import { TimeSynchronization } from "@matter/main/clusters/time-synchronization";
import type { PairedNode } from "@project-chip/matter.js/device";
import type { TimeSyncSummary } from "./inspection.js";
import { Log } from "./logging.js";
import {
  compareDeviceClock,
  currentUnixUtcMicroseconds,
  formatDurationMicros,
  formatUnixMicros,
  type ClockComparison,
} from "./sync.js";
import {
  buildDstOffsetList,
  buildTimeZoneList,
  formatUtcOffset,
  type MatterDstOffsetEntry,
  type MatterTimeZoneEntry,
} from "./timezone.js";

const log = new Log("sync");

/**
 * One clock synchronization against a live device, driven entirely by the
 * capabilities the device itself reports: SetUTCTime always (it is the
 * mandatory command), SetTimeZone/SetDSTOffset only when the TimeZone
 * feature and the commands are present, and the DST list bounded by the
 * device's DSTOffsetListMaxSize. Devices without optional features degrade
 * gracefully; a missing Time Synchronization cluster is skipped with a
 * warning.
 */

/** What the device's Time Synchronization cluster supports. */
export interface TimeSyncCapabilities {
  timeZoneFeature: boolean;
  supportsSetUtcTime: boolean;
  supportsSetTimeZone: boolean;
  supportsSetDstOffset: boolean;
  timeZoneListMaxSize: number;
  dstOffsetListMaxSize: number;
}

/** Derives capabilities from an inspection summary (live or captured fixture). */
export function capabilitiesFromTimeSync(summary: TimeSyncSummary): TimeSyncCapabilities {
  const attributeValue = (name: string): unknown =>
    summary.attributes.find(attribute => attribute.name === name)?.value;
  const sizeAttribute = (name: string): number => {
    const value = attributeValue(name);
    // The spec minimum for both list sizes is 1; assume it when unreported.
    return typeof value === "number" && Number.isInteger(value) && value >= 1 ? value : 1;
  };
  return {
    timeZoneFeature: summary.supportedFeatures["timeZone"] === true,
    supportsSetUtcTime: summary.supportedCommands["setUtcTime"] === true,
    supportsSetTimeZone: summary.supportedCommands["setTimeZone"] === true,
    supportsSetDstOffset: summary.supportedCommands["setDstOffset"] === true,
    timeZoneListMaxSize: sizeAttribute("timeZoneListMaxSize"),
    dstOffsetListMaxSize: sizeAttribute("dstOffsetListMaxSize"),
  };
}

/** The writes one sync run will perform, decided before touching the device. */
export interface TimeSyncPlan {
  setUtcTime: boolean;
  timeZone: MatterTimeZoneEntry[] | null;
  dstOffsets: MatterDstOffsetEntry[] | null;
}

export function planTimeSync(
  capabilities: TimeSyncCapabilities,
  timezone: string,
  from: Date = new Date(),
): TimeSyncPlan {
  const timeZoneSupported = capabilities.timeZoneFeature && capabilities.supportsSetTimeZone;
  return {
    setUtcTime: capabilities.supportsSetUtcTime,
    timeZone: timeZoneSupported ? buildTimeZoneList(timezone, from) : null,
    dstOffsets:
      timeZoneSupported && capabilities.supportsSetDstOffset
        ? buildDstOffsetList(timezone, capabilities.dstOffsetListMaxSize, from)
        : null,
  };
}

