/**
 * Provides identifier generation for AI features.
 *
 * The `IdGenerator` service exposes one operation, `generateId`, which returns
 * a string inside `Effect`. AI modules use it for values such as tool call ids
 * and generated response item ids. This module includes the service tag,
 * service interface, default generator, configurable custom generator, and layer
 * for providing the service.
 *
 * @since 4.0.0
 */
import * as Cause from "../../Cause.ts"
import * as Context from "../../Context.ts"
import * as Effect from "../../Effect.ts"
import * as Layer from "../../Layer.ts"
import * as Predicate from "../../Predicate.ts"
import * as Random from "../../Random.ts"

/**
 * Service tag for AI identifier generation services.
 *
 * **When to use**
 *
 * Use to access or provide the service that creates identifiers for AI tool
 * calls and related generated values.
 *
 * **Details**
 *
 * This tag is used to provide and access ID generation functionality throughout
 * the application. It follows Effect's standard service pattern for type-safe
 * dependency injection.
 *
 * **Example** (Accessing the ID generator service)
 *
 * ```ts
 * import { Effect } from "effect"
 * import { IdGenerator } from "effect/unstable/ai"
 *
 * const useIdGenerator = Effect.gen(function*() {
 *   const idGenerator = yield* IdGenerator.IdGenerator
 *   const newId = yield* idGenerator.generateId()
 *   return newId
 * })
 * ```
 *
 * @category services
 * @since 4.0.0
 */
export class IdGenerator extends Context.Service<IdGenerator, Service>()(
  "@effect/ai/IdGenerator"
) {}

/**
 * The service interface for ID generation.
 *
 * **Details**
 *
 * Defines the contract that all ID generator implementations must fulfill.
 * The service provides a single method for generating unique identifiers
 * in an effectful context.
 *
 * **Example** (Implementing a custom ID generator)
 *
 * ```ts
 * import { Effect } from "effect"
 * import type { IdGenerator } from "effect/unstable/ai"
 *
 * // Custom deterministic implementation
 * let nextId = 0
 * const customService: IdGenerator.Service = {
 *   generateId: () => Effect.sync(() => `custom_${++nextId}`)
 * }
 *
 * const program = Effect.gen(function*() {
 *   const id = yield* customService.generateId()
 *   console.log(id) // "custom_1"
 *   return id
 * })
 * ```
 *
 * @category models
 * @since 4.0.0
 */
export interface Service {
  readonly generateId: () => Effect.Effect<string>
}

/**
 * Configuration options for creating custom ID generators.
 *
 * **Example** (Configuring generated IDs)
 *
 * ```ts
 * import type { IdGenerator } from "effect/unstable/ai"
 *
 * // Configuration for tool call IDs
 * const toolCallOptions: IdGenerator.MakeOptions = {
 *   alphabet: "0123456789ABCDEF",
 *   prefix: "tool",
 *   separator: "_",
 *   size: 8
 * }
 *
 * // This will generate IDs like: "tool_A1B2C3D4"
 * ```
 *
 * @category options
 * @since 4.0.0
 */
export interface MakeOptions {
  /**
   * The character set to use for generating the random portion of IDs.
   */
  readonly alphabet: string
  /**
   * Optional prefix to prepend to generated IDs.
   */
  readonly prefix?: string | undefined
  /**
   * Character used to separate the prefix from the random portion.
   */
  readonly separator: string
  /**
   * Length of the random portion of the generated ID.
   */
  readonly size: number
}

const DEFAULT_ALPHABET = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
const DEFAULT_SEPARATOR = "_"
const DEFAULT_SIZE = 16

const makeGenerator = ({
  alphabet = DEFAULT_ALPHABET,
  prefix,
  separator = DEFAULT_SEPARATOR,
  size = DEFAULT_SIZE
}: Partial<MakeOptions>) => {
  const alphabetLength = alphabet.length
  return Effect.fnUntraced(function*() {
    const chars = new Array(size)
    for (let i = 0; i < size; i++) {
      const index = yield* Random.next
      chars[i] = alphabet[(index * alphabetLength) | 0]
    }
    const identifier = chars.join("")
    if (Predicate.isUndefined(prefix)) {
      return identifier
    }
    return `${prefix}${separator}${identifier}`
  })
}

