reports func must be more Swifty.

reports.swift

//: Playground - noun: a place where people can play

enum State {
    case Happy
    case Sad
}

struct Day {
    var name: String
    var state: State
}

struct Month {
    var name: String
    var days: [Day]
}

func reports(months: [Month]) -> (happy: Int, sad: Int, total: Int) {
    
    var total: Int = 0
    var happy: Int = 0
    var sad: Int = 0
    
    for month in months {
        for day in month.days {
            if day.state == .Happy {
                happy += 1;
            } else {
                sad += 1;
            }
            total += 1;
        }
    }
    
    return (happy, sad, total)
}

let months = [Month(name: "Month 1", days: [
                Day(name: "Day 1", state: .Happy),
                Day(name: "Day 2", state: .Happy),
                Day(name: "Day 3", state: .Sad)]),
              Month(name: "Month 2", days: [
                Day(name: "Day 1", state: .Happy),
                Day(name: "Day 2", state: .Sad),
                Day(name: "Day 3", state: .Happy),
                Day(name: "Day 4", state: .Happy)])]

let report = reports(months)

print("\(report.happy) happy days, \(report.sad) sad days, \(report.total) total")