KMPCharts/chart-realtime/src/commonMain/kotlin/dev/dtrentin/chart/buffer/TieredBuffer.kt

package dev.dtrentin.chart.buffer

internal class TieredBuffer {

    private val tier0 = CircularBuffer(TIER0_CAPACITY)
    private val tier1 = CircularBuffer(TIER1_CAPACITY)
    private val tier2 = CircularBuffer(TIER2_CAPACITY)

    // M4 per-bin accumulator: first/min/max/last (ts, value) pairs.
    // Preserves visual shape across bin boundaries vs (midTs, min)/(midTs, max) pairs
    // that collapse to a vertical spike at flush time (C7 artifact).
    private var tier1BinStartMs = -1L
    private var tier1BinFirstTs = 0L; private var tier1BinFirstV = 0f
    private var tier1BinLastTs = 0L;  private var tier1BinLastV = 0f
    private var tier1BinMinTs = 0L;   private var tier1BinMinV = 0f
    private var tier1BinMaxTs = 0L;   private var tier1BinMaxV = 0f
    private var tier1BinHasData = false

    private var tier2BinStartMs = -1L
    private var tier2BinFirstTs = 0L; private var tier2BinFirstV = 0f
    private var tier2BinLastTs = 0L;  private var tier2BinLastV = 0f
    private var tier2BinMinTs = 0L;   private var tier2BinMinV = 0f
    private var tier2BinMaxTs = 0L;   private var tier2BinMaxV = 0f
    private var tier2BinHasData = false

    private val t0Ts = LongArray(TIER0_CAPACITY)
    private val t0Vs = FloatArray(TIER0_CAPACITY)
    private val t1Ts = LongArray(TIER1_CAPACITY)
    private val t1Vs = FloatArray(TIER1_CAPACITY)
    private val t2Ts = LongArray(TIER2_CAPACITY)
    private val t2Vs = FloatArray(TIER2_CAPACITY)

    // Reusable scratch for M4 flush sort/dedup (4 records max per bin). Avoids per-call alloc.
    private val flushTs = LongArray(4)
    private val flushVs = FloatArray(4)

    fun push(timestampMs: Long, value: Float) {
        tier0.push(timestampMs, value)
        feedTier1(timestampMs, value)
        feedTier2(timestampMs, value)
    }

    private fun feedTier1(ts: Long, value: Float) {
        if (tier1BinStartMs < 0L) {
            tier1BinStartMs = (ts / TIER1_BIN_MS) * TIER1_BIN_MS
        }
        if (ts >= tier1BinStartMs + TIER1_BIN_MS) {
            if (tier1BinHasData) {
                flushM4ToTier1()
            }
            tier1BinStartMs = (ts / TIER1_BIN_MS) * TIER1_BIN_MS
            tier1BinFirstTs = ts; tier1BinFirstV = value
            tier1BinLastTs = ts;  tier1BinLastV = value
            tier1BinMinTs = ts;   tier1BinMinV = value
            tier1BinMaxTs = ts;   tier1BinMaxV = value
            tier1BinHasData = true
        } else {
            if (!tier1BinHasData) {
                tier1BinFirstTs = ts; tier1BinFirstV = value
                tier1BinLastTs = ts;  tier1BinLastV = value
                tier1BinMinTs = ts;   tier1BinMinV = value
                tier1BinMaxTs = ts;   tier1BinMaxV = value
                tier1BinHasData = true
            } else {
                // Samples arrive in chronological order → always update last.
                tier1BinLastTs = ts; tier1BinLastV = value
                if (value < tier1BinMinV) { tier1BinMinV = value; tier1BinMinTs = ts }
                if (value > tier1BinMaxV) { tier1BinMaxV = value; tier1BinMaxTs = ts }
            }
        }
    }

