import { existsSync, readdirSync, readFileSync } from 'node:fs';
import { join } from 'node:path';

const BUILTIN_SKILLS_DIR = join(import.meta.dir, '..', '..', 'skills');

interface SkillEntry {
  name: string;
  path: string;
  source: 'workspace' | 'builtin';
}

interface SkillMeta {
  description?: string;
  always?: boolean;
  metadata?: string; // JSON string with nanobot-specific config
}

interface NanobotMeta {
  always?: boolean;
  description?: string;
  requires?: {
    bins?: string[];
    env?: string[];
  };
}

export class SkillsLoader {
  private _workspace: string;
  private _workspaceSkills: string;
  private _builtinSkills: string;

  constructor(workspace: string, builtinSkillsDir?: string) {
    this._workspace = workspace;
    this._workspaceSkills = join(workspace, 'skills');
    this._builtinSkills = builtinSkillsDir ?? BUILTIN_SKILLS_DIR;
  }

  listSkills(filterUnavailable = true): SkillEntry[] {
    const skills: SkillEntry[] = [];

    // Workspace skills take priority
    if (existsSync(this._workspaceSkills)) {
      for (const name of readdirSync(this._workspaceSkills)) {
        const skillFile = join(this._workspaceSkills, name, 'SKILL.md');
        if (existsSync(skillFile)) {
          skills.push({ name, path: skillFile, source: 'workspace' });
        }
      }
    }

    // Builtin skills — skip if workspace already has one with the same name
    if (existsSync(this._builtinSkills)) {
      for (const name of readdirSync(this._builtinSkills)) {
        const skillFile = join(this._builtinSkills, name, 'SKILL.md');
        if (existsSync(skillFile) && !skills.some((s) => s.name === name)) {
          skills.push({ name, path: skillFile, source: 'builtin' });
        }
      }
    }

    if (!filterUnavailable) return skills;
    return skills.filter((s) => this._isAvailable(this._getNanobotMeta(s.name)));
  }

  loadSkill(name: string): string | null {
    const workspacePath = join(this._workspaceSkills, name, 'SKILL.md');
    if (existsSync(workspacePath)) return readFileSync(workspacePath, 'utf8');

    const builtinPath = join(this._builtinSkills, name, 'SKILL.md');
    if (existsSync(builtinPath)) return readFileSync(builtinPath, 'utf8');

    return null;
  }

  loadSkillsForContext(names: string[]): string {
    const parts: string[] = [];
    for (const name of names) {
      const content = this.loadSkill(name);
      if (content) {
        parts.push(`### Skill: ${name}\n\n${this._stripFrontmatter(content)}`);
      }
    }
    return parts.join('\n\n---\n\n');
  }

  buildSkillsSummary(): string {
    const all = this.listSkills(false);
    if (all.length === 0) return '';

    const esc = (s: string) => s.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;');

    const lines = ['<skills>'];
    for (const s of all) {
      const meta = this._getNanobotMeta(s.name);
      const available = this._isAvailable(meta);
      const desc = esc(meta.description ?? s.name);
      lines.push(`  <skill available="${available}">`);
      lines.push(`    <name>${esc(s.name)}</name>`);
      lines.push(`    <description>${desc}</description>`);
      lines.push(`    <location>${s.path}</location>`);
      if (!available) {
        const missing = this._getMissing(meta);
        if (missing) lines.push(`    <requires>${esc(missing)}</requires>`);
      }
      lines.push('  </skill>');
    }
    lines.push('</skills>');
    return lines.join('\n');
  }

  getAlwaysSkills(): string[] {
    return this.listSkills(true)
      .filter((s) => {
        const raw = this._getRawMeta(s.name);
        const nano = this._getNanobotMeta(s.name);
        return nano.always === true || raw?.always === true;
      })
      .map((s) => s.name);
  }

  // ---------------------------------------------------------------------------
  // Private helpers
  // ---------------------------------------------------------------------------

  private _stripFrontmatter(content: string): string {
    if (!content.startsWith('---')) return content;
    const match = /^---\n[\s\S]*?\n---\n/.exec(content);
    return match ? content.slice(match[0].length).trimStart() : content;
  }

  private _getRawMeta(name: string): SkillMeta | null {
    const content = this.loadSkill(name);
    if (!content?.startsWith('---')) return null;
    const match = /^---\n([\s\S]*?)\n---/.exec(content);
    if (!match) return null;
    const meta: SkillMeta = {};
    for (const line of match[1]!.split('\n')) {
      const colon = line.indexOf(':');
      if (colon < 0) continue;
      const key = line.slice(0, colon).trim();
      const val = line.slice(colon + 1).trim().replace(/^["']|["']$/g, '');
      if (key === 'description') meta.description = val;
      if (key === 'always') meta.always = val === 'true';
      if (key === 'metadata') meta.metadata = val;
    }
    return meta;
  }

  private _getNanobotMeta(name: string): NanobotMeta {
    const raw = this._getRawMeta(name);
    if (!raw?.metadata) return { description: raw?.description, always: raw?.always };
    try {
      const parsed = JSON.parse(raw.metadata) as Record<string, unknown>;
      const nano = (parsed['nanobot'] ?? parsed['openclaw'] ?? parsed) as NanobotMeta;
      return { description: raw.description, always: raw.always, ...nano };
    } catch {
      return { description: raw.description, always: raw.always };
    }
  }

  private _isAvailable(meta: NanobotMeta): boolean {
    const req = meta.requires;
    if (!req) return true;
    for (const bin of req.bins ?? []) {
      if (!this._which(bin)) return false;
    }
    for (const env of req.env ?? []) {
      if (!process.env[env]) return false;
    }
    return true;
  }

  private _getMissing(meta: NanobotMeta): string {
    const missing: string[] = [];
    const req = meta.requires;
    if (!req) return '';
    for (const bin of req.bins ?? []) {
      if (!this._which(bin)) missing.push(`CLI: ${bin}`);
    }
    for (const env of req.env ?? []) {
      if (!process.env[env]) missing.push(`ENV: ${env}`);
    }
    return missing.join(', ');
  }

  private _which(bin: string): boolean {
    try {
      const result = Bun.spawnSync(['which', bin]);
      return result.exitCode === 0;
    } catch {
      return false;
    }
  }
}