import { Context, Effect, Layer } from "effect"

class Database extends Context.Service<Database, {
  readonly query: (sql: string) => Effect.Effect<string>
}>()("Database") {}

class Logger extends Context.Service<Logger, {
  readonly log: (msg: string) => Effect.Effect<void>
}>()("Logger") {}

class UserService extends Context.Service<UserService, {
  readonly getUser: (id: string) => Effect.Effect<{
    id: string
    name: string
  }>
}>()("UserService") {}

// Create dependency layers
const databaseLayer = Layer.succeed(Database, {
  query: Effect.fn("Database.query")((sql: string) => Effect.succeed(`DB: ${sql}`))
})

const loggerLayer = Layer.succeed(Logger, {
  log: Effect.fn("Logger.log")((msg: string) => Effect.sync(() => console.log(`[LOG] ${msg}`)))
})

// UserService depends on Database and Logger
const userServiceLayer = Layer.effect(UserService, Effect.gen(function*() {
  const database = yield* Database
  const logger = yield* Logger

  return {
    getUser: Effect.fn("UserService.getUser")(function*(id: string) {
        yield* logger.log(`Looking up user ${id}`)
        const result = yield* database.query(
          `SELECT * FROM users WHERE id = ${id}`
        )
        return { id, name: result }
      })
  }
}))

// Provide dependencies and merge all services together
const allServicesLayer = userServiceLayer.pipe(
  Layer.provideMerge(Layer.mergeAll(databaseLayer, loggerLayer))
)

// Now the resulting layer provides UserService, Database, AND Logger
const program = Effect.gen(function*() {
  const userService = yield* UserService
  const logger = yield* Logger // Still available!
  const database = yield* Database // Still available!

  const user = yield* userService.getUser("123")
  yield* logger.log(`Found user: ${user.name}`)

  return user
}).pipe(
  Effect.provide(allServicesLayer)
)