import Foundation

/// 上游返回的时间戳格式并不统一（`yyyy-MM-dd HH:mm:ss`、ISO8601、秒/毫秒时间戳都出现过），
/// 列表里需要一个稳定的短读法，解析不出来时原样回退，避免出现"--"这种假结论。
public enum TimestampText {
    private static let parsers: [DateFormatter] = {
        let patterns = [
            "yyyy-MM-dd HH:mm:ss",
            "yyyy-MM-dd'T'HH:mm:ss",
            "yyyy-MM-dd HH:mm",
            "yyyy/MM/dd HH:mm:ss",
            "yyyy-MM-dd",
        ]
        return patterns.map { pattern in
            let formatter = DateFormatter()
            formatter.locale = Locale(identifier: "en_US_POSIX")
            formatter.calendar = Calendar(identifier: .gregorian)
            formatter.timeZone = .current
            formatter.dateFormat = pattern
            return formatter
        }
    }()

    private static let utcParser: DateFormatter = {
        let formatter = DateFormatter()
        formatter.locale = Locale(identifier: "en_US_POSIX")
        formatter.calendar = Calendar(identifier: .gregorian)
        formatter.timeZone = TimeZone(secondsFromGMT: 0)
        formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss"
        return formatter
    }()

    private static let timeFormat: DateFormatter = {
        let formatter = DateFormatter()
        formatter.locale = Locale(identifier: "zh_CN")
        formatter.dateFormat = "HH:mm"
        return formatter
    }()

    private static let monthDayFormat: DateFormatter = {
        let formatter = DateFormatter()
        formatter.locale = Locale(identifier: "zh_CN")
        formatter.dateFormat = "MM-dd HH:mm"
        return formatter
    }()

    private static let fullFormat: DateFormatter = {
        let formatter = DateFormatter()
        formatter.locale = Locale(identifier: "zh_CN")
        formatter.dateFormat = "yyyy-MM-dd"
        return formatter
    }()

    public static func date(from raw: String) -> Date? {
        let text = raw.trimmingCharacters(in: .whitespacesAndNewlines)
        guard text.isEmpty == false else { return nil }
        if let number = Double(text), text.allSatisfy({ $0.isNumber }) {
            // 13 位是毫秒，10 位是秒。
            return Date(timeIntervalSince1970: text.count > 11 ? number / 1000 : number)
        }
        let head = text.hasSuffix("Z") ? String(text.dropLast()) : text
        for parser in parsers {
            if let parsed = parser.date(from: head) {
                return text.hasSuffix("Z") ? utcParser.date(from: head) ?? parsed : parsed
            }
        }
        return nil
    }

    /// 今天只看时分，今年看月日，跨年才写全年份。
    public static func short(_ raw: String, now: Date = Date()) -> String {
        guard let parsed = date(from: raw) else {
            return raw.trimmingCharacters(in: .whitespacesAndNewlines)
        }
        let calendar = Calendar.current
        if calendar.isDate(parsed, inSameDayAs: now) {
            return timeFormat.string(from: parsed)
        }
        if calendar.isDate(parsed, equalTo: now, toGranularity: .year) {
            return monthDayFormat.string(from: parsed)
        }
        return fullFormat.string(from: parsed)
    }
}