// EGL / GLES state save and restore. rn-webrtc's EglRenderer (and downstream
// encoder paths) expect their GL state to survive our process() call;
// corrupting it surfaces as garbled output or hard-to-reproduce crashes one
// frame later. Snapshot before render, restore after, regardless of how the
// render returned.

package com.simiancraft.kaleidoscope.gpu

import android.opengl.GLES30

internal object Egl {
    private const val GL_TEXTURE_BINDING_EXTERNAL_OES = 0x8D67
    private const val GL_TEXTURE_EXTERNAL_OES = 0x8D65

    /**
     * Convert an android.graphics.Matrix (3x3 row-major affine) into a flat 16-
     * element column-major float array suitable for glUniformMatrix4fv. Z row
     * and column become identity.
     *
     * android.graphics.Matrix values layout (from Matrix.getValues):
     *   [m00 m01 m02]   [a b c]
     *   [m10 m11 m12] = [d e f]
     *   [m20 m21 m22]   [g h i]
     *
     * Caller is responsible for the float array's lifetime (no per-call alloc
     * mitigation here; if it matters, reuse a buffer).
     */
    fun matrixToGl(matrix: android.graphics.Matrix): FloatArray {
        val v = FloatArray(9)
        matrix.getValues(v)
        return floatArrayOf(
            v[0],
            v[3],
            0f,
            v[6],
            v[1],
            v[4],
            0f,
            v[7],
            0f,
            0f,
            1f,
            0f,
            v[2],
            v[5],
            0f,
            v[8],
        )
    }

    data class State(
        val viewport: IntArray,
        val activeTexture: Int,
        val texture2DBinding: Int,
        val textureExternalBinding: Int,
        val program: Int,
        val arrayBuffer: Int,
        val vao: Int,
        val framebuffer: Int,
        val blendEnabled: Boolean,
        val depthTestEnabled: Boolean,
    )

    fun save(): State =
        State(
            viewport = IntArray(4).also { GLES30.glGetIntegerv(GLES30.GL_VIEWPORT, it, 0) },
            activeTexture = getInt(GLES30.GL_ACTIVE_TEXTURE),
            texture2DBinding = getInt(GLES30.GL_TEXTURE_BINDING_2D),
            textureExternalBinding = getInt(GL_TEXTURE_BINDING_EXTERNAL_OES),
            program = getInt(GLES30.GL_CURRENT_PROGRAM),
            arrayBuffer = getInt(GLES30.GL_ARRAY_BUFFER_BINDING),
            vao = getInt(GLES30.GL_VERTEX_ARRAY_BINDING),
            framebuffer = getInt(GLES30.GL_FRAMEBUFFER_BINDING),
            blendEnabled = GLES30.glIsEnabled(GLES30.GL_BLEND),
            depthTestEnabled = GLES30.glIsEnabled(GLES30.GL_DEPTH_TEST),
        )

    fun restore(s: State) {
        GLES30.glViewport(s.viewport[0], s.viewport[1], s.viewport[2], s.viewport[3])
        GLES30.glActiveTexture(s.activeTexture)
        GLES30.glBindTexture(GLES30.GL_TEXTURE_2D, s.texture2DBinding)
        GLES30.glBindTexture(GL_TEXTURE_EXTERNAL_OES, s.textureExternalBinding)
        GLES30.glUseProgram(s.program)
        GLES30.glBindBuffer(GLES30.GL_ARRAY_BUFFER, s.arrayBuffer)
        GLES30.glBindVertexArray(s.vao)
        GLES30.glBindFramebuffer(GLES30.GL_FRAMEBUFFER, s.framebuffer)
        if (s.blendEnabled) GLES30.glEnable(GLES30.GL_BLEND) else GLES30.glDisable(GLES30.GL_BLEND)
        if (s.depthTestEnabled) {
            GLES30.glEnable(GLES30.GL_DEPTH_TEST)
        } else {
            GLES30.glDisable(GLES30.GL_DEPTH_TEST)
        }
    }

    private fun getInt(pname: Int): Int {
        val out = IntArray(1)
        GLES30.glGetIntegerv(pname, out, 0)
        return out[0]
    }
}