KMPCharts/chart-realtime/src/commonTest/kotlin/dev/dtrentin/chart/buffer/TieredBufferTest.kt

package dev.dtrentin.chart.buffer

import kotlin.test.Test
import kotlin.test.assertEquals
import kotlin.test.assertTrue

class TieredBufferTest {

    private fun outTs() = LongArray(TieredBuffer.TOTAL_CAPACITY)
    private fun outVs() = FloatArray(TieredBuffer.TOTAL_CAPACITY)


    /**
     * Regression test for T8: legitimate sample equal to former sentinel value
     * (Float.MAX_VALUE) must not be dropped or misclassified by tier1 bin
     * accumulator. After T8 swaps sentinel-based "empty" detection for explicit
     * hasData flag, MAX_VALUE samples are retained.
     */
    @Test fun tier1BinAcceptsFloatMaxValueSample() {
        val buf = TieredBuffer()
        // All 4 pushes in tier0 (5min retention); tier1 bin = 100ms.
        // ts=0,50,99 share bin [0,100); ts=100 rolls bin and flushes prior.
        buf.push(0L, Float.MAX_VALUE)
        buf.push(50L, Float.MAX_VALUE)
        buf.push(99L, Float.MAX_VALUE)
        buf.push(100L, 1f)

        val outTs = LongArray(TieredBuffer.TOTAL_CAPACITY)
        val outV = FloatArray(TieredBuffer.TOTAL_CAPACITY)
        // Wide window covering tier0 region — should include raw samples.
        val n = buf.snapshot(0L, 10_000L, outTs, outV)
        assertTrue(n >= 4, "expected at least 4 samples in tier0 snapshot, got $n")

        var found = 0
        for (i in 0 until n) {
            if (outV[i] == Float.MAX_VALUE) found++
        }
        assertTrue(found >= 3, "expected ≥3 MAX_VALUE samples retained, got $found")
    }

    /**
     * T12: tier1 M4 bin emits first/min/max/last with their original timestamps,
     * preserving visual shape. Snapshot via direct tier1 access (no tier0 fallback)
     * by forcing time advancement well past tier0 retention.
     */
    @Test fun tier1BinPreservesM4() {
        val buf = TieredBuffer()
        // Tier1 bin = 100ms. Push 4 distinct samples into bin [0, 100):
        //   ts=0  v=5   (first)
        //   ts=30 v=1   (min)
        //   ts=60 v=10  (max)
        //   ts=90 v=3   (last)
        buf.push(0L, 5f)
        buf.push(30L, 1f)
        buf.push(60L, 10f)
        buf.push(90L, 3f)
        // Roll bin: push a sample past 100ms to trigger flush of prior bin.
        buf.push(100L, 7f)

        // Force snapshot to read from tier1 (not tier0) by advancing time past
        // tier0 retention. Push sample at tier0-window-far-future.
        val farFuture = TieredBuffer.TIER0_DURATION_MS + 200L
        buf.push(farFuture, 0f)

        val outTs = LongArray(TieredBuffer.TOTAL_CAPACITY)
        val outV = FloatArray(TieredBuffer.TOTAL_CAPACITY)
        // Window covers ts=[0, 100) — should hit tier1 (not tier0, since now - TIER0_DUR > 100).
        val n = buf.snapshot(0L, 100L, outTs, outV)

        assertTrue(n in 1..4, "expected 1..4 M4 records, got $n")

        // Strict chronological order.
        for (i in 1 until n) {
            assertTrue(outTs[i] > outTs[i - 1], "ts must be strictly increasing across M4 records at i=$i: ${outTs[i - 1]} -> ${outTs[i]}")
        }

        // First record = (ts=0, v=5f)
        assertEquals(0L, outTs[0])
        assertEquals(5f, outV[0])
        // Last record = (ts=90, v=3f)
        assertEquals(90L, outTs[n - 1])
        assertEquals(3f, outV[n - 1])

        // Min (1f) and max (10f) must appear in the snapshot.
        var hasMin = false; var hasMax = false
        for (i in 0 until n) {
            if (outV[i] == 1f) hasMin = true
            if (outV[i] == 10f) hasMax = true
        }
        assertTrue(hasMin, "min value 1f missing from M4 records")
        assertTrue(hasMax, "max value 10f missing from M4 records")
    }

    /**
     * T12: tier2 M4 bin (1Hz, 1000ms) analogous to tier1 test.
     * Forces snapshot to read from tier2 by pushing past tier0+tier1 retention.
     */
    @Test fun tier2BinPreservesM4() {
        val buf = TieredBuffer()
        // Tier2 bin = 1000ms. Push 4 distinct samples into bin [0, 1000):
        //   ts=0   v=2  (first)
        //   ts=300 v=8  (max)
        //   ts=600 v=1  (min)
        //   ts=900 v=5  (last)
        buf.push(0L, 2f)
        buf.push(300L, 8f)
        buf.push(600L, 1f)
        buf.push(900L, 5f)
        // Roll bin: push sample past 1000ms to flush prior tier2 bin.
        buf.push(1000L, 4f)