    private fun feedTier2(ts: Long, value: Float) {
        if (tier2BinStartMs < 0L) {
            tier2BinStartMs = (ts / TIER2_BIN_MS) * TIER2_BIN_MS
        }
        if (ts >= tier2BinStartMs + TIER2_BIN_MS) {
            if (tier2BinHasData) {
                flushM4ToTier2()
            }
            tier2BinStartMs = (ts / TIER2_BIN_MS) * TIER2_BIN_MS
            tier2BinFirstTs = ts; tier2BinFirstV = value
            tier2BinLastTs = ts;  tier2BinLastV = value
            tier2BinMinTs = ts;   tier2BinMinV = value
            tier2BinMaxTs = ts;   tier2BinMaxV = value
            tier2BinHasData = true
        } else {
            if (!tier2BinHasData) {
                tier2BinFirstTs = ts; tier2BinFirstV = value
                tier2BinLastTs = ts;  tier2BinLastV = value
                tier2BinMinTs = ts;   tier2BinMinV = value
                tier2BinMaxTs = ts;   tier2BinMaxV = value
                tier2BinHasData = true
            } else {
                tier2BinLastTs = ts; tier2BinLastV = value
                if (value < tier2BinMinV) { tier2BinMinV = value; tier2BinMinTs = ts }
                if (value > tier2BinMaxV) { tier2BinMaxV = value; tier2BinMaxTs = ts }
            }
        }
    }

    /**
     * Push M4 records (first/min/max/last) for current tier1 bin in chronological order,
     * deduplicated by (ts, v). 4-element insertion sort. Worst case 4 distinct pushes,
     * best case 1 (single-sample bin).
     */
    private fun flushM4ToTier1() {
        flushTs[0] = tier1BinFirstTs; flushVs[0] = tier1BinFirstV
        flushTs[1] = tier1BinMinTs;   flushVs[1] = tier1BinMinV
        flushTs[2] = tier1BinMaxTs;   flushVs[2] = tier1BinMaxV
        flushTs[3] = tier1BinLastTs;  flushVs[3] = tier1BinLastV
        sort4ByTs(flushTs, flushVs)
        pushDistinctRecords(tier1, flushTs, flushVs)
    }

    private fun flushM4ToTier2() {
        flushTs[0] = tier2BinFirstTs; flushVs[0] = tier2BinFirstV
        flushTs[1] = tier2BinMinTs;   flushVs[1] = tier2BinMinV
        flushTs[2] = tier2BinMaxTs;   flushVs[2] = tier2BinMaxV
        flushTs[3] = tier2BinLastTs;  flushVs[3] = tier2BinLastV
        sort4ByTs(flushTs, flushVs)
        pushDistinctRecords(tier2, flushTs, flushVs)
    }

    private fun sort4ByTs(ts: LongArray, vs: FloatArray) {
        // Insertion sort on 4 elements. Co-sorts vs alongside ts.
        for (i in 1 until 4) {
            val tk = ts[i]; val vk = vs[i]
            var j = i - 1
            while (j >= 0 && ts[j] > tk) {
                ts[j + 1] = ts[j]; vs[j + 1] = vs[j]
                j--
            }
            ts[j + 1] = tk; vs[j + 1] = vk
        }
    }

    private fun pushDistinctRecords(target: CircularBuffer, ts: LongArray, vs: FloatArray) {
        // Push first; subsequent only if (ts, v) differs from previous pushed pair.
        target.push(ts[0], vs[0])
        var prevTs = ts[0]; var prevV = vs[0]
        for (i in 1 until 4) {
            if (ts[i] != prevTs || vs[i] != prevV) {
                target.push(ts[i], vs[i])
                prevTs = ts[i]; prevV = vs[i]
            }
        }
    }

    fun latestTimestampMs(): Long = tier0.latestTimestampMs()

    fun snapshot(
        windowStartMs: Long,
        windowMs: Long,
        outTimestamps: LongArray,
        outValues: FloatArray,
    ): Int {
        val nowMs = tier0.latestTimestampMs()
        if (nowMs < 0L) return 0

