package com.peachpasswords.sync

import kotlinx.serialization.Serializable

/**
 * Why a sync attempt ended, in the same vocabulary the browser uses
 * (`src/shared/sync-outcome.ts`). June runs both clients side by side, so the
 * names, the state machine and the user-facing wording are deliberately kept
 * identical; only the Kotlin spelling differs.
 *
 * Before this existed Android had [SyncOutcomeSummary]'s ancestor `SyncStatus`,
 * whose `LastSynced` was set the instant the sync *service* was asked to start
 * — a claim of success it had not earned. Every real failure below it was
 * swallowed by the reconnect loop's `runCatching`, so "synced fine", "the peer
 * refused us" and "the vault was locked" were one indistinguishable state.
 *
 * Two browser outcomes are deliberately absent, because on Android they name
 * states that cannot occur:
 *  - `runner_unavailable` — the browser injects its per-device sync runner and
 *    can find it missing. Android's runner is [PeachSyncService], which is
 *    always present; the only way it fails to run is a locked vault, which is
 *    [VAULT_LOCKED].
 *  - `private_relay_unset` — the browser treats "private mode, no address" as
 *    terminal. `RelaySettingsStore.relayUrl()` always falls back to the public
 *    relay instead, so here that configuration syncs rather than failing, and
 *    a private URL equal to the public one is indistinguishable from none.
 *    Reporting it would be a guess.
 *
 * `no_eligible_host` is kept but means something narrower than the browser's:
 * the browser rejects peers it cannot dial, whereas this phone usually *waits*
 * and can talk to any peer type. What it cannot talk to is a peer with no
 * rendezvous secret, which the reconnect loop skips in silence. See
 * [weDialPeer] for why the roles differ.
 */
enum class SyncOutcomeReason {
    COMPLETED_CHANGES,
    COMPLETED_NO_CHANGES,
    NO_PAIRED_DEVICES,
    NO_ELIGIBLE_HOST,
    SYNC_DISABLED,
    VAULT_LOCKED,
    RELAY_UNREACHABLE,
    HANDSHAKE_FAILED,
    VAULT_ID_MISMATCH,
    SYNC_TIMEOUT,
    RUN_FAILED,
    ;

    /** Outcomes where sync did not do what was asked, so the light goes red. */
    val isFailure: Boolean
        get() = when (this) {
            NO_ELIGIBLE_HOST,
            VAULT_LOCKED,
            RELAY_UNREACHABLE,
            HANDSHAKE_FAILED,
            VAULT_ID_MISMATCH,
            SYNC_TIMEOUT,
            RUN_FAILED,
            -> true

            COMPLETED_CHANGES,
            COMPLETED_NO_CHANGES,
            NO_PAIRED_DEVICES,
            SYNC_DISABLED,
            -> false
        }
}

/**
 * The last sync attempt, whatever happened. Persisted by [SyncOutcomeStore] so
 * a failure that happened before the process was killed is still explicable —
 * a reason that vanishes is useless for diagnosing real hardware.
 */
@Serializable
data class SyncOutcomeSummary(
    val reason: SyncOutcomeReason? = null,
    /** Raw internal code, or the peer inventory behind [SyncOutcomeReason.NO_ELIGIBLE_HOST]. */
    val detail: String? = null,
    val entriesSent: Int = 0,
    val entriesReceived: Int = 0,
    /** When the attempt ended, success or not. */
    val finishedAt: Long? = null,
    /** In flight right now. Transient by definition, so never persisted. */
    val syncing: Boolean = false,
)

/**
 * The one indicator light. [BUSY] pulses green, [OK] is solid green, [ERROR] is
 * red, [IDLE] is unlit. Nothing that is actually broken may resolve to [OK] — a
 * paired-but-unsyncable device is red, not green.
 */
enum class SyncIndicator { BUSY, OK, ERROR, IDLE }

fun syncIndicator(summary: SyncOutcomeSummary, pairedCount: Int): SyncIndicator {
    if (summary.syncing) return SyncIndicator.BUSY
    val reason = summary.reason
    if (reason != null && reason.isFailure) return SyncIndicator.ERROR
    if (reason == SyncOutcomeReason.COMPLETED_CHANGES ||
        reason == SyncOutcomeReason.COMPLETED_NO_CHANGES
    ) {
        return SyncIndicator.OK
    }
    // Paired with a healthy history but nothing attempted since launch: still a
    // successful pair, which is what the light is claiming.
    if (pairedCount > 0 && reason == null) return SyncIndicator.OK
    return SyncIndicator.IDLE
}

private fun indicatorHeadline(indicator: SyncIndicator): String = when (indicator) {
    SyncIndicator.BUSY -> "Syncing"
    SyncIndicator.OK -> "Sync healthy"
    SyncIndicator.ERROR -> "Sync problem"
    SyncIndicator.IDLE -> "Not syncing"
}

