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Http4k support for Approval Testing
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package org.http4k.testing

import com.natpryce.hamkrest.MatchResult
import com.natpryce.hamkrest.MatchResult.Match
import com.natpryce.hamkrest.MatchResult.Mismatch
import com.natpryce.hamkrest.Matcher
import org.http4k.core.ContentType
import org.http4k.core.HttpMessage
import org.http4k.core.Response
import org.http4k.core.Status
import org.http4k.core.with
import org.http4k.lens.Header
import org.junit.jupiter.api.Assertions.assertEquals
import org.junit.jupiter.api.Assertions.assertNull
import org.opentest4j.AssertionFailedError
import java.io.ByteArrayInputStream
import java.io.InputStream

/**
 * Coordinates the comparison of the content for a test.
 */
interface Approver {

    /**
     * Check the content of the passed message against the previously approved content.
     */
    fun  assertApproved(httpMessage: T)

    fun withNameSuffix(suffix: String): Approver
}

class NamedResourceApprover(
    private val name: String,
    private val approvalContent: ApprovalContent,
    private val approvalSource: ApprovalSource,
    private val transformer: ApprovalTransformer<*> = ApprovalTransformer.StringWithNormalisedLineEndings()
) : Approver {

    override fun withNameSuffix(suffix: String) = NamedResourceApprover(
        name = "$name.$suffix",
        approvalContent = approvalContent,
        approvalSource = approvalSource,
        transformer = transformer,
    )

    override fun  assertApproved(httpMessage: T) {
        val approved = approvalSource.approvedFor(name)
        val actual = approvalSource.actualFor(name)
        val actualBytes = approvalContent(httpMessage).readBytes()

        with(approved.input()) {
            actual.output() // ensure the actual is removed

            when (this) {
                null -> when {
                    actualBytes.isNotEmpty() -> {
                        actual.output().write(actualBytes)
                        assertNull(actualBytes.toString(Charsets.UTF_8)) {
                            "No approved content found. To approve output:\nmv '$actual' '$approved'"
                        }
                    }

                    else -> {}
                }

                else -> try {
                    assertEquals(transformer(approvalContent(this)), transformer(ByteArrayInputStream(actualBytes))) {
                        "Mismatch. To approve output:\nmv '$actual' '$approved'"
                    }
                } catch (e: AssertionError) {
                    ByteArrayInputStream(actualBytes).copyTo(actual.output())
                    throw e
                }
            }
        }
    }
}

fun Approver.assertApproved(response: Response, expectedStatus: Status) =
    assertApproved(response.apply { assertEquals(expectedStatus, response.status) })

fun Approver.assertApproved(content: String, contentType: ContentType? = null) =
    assertApproved(Response(Status.OK).body(content).with(Header.CONTENT_TYPE of contentType))

fun Approver.assertApproved(content: InputStream, contentType: ContentType? = null) =
    assertApproved(Response(Status.OK).body(content).with(Header.CONTENT_TYPE of contentType))

/**
 * Create a Hamkrest Matcher for this message that can be combined with other Matchers
 */
fun  Approver.hasApprovedContent(): Matcher = object : Matcher {

    override val description = "has previously approved content"

    override fun invoke(actual: T): MatchResult =
        try {
            assertApproved(actual)
            Match
        } catch (e: AssertionFailedError) {
            Mismatch(e.localizedMessage)
        }
}