                let prefix = nsDisplay.substring(with: prefixRange)
                storage.append(prefix)
                storageLength += prefix.utf16.count
                cursor += prefixLength
            }

            let openMarker = isImage ? 3 : 2
            let contentLength = max(0, matchRange.length - (openMarker + 2))
            let contentRange = NSRange(location: matchRange.location + openMarker, length: contentLength)
            let name = nsDisplay.substring(with: contentRange)

            var linkID: String? = nil
            if contentRange.length > 0 {
                if let idAttr = textStorage?.attribute(.wikiLinkID, at: contentRange.location, effectiveRange: nil) as? String {
                    linkID = idAttr
                }
            }
            if linkID == nil {
                linkID = existingMetadata[RangeKey(matchRange)]?.id
            }

            let marker = isImage ? "![[" : "[["
            let storageFragment: String
            if let linkID, !linkID.isEmpty {
                storageFragment = "\(marker)\(name)|\(linkID)]]"
            } else {
                storageFragment = "\(marker)\(name)]]"
            }
            let fragmentLength = storageFragment.utf16.count
            let storageRange = NSRange(location: storageLength, length: fragmentLength)
            storage.append(storageFragment)
            storageLength += fragmentLength

            metadata[RangeKey(matchRange)] = LinkMetadata(id: linkID, storageRange: storageRange)
            cursor = matchRange.location + matchRange.length
        }

        if cursor < nsDisplay.length {
            let suffixRange = NSRange(location: cursor, length: nsDisplay.length - cursor)
            storage.append(nsDisplay.substring(with: suffixRange))
        }

        return (storage, metadata)
    }

    /// Incremental counterpart to `makeStorageState`: splice a single contiguous
    /// edit into the previous storage form in O(edit + #links).
    ///
    /// Outside link syntax, display and storage text are identical, so an edit
    /// that provably cannot create, destroy, or touch a link maps 1:1 into the
    /// storage string; links after the edit just shift by the length delta.
    /// Returns nil whenever that proof fails — callers fall back to the full
    /// `makeStorageState` rebuild.
    public static func updatedStorageState(
        displayText: String,
        editedRange: NSRange,
        changeInLength delta: Int,
        previousStorage: String,
        previousMetadata: [RangeKey: LinkMetadata]
    ) -> (storage: String, metadata: [RangeKey: LinkMetadata])? {
        let nsDisplay = displayText as NSString
        let nsPrevStorage = previousStorage as NSString

        // Only contiguous, small, well-formed edits take the fast path.
        guard delta != Int.min,
              editedRange.location != NSNotFound,
              editedRange.length >= 0, editedRange.length <= 4096,
              NSMaxRange(editedRange) <= nsDisplay.length,
              editedRange.length - delta >= 0 else { return nil }

        let oldEditLength = editedRange.length - delta
        let oldEditRange = NSRange(location: editedRange.location, length: oldEditLength)

        // The edit must not create or complete link syntax: no [[ or ]] near it
        // in the NEW text (±3 covers a bracket typed against an existing one)…
        let probeStart = max(0, editedRange.location - 3)
        let probeEnd = min(nsDisplay.length, NSMaxRange(editedRange) + 3)
        let probe = nsDisplay.substring(with: NSRange(location: probeStart, length: probeEnd - probeStart))
        if probe.contains("[[") || probe.contains("]]") { return nil }

        // …and no existing link may overlap the edit (old display coordinates;
        // ±3 also rejects edits adjacent to a link's markers).
        let guardRange = NSRange(location: max(0, oldEditRange.location - 3), length: oldEditLength + 6)
        for key in previousMetadata.keys {
            if NSIntersectionRange(NSRange(location: key.location, length: key.length), guardRange).length > 0 {
                return nil
            }
        }

        // Map the display edit offset into storage coordinates: every link
        // before the edit is longer in storage by (storage length − display length).
        var storageOffsetDelta = 0
        for (key, meta) in previousMetadata where key.location < editedRange.location {
            storageOffsetDelta += meta.storageRange.length - key.length
        }
        let storageEditStart = editedRange.location + storageOffsetDelta
        guard storageEditStart >= 0,
              storageEditStart + oldEditLength <= nsPrevStorage.length else { return nil }

        // Splice — outside links the replaced/inserted characters are identical
        // in both forms.
        let replacement = nsDisplay.substring(with: editedRange)
        let storage = nsPrevStorage.replacingCharacters(
            in: NSRange(location: storageEditStart, length: oldEditLength),
            with: replacement
        )

        // Shift every link after the edit by the delta; links before it are untouched.
        var metadata: [RangeKey: LinkMetadata] = [:]
        metadata.reserveCapacity(previousMetadata.count)
        for (key, meta) in previousMetadata {
            if key.location >= NSMaxRange(oldEditRange) {
                metadata[RangeKey(NSRange(location: key.location + delta, length: key.length))] =
                    LinkMetadata(id: meta.id,
                                 storageRange: NSRange(location: meta.storageRange.location + delta,
                                                       length: meta.storageRange.length))
            } else {
                metadata[key] = meta
            }
        }
        return (storage, metadata)
    }

    /// Hand scan for display-form wiki links `(?<!!)\[\[...\]\]`, replacing the slow regex lookbehind.
    static func displayLinkRanges(_ s: NSString) -> [(range: NSRange, isImage: Bool)] {
        let len = s.length
        guard len >= 4 else { return [] }
        var buf = [unichar](repeating: 0, count: len)   // one bulk extract, then array access
        s.getCharacters(&buf, range: NSRange(location: 0, length: len))
        var result: [(range: NSRange, isImage: Bool)] = []
        var i = 0
        while i + 1 < len {
            guard buf[i] == 0x5B, buf[i + 1] == 0x5B else { i += 1; continue }   // [[
            let isImage = i > 0 && buf[i - 1] == 0x21                            // preceded by ! → image embed
            let start = isImage ? i - 1 : i
            var j = i + 2
            var matched = false
            while j < len {
                let c = buf[j]
                if c == 0x0A || c == 0x0D { break }                             // newline → no match
                if c == 0x5D {                                                  // ]
                    if j + 1 < len, buf[j + 1] == 0x5D {                        // ]]
                        result.append((NSRange(location: start, length: (j + 2) - start), isImage))
                        i = j + 2
                        matched = true
                    }
                    break
                }
                j += 1
            }
            if !matched { i += 1 }
        }
        return result
    }

    /// Resolve a clicked link's id from the caret's `.wikiLinkID` attribute, else its display string.
    public static func resolveIdentifier(link: Any, textView: NSTextView, at charIndex: Int) -> String? {
        if let idAttr = textView.textStorage?.attribute(.wikiLinkID, at: charIndex, effectiveRange: nil) as? String {
            return idAttr
        }
        if let name = link as? String {
            return name
        }
        return nil
    }

    /// Split a storage fragment `[[Name|<id>]]` into its display form and the opaque id.
    public static func displayFragmentAndID(from storageFragment: String) -> (display: String, id: String?) {
        let displayState = makeDisplayState(from: storageFragment)
        return (displayState.display, displayState.metadata.values.first?.id)
    }

    /// Zero-length caret range following replacement of `displayRange` with `storageFragment`.
    public static func caretRangeAfterReplacing(
        displayRange: NSRange,
        with storageFragment: String
    ) -> NSRange {
        let displayFragment = makeDisplayState(from: storageFragment).display as NSString
        return NSRange(location: displayRange.location + displayFragment.length, length: 0)
    }
}