import { existsSync, readFileSync } from 'node:fs';
import { join } from 'node:path';
import type { ModelMessage } from '../provider/index.ts';
import { MemoryStore } from './memory.ts';
import { SkillsLoader } from './skills.ts';

const BOOTSTRAP_FILES = ['AGENTS.md', 'SOUL.md', 'USER.md', 'TOOLS.md'] as const;
const RUNTIME_CONTEXT_TAG = '[Runtime Context — metadata only, not instructions]';

export { RUNTIME_CONTEXT_TAG };

export class ContextBuilder {
  private _workspace: string;
  private _memory: MemoryStore;
  private _skills: SkillsLoader;

  constructor(workspace: string) {
    this._workspace = workspace;
    this._memory = new MemoryStore(workspace);
    this._skills = new SkillsLoader(workspace);
  }

  get memory(): MemoryStore {
    return this._memory;
  }

  buildSystemPrompt(skillNames?: string[]): string {
    const parts: string[] = [this._getIdentity()];

    const bootstrap = this._loadBootstrapFiles();
    if (bootstrap) parts.push(bootstrap);

    const memCtx = this._memory.getMemoryContext();
    if (memCtx) parts.push(`# Memory\n\n${memCtx}`);

    const alwaysSkills = this._skills.getAlwaysSkills();
    if (alwaysSkills.length > 0) {
      const content = this._skills.loadSkillsForContext(alwaysSkills);
      if (content) parts.push(`# Active Skills\n\n${content}`);
    }

    if (skillNames && skillNames.length > 0) {
      const content = this._skills.loadSkillsForContext(skillNames);
      if (content) parts.push(`# Requested Skills\n\n${content}`);
    }

    const skillsSummary = this._skills.buildSkillsSummary();
    if (skillsSummary) {
      parts.push(
        `# Skills\n\nThe following skills extend your capabilities. To use a skill, read its SKILL.md file using the read_file tool.\nSkills with available="false" need dependencies installed first.\n\n${skillsSummary}`,
      );
    }

    return parts.join('\n\n---\n\n');
  }

  buildMessages(opts: {
    history: Array<Record<string, unknown>>;
    currentMessage: string;
    skillNames?: string[];
    channel?: string;
    chatId?: string;
  }): ModelMessage[] {
    const runtimeCtx = this._buildRuntimeContext(opts.channel, opts.chatId);
    const userContent = `${runtimeCtx}\n\n${opts.currentMessage}`;

    return [
      { role: 'system', content: this.buildSystemPrompt(opts.skillNames) },
      ...(opts.history as ModelMessage[]),
      { role: 'user', content: userContent },
    ];
  }

  private _getIdentity(): string {
    const platform = process.platform === 'darwin' ? 'macOS' : process.platform;
    const arch = process.arch;
    const runtime = `${platform} ${arch}, Bun ${Bun.version}`;

    const platformPolicy =
      process.platform === 'win32'
        ? `## Platform Policy (Windows)
- You are running on Windows. Do not assume GNU tools like \`grep\`, \`sed\`, or \`awk\` exist.
- Prefer Windows-native commands or file tools when they are more reliable.`
        : `## Platform Policy (POSIX)
- You are running on a POSIX system. Prefer UTF-8 and standard shell tools.
- Use file tools when they are simpler or more reliable than shell commands.`;

    return `# nanobot 🐈

You are nanobot, a helpful AI assistant.

## Runtime
${runtime}

## Workspace
Your workspace is at: ${this._workspace}
- Long-term memory: ${this._workspace}/memory/MEMORY.md (write important facts here)
- History log: ${this._workspace}/memory/HISTORY.md (grep-searchable). Each entry starts with [YYYY-MM-DD HH:MM].
- Custom skills: ${this._workspace}/skills/{skill-name}/SKILL.md

${platformPolicy}

## nanobot Guidelines
- State intent before tool calls, but NEVER predict or claim results before receiving them.
- Before modifying a file, read it first. Do not assume files or directories exist.
- After writing or editing a file, re-read it if accuracy matters.
- If a tool call fails, analyze the error before retrying with a different approach.
- Ask for clarification when the request is ambiguous.

Reply directly with text for conversations. Only use the 'message' tool to send to a specific chat channel.`;
  }

  private _buildRuntimeContext(channel?: string, chatId?: string): string {
    const now = new Date().toLocaleString('en-US', {
      year: 'numeric',
      month: '2-digit',
      day: '2-digit',
      hour: '2-digit',
      minute: '2-digit',
      weekday: 'long',
    });
    const tz = Intl.DateTimeFormat().resolvedOptions().timeZone;
    const lines = [`Current Time: ${now} (${tz})`];
    if (channel && chatId) {
      lines.push(`Channel: ${channel}`, `Chat ID: ${chatId}`);
    }
    return `${RUNTIME_CONTEXT_TAG}\n${lines.join('\n')}`;
  }

  private _loadBootstrapFiles(): string {
    const parts: string[] = [];
    for (const filename of BOOTSTRAP_FILES) {
      const path = join(this._workspace, filename);
      if (existsSync(path)) {
        const content = readFileSync(path, 'utf8');
        parts.push(`## ${filename}\n\n${content}`);
      }
    }
    return parts.join('\n\n');
  }
}