        // Force snapshot to read from tier2 by advancing past tier0 + tier1 retention.
        val farFuture = TieredBuffer.TIER0_DURATION_MS + TieredBuffer.TIER1_DURATION_MS + 2000L
        buf.push(farFuture, 0f)

        val outTs = LongArray(TieredBuffer.TOTAL_CAPACITY)
        val outV = FloatArray(TieredBuffer.TOTAL_CAPACITY)
        // Window covers ts=[0, 1000) — should hit tier2 only.
        val n = buf.snapshot(0L, 1000L, outTs, outV)

        assertTrue(n in 1..4, "expected 1..4 M4 records in tier2, got $n")

        // Strict chronological order.
        for (i in 1 until n) {
            assertTrue(outTs[i] > outTs[i - 1], "tier2 ts must be strictly increasing at i=$i")
        }

        // First & last anchors.
        assertEquals(0L, outTs[0])
        assertEquals(2f, outV[0])
        assertEquals(900L, outTs[n - 1])
        assertEquals(5f, outV[n - 1])

        var hasMin = false; var hasMax = false
        for (i in 0 until n) {
            if (outV[i] == 1f) hasMin = true
            if (outV[i] == 8f) hasMax = true
        }
        assertTrue(hasMin, "tier2 min 1f missing")
        assertTrue(hasMax, "tier2 max 8f missing")
    }

    /**
     * T12 (C7 fix): adjacent bins must not collide at the same timestamp.
     * Previous (midTs, min)/(midTs, max) pair produced a vertical spike at flush time;
     * with M4 each record carries its original ts → strict monotonicity preserved
     * across bin boundaries.
     */
    @Test fun noVerticalSpikesAtBinBoundaries() {
        val buf = TieredBuffer()
        // Bin A [0, 100): push samples that span the bin's value range.
        buf.push(10L, 4f)
        buf.push(40L, 1f)
        buf.push(70L, 9f)
        buf.push(99L, 3f)
        // Bin B [100, 200): distinct values.
        buf.push(110L, 6f)
        buf.push(140L, 2f)
        buf.push(170L, 8f)
        buf.push(199L, 5f)
        // Flush bin B by triggering a rollover.
        buf.push(200L, 7f)

        // Force snapshot from tier1.
        val farFuture = TieredBuffer.TIER0_DURATION_MS + 500L
        buf.push(farFuture, 0f)

        val outTs = LongArray(TieredBuffer.TOTAL_CAPACITY)
        val outV = FloatArray(TieredBuffer.TOTAL_CAPACITY)
        val n = buf.snapshot(0L, 200L, outTs, outV)

        assertTrue(n >= 4, "expected ≥4 tier1 records across two bins, got $n")

        // Strict monotonicity across all records, including the bin A→B boundary.
        for (i in 1 until n) {
            assertTrue(
                outTs[i] > outTs[i - 1],
                "C7 regression: ts not strictly increasing at i=$i (${outTs[i - 1]} -> ${outTs[i]})",
            )
        }
    }

    // ---------- T15: empty state ----------

    @Test fun snapshot_emptyBuffer_returnsZero() {
        val buf = TieredBuffer()
        val n = buf.snapshot(0L, 10_000L, outTs(), outVs())
        assertEquals(0, n)
    }

    @Test fun latestTimestampMs_emptyBuffer_returnsNegative() {
        val buf = TieredBuffer()
        assertEquals(-1L, buf.latestTimestampMs())
    }

    // ---------- T15: tier0 only ----------

    @Test fun tier0_singleSample_snapshotReturnsIt() {
        val buf = TieredBuffer()
        buf.push(100L, 1.5f)
        val ts = outTs(); val vs = outVs()
        val n = buf.snapshot(0L, 10_000L, ts, vs)
        assertEquals(1, n)
        assertEquals(100L, ts[0])
        assertEquals(1.5f, vs[0])
    }

    @Test fun tier0_multipleSamples_preservesOrder() {
        val buf = TieredBuffer()
        val srcTs = longArrayOf(10L, 20L, 30L, 40L, 50L)
        val srcVs = floatArrayOf(1f, 2f, 3f, 4f, 5f)
        for (i in srcTs.indices) buf.push(srcTs[i], srcVs[i])
        val ts = outTs(); val vs = outVs()
        val n = buf.snapshot(0L, 10_000L, ts, vs)
        assertEquals(5, n)
        for (i in 1 until n) {
            assertTrue(ts[i] >= ts[i - 1], "expected non-decreasing ts at i=$i")
        }
        // Values match source in order.
        for (i in 0 until n) {
            assertEquals(srcTs[i], ts[i])
            assertEquals(srcVs[i], vs[i])
        }
    }

