import Foundation
import SourceKittenFramework

public struct OperatorUsageWhitespaceRule: OptInRule, CorrectableRule, ConfigurationProviderRule {

    public var configuration = SeverityConfiguration(.warning)

    public init() {}

    public static let description = RuleDescription(
        identifier: "operator_usage_whitespace",
        name: "Operator Usage Whitespace",
        description: "Operators should be surrounded by a single whitespace " +
                     "when they are being used.",
        kind: .style,
        nonTriggeringExamples: [
            "let foo = 1 + 2\n",
            "let foo = 1 > 2\n",
            "let foo = !false\n",
            "let foo: Int?\n",
            "let foo: Array<String>\n",
            "let model = CustomView<Container<Button>, NSAttributedString>()\n",
            "let foo: [String]\n",
            "let foo = 1 + \n  2\n",
            "let range = 1...3\n",
            "let range = 1 ... 3\n",
            "let range = 1..<3\n",
            "#if swift(>=3.0)\n    foo()\n#endif\n",
            "array.removeAtIndex(-200)\n",
            "let name = \"image-1\"\n",
            "button.setImage(#imageLiteral(resourceName: \"image-1\"), for: .normal)\n",
            "let doubleValue = -9e-11\n",
            "let foo = GenericType<(UIViewController) -> Void>()\n",
            "let foo = Foo<Bar<T>, Baz>()\n"
        ],
        triggeringExamples: [
            "let foo = 1↓+2\n",
            "let foo = 1↓   + 2\n",
            "let foo = 1↓   +    2\n",
            "let foo = 1↓ +    2\n",
            "let foo↓=1↓+2\n",
            "let foo↓=1 + 2\n",
            "let foo↓=bar\n",
            "let range = 1↓ ..<  3\n",
            "let foo = bar↓   ?? 0\n",
            "let foo = bar↓??0\n",
            "let foo = bar↓ !=  0\n",
            "let foo = bar↓ !==  bar2\n",
            "let v8 = Int8(1)↓  << 6\n",
            "let v8 = 1↓ <<  (6)\n",
            "let v8 = 1↓ <<  (6)\n let foo = 1 > 2\n"
        ],
        corrections: [
            "let foo = 1↓+2\n": "let foo = 1 + 2\n",
            "let foo = 1↓   + 2\n": "let foo = 1 + 2\n",
            "let foo = 1↓   +    2\n": "let foo = 1 + 2\n",
            "let foo = 1↓ +    2\n": "let foo = 1 + 2\n",
            "let foo↓=1↓+2\n": "let foo = 1 + 2\n",
            "let foo↓=1 + 2\n": "let foo = 1 + 2\n",
            "let foo↓=bar\n": "let foo = bar\n",
            "let range = 1↓ ..<  3\n": "let range = 1..<3\n",
            "let foo = bar↓   ?? 0\n": "let foo = bar ?? 0\n",
            "let foo = bar↓??0\n": "let foo = bar ?? 0\n",
            "let foo = bar↓ !=  0\n": "let foo = bar != 0\n",
            "let foo = bar↓ !==  bar2\n": "let foo = bar !== bar2\n",
            "let v8 = Int8(1)↓  << 6\n": "let v8 = Int8(1) << 6\n",
            "let v8 = 1↓ <<  (6)\n": "let v8 = 1 << (6)\n",
            "let v8 = 1↓ <<  (6)\n let foo = 1 > 2\n": "let v8 = 1 << (6)\n let foo = 1 > 2\n"
        ]
    )

    public func validate(file: File) -> [StyleViolation] {
        return violationRanges(file: file).map { range, _ in
            StyleViolation(ruleDescription: type(of: self).description,
                           severity: configuration.severity,
                           location: Location(file: file, characterOffset: range.location))
        }
    }

