/**
 * Migration report writer — turns a `MigrationPlan` (from
 * `migration-transform.ts`) into a CSV + a human-readable Markdown
 * summary on disk under `.migration/<timestamp>/`.
 *
 * The CSV format is intentionally machine-friendly (one row per
 * planned operation) so it can be diffed across runs and inspected
 * by hand. The summary is designed for "open this in your editor and
 * eyeball it for 5 minutes before --apply."
 */

import { promises as fs } from 'node:fs';
import path from 'node:path';

import type { MigrationPlan } from './migration-transform';

// ─── Output directory ───────────────────────────────────────────────────────

export interface ReportPaths {
  rootDir: string;
  csvPath: string;
  summaryPath: string;
  planJsonPath: string;
}

/** Resolve report paths relative to the worktree root. The timestamped
 *  directory is created lazily by `writeReport`. */
export function resolveReportPaths(
  rootDir: string,
  timestamp: string = new Date().toISOString().replace(/[:.]/g, '-'),
): ReportPaths {
  const dir = path.join(rootDir, '.migration', timestamp);
  return {
    rootDir: dir,
    csvPath: path.join(dir, 'report.csv'),
    summaryPath: path.join(dir, 'summary.md'),
    planJsonPath: path.join(dir, 'plan.json'),
  };
}

// ─── CSV row shape ──────────────────────────────────────────────────────────

interface CsvRow {
  op: string; // create_client / create_contact / create_interest / auto_link / flag / needs_review
  reason: string;
  source_id: string;
  target_table: string;
  target_value: string;
  confidence: string;
  manual_review: 'true' | 'false';
}

// Trivial CSV escape: quote any cell that contains comma / quote / newline,
// double up internal quotes per RFC 4180. No need for a dependency.
function csvEscape(s: string): string {
  if (/[",\n\r]/.test(s)) {
    return `"${s.replace(/"/g, '""')}"`;
  }
  return s;
}

function rowToCsvLine(r: CsvRow): string {
  return [
    r.op,
    r.reason,
    r.source_id,
    r.target_table,
    r.target_value,
    r.confidence,
    r.manual_review,
  ]
    .map(csvEscape)
    .join(',');
}

// ─── Build CSV ──────────────────────────────────────────────────────────────

export function buildCsv(plan: MigrationPlan): string {
  const lines: string[] = [];
  lines.push(
    [
      'op',
      'reason',
      'source_id',
      'target_table',
      'target_value',
      'confidence',
      'manual_review',
    ].join(','),
  );

  for (const client of plan.clients) {
    lines.push(
      rowToCsvLine({
        op: 'create_client',
        reason: client.sourceIds.length > 1 ? 'auto-merged cluster' : 'new',
        source_id: client.sourceIds.join('|'),
        target_table: 'clients.fullName',
        target_value: client.fullName,
        confidence: 'N/A',
        manual_review: 'false',
      }),
    );
    for (const c of client.contacts) {
      lines.push(
        rowToCsvLine({
          op: 'create_contact',
          reason: c.flagged ?? 'new',
          source_id: client.sourceIds.join('|'),
          target_table: `clientContacts.${c.channel}`,
          target_value: c.value,
          confidence: 'N/A',
          manual_review: c.flagged ? 'true' : 'false',
        }),
      );
    }
    for (const a of client.addresses) {
      lines.push(
        rowToCsvLine({
          op: 'create_address',
          reason: 'address text present',
          source_id: client.sourceIds.join('|'),
          target_table: 'clientAddresses.countryIso',
          target_value: a.countryIso ?? '(unresolved)',
          confidence: a.countryConfidence ?? 'fallback',
          manual_review: a.countryConfidence === 'fallback' || !a.countryIso ? 'true' : 'false',
        }),
      );
    }
  }

  for (const interest of plan.interests) {
    lines.push(
      rowToCsvLine({
        op: 'create_interest',
        reason: `pipelineStage=${interest.pipelineStage}`,
        source_id: String(interest.sourceId),
        target_table: 'interests',
        target_value: `${interest.berthMooringNumber ?? '(no berth)'} / ${interest.yachtName ?? '(no yacht)'}`,
        confidence: 'N/A',
        manual_review: 'false',
      }),
    );
  }

  for (const link of plan.autoLinks) {
    lines.push(
      rowToCsvLine({
        op: 'auto_link',
        reason: link.reasons.join(' + '),
        source_id: `${link.leadSourceId}<-${link.mergedSourceIds.join(',')}`,
        target_table: 'clients',
        target_value: '(merged into lead)',
        confidence: `score=${link.score}`,
        manual_review: 'false',
      }),
    );
  }

