ClosureSpacingRule.swift

//
//  ClosureSpacingRule.swift
//  SwiftLint
//
//  Created by J. Cheyo Jimenez on 8/26/16.
//  Copyright © 2016 Realm. All rights reserved.
//

import Foundation
import SourceKittenFramework

public struct ClosureSpacingRule: Rule, ConfigurationProviderRule, OptInRule {

    public var configuration = SeverityConfiguration(.warning)

    public init() {}

    public static let description = RuleDescription(
        identifier: "closure_spacing",
        name: "Closure Spacing",
        description: "Closure expressions should have a single space inside each brace.",
        nonTriggeringExamples: [
            "[].map ({ $0.description })",
            "[].filter { $0.contains(location) }",
            "extension UITableViewCell: ReusableView { }",
            "extension UITableViewCell: ReusableView {}"
        ],
        triggeringExamples: [
            "[].filter(↓{$0.contains(location)})",
            "[].map(↓{$0})"
        ]
    )

    // this helps cut down the time to search through a file by
    // skipping lines that do not have at least one { and one } brace
    private func lineContainsBraces(in range: NSRange, content: NSString) -> NSRange? {
        let start = content.range(of: "{", options: [.literal], range: range)
        guard start.length != 0 else { return nil }
        let end = content.range(of: "}", options: [.literal, .backwards], range: range)
        guard end.length != 0 else { return nil }
        guard start.location < end.location else { return nil }
        return NSRange(location: start.location, length: end.location - start.location + 1)
    }

    // returns ranges of braces { or } in the same line
    private func validBraces(in file: File) -> [NSRange] {
        let nsstring = file.contents.bridge()
        let bracePattern = regex("\\{|\\}")
        let linesTokens = file.syntaxTokensByLines
        let kindsToExclude = SyntaxKind.commentAndStringKinds().map { $0.rawValue }

        // find all lines and accurences of open { and closed } braces
        var linesWithBraces = [[NSRange]]()
        for eachLine in file.lines {
            guard let nsrange = lineContainsBraces(in: eachLine.range, content: nsstring) else {
                continue
            }

            let braces = bracePattern.matches(in: file.contents, options: [],
                                              range: nsrange).map { $0.range }
            // filter out braces in comments and strings
            let tokens = linesTokens[eachLine.index].filter { kindsToExclude.contains($0.type) }
            let tokenRanges = tokens.flatMap {
                file.contents.bridge().byteRangeToNSRange(start: $0.offset, length: $0.length)
            }
            linesWithBraces.append(braces.filter({ !$0.intersects(tokenRanges) }))
        }
        return linesWithBraces.flatMap { $0 }
    }

    public func validate(file: File) -> [StyleViolation] {
        // match open braces to corresponding closing braces
        func matchBraces(validBraceLocations: [NSRange]) -> [NSRange] {
            if validBraceLocations.isEmpty { return [] }
            var validBraces = validBraceLocations
            var ranges = [NSRange]()
            var bracesAsString = validBraces.map({
                file.contents.substring(from: $0.location, length: $0.length)
            }).joined()
            while let foundRange = bracesAsString.range(of: "{}") {
                let startIndex = bracesAsString.distance(from: bracesAsString.startIndex,
                                                         to: foundRange.lowerBound)
                let location = validBraces[startIndex].location
                let length = validBraces[startIndex + 1 ].location + 1 - location
                ranges.append(NSRange(location:location, length: length))
                bracesAsString.replaceSubrange(foundRange, with: "")
                validBraces.removeSubrange(startIndex...startIndex + 1)
            }
            return ranges
        }

        // matching ranges of {}
        let matchedUpBraces = matchBraces(validBraceLocations: validBraces(in: file))

        var violationRanges = matchedUpBraces.filter {
            // removes enclosing brances to just content
            let content = file.contents.substring(from: $0.location + 1, length: $0.length - 2)
            if content.isEmpty || content == " " {
                // case when {} is not a closure
                return false
            }
            let cleaned = content.trimmingCharacters(in: .whitespaces)
            return content != " " + cleaned + " "
        }

        // filter out ranges where rule is disabled
        violationRanges = file.ruleEnabled(violatingRanges: violationRanges, for: self)

        return violationRanges.flatMap {
            StyleViolation(ruleDescription: type(of: self).description,
                           severity: configuration.severity,
                           location: Location(file: file, characterOffset: $0.location))
        }
    }
}