/** Read-back verification after the writes. */
export interface SyncVerification {
  /** Device utcTime after sync as ISO-8601 (epoch-corrected), or null if unreadable. */
  utcTimeAfter: string | null;
  /** Effective clock error after sync in microseconds (epoch shift removed). */
  deltaAfterMicroseconds: bigint | null;
  /** True when the device reports Unix-epoch instead of Matter-epoch time. */
  epochShifted: boolean;
  verified: boolean;
}

const VERIFY_TOLERANCE_MICROS = 5_000_000n;

export interface SyncNodeResult {
  nodeId: string;
  success: boolean;
  /** Set (with success=false) when the device has no Time Synchronization cluster. */
  skipped: boolean;
  error: string | null;
  clockBefore: ClockComparison | null;
  /** The UTC instant written, ISO-8601 and Unix-epoch microseconds (matter.js convention). */
  utcTimeWritten: string | null;
  utcTimeWrittenUnixMicroseconds: bigint | null;
  timeZoneWritten: MatterTimeZoneEntry[] | null;
  dstOffsetsWritten: MatterDstOffsetEntry[] | null;
  verification: SyncVerification | null;
}

function emptyResult(nodeId: bigint): SyncNodeResult {
  return {
    nodeId: nodeId.toString(),
    success: false,
    skipped: false,
    error: null,
    clockBefore: null,
    utcTimeWritten: null,
    utcTimeWrittenUnixMicroseconds: null,
    timeZoneWritten: null,
    dstOffsetsWritten: null,
    verification: null,
  };
}

/** Coerces a utcTime attribute value (number | bigint | null | undefined) to bigint | null. */
function utcTimeToBigint(value: number | bigint | null | undefined): bigint | null {
  if (value === null || value === undefined) return null;
  return BigInt(value);
}

/**
 * Synchronizes one connected node's clock. Throws only on programming
 * errors; device and interaction failures are reported in the result so the
 * caller can continue with other nodes.
 */
export async function syncNode(node: PairedNode, timezone: string): Promise<SyncNodeResult> {
  const nodeId = BigInt(node.nodeId);
  const result = emptyResult(nodeId);

  const client = node.getRootClusterClient(TimeSynchronization.Complete);
  if (client === undefined) {
    result.skipped = true;
    result.error = "no Time Synchronization cluster on the root endpoint";
    log.warn(`Node ${nodeId}: ${result.error}; skipping`);
    return result;
  }

  try {
    const supportedCommands = {
      setUtcTime: client.isCommandSupportedByName("setUtcTime"),
      setTimeZone: client.isCommandSupportedByName("setTimeZone"),
      setDstOffset: client.isCommandSupportedByName("setDstOffset"),
    };
    const capabilities: TimeSyncCapabilities = {
      timeZoneFeature: client.supportedFeatures["timeZone"] === true,
      supportsSetUtcTime: supportedCommands.setUtcTime,
      supportsSetTimeZone: supportedCommands.setTimeZone,
      supportsSetDstOffset: supportedCommands.setDstOffset,
      timeZoneListMaxSize: (await client.attributes.timeZoneListMaxSize.get()) ?? 1,
      dstOffsetListMaxSize: (await client.attributes.dstOffsetListMaxSize.get()) ?? 1,
    };
    if (!capabilities.supportsSetUtcTime) {
      throw new Error("device does not accept SetUTCTime; its clock cannot be synchronized");
    }
    const plan = planTimeSync(capabilities, timezone);

    // Read the device clock live (not from cache) for the before/after report.
    const deviceBefore = utcTimeToBigint(await client.attributes.utcTime.get(true));
    result.clockBefore = compareDeviceClock(deviceBefore, currentUnixUtcMicroseconds());
    log.info(`Node ${nodeId}: ${result.clockBefore.description}`);

    // Write UTC time last-moment-fresh, as Unix-epoch microseconds:
    // matter.js's TlvEpochUs converts to the Matter epoch on the wire.
    // Granularity and time source matter for acceptance: a device that
    // already has good time may reject (TimeNotAccepted) a claim no better
    // than what it holds, so state the strongest truthful claim: the host
    // clock is NTP-disciplined (NonMatterSntp) and the timestamp is
    // microsecond-precise at send time.
    const utcTime = currentUnixUtcMicroseconds();
    await client.commands.setUtcTime({
      utcTime,
      granularity: TimeSynchronization.Granularity.MicrosecondsGranularity,
      timeSource: TimeSynchronization.TimeSource.NonMatterSntp,
    });
    result.utcTimeWritten = formatUnixMicros(utcTime);
    result.utcTimeWrittenUnixMicroseconds = utcTime;
    log.info(`Node ${nodeId}: SetUTCTime ${result.utcTimeWritten}`);

