/**
 * Module-level registry of shell process sessions — both running and finished —
 * backing ShellService's session tracking. State lives in module-scope Maps, so
 * tests reset it via resetProcessRegistryForTests(). Enforces per-session output
 * caps and a TTL sweep that evicts finished-session records.
 */

import type { FinishedSession, ProcessSession, ProcessStatus } from "../types";

const DEFAULT_JOB_TTL_MS = 30 * 60 * 1000; // 30 minutes
const MIN_JOB_TTL_MS = 60 * 1000; // 1 minute
const MAX_JOB_TTL_MS = 3 * 60 * 60 * 1000; // 3 hours
const DEFAULT_PENDING_OUTPUT_CHARS = 30_000;

function clampTtl(value: number | undefined): number {
  if (!value || Number.isNaN(value)) {
    return DEFAULT_JOB_TTL_MS;
  }
  return Math.min(Math.max(value, MIN_JOB_TTL_MS), MAX_JOB_TTL_MS);
}

let jobTtlMs = clampTtl(Number.parseInt(process.env.SHELL_JOB_TTL_MS ?? "", 10));

const runningSessions = new Map<string, ProcessSession>();
const finishedSessions = new Map<string, FinishedSession>();

let sweeper: NodeJS.Timeout | null = null;

function isSessionIdTaken(id: string): boolean {
  return runningSessions.has(id) || finishedSessions.has(id);
}

// Session slug generation
const SLUG_ADJECTIVES = [
  "amber",
  "briny",
  "brisk",
  "calm",
  "clear",
  "cool",
  "crisp",
  "dawn",
  "delta",
  "ember",
  "faint",
  "fast",
  "fresh",
  "gentle",
  "glow",
  "good",
  "grand",
  "keen",
  "kind",
  "lucky",
  "marine",
  "mellow",
  "mild",
  "neat",
  "nimble",
  "nova",
  "oceanic",
  "plaid",
  "quick",
  "quiet",
  "rapid",
  "salty",
  "sharp",
  "swift",
  "tender",
  "tidal",
  "tidy",
  "tide",
  "vivid",
  "warm",
  "wild",
  "young",
];

const SLUG_NOUNS = [
  "atlas",
  "basil",
  "bison",
  "bloom",
  "breeze",
  "canyon",
  "cedar",
  "claw",
  "cloud",
  "comet",
  "coral",
  "cove",
  "crest",
  "daisy",
  "dune",
  "ember",
  "falcon",
  "fjord",
  "forest",
  "glade",
  "gulf",
  "harbor",
  "haven",
  "kelp",
  "lagoon",
  "meadow",
  "mist",
  "nexus",
  "ocean",
  "orbit",
  "otter",
  "pine",
  "prairie",
  "reef",
  "ridge",
  "river",
  "rook",
  "sable",
  "sage",
  "shell",
  "shoal",
  "shore",
  "slug",
  "summit",
  "trail",
  "valley",
  "wharf",
  "willow",
  "zephyr",
];

function randomChoice(values: string[], fallback: string): string {
  return values[Math.floor(Math.random() * values.length)] ?? fallback;
}

function createSlugBase(words = 2): string {
  const parts = [randomChoice(SLUG_ADJECTIVES, "steady"), randomChoice(SLUG_NOUNS, "harbor")];
  if (words > 2) {
    parts.push(randomChoice(SLUG_NOUNS, "reef"));
  }
  return parts.join("-");
}

export function createSessionSlug(isTaken?: (id: string) => boolean): string {
  const isIdTaken = isTaken ?? isSessionIdTaken;
  for (let attempt = 0; attempt < 12; attempt += 1) {
    const base = createSlugBase(2);
    if (!isIdTaken(base)) {
      return base;
    }
    for (let i = 2; i <= 12; i += 1) {
      const candidate = `${base}-${i}`;
      if (!isIdTaken(candidate)) {
        return candidate;
      }
    }
  }
  for (let attempt = 0; attempt < 12; attempt += 1) {
    const base = createSlugBase(3);
    if (!isIdTaken(base)) {
      return base;
    }
    for (let i = 2; i <= 12; i += 1) {
      const candidate = `${base}-${i}`;
      if (!isIdTaken(candidate)) {
        return candidate;
      }
    }
  }
  const fallback = `${createSlugBase(3)}-${Math.random().toString(36).slice(2, 5)}`;
  return isIdTaken(fallback) ? `${fallback}-${Date.now().toString(36)}` : fallback;
}

export function addSession(session: ProcessSession): void {
  runningSessions.set(session.id, session);
  startSweeper();
}

export function getSession(id: string): ProcessSession | undefined {
  return runningSessions.get(id);
}

export function getFinishedSession(id: string): FinishedSession | undefined {
  return finishedSessions.get(id);
}

export function deleteSession(id: string): void {
  runningSessions.delete(id);
  finishedSessions.delete(id);
}

function sumPendingChars(buffer: string[]): number {
  let total = 0;
  for (const chunk of buffer) {
    total += chunk.length;
  }
  return total;
}

