SwiftLint/Source/SwiftLintFramework/Rules/PrefixedTopLevelConstantRule.swift

//
//  PrefixedConstantRule.swift
//  SwiftLint
//
//  Created by Ornithologist Coder on 1/5/18.
//  Copyright © 2018 Realm. All rights reserved.
//

import Foundation
import SourceKittenFramework

public struct PrefixedTopLevelConstantRule: ASTRule, OptInRule, ConfigurationProviderRule {
    public var configuration = SeverityConfiguration(.warning)

    private let topLevelPrefix = "k"

    public init() {}

    public static let description = RuleDescription(
        identifier: "prefixed_toplevel_constant",
        name: "Prefixed Top-Level Constant",
        description: "Top-level constants should be prefixed by `k`.",
        kind: .style,
        nonTriggeringExamples: [
            "private let kFoo = 20.0",
            "public let kFoo = false",
            "internal let kFoo = \"Foo\"",
            "let kFoo = true",
            "struct Foo {\n" +
            "   let bar = 20.0\n" +
            "}",
            "private var foo = 20.0",
            "public var foo = false",
            "internal var foo = \"Foo\"",
            "var foo = true",
            "var foo = true, bar = true",
            "var foo = true, let kFoo = true",
            "let\n" +
            "    kFoo = true"
        ],
        triggeringExamples: [
            "private let ↓Foo = 20.0",
            "public let ↓Foo = false",
            "internal let ↓Foo = \"Foo\"",
            "let ↓Foo = true",
            "let ↓foo = 2, ↓bar = true",
            "var foo = true, let ↓Foo = true",
            "let\n" +
            "    ↓foo = true"
        ]
    )

    public func validate(file: File,
                         kind: SwiftDeclarationKind,
                         dictionary: [String: SourceKitRepresentable]) -> [StyleViolation] {
        guard
            kind == .varGlobal,
            let offset = dictionary.offset,
            let nameOffset = dictionary.nameOffset,
            let name = dictionary.name
            else {
                return []
        }

        let range = NSRange(location: offset, length: nameOffset - offset)

        guard isDeclaredAsConstant(in: range, on: file) && !name.hasPrefix(topLevelPrefix) else {
            return []
        }

        return [
            StyleViolation(ruleDescription: type(of: self).description,
                           severity: configuration.severity,
                           location: Location(file: file, byteOffset: nameOffset))
        ]
    }

    private func isDeclaredAsConstant(in range: NSRange, on file: File) -> Bool {
        let tokens = file.syntaxMap.tokens(inByteRange: range)
        let contents = file.contents.bridge()

        let letKeywords = tokens.filter { token in
            guard
                SyntaxKind(rawValue: token.type) == .keyword,
                let keyword = contents.substringWithByteRange(start: token.offset, length: token.length)
                else {
                    return false
            }

            return keyword == "let"
        }

        return !letKeywords.isEmpty
    }
}