/**
 * up / ls / open / close.
 *
 * These are the plumbing on top of the planner. The rule they all obey: read
 * the world (discovery + list-tabs), compute a plan, then apply it — never
 * mutate opportunistically while walking, because that is how `up` stops being
 * idempotent.
 */

import { existsSync, readFileSync } from "node:fs";
import { basename, join, resolve } from "node:path";
import { mkdtempSync, writeFileSync } from "node:fs";
import { tmpdir } from "node:os";
import { checkFragment } from "./doctor.ts";
import { discoverProjects, LAYOUT_FILE, MARKER_DIR } from "../core/discover.ts";
import { UserError } from "../core/errors.ts";
import {
  templatesFrom,
  sessionLayoutKdl,
  singleTabLayoutKdl,
  type TabSpec,
} from "../core/layout.ts";
import { isNoOp, planTabs, type Plan } from "../core/plan.ts";
import { projectPurpose } from "../core/purpose.ts";
import { rememberRoot, rootExists, type ResolvedRoot } from "../core/root.ts";
import { Sl0ppij, type TabInfo } from "../core/sl0ppij.ts";

export interface Context {
  resolved: ResolvedRoot;
  client: Sl0ppij;
  depth: number;
  dryRun: boolean;
  /** Discard a dead session of the same name instead of resurrecting it. */
  fresh?: boolean;
  /**
   * Do not create the session here; return the layout so the caller can create
   * it BY ATTACHING to it. See `UpResult.createWith`.
   */
  deferCreate?: boolean;
  /** Cached tab template; "" means "looked, found none". */
  tabTemplate?: string;
  /** Cached pane_template definitions the tab template may refer to. */
  paneTemplates?: string[];
  log: (message: string) => void;
}

/**
 * The tab template every generated tab is wrapped in, so sessions keep the
 * status/tab bar the shipped config provides. Without it a multi-project
 * session shows no tab bar at all and the other projects are invisible.
 */
function tabTemplate(ctx: Context): string | undefined {
  loadTemplates(ctx);
  return ctx.tabTemplate === "" ? undefined : ctx.tabTemplate;
}

/**
 * The `pane_template` definitions the tab template refers to.
 *
 * A generated layout is a file of its own: if the template body says
 * `sl0pbar size=3`, the definition has to travel with it or the session fails
 * to parse with "Invalid tab property: sl0pbar".
 */
function paneTemplates(ctx: Context): string[] {
  loadTemplates(ctx);
  return ctx.paneTemplates ?? [];
}

function loadTemplates(ctx: Context): void {
  if (ctx.tabTemplate !== undefined) return;
  const templates = templatesFrom(sl0ppijConfigDir());
  ctx.tabTemplate = templates.tabTemplate ?? "";
  ctx.paneTemplates = templates.paneTemplates;
}

export function sl0ppijConfigDir(env: NodeJS.ProcessEnv = process.env): string {
  if (env.SL0PPIJ_CONFIG_DIR) return env.SL0PPIJ_CONFIG_DIR;
  return join(env.HOME ?? "", ".config", "sl0ppij");
}

function fragmentFor(root: string, relPath: string): string | undefined {
  const path = join(root, relPath, MARKER_DIR, LAYOUT_FILE);
  try {
    const text = readFileSync(path, "utf8").trim();
    return text.length > 0 ? text : undefined;
  } catch {
    return undefined; // no fragment: the default (one suspended agent) applies
  }
}

function specFor(root: string, relPath: string): TabSpec {
  return {
    name: basename(relPath),
    relPath,
    cwd: join(root, relPath),
    fragment: fragmentFor(root, relPath),
  };
}

/**
 * Specs for the projects we can actually open, plus what went wrong with the
 * rest.
 *
 * A fragment is checked before it is used, on BOTH paths. This matters most
 * when creating a session, where every tab goes into one layout: a single
 * unbalanced brace would otherwise take down the whole root rather than the one
 * project that is broken.
 */
export function usableSpecs(
  root: string,
  relPaths: string[],
): { specs: TabSpec[]; failures: string[] } {
  const specs: TabSpec[] = [];
  const failures: string[] = [];
  for (const relPath of relPaths) {
    const spec = specFor(root, relPath);
    const issue = spec.fragment ? checkFragment(spec.fragment) : undefined;
    if (issue && !issue.startsWith("empty")) {
      failures.push(`${relPath}: ${issue}`);
      continue;
    }
    specs.push(spec);
  }
  return { specs, failures };
}

function computePlan(ctx: Context, tabs: TabInfo[]): Plan {
  const { root } = ctx.resolved;
  return planTabs({
    root,
    rootExists: rootExists(root),
    projects: discoverProjects(root, { depth: ctx.depth }),
    tabs,
    pathExists: existsSync,
  });
}

