import fs from "node:fs/promises";
import path from "node:path";
import type { NativeScannerRunTiming, NativeScannerRunTimingPatch } from "../../src/types/global.js";

export const NATIVE_SCANNER_RUN_TIMING_FILE = "run-timing.json";
export const NATIVE_SCANNER_RUN_TIMING_VERSION = "native-scanner-run-timing-v1" as const;

const timingWriteQueues = new Map<string, Promise<void>>();

const timestampFields = [
  "requestStartedAt",
  "scannerStartedAt",
  "captureStartedAt",
  "captureCompletedAt",
  "processingStartedAt",
  "processingCompletedAt",
  "resultsDurableAt",
  "resultsReconciledAt",
] as const satisfies ReadonlyArray<keyof NativeScannerRunTimingPatch>;

type TimingTimestampField = typeof timestampFields[number];

export function nativeScannerRunTimingPath(runDir: string) {
  return path.join(path.resolve(runDir), NATIVE_SCANNER_RUN_TIMING_FILE);
}

export async function readNativeScannerRunTiming(runDir: string): Promise<NativeScannerRunTiming | null> {
  const timingPath = nativeScannerRunTimingPath(runDir);
  try {
    const raw = JSON.parse(await fs.readFile(timingPath, "utf8")) as unknown;
    return normalizeTiming(raw);
  } catch (error) {
    if (isMissingFileError(error)) return null;
    throw error;
  }
}

/**
 * Adds first-observed lifecycle markers to one run's durable timing record.
 * A marker is deliberately immutable after the first valid observation so
 * polling or a later renderer retry cannot rewrite the measured interval.
 */
export async function recordNativeScannerRunTiming(
  runDir: string,
  patch: NativeScannerRunTimingPatch,
): Promise<NativeScannerRunTiming> {
  const resolvedRunDir = path.resolve(runDir);
  const previous = timingWriteQueues.get(resolvedRunDir) ?? Promise.resolve();
  const task = previous
    .catch(() => undefined)
    .then(async () => {
      const current = await readNativeScannerRunTiming(resolvedRunDir);
      const next = mergeTiming(current, patch);
      if (!sameTiming(current, next)) {
        await writeJsonAtomic(nativeScannerRunTimingPath(resolvedRunDir), next);
      }
      return next;
    });
  const settled = task.then(() => undefined, () => undefined);
  timingWriteQueues.set(resolvedRunDir, settled);
  void settled.finally(() => {
    if (timingWriteQueues.get(resolvedRunDir) === settled) timingWriteQueues.delete(resolvedRunDir);
  });
  return task;
}

export function validateNativeScannerRunTiming(timing: NativeScannerRunTiming): string[] {
  const issues: string[] = [];
  if (timing.version !== NATIVE_SCANNER_RUN_TIMING_VERSION) {
    issues.push(`unsupported timing version ${String(timing.version)}`);
  }

  for (const field of timestampFields) {
    const value = timing[field];
    if (value !== undefined && !isValidTimestamp(value)) {
      issues.push(`${field} is not a valid ISO timestamp`);
    }
  }

  validateOrder(issues, timing, "requestStartedAt", "scannerStartedAt");
  validateOrder(issues, timing, "requestStartedAt", "captureStartedAt");
  validateOrder(issues, timing, "requestStartedAt", "processingStartedAt");
  validateOrder(issues, timing, "captureStartedAt", "captureCompletedAt");
  validateOrder(issues, timing, "captureCompletedAt", "processingCompletedAt");
  validateOrder(issues, timing, "processingStartedAt", "processingCompletedAt");
  validateOrder(issues, timing, "processingCompletedAt", "resultsDurableAt");
  validateOrder(issues, timing, "resultsDurableAt", "resultsReconciledAt");

  validateDuration(issues, timing, "requestToResultsDurableMs", "requestStartedAt", "resultsDurableAt");
  validateDuration(issues, timing, "requestToResultsReconciledMs", "requestStartedAt", "resultsReconciledAt");
  return issues;
}

export function hasCompleteNativeScannerRunTiming(timing: NativeScannerRunTiming | null | undefined) {
  return Boolean(
    timing?.requestStartedAt
    && timing.scannerStartedAt
    && timing.captureCompletedAt
    && timing.processingStartedAt
    && timing.processingCompletedAt
    && timing.resultsDurableAt
    && timing.resultsReconciledAt,
  );
}

