#!/usr/bin/env bun
/**
 * migrate-db.ts — Migrate AGOR data from a Tauri (source) database to an
 * Electrobun (target) database using the canonical schema.
 *
 * Usage:
 *   bun tools/migrate-db.ts --from <source.db> --to <target.db>
 *   bun tools/migrate-db.ts --from ~/.local/share/agor/sessions.db \
 *                           --to   ~/.config/agor/settings.db
 *
 * Behavior:
 * - Opens source DB read-only (never modifies it).
 * - Creates/opens target DB, applies canonical.sql if schema_version absent.
 * - Copies rows for every table present in BOTH source and target.
 * - Wraps all inserts in a single transaction (atomic rollback on failure).
 * - Reports per-table row counts.
 * - Writes migration fence to schema_version in target.
 */

import { Database } from "bun:sqlite";
import { readFileSync, existsSync } from "fs";
import { join, resolve } from "path";

// ── CLI args ──────────────────────────────────────────────────────────────────

function usage(): never {
  console.error("Usage: bun tools/migrate-db.ts --from <source.db> --to <target.db>");
  process.exit(1);
}

const args = process.argv.slice(2);
let fromPath = "";
let toPath = "";

for (let i = 0; i < args.length; i++) {
  if (args[i] === "--from" && args[i + 1]) fromPath = args[++i];
  else if (args[i] === "--to" && args[i + 1]) toPath = args[++i];
  else if (args[i] === "--help" || args[i] === "-h") usage();
}

if (!fromPath || !toPath) usage();

fromPath = resolve(fromPath);
toPath = resolve(toPath);

if (!existsSync(fromPath)) {
  console.error(`Source database not found: ${fromPath}`);
  process.exit(1);
}

// ── Load canonical DDL ────────────────────────────────────────────────────────

const schemaPath = join(import.meta.dir, "..", "schema", "canonical.sql");
let ddl: string;
try {
  ddl = readFileSync(schemaPath, "utf-8");
} catch (err) {
  console.error(`Failed to read canonical schema: ${err}`);
  process.exit(1);
}

// ── Open databases ────────────────────────────────────────────────────────────

const sourceDb = new Database(fromPath, { readonly: true });
const targetDb = new Database(toPath);

// Apply pragmas to target
targetDb.exec("PRAGMA journal_mode = WAL");
targetDb.exec("PRAGMA foreign_keys = OFF"); // Disable during migration for insert order flexibility
targetDb.exec("PRAGMA busy_timeout = 5000");

// Apply canonical schema to target if needed
const hasVersion = (() => {
  try {
    const row = targetDb
      .query<{ cnt: number }, []>("SELECT COUNT(*) AS cnt FROM schema_version")
      .get();
    return (row?.cnt ?? 0) > 0;
  } catch {
    return false;
  }
})();

if (!hasVersion) {
  console.log("Applying canonical schema to target database...");
  targetDb.exec(ddl);
}

// ── Discover migratable tables ────────────────────────────────────────────────

/** Get regular (non-virtual, non-internal) table names from a database. */
function getTableNames(db: Database): Set<string> {
  const rows = db
    .prepare(
      `SELECT name FROM sqlite_master
       WHERE type = 'table'
         AND name NOT LIKE 'sqlite_%'
         AND name NOT LIKE '%_content'
         AND name NOT LIKE '%_data'
         AND name NOT LIKE '%_idx'
         AND name NOT LIKE '%_config'
         AND name NOT LIKE '%_docsize'
       ORDER BY name`,
    )
    .all() as Array<{ name: string }>;
  return new Set(rows.map((r) => r.name));
}

const sourceTables = getTableNames(sourceDb);
const targetTables = getTableNames(targetDb);

// Only migrate tables present in both source and target
const migratable = [...sourceTables].filter((t) => targetTables.has(t));

if (migratable.length === 0) {
  console.log("No overlapping tables found between source and target.");
  sourceDb.close();
  targetDb.close();
  process.exit(0);
}

console.log(`\nMigrating ${migratable.length} tables from:`);
console.log(`  source: ${fromPath}`);
console.log(`  target: ${toPath}\n`);

// ── Migrate data ──────────────────────────────────────────────────────────────

interface MigrationResult {
  table: string;
  rows: number;
  skipped: boolean;
  error?: string;
}

const results: MigrationResult[] = [];

const migrate = targetDb.transaction(() => {
  for (const table of migratable) {
    // Skip schema_version — we write our own fence
    if (table === "schema_version") {
      results.push({ table, rows: 0, skipped: true });
      continue;
    }

    try {
      // Read all rows from source
      const rows = sourceDb.prepare(`SELECT * FROM "${table}"`).all();

      if (rows.length === 0) {
        results.push({ table, rows: 0, skipped: false });
        continue;
      }

      // Get column names from the first row
      const columns = Object.keys(rows[0] as Record<string, unknown>);
      const placeholders = columns.map(() => "?").join(", ");
      const colList = columns.map((c) => `"${c}"`).join(", ");

      const insertStmt = targetDb.prepare(
        `INSERT OR IGNORE INTO "${table}" (${colList}) VALUES (${placeholders})`,
      );

      let count = 0;
      for (const row of rows) {
        const values = columns.map((c) => (row as Record<string, unknown>)[c] ?? null);
        insertStmt.run(...values);
        count++;
      }

      results.push({ table, rows: count, skipped: false });
    } catch (err) {
      const msg = err instanceof Error ? err.message : String(err);
      results.push({ table, rows: 0, skipped: false, error: msg });
      throw new Error(`Migration failed on table '${table}': ${msg}`);
    }
  }
});

try {
  migrate();
} catch (err) {
  console.error(`\nMIGRATION ROLLED BACK: ${err}`);
  sourceDb.close();
  targetDb.close();
  process.exit(1);
}

// ── Write version fence ───────────────────────────────────────────────────────

const timestamp = new Date().toISOString();
targetDb.exec("DELETE FROM schema_version");
targetDb
  .prepare(
    "INSERT INTO schema_version (version, migration_source, migration_timestamp) VALUES (?, ?, ?)",
  )
  .run(1, "migrate-db", timestamp);

// Re-enable foreign keys
targetDb.exec("PRAGMA foreign_keys = ON");

// ── Report ────────────────────────────────────────────────────────────────────

console.log("Table                    Rows    Status");
console.log("─".repeat(50));

let totalRows = 0;
for (const r of results) {
  const status = r.skipped ? "skipped" : r.error ? `ERROR: ${r.error}` : "ok";
  const rowStr = String(r.rows).padStart(8);
  console.log(`${r.table.padEnd(25)}${rowStr}    ${status}`);
  totalRows += r.rows;
}

console.log("─".repeat(50));
console.log(`Total: ${totalRows} rows migrated across ${results.filter((r) => !r.skipped && !r.error).length} tables`);
console.log(`Version fence: v1 at ${timestamp}`);

sourceDb.close();
targetDb.close();