    // ---------- T15: tier roll boundaries ----------

    @Test fun tier1Roll_singleBinFlush() {
        val buf = TieredBuffer()
        // 3 samples in tier1 bin [0, 100), then roll bin with ts=100.
        buf.push(10L, 1f)
        buf.push(40L, 2f)
        buf.push(80L, 3f)
        buf.push(100L, 4f)
        // Force tier1 snapshot path: push far-future.
        val farFuture = TieredBuffer.TIER0_DURATION_MS + 300L
        buf.push(farFuture, 9f)

        val ts = outTs(); val vs = outVs()
        val n = buf.snapshot(0L, 100L, ts, vs)
        assertTrue(n >= 1, "expected ≥1 tier1 flushed record, got $n")
        // All records inside [0, 100).
        for (i in 0 until n) {
            assertTrue(ts[i] in 0L..99L, "tier1 record out of window at i=$i: ${ts[i]}")
        }
    }

    @Test fun tier1Roll_emptyBinSkipped() {
        val buf = TieredBuffer()
        // Single sample in bin [0, 100).
        buf.push(50L, 7f)
        // Jump several empty bins ahead → roll directly to bin [500, 600).
        buf.push(550L, 8f)
        // Push another to flush bin [500, 600).
        buf.push(600L, 9f)
        // Force tier1 path.
        val farFuture = TieredBuffer.TIER0_DURATION_MS + 300L
        buf.push(farFuture, 0f)

        val ts = outTs(); val vs = outVs()
        // Window over the empty span [100, 500): expect zero records (no spurious flush).
        val n = buf.snapshot(100L, 400L, ts, vs)
        assertEquals(0, n, "empty bins between sparse samples must not produce records")
    }

    @Test fun tier2Roll_singleBinFlush() {
        val buf = TieredBuffer()
        // tier2 bin = 1000ms.
        buf.push(100L, 1f)
        buf.push(400L, 2f)
        buf.push(800L, 3f)
        // Roll tier2 bin.
        buf.push(1000L, 4f)
        // Force tier2 snapshot: push past tier0 + tier1 retention.
        val farFuture = TieredBuffer.TIER0_DURATION_MS + TieredBuffer.TIER1_DURATION_MS + 2000L
        buf.push(farFuture, 9f)

        val ts = outTs(); val vs = outVs()
        val n = buf.snapshot(0L, 1000L, ts, vs)
        assertTrue(n >= 1, "expected ≥1 tier2 record, got $n")
        for (i in 0 until n) {
            assertTrue(ts[i] in 0L..999L, "tier2 record out of window at i=$i: ${ts[i]}")
        }
    }

    // ---------- T15: window crossing tier boundaries ----------

    @Test fun snapshot_windowSpansT0T1Boundary() {
        val buf = TieredBuffer()
        // Old data destined for tier1 flush.
        buf.push(0L, 1f)
        buf.push(50L, 2f)
        buf.push(99L, 3f)
        // Flush bin [0,100).
        buf.push(100L, 4f)
        // Advance now past tier0 retention so old data exits tier0.
        val nowTs = TieredBuffer.TIER0_DURATION_MS + 1000L
        buf.push(nowTs, 5f)
        // Recent sample fresh in tier0.
        buf.push(nowTs + 100L, 6f)

        val ts = outTs(); val vs = outVs()
        // Window spans from before tier0Boundary to now → should pick up both tier1 and tier0 ranges.
        val n = buf.snapshot(0L, nowTs + 200L, ts, vs)
        assertTrue(n >= 2, "expected ≥2 samples across t0/t1, got $n")
        // Chronological non-decreasing.
        for (i in 1 until n) {
            assertTrue(ts[i] >= ts[i - 1], "non-monotonic at i=$i: ${ts[i - 1]} -> ${ts[i]}")
        }
    }

    @Test fun snapshot_windowSpansT1T2Boundary() {
        val buf = TieredBuffer()
        // Very old samples for tier2.
        buf.push(0L, 1f)
        buf.push(500L, 2f)
        // Roll tier2 bin.
        buf.push(1000L, 3f)
        // Mid-age samples for tier1.
        val tier1Start = TieredBuffer.TIER1_DURATION_MS
        buf.push(tier1Start, 10f)
        buf.push(tier1Start + 50L, 11f)
        buf.push(tier1Start + 100L, 12f)
        // Force snapshot past both tier0 + tier1 retention.
        val nowTs = TieredBuffer.TIER0_DURATION_MS + TieredBuffer.TIER1_DURATION_MS + 2000L
        buf.push(nowTs, 99f)

        val ts = outTs(); val vs = outVs()
        // Wide window covering both tier1 and tier2 regions.
        val n = buf.snapshot(0L, nowTs + 100L, ts, vs)
        assertTrue(n >= 2, "expected ≥2 records across t1/t2, got $n")
        for (i in 1 until n) {
            assertTrue(ts[i] >= ts[i - 1], "non-monotonic at i=$i")
        }
    }

