KMPCharts/chart-realtime/src/commonTest/kotlin/dev/dtrentin/chart/interaction/InverseProjectionTest.kt

package dev.dtrentin.chart.interaction

import androidx.compose.ui.graphics.Color
import dev.dtrentin.chart.SignalEntry
import dev.dtrentin.chart.buffer.TieredBuffer
import dev.dtrentin.chart.model.SignalConfig
import kotlin.test.Test
import kotlin.test.assertEquals
import kotlin.test.assertTrue

class InverseProjectionTest {

    // ── pixelXToTimestampMs ───────────────────────────────────────────────────

    @Test fun pixelXToTimestampMs_leftEdge() {
        val ts = InverseProjection.pixelXToTimestampMs(
            pixelX = 0f,
            chartLeft = 0f,
            chartRight = 1000f,
            windowStartMs = 100_000L,
            windowMs = 10_000L,
        )
        assertEquals(100_000L, ts)
    }

    @Test fun pixelXToTimestampMs_rightEdge() {
        val ts = InverseProjection.pixelXToTimestampMs(
            pixelX = 1000f,
            chartLeft = 0f,
            chartRight = 1000f,
            windowStartMs = 100_000L,
            windowMs = 10_000L,
        )
        assertEquals(110_000L, ts)
    }

    @Test fun pixelXToTimestampMs_middle() {
        val ts = InverseProjection.pixelXToTimestampMs(
            pixelX = 500f,
            chartLeft = 0f,
            chartRight = 1000f,
            windowStartMs = 100_000L,
            windowMs = 10_000L,
        )
        assertEquals(105_000L, ts)
    }

    @Test fun pixelXToTimestampMs_clampsBelowChartLeft() {
        val ts = InverseProjection.pixelXToTimestampMs(
            pixelX = -50f,
            chartLeft = 0f,
            chartRight = 1000f,
            windowStartMs = 100_000L,
            windowMs = 10_000L,
        )
        assertEquals(100_000L, ts) // clamped to left edge
    }

    @Test fun pixelXToTimestampMs_clampsAboveChartRight() {
        val ts = InverseProjection.pixelXToTimestampMs(
            pixelX = 5000f,
            chartLeft = 0f,
            chartRight = 1000f,
            windowStartMs = 100_000L,
            windowMs = 10_000L,
        )
        assertEquals(110_000L, ts) // clamped to right edge
    }

    @Test fun pixelXToTimestampMs_withChartLeftInset() {
        // chartLeft=52 (Y-axis label inset), chartRight=552 → 500px chart area.
        val ts = InverseProjection.pixelXToTimestampMs(
            pixelX = 302f, // 250 px into chart area = 50%
            chartLeft = 52f,
            chartRight = 552f,
            windowStartMs = 200_000L,
            windowMs = 4_000L,
        )
        assertEquals(202_000L, ts)
    }

    @Test fun pixelXToTimestampMs_degenerateChartWidth_returnsWindowStart() {
        // chartRight == chartLeft → coerced to width 1; frac clamped to [0,1].
        val ts = InverseProjection.pixelXToTimestampMs(
            pixelX = 100f,
            chartLeft = 100f,
            chartRight = 100f,
            windowStartMs = 50_000L,
            windowMs = 1000L,
        )
        // pixelX - chartLeft = 0 → frac = 0 → windowStartMs.
        assertEquals(50_000L, ts)
    }

    // ── nearestSampleValue ────────────────────────────────────────────────────

    private fun newEntry(): SignalEntry =
        SignalEntry(SignalConfig(color = Color.Red), TieredBuffer())

    /** Populate [entry] scratch arrays directly with [samples] (ts, v). */
    private fun populate(entry: SignalEntry, samples: List<Pair<Long, Float>>) {
        for ((i, s) in samples.withIndex()) {
            entry.scratchTs[i] = s.first
            entry.scratchV[i] = s.second
        }
        entry.scratchCount = samples.size
    }

    @Test fun nearestSampleValue_exactMatch() {
        val e = newEntry()
        populate(e, listOf(100L to 1f, 200L to 2f, 300L to 3f))
        assertEquals(2f, InverseProjection.nearestSampleValue(e, 200L))
    }

    @Test fun nearestSampleValue_betweenSamples_picksNearer() {
        val e = newEntry()
        populate(e, listOf(100L to 1f, 200L to 2f, 300L to 3f))
        assertEquals(2f, InverseProjection.nearestSampleValue(e, 230L)) // closer to 200
        assertEquals(3f, InverseProjection.nearestSampleValue(e, 270L)) // closer to 300
    }

    @Test fun nearestSampleValue_tieBreaksLower() {
        val e = newEntry()
        populate(e, listOf(100L to 1f, 200L to 2f))
        // Midpoint 150: |100-150| == |200-150| == 50; idxA <= idxB → idxA = lo-1 = 0 → value 1f.
        assertEquals(1f, InverseProjection.nearestSampleValue(e, 150L))
    }

    @Test fun nearestSampleValue_targetBeforeAllSamples() {
        val e = newEntry()
        populate(e, listOf(500L to 5f, 600L to 6f))
        assertEquals(5f, InverseProjection.nearestSampleValue(e, 100L))
    }

    @Test fun nearestSampleValue_targetAfterAllSamples() {
        val e = newEntry()
        populate(e, listOf(500L to 5f, 600L to 6f))
        assertEquals(6f, InverseProjection.nearestSampleValue(e, 10_000L))
    }

    @Test fun nearestSampleValue_emptyEntry_returnsNaN() {
        val e = newEntry()
        // scratchCount stays 0
        val v = InverseProjection.nearestSampleValue(e, 100L)
        assertTrue(v.isNaN())
    }

    @Test fun nearestSampleIndex_emptyReturnsNegOne() {
        val e = newEntry()
        assertEquals(-1, InverseProjection.nearestSampleIndex(e, 100L))
    }

    @Test fun nearestSampleIndex_findsClosest() {
        val e = newEntry()
        populate(e, listOf(100L to 1f, 200L to 2f, 300L to 3f))
        assertEquals(1, InverseProjection.nearestSampleIndex(e, 220L))
    }
}