package com.peachpasswords.ui.vault

import android.content.Context
import com.peachpasswords.shared.PeachClipboard
import android.net.Uri
import androidx.activity.compose.rememberLauncherForActivityResult
import androidx.activity.result.contract.ActivityResultContracts
import androidx.compose.foundation.background
import androidx.compose.foundation.border
import androidx.compose.foundation.clickable
import androidx.compose.foundation.layout.Box
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.size
import androidx.compose.foundation.layout.systemBarsPadding
import androidx.compose.foundation.layout.width
import androidx.compose.foundation.rememberScrollState
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.foundation.text.BasicTextField
import androidx.compose.foundation.verticalScroll
import androidx.compose.material.icons.Icons
import androidx.compose.material.icons.automirrored.rounded.ArrowBack
import androidx.compose.material3.Icon
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.draw.clip
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.graphics.SolidColor
import androidx.compose.ui.platform.LocalContext
import androidx.compose.ui.text.TextStyle
import androidx.compose.ui.text.font.FontStyle
import androidx.compose.ui.text.input.PasswordVisualTransformation
import androidx.compose.ui.text.input.VisualTransformation
import androidx.compose.ui.unit.dp
import androidx.compose.ui.unit.sp
import androidx.hilt.navigation.compose.hiltViewModel
import androidx.lifecycle.ViewModel
import com.peachpasswords.license.LicenseRepository
import com.peachpasswords.ui.components.PeachEmptyOrEndState
import com.peachpasswords.ui.components.PeachField as DesignPeachField
import com.peachpasswords.ui.components.PeachSectionHeader
import com.peachpasswords.ui.components.SecureFlagEffect
import com.peachpasswords.ui.theme.LocalPeachAccent
import com.peachpasswords.ui.theme.PeachSpacing
import com.peachpasswords.ui.theme.peachColors
import com.peachpasswords.ui.theme.PeachType
import com.peachpasswords.ui.security.StrengthBar
import com.peachpasswords.ui.security.scorePassword
import com.peachpasswords.ui.security.strengthLabel
import com.peachpasswords.ui.theme.ShellBackground
import com.peachpasswords.vault.VaultEntry
import com.peachpasswords.vault.VaultRepository
import dagger.hilt.android.lifecycle.HiltViewModel
import dagger.hilt.android.qualifiers.ApplicationContext
import java.time.LocalDate
import javax.inject.Inject

// ─────────────────────────────────────────────────────────────────────────────
// Password strength scorer (local, dependency-free)
// ─────────────────────────────────────────────────────────────────────────────

/**
 * Lightweight 0–4 strength score from length + character-class variety. No
 * external lib, no network — this is a UI gate, not a security guarantee.
 *
 * Thresholds (deliberately simple and explainable):
 *   - +1 if length >= 8
 *   - +1 if length >= 12
 *   - +1 if at least 3 of {lowercase, uppercase, digit, symbol} are present
 *   - +1 if all 4 classes are present
 * Empty input scores 0. Result is clamped to 0..4. The C2 gate requires >= 3
 * ("good"); see [strengthLabel].
 */
// Password strength scoring now lives in com.peachpasswords.ui.security (E1, shared).

// ─────────────────────────────────────────────────────────────────────────────
// ViewModel
// ─────────────────────────────────────────────────────────────────────────────

@HiltViewModel
class ExportViewModel @Inject constructor(
    private val vault: VaultRepository,
    private val license: LicenseRepository,
    @ApplicationContext private val appContext: Context,
) : ViewModel() {

    /** Active (non-deleted) entries to export. */
    fun entries(): List<VaultEntry> = vault.getEntries()

    fun entryCount(): Int = vault.getEntries().size

    /**
     * Call right before launching the SAF save dialog — it briefly takes the
     * whole process out of the foreground, which would otherwise trip the
     * app-wide background lock and wipe the vault before the save callback
     * (which reads live entries) ever runs. See VaultRepository docs.
     */
    fun expectTransientBackground() = vault.expectTransientBackground()

    /** Encrypted PeachScript export (backup-password protected). */
    fun buildPeachScript(backupPassword: String): String =
        PeachScriptExport.buildEncrypted(
            entries = entries(),
            backupPassword = backupPassword,
            settings = vault.settings.value,
            licenseKey = license.getLicenseKey()?.takeIf { license.validateLicense(it) },
            licenseActivatedAt = license.getLicenseIssuedAtMillis(),
        )

    /** Unencrypted CSV export. */
    fun buildCsv(): String = CsvExport.toCsv(entries())

