import fs from "node:fs";
import os from "node:os";
import path from "node:path";
import { lookupContextTokens } from "../agents/context.js";
import {
  DEFAULT_CONTEXT_TOKENS,
  DEFAULT_MODEL,
  DEFAULT_PROVIDER,
} from "../agents/defaults.js";
import { resolveConfiguredModelRef } from "../agents/model-selection.js";
import { type ClawdisConfig, loadConfig } from "../config/config.js";
import {
  buildGroupDisplayName,
  loadSessionStore,
  resolveStorePath,
  type SessionEntry,
} from "../config/sessions.js";

export type GatewaySessionsDefaults = {
  model: string | null;
  contextTokens: number | null;
};

export type GatewaySessionRow = {
  key: string;
  kind: "direct" | "group" | "global" | "unknown";
  displayName?: string;
  surface?: string;
  subject?: string;
  room?: string;
  space?: string;
  chatType?: "direct" | "group" | "room";
  updatedAt: number | null;
  sessionId?: string;
  systemSent?: boolean;
  abortedLastRun?: boolean;
  thinkingLevel?: string;
  verboseLevel?: string;
  sendPolicy?: "allow" | "deny";
  inputTokens?: number;
  outputTokens?: number;
  totalTokens?: number;
  model?: string;
  contextTokens?: number;
  lastChannel?: SessionEntry["lastChannel"];
  lastTo?: string;
};

export type SessionsListResult = {
  ts: number;
  path: string;
  count: number;
  defaults: GatewaySessionsDefaults;
  sessions: GatewaySessionRow[];
};

export type SessionsPatchResult = {
  ok: true;
  path: string;
  key: string;
  entry: SessionEntry;
};

export function readSessionMessages(
  sessionId: string,
  storePath: string | undefined,
): unknown[] {
  const candidates = resolveSessionTranscriptCandidates(sessionId, storePath);

  const filePath = candidates.find((p) => fs.existsSync(p));
  if (!filePath) return [];

  const lines = fs.readFileSync(filePath, "utf-8").split(/\r?\n/);
  const messages: unknown[] = [];
  for (const line of lines) {
    if (!line.trim()) continue;
    try {
      const parsed = JSON.parse(line);
      if (parsed?.message) {
        messages.push(parsed.message);
      }
    } catch {
      // ignore bad lines
    }
  }
  return messages;
}

export function resolveSessionTranscriptCandidates(
  sessionId: string,
  storePath: string | undefined,
): string[] {
  const candidates: string[] = [];
  if (storePath) {
    const dir = path.dirname(storePath);
    candidates.push(path.join(dir, `${sessionId}.jsonl`));
  }
  candidates.push(
    path.join(os.homedir(), ".clawdis", "sessions", `${sessionId}.jsonl`),
  );
  return candidates;
}

export function archiveFileOnDisk(filePath: string, reason: string): string {
  const ts = new Date().toISOString().replaceAll(":", "-");
  const archived = `${filePath}.${reason}.${ts}`;
  fs.renameSync(filePath, archived);
  return archived;
}

function jsonUtf8Bytes(value: unknown): number {
  try {
    return Buffer.byteLength(JSON.stringify(value), "utf8");
  } catch {
    return Buffer.byteLength(String(value), "utf8");
  }
}

export function capArrayByJsonBytes<T>(
  items: T[],
  maxBytes: number,
): { items: T[]; bytes: number } {
  if (items.length === 0) return { items, bytes: 2 };
  const parts = items.map((item) => jsonUtf8Bytes(item));
  let bytes = 2 + parts.reduce((a, b) => a + b, 0) + (items.length - 1);
  let start = 0;
  while (bytes > maxBytes && start < items.length - 1) {
    bytes -= parts[start] + 1;
    start += 1;
  }
  const next = start > 0 ? items.slice(start) : items;
  return { items: next, bytes };
}

export function loadSessionEntry(sessionKey: string) {
  const cfg = loadConfig();
  const sessionCfg = cfg.session;
  const storePath = sessionCfg?.store
    ? resolveStorePath(sessionCfg.store)
    : resolveStorePath(undefined);
  const store = loadSessionStore(storePath);
  const entry = store[sessionKey];
  return { cfg, storePath, store, entry };
}

export function classifySessionKey(
  key: string,
  entry?: SessionEntry,
): GatewaySessionRow["kind"] {
  if (key === "global") return "global";
  if (key === "unknown") return "unknown";
  if (entry?.chatType === "group" || entry?.chatType === "room") return "group";
  if (
    key.startsWith("group:") ||
    key.includes(":group:") ||
    key.includes(":channel:")
  ) {
    return "group";
  }
  return "direct";
}

