import { access, mkdir, mkdtemp, readFile, realpath, stat, writeFile } from "node:fs/promises";
import { realpathSync } from "node:fs";
import { delimiter, dirname, isAbsolute, join, relative, resolve, sep } from "node:path";
import { SafeWorkspace } from "../workspace/safe-workspace.js";
import {
  DefaultResourceLoader,
  SettingsManager,
  type ResourceDiagnostic,
  type Skill,
} from "@earendil-works/pi-coding-agent";

export type SkillDiagnostic = {
  level: "warning" | "error";
  message: string;
  filePath?: string;
};

export type SkillCatalogEntry = {
  name: string;
  description: string;
  source: string;
  filePath: string;
  diagnostics: SkillDiagnostic[];
};

export type IndexedSkill = {
  name: string;
  source: string;
  canonicalFilePath: string;
};

export class SkillIndex {
  readonly #skillsByPath = new Map<string, IndexedSkill>();

  public constructor(skills: IndexedSkill[]) {
    for (const skill of skills) {
      this.#skillsByPath.set(canonicalPathSync(skill.canonicalFilePath), {
        ...skill,
        canonicalFilePath: canonicalPathSync(skill.canonicalFilePath),
      });
    }
  }

  public find(canonicalFilePath: string): IndexedSkill | undefined {
    return this.#skillsByPath.get(canonicalFilePath);
  }
}

export type SkillCatalogOptions = {
  cwd: string;
  agentDir: string;
  extraDirsValue?: string;
  resources?: Record<string, readonly string[]>;
};

export class SkillCatalog {
  readonly #cwd: string;
  readonly #agentDir: string;
  readonly #extraDirsValue: string | undefined;
  readonly #resources: Record<string, readonly string[]>;
  #entries: SkillCatalogEntry[] = [];
  #skills: Skill[] = [];
  #indexedSkills: IndexedSkill[] = [];
  #diagnostics: SkillDiagnostic[] = [];

  public constructor(options: SkillCatalogOptions) {
    this.#cwd = canonicalPathSync(options.cwd);
    this.#agentDir = canonicalPathSync(options.agentDir);
    this.#extraDirsValue = options.extraDirsValue;
    this.#resources = Object.fromEntries(Object.entries(options.resources ?? {}).map(([path, files]) => [canonicalPathSync(path), files]));
  }

  public async reload(): Promise<void> {
    const { paths: additionalSkillPaths, diagnostics: pathDiagnostics } =
      await resolveExtraSkillPaths(this.#extraDirsValue);
    const loader = new DefaultResourceLoader({
      cwd: this.#cwd,
      agentDir: this.#agentDir,
      settingsManager: SettingsManager.inMemory(),
      additionalSkillPaths,
      noExtensions: true,
      noPromptTemplates: true,
      noThemes: true,
      noContextFiles: true,
    });

    await loader.reload();
    const loaded = loader.getSkills();
    this.#skills = loaded.skills;
    const loaderDiagnostics = loaded.diagnostics.map((diagnostic) =>
      mapDiagnostic(diagnostic, this.#cwd),
    );
    this.#diagnostics = [...pathDiagnostics, ...loaderDiagnostics];
    this.#indexedSkills = loaded.skills.map((skill) => ({
      name: skill.name,
      source: displaySource(skill),
      canonicalFilePath: canonicalPathSync(skill.filePath),
    }));
    this.#entries = loaded.skills
      .map((skill) => this.#toEntry(skill, loaded.diagnostics))
      .sort((left, right) => left.name.localeCompare(right.name));
  }

  public list(): SkillCatalogEntry[] {
    return this.#entries.map((entry) => ({
      ...entry,
      diagnostics: entry.diagnostics.map((diagnostic) => ({ ...diagnostic })),
    }));
  }