    /** Write [content] to the SAF [uri]; returns false on any IO failure. */
    fun writeToUri(uri: Uri, content: String): Boolean =
        runCatching {
            appContext.contentResolver.openOutputStream(uri)?.use {
                it.write(content.toByteArray(Charsets.UTF_8))
            } ?: return false
            true
        }.getOrDefault(false)
}

// ─────────────────────────────────────────────────────────────────────────────
// Screen
// ─────────────────────────────────────────────────────────────────────────────

object ExportStrings {
    const val EMPTY_VAULT = "Your vault is empty — nothing to export."
    const val WEAK_PASSWORD = "Backup password too weak (score < 3)"
    const val MISMATCH = "Passwords don't match."
    const val SAVE_FAILED = "Couldn't write that file."
    const val SAVED = "Saved."
    const val COPIED = "Copied to clipboard."
}

internal fun exportFileName(prefix: String, extension: String, date: LocalDate = LocalDate.now()): String =
    "$prefix-${date}.$extension"

private enum class ExportRoute { CHOOSE, PEACHSCRIPT, CSV }

@Composable
fun ExportScreen(
    onBack: () -> Unit,
    vm: ExportViewModel = hiltViewModel(),
) {
    var route by remember { mutableStateOf(ExportRoute.CHOOSE) }

    SecureFlagEffect() // MN-3: never screenshot the export backup blob

    ShellBackground {
        Column(
            modifier = Modifier
                .fillMaxSize()
                .systemBarsPadding()
                .padding(horizontal = PeachSpacing.lg, vertical = PeachSpacing.md),
        ) {
            PeachSectionHeader(
                section = "export",
                onHome = { if (route != ExportRoute.CHOOSE) route = ExportRoute.CHOOSE else onBack() },
            )

            Spacer(Modifier.size(PeachSpacing.lg))

            if (route == ExportRoute.CHOOSE) {
                // Never needs to scroll — give it the real remaining height so
                // the prompt composes into it instead of trailing into dead
                // space below the two option cards.
                ChooseView(
                    onPeachScript = { route = ExportRoute.PEACHSCRIPT },
                    onCsv = { route = ExportRoute.CSV },
                    modifier = Modifier.weight(1f).fillMaxWidth(),
                )
            } else {
                Column(Modifier.fillMaxSize().verticalScroll(rememberScrollState())) {
                    when (route) {
                        ExportRoute.PEACHSCRIPT -> PeachScriptExportView(vm)
                        ExportRoute.CSV -> CsvExportView(vm)
                        ExportRoute.CHOOSE -> Unit // handled above, outside the scroll container
                    }
                }
            }
        }
    }
}

// ---- Choose view ----------------------------------------------------------

@Composable
private fun ChooseView(onPeachScript: () -> Unit, onCsv: () -> Unit, modifier: Modifier = Modifier) {
    Column(modifier) {
        OptionCard(
            title = "PeachScript (encrypted)",
            subtitle = "A backup encrypted with a separate password. Restores into Peach.",
            onClick = onPeachScript,
        )
        Spacer(Modifier.size(PeachSpacing.md))
        OptionCard(
            title = "CSV (unencrypted)",
            subtitle = "Plain text for moving into another manager. Not encrypted.",
            onClick = onCsv,
        )
        Box(Modifier.weight(1f).fillMaxWidth(), contentAlignment = Alignment.Center) {
            PeachEmptyOrEndState(
                message = "Choose an export format.",
                detail = "Encrypted PeachScript is safest for Peach-to-Peach backups.",
            )
        }
    }
}

@Composable
private fun OptionCard(title: String, subtitle: String, onClick: () -> Unit) {
    Column(
        modifier = Modifier
            .fillMaxWidth()
            .clip(RoundedCornerShape(18.dp))
            .background(peachColors.SurfaceElevated)
            .border(1.dp, peachColors.T3, RoundedCornerShape(18.dp))
            .clickable(onClick = onClick)
            .padding(20.dp),
    ) {
        Text(
            title,
            color = peachColors.T0,
            style = TextStyle(fontFamily = PeachType.Display, fontStyle = FontStyle.Italic, fontSize = 22.sp),
        )
        Spacer(Modifier.size(6.dp))
        Text(subtitle, color = peachColors.T1, style = PeachType.body)
    }
}

// ---- PeachScript sub-view -------------------------------------------------

@Composable
private fun PeachScriptExportView(vm: ExportViewModel) {
    val accent = LocalPeachAccent.current
    val context = LocalContext.current
    val isEmpty = remember { vm.entryCount() == 0 }

    var password by remember { mutableStateOf("") }
    var confirm by remember { mutableStateOf("") }

