import Testing
import Foundation
import GRDB
@testable import Music

/// Tests for the remote-DB transfer integrity guard. The bug under test: connecting to
/// a remote host downloaded a database that opened with "database disk image is malformed"
/// (SQLITE_CORRUPT) on `SELECT * FROM sqlite_master`. The fix validates the database with
/// `PRAGMA quick_check` on both ends (host before serving, client after writing) so a
/// malformed image is rejected with a clear error instead of crashing the UI.
@MainActor
struct RemoteDBIntegrityTests {

    /// Build a real DatabaseService (DatabasePool/WAL, like the running app) at a fresh
    /// temp path, populated with `count` tracks, and return (tempDir, dbPath).
    private func makePopulatedDB(count: Int) throws -> (dir: URL, path: String) {
        let tempDir = FileManager.default.temporaryDirectory.appendingPathComponent(UUID().uuidString)
        try FileManager.default.createDirectory(at: tempDir, withIntermediateDirectories: true)
        let path = tempDir.appendingPathComponent("src.sqlite").path
        let db = try DatabaseService(path: path)
        for i in 1...count {
            var t = Track.fixture(fileURL: "/track\(i).mp3", title: "Song number \(i) with several words")
            try db.insert(&t)
        }
        return (tempDir, path)
    }

    @Test
    func backupCopyIsWellFormedAndSurvivesHTTPFraming() throws {
        // 1. Build a source DB large enough to span many pages, like the real ~5.8MB library.
        let (tempDir, srcPath) = try makePopulatedDB(count: 2000)
        defer { try? FileManager.default.removeItem(at: tempDir) }

        // 2. Produce the served copy exactly as the host does (VACUUM INTO via backup()).
        let copyPath = tempDir.appendingPathComponent("copy.sqlite").path
        try DatabaseService(path: srcPath).backup(to: copyPath)

        // 3. The copy must pass the integrity gate the host now applies before serving.
        #expect(DatabaseService.isWellFormedDatabase(atPath: copyPath))

        // 4. Frame the copy into an HTTP response byte-for-byte like HostServer.sendHTTP,
        //    then parse it back like RemoteClient.handleDBData (split on the first \r\n\r\n).
        let bodyBytes = try Data(contentsOf: URL(fileURLWithPath: copyPath))
        var response = Data("HTTP/1.1 200 OK\r\nContent-Type: application/octet-stream\r\nContent-Length: \(bodyBytes.count)\r\nConnection: close\r\n\r\n".utf8)
        response.append(bodyBytes)
        let separator: [UInt8] = [0x0D, 0x0A, 0x0D, 0x0A]
        let sepRange = try #require(response.range(of: Data(separator)))
        let parsedBody = Data(response[sepRange.upperBound...])

        // 5. The framed-then-parsed body must be byte-identical to the original copy.
        #expect(parsedBody == bodyBytes)

        // 6. Writing it out yields a DB that passes the gate, opens cleanly, and has all rows.
        let recvPath = tempDir.appendingPathComponent("received.sqlite").path
        try parsedBody.write(to: URL(fileURLWithPath: recvPath))
        #expect(DatabaseService.isWellFormedDatabase(atPath: recvPath))
        let reopened = try DatabaseService(path: recvPath)
        let n = try reopened.dbPool.read { db in try Int.fetchOne(db, sql: "SELECT count(*) FROM tracks") }
        #expect(n == 2000)
    }

    @Test
    func truncatedDownloadIsRejected() throws {
        // Reproduces the user's exact symptom: a page-aligned but incomplete SQLite image.
        // 1. Build a valid served copy.
        let (tempDir, srcPath) = try makePopulatedDB(count: 2000)
        defer { try? FileManager.default.removeItem(at: tempDir) }
        let copyPath = tempDir.appendingPathComponent("copy.sqlite").path
        try DatabaseService(path: srcPath).backup(to: copyPath)
        let full = try Data(contentsOf: URL(fileURLWithPath: copyPath))

        // 2. Keep the first half — still a whole number of 4096-byte pages with a valid
        //    SQLite header, exactly the shape of the user's "5828608 bytes" malformed file.
        let truncatedLen = (full.count / 2 / 4096) * 4096
        let truncated = Data(full.prefix(truncatedLen))
        let truncPath = tempDir.appendingPathComponent("truncated.sqlite").path
        try truncated.write(to: URL(fileURLWithPath: truncPath))

        // 3. The gate must reject it. Before the fix the client handed this straight to
        //    GRDB, which crashed with "database disk image is malformed".
        #expect(DatabaseService.isWellFormedDatabase(atPath: truncPath) == false)
    }

    @Test
    func corruptInteriorBytesAreRejected() throws {
        // 1. Build a valid served copy.
        let (tempDir, srcPath) = try makePopulatedDB(count: 2000)
        defer { try? FileManager.default.removeItem(at: tempDir) }
        let copyPath = tempDir.appendingPathComponent("copy.sqlite").path
        try DatabaseService(path: srcPath).backup(to: copyPath)
        var bytes = try Data(contentsOf: URL(fileURLWithPath: copyPath))

        // 2. Leave the SQLite header intact (so it's still recognized as a database — this
        //    yields SQLITE_CORRUPT/error 11, like the user saw, not "not a database"/error 26)
        //    but smash a stretch of an interior b-tree page.
        for i in 4096..<4600 { bytes[i] = 0xFF }
        let corruptPath = tempDir.appendingPathComponent("corrupt.sqlite").path
        try bytes.write(to: URL(fileURLWithPath: corruptPath))

        // 3. The gate must reject the malformed image.
        #expect(DatabaseService.isWellFormedDatabase(atPath: corruptPath) == false)
    }

    @Test
    func emptyMissingAndGarbageFilesAreRejected() throws {
        let tempDir = FileManager.default.temporaryDirectory.appendingPathComponent(UUID().uuidString)
        try FileManager.default.createDirectory(at: tempDir, withIntermediateDirectories: true)
        defer { try? FileManager.default.removeItem(at: tempDir) }

        // 1. A missing file is not well-formed.
        #expect(DatabaseService.isWellFormedDatabase(atPath: tempDir.appendingPathComponent("nope.sqlite").path) == false)

        // 2. An empty file (0 bytes) is not well-formed.
        let emptyPath = tempDir.appendingPathComponent("empty.sqlite").path
        try Data().write(to: URL(fileURLWithPath: emptyPath))
        #expect(DatabaseService.isWellFormedDatabase(atPath: emptyPath) == false)

        // 3. A short text body (e.g. an HTTP error message written as if it were a DB) is rejected.
        let garbagePath = tempDir.appendingPathComponent("garbage.sqlite").path
        try Data("Failed to read database".utf8).write(to: URL(fileURLWithPath: garbagePath))
        #expect(DatabaseService.isWellFormedDatabase(atPath: garbagePath) == false)
    }
}