// Deterministic state mutation functions for linkedin-thought-leadership plugin.
// Pure functions operate on string content (same pattern as week-rollover.mjs).
// I/O wrapper (writeState) handles file reads/writes (same pattern as queue-manager.mjs).

import { readFileSync, writeFileSync, renameSync } from 'node:fs';
import { join, dirname } from 'node:path';
import { fileURLToPath } from 'node:url';
import { applyWeekRollover } from './week-rollover.mjs';

const __dirname = dirname(fileURLToPath(import.meta.url));
const HOME = process.env.HOME || process.env.USERPROFILE || '';
const STATE_FILE = process.env.STATE_FILE || join(HOME, '.claude', 'linkedin-thought-leadership.local.md');

function replaceField(content, field, value) {
  return content.replace(
    new RegExp(`^${field}: .*`, 'm'),
    `${field}: ${value}`
  );
}

function isoWeekFromDate(dateStr) {
  const d = new Date(dateStr + 'T12:00:00Z');
  const dayNum = d.getUTCDay() || 7;
  d.setUTCDate(d.getUTCDate() + 4 - dayNum);
  const yearStart = new Date(Date.UTC(d.getUTCFullYear(), 0, 1));
  const weekNo = Math.ceil(((d - yearStart) / 86400000 + 1) / 7);
  return `${d.getUTCFullYear()}-W${String(weekNo).padStart(2, '0')}`;
}

function daysBetween(dateA, dateB) {
  const a = new Date(dateA + 'T12:00:00Z').getTime();
  const b = new Date(dateB + 'T12:00:00Z').getTime();
  if (isNaN(a) || isNaN(b)) return null;
  return Math.abs(Math.round((b - a) / 86400000));
}

function extractField(content, field) {
  const re = new RegExp(`^${field}: *"?([^"\\n]*)"?`, 'm');
  const m = content.match(re);
  return m ? m[1].trim() : '';
}

/**
 * Update post tracking fields deterministically.
 * @param {string} stateContent - Full state file content
 * @param {{ postDate: string, postTopic: string, hookText: string, charCount: number, format: string }} opts
 * @returns {{ content: string, changes: string[] } | null}
 */
export function updatePostTracking(stateContent, { postDate, postTopic, hookText, charCount, format }) {
  let content = stateContent;
  const changes = [];

  // 1. Update last_post_date
  content = replaceField(content, 'last_post_date', `"${postDate}"`);
  changes.push(`last_post_date → ${postDate}`);

  // 2. Update last_post_topic
  content = replaceField(content, 'last_post_topic', `"${postTopic}"`);
  changes.push(`last_post_topic → ${postTopic}`);

  // 3. Set first_post_date if null
  const existingFirst = extractField(content, 'first_post_date');
  if (!existingFirst || existingFirst === 'null') {
    content = replaceField(content, 'first_post_date', `"${postDate}"`);
    changes.push(`first_post_date → ${postDate} (first post!)`);
  }

  // 4. Week rollover — check if ISO week changed
  const currentWeek = extractField(content, 'current_week');
  const postWeek = isoWeekFromDate(postDate);
  const rollover = applyWeekRollover(content, currentWeek, postWeek);
  if (rollover) {
    content = rollover.content;
    changes.push(rollover.message);
  }

  // 5. Increment posts_this_week
  const currentPosts = parseInt(extractField(content, 'posts_this_week') || '0', 10);
  content = replaceField(content, 'posts_this_week', String(currentPosts + 1));
  changes.push(`posts_this_week → ${currentPosts + 1}`);

  // 6. Update streak
  const lastPostDate = extractField(stateContent, 'last_post_date');
  let currentStreak = parseInt(extractField(content, 'current_streak') || '0', 10);

  if (lastPostDate && lastPostDate !== 'null') {
    const gap = daysBetween(lastPostDate, postDate);
    if (gap !== null && gap <= 2) {
      currentStreak += 1;
      changes.push(`current_streak → ${currentStreak} (gap: ${gap}d)`);
    } else {
      currentStreak = 1;
      changes.push(`current_streak → 1 (gap: ${gap}d, reset)`);
    }
  } else {
    currentStreak = 1;
    changes.push('current_streak → 1 (first post)');
  }
  content = replaceField(content, 'current_streak', String(currentStreak));

  // 7. Update longest_streak if exceeded
  const longestStreak = parseInt(extractField(content, 'longest_streak') || '0', 10);
  if (currentStreak > longestStreak) {
    content = replaceField(content, 'longest_streak', String(currentStreak));
    changes.push(`longest_streak → ${currentStreak}`);
  }

  // 8. Append to Recent Posts section
  const hookPreview = hookText.length > 60 ? hookText.slice(0, 57) + '...' : hookText;
  const entry = `- [${postDate}] "${hookPreview}" (${charCount}) - ${postTopic}`;
  content = content.replace(
    /^(## Recent Posts\n\n?)/m,
    `$1${entry}\n`
  );
  changes.push(`Recent Posts += ${postDate} "${hookPreview.slice(0, 30)}..."`);

  if (content === stateContent) return null;
  return { content, changes };
}

/**
 * Remove Recent Posts entries older than maxAgeDays.
 * @param {string} stateContent - Full state file content
 * @param {number} [maxAgeDays=90]
 * @returns {{ content: string, pruned: number } | null}
 */
export function pruneContentHistory(stateContent, maxAgeDays = 90) {
  const today = new Date();
  const cutoff = new Date(today);
  cutoff.setDate(cutoff.getDate() - maxAgeDays);
  const cutoffStr = cutoff.toISOString().slice(0, 10);