function capPendingBuffer(buffer: string[], pendingChars: number, cap: number): number {
  if (pendingChars <= cap) {
    return pendingChars;
  }
  const last = buffer.at(-1);
  if (last && last.length >= cap) {
    buffer.length = 0;
    buffer.push(last.slice(last.length - cap));
    return cap;
  }
  while (buffer.length && pendingChars - buffer[0].length >= cap) {
    pendingChars -= buffer[0].length;
    buffer.shift();
  }
  if (buffer.length && pendingChars > cap) {
    const overflow = pendingChars - cap;
    buffer[0] = buffer[0].slice(overflow);
    pendingChars = cap;
  }
  return pendingChars;
}

export function tail(text: string, max = 2000): string {
  if (text.length <= max) {
    return text;
  }
  return text.slice(text.length - max);
}

export function trimWithCap(text: string, max: number): string {
  if (text.length <= max) {
    return text;
  }
  return text.slice(text.length - max);
}

export function appendOutput(
  session: ProcessSession,
  stream: "stdout" | "stderr",
  chunk: string
): void {
  session.pendingStdout ??= [];
  session.pendingStderr ??= [];
  session.pendingStdoutChars ??= sumPendingChars(session.pendingStdout);
  session.pendingStderrChars ??= sumPendingChars(session.pendingStderr);
  const buffer = stream === "stdout" ? session.pendingStdout : session.pendingStderr;
  const bufferChars = stream === "stdout" ? session.pendingStdoutChars : session.pendingStderrChars;
  const pendingCap = Math.min(
    session.pendingMaxOutputChars ?? DEFAULT_PENDING_OUTPUT_CHARS,
    session.maxOutputChars
  );
  buffer.push(chunk);
  let pendingChars = bufferChars + chunk.length;
  if (pendingChars > pendingCap) {
    session.truncated = true;
    pendingChars = capPendingBuffer(buffer, pendingChars, pendingCap);
  }
  if (stream === "stdout") {
    session.pendingStdoutChars = pendingChars;
  } else {
    session.pendingStderrChars = pendingChars;
  }
  session.totalOutputChars += chunk.length;
  const aggregated = trimWithCap(session.aggregated + chunk, session.maxOutputChars);
  session.truncated =
    session.truncated || aggregated.length < session.aggregated.length + chunk.length;
  session.aggregated = aggregated;
  session.tail = tail(session.aggregated, 2000);
}

export function drainSession(session: ProcessSession): {
  stdout: string;
  stderr: string;
} {
  const stdout = session.pendingStdout.join("");
  const stderr = session.pendingStderr.join("");
  session.pendingStdout = [];
  session.pendingStderr = [];
  session.pendingStdoutChars = 0;
  session.pendingStderrChars = 0;
  return { stdout, stderr };
}

function moveToFinished(session: ProcessSession, status: ProcessStatus): void {
  runningSessions.delete(session.id);
  if (!session.backgrounded) {
    return;
  }
  finishedSessions.set(session.id, {
    id: session.id,
    command: session.command,
    scopeKey: session.scopeKey,
    startedAt: session.startedAt,
    endedAt: Date.now(),
    cwd: session.cwd,
    status,
    exitCode: session.exitCode,
    exitSignal: session.exitSignal,
    aggregated: session.aggregated,
    tail: session.tail,
    truncated: session.truncated,
    totalOutputChars: session.totalOutputChars,
  });
}

export function markExited(
  session: ProcessSession,
  exitCode: number | null,
  exitSignal: NodeJS.Signals | number | null,
  status: ProcessStatus
): void {
  session.exited = true;
  session.exitCode = exitCode;
  session.exitSignal = exitSignal;
  session.tail = tail(session.aggregated, 2000);
  moveToFinished(session, status);
}

export function markBackgrounded(session: ProcessSession): void {
  session.backgrounded = true;
}

export function listRunningSessions(): ProcessSession[] {
  return Array.from(runningSessions.values()).filter((s) => s.backgrounded);
}

export function listFinishedSessions(): FinishedSession[] {
  return Array.from(finishedSessions.values());
}

export function clearFinished(): void {
  finishedSessions.clear();
}

export function resetProcessRegistryForTests(): void {
  runningSessions.clear();
  finishedSessions.clear();
  stopSweeper();
}

export function setJobTtlMs(value?: number): void {
  if (value === undefined || Number.isNaN(value)) {
    return;
  }
  jobTtlMs = clampTtl(value);
  stopSweeper();
  startSweeper();
}

function pruneFinishedSessions(): void {
  const cutoff = Date.now() - jobTtlMs;
  for (const [id, session] of finishedSessions.entries()) {
    if (session.endedAt < cutoff) {
      finishedSessions.delete(id);
    }
  }
}

function startSweeper(): void {
  if (sweeper) {
    return;
  }
  sweeper = setInterval(pruneFinishedSessions, Math.max(30_000, jobTtlMs / 6));
  sweeper.unref();
}

function stopSweeper(): void {
  if (!sweeper) {
    return;
  }
  clearInterval(sweeper);
  sweeper = null;
}