    // Generated artefact (the encrypted JSON string), set after [Generate backup].
    var output by remember { mutableStateOf<String?>(null) }
    var status by remember { mutableStateOf<String?>(null) }

    val score = remember(password) { scorePassword(password) }
    val matches = password.isNotEmpty() && password == confirm
    val strongEnough = score >= 3
    val canGenerate = !isEmpty && strongEnough && matches

    val saveLauncher = rememberLauncherForActivityResult(
        ActivityResultContracts.CreateDocument("*/*"),
    ) { uri ->
        val text = output
        if (uri != null && text != null) {
            status = if (vm.writeToUri(uri, text)) ExportStrings.SAVED else ExportStrings.SAVE_FAILED
        }
    }

    GlassCard {
        Text(
            "create a\nbackup.",
            color = peachColors.T0,
            style = TextStyle(
                fontFamily = PeachType.Display, fontStyle = FontStyle.Italic,
                fontSize = 24.sp, lineHeight = 26.sp,
            ),
        )
        Spacer(Modifier.size(PeachSpacing.sm))
        Text(
            "Your vault will be encrypted with a separate backup password.",
            color = peachColors.T1, style = PeachType.body,
        )

        if (isEmpty) {
            Spacer(Modifier.size(PeachSpacing.lg))
            InlineError(ExportStrings.EMPTY_VAULT)
        }

        Spacer(Modifier.size(PeachSpacing.lg))
        PeachUnderlineField(
            label = "Backup password",
            value = password,
            onValueChange = { password = it; output = null; status = null },
            isPassword = true,
        )

        Spacer(Modifier.size(PeachSpacing.sm))
        PeachUnderlineField(
            label = "Confirm backup password",
            value = confirm,
            onValueChange = { confirm = it; output = null; status = null },
            isPassword = true,
        )

        Spacer(Modifier.size(PeachSpacing.sm))
        StrengthBar(score = score)
        Spacer(Modifier.size(PeachSpacing.xs))
        Row(modifier = Modifier.fillMaxWidth(), verticalAlignment = Alignment.CenterVertically) {
            Text(
                "strength: ${strengthLabel(score)}",
                color = if (strongEnough) accent else peachColors.T2,
                style = PeachType.labelMono,
            )
        }

        if (password.isNotEmpty() && !strongEnough) {
            Spacer(Modifier.size(PeachSpacing.sm))
            Text(ExportStrings.WEAK_PASSWORD, color = peachColors.Breach, style = PeachType.bodyMono)
        }
        if (confirm.isNotEmpty() && !matches) {
            Spacer(Modifier.size(PeachSpacing.sm))
            Text(ExportStrings.MISMATCH, color = peachColors.Breach, style = PeachType.bodyMono)
        }
    }

    Spacer(Modifier.size(PeachSpacing.lg))

    if (output == null) {
        AccentButton(
            label = "Generate backup",
            enabled = canGenerate,
            onClick = {
                output = vm.buildPeachScript(password)
                status = null
            },
        )
    } else {
        val text = output!!
        GhostButton("Copy to clipboard", accent) {
            PeachClipboard.copy(context, "peach backup", text)
            status = ExportStrings.COPIED
        }
        Spacer(Modifier.size(PeachSpacing.sm))
        GhostButton("Save to file", peachColors.T1) {
            vm.expectTransientBackground()
            saveLauncher.launch(exportFileName("peach-backup", "peach"))
        }
        status?.let {
            Spacer(Modifier.size(PeachSpacing.md))
            Text(
                it,
                color = if (it == ExportStrings.SAVE_FAILED) peachColors.Breach else accent,
                style = PeachType.labelMono,
            )
        }
    }
}

// ---- CSV sub-view ---------------------------------------------------------

@Composable
private fun CsvExportView(vm: ExportViewModel) {
    val accent = LocalPeachAccent.current
    val isEmpty = remember { vm.entryCount() == 0 }

    var acknowledged by remember { mutableStateOf(false) }
    var status by remember { mutableStateOf<String?>(null) }

    val saveLauncher = rememberLauncherForActivityResult(
        ActivityResultContracts.CreateDocument("text/csv"),
    ) { uri ->
        if (uri != null) {
            val csv = vm.buildCsv()
            status = if (vm.writeToUri(uri, csv)) ExportStrings.SAVED else ExportStrings.SAVE_FAILED
        }
    }

    WarningCard(accent) {
        Text(
            "⚠ CSV exports are not encrypted. Store this file securely and delete it after importing.",
            color = peachColors.T0, style = PeachType.body,
        )
        Spacer(Modifier.size(PeachSpacing.lg))
        CheckboxRow(
            label = "I understand this file is unencrypted",
            checked = acknowledged,
            accent = accent,
            onToggle = { acknowledged = !acknowledged },
        )
    }

    if (isEmpty) {
        Spacer(Modifier.size(PeachSpacing.lg))
        InlineError(ExportStrings.EMPTY_VAULT)
    }

