#!/usr/bin/env bun
/**
 * Generate SKILL.md files from .tmpl templates.
 *
 * Pipeline:
 *   read .tmpl → find {{PLACEHOLDERS}} → resolve from source → format → write .md
 *
 * Supports --dry-run: generate to memory, exit 1 if different from committed file.
 * Used by skill:check and CI freshness checks.
 */

import { COMMAND_DESCRIPTIONS } from '../browse/src/commands';
import { SNAPSHOT_FLAGS } from '../browse/src/snapshot';
import * as fs from 'fs';
import * as path from 'path';

const ROOT = path.resolve(import.meta.dir, '..');
const DRY_RUN = process.argv.includes('--dry-run');

// ─── Placeholder Resolvers ──────────────────────────────────

function generateCommandReference(): string {
  // Group commands by category
  const groups = new Map<string, Array<{ command: string; description: string; usage?: string }>>();
  for (const [cmd, meta] of Object.entries(COMMAND_DESCRIPTIONS)) {
    const list = groups.get(meta.category) || [];
    list.push({ command: cmd, description: meta.description, usage: meta.usage });
    groups.set(meta.category, list);
  }

  // Category display order
  const categoryOrder = [
    'Navigation', 'Reading', 'Interaction', 'Inspection',
    'Visual', 'Snapshot', 'Meta', 'Tabs', 'Server',
  ];

  const sections: string[] = [];
  for (const category of categoryOrder) {
    const commands = groups.get(category);
    if (!commands || commands.length === 0) continue;

    // Sort alphabetically within category
    commands.sort((a, b) => a.command.localeCompare(b.command));

    sections.push(`### ${category}`);
    sections.push('| Command | Description |');
    sections.push('|---------|-------------|');
    for (const cmd of commands) {
      const display = cmd.usage ? `\`${cmd.usage}\`` : `\`${cmd.command}\``;
      sections.push(`| ${display} | ${cmd.description} |`);
    }
    sections.push('');
  }

  return sections.join('\n').trimEnd();
}

function generateSnapshotFlags(): string {
  const lines: string[] = [
    'The snapshot is your primary tool for understanding and interacting with pages.',
    '',
    '```',
  ];

  for (const flag of SNAPSHOT_FLAGS) {
    const label = flag.valueHint ? `${flag.short} ${flag.valueHint}` : flag.short;
    lines.push(`${label.padEnd(10)}${flag.description}`);
  }

  lines.push('```');
  lines.push('');
  lines.push('Combine flags: `$B snapshot -i -a -C -o /tmp/annotated.png`');
  lines.push('');
  lines.push('After snapshot, use @refs everywhere:');
  lines.push('```bash');
  lines.push('$B click @e3       $B fill @e4 "value"     $B hover @e1');
  lines.push('$B html @e2        $B css @e5 "color"      $B attrs @e6');
  lines.push('$B click @c1       # cursor-interactive ref (from -C)');
  lines.push('```');
  lines.push('');
  lines.push('Refs are invalidated on navigation — run `snapshot` again after `goto`.');

  return lines.join('\n');
}

const RESOLVERS: Record<string, () => string> = {
  COMMAND_REFERENCE: generateCommandReference,
  SNAPSHOT_FLAGS: generateSnapshotFlags,
};

// ─── Template Processing ────────────────────────────────────

const GENERATED_HEADER = `<!-- AUTO-GENERATED from {{SOURCE}} — do not edit directly -->\n<!-- Regenerate: bun run gen:skill-docs -->\n`;

function processTemplate(tmplPath: string): { outputPath: string; content: string } {
  const tmplContent = fs.readFileSync(tmplPath, 'utf-8');
  const relTmplPath = path.relative(ROOT, tmplPath);
  const outputPath = tmplPath.replace(/\.tmpl$/, '');

  // Replace placeholders
  let content = tmplContent.replace(/\{\{(\w+)\}\}/g, (match, name) => {
    const resolver = RESOLVERS[name];
    if (!resolver) throw new Error(`Unknown placeholder {{${name}}} in ${relTmplPath}`);
    return resolver();
  });

  // Check for any remaining unresolved placeholders
  const remaining = content.match(/\{\{(\w+)\}\}/g);
  if (remaining) {
    throw new Error(`Unresolved placeholders in ${relTmplPath}: ${remaining.join(', ')}`);
  }

  // Prepend generated header (after frontmatter)
  const header = GENERATED_HEADER.replace('{{SOURCE}}', path.basename(tmplPath));
  const fmEnd = content.indexOf('---', content.indexOf('---') + 3);
  if (fmEnd !== -1) {
    const insertAt = content.indexOf('\n', fmEnd) + 1;
    content = content.slice(0, insertAt) + header + content.slice(insertAt);
  } else {
    content = header + content;
  }

  return { outputPath, content };
}

// ─── Main ───────────────────────────────────────────────────

function findTemplates(): string[] {
  const templates: string[] = [];
  const candidates = [
    path.join(ROOT, 'SKILL.md.tmpl'),
    path.join(ROOT, 'browse', 'SKILL.md.tmpl'),
  ];
  for (const p of candidates) {
    if (fs.existsSync(p)) templates.push(p);
  }
  return templates;
}

let hasChanges = false;

for (const tmplPath of findTemplates()) {
  const { outputPath, content } = processTemplate(tmplPath);
  const relOutput = path.relative(ROOT, outputPath);

  if (DRY_RUN) {
    const existing = fs.existsSync(outputPath) ? fs.readFileSync(outputPath, 'utf-8') : '';
    if (existing !== content) {
      console.log(`STALE: ${relOutput}`);
      hasChanges = true;
    } else {
      console.log(`FRESH: ${relOutput}`);
    }
  } else {
    fs.writeFileSync(outputPath, content);
    console.log(`GENERATED: ${relOutput}`);
  }
}

if (DRY_RUN && hasChanges) {
  console.error('\nGenerated SKILL.md files are stale. Run: bun run gen:skill-docs');
  process.exit(1);
}