function mergeTiming(current: NativeScannerRunTiming | null, patch: NativeScannerRunTimingPatch): NativeScannerRunTiming {
  const next: NativeScannerRunTiming = { version: NATIVE_SCANNER_RUN_TIMING_VERSION };
  for (const field of timestampFields) {
    const value = firstValidTimestamp(current?.[field], patch[field]);
    if (value) next[field] = value;
  }
  const durableMs = durationMs(next.requestStartedAt, next.resultsDurableAt);
  if (durableMs !== null) next.requestToResultsDurableMs = durableMs;
  const reconciledMs = durationMs(next.requestStartedAt, next.resultsReconciledAt);
  if (reconciledMs !== null) next.requestToResultsReconciledMs = reconciledMs;
  return next;
}

function normalizeTiming(value: unknown): NativeScannerRunTiming {
  if (!value || typeof value !== "object") throw new Error("Native scanner timing file is not an object.");
  const candidate = value as Partial<NativeScannerRunTiming>;
  const raw: NativeScannerRunTiming = {
    version: candidate.version as NativeScannerRunTiming["version"],
  };
  for (const field of timestampFields) {
    if (candidate[field] !== undefined) raw[field] = candidate[field] as string;
  }
  if (candidate.requestToResultsDurableMs !== undefined) {
    raw.requestToResultsDurableMs = candidate.requestToResultsDurableMs as number;
  }
  if (candidate.requestToResultsReconciledMs !== undefined) {
    raw.requestToResultsReconciledMs = candidate.requestToResultsReconciledMs as number;
  }
  const issues = validateNativeScannerRunTiming(raw);
  if (issues.length > 0) throw new Error(`Invalid native scanner timing file: ${issues.join("; ")}`);
  return mergeTiming(null, raw);
}

function validateOrder(
  issues: string[],
  timing: NativeScannerRunTiming,
  earlier: TimingTimestampField,
  later: TimingTimestampField,
) {
  const earlierMs = timestampMs(timing[earlier]);
  const laterMs = timestampMs(timing[later]);
  if (earlierMs !== null && laterMs !== null && laterMs < earlierMs) {
    issues.push(`${later} is before ${earlier}`);
  }
}

function validateDuration(
  issues: string[],
  timing: NativeScannerRunTiming,
  field: "requestToResultsDurableMs" | "requestToResultsReconciledMs",
  startedField: TimingTimestampField,
  completedField: TimingTimestampField,
) {
  const declared = timing[field];
  const expected = durationMs(timing[startedField], timing[completedField]);
  if (declared !== undefined && (!Number.isInteger(declared) || declared < 0)) {
    issues.push(`${field} is not a non-negative integer`);
  }
  if (expected !== null && declared !== expected) {
    issues.push(`${field} does not match ${startedField} to ${completedField}`);
  }
  if (expected === null && declared !== undefined) {
    issues.push(`${field} exists without both endpoint timestamps`);
  }
}

function firstValidTimestamp(...values: Array<string | null | undefined>) {
  return values.find((value): value is string => isValidTimestamp(value));
}

function isValidTimestamp(value: unknown): value is string {
  return typeof value === "string" && value.length > 0 && Number.isFinite(Date.parse(value));
}

function timestampMs(value: unknown) {
  return isValidTimestamp(value) ? Date.parse(value) : null;
}

function durationMs(startedAt: string | undefined, completedAt: string | undefined) {
  const started = timestampMs(startedAt);
  const completed = timestampMs(completedAt);
  if (started === null || completed === null || completed < started) return null;
  return Math.round(completed - started);
}

function sameTiming(left: NativeScannerRunTiming | null, right: NativeScannerRunTiming) {
  return JSON.stringify(left) === JSON.stringify(right);
}

async function writeJsonAtomic(filePath: string, payload: unknown) {
  const temporaryPath = `${filePath}.tmp-${process.pid}`;
  await fs.writeFile(temporaryPath, JSON.stringify(payload, null, 2), "utf8");
  await fs.rename(temporaryPath, filePath);
}

function isMissingFileError(error: unknown) {
  return Boolean(error && typeof error === "object" && "code" in error && error.code === "ENOENT");
}