    if (plan.timeZone !== null) {
      const response = await client.commands.setTimeZone({ timeZone: plan.timeZone });
      result.timeZoneWritten = plan.timeZone;
      log.info(
        `Node ${nodeId}: SetTimeZone ${plan.timeZone[0]!.name} ` +
          `(standard offset ${formatUtcOffset(plan.timeZone[0]!.offset)})`,
      );
      // dstOffsetRequired=false means the device knows this zone's DST
      // rules itself; pushing our list anyway would be redundant.
      const dstRequired = response?.dstOffsetRequired !== false;
      if (plan.dstOffsets !== null && dstRequired) {
        await client.commands.setDstOffset({ dstOffset: plan.dstOffsets });
        result.dstOffsetsWritten = plan.dstOffsets;
        log.info(`Node ${nodeId}: SetDSTOffset with ${plan.dstOffsets.length} entries`);
      }
    }

    // Read back and verify against the host clock at read time.
    const deviceAfter = utcTimeToBigint(await client.attributes.utcTime.get(true));
    const after = compareDeviceClock(deviceAfter, currentUnixUtcMicroseconds());
    const effective = after.effectiveDeltaMicroseconds;
    const verified =
      effective !== null && (effective < 0n ? -effective : effective) <= VERIFY_TOLERANCE_MICROS;
    result.verification = {
      utcTimeAfter: after.deviceTime,
      deltaAfterMicroseconds: effective,
      epochShifted: after.epochShifted,
      verified,
    };
    if (!verified) {
      throw new Error(
        `read-back verification failed: device utcTime is ${after.deviceTime ?? "unset"} ` +
          `(${after.description})`,
      );
    }

    result.success = true;
    return result;
  } catch (cause) {
    result.error = cause instanceof Error ? cause.message : String(cause);
    return result;
  }
}

export function formatSyncResult(result: SyncNodeResult): string {
  const lines: string[] = [`Node ${result.nodeId}:`];
  if (result.skipped) {
    lines.push(`  Skipped: ${result.error}`);
    return lines.join("\n");
  }
  if (result.clockBefore !== null) {
    lines.push(`  Device clock: ${result.clockBefore.deviceTime ?? "unset"}`);
    lines.push(`  Assessment:   ${result.clockBefore.description}`);
  }
  if (result.utcTimeWritten !== null) {
    lines.push(`  Time written: ${result.utcTimeWritten}`);
  }
  if (result.timeZoneWritten !== null) {
    const zone = result.timeZoneWritten[0]!;
    lines.push(`  Time zone:    ${zone.name} (standard offset ${formatUtcOffset(zone.offset)})`);
  }
  if (result.dstOffsetsWritten !== null && result.dstOffsetsWritten.length > 0) {
    const last = result.dstOffsetsWritten[result.dstOffsetsWritten.length - 1]!;
    const horizon =
      last.validUntil === null ? "indefinitely" : `through ${formatUnixMicros(last.validUntil)}`;
    lines.push(`  DST offsets:  ${result.dstOffsetsWritten.length} entries, valid ${horizon}`);
  }
  if (result.verification !== null && result.verification.deltaAfterMicroseconds !== null) {
    const delta = result.verification.deltaAfterMicroseconds;
    const magnitude = delta < 0n ? -delta : delta;
    lines.push(
      `  Verification: device clock within ${formatDurationMicros(magnitude)} of host after sync` +
        `${result.verification.epochShifted ? " (device reports Unix-epoch time; corrected)" : ""}`,
    );
  }
  lines.push(result.success ? "  Result:       OK" : `  Result:       FAILED (${result.error})`);
  return lines.join("\n");
}