/**
 * `sl0ppi doctor` — is this installation coherent?
 *
 * Split into "gather facts" (IO) and "judge them" (pure), so the judging is
 * testable and the output cannot drift from the rules.
 *
 * It reports what it can actually verify. Notably it CANNOT fully validate a
 * project's layout fragment: sl0ppij has no parse-only mode, so a fragment is
 * only really checked when a tab is created from it. The structural check here
 * catches the common breakages (empty file, unbalanced braces, someone wrapping
 * the fragment in `layout {}`) and says so rather than implying more.
 */

import { existsSync, readFileSync } from "node:fs";
import { join } from "node:path";
import { discoverProjects, LAYOUT_FILE, MARKER_DIR } from "../core/discover.ts";
import { loadRegistry, registryPath, type Registry } from "../core/root.ts";
import { Sl0ppij } from "../core/sl0ppij.ts";

export type Level = "ok" | "warn" | "fail";

export interface Check {
  level: Level;
  label: string;
  detail: string;
  /** What the user should do about it. */
  fix?: string;
}

export interface Facts {
  sl0ppijVersion?: string;
  piVersion?: string;
  configDir?: string;
  configFile: boolean;
  plugins: { name: string; present: boolean }[];
  registry: Registry;
  liveSessions: string[];
  roots: { session: string; root: string; exists: boolean; projects: number }[];
  fragments: { relPath: string; issue?: string }[];
  externalTools: { name: string; present: boolean; neededBy: string }[];
}

/** The judging half: pure, so the rules are testable. */
export function report(facts: Facts): Check[] {
  const checks: Check[] = [];

  checks.push(
    facts.sl0ppijVersion
      ? { level: "ok", label: "sl0ppij", detail: facts.sl0ppijVersion }
      : {
          level: "fail",
          label: "sl0ppij",
          detail: "not found on PATH",
          fix: "install sl0ppi, or set SL0PPI_BIN to the binary",
        },
  );

  checks.push(
    facts.piVersion
      ? { level: "ok", label: "pi", detail: facts.piVersion }
      : {
          level: "warn",
          label: "pi",
          detail: "not found on PATH",
          fix: "agent panes will fail to start; install pi",
        },
  );

  checks.push(
    facts.configFile
      ? { level: "ok", label: "config", detail: facts.configDir ?? "found" }
      : {
          level: "warn",
          label: "config",
          detail: `no config.kdl in ${facts.configDir ?? "the config dir"}`,
          fix: "run the installer, or `make install-config` from a checkout",
        },
  );

  for (const plugin of facts.plugins) {
    checks.push(
      plugin.present
        ? { level: "ok", label: `plugin ${plugin.name}`, detail: "installed" }
        : {
            level: "warn",
            label: `plugin ${plugin.name}`,
            detail: "missing",
            fix: "the shipped layout expects it; reinstall to restore it",
          },
    );
  }

  for (const tool of facts.externalTools) {
    if (!tool.present) {
      checks.push({
        level: "warn",
        label: tool.name,
        detail: `not found; ${tool.neededBy} needs it`,
        fix: `install ${tool.name}`,
      });
    }
  }

  if (Object.keys(facts.registry).length === 0) {
    checks.push({
      level: "ok",
      label: "roots",
      detail: "none registered yet",
      fix: "run `sl0ppi up` in a directory of projects",
    });
  }

  for (const root of facts.roots) {
    if (!root.exists) {
      checks.push({
        level: "warn",
        label: `root ${root.session}`,
        detail: `${root.root} does not exist`,
        fix: "if it is an unmounted filesystem, mount it; otherwise remove it from " +
          registryPath(),
      });
      continue;
    }
    const live = facts.liveSessions.includes(root.session) ? "session live" : "session not running";
    checks.push({
      level: "ok",
      label: `root ${root.session}`,
      detail: `${root.root} — ${root.projects} project(s), ${live}`,
    });
  }

  for (const fragment of facts.fragments) {
    if (fragment.issue) {
      checks.push({
        level: "warn",
        label: `layout ${fragment.relPath}`,
        detail: fragment.issue,
        fix: "see `sl0ppi init` for the expected shape (pane nodes only)",
      });
    }
  }

