/**
 * Generates the Kysely database type from the migrated schema.
 *
 * Repositories that need a statement the MikroORM QueryBuilder cannot express
 * go through `this.kysely<...>()`, and Kysely types every table and column it
 * touches from the type parameter. Those parameters used to be interfaces
 * written by hand in each repository, so a migration that renamed a column or
 * made it nullable left them stale while `tsc` stayed green. This script
 * derives them instead, the same way `generate-entities.ts` derives the
 * entities: it migrates a throwaway SQLite file with the real migrations,
 * reads every table's columns back and writes
 *
 *   src/db/kysely/<Table>.table.ts   one interface per table
 *   src/db/kysely/db.ts              `DB`, the map from table name to interface
 *
 * A repository narrows it with `Pick<DB, 'trips' | 'days'>`.
 *
 * The column types describe what the driver hands back, which is the storage
 * model, not the domain one: an INTEGER flag is `number`, a timestamp is the
 * `string` it is stored as. A column an insert may leave out (an integer
 * primary key, anything with a DEFAULT, anything nullable) is
 * `InsertOptional<T>`, declared in the generated `columns.ts`.
 *
 * Usage:
 *   node --import tsx scripts/generate-db-types.ts           # rewrite src/db/kysely/
 *   node --import tsx scripts/generate-db-types.ts --check   # exit 1 when src/db/kysely/ drifted (CI)
 */

import fs from 'node:fs';
import path from 'node:path';

import Database from 'better-sqlite3';

import { migrateTempDb, tempDbPath } from './generate-entities';

const SERVER_ROOT = path.join(__dirname, '..');
export const KYSELY_DIR = path.join(SERVER_ROOT, 'src/db/kysely');

/** Tables the application never queries: the migrator's own bookkeeping. */
const SKIPPED_TABLES: ReadonlySet<string> = new Set(['mikro_orm_migrations']);

const HEADER = '// Generated by scripts/generate-db-types.ts from the migrated schema. Do not edit by hand:\n' +
  '// change the migration, then run `npm run gen:db-types`.\n';

export interface ColumnInfo {
  name: string;
  /** The declared type as `PRAGMA table_xinfo` reports it (may be empty). */
  type: string;
  notnull: boolean;
  hasDefault: boolean;
  /** Position in the primary key, 0 when the column is not part of it. */
  pk: number;
  /** 0 for an ordinary column, 2 or 3 for a generated (computed) one. */
  hidden: number;
}

export interface TableInfo {
  name: string;
  columns: ColumnInfo[];
}

/**
 * The TypeScript type a value of this declared type comes back as from
 * better-sqlite3, following SQLite's affinity rules (sqlite.org/datatype3.html
 * section 3.1). Date-like declarations have NUMERIC affinity on paper, but
 * every one of them in this schema holds ISO text, so they read as strings.
 */
export function tsTypeFor(declared: string): string {
  const t = declared.toUpperCase();
  if (t.includes('INT')) return 'number';
  if (t.includes('CHAR') || t.includes('CLOB') || t.includes('TEXT')) return 'string';
  if (t.includes('BLOB')) return 'Buffer';
  if (t.includes('REAL') || t.includes('FLOA') || t.includes('DOUB')) return 'number';
  if (t.includes('DATE') || t.includes('TIME')) return 'string';
  if (t.includes('BOOL') || t.includes('NUMERIC') || t.includes('DECIMAL')) return 'number';
  if (t === '') return 'unknown';
  throw new Error(`generate-db-types: no TypeScript mapping for the declared column type "${declared}"`);
}

/** `budget_items` -> `BudgetItems`. */
export function pascalCase(table: string): string {
  return table
    .split('_')
    .filter((part) => part !== '')
    .map((part) => part[0].toUpperCase() + part.slice(1))
    .join('');
}

/** The interface name for a table: `BudgetItemsTable`. */
export function interfaceName(table: string): string {
  return `${pascalCase(table)}Table`;
}

function columnType(table: TableInfo, column: ColumnInfo): string {
  // A lone INTEGER primary key aliases the rowid: it is never null and the
  // database assigns it when the insert leaves it out.
  const pkColumns = table.columns.filter((c) => c.pk > 0);
  const isRowid = column.pk > 0 && pkColumns.length === 1 && column.type.toUpperCase() === 'INTEGER';
  const base = tsTypeFor(column.type);
  const nullable = !column.notnull && column.pk === 0;
  const value = nullable ? `${base} | null` : base;
  if (column.hidden === 2 || column.hidden === 3) return `GeneratedAlways<${value}>`;
  if (isRowid || column.hasDefault || nullable) return `InsertOptional<${value}>`;
  return value;
}

const IDENTIFIER = /^[A-Za-z_$][A-Za-z0-9_$]*$/;

function propertyKey(name: string): string {
  return IDENTIFIER.test(name) ? name : `'${name.replace(/'/g, "\\'")}'`;
}

/** The source of `<Table>.table.ts`. */
export function renderTable(table: TableInfo): string {
  const types = table.columns.map((c) => columnType(table, c));
  const has = (marker: string) => types.some((t) => t.startsWith(`${marker}<`));
  const imports =
    (has('GeneratedAlways') ? "import type { GeneratedAlways } from 'kysely';\n" : '') +
    (has('InsertOptional') ? "import type { InsertOptional } from './columns';\n" : '');
  const importBlock = imports === '' ? '' : `${imports}\n`;
  const body = table.columns.map((c, i) => `  ${propertyKey(c.name)}: ${types[i]};`).join('\n');
  return `${HEADER}\n${importBlock}export interface ${interfaceName(table.name)} {\n${body}\n}\n`;
}

