import { drizzle as drizzlePg } from "drizzle-orm/postgres-js";
import { migrate as migratePg } from "drizzle-orm/postgres-js/migrator";
import { readdir, readFile } from "node:fs/promises";
import postgres from "postgres";
import * as schema from "./schema/index.js";

const MIGRATIONS_FOLDER = new URL("./migrations", import.meta.url).pathname;
const DRIZZLE_MIGRATIONS_TABLE = "__drizzle_migrations";
const MIGRATIONS_JOURNAL_JSON = new URL("./migrations/meta/_journal.json", import.meta.url).pathname;

function isSafeIdentifier(value: string): boolean {
  return /^[A-Za-z_][A-Za-z0-9_]*$/.test(value);
}

function quoteIdentifier(value: string): string {
  if (!isSafeIdentifier(value)) throw new Error(`Unsafe SQL identifier: ${value}`);
  return `"${value.replaceAll("\"", "\"\"")}"`;
}

export type MigrationState =
  | { status: "upToDate"; tableCount: number; availableMigrations: string[]; appliedMigrations: string[] }
  | {
      status: "needsMigrations";
      tableCount: number;
      availableMigrations: string[];
      appliedMigrations: string[];
      pendingMigrations: string[];
      reason: "no-migration-journal-empty-db" | "no-migration-journal-non-empty-db" | "pending-migrations";
    };

export function createDb(url: string) {
  const sql = postgres(url);
  return drizzlePg(sql, { schema });
}

async function listMigrationFiles(): Promise<string[]> {
  const entries = await readdir(MIGRATIONS_FOLDER, { withFileTypes: true });
  return entries
    .filter((entry) => entry.isFile() && entry.name.endsWith(".sql"))
    .map((entry) => entry.name)
    .sort((a, b) => a.localeCompare(b));
}

type MigrationJournalFile = {
  entries?: Array<{ tag?: string }>;
};

async function listJournalMigrationFiles(): Promise<string[]> {
  try {
    const raw = await readFile(MIGRATIONS_JOURNAL_JSON, "utf8");
    const parsed = JSON.parse(raw) as MigrationJournalFile;
    if (!Array.isArray(parsed.entries)) return [];
    return parsed.entries
      .map((entry) => (typeof entry?.tag === "string" ? `${entry.tag}.sql` : null))
      .filter((name): name is string => typeof name === "string");
  } catch {
    return [];
  }
}

async function loadAppliedMigrations(
  sql: ReturnType<typeof postgres>,
  migrationTableSchema: string,
  availableMigrations: string[],
): Promise<string[]> {
  const qualifiedTable = `${quoteIdentifier(migrationTableSchema)}.${quoteIdentifier(DRIZZLE_MIGRATIONS_TABLE)}`;
  try {
    const rows = await sql.unsafe<{ name: string }[]>(`SELECT name FROM ${qualifiedTable} ORDER BY id`);
    return rows.map((row) => row.name).filter((name): name is string => Boolean(name));
  } catch (error) {
    if (!(error instanceof Error) || !error.message.includes('column "name" does not exist')) {
      throw error;
    }
  }

  const rows = await sql.unsafe<{ id: number }[]>(`SELECT id FROM ${qualifiedTable} ORDER BY id`);
  const journalMigrationFiles = await listJournalMigrationFiles();
  const appliedFromIds = rows
    .map((row) => journalMigrationFiles[row.id - 1])
    .filter((name): name is string => Boolean(name));
  if (appliedFromIds.length > 0) return appliedFromIds;

  return availableMigrations.slice(0, Math.max(0, rows.length));
}

async function discoverMigrationTableSchema(sql: ReturnType<typeof postgres>): Promise<string | null> {
  const rows = await sql<{ schemaName: string }[]>`
    SELECT n.nspname AS "schemaName"
    FROM pg_class c
    JOIN pg_namespace n ON n.oid = c.relnamespace
    WHERE c.relname = ${DRIZZLE_MIGRATIONS_TABLE} AND c.relkind = 'r'
  `;

  if (rows.length === 0) return null;

  const drizzleSchema = rows.find(({ schemaName }) => schemaName === "drizzle");
  if (drizzleSchema) return drizzleSchema.schemaName;

