KMPCharts/chart-realtime/src/commonTest/kotlin/dev/dtrentin/chart/lod/MinMaxLttbLodStrategyTest.kt

package dev.dtrentin.chart.lod

import kotlin.math.PI
import kotlin.math.abs
import kotlin.math.sin
import kotlin.random.Random
import kotlin.test.*
import kotlin.time.Duration
import kotlin.time.measureTime

class MinMaxLttbLodStrategyTest {

    // Tests run up to 100k samples → enlarge scratch beyond default TieredBuffer.TOTAL_CAPACITY (94_800).
    private val strategy = MinMaxLttbLodStrategy(maxCount = 100_000)
    private val outX = FloatArray(8192)
    private val outY = FloatArray(8192)

    @Test fun emptyInput_returnsZero() {
        assertEquals(0, strategy.decimate(LongArray(0), FloatArray(0), 0, 0L, 1000L, 100, outX, outY))
    }

    @Test fun zeroPixelWidth_returnsZero() {
        assertEquals(0, strategy.decimate(longArrayOf(0L), floatArrayOf(1f), 1, 0L, 1000L, 0, outX, outY))
    }

    @Test fun zeroWindowMs_returnsZero() {
        assertEquals(0, strategy.decimate(longArrayOf(0L), floatArrayOf(1f), 1, 0L, 0L, 100, outX, outY))
    }

    @Test fun fewerSamplesThanPixels_passThrough() {
        val ts = longArrayOf(0L, 500L, 1000L)
        val v = floatArrayOf(1f, 2f, 3f)
        // windowMs=1001 keeps the 1000L sample inside half-open [0, 1001).
        val n = strategy.decimate(ts, v, 3, 0L, 1001L, 100, outX, outY)
        assertEquals(3, n)
        assertEquals(1f, outY[0]); assertEquals(2f, outY[1]); assertEquals(3f, outY[2])
    }

    @Test fun upperBoundIsHalfOpen() {
        // D3: snapshot semantic is half-open [windowStartMs, windowStartMs+windowMs).
        // Sample at tRel == windowMs must be excluded.
        val ts = longArrayOf(0L, 50L, 100L, 200L)
        val v  = floatArrayOf(1f, 2f, 3f, 999f)
        val count = strategy.decimate(ts, v, 4, 0L, 200L, 100, outX, outY)
        // Boundary sample excluded → n=3 ≤ pixelWidth=100 → pass-through path with 3 points.
        assertEquals(3, count)
        for (i in 0 until count) {
            assertTrue(outY[i] != 999f, "boundary sample at tRel==windowMs must be excluded")
        }
    }

    @Test fun output_neverExceedsPixelWidth() {
        val n = 100_000
        val ts = LongArray(n) { it.toLong() }
        val v = FloatArray(n) { sin(it.toFloat() / 100f) }
        val pixels = 512
        val count = strategy.decimate(ts, v, n, 0L, n.toLong(), pixels, outX, outY)
        assertTrue(count <= pixels, "count=$count > pixelWidth=$pixels")
        assertTrue(count > 0)
    }

    @Test fun outputX_monotonicallyIncreasing() {
        val n = 100_000
        val ts = LongArray(n) { it.toLong() }
        val v = FloatArray(n) { sin(it.toFloat() / 100f) }
        val pixels = 512
        val count = strategy.decimate(ts, v, n, 0L, n.toLong(), pixels, outX, outY)
        for (i in 1 until count) {
            assertTrue(outX[i] >= outX[i - 1], "outX must be non-decreasing at $i: ${outX[i - 1]} -> ${outX[i]}")
        }
    }

    @Test fun spikePreserved_singleTallOutlier() {
        // 100k samples baseline 1f + single 1000f spike. pixelWidth=512.
        // Preselection guarantees this — bucket containing spike must emit it as max.
        val n = 100_000
        val ts = LongArray(n) { it.toLong() }
        val v = FloatArray(n) { 1f }
        v[50_000] = 1000f
        val pixels = 512
        val count = strategy.decimate(ts, v, n, 0L, n.toLong(), pixels, outX, outY)
        val maxOut = outY.copyOf(count).max()
        assertEquals(1000f, maxOut, "spike must survive preselection, got max=$maxOut")
    }

