// API/APIClient.swift

import Foundation
import Combine

enum APIError: Error, LocalizedError, Sendable {
    case invalidURL
    case notAuthenticated
    case serverError(String)
    case decodingError(String)
    case networkError(String)

    var errorDescription: String? {
        switch self {
        case .invalidURL:             return "Invalid URL."
        case .notAuthenticated:       return "Session expired. Please log in again."
        case .serverError(let msg):   return msg
        case .decodingError(let msg): return "Data error: \(msg)"
        case .networkError(let msg):  return "Network error: \(msg)"
        }
    }
}

// File-scope envelope — cannot be nested in a generic function (Swift restriction).
// T is constrained to Sendable so `data: T?` does not inherit @MainActor isolation.
private struct _Envelope<T: Decodable & Sendable>: Decodable, Sendable {
    let ok: Bool
    let data: T?
    let error: String?

    nonisolated init(from decoder: any Decoder) throws {
        let c = try decoder.container(keyedBy: CodingKeys.self)
        ok    = try  c.decode(Bool.self,   forKey: .ok)
        data  = try? c.decode(T.self,      forKey: .data)
        error = try? c.decode(String.self, forKey: .error)
    }
    private enum CodingKeys: String, CodingKey { case ok, data, error }
}

// Free function removed — see refreshAccessToken() which decodes using a
// local JSONDecoder to avoid Swift 6 actor-isolation errors.

// Refresh-only envelope — Sendable so it can cross actor boundaries in Swift 6.
private struct _RefreshEnvelope: Decodable, Sendable {
    struct Tokens: Decodable, Sendable {
        let accessToken: String
        let refreshToken: String
    }
    let ok: Bool
    let data: Tokens?
}

actor APIClient {
    static let shared = APIClient()

    private let session: URLSession
    private let decoder: JSONDecoder

    private init() {
        let config = URLSessionConfiguration.default
        config.timeoutIntervalForRequest = 30
        self.session = URLSession(configuration: config)
        self.decoder = JSONDecoder()
        self.decoder.keyDecodingStrategy = .convertFromSnakeCase
    }

    // ── Generic JSON Request ──────────────────────────────────────────────

    func request<T: Decodable & Sendable>(
        _ endpoint: String,
        method: String = "GET",
        body: [String: Any]? = nil,
        retrying: Bool = false
    ) async throws -> T {
        let url = try buildURL(endpoint)
        var req = buildRequest(url: url, method: method, body: body)
        injectToken(&req)

        let (data, response) = try await performRequest(req)

        if shouldRefresh(response, retrying: retrying) {
            let refreshed = await refreshAccessToken()
            if refreshed {
                return try await request(endpoint, method: method, body: body, retrying: true)
            }
            throw APIError.notAuthenticated
        }

        return try decode(data)
    }

    func post<T: Decodable & Sendable>(_ endpoint: String, body: [String: Any]) async throws -> T {
        return try await request(endpoint, method: "POST", body: body)
    }

    // ── Inspection History ────────────────────────────────────────────────

    func fetchInspectionHistory(
        limit: Int = 50,
        offset: Int = 0,
        facilityId: Int? = nil
    ) async throws -> InspectionHistoryResponseData {
        var ep = "/api/v1/inspections?limit=\(limit)&offset=\(offset)&status=completed"
        if let fid = facilityId { ep += "&facility_id=\(fid)" }
        return try await request(ep)
    }

    // ── Photo Upload ──────────────────────────────────────────────────────

    func uploadPhoto(localPath: String, entityType: String) async throws -> String {
        let url = try buildURL("/api/v1/photos/upload")

        guard let imageData = FileManager.default.contents(atPath: localPath) else {
            throw APIError.networkError("Could not read photo: \(localPath)")
        }

        let boundary = "Boundary-\(UUID().uuidString)"
        let filename = URL(fileURLWithPath: localPath).lastPathComponent
        let ext      = (filename as NSString).pathExtension.lowercased()
        let mime     = ext == "png" ? "image/png" : "image/jpeg"

        var body = Data()
        body.append("--\(boundary)\r\nContent-Disposition: form-data; name=\"entity_type\"\r\n\r\n\(entityType)\r\n".data(using: .utf8)!)
        body.append("--\(boundary)\r\nContent-Disposition: form-data; name=\"file\"; filename=\"\(filename)\"\r\nContent-Type: \(mime)\r\n\r\n".data(using: .utf8)!)
        body.append(imageData)
        body.append("\r\n--\(boundary)--\r\n".data(using: .utf8)!)

        var req = URLRequest(url: url)
        req.httpMethod = "POST"
        req.setValue("multipart/form-data; boundary=\(boundary)", forHTTPHeaderField: "Content-Type")
        injectToken(&req)
        req.httpBody = body

        let (data, response) = try await performRequest(req)

        if shouldRefresh(response, retrying: false) {
            let refreshed = await refreshAccessToken()
            if refreshed { return try await uploadPhoto(localPath: localPath, entityType: entityType) }
            throw APIError.notAuthenticated
        }

        struct PhotoResult: Decodable, Sendable { let serverPath: String }
        if let env = try? decoder.decode(_Envelope<PhotoResult>.self, from: data),
           env.ok, let r = env.data { return r.serverPath }
        throw APIError.serverError("Photo upload failed")
    }