/** Colour alone is never the signal — this is the same claim in words. */
fun syncIndicatorLabel(indicator: SyncIndicator, summary: SyncOutcomeSummary): String =
    "${indicatorHeadline(indicator)} — ${describeSyncOutcome(summary)}"

/**
 * One plain-English line for a sync outcome, word for word the browser's copy.
 * [SyncOutcomeSummary.detail] is appended rather than hidden: on a real handset
 * it is the whole diagnostic, and there is no devtools to fall back on.
 */
fun describeSyncOutcome(summary: SyncOutcomeSummary): String {
    val reason = summary.reason ?: return "Not synced yet"
    val base = when (reason) {
        SyncOutcomeReason.COMPLETED_CHANGES -> "Synced"
        SyncOutcomeReason.COMPLETED_NO_CHANGES -> "Up to date — nothing to send or receive"
        SyncOutcomeReason.NO_PAIRED_DEVICES -> "No devices paired yet"
        SyncOutcomeReason.NO_ELIGIBLE_HOST -> "Paired, but no device here can accept a sync"
        SyncOutcomeReason.SYNC_DISABLED -> "Sync is switched off"
        SyncOutcomeReason.VAULT_LOCKED -> "Vault was locked — unlock and sync again"
        SyncOutcomeReason.RELAY_UNREACHABLE -> "Couldn't reach the relay"
        SyncOutcomeReason.HANDSHAKE_FAILED -> "Reached the relay, but the device didn't answer"
        SyncOutcomeReason.VAULT_ID_MISMATCH -> "That device holds a different vault"
        SyncOutcomeReason.SYNC_TIMEOUT -> "The device stopped responding mid-sync"
        SyncOutcomeReason.RUN_FAILED -> "Sync failed"
    }
    if (reason == SyncOutcomeReason.COMPLETED_CHANGES) {
        val moved = listOfNotNull(
            "${summary.entriesSent} sent".takeIf { summary.entriesSent > 0 },
            "${summary.entriesReceived} received".takeIf { summary.entriesReceived > 0 },
        )
        return if (moved.isEmpty()) base else "$base — ${moved.joinToString(", ")}"
    }
    return summary.detail?.let { "$base ($it)" } ?: base
}

/**
 * Session errors reach us as opaque strings by contract ([SyncOutcome.error]
 * and any throw out of the relay socket). Classifying them in one place is what
 * lets the copy above key off something stable.
 */
internal fun classifySyncError(error: String): SyncOutcomeReason = when {
    error.contains("VAULT_LOCKED") -> SyncOutcomeReason.VAULT_LOCKED
    error.contains("vault_id_mismatch") -> SyncOutcomeReason.VAULT_ID_MISMATCH
    error.contains("timed out") || error.contains("sync_timeout") -> SyncOutcomeReason.SYNC_TIMEOUT
    // A KK failure, a mismatched PAIR_IDENTITY or a wrong room all mean the
    // relay was fine and the peer was not who we expected.
    Regex("handshake|PAIR_IDENTITY|identity does not match|capability does not match|clock-skew")
        .containsMatchIn(error) -> SyncOutcomeReason.HANDSHAKE_FAILED
    Regex("relay_|websocket|Connection|connect|socket|Unable to resolve host", RegexOption.IGNORE_CASE)
        .containsMatchIn(error) -> SyncOutcomeReason.RELAY_UNREACHABLE
    else -> SyncOutcomeReason.RUN_FAILED
}

/**
 * Translate one finished session ([SyncCoordinator]'s per-round result) into the
 * user-facing vocabulary. Tombstones count as changes: a deletion that crossed
 * the wire is not "nothing to send or receive".
 */
internal fun SyncOutcome.toSummary(): SyncOutcomeSummary = when (status) {
    SyncOutcomeStatus.COMPLETED -> SyncOutcomeSummary(
        reason = if (entriesSent + entriesReceived + tombstonesSent + tombstonesReceived > 0) {
            SyncOutcomeReason.COMPLETED_CHANGES
        } else {
            SyncOutcomeReason.COMPLETED_NO_CHANGES
        },
        entriesSent = entriesSent,
        entriesReceived = entriesReceived,
    )

    SyncOutcomeStatus.VAULT_MISMATCH ->
        SyncOutcomeSummary(reason = SyncOutcomeReason.VAULT_ID_MISMATCH, detail = error)

    SyncOutcomeStatus.TIMEOUT ->
        SyncOutcomeSummary(reason = SyncOutcomeReason.SYNC_TIMEOUT, detail = error)

    SyncOutcomeStatus.ERRORED -> SyncOutcomeSummary(
        reason = classifySyncError(error ?: "sync_failed"),
        detail = error,
    )
}