    Spacer(Modifier.size(PeachSpacing.lg))
    AccentButton(
        label = "Export CSV",
        enabled = acknowledged && !isEmpty,
        onClick = {
            vm.expectTransientBackground()
            saveLauncher.launch(exportFileName("peach-export", "csv"))
        },
    )
    status?.let {
        Spacer(Modifier.size(PeachSpacing.md))
        Text(
            it,
            color = if (it == ExportStrings.SAVE_FAILED) peachColors.Breach else accent,
            style = PeachType.labelMono,
        )
    }
}

@Composable
private fun WarningCard(accent: Color, content: @Composable () -> Unit) {
    Column(
        modifier = Modifier
            .fillMaxWidth()
            .clip(RoundedCornerShape(18.dp))
            .background(accent.copy(alpha = 0.08f))
            .border(1.dp, accent.copy(alpha = 0.35f), RoundedCornerShape(18.dp))
            .padding(20.dp),
        content = { content() },
    )
}

@Composable
private fun CheckboxRow(label: String, checked: Boolean, accent: Color, onToggle: () -> Unit) {
    Row(
        verticalAlignment = Alignment.CenterVertically,
        modifier = Modifier.fillMaxWidth().clickable(onClick = onToggle).padding(vertical = 4.dp),
    ) {
        Box(
            modifier = Modifier
                .size(18.dp)
                .clip(RoundedCornerShape(5.dp))
                .background(if (checked) accent else Color.Transparent)
                .border(1.5.dp, if (checked) accent else peachColors.T2, RoundedCornerShape(5.dp)),
            contentAlignment = Alignment.Center,
        ) {
            if (checked) Text("✓", color = Color(0xFF0C0A06), style = PeachType.tinyMono.copy(fontSize = 12.sp))
        }
        Spacer(Modifier.width(12.dp))
        Text(label, color = peachColors.T0, style = PeachType.body)
    }
}

// ---- Shared building blocks (private to this draft) -----------------------

@Composable
private fun InlineError(message: String) {
    Box(
        modifier = Modifier
            .fillMaxWidth()
            .clip(RoundedCornerShape(12.dp))
            .background(peachColors.BreachBg)
            .border(1.dp, peachColors.BreachBorder, RoundedCornerShape(12.dp))
            .padding(14.dp),
    ) {
        Text(message, color = peachColors.Breach, style = PeachType.bodyMono)
    }
}

@Composable
private fun FieldLabel(text: String) {
    Text(text.uppercase(), color = peachColors.T2, style = PeachType.labelMono)
}

@Composable
private fun PeachUnderlineField(
    label: String,
    value: String,
    onValueChange: (String) -> Unit,
    isPassword: Boolean = false,
) {
    DesignPeachField(
        label = label,
        value = value,
        onValueChange = onValueChange,
        visualTransformation = if (isPassword) PasswordVisualTransformation() else VisualTransformation.None,
    )
}

@Composable
private fun GlassCard(content: @Composable () -> Unit) {
    Column(
        modifier = Modifier
            .fillMaxWidth()
            .clip(RoundedCornerShape(18.dp))
            .background(peachColors.SurfaceElevated)
            .border(1.dp, peachColors.T3, RoundedCornerShape(18.dp))
            .padding(20.dp),
        content = { content() },
    )
}

@Composable
private fun GhostButton(label: String, color: Color, onClick: () -> Unit) {
    Box(
        modifier = Modifier
            .fillMaxWidth()
            .clip(RoundedCornerShape(12.dp))
            .border(1.dp, color.copy(alpha = 0.4f), RoundedCornerShape(12.dp))
            .clickable(onClick = onClick)
            .padding(vertical = 12.dp),
        contentAlignment = Alignment.Center,
    ) {
        Text(label, color = color, style = PeachType.bodyMono)
    }
}

@Composable
private fun AccentButton(label: String, onClick: () -> Unit, enabled: Boolean = true) {
    val accent = LocalPeachAccent.current
    Box(
        modifier = Modifier
            .fillMaxWidth()
            .clip(RoundedCornerShape(12.dp))
            .background(if (enabled) accent else accent.copy(alpha = 0.3f))
            .clickable(enabled = enabled, onClick = onClick)
            .padding(vertical = 14.dp),
        contentAlignment = Alignment.Center,
    ) {
        Text(label, color = Color(0xFF0C0A06), style = PeachType.bodyMono)
    }
}