// TypeScript Version: 3.4

import {Node} from 'unist'
import {VFile, VFileCompatible} from 'vfile'

declare namespace unified {
  /**
   * Processor allows plugins, parsers, and compilers to be chained together to transform content.
   *
   * @typeParam P Processor settings. Useful when packaging unified with a preset parser and compiler.
   */
  interface Processor<P = Settings> extends FrozenProcessor<P> {
    /**
     * Configure the processor to use a plugin and optionally configure that plugin with options.
     *
     * @param plugin unified plugin
     * @param settings Configuration for plugin
     * @typeParam S Plugin settings
     * @returns The processor on which use is invoked
     */
    use<S extends any[] = [Settings?]>(
      plugin: Plugin<S, P>,
      ...settings: S
    ): Processor<P>

    /**
     * Configure the processor with a preset to use
     *
     * @param preset `Object` with an plugins (set to list), and/or an optional settings object
     */
    use<S extends any[] = [Settings?]>(preset: Preset<S, P>): Processor<P>

    /**
     * Configure using a tuple of plugin and setting(s)
     *
     * @param pluginTuple pairs, plugin and settings in an array
     * @typeParam S Plugin settings
     */
    use<S extends any[] = [Settings?]>(
      pluginTuple: PluginTuple<S, P>
    ): Processor<P>

    /**
     * A list of plugins and presets to be applied to processor
     *
     * @param list List of plugins, presets, and pairs
     */
    use(list: PluggableList<P>): Processor<P>

    /**
     * Configuration passed to a frozen processor
     *
     * @param processorSettings Settings passed to processor
     */
    use(processorSettings: ProcessorSettings<P>): Processor<P>
  }

  /**
   * A frozen processor is just like a regular processor, except no additional plugins can be added.
   * A frozen processor can be created by calling `.freeze()` on a processor.
   *
   * @see Processor
   */
  interface FrozenProcessor<P = Settings> {
    /**
     * Clone current processor
     *
     * @returns New unfrozen processor which is configured to function the same as its ancestor.
     * But when the descendant processor is configured in the future it does not affect the ancestral processor.
     */
    (): Processor<P>

    /**
     * Parse text to a syntax tree.
     *
     * @param file VFile or anything which can be given to vfile()
     * @returns Syntax tree representation of input.
     */
    parse(file: VFileCompatible): Node

    /**
     * Function handling the parsing of text to a syntax tree.
     * Used in the parse phase in the process and invoked with a `string` and `VFile` representation of the document to parse.
     *
     * `Parser` can be a normal function in which case it must return a `Node`: the syntax tree representation of the given file.
     *
     * `Parser` can also be a constructor function (a function with keys in its `prototype`) in which case it’s invoked with `new`.
     * Instances must have a parse method which is invoked without arguments and must return a `Node`.
     */
    Parser: ParserConstructor | ParserFunction

    /**
     * Compile a syntax tree to text.
     *
     * @param node unist node
     * @param file `VFile` or anything which can be given to `vfile()`
     * @returns String representation of the syntax tree file
     */
    stringify(node: Node, file?: VFileCompatible): string

    /**
     * Function handling the compilation of syntax tree to a text.
     * Used in the stringify phase in the process and invoked with a `Node` and `VFile` representation of the document to stringify.
     *
     * `Compiler` can be a normal function in which case it must return a `string`: the text representation of the given syntax tree.
     *
     * `Compiler` can also be a constructor function (a function with keys in its `prototype`) in which case it’s invoked with `new`.
     * Instances must have a `compile` method which is invoked without arguments and must return a `string`.
     */
    Compiler: CompilerConstructor | CompilerFunction

    /**
     * Transform a syntax tree by applying plugins to it.
     *
     * @param node Node to transform
     * @returns `Promise` if `done` is not given. Rejected with an error, or resolved with the resulting syntax tree.
     */
    run(node: Node): Promise<Node>

    /**
     * Transform a syntax tree by applying plugins to it.
     *
     * @param node Node to transform
     * @param file `VFile` or anything which can be given to `vfile()`
     * @returns `Promise` if `done` is not given. Rejected with an error, or resolved with the resulting syntax tree.
     */
    run(node: Node, file: VFileCompatible): Promise<Node>