  // Find all Recent Posts entries
  const entryPattern = /^- \[(\d{4}-\d{2}-\d{2})\] .+$/gm;
  const recentSection = stateContent.match(/## Recent Posts\n\n?([\s\S]*?)(?=\n## [^R]|\n## $|$)/m);
  if (!recentSection || !recentSection[1].trim()) return null;

  const sectionContent = recentSection[1];
  let pruned = 0;
  const lines = sectionContent.split('\n');
  const kept = [];

  for (const line of lines) {
    const dateMatch = line.match(/^- \[(\d{4}-\d{2}-\d{2})\]/);
    if (dateMatch) {
      if (dateMatch[1] < cutoffStr) {
        pruned++;
        continue;
      }
    }
    kept.push(line);
  }

  if (pruned === 0) return null;

  const newSection = kept.join('\n');
  const content = stateContent.replace(recentSection[1], newSection);
  return { content, pruned };
}

/**
 * Update follower count and recalculate growth metrics.
 * @param {string} stateContent - Full state file content
 * @param {{ count: number, month: string }} opts
 * @returns {{ content: string, changes: string[] } | null}
 */
export function updateFollowerCount(stateContent, { count, month }) {
  let content = stateContent;
  const changes = [];

  const previousCount = parseInt(extractField(content, 'follower_count') || '0', 10);
  const delta = count - previousCount;

  // Update follower_count
  content = replaceField(content, 'follower_count', String(count));
  changes.push(`follower_count → ${count} (${delta >= 0 ? '+' : ''}${delta})`);

  // Recalculate growth_rate_needed
  const target = parseInt(extractField(content, 'follower_target') || '10000', 10);
  const targetDate = extractField(content, 'target_date');
  const remaining = target - count;

  if (targetDate && targetDate !== 'null' && targetDate !== '""') {
    const [tYear, tMonth] = targetDate.split('-').map(Number);
    const [mYear, mMonth] = month.split('-').map(Number);
    const monthsLeft = (tYear - mYear) * 12 + (tMonth - mMonth);
    const effectiveMonths = Math.max(1, monthsLeft);
    const rateNeeded = Math.ceil(remaining / effectiveMonths);
    content = replaceField(content, 'growth_rate_needed', String(rateNeeded));
    changes.push(`growth_rate_needed → ${rateNeeded}/month`);
  }

  // Append to Milestone Log section
  const logEntry = `- [${month}] ${count} (${delta >= 0 ? '+' : ''}${delta})`;
  content = content.replace(
    /^(## Milestone Log\n)/m,
    `$1${logEntry}\n`
  );
  changes.push(`Milestone Log += ${month}`);

  if (content === stateContent) return null;
  return { content, changes };
}

/**
 * I/O wrapper: read state file, apply update function, write atomically.
 * @param {function(string): {content: string}|null} updateFn - Pure update function
 */
export function writeState(updateFn) {
  const content = readFileSync(STATE_FILE, 'utf-8');
  const result = updateFn(content);
  if (!result) {
    console.log('No changes needed.');
    return;
  }
  const tmpPath = STATE_FILE + '.tmp';
  writeFileSync(tmpPath, result.content, 'utf-8');
  renameSync(tmpPath, STATE_FILE);
  if (result.changes) {
    console.log('State updated:', result.changes.join(', '));
  } else if (result.pruned !== undefined) {
    console.log(`Pruned ${result.pruned} old entries.`);
  }
}

// Standalone mode
if (import.meta.url === `file://${process.argv[1]}`) {
  const args = process.argv.slice(2);
  if (args.includes('--update-post')) {
    const getArg = (flag) => { const i = args.indexOf(flag); return i >= 0 ? args[i + 1] : ''; };
    writeState(content => updatePostTracking(content, {
      postDate: getArg('--date') || new Date().toISOString().slice(0, 10),
      postTopic: getArg('--topic') || 'unknown',
      hookText: getArg('--hook') || '',
      charCount: parseInt(getArg('--chars') || '0', 10),
      format: getArg('--format') || 'post'
    }));
  } else if (args.includes('--prune')) {
    const days = parseInt(args[args.indexOf('--prune') + 1] || '90', 10);
    writeState(content => pruneContentHistory(content, days));
  } else if (args.includes('--update-followers')) {
    const getArg = (flag) => { const i = args.indexOf(flag); return i >= 0 ? args[i + 1] : ''; };
    writeState(content => updateFollowerCount(content, {
      count: parseInt(getArg('--count') || '0', 10),
      month: getArg('--month') || new Date().toISOString().slice(0, 7)
    }));
  } else {
    console.log('Usage:');
    console.log('  node state-updater.mjs --update-post --date YYYY-MM-DD --topic "topic" --hook "Hook text" --chars 1500 --format post');
    console.log('  node state-updater.mjs --prune [days]');
    console.log('  node state-updater.mjs --update-followers --count 920 --month 2026-04');
  }
}