  return checks;
}

/**
 * Cheap structural check of a fragment.
 *
 * Deliberately conservative: sl0ppij has no parse-only mode, so anything
 * subtler than this would be guessing at the KDL dialect.
 */
export function checkFragment(text: string): string | undefined {
  const stripped = text
    .split("\n")
    .map((line) => line.replace(/\/\/.*$/, "").trim())
    .join("\n")
    .trim();

  if (stripped.length === 0) return "empty (the default single-agent pane will be used)";

  const open = (stripped.match(/\{/g) ?? []).length;
  const close = (stripped.match(/\}/g) ?? []).length;
  if (open !== close) return `unbalanced braces (${open} open, ${close} close)`;

  if (/^\s*layout\s*\{/m.test(stripped)) {
    return "wraps its panes in `layout {}`; a fragment is pane nodes only";
  }
  if (/^\s*tab\b/m.test(stripped)) {
    return "declares a `tab`; sl0ppi adds that (it carries the project's identity)";
  }
  return undefined;
}

export interface GatherOptions {
  client: Sl0ppij;
  configDir?: string;
  depth: number;
}

export function gather(options: GatherOptions): Facts {
  const { client } = options;

  const version = (bin: string, args: string[]): string | undefined => {
    try {
      const proc = new Sl0ppij({ bin }).run(args, { session: false });
      return proc.code === 0 ? proc.stdout.trim().split("\n")[0] : undefined;
    } catch {
      return undefined;
    }
  };

  const configDir = options.configDir ?? defaultConfigDir();
  const registry = loadRegistry();

  const roots = Object.entries(registry).map(([session, root]) => ({
    session,
    root,
    exists: existsSync(root),
    projects: existsSync(root) ? discoverProjects(root, { depth: options.depth }).length : 0,
  }));

  const fragments: { relPath: string; issue?: string }[] = [];
  for (const root of roots) {
    if (!root.exists) continue;
    for (const relPath of discoverProjects(root.root, { depth: options.depth })) {
      const path = join(root.root, relPath, MARKER_DIR, LAYOUT_FILE);
      if (!existsSync(path)) continue; // no fragment is fine: the default applies
      fragments.push({ relPath, issue: checkFragment(readFileSync(path, "utf8")) });
    }
  }

  return {
    sl0ppijVersion: version(client.bin, ["--version"]),
    piVersion: version(process.env.SL0PPI_PI ?? "pi", ["--version"]),
    configDir,
    configFile: existsSync(join(configDir, "config.kdl")),
    plugins: ["pane-finder.wasm", "zjstatus.wasm"].map((name) => ({
      name,
      present: existsSync(join(configDir, "plugins", name)),
    })),
    registry,
    liveSessions: safe(() => client.liveSessions(), []),
    roots,
    fragments,
    // The known packaging hole: `pir` ships in the tarball but its runtime deps
    // do not. Better to say so than to let it fail at the moment of use.
    externalTools: [
      { name: "python3", present: onPath("python3"), neededBy: "pir" },
      { name: "fzf", present: onPath("fzf"), neededBy: "pir" },
    ],
  };
}

export function worstLevel(checks: Check[]): Level {
  if (checks.some((c) => c.level === "fail")) return "fail";
  if (checks.some((c) => c.level === "warn")) return "warn";
  return "ok";
}

export function formatCheck(check: Check): string {
  const mark = check.level === "ok" ? "ok  " : check.level === "warn" ? "warn" : "FAIL";
  const fix = check.fix && check.level !== "ok" ? `\n         -> ${check.fix}` : "";
  return `  ${mark}  ${check.label.padEnd(22)} ${check.detail}${fix}`;
}

function defaultConfigDir(): string {
  const env = process.env;
  if (env.SL0PPIJ_CONFIG_DIR) return env.SL0PPIJ_CONFIG_DIR;
  const home = env.HOME ?? "";
  return join(home, ".config", "sl0ppij");
}

function onPath(tool: string): boolean {
  const dirs = (process.env.PATH ?? "").split(":").filter(Boolean);
  return dirs.some((dir) => existsSync(join(dir, tool)));
}

function safe<T>(fn: () => T, fallback: T): T {
  try {
    return fn();
  } catch {
    return fallback;
  }
}