  const publicSchema = rows.find(({ schemaName }) => schemaName === "public");
  if (publicSchema) return publicSchema.schemaName;

  return rows[0]?.schemaName ?? null;
}

export async function inspectMigrations(url: string): Promise<MigrationState> {
  const sql = postgres(url, { max: 1 });

  try {
    const availableMigrations = await listMigrationFiles();
    const tableCountResult = await sql<{ count: number }[]>`
      select count(*)::int as count
      from information_schema.tables
      where table_schema = 'public'
        and table_type = 'BASE TABLE'
    `;
    const tableCount = tableCountResult[0]?.count ?? 0;

    const migrationTableSchema = await discoverMigrationTableSchema(sql);
    if (!migrationTableSchema) {
      if (tableCount > 0) {
        return {
          status: "needsMigrations",
          tableCount,
          availableMigrations,
          appliedMigrations: [],
          pendingMigrations: availableMigrations,
          reason: "no-migration-journal-non-empty-db",
        };
      }

      return {
        status: "needsMigrations",
        tableCount,
        availableMigrations,
        appliedMigrations: [],
        pendingMigrations: availableMigrations,
        reason: "no-migration-journal-empty-db",
      };
    }

    const appliedMigrations = await loadAppliedMigrations(sql, migrationTableSchema, availableMigrations);
    const pendingMigrations = availableMigrations.filter((name) => !appliedMigrations.includes(name));
    if (pendingMigrations.length === 0) {
      return {
        status: "upToDate",
        tableCount,
        availableMigrations,
        appliedMigrations,
      };
    }

    return {
      status: "needsMigrations",
      tableCount,
      availableMigrations,
      appliedMigrations,
      pendingMigrations,
      reason: "pending-migrations",
    };
  } finally {
    await sql.end();
  }
}

export async function applyPendingMigrations(url: string): Promise<void> {
  const sql = postgres(url, { max: 1 });

  try {
    const db = drizzlePg(sql);
    await migratePg(db, { migrationsFolder: MIGRATIONS_FOLDER });
  } finally {
    await sql.end();
  }
}

export type MigrationBootstrapResult =
  | { migrated: true; reason: "migrated-empty-db"; tableCount: 0 }
  | { migrated: false; reason: "already-migrated"; tableCount: number }
  | { migrated: false; reason: "not-empty-no-migration-journal"; tableCount: number };

export async function migratePostgresIfEmpty(url: string): Promise<MigrationBootstrapResult> {
  const sql = postgres(url, { max: 1 });

  try {
    const migrationTableSchema = await discoverMigrationTableSchema(sql);

    const tableCountResult = await sql<{ count: number }[]>`
      select count(*)::int as count
      from information_schema.tables
      where table_schema = 'public'
        and table_type = 'BASE TABLE'
    `;

    const tableCount = tableCountResult[0]?.count ?? 0;

    if (migrationTableSchema) {
      return { migrated: false, reason: "already-migrated", tableCount };
    }

    if (tableCount > 0) {
      return { migrated: false, reason: "not-empty-no-migration-journal", tableCount };
    }

    const db = drizzlePg(sql);
    const migrationsFolder = new URL("./migrations", import.meta.url).pathname;
    await migratePg(db, { migrationsFolder });

    return { migrated: true, reason: "migrated-empty-db", tableCount: 0 };
  } finally {
    await sql.end();
  }
}

export async function ensurePostgresDatabase(
  url: string,
  databaseName: string,
): Promise<"created" | "exists"> {
  if (!/^[A-Za-z_][A-Za-z0-9_]*$/.test(databaseName)) {
    throw new Error(`Unsafe database name: ${databaseName}`);
  }

  const sql = postgres(url, { max: 1 });
  try {
    const existing = await sql<{ one: number }[]>`
      select 1 as one from pg_database where datname = ${databaseName} limit 1
    `;
    if (existing.length > 0) return "exists";

    await sql.unsafe(`create database "${databaseName}"`);
    return "created";
  } finally {
    await sql.end();
  }
}

export type Db = ReturnType<typeof createDb>;