// ===----------------------------------------------------------------------===
//
// This source file is part of the ASConnectService open source project
//
// Copyright (c) 2026 Röck+Cöde VoF. and the ASConnectService project authors
// Licensed under Apache license v2.0
//
// See LICENSE for license information
// See CONTRIBUTORS for the list of ASConnectService project authors
//
// SPDX-License-Identifier: Apache-2.0
//
// ===----------------------------------------------------------------------===

import Foundation
import HTTPTypes
import OpenAPIRuntime
import Testing

// A non-testable import ensures that the sequence can be created from outside the module.
import ASConnectService

@Suite("PagedSequence")
struct PagedSequenceTests {
    // MARK: Properties

    private let server = Server(pages: 3)

    // MARK: Tests

    @Test("Fetches every page, passing the cursor of each next link")
    func fetchesEveryPage() async throws {
        var pages: [Int] = []

        for try await page in makeSequence() {
            pages.append(page.number)
        }

        #expect(pages == [1, 2, 3])
        #expect(await server.cursors == [nil, "2", "3"])
    }

    @Test("Does not fetch any page until the sequence is iterated")
    func fetchesLazily() async throws {
        _ = makeSequence()

        #expect(await server.cursors.isEmpty)
    }

    @Test("Finishes the iteration after a fetch throws")
    func finishesAfterError() async throws {
        await server.fail(atPage: 2)

        var iterator = makeSequence().makeAsyncIterator()

        #expect(try await iterator.next()?.number == 1)

        do {
            _ = try await iterator.next()

            Issue.record("Fetching the second page should throw")
        } catch {
            #expect(error is ServerError)
        }

        #expect(try await iterator.next() == nil)
        #expect(await server.cursors == [nil, "2"])
    }

    @Test("Pages through a generated operation, sending the cursor as a query parameter")
    func pagesThroughGeneratedOperation() async throws {
        let transport = PagedTransport()
        let client = Client(
            serverURL: try Servers.Server1.url(),
            transport: transport
        )

        let pages = PagedSequence(links: \.links) { cursor in
            try await client.appsGetCollection(query: .init(limit: 200, cursor: cursor)).ok.body.json
        }

        var count = 0

        for try await _ in pages {
            count += 1
        }

        #expect(count == 2)
        #expect(await transport.paths == ["/v1/apps?limit=200", "/v1/apps?limit=200&cursor=Mg"])
    }
}

// MARK: - Helpers

private extension PagedSequenceTests {
    func makeSequence() -> PagedSequence<TestPage> {
        let server = server

        return PagedSequence(links: \.links) { cursor in
            try await server.page(at: cursor)
        }
    }
}

/// A page of a paged operation.
private struct TestPage: Sendable {
    let number: Int
    let links: Components.Schemas.PagedDocumentLinks
}

/// An actor that serves a number of pages, and records the cursors it is asked for.
private actor Server {
    private let pages: Int
    private var failingPage: Int?

    private(set) var cursors: [String?] = []

    init(pages: Int) {
        self.pages = pages
    }

    func fail(atPage page: Int) {
        failingPage = page
    }

    func page(at cursor: String?) throws -> TestPage {
        cursors.append(cursor)

        let number = cursor.flatMap { Int($0) } ?? 1

        if number == failingPage {
            throw ServerError.unavailable
        }

        let base = "https://api.appstoreconnect.apple.com/v1/apps"

        return TestPage(
            number: number,
            links: .init(
                _self: base,
                next: number < pages ? "\(base)?cursor=\(number + 1)" : nil
            )
        )
    }
}

/// An error thrown by the server.
private enum ServerError: Error {
    case unavailable
}

/// A transport that serves two pages of apps, and records the paths of the requests it sends.
private actor PagedTransport: ClientTransport {
    private(set) var paths: [String?] = []

    func send(
        _ request: HTTPRequest,
        body: HTTPBody?,
        baseURL: URL,
        operationID: String
    ) async throws -> (HTTPResponse, HTTPBody?) {
        paths.append(request.path)

        let isFirstPage = paths.count == 1
        let next = isFirstPage ? #", "next": "https://api.appstoreconnect.apple.com/v1/apps?cursor=Mg&limit=200""# : ""
        let json = #"{ "data": [], "links": { "self": "https://api.appstoreconnect.apple.com/v1/apps"\#(next) } }"#

        return (
            HTTPResponse(status: .ok, headerFields: [.contentType: "application/json"]),
            HTTPBody(json)
        )
    }
}