correx/testing/projections/src/test/kotlin/DefaultSessionReducerTest.kt

import com.correx.core.events.events.SessionCompletedEvent
import com.correx.core.events.events.SessionFailedEvent
import com.correx.core.events.events.SessionPausedEvent
import com.correx.core.events.events.SessionResumedEvent
import com.correx.core.events.events.SessionStartedEvent
import com.correx.core.events.events.StageCompletedEvent
import com.correx.core.events.events.StageFailedEvent
import com.correx.core.events.events.StageStartedEvent
import com.correx.core.events.events.TransitionExecutedEvent
import com.correx.core.events.types.SessionId
import com.correx.core.events.types.StageId
import com.correx.core.events.types.TransitionId
import com.correx.core.sessions.DefaultSessionReducer
import com.correx.core.sessions.SessionState
import com.correx.core.sessions.SessionStatus
import com.correx.testing.fixtures.EventFixtures.stored
import kotlinx.datetime.Instant
import org.junit.jupiter.api.Assertions.assertEquals
import org.junit.jupiter.api.Test

class DefaultSessionReducerTest {

    private val reducer = DefaultSessionReducer()

    private val sessionId = SessionId("session-1")

    @Test
    fun `SessionStartedEvent sets ACTIVE status`() {
        val state = initialState()

        val result = reducer.reduce(
            state = state,
            event = stored(
                sessionId = sessionId,
                payload = SessionStartedEvent(sessionId)
            )
        )

        assertEquals(SessionStatus.ACTIVE, result.status)
    }

    @Test
    fun `SessionPausedEvent sets PAUSED status`() {
        val state = activeState()

        val result = reducer.reduce(
            state = state,
            event = stored(
                sessionId = sessionId,
                payload = SessionPausedEvent(sessionId)
            )
        )

        assertEquals(SessionStatus.PAUSED, result.status)
    }

    @Test
    fun `SessionResumedEvent sets ACTIVE status`() {
        val state = pausedState()

        val result = reducer.reduce(
            state = state,
            event = stored(
                sessionId = sessionId,
                payload = SessionResumedEvent(sessionId)
            )
        )

        assertEquals(SessionStatus.ACTIVE, result.status)
    }

    @Test
    fun `SessionCompletedEvent sets COMPLETED status`() {
        val state = activeState()

        val result = reducer.reduce(
            state = state,
            event = stored(
                sessionId = sessionId,
                payload = SessionCompletedEvent(sessionId)
            )
        )

        assertEquals(SessionStatus.COMPLETED, result.status)
    }

    @Test
    fun `SessionFailedEvent sets FAILED status`() {
        val state = activeState()

        val result = reducer.reduce(
            state = state,
            event = stored(
                sessionId = sessionId,
                payload = SessionFailedEvent(sessionId)
            )
        )

        assertEquals(SessionStatus.FAILED, result.status)
    }

    @Test
    fun `StageStartedEvent sets ACTIVE status`() {
        val state = pausedState()

        val result = reducer.reduce(
            state = state,
            event = stored(
                sessionId = sessionId,
                payload = StageStartedEvent(
                    sessionId,
                    stageId = StageId("stage-a"),
                    transitionId = TransitionId("transition-a")
                )
            )
        )

        assertEquals(SessionStatus.ACTIVE, result.status)
    }

    @Test
    fun `StageCompletedEvent sets ACTIVE status`() {
        val state = pausedState()

        val result = reducer.reduce(
            state = state,
            event = stored(
                sessionId = sessionId,
                payload = StageCompletedEvent(
                    sessionId,
                    stageId = StageId("stage-a"),
                    transitionId = TransitionId("transition-a")
                )
            )
        )

        assertEquals(SessionStatus.ACTIVE, result.status)
    }

    @Test
    fun `StageFailedEvent sets FAILED status`() {
        val state = activeState()

        val result = reducer.reduce(
            state = state,
            event = stored(
                sessionId = sessionId,
                payload = StageFailedEvent(
                    sessionId,
                    stageId = StageId("stage-a"),
                    transitionId = TransitionId("transition-a"),
                    reason = "boom"
                )
            )
        )

        assertEquals(SessionStatus.FAILED, result.status)
    }

    @Test
    fun `TransitionExecutedEvent sets ACTIVE status`() {
        val state = pausedState()

        val result = reducer.reduce(
            state = state,
            event = stored(
                sessionId = sessionId,
                payload = TransitionExecutedEvent(
                    sessionId,
                    from = StageId("stage-a"),
                    to = StageId("stage-b"),
                    transitionId = TransitionId("transition-a"),
                )
            )
        )

        assertEquals(SessionStatus.ACTIVE, result.status)
    }

    @Test
    fun `createdAt is initialized once`() {
        val timestamp = Instant.parse("2026-01-01T00:00:00Z")

        val result = reducer.reduce(
            state = initialState(),
            event = stored(
                payload = SessionStartedEvent(sessionId),
                timestamp = timestamp
            )
        )

        assertEquals(timestamp, result.createdAt)
    }

    @Test
    fun `createdAt is preserved after initialization`() {
        val createdAt = Instant.parse("2026-01-01T00:00:00Z")
        val updatedAt = Instant.parse("2026-01-02T00:00:00Z")

        val state = activeState().copy(
            createdAt = createdAt
        )

        val result = reducer.reduce(
            state = state,
            event = stored(
                payload = SessionPausedEvent(sessionId),
                timestamp = updatedAt
            )
        )

        assertEquals(createdAt, result.createdAt)
    }

    @Test
    fun `updatedAt always reflects latest event timestamp`() {
        val timestamp = Instant.parse("2026-01-02T00:00:00Z")

        val result = reducer.reduce(
            state = activeState(),
            event = stored(
                payload = SessionPausedEvent(sessionId),
                timestamp = timestamp
            )
        )

        assertEquals(timestamp, result.updatedAt)
    }

    private fun initialState() =
        SessionState(
            status = SessionStatus.CREATED
        )

    private fun activeState() =
        SessionState(
            status = SessionStatus.ACTIVE
        )

    private fun pausedState() =
        SessionState(
            status = SessionStatus.PAUSED
        )
}