//
//  DateResolver.swift
//  Poche
//
//  Author:  Simon-Pierre Boucher
//  Contact: contact@spboucher.ai
//

import Foundation

/// Dates are validated by the app, never trusted from the model
/// (CLAUDE.md §4). The model supplies ISO 8601; Swift resolves and the
/// resolved date is displayed in clear text on the confirmation card.
enum DateResolutionError: LocalizedError {
    case unparseable(String)
    case inPast(Date)
    case unreasonablyFar(Date)

    var errorDescription: String? {
        switch self {
        case .unparseable(let raw):
            "la date « \(raw) » n'est pas au format ISO 8601. Redemande la date à l'utilisateur si nécessaire."
        case .inPast:
            "cette date est déjà passée. Demande à l'utilisateur la bonne date."
        case .unreasonablyFar:
            "cette date est à plus de cinq ans. Vérifie avec l'utilisateur."
        }
    }
}

enum DateResolver {
    private static let maxHorizon: TimeInterval = 5 * 365.25 * 24 * 3600

    /// Accepts "2026-08-12T09:00:00" (with or without seconds/timezone) and
    /// bare dates "2026-08-12" (resolved to 09:00 local — always shown on
    /// the confirmation card before anything is written).
    static func resolve(iso raw: String, now: Date = .now, calendar: Calendar = .current) throws -> Date {
        let trimmed = raw.trimmingCharacters(in: .whitespacesAndNewlines)
        guard let date = parse(trimmed, calendar: calendar) else {
            throw DateResolutionError.unparseable(trimmed)
        }
        guard date > now else {
            throw DateResolutionError.inPast(date)
        }
        guard date < now.addingTimeInterval(maxHorizon) else {
            throw DateResolutionError.unreasonablyFar(date)
        }
        return date
    }

    static func display(_ date: Date) -> String {
        date.formatted(date: .complete, time: .shortened)
    }

    private static func parse(_ text: String, calendar: Calendar) -> Date? {
        let withTZ = ISO8601DateFormatter()
        withTZ.formatOptions = [.withInternetDateTime]
        if let date = withTZ.date(from: text) { return date }

        // Local wall-clock time, no timezone suffix — the common model output.
        for format in ["yyyy-MM-dd'T'HH:mm:ss", "yyyy-MM-dd'T'HH:mm", "yyyy-MM-dd HH:mm"] {
            let formatter = DateFormatter()
            formatter.locale = Locale(identifier: "en_US_POSIX")
            formatter.calendar = calendar
            formatter.timeZone = calendar.timeZone
            formatter.dateFormat = format
            if let date = formatter.date(from: text) { return date }
        }

        // Bare date: default to 09:00 local.
        let dateOnly = DateFormatter()
        dateOnly.locale = Locale(identifier: "en_US_POSIX")
        dateOnly.calendar = calendar
        dateOnly.timeZone = calendar.timeZone
        dateOnly.dateFormat = "yyyy-MM-dd"
        if let day = dateOnly.date(from: text) {
            return calendar.date(bySettingHour: 9, minute: 0, second: 0, of: day)
        }
        return nil
    }
}