import XCTest
@testable import ForgeColor

final class CurveTests: XCTestCase {

    // Default 2-point identity curve is a no-op.
    func testIdentityNoOp() {
        let c = Curve.identity
        for x: Float in [0, 0.1, 0.18, 0.5, 0.9, 1] {
            XCTAssertEqual(c.evaluate(x), x, accuracy: 1e-6)
        }
    }

    // Curve passes exactly through its control points.
    func testInterpolatesControlPoints() {
        let c = Curve(points: [
            .init(x: 0, y: 0),
            .init(x: 0.25, y: 0.4),
            .init(x: 0.75, y: 0.7),
            .init(x: 1, y: 1),
        ])
        XCTAssertEqual(c.evaluate(0.25), 0.4, accuracy: 1e-5)
        XCTAssertEqual(c.evaluate(0.75), 0.7, accuracy: 1e-5)
        XCTAssertEqual(c.evaluate(0), 0, accuracy: 1e-5)
        XCTAssertEqual(c.evaluate(1), 1, accuracy: 1e-5)
    }

    // Monotonic control points -> monotonic output (no spline overshoot ringing).
    func testMonotonicPreserved() {
        let c = Curve(points: [
            .init(x: 0, y: 0),
            .init(x: 0.1, y: 0.5),   // steep segment then flat — classic overshoot trap
            .init(x: 0.2, y: 0.55),
            .init(x: 1, y: 1),
        ])
        var prev: Float = -1
        for i in 0...1000 {
            let y = c.evaluate(Float(i) / 1000)
            XCTAssertGreaterThanOrEqual(y, prev - 1e-6, "non-monotonic at x=\(Float(i) / 1000)")
            prev = y
        }
    }

    // Input outside domain pins to endpoint values.
    func testEndpointPinning() {
        let c = Curve(points: [.init(x: 0.2, y: 0.3), .init(x: 0.8, y: 0.9)])
        XCTAssertEqual(c.evaluate(0), 0.3, accuracy: 1e-6)
        XCTAssertEqual(c.evaluate(-5), 0.3, accuracy: 1e-6)
        XCTAssertEqual(c.evaluate(1), 0.9, accuracy: 1e-6)
        XCTAssertEqual(c.evaluate(99), 0.9, accuracy: 1e-6)
    }

    // Points auto-sorted by x.
    func testUnsortedPointsSorted() {
        let c = Curve(points: [.init(x: 1, y: 1), .init(x: 0, y: 0), .init(x: 0.5, y: 0.6)])
        XCTAssertEqual(c.evaluate(0.5), 0.6, accuracy: 1e-5)
    }

    // CurveSet: master applies to all channels, then per-channel.
    func testCurveSetMasterThenChannel() {
        var set = CurveSet.identity
        set.master = Curve(points: [.init(x: 0, y: 0), .init(x: 1, y: 0.5)]) // halve
        set.red = Curve(points: [.init(x: 0, y: 0.1), .init(x: 1, y: 1.1)])  // +0.1
        let out = set.apply(SIMD3<Float>(1, 1, 1))
        XCTAssertEqual(out.x, 0.6, accuracy: 1e-4) // master 1->0.5, red 0.5->0.6
        XCTAssertEqual(out.y, 0.5, accuracy: 1e-4)
        XCTAssertEqual(out.z, 0.5, accuracy: 1e-4)
    }

    func testCurveSetIdentityNoOp() {
        let out = CurveSet.identity.apply(SIMD3<Float>(0.3, 0.6, 0.9))
        XCTAssertEqual(out.x, 0.3, accuracy: 1e-6)
        XCTAssertEqual(out.y, 0.6, accuracy: 1e-6)
        XCTAssertEqual(out.z, 0.9, accuracy: 1e-6)
    }
}