/**
 * Create the session, or bring an existing one in line with the filesystem.
 *
 * Two paths, one composer: a brand new session is created from a whole-session
 * layout (which is also the only way tab purposes survived before the fork fix),
 * and an existing one gets tabs added individually.
 */
export interface UpResult {
  plan: Plan;
  created: boolean;
  /**
   * Set when the session still needs creating and the caller should do it by
   * attaching: `sl0ppij --layout <createWith> attach --create <session>`.
   *
   * Creating with `attach --create-background` leaves a phantom client in the
   * session for its whole life -- measured: a background-created session shows
   * "MY FOCUS AND:" on its very first attach, one created by an ordinary attach
   * never does. Deferring to the attach we were about to do anyway avoids it
   * entirely; the background path stays for headless use, where nobody is
   * looking at a pane frame.
   */
  createWith?: string;
}

export function up(ctx: Context): UpResult {
  const { root, session } = ctx.resolved;
  const client = ctx.client.forSession(session);

  if (!rootExists(root)) {
    throw new UserError(`root does not exist: ${root}`);
  }

  const projects = discoverProjects(root, { depth: ctx.depth });

  if (!client.sessionExists(session)) {
    // A dead session of this name is not an empty slot: `attach
    // --create-background NAME` RESURRECTS it from the serialised copy and
    // silently ignores --layout. Observed consequences, in order of nastiness:
    // the tabs come back without pane purposes or commands (so no agents), and
    // the resurrected background session then exits again within seconds.
    //
    // So sl0ppi refuses to guess. Resurrecting is still available -- from
    // sl0ppij itself, in a terminal, which is where it actually works.
    const resurrectable = client.deadSessions().includes(session);
    if (resurrectable && !ctx.fresh) {
      throw new UserError(
        [
          `session "${session}" already exists as a saved (dead) copy.`,
          ``,
          `  sl0ppi up --fresh        discard it and rebuild from your project layouts`,
          `  sl0ppij attach ${session}${" ".repeat(Math.max(1, 16 - session.length))}restore it as it was, in a terminal`,
          ``,
          `sl0ppi will not resurrect it for you: restoring in the background brings`,
          `the tabs back without their agents, and the session exits again seconds later.`,
        ].join("\n"),
      );
    }
    if (resurrectable && ctx.fresh) {
      if (!ctx.dryRun) client.deleteSession(session);
      ctx.log(`discarded the saved copy of ${session}`);
    }

    const { specs, failures } = usableSpecs(root, projects);
    for (const failure of failures) ctx.log(`! ${failure}`);
    if (ctx.dryRun) {
      ctx.log(`would create session ${session} with ${specs.length} tab(s)`);
      for (const spec of specs) ctx.log(`  + ${spec.relPath}`);
      return { plan: emptyPlan(), created: true };
    }
    // A session must be born with at least one tab; an empty root gets a plain
    // one rather than an error, so `sl0ppi` still gives you a terminal.
    const layout =
      specs.length > 0
        ? sessionLayoutKdl(specs, tabTemplate(ctx), paneTemplates(ctx))
        : "layout {\n    tab name=\"scratch\" {\n        pane\n    }\n}\n";
    const dir = mkdtempSync(join(tmpdir(), "sl0ppi-layout-"));
    const layoutPath = join(dir, "session.kdl");
    writeFileSync(layoutPath, layout);

    if (ctx.deferCreate) {
      rememberRoot(session, root);
      ctx.log(`creating session ${session} (${specs.length} project tab(s))`);
      return { plan: emptyPlan(), created: true, createWith: layoutPath };
    }

    client.createBackground(session, layoutPath);
    rememberRoot(session, root);

    // Creation returns before the server is registered; without this, the very
    // next query fails with "There is no active session!".
    if (!client.waitForSession(session)) {
      throw new Error(`session ${session} did not come up`);
    }

    ctx.log(`created session ${session} (${specs.length} project tab(s))`);
    return { plan: emptyPlan(), created: true };
  }

  const plan = computePlan(ctx, client.listTabs());

  if (ctx.dryRun) {
    if (isNoOp(plan)) ctx.log("nothing to do");
    for (const action of plan.create) ctx.log(`  + ${action.relPath}`);
    for (const tab of plan.close) ctx.log(`  - ${tab.name} (stale)`);
    return { plan, created: false };
  }

  // Closes first, in DESCENDING position order: closing a tab renumbers every
  // tab after it, so ascending order would target the wrong ones.
  for (const tab of [...plan.close].sort((a, b) => b.position - a.position)) {
    client.closeTab(tab.position);
    ctx.log(`- ${tab.name} (project gone)`);
  }

  // One project must not be able to stop the others opening. A broken fragment
  // is the project's problem; `up` reports it and carries on, because the whole
  // point is to bring up a working root.
  const { specs, failures } = usableSpecs(
    root,
    plan.create.map((action) => action.relPath),
  );
  for (const failure of failures) ctx.log(`! ${failure}`);

  for (const spec of specs) {
    try {
      client.newTab(singleTabLayoutKdl(spec, tabTemplate(ctx), paneTemplates(ctx)));
      ctx.log(`+ ${spec.relPath}`);
    } catch (error) {
      const message = error instanceof Error ? error.message.split("\n")[0] : String(error);
      failures.push(`${spec.relPath}: ${message}`);
      ctx.log(`! ${spec.relPath} failed — ${message}`);
    }
  }