  public index(): SkillIndex {
    return new SkillIndex(this.#indexedSkills);
  }

  /** Copy only catalogued instruction bodies, never arbitrary project files or credentials. */
  public async createSessionSnapshot(workspaceRoot: string): Promise<{ skills: Skill[]; index: SkillIndex }> {
    const root = await realpath(workspaceRoot);
    const snapshotRoot = await mkdtemp(join(root, ".skills-"));
    const skills = await Promise.all(this.#skills.map(async (skill, index) => {
      const baseDir = join(snapshotRoot, String(index));
      await mkdir(baseDir, { mode: 0o700 });
      const filePath = join(baseDir, "SKILL.md");
      await writeFile(filePath, await readFile(skill.filePath), { flag: "wx", mode: 0o400 });
      const source = await SafeWorkspace.create(skill.baseDir);
      for (const resource of this.#resources[canonicalPathSync(skill.filePath)] ?? []) {
        if (isAbsolute(resource) || resource.split(/[\\/]/).includes("..")) throw new Error("Unsafe Skill resource path");
        const from = await source.resolveReadable(resource);
        if ((await stat(from)).size > 1_048_576) throw new Error("Skill resource exceeds size limit");
        const target = join(baseDir, resource);
        await mkdir(dirname(target), { recursive: true, mode: 0o700 });
        await writeFile(target, await readFile(from), { flag: "wx", mode: 0o400 });
      }
      return { ...skill, baseDir, filePath };
    }));
    return {
      skills,
      index: new SkillIndex(skills.map((skill) => ({
        name: skill.name, source: displaySource(skill), canonicalFilePath: skill.filePath,
      }))),
    };
  }

  public readonly diagnostics = (): SkillDiagnostic[] => {
    return this.#diagnostics.map((diagnostic) => ({ ...diagnostic }));
  };

  #toEntry(skill: Skill, diagnostics: ResourceDiagnostic[]): SkillCatalogEntry {
    const canonicalFilePath = canonicalPathSync(skill.filePath);
    return {
      name: skill.name,
      description: skill.description,
      source: displaySource(skill),
      filePath: safeDisplayPath(canonicalFilePath, this.#cwd),
      diagnostics: diagnostics
        .filter(
          (diagnostic) =>
            diagnostic.path !== undefined &&
            canonicalPathSync(diagnostic.path) === canonicalFilePath,
        )
        .map((diagnostic) => mapDiagnostic(diagnostic, this.#cwd)),
    };
  }
}

async function resolveExtraSkillPaths(value?: string): Promise<{
  paths: string[];
  diagnostics: SkillDiagnostic[];
}> {
  if (value === undefined || value.trim() === "") {
    return { paths: [], diagnostics: [] };
  }

  const paths: string[] = [];
  const diagnostics: SkillDiagnostic[] = [];
  const seen = new Set<string>();
  for (const rawPath of value.split(delimiter).map((entry) => entry.trim()).filter(Boolean)) {
    const resolved = resolve(rawPath);
    try {
      await access(resolved);
      const pathStat = await stat(resolved);
      if (!pathStat.isDirectory()) {
        diagnostics.push({ level: "error", message: `Extra skill root is not a directory: ${resolved}` });
        continue;
      }
      const canonical = await realpath(resolved);
      if (!seen.has(canonical)) {
        seen.add(canonical);
        paths.push(canonical);
      }
    } catch {
      diagnostics.push({ level: "error", message: `Extra skill root is unavailable: ${resolved}` });
    }
  }
  return { paths, diagnostics };
}

function canonicalPathSync(filePath: string): string {
  try {
    return realpathSync(filePath);
  } catch {
    return resolve(filePath);
  }
}

function displaySource(skill: Skill): string {
  return skill.sourceInfo.scope === "temporary" ? skill.sourceInfo.source : skill.sourceInfo.scope;
}

function safeDisplayPath(filePath: string, cwd: string): string {
  const relativePath = relative(cwd, filePath);
  if (relativePath !== "" && !relativePath.startsWith(`..${sep}`) && relativePath !== ".." && !isAbsolute(relativePath)) {
    return relativePath;
  }
  return `external/${skillBasename(filePath)}/SKILL.md`;
}

function skillBasename(filePath: string): string {
  const segments = filePath.split(sep).filter(Boolean);
  return segments.at(-2) ?? "skill";
}

function mapDiagnostic(diagnostic: ResourceDiagnostic, cwd: string): SkillDiagnostic {
  return {
    level: diagnostic.type === "error" ? "error" : "warning",
    message: diagnostic.message,
    ...(diagnostic.path === undefined
      ? {}
      : { filePath: safeDisplayPath(canonicalPathSync(diagnostic.path), cwd) }),
  };
}