  for (const pair of plan.needsReview) {
    lines.push(
      rowToCsvLine({
        op: 'needs_review',
        reason: pair.reasons.join(' + '),
        source_id: `${pair.aSourceId}<->${pair.bSourceId}`,
        target_table: 'clients',
        target_value: '(human review required)',
        confidence: `score=${pair.score}`,
        manual_review: 'true',
      }),
    );
  }

  for (const flag of plan.flags) {
    lines.push(
      rowToCsvLine({
        op: 'flag',
        reason: flag.reason,
        source_id: String(flag.sourceId),
        target_table: flag.sourceTable,
        target_value: JSON.stringify(flag.details ?? {}),
        confidence: 'N/A',
        manual_review: 'true',
      }),
    );
  }

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

// ─── Build summary markdown ─────────────────────────────────────────────────

export function buildSummary(plan: MigrationPlan, generatedAt: string): string {
  const s = plan.stats;
  const lines: string[] = [];
  lines.push(`# Migration Dry-Run — ${generatedAt}`);
  lines.push('');
  lines.push('## Input');
  lines.push(`- ${s.inputInterestRows} NocoDB Interests`);
  lines.push(`- ${s.inputResidentialRows} NocoDB Residential Interests`);
  lines.push('');
  lines.push('## Outcome');
  lines.push(`- ${s.outputClients} clients`);
  lines.push(`- ${s.outputInterests} interests (one per source row, linked to deduped client)`);
  lines.push(`- ${s.outputContacts} client_contacts`);
  lines.push(`- ${s.outputAddresses} client_addresses`);
  lines.push('');
  lines.push('## Auto-linked clusters');
  if (plan.autoLinks.length === 0) {
    lines.push('_None — every input row maps to a unique client._');
  } else {
    for (const link of plan.autoLinks) {
      const merged = link.mergedSourceIds.length;
      lines.push(
        `- Lead row \`${link.leadSourceId}\` ← merged ${merged} other row${merged === 1 ? '' : 's'} (\`${link.mergedSourceIds.join(', ')}\`) — score ${link.score} via ${link.reasons.join(' + ')}`,
      );
    }
  }
  lines.push('');
  lines.push('## Pairs flagged for human review');
  if (plan.needsReview.length === 0) {
    lines.push('_None._');
  } else {
    for (const pair of plan.needsReview) {
      lines.push(
        `- Rows \`${pair.aSourceId}\` ↔ \`${pair.bSourceId}\` — score ${pair.score} (${pair.reasons.join(' + ')})`,
      );
    }
  }
  lines.push('');
  lines.push('## Data quality flags');
  if (plan.flags.length === 0) {
    lines.push('_No quality issues._');
  } else {
    const byReason = new Map<string, number>();
    for (const f of plan.flags) {
      byReason.set(f.reason, (byReason.get(f.reason) ?? 0) + 1);
    }
    for (const [reason, count] of [...byReason].sort((a, b) => b[1] - a[1])) {
      lines.push(`- **${count}× ${reason}**`);
    }
    lines.push('');
    lines.push('### Detail');
    for (const f of plan.flags.slice(0, 30)) {
      lines.push(
        `- \`${f.sourceTable}#${f.sourceId}\`: ${f.reason}${f.details ? ` — \`${JSON.stringify(f.details)}\`` : ''}`,
      );
    }
    if (plan.flags.length > 30) {
      lines.push(`- _… and ${plan.flags.length - 30} more (see report.csv for full list)_`);
    }
  }
  lines.push('');
  lines.push('## Next step');
  lines.push('');
  lines.push('Eyeball the auto-linked + flagged-for-review pairs above.');
  lines.push('When satisfied, re-run the script with `--apply --report .migration/<this-dir>/`.');
  lines.push('Apply will refuse to run if the source NocoDB has changed since this dry-run.');

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

// ─── Write to disk ──────────────────────────────────────────────────────────

export async function writeReport(
  paths: ReportPaths,
  plan: MigrationPlan,
  generatedAt: string,
): Promise<void> {
  await fs.mkdir(paths.rootDir, { recursive: true });
  await fs.writeFile(paths.csvPath, buildCsv(plan), 'utf-8');
  await fs.writeFile(paths.summaryPath, buildSummary(plan, generatedAt), 'utf-8');
  await fs.writeFile(paths.planJsonPath, JSON.stringify(plan, null, 2), 'utf-8');
}