  // Registered even when some projects failed: the session exists and is ours,
  // and forgetting it would orphan every tab that did open.
  rememberRoot(session, root);
  if (isNoOp(plan)) ctx.log("up to date");
  if (failures.length > 0) {
    ctx.log(`${failures.length} project(s) did not open; \`sl0ppi doctor\` explains why`);
  }
  return { plan, created: false };
}

export type AgentState = "running" | "suspended" | "exited" | "none";

export interface ProjectStatus {
  relPath: string;
  tab?: TabInfo;
  /** Terminal panes only; plugin panes (status bar, link handler) are chrome. */
  panes: number;
  agent: AgentState;
}

/**
 * `is_held` is how a `start_suspended` pane reports itself: the command is
 * staged but has not run, waiting for a keypress. It is NOT `exited` — that
 * means the command ran and finished.
 */
export function agentStateOf(pane: { is_held?: boolean; exited?: boolean } | undefined): AgentState {
  if (pane === undefined) return "none";
  if (pane.is_held) return "suspended";
  if (pane.exited) return "exited";
  return "running";
}

export function ls(ctx: Context): { projects: ProjectStatus[]; stale: TabInfo[] } {
  const { root, session } = ctx.resolved;
  const client = ctx.client.forSession(session);
  const projects = discoverProjects(root, { depth: ctx.depth });

  if (!client.sessionExists(session)) {
    return {
      projects: projects.map((relPath) => ({ relPath, panes: 0, agent: "none" })),
      stale: [],
    };
  }

  const tabs = client.listTabs();
  const panes = client.listPanes();
  const byPurpose = new Map(tabs.filter((t) => t.purpose).map((t) => [t.purpose as string, t]));

  const statuses: ProjectStatus[] = projects.map((relPath) => {
    const tab = byPurpose.get(projectPurpose(relPath));
    if (!tab) return { relPath, panes: 0, agent: "none" };
    const tabPanes = panes.filter((p) => p.tab_id === tab.position && !p.is_plugin);
    const agentPane = tabPanes.find((p) => p.purpose?.startsWith("agent:"));
    return { relPath, tab, panes: tabPanes.length, agent: agentStateOf(agentPane) };
  });

  const plan = computePlan(ctx, tabs);
  return { projects: statuses, stale: plan.close };
}

/** Ensure a tab exists for `name`, then focus it. */
export function open(ctx: Context, name: string): TabInfo {
  const { root, session } = ctx.resolved;
  const client = ctx.client.forSession(session);
  const relPath = resolveProjectName(ctx, name);

  if (!client.sessionExists(session)) {
    throw new UserError(`no session ${session}; run \`sl0ppi up\` first`);
  }

  const purpose = projectPurpose(relPath);
  let tab = client.listTabs().find((t) => t.purpose === purpose);
  if (!tab) {
    const position = client.newTab(
      singleTabLayoutKdl(specFor(root, relPath), tabTemplate(ctx), paneTemplates(ctx)),
    );
    ctx.log(`+ ${relPath}`);
    tab = client.listTabs().find((t) => t.position === position) ?? {
      position,
      name: basename(relPath),
      purpose,
    };
  }
  client.focusTab(tab.position);
  return tab;
}

export function close(ctx: Context, name: string): void {
  const { session } = ctx.resolved;
  const client = ctx.client.forSession(session);
  const purpose = projectPurpose(resolveProjectName(ctx, name));
  const tab = client.listTabs().find((t) => t.purpose === purpose);
  if (!tab) throw new UserError(`no open tab for ${name}`);
  client.closeTab(tab.position);
  ctx.log(`- ${tab.name}`);
}

/**
 * Turn what the user typed into a project path.
 *
 * Exact match wins, then unique prefix. An ambiguous prefix is an error rather
 * than a guess — picking one for them is how you end up closing the wrong tab.
 */
export function resolveProjectName(ctx: Context, name: string): string {
  const { root } = ctx.resolved;
  const projects = discoverProjects(root, { depth: ctx.depth });
  if (projects.includes(name)) return name;

  const asPath = resolve(ctx.resolved.root, name);
  if (existsSync(join(asPath, MARKER_DIR))) {
    const rel = asPath.startsWith(`${root}/`) ? asPath.slice(root.length + 1) : null;
    if (rel) return rel;
  }

  const matches = projects.filter((p) => p.startsWith(name) || basename(p) === name);
  if (matches.length === 1) return matches[0] as string;
  if (matches.length > 1) {
    throw new UserError(`ambiguous: ${name} matches ${matches.join(", ")}`);
  }
  throw new UserError(`no project ${name} under ${root}`);
}

function emptyPlan(): Plan {
  return { create: [], close: [], keep: [], foreign: [] };
}

/** The layout sl0ppi would use for a project — for eyeballing and debugging. */
export function print(ctx: Context, name: string): string {
  const relPath = resolveProjectName(ctx, name);
  return singleTabLayoutKdl(
    specFor(ctx.resolved.root, relPath),
    tabTemplate(ctx),
    paneTemplates(ctx),
  );
}