export function parseGroupKey(
  key: string,
): { surface?: string; kind?: "group" | "channel"; id?: string } | null {
  if (key.startsWith("group:")) {
    const raw = key.slice("group:".length);
    return raw ? { id: raw } : null;
  }
  const parts = key.split(":").filter(Boolean);
  if (parts.length >= 3) {
    const [surface, kind, ...rest] = parts;
    if (kind === "group" || kind === "channel") {
      const id = rest.join(":");
      return { surface, kind, id };
    }
  }
  return null;
}

export function getSessionDefaults(
  cfg: ClawdisConfig,
): GatewaySessionsDefaults {
  const resolved = resolveConfiguredModelRef({
    cfg,
    defaultProvider: DEFAULT_PROVIDER,
    defaultModel: DEFAULT_MODEL,
  });
  const contextTokens =
    cfg.agent?.contextTokens ??
    lookupContextTokens(resolved.model) ??
    DEFAULT_CONTEXT_TOKENS;
  return {
    model: resolved.model ?? null,
    contextTokens: contextTokens ?? null,
  };
}

export function resolveSessionModelRef(
  cfg: ClawdisConfig,
  entry?: SessionEntry,
): { provider: string; model: string } {
  const resolved = resolveConfiguredModelRef({
    cfg,
    defaultProvider: DEFAULT_PROVIDER,
    defaultModel: DEFAULT_MODEL,
  });
  let provider = resolved.provider;
  let model = resolved.model;
  const storedModelOverride = entry?.modelOverride?.trim();
  if (storedModelOverride) {
    provider = entry?.providerOverride?.trim() || provider;
    model = storedModelOverride;
  }
  return { provider, model };
}

export function listSessionsFromStore(params: {
  cfg: ClawdisConfig;
  storePath: string;
  store: Record<string, SessionEntry>;
  opts: import("./protocol/index.js").SessionsListParams;
}): SessionsListResult {
  const { cfg, storePath, store, opts } = params;
  const now = Date.now();

  const includeGlobal = opts.includeGlobal === true;
  const includeUnknown = opts.includeUnknown === true;
  const activeMinutes =
    typeof opts.activeMinutes === "number" &&
    Number.isFinite(opts.activeMinutes)
      ? Math.max(1, Math.floor(opts.activeMinutes))
      : undefined;

  let sessions = Object.entries(store)
    .filter(([key]) => {
      if (!includeGlobal && key === "global") return false;
      if (!includeUnknown && key === "unknown") return false;
      return true;
    })
    .map(([key, entry]) => {
      const updatedAt = entry?.updatedAt ?? null;
      const input = entry?.inputTokens ?? 0;
      const output = entry?.outputTokens ?? 0;
      const total = entry?.totalTokens ?? input + output;
      const parsed = parseGroupKey(key);
      const surface = entry?.surface ?? parsed?.surface;
      const subject = entry?.subject;
      const room = entry?.room;
      const space = entry?.space;
      const id = parsed?.id;
      const displayName =
        entry?.displayName ??
        (surface
          ? buildGroupDisplayName({
              surface,
              subject,
              room,
              space,
              id,
              key,
            })
          : undefined);
      return {
        key,
        kind: classifySessionKey(key, entry),
        displayName,
        surface,
        subject,
        room,
        space,
        chatType: entry?.chatType,
        updatedAt,
        sessionId: entry?.sessionId,
        systemSent: entry?.systemSent,
        abortedLastRun: entry?.abortedLastRun,
        thinkingLevel: entry?.thinkingLevel,
        verboseLevel: entry?.verboseLevel,
        sendPolicy: entry?.sendPolicy,
        inputTokens: entry?.inputTokens,
        outputTokens: entry?.outputTokens,
        totalTokens: total,
        model: entry?.model,
        contextTokens: entry?.contextTokens,
        lastChannel: entry?.lastChannel,
        lastTo: entry?.lastTo,
      } satisfies GatewaySessionRow;
    })
    .sort((a, b) => (b.updatedAt ?? 0) - (a.updatedAt ?? 0));

  if (activeMinutes !== undefined) {
    const cutoff = now - activeMinutes * 60_000;
    sessions = sessions.filter((s) => (s.updatedAt ?? 0) >= cutoff);
  }

  if (typeof opts.limit === "number" && Number.isFinite(opts.limit)) {
    const limit = Math.max(1, Math.floor(opts.limit));
    sessions = sessions.slice(0, limit);
  }

  return {
    ts: now,
    path: storePath,
    count: sessions.length,
    defaults: getSessionDefaults(cfg),
    sessions,
  };
}