    @Test fun snapshot_windowSpansAll3Tiers() {
        val buf = TieredBuffer()
        // Oldest tier2 sample.
        buf.push(0L, 1f)
        buf.push(1000L, 2f) // flush bin [0,1000)
        // Mid tier1 region.
        val tier1Start = TieredBuffer.TIER1_DURATION_MS
        buf.push(tier1Start, 5f)
        buf.push(tier1Start + 100L, 6f) // flush bin
        // Recent tier0.
        val nowTs = TieredBuffer.TIER0_DURATION_MS + TieredBuffer.TIER1_DURATION_MS + 1000L
        buf.push(nowTs, 10f)
        buf.push(nowTs + 50L, 11f)

        val ts = outTs(); val vs = outVs()
        val n = buf.snapshot(0L, nowTs + 200L, ts, vs)
        assertTrue(n >= 3, "expected ≥3 records across all tiers, got $n")
        for (i in 1 until n) {
            assertTrue(ts[i] >= ts[i - 1], "non-monotonic at i=$i: ${ts[i - 1]} -> ${ts[i]}")
        }
    }

    // ---------- T15: clear() ----------

    @Test fun clear_resetsBuffer() {
        val buf = TieredBuffer()
        for (i in 0 until 10) buf.push(i * 10L, i.toFloat())
        buf.clear()
        val n = buf.snapshot(0L, 10_000L, outTs(), outVs())
        assertEquals(0, n)
        assertEquals(-1L, buf.latestTimestampMs())
    }

    @Test fun clear_resetsBinAccumulators() {
        val buf = TieredBuffer()
        // Seed tier1 bin [0, 100) with 3 samples — pre-flush, accumulator holds state.
        buf.push(10L, 100f)
        buf.push(40L, 200f)
        buf.push(80L, 300f)
        buf.clear()

        // Push 1 fresh sample into bin [0, 100) and roll.
        buf.push(20L, 1f)
        buf.push(100L, 2f) // roll flushes the post-clear single-sample bin
        // Force tier1 snapshot.
        val farFuture = TieredBuffer.TIER0_DURATION_MS + 300L
        buf.push(farFuture, 0f)

        val ts = outTs(); val vs = outVs()
        val n = buf.snapshot(0L, 100L, ts, vs)
        assertTrue(n >= 1, "expected ≥1 post-clear tier1 record, got $n")
        // Records must only reflect post-clear data (single sample at ts=20, v=1f).
        for (i in 0 until n) {
            assertEquals(20L, ts[i], "stale ts leaked through clear at i=$i")
            assertEquals(1f, vs[i], "stale value leaked through clear at i=$i")
        }
    }

    // ---------- T15: edge cases ----------

    @Test fun snapshot_windowEntirelyBeforeData_returnsZero() {
        val buf = TieredBuffer()
        buf.push(10_000L, 1f)
        buf.push(10_500L, 2f)
        val n = buf.snapshot(0L, 5_000L, outTs(), outVs())
        assertEquals(0, n)
    }

    @Test fun snapshot_windowEntirelyAfterData_returnsZero() {
        val buf = TieredBuffer()
        buf.push(500L, 1f)
        buf.push(1_000L, 2f)
        val n = buf.snapshot(10_000L, 10_000L, outTs(), outVs())
        assertEquals(0, n)
    }

    @Test fun tier1BinHandlesSamePostFlushTimestamp() {
        val buf = TieredBuffer()
        // Bin [0, 100): single sample.
        buf.push(50L, 1f)
        // Roll to bin [100, 200) at exactly ts=100.
        buf.push(100L, 2f)
        // Another sample at the same ts=100 within new bin.
        buf.push(100L, 3f)
        // Continue with monotonic-non-decreasing ts.
        buf.push(150L, 4f)
        buf.push(200L, 5f) // roll again

        val ts = outTs(); val vs = outVs()
        // Wide window via tier0 fallback — no crash expected, sane ordering.
        val n = buf.snapshot(0L, 1_000L, ts, vs)
        assertTrue(n >= 5, "expected raw samples retained in tier0, got $n")
        for (i in 1 until n) {
            assertTrue(ts[i] >= ts[i - 1], "monotonic-non-decreasing ts violated at i=$i")
        }
    }
}