    // ── Submit Inspection ─────────────────────────────────────────────────

    func submitInspection(_ inspection: LocalInspection) async throws -> Int {
        // Sanitise form_data: replace any field values that are still a local
        // file reference ("local://...") with an empty string.  This happens
        // when a photo upload failed but the inspection was submitted anyway.
        // JSONSerialization silently drops non-serialisable values, so without
        // this guard the server would receive a dict missing those fields
        // entirely — worse than receiving an empty string.
        var sanitisedFormData: [String: Any] = [:]
        for (k, v) in inspection.formData {
            if let s = v as? String, s.hasPrefix("local://") {
                sanitisedFormData[k] = ""   // upload failed; clear the field
            } else {
                sanitisedFormData[k] = v
            }
        }

        var body: [String: Any] = [
            "template_id":     inspection.templateServerId,
            "facility_id":     inspection.facilityServerId,
            "status":          "completed",
            "form_data":       sanitisedFormData,
            "mobile_local_id": inspection.localId,
        ]
        if let score    = inspection.overallScore  { body["overall_score"]        = score }
        if let areaId   = inspection.areaServerId  { body["area_id"]              = areaId }
        if let parentId = inspection.parentServerId { body["parent_inspection_id"] = parentId }
        if !inspection.inspectorNotes.isEmpty       { body["notes"]               = inspection.inspectorNotes }

        let fmt = ISO8601DateFormatter()
        body["inspection_date"] = fmt.string(from: inspection.inspectionDate)
        if let c = inspection.completedAt { body["completed_at"] = fmt.string(from: c) }

        struct R: Decodable, Sendable { let inspectionId: Int; let duplicate: Bool }
        let r: R = try await post("/api/v1/inspections", body: body)
        return r.inspectionId
    }

    // ── Submit Issue ──────────────────────────────────────────────────────

    func submitIssue(_ issue: LocalIssue) async throws -> Int {
        var body: [String: Any] = [
            "facility_id":     issue.facilityServerId,
            "severity":        issue.severity,
            "description":     issue.issueDescription,
            "mobile_local_id": issue.localId,
        ]
        if let id   = issue.inspection?.serverId { body["inspection_id"] = id }
        // Send the first uploaded photo as photo_path (server Issue.photo_path is a single column)
        if let firstPhoto = issue.photoServerPaths.first { body["photo_path"] = firstPhoto }

        struct R: Decodable, Sendable { let issueId: Int; let duplicate: Bool }
        let r: R = try await post("/api/v1/issues", body: body)
        return r.issueId
    }

    // ── Fetch Issue Detail (status + assigned_to) ─────────────────────────

    func fetchIssueDetail(issueId: Int) async throws -> APIIssueDetail {
        return try await request("/api/v1/issues/\(issueId)")
    }

    // ── Update Issue Status ───────────────────────────────────────────────

    func updateIssueStatus(issueId: Int, status: String) async throws -> String {
        let result: APIIssueStatusUpdate = try await request(
            "/api/v1/issues/\(issueId)/status",
            method: "PATCH",
            body: ["status": status]
        )
        return result.status
    }

    // ── Token Refresh ─────────────────────────────────────────────────────

    private func refreshAccessToken() async -> Bool {
        guard let token = KeychainHelper.get(Constants.Keychain.refreshToken),
              let url   = URL(string: Constants.baseURL + "/api/v1/auth/refresh")
        else { return false }

        var req = URLRequest(url: url)
        req.httpMethod = "POST"
        req.setValue("application/json", forHTTPHeaderField: "Content-Type")
        req.httpBody   = try? JSONSerialization.data(withJSONObject: ["refresh_token": token])

        guard let (data, response) = try? await session.data(for: req),
              let http = response as? HTTPURLResponse, http.statusCode == 200
        else { return false }

        // Use a local decoder — avoids referencing the actor-isolated self.decoder
        // which would trigger a Swift 6 main-actor isolation error.
        let localDecoder = JSONDecoder()
        localDecoder.keyDecodingStrategy = .convertFromSnakeCase
        guard let env    = try? localDecoder.decode(_RefreshEnvelope.self, from: data),
              env.ok,
              let tokens = env.data
        else { return false }

        KeychainHelper.set(tokens.accessToken,  forKey: Constants.Keychain.accessToken)
        KeychainHelper.set(tokens.refreshToken, forKey: Constants.Keychain.refreshToken)
        return true
    }

    // ── Private Helpers ───────────────────────────────────────────────────

    private func buildURL(_ endpoint: String) throws -> URL {
        guard let url = URL(string: Constants.baseURL + endpoint) else {
            throw APIError.invalidURL
        }
        return url
    }

    private func buildRequest(url: URL, method: String, body: [String: Any]?) -> URLRequest {
        var req = URLRequest(url: url)
        req.httpMethod = method
        req.setValue("application/json", forHTTPHeaderField: "Content-Type")
        if let body { req.httpBody = try? JSONSerialization.data(withJSONObject: body) }
        return req
    }

    private func injectToken(_ req: inout URLRequest) {
        if let token = KeychainHelper.get(Constants.Keychain.accessToken) {
            req.setValue("Bearer \(token)", forHTTPHeaderField: "Authorization")
        }
    }

    private func performRequest(_ req: URLRequest) async throws -> (Data, URLResponse) {
        do {
            return try await session.data(for: req)
        } catch {
            throw APIError.networkError(error.localizedDescription)
        }
    }

    private func shouldRefresh(_ response: URLResponse, retrying: Bool) -> Bool {
        guard !retrying, let http = response as? HTTPURLResponse else { return false }
        return http.statusCode == 401
    }

    private func decode<T: Decodable & Sendable>(_ data: Data) throws -> T {
        if let env = try? decoder.decode(_Envelope<T>.self, from: data) {
            if env.ok, let result = env.data { return result }
            throw APIError.serverError(env.error ?? "Unknown server error")
        }
        do {
            return try decoder.decode(T.self, from: data)
        } catch {
            throw APIError.decodingError(error.localizedDescription)
        }
    }
}