    private func violationRanges(file: File) -> [(NSRange, String)] {
        let escapedOperators = ["/", "=", "-", "+", "*", "|", "^", "~"].map({ "\\\($0)" }).joined()
        let rangePattern = "\\.\\.(?:\\.|<)" // ... or ..<
        let notEqualsPattern = "\\!\\=\\=?" // != or !==
        let coalescingPattern = "\\?{2}"

        let operators = "(?:[\(escapedOperators)%<>&]+|\(rangePattern)|\(coalescingPattern)|" +
            "\(notEqualsPattern))"

        let oneSpace = "[^\\S\\r\\n]" // to allow lines ending with operators to be valid
        let zeroSpaces = oneSpace + "{0}"
        let manySpaces = oneSpace + "{2,}"
        let leadingVariableOrNumber = "(?:\\b|\\))"
        let trailingVariableOrNumber = "(?:\\b|\\()"

        let spaces = [(zeroSpaces, zeroSpaces), (oneSpace, manySpaces),
                      (manySpaces, oneSpace), (manySpaces, manySpaces)]
        let patterns = spaces.map { first, second in
            leadingVariableOrNumber + first + operators + second + trailingVariableOrNumber
        }
        let pattern = "(?:\(patterns.joined(separator: "|")))"

        let genericPattern = "<(?:\(oneSpace)|\\S)*>" // not using dot to avoid matching new line
        let validRangePattern = leadingVariableOrNumber + zeroSpaces + rangePattern +
            zeroSpaces + trailingVariableOrNumber
        let excludingPattern = "(?:\(genericPattern)|\(validRangePattern))"

        let excludingKinds = SyntaxKind.commentAndStringKinds.union([.objectLiteral])

        return file.match(pattern: pattern, excludingSyntaxKinds: excludingKinds,
                          excludingPattern: excludingPattern).compactMap { range in

            // if it's only a number (i.e. -9e-11), it shouldn't trigger
            guard kinds(in: range, file: file) != [.number] else {
                return nil
            }

            let spacesPattern = oneSpace + "*"
            let rangeRegex = regex(spacesPattern + rangePattern + spacesPattern)

            // if it's a range operator, the correction shouldn't have spaces
            if let matchRange = rangeRegex.firstMatch(in: file.contents, options: [], range: range)?.range {
                let correction = operatorInRange(file: file, range: matchRange)
                return (matchRange, correction)
            }

            let pattern = spacesPattern + operators + spacesPattern
            let operatorsRegex = regex(pattern)

            guard let matchRange = operatorsRegex.firstMatch(in: file.contents,
                                                             options: [], range: range)?.range else {
                return nil
            }

            let operatorContent = operatorInRange(file: file, range: matchRange)
            let correction = " " + operatorContent + " "

            return (matchRange, correction)
        }
    }

    private func kinds(in range: NSRange, file: File) -> [SyntaxKind] {
        let contents = file.contents.bridge()
        guard let byteRange = contents.NSRangeToByteRange(start: range.location, length: range.length) else {
            return []
        }

        return file.syntaxMap.kinds(inByteRange: byteRange)
    }

    private func operatorInRange(file: File, range: NSRange) -> String {
        return file.contents.bridge().substring(with: range).trimmingCharacters(in: .whitespaces)
    }

    public func correct(file: File) -> [Correction] {
        let violatingRanges = violationRanges(file: file).filter { range, _ in
            return !file.ruleEnabled(violatingRanges: [range], for: self).isEmpty
        }

        var correctedContents = file.contents
        var adjustedLocations = [Int]()

        for (violatingRange, correction) in violatingRanges.reversed() {
            if let indexRange = correctedContents.nsrangeToIndexRange(violatingRange) {
                correctedContents = correctedContents
                    .replacingCharacters(in: indexRange, with: correction)
                adjustedLocations.insert(violatingRange.location, at: 0)
            }
        }

        file.write(correctedContents)

        return adjustedLocations.map {
            Correction(ruleDescription: type(of: self).description,
                       location: Location(file: file, characterOffset: $0))
        }
    }
}