/**
 * Default ID generator service implementation.
 *
 * **Details**
 *
 * Uses the standard configuration with "id" prefix and generates IDs in the
 * format "id_XXXXXXXXXXXXXXXX" where X represents random alphanumeric
 * characters.
 *
 * **Example** (Generating default IDs)
 *
 * ```ts
 * import { Effect } from "effect"
 * import { IdGenerator } from "effect/unstable/ai"
 *
 * const program = Effect.gen(function*() {
 *   const id = yield* IdGenerator.defaultIdGenerator.generateId()
 *   console.log(id) // "id_A7xK9mP2qR5tY8uV"
 *   return id
 * })
 *
 * // Or provide it as a service
 * const withDefault = program.pipe(
 *   Effect.provideService(
 *     IdGenerator.IdGenerator,
 *     IdGenerator.defaultIdGenerator
 *   )
 * )
 * ```
 *
 * @category constructors
 * @since 4.0.0
 */
export const defaultIdGenerator: Service = {
  generateId: makeGenerator({ prefix: "id" })
}

/**
 * Creates a custom ID generator service with the specified options.
 *
 * **Details**
 *
 * Validates the configuration to ensure the separator is not part of the
 * alphabet, which would cause ambiguity in parsing generated IDs.
 *
 * **Example** (Creating a custom generator)
 *
 * ```ts
 * import { Effect } from "effect"
 * import { IdGenerator } from "effect/unstable/ai"
 *
 * const program = Effect.gen(function*() {
 *   // Create a generator for AI assistant message IDs
 *   const messageIdGen = yield* IdGenerator.make({
 *     alphabet: "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ",
 *     prefix: "msg",
 *     separator: "-",
 *     size: 10
 *   })
 *
 *   const messageId = yield* messageIdGen.generateId()
 *   console.log(messageId) // "msg-A7X9K2M5P8"
 *   return messageId
 * })
 * ```
 *
 * **Example** (Handling invalid generator options)
 *
 * ```ts
 * import { Effect } from "effect"
 * import { IdGenerator } from "effect/unstable/ai"
 *
 * // This will fail with IllegalArgumentError
 * const invalidConfig = IdGenerator.make({
 *   alphabet: "ABC123",
 *   prefix: "test",
 *   separator: "A", // Error: separator is part of alphabet
 *   size: 8
 * })
 *
 * const program = Effect.gen(function*() {
 *   const generator = yield* invalidConfig
 *   return generator
 * }).pipe(
 *   Effect.catch((error) =>
 *     Effect.succeed(`Configuration error: ${error.message}`)
 *   )
 * )
 * ```
 *
 * @category constructors
 * @since 4.0.0
 */
export const make = Effect.fnUntraced(function*({
  alphabet = DEFAULT_ALPHABET,
  prefix,
  separator = DEFAULT_SEPARATOR,
  size = DEFAULT_SIZE
}: MakeOptions) {
  if (alphabet.includes(separator)) {
    const message = `The separator "${separator}" must not be part of the alphabet "${alphabet}".`
    return yield* new Cause.IllegalArgumentError(message)
  }

  const generateId = makeGenerator({ alphabet, prefix, separator, size })

  return {
    generateId
  } as const
})

/**
 * Creates a Layer that provides the IdGenerator service with custom
 * configuration.
 *
 * **When to use**
 *
 * Use when you need to provide ID generation capabilities from validated
 * configuration.
 *
 * **Example** (Providing an ID generator layer)
 *
 * ```ts
 * import { Effect } from "effect"
 * import { IdGenerator } from "effect/unstable/ai"
 *
 * // Create a layer for generating AI tool call IDs
 * const toolCallIdLayer = IdGenerator.layer({
 *   alphabet: "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ",
 *   prefix: "tool_call",
 *   separator: "_",
 *   size: 12
 * })
 *
 * const program = Effect.gen(function*() {
 *   const idGen = yield* IdGenerator.IdGenerator
 *   const toolCallId = yield* idGen.generateId()
 *   console.log(toolCallId) // "tool_call_A7XK9MP2QR5T"
 *   return toolCallId
 * }).pipe(Effect.provide(toolCallIdLayer))
 * ```
 *
 * @category constructors
 * @since 4.0.0
 */
export const layer = (options: MakeOptions): Layer.Layer<IdGenerator, Cause.IllegalArgumentError> =>
  Layer.effect(IdGenerator)(make(options))
