//
//  TFLDataSource.swift
//  iris
//

import Foundation

struct TFLDataSourceConfig: Sendable {
    var cacheValiditySec: Int = 120
    var ttlSec: Int = 300
    var maxDisruptions: Int = 3

    init() {}
}

@MainActor
final class TFLDataSource {
    struct Disruption: Sendable, Equatable {
        let id: String
        let lineName: String
        let lineId: String
        let severity: Int
        let severityDescription: String
        let reason: String?
        let isMajor: Bool
    }

    struct TFLData: Sendable, Equatable {
        let disruptions: [Disruption]
    }

    struct Snapshot: Sendable {
        let data: TFLData
        let diagnostics: [String: String]
    }

    enum TFLError: Error, LocalizedError, Sendable {
        case networkFailed(message: String, diagnostics: [String: String])
        case invalidResponse(diagnostics: [String: String])

        var errorDescription: String? {
            switch self {
            case .networkFailed(let message, _):
                return message
            case .invalidResponse:
                return "Invalid TFL response"
            }
        }
    }

    private let config: TFLDataSourceConfig
    private var cache: (timestamp: Int, data: TFLData)?

    var ttlSec: Int { config.ttlSec }

    init(config: TFLDataSourceConfig = .init()) {
        self.config = config
    }

    func dataWithDiagnostics(now: Int) async throws -> Snapshot {
        var diagnostics: [String: String] = [
            "now": String(now),
            "cache_validity_sec": String(config.cacheValiditySec),
        ]

        if let cache = cache, now - cache.timestamp < config.cacheValiditySec {
            diagnostics["source"] = "cache"
            diagnostics["cache_age_sec"] = String(now - cache.timestamp)
            return Snapshot(data: cache.data, diagnostics: diagnostics)
        }

        guard let url = URL(string: "https://api.tfl.gov.uk/Line/Mode/tube,elizabeth-line/Status") else {
            throw TFLError.invalidResponse(diagnostics: diagnostics)
        }

        var request = URLRequest(url: url)
        request.setValue("application/json", forHTTPHeaderField: "Accept")

        let (data, response) = try await URLSession.shared.data(for: request)

        if let httpResponse = response as? HTTPURLResponse {
            diagnostics["http_status"] = String(httpResponse.statusCode)
            guard (200..<300).contains(httpResponse.statusCode) else {
                throw TFLError.networkFailed(
                    message: "HTTP \(httpResponse.statusCode)",
                    diagnostics: diagnostics
                )
            }
        }

        let lines = try JSONDecoder().decode([TFLLineStatus].self, from: data)
        diagnostics["source"] = "network"
        diagnostics["lines_returned"] = String(lines.count)

        var disruptions: [Disruption] = []
        var seenLines: Set<String> = []

        for line in lines {
            guard !seenLines.contains(line.id) else { continue }

            for status in line.lineStatuses {
                guard status.statusSeverity < 10 else { continue }

                seenLines.insert(line.id)
                let isMajor = status.statusSeverity <= 6

                let disruption = Disruption(
                    id: "\(line.id):\(status.statusSeverity)",
                    lineName: line.name,
                    lineId: line.id,
                    severity: status.statusSeverity,
                    severityDescription: status.statusSeverityDescription,
                    reason: status.reason ?? status.disruption?.description,
                    isMajor: isMajor
                )
                disruptions.append(disruption)
                break
            }
        }

        disruptions.sort { $0.severity < $1.severity }

        let limited = Array(disruptions.prefix(config.maxDisruptions))
        diagnostics["disruptions_found"] = String(disruptions.count)
        diagnostics["disruptions_returned"] = String(limited.count)

        let tflData = TFLData(disruptions: limited)
        cache = (timestamp: now, data: tflData)

        return Snapshot(data: tflData, diagnostics: diagnostics)
    }

    func disruptionTitle(_ disruption: Disruption) -> String {
        var name = disruption.lineName
        name = name.replacingOccurrences(of: " & City", with: "")
        name = name.replacingOccurrences(of: "Hammersmith", with: "H'smith")
        name = name.replacingOccurrences(of: "Metropolitan", with: "Met")
        name = name.replacingOccurrences(of: "Waterloo", with: "W'loo")
        name = name.replacingOccurrences(of: "Elizabeth line", with: "Eliz.")

        var severity = disruption.severityDescription
        severity = severity.replacingOccurrences(of: "Minor Delays", with: "Delays")
        severity = severity.replacingOccurrences(of: "Severe Delays", with: "Severe")
        severity = severity.replacingOccurrences(of: "Part Closure", with: "Part Closed")
        severity = severity.replacingOccurrences(of: "Part Suspended", with: "Part Susp.")

        return "\(name): \(severity)"
    }

    func disruptionSubtitle(_ disruption: Disruption) -> String {
        guard let reason = disruption.reason else {
            return "Check TFL for details"
        }
        let phrases = reason.components(separatedBy: ".")
        if let first = phrases.first?.trimmingCharacters(in: .whitespacesAndNewlines), !first.isEmpty {
            return first
        }
        return "Check TFL for details"
    }
}

// MARK: - TFL API Response Models

private struct TFLLineStatus: Codable {
    let id: String
    let name: String
    let modeName: String
    let lineStatuses: [LineStatus]

    struct LineStatus: Codable {
        let statusSeverity: Int
        let statusSeverityDescription: String
        let reason: String?
        let validityPeriods: [ValidityPeriod]?
        let disruption: Disruption?
    }

    struct ValidityPeriod: Codable {
        let fromDate: String?
        let toDate: String?
    }

    struct Disruption: Codable {
        let category: String?
        let description: String?
        let closureText: String?
    }
}