    @Test fun visualFidelity_envelopePreservedVsMinMax() {
        // Synthetic sin + noise, 100k samples, n_out=512.
        // MinMaxLttb must preserve the global min/max envelope close to pure MIN_MAX.
        val n = 100_000
        val rng = Random(seed = 42L)
        val ts = LongArray(n) { it.toLong() }
        val v = FloatArray(n) {
            (sin(2.0 * PI * it / 1000.0) * 10.0 + rng.nextDouble(-0.5, 0.5)).toFloat()
        }
        val pixels = 512

        // Pure MIN_MAX baseline.
        val minMax = MinMaxLodStrategy(maxCount = 100_000)
        val mmX = FloatArray(8192); val mmY = FloatArray(8192)
        val mmCount = minMax.decimate(ts, v, n, 0L, n.toLong(), pixels, mmX, mmY)
        val mmMin = mmY.copyOf(mmCount).min()
        val mmMax = mmY.copyOf(mmCount).max()

        // MinMaxLttb under test.
        val count = strategy.decimate(ts, v, n, 0L, n.toLong(), pixels, outX, outY)
        val outMin = outY.copyOf(count).min()
        val outMax = outY.copyOf(count).max()

        // Tolerance: 5% of (mmMax - mmMin). Preselection bound says we should see at least
        // one of the global min/max per bucket — global envelope should be near-exact.
        val tol = (mmMax - mmMin) * 0.05f
        assertTrue(abs(outMin - mmMin) <= tol, "min envelope drift: outMin=$outMin vs mmMin=$mmMin tol=$tol")
        assertTrue(abs(outMax - mmMax) <= tol, "max envelope drift: outMax=$outMax vs mmMax=$mmMax tol=$tol")
    }

    @Test fun performance_minMaxLttbNotSlowerThanPureLttb() {
        // 100k samples → 512 output. MinMaxLttb should be ≤ pure LTTB time.
        // Paper claim is ~10x; acceptance gate is ≥ 1x (≤ pure LTTB time).
        val n = 100_000
        val ts = LongArray(n) { it.toLong() }
        val v = FloatArray(n) { sin(it.toFloat() / 100f) * 10f }
        val pixels = 512

        val pureLttb = LttbLodStrategy(maxCount = 100_000)
        val minMaxLttb = MinMaxLttbLodStrategy(maxCount = 100_000)
        // Warm up both.
        repeat(3) {
            pureLttb.decimate(ts, v, n, 0L, n.toLong(), pixels, outX, outY)
            minMaxLttb.decimate(ts, v, n, 0L, n.toLong(), pixels, outX, outY)
        }

        val pureRuns = LongArray(5)
        val mmltRuns = LongArray(5)
        for (i in 0 until 5) {
            pureRuns[i] = measureTime { pureLttb.decimate(ts, v, n, 0L, n.toLong(), pixels, outX, outY) }.inWholeMicroseconds
            mmltRuns[i] = measureTime { minMaxLttb.decimate(ts, v, n, 0L, n.toLong(), pixels, outX, outY) }.inWholeMicroseconds
        }
        pureRuns.sort(); mmltRuns.sort()
        val purMedian = pureRuns[2]
        val mmlMedian = mmltRuns[2]

        // Acceptance gate per spec: MinMaxLttb ≤ pure LTTB (paper claim 10x; we require ≥1x).
        // Give 20% slack for JIT noise on shared infra.
        val slackUs = (purMedian * 0.20).toLong()
        assertTrue(
            mmlMedian <= purMedian + slackUs,
            "MinMaxLttb median=$mmlMedian us > pure LTTB median=$purMedian us (slack=$slackUs us)"
        )
        println("[perf] pureLttb median=${purMedian}us  minMaxLttb median=${mmlMedian}us  ratio=${purMedian.toDouble() / mmlMedian}x")
    }

    @Test fun customRatio_ratio2_stillValid() {
        val n = 100_000
        val ts = LongArray(n) { it.toLong() }
        val v = FloatArray(n) { sin(it.toFloat() / 100f) * 10f }
        val pixels = 512

        val s2 = MinMaxLttbLodStrategy(ratio = 2, maxCount = 100_000)
        val count = s2.decimate(ts, v, n, 0L, n.toLong(), pixels, outX, outY)
        assertTrue(count <= pixels, "ratio=2 output should still be ≤ pixelWidth, got $count")
        assertTrue(count > 0)
        // Monotonic X.
        for (i in 1 until count) {
            assertTrue(outX[i] >= outX[i - 1], "outX must be non-decreasing at $i")
        }
    }

    @Test fun ratio_lessThan1_throws() {
        assertFailsWith<IllegalArgumentException> { MinMaxLttbLodStrategy(ratio = 0) }
    }
}