        val windowEndMs = windowStartMs + windowMs
        val tier0BoundaryMs = nowMs - TIER0_DURATION_MS
        val tier1BoundaryMs = nowMs - TIER0_DURATION_MS - TIER1_DURATION_MS

        var outIdx = 0

        if (windowStartMs < tier1BoundaryMs) {
            val n2 = tier2.snapshot(t2Ts, t2Vs)
            for (i in 0 until n2) {
                val ts = t2Ts[i]
                if (ts >= windowStartMs && ts < windowEndMs && ts < tier1BoundaryMs) {
                    if (outIdx >= outTimestamps.size) break
                    outTimestamps[outIdx] = ts; outValues[outIdx] = t2Vs[i]; outIdx++
                }
            }
        }

        if (windowStartMs < tier0BoundaryMs && windowEndMs > tier1BoundaryMs) {
            val n1 = tier1.snapshot(t1Ts, t1Vs)
            for (i in 0 until n1) {
                val ts = t1Ts[i]
                if (ts >= windowStartMs && ts < windowEndMs && ts >= tier1BoundaryMs && ts < tier0BoundaryMs) {
                    if (outIdx >= outTimestamps.size) break
                    outTimestamps[outIdx] = ts; outValues[outIdx] = t1Vs[i]; outIdx++
                }
            }
        }

        val tier0Start = maxOf(windowStartMs, tier0BoundaryMs)
        val n0 = tier0.snapshot(t0Ts, t0Vs)
        for (i in 0 until n0) {
            val ts = t0Ts[i]
            if (ts >= tier0Start && ts < windowEndMs) {
                if (outIdx >= outTimestamps.size) break
                outTimestamps[outIdx] = ts; outValues[outIdx] = t0Vs[i]; outIdx++
            }
        }

        return outIdx
    }

    /**
     * Bisect-based variant of [snapshot]. Returns identical content + ordering for the
     * same (windowStartMs, windowMs) args, but locates the window-start index in each
     * tier's chronologically-sorted snapshot via O(log n) bisect instead of an
     * O(n) linear pre-scan. Linear walk runs only over the in-window subrange.
     *
     * Output ordering: tier2 oldest first, then tier1, then tier0 newest — same as [snapshot].
     * Tier boundary clamps (tier0BoundaryMs / tier1BoundaryMs) preserved verbatim.
     *
     * Returns 0 on empty buffer or window entirely outside data.
     */
    fun snapshotWindow(
        windowStartMs: Long,
        windowMs: Long,
        outTimestamps: LongArray,
        outValues: FloatArray,
    ): Int {
        val nowMs = tier0.latestTimestampMs()
        if (nowMs < 0L) return 0

        val windowEndMs = windowStartMs + windowMs
        val tier0BoundaryMs = nowMs - TIER0_DURATION_MS
        val tier1BoundaryMs = nowMs - TIER0_DURATION_MS - TIER1_DURATION_MS

        var outIdx = 0

        if (windowStartMs < tier1BoundaryMs) {
            val n2 = tier2.snapshot(t2Ts, t2Vs)
            // Tier2 records satisfy ts < tier1BoundaryMs (older than tier1 horizon),
            // so upper clamp is min(windowEndMs, tier1BoundaryMs).
            val tier2UpperExclusive = if (windowEndMs < tier1BoundaryMs) windowEndMs else tier1BoundaryMs
            val start = bisectStart(t2Ts, n2, windowStartMs)
            var i = start
            while (i < n2) {
                val ts = t2Ts[i]
                if (ts >= tier2UpperExclusive) break
                if (outIdx >= outTimestamps.size) return outIdx
                outTimestamps[outIdx] = ts; outValues[outIdx] = t2Vs[i]; outIdx++
                i++
            }
        }

