ai-app/app/androidApp/src/main/kotlin/com/example/aiapp/SettingsScreen.kt

package com.example.aiapp

import android.Manifest
import android.content.pm.PackageManager
import androidx.activity.compose.rememberLauncherForActivityResult
import androidx.activity.result.contract.ActivityResultContracts
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.Row
import androidx.compose.foundation.layout.Spacer
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.height
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.layout.width
import androidx.compose.material3.Button
import androidx.compose.material3.MaterialTheme
import androidx.compose.material3.OutlinedButton
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.setValue
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.platform.LocalContext
import androidx.compose.ui.unit.dp
import androidx.core.net.toUri
import com.example.wgapplink.EnrollmentScanActivity
import com.google.zxing.client.android.Intents
import com.journeyapps.barcodescanner.ScanContract
import com.journeyapps.barcodescanner.ScanIntentResult
import com.journeyapps.barcodescanner.ScanOptions

/**
 * Server address and token. The normal path is the "Scan QR code" button below, which decodes the
 * server's terminal QR itself; these fields are the fallback for typing the same three values by
 * hand. [onBack] is null on first run, when there is nothing to go back to.
 */
@Composable
fun SettingsScreen(
    existing: ServerSettings?,
    onSaved: (ServerSettings) -> Unit,
    onBack: (() -> Unit)?,
) {
    val context = LocalContext.current
    var host by remember { mutableStateOf(existing?.host ?: "10.66.0.1") }
    var port by remember { mutableStateOf((existing?.port ?: 8443).toString()) }
    // Never pre-filled from the stored token: this screen shouldn't be a way to read the credential
    // back off the device.
    var token by remember { mutableStateOf("") }
    var error by remember { mutableStateOf<String?>(null) }

    val scanLauncher =
        rememberLauncherForActivityResult(ScanContract()) { result: ScanIntentResult ->
            // Null contents means the user backed out of the scanner -- not an error.
            val contents = result.contents ?: return@rememberLauncherForActivityResult
            val settings = parseEnrollmentUri(contents.toUri())
            if (settings == null) {
                error = "Not a valid enrollment code"
            } else {
                saveServerSettings(context, settings)
                onSaved(settings)
            }
        }

    val requestCamera =
        rememberLauncherForActivityResult(ActivityResultContracts.RequestPermission()) { granted ->
            if (granted) {
                scanLauncher.launch(enrollmentScanOptions())
            } else {
                error =
                    "Scanning needs the camera. Grant it in the system settings, " +
                        "or type the host, port and token in below."
            }
        }

    Column(Modifier.fillMaxSize().padding(16.dp)) {
        Row(verticalAlignment = Alignment.CenterVertically, modifier = Modifier.fillMaxWidth()) {
            // Leading, where a back arrow points at what it returns to. Trailing it would put a
            // left-pointing arrow at the right edge, aimed across the title it sits beside.
            //
            // Absent rather than disabled on first run, which is the one place this app lets a
            // control come and go: there is no screen underneath yet, so a Back here would not be a
            // capability being withheld but a promise it could not keep.
            if (onBack != null) {
                GlyphButton(BACK_GLYPH, "Back", onBack)
                Spacer(Modifier.width(GLYPH_BUTTON_MARGIN))
            }
            Text(
                "Server",
                style = MaterialTheme.typography.headlineSmall,
                modifier = Modifier.weight(1f),
            )
        }
        Spacer(Modifier.height(8.dp))
        Text(
            "The easy way: run ai-server on the backend and scan the QR it prints. " +
                "Or type the same values here.",
            style = MaterialTheme.typography.bodyMedium,
            color = MaterialTheme.colorScheme.onSurfaceVariant,
        )
        Spacer(Modifier.height(16.dp))

        OutlinedButton(
            onClick = {
                // Hold the camera permission before the scanner starts. Letting its activity ask on
                // our behalf is what the library does by default, and it opens the camera without
                // waiting for the answer: the first-ever scan comes up as a live preview with
                // "Sorry, the Android camera encountered a problem" over it, and works on the
                // second try.
                if (
                    context.checkSelfPermission(Manifest.permission.CAMERA) ==
                        PackageManager.PERMISSION_GRANTED
                ) {
                    scanLauncher.launch(enrollmentScanOptions())
                } else {
                    requestCamera.launch(Manifest.permission.CAMERA)
                }
            },
            modifier = Modifier.fillMaxWidth(),
        ) {
            Text("Scan QR code")
        }
        Spacer(Modifier.height(16.dp))

        LabelledField(label = "Host", value = host, onValueChange = { host = it })
        Spacer(Modifier.height(8.dp))
        LabelledField(label = "Port", value = port, onValueChange = { port = it })
        Spacer(Modifier.height(8.dp))
        LabelledField(
            label = if (existing != null) "Token (unchanged if left blank)" else "Token",
            value = token,
            onValueChange = { token = it },
        )
        Spacer(Modifier.height(24.dp))

        error?.let {
            Text(it, color = MaterialTheme.colorScheme.error)
            Spacer(Modifier.height(8.dp))
        }

        Button(
            onClick = {
                val portNumber = port.trim().toIntOrNull()
                val effectiveToken = token.trim().ifEmpty { existing?.token ?: "" }
                when {
                    host.isBlank() -> error = "Host is required"
                    portNumber == null || portNumber !in 1..65535 -> error = "Port must be 1-65535"
                    effectiveToken.isEmpty() ->
                        error = "Token is required -- scan the server's QR or paste it"
                    else -> {
                        val settings = ServerSettings(host.trim(), portNumber, effectiveToken)
                        saveServerSettings(context, settings)
                        onSaved(settings)
                    }
                }
            }
        ) {
            Text("Save")
        }
    }
}

/**
 * How the enrollment QR is scanned, in one place because two callers reach it -- straight from the
 * button when the camera permission is already held, and from the permission result when it has
 * just been granted.
 *
 * MIXED_SCAN is the load-bearing part: ZXing otherwise looks only for a dark code on a light
 * ground, and ai-server's QR is block characters in the terminal's foreground colour, so on a dark-
 * themed terminal it comes out as a photographic negative the scanner silently never matches. The
 * mixed decoder alternates normal and inverted frames, costing half the frame rate at each
 * polarity.
 */
private fun enrollmentScanOptions(): ScanOptions =
    ScanOptions()
        .setDesiredBarcodeFormats(ScanOptions.QR_CODE)
        .setCaptureActivity(EnrollmentScanActivity::class.java)
        // Follow the phone, not the library's landscape pin.
        .setOrientationLocked(false)
        .addExtra(Intents.Scan.SCAN_TYPE, Intents.Scan.MIXED_SCAN)