//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2020 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 the list of Swift project authors
//
//===----------------------------------------------------------------------===//

import Foundation
import LSPLogging
import LanguageServerProtocol
import SourceKitD

extension SwiftLanguageServer {

  public func completion(_ req: CompletionRequest) async throws -> CompletionList {
    guard let snapshot = documentManager.latestSnapshot(req.textDocument.uri) else {
      logger.error("failed to find snapshot for url \(req.textDocument.uri.forLogging)")
      return CompletionList(isIncomplete: true, items: [])
    }

    guard let completionPos = adjustCompletionLocation(req.position, in: snapshot) else {
      logger.error("invalid completion position \(req.position, privacy: .public)")
      return CompletionList(isIncomplete: true, items: [])
    }

    guard let offset = snapshot.utf8Offset(of: completionPos) else {
      logger.error(
        "invalid completion position \(req.position, privacy: .public) (adjusted: \(completionPos, privacy: .public)"
      )
      return CompletionList(isIncomplete: true, items: [])
    }

    let options = req.sourcekitlspOptions ?? serverOptions.completionOptions

    guard let start = snapshot.indexOf(utf8Offset: offset),
      let end = snapshot.index(of: req.position)
    else {
      logger.error("invalid completion position \(req.position, privacy: .public)")
      return CompletionList(isIncomplete: true, items: [])
    }

    let filterText = String(snapshot.text[start..<end])

    let clientSupportsSnippets = capabilityRegistry.clientCapabilities.textDocument?.completion?.completionItem?.snippetSupport ?? false
    let buildSettings = await buildSettings(for: snapshot.uri)
    return try await CodeCompletionSession.completionList(
      sourcekitd: sourcekitd,
      snapshot: snapshot,
      completionPosition: completionPos,
      completionUtf8Offset: offset,
      cursorPosition: req.position,
      compileCommand: buildSettings,
      options: options,
      clientSupportsSnippets: clientSupportsSnippets,
      filterText: filterText,
      mustReuse: req.context?.triggerKind == .triggerFromIncompleteCompletions
    )
  }

   /// Adjust completion position to the start of identifier characters.
  private func adjustCompletionLocation(_ pos: Position, in snapshot: DocumentSnapshot) -> Position? {
    guard pos.line < snapshot.lineTable.count else {
      // Line out of range.
      return nil
    }
    let lineSlice = snapshot.lineTable[pos.line]
    let startIndex = lineSlice.startIndex

    let identifierChars = CharacterSet.alphanumerics.union(CharacterSet(charactersIn: "_"))

    guard var loc = lineSlice.utf16.index(startIndex, offsetBy: pos.utf16index, limitedBy: lineSlice.endIndex) else {
      // Column out of range.
      return nil
    }
    while loc != startIndex {
      let prev = lineSlice.index(before: loc)
      if !identifierChars.contains(lineSlice.unicodeScalars[prev]) {
        break
      }
      loc = prev
    }

    // ###aabccccccdddddd
    // ^  ^- loc  ^-requestedLoc
    // `- startIndex

    let adjustedOffset = lineSlice.utf16.distance(from: startIndex, to: loc)
    return Position(line: pos.line, utf16index: adjustedOffset)
  }
}