        if (windowStartMs < tier0BoundaryMs && windowEndMs > tier1BoundaryMs) {
            val n1 = tier1.snapshot(t1Ts, t1Vs)
            // Tier1 records satisfy tier1BoundaryMs <= ts < tier0BoundaryMs.
            val tier1Lower = if (windowStartMs > tier1BoundaryMs) windowStartMs else tier1BoundaryMs
            val tier1UpperExclusive = if (windowEndMs < tier0BoundaryMs) windowEndMs else tier0BoundaryMs
            val start = bisectStart(t1Ts, n1, tier1Lower)
            var i = start
            while (i < n1) {
                val ts = t1Ts[i]
                if (ts >= tier1UpperExclusive) break
                if (outIdx >= outTimestamps.size) return outIdx
                outTimestamps[outIdx] = ts; outValues[outIdx] = t1Vs[i]; outIdx++
                i++
            }
        }

        val tier0Start = if (windowStartMs > tier0BoundaryMs) windowStartMs else tier0BoundaryMs
        val n0 = tier0.snapshot(t0Ts, t0Vs)
        val start0 = bisectStart(t0Ts, n0, tier0Start)
        var i = start0
        while (i < n0) {
            val ts = t0Ts[i]
            if (ts >= windowEndMs) break
            if (outIdx >= outTimestamps.size) return outIdx
            outTimestamps[outIdx] = ts; outValues[outIdx] = t0Vs[i]; outIdx++
            i++
        }

        return outIdx
    }

    fun clear() {
        tier0.clear(); tier1.clear(); tier2.clear()
        tier1BinStartMs = -1L
        tier1BinFirstTs = 0L; tier1BinFirstV = 0f
        tier1BinLastTs = 0L;  tier1BinLastV = 0f
        tier1BinMinTs = 0L;   tier1BinMinV = 0f
        tier1BinMaxTs = 0L;   tier1BinMaxV = 0f
        tier1BinHasData = false
        tier2BinStartMs = -1L
        tier2BinFirstTs = 0L; tier2BinFirstV = 0f
        tier2BinLastTs = 0L;  tier2BinLastV = 0f
        tier2BinMinTs = 0L;   tier2BinMinV = 0f
        tier2BinMaxTs = 0L;   tier2BinMaxV = 0f
        tier2BinHasData = false
    }

    /**
     * Tier capacities. TIER1/TIER2 multiplied by 4 because M4 binning (T12) emits up to
     * 4 records per bin (first, min, max, last) instead of the previous 2 (min, max).
     * Steady-state average likely 2–3 records/bin after (ts, v) dedup; ×4 is safe upper bound.
     *
     * TIER0_CAPACITY: 5 min × 200 Hz = 60_000 raw samples.
     * TIER1_CAPACITY: 10 min × 10 Hz × 4 M4 records = 24_000 records.
     * TIER2_CAPACITY: 45 min × 1  Hz × 4 M4 records = 10_800 records.
     * TOTAL_CAPACITY: 94_800 samples per signal.
     */
    internal companion object {
        const val TIER0_MAX_HZ = 200
        const val TIER1_HZ = 10
        const val TIER2_HZ = 1

        const val TIER0_DURATION_MS = 5L * 60_000L
        const val TIER1_DURATION_MS = 10L * 60_000L
        const val TIER2_DURATION_MS = 45L * 60_000L

        const val TIER1_BIN_MS = 1000L / TIER1_HZ
        const val TIER2_BIN_MS = 1000L / TIER2_HZ

        val TIER0_CAPACITY = ((TIER0_DURATION_MS / 1000L) * TIER0_MAX_HZ).toInt()
        val TIER1_CAPACITY = ((TIER1_DURATION_MS / 1000L) * TIER1_HZ).toInt() * 4
        val TIER2_CAPACITY = ((TIER2_DURATION_MS / 1000L) * TIER2_HZ).toInt() * 4
        val TOTAL_CAPACITY = TIER0_CAPACITY + TIER1_CAPACITY + TIER2_CAPACITY
    }
}