    /**
     * Transform a syntax tree by applying plugins to it.
     *
     * @param node Node to transform
     * @param done Invoked when transformation is complete.
     */
    run(node: Node, done: RunCallback): void

    /**
     * Transform a syntax tree by applying plugins to it.
     *
     * @param node Node to transform
     * @param file `VFile` or anything which can be given to `vfile()`
     * @param done Invoked when transformation is complete.
     */
    run(node: Node, file: VFileCompatible, done: RunCallback): void

    /**
     * Transform a syntax tree by applying plugins to it.
     *
     * If asynchronous plugins are configured an error is thrown.
     *
     * @param node Node to transform
     * @param file `VFile` or anything which can be given to `vfile()`
     * @returns The given syntax tree.
     */
    runSync(node: Node, file?: VFileCompatible): Node

    /**
     * Process the given representation of a file as configured on the processor. The process invokes `parse`, `run`, and `stringify` internally.
     * @param file `VFile` or anything which can be given to `vfile()`
     * @returns `Promise` if `done` is not given.
     * Rejected with an error or resolved with the resulting file.
     */
    process(file: VFileCompatible): Promise<VFile>

    /**
     * Process the given representation of a file as configured on the processor. The process invokes `parse`, `run`, and `stringify` internally.
     * @param file `VFile` or anything which can be given to `vfile()`
     * @param done Invoked when the process is complete. Invoked with a fatal error, if any, and the VFile.
     */
    process(file: VFileCompatible, done: ProcessCallback): void

    /**
     * Process the given representation of a file as configured on the processor. The process invokes `parse`, `run`, and `stringify` internally.
     *
     * If asynchronous plugins are configured an error is thrown.
     *
     * @param file `VFile` or anything which can be given to `vfile()`
     * @returns Virtual file with modified contents.
     */
    processSync(file: VFileCompatible): VFile

    /**
     * Get or set information in an in-memory key-value store accessible to all phases of the process.
     * An example is a list of HTML elements which are self-closing, which is needed when parsing, transforming, and compiling HTML.
     *
     * @returns key-value store object
     */
    data(): {[key: string]: unknown}

    /**
     * @param key Identifier
     * @returns If getting, the value at key
     */
    data(key: string): unknown

    /**
     * @param value Value to set. Omit if getting key
     * @returns If setting, the processor on which data is invoked
     */
    data(key: string, value: any): Processor<P>

    /**
     * Freeze a processor. Frozen processors are meant to be extended and not to be configured or processed directly.
     *
     * Once a processor is frozen it cannot be unfrozen. New processors functioning just like it can be created by invoking the processor.
     *
     * It’s possible to freeze processors explicitly, by calling `.freeze()`, but `.parse()`, `.run()`, `.stringify()`, and `.process()` call `.freeze()` to freeze a processor too.
     *
     * @returns The processor on which freeze is invoked.
     */
    freeze(): FrozenProcessor<P>
  }

  /**
   * A Plugin (Attacher) is the thing passed to `use`.
   * It configures the processor and in turn can receive options.
   *
   * Attachers can configure processors, such as by interacting with parsers and compilers, linking them to other processors, or by specifying how the syntax tree is handled.
   *
   * @param settings Configuration
   * @typeParam S Plugin settings
   * @typeParam P Processor settings
   * @returns Optional Transformer.
   */
  type Plugin<S extends any[] = [Settings?], P = Settings> = Attacher<S, P>

  /**
   * Configuration passed to a Plugin or Processor
   */
  interface Settings {
    [key: string]: unknown
  }

  /**
   * Presets provide a potentially sharable way to configure processors.
   * They can contain multiple plugins and optionally settings as well.
   *
   * @typeParam P Processor settings
   */
  interface Preset<S = Settings, P = Settings> {
    plugins: PluggableList<P>
    settings?: Settings
  }

  /**
   * Settings can be passed directly to the processor
   *
   * @typeParam P Settings applied to a processor. Useful when packaging unified with a preset parser and compiler.
   */
  interface ProcessorSettings<P = Settings> {
    settings: P
  }