/**
 * The source of `columns.ts`. Kysely makes a column optional on insert when its
 * insert type can be null or undefined, which it tests with `NonNullable`. The
 * server compiles without `strictNullChecks`, where `T | undefined` and
 * `T | null` collapse to `T`, so Kysely's own `Generated<T>` would still demand
 * the column. `void` survives that collapse and still refuses any other value,
 * so the insert stays typed.
 */
export function renderColumns(): string {
  return (
    `${HEADER}\nimport type { ColumnType } from 'kysely';\n\n` +
    '/** A column an insert may leave out: the database assigns it (rowid, DEFAULT) or stores NULL. */\n' +
    'export type InsertOptional<T> = ColumnType<T, T | void, T>;\n'
  );
}

/** The source of `db.ts`. */
export function renderDb(tables: readonly TableInfo[]): string {
  const imports = tables
    .map((t) => `import type { ${interfaceName(t.name)} } from './${pascalCase(t.name)}.table';`)
    .join('\n');
  const body = tables.map((t) => `  ${propertyKey(t.name)}: ${interfaceName(t.name)};`).join('\n');
  return (
    `${HEADER}\n${imports}\n\n` +
    '/** Every table of the migrated schema. A repository narrows it: `this.kysely<Pick<DB, \'trips\'>>()`. */\n' +
    `export interface DB {\n${body}\n}\n`
  );
}

/** Reads every application table of a migrated database, sorted by name, columns in declaration order. */
export function readSchema(dbPath: string): TableInfo[] {
  const conn = new Database(dbPath, { readonly: true });
  try {
    const names = conn
      .prepare("SELECT name FROM sqlite_master WHERE type = 'table' AND name NOT LIKE 'sqlite_%' ORDER BY name")
      .all() as { name: string }[];
    return names
      .filter(({ name }) => !SKIPPED_TABLES.has(name))
      .map(({ name }) => {
        const rows = conn.prepare(`PRAGMA table_xinfo("${name.replace(/"/g, '""')}")`).all() as {
          name: string;
          type: string;
          notnull: number;
          dflt_value: string | null;
          pk: number;
          hidden: number;
        }[];
        return {
          name,
          columns: rows
            .filter((r) => r.hidden !== 1)
            .map((r) => ({
              name: r.name,
              type: r.type,
              notnull: r.notnull === 1,
              hasDefault: r.dflt_value !== null,
              pk: r.pk,
              hidden: r.hidden,
            })),
        };
      });
  } finally {
    conn.close();
  }
}

/** File name -> content for everything under src/db/kysely/. */
export function renderAll(tables: readonly TableInfo[]): Map<string, string> {
  if (tables.length === 0) {
    throw new Error('generate-db-types: the migrated schema has no tables; check the migrations path');
  }
  const files = new Map<string, string>();
  for (const table of tables) files.set(`${pascalCase(table.name)}.table.ts`, renderTable(table));
  files.set('columns.ts', renderColumns());
  files.set('db.ts', renderDb(tables));
  return files;
}

export async function generateDbTypes(): Promise<Map<string, string>> {
  const dbPath = tempDbPath();
  try {
    await migrateTempDb(dbPath);
    return renderAll(readSchema(dbPath));
  } finally {
    fs.rmSync(dbPath, { force: true });
  }
}

/** Every file that differs from, is missing from or is extra in `dir`. Read-only. */
export function checkDbTypes(dir: string, files: ReadonlyMap<string, string>): string[] {
  const drift: string[] = [];
  for (const [fileName, content] of files) {
    const onDisk = path.join(dir, fileName);
    const current = fs.existsSync(onDisk) ? fs.readFileSync(onDisk, 'utf8').replace(/\r\n/g, '\n') : undefined;
    if (current !== content) drift.push(fileName);
  }
  const onDiskFiles = fs.existsSync(dir) ? fs.readdirSync(dir).filter((f) => f.endsWith('.ts')) : [];
  for (const fileName of onDiskFiles) {
    if (!files.has(fileName)) drift.push(`${fileName} (not produced by the generator)`);
  }
  return drift.sort();
}

/** Replaces the contents of `dir` with `files`, removing any .ts file the generator no longer produces. */
export function writeDbTypes(dir: string, files: ReadonlyMap<string, string>): void {
  fs.mkdirSync(dir, { recursive: true });
  for (const fileName of fs.readdirSync(dir)) {
    if (fileName.endsWith('.ts') && !files.has(fileName)) fs.rmSync(path.join(dir, fileName));
  }
  for (const [fileName, content] of files) fs.writeFileSync(path.join(dir, fileName), content);
}

async function main(): Promise<void> {
  const check = process.argv.slice(2).includes('--check');
  const files = await generateDbTypes();
  if (check) {
    const drift = checkDbTypes(KYSELY_DIR, files);
    for (const fileName of drift) console.error(`[generate-db-types] DRIFT: src/db/kysely/${fileName}`);
    if (drift.length > 0) {
      console.error('[generate-db-types] --check failed. Run: npm run gen:db-types');
      process.exit(1);
    }
    console.log(`[generate-db-types] --check: ${files.size} files match the migrated schema`);
    return;
  }
  writeDbTypes(KYSELY_DIR, files);
  console.log(`[generate-db-types] wrote ${files.size} files to src/db/kysely/`);
}

if (require.main === module) {
  main().catch((err: unknown) => {
    console.error('[generate-db-types] failed:', err);
    process.exit(1);
  });
}