import Foundation
import XCTest

final class ViewDerivedDataTests: XCTestCase {
  func testGenericListViewDerivedCollectionsAreReferencedOncePerRenderPass() throws {
    let source = try loadSource(at: "Sora/Views/Generic/GenericListView.swift")
    let normalizedSource = strippingCommentsAndStrings(from: source)

    let filteredItemsUsages = referenceCount(
      for: "filteredItems",
      in: normalizedSource
    )
    let sortedFilteredItemsUsages = referenceCount(
      for: "sortedFilteredItems",
      in: normalizedSource
    )

    // swiftlint:disable:next prefer_nimble
    XCTAssertLessThanOrEqual(
      filteredItemsUsages,
      1,
      "filteredItems should be consumed once per dependency change."
    )
    // swiftlint:disable:next prefer_nimble
    XCTAssertLessThanOrEqual(
      sortedFilteredItemsUsages,
      1,
      "sortedFilteredItems should be consumed once per dependency change."
    )
  }

  func testPostGridViewDerivedCollectionsAreReferencedOncePerRenderPass() throws {
    let source = try loadSource(at: "Sora/Views/Post/Grid/PostGridView.swift")
    let normalizedSource = strippingCommentsAndStrings(from: source)

    let activePostsUsages = referenceCount(
      for: "activePosts",
      in: normalizedSource
    )
    let getColumnsDataUsages = invocationCount(
      forFunction: "getColumnsData",
      in: normalizedSource
    )

    // swiftlint:disable:next prefer_nimble
    XCTAssertLessThanOrEqual(
      activePostsUsages,
      1,
      "activePosts-derived data should be consumed once per dependency change."
    )
    // swiftlint:disable:next prefer_nimble
    XCTAssertLessThanOrEqual(
      getColumnsDataUsages,
      1,
      "getColumnsData should be invoked once per dependency change."
    )
  }

  private func loadSource(at relativePath: String) throws -> String {
    let currentFile = URL(fileURLWithPath: #filePath)
    let repositoryRoot = currentFile.deletingLastPathComponent().deletingLastPathComponent()
    let fileURL = repositoryRoot.appendingPathComponent(relativePath)

    return try String(contentsOf: fileURL, encoding: .utf8)
  }

  // swiftlint:disable:next cyclomatic_complexity
  private func strippingCommentsAndStrings(from source: String) -> String {
    let characters = Array(source)
    var result: [Character] = []
    result.reserveCapacity(characters.count)

    var currentOffset = 0
    var inLineComment = false
    var blockCommentDepth = 0
    var inString = false
    var isEscaped = false

    while currentOffset < characters.count {
      let current = characters[currentOffset]
      let next: Character? = currentOffset + 1 < characters.count ? characters[currentOffset + 1] : nil

      if inLineComment {
        if current == "\n" {
          inLineComment = false
          result.append("\n")
        } else {
          result.append(" ")
        }
        currentOffset += 1
        continue
      }

      if blockCommentDepth > 0 {
        if current == "/", next == "*" {
          blockCommentDepth += 1
          result.append(" ")
          result.append(" ")
          currentOffset += 2
          continue
        }

        if current == "*", next == "/" {
          blockCommentDepth -= 1
          result.append(" ")
          result.append(" ")
          currentOffset += 2
          continue
        }

        result.append(current == "\n" ? "\n" : " ")
        currentOffset += 1
        continue
      }

      if inString {
        if isEscaped {
          isEscaped = false
        } else if current == "\\" {
          isEscaped = true
        } else if current == "\"" {
          inString = false
        }

        result.append(current == "\n" ? "\n" : " ")
        currentOffset += 1
        continue
      }

      if current == "/", next == "/" {
        inLineComment = true
        result.append(" ")
        result.append(" ")
        currentOffset += 2
        continue
      }

      if current == "/", next == "*" {
        blockCommentDepth = 1
        result.append(" ")
        result.append(" ")
        currentOffset += 2
        continue
      }

      if current == "\"" {
        inString = true
        result.append(" ")
        currentOffset += 1
        continue
      }

      result.append(current)
      currentOffset += 1
    }

    return String(result)
  }

  private func referenceCount(for symbol: String, in source: String) -> Int {
    let totalMatches = tokenCount(
      matching: #"\b\#(symbol)\b"#,
      in: source
    )
    let declarationMatches = tokenCount(
      matching: #"\b(?:var|let)\s+\#(symbol)\b"#,
      in: source
    )

    return max(0, totalMatches - declarationMatches)
  }

  private func invocationCount(forFunction name: String, in source: String) -> Int {
    let totalMatches = tokenCount(
      matching: #"\b\#(name)\s*\("#,
      in: source
    )
    let declarationMatches = tokenCount(
      matching: #"\bfunc\s+\#(name)\s*\("#,
      in: source
    )

    return max(0, totalMatches - declarationMatches)
  }

  private func tokenCount(matching pattern: String, in source: String) -> Int {
    guard let regex = try? NSRegularExpression(pattern: pattern) else { return 0 }
    let range = NSRange(source.startIndex..<source.endIndex, in: source)

    return regex.numberOfMatches(in: source, range: range)
  }
}