//
//  FixtureSupport.swift
//  Metrika
//
//  Author:  Simon-Pierre Boucher
//  Contact: contact@spboucher.ai
//  Copyright © 2026 Simon-Pierre Boucher. All rights reserved.
//

import Foundation
import Testing

/// Golden values produced by Tests/Fixtures/generate.R.
struct Fixtures {
    let expected: [String: Double]
    let datasetURL: URL

    init() throws {
        guard let tsv = Bundle.module.url(
            forResource: "expected", withExtension: "tsv", subdirectory: "Fixtures"
        ), let csv = Bundle.module.url(
            forResource: "regression", withExtension: "csv", subdirectory: "Fixtures"
        ) else {
            throw NSError(domain: "Fixtures", code: 1, userInfo: [
                NSLocalizedDescriptionKey: "fixture resources missing — run Tests/Fixtures/generate.R",
            ])
        }
        var values: [String: Double] = [:]
        for line in try String(contentsOf: tsv, encoding: .utf8)
            .split(separator: "\n") {
            let parts = line.split(separator: "\t")
            guard parts.count == 2, let value = Double(parts[1]) else { continue }
            values[String(parts[0])] = value
        }
        self.expected = values
        self.datasetURL = csv
    }

    subscript(key: String) -> Double {
        guard let value = expected[key] else {
            Issue.record("missing fixture key '\(key)'")
            return .nan
        }
        return value
    }
}

/// Relative-tolerance comparison (CLAUDE.md §0: CPU paths match reference
/// implementations to at least 1e-10 relative tolerance).
func expectClose(
    _ actual: Double, _ expected: Double, rtol: Double = 1e-10,
    _ label: String = "", sourceLocation: SourceLocation = #_sourceLocation
) {
    let scale = max(abs(expected), abs(actual), 1e-300)
    let relative = abs(actual - expected) / scale
    #expect(
        relative <= rtol,
        "\(label): actual \(actual) vs expected \(expected) (rel. err. \(relative))",
        sourceLocation: sourceLocation
    )
}