  /**
   * A pairing of a plugin with its settings
   *
   * @typeParam S Plugin settings
   * @typeParam P Processor settings
   */
  type PluginTuple<S extends any[] = [Settings?], P = Settings> = [
    Plugin<S, P>,
    /**
     * NOTE: ideally this would be S instead of any[]
     * As of TypeScript 3.5.2 generic tuples cannot be spread
     * See: https://github.com/microsoft/TypeScript/issues/26113
     */
    ...any[]
  ]

  /**
   * A union of the different ways to add plugins to unified
   *
   * @typeParam S Plugin settings
   * @typeParam P Processor settings
   */
  type Pluggable<S extends any[] = [Settings?], P = Settings> =
    | Plugin<S, P>
    | Preset<S, P>
    | PluginTuple<S, P>

  /**
   * A list of plugins and presets
   *
   * @typeParam P Processor settings
   */
  type PluggableList<P = Settings> = Array<Pluggable<[any?], P>>

  /**
   * An attacher is the thing passed to `use`.
   * It configures the processor and in turn can receive options.
   *
   * Attachers can configure processors, such as by interacting with parsers and compilers, linking them to other processors, or by specifying how the syntax tree is handled.
   *
   * @param settings Configuration
   * @typeParam S Plugin settings
   * @typeParam P Processor settings
   * @returns Optional Transformer.
   */
  type Attacher<S extends any[] = [Settings?], P = Settings> = (
    this: Processor<P>,
    ...settings: S
  ) => Transformer | void

  /**
   * Transformers modify the syntax tree or metadata of a file. A transformer is a function which is invoked each time a file is passed through the transform phase.
   * If an error occurs (either because it’s thrown, returned, rejected, or passed to `next`), the process stops.
   *
   * The transformation process in unified is handled by `trough`, see it’s documentation for the exact semantics of transformers.
   *
   * @param node Node or tree to be transformed
   * @param file File associated with node or tree
   * @param next If the signature of a transformer includes `next` (third argument), the function may finish asynchronous, and must invoke `next()`.
   * @returns
   * - `void` — If nothing is returned, the next transformer keeps using same tree.
   * - `Error` — Can be returned to stop the process
   * - `Node` — Can be returned and results in further transformations and `stringify`s to be performed on the new tree
   * - `Promise` — If a promise is returned, the function is asynchronous, and must be resolved (optionally with a `Node`) or rejected (optionally with an `Error`)
   */
  type Transformer = (
    node: Node,
    file: VFile,
    next?: (
      error: Error | null,
      tree: Node,
      file: VFile
    ) => Record<string, unknown>
  ) => Error | Node | Promise<Node> | void | Promise<void>

  /**
   * Transform file contents into an AST
   */
  interface Parser {
    /**
     * Transform file contents into an AST
     *
     * @returns Parsed AST node/tree
     */
    parse(): Node
  }

  /**
   * A constructor function (a function with keys in its `prototype`) or class that implements a
   * `parse` method.
   */
  type ParserConstructor = new (text: string, file: VFile) => Parser

  /**
   * Transform file contents into an AST
   *
   * @param text Text to transform into AST node(s)
   * @param file File associated with text
   * @returns Parsed AST node/tree
   */
  type ParserFunction = (text: string, file: VFile) => Node

  /**
   * Transform an AST node/tree into text
   */
  interface Compiler {
    /**
     * Transform an AST node/tree into text
     *
     * @returns Compiled text
     */
    compile(): string
  }

  /**
   * A constructor function (a function with keys in its `prototype`) or class that implements a
   * `compile` method.
   */
  type CompilerConstructor = new (node: Node, file: VFile) => Compiler

  /**
   * Transform an AST node/tree into text
   *
   * @param node Node/tree to be stringified
   * @param file File associated with node
   * @returns Compiled text
   */
  type CompilerFunction = (node: Node, file: VFile) => string

  /**
   * Access results from transforms
   *
   * @param error Error if any occurred
   * @param node Transformed AST tree/node
   * @param vfile File associated with node
   */
  type RunCallback = (error: Error | null, node: Node, file: VFile) => void

  /**
   * Access results from transforms
   *
   * @param error Error if any occurred
   * @param vfile File with updated content
   */
  type ProcessCallback = (error: Error | null, file: VFile) => void
}

/**
 * Unified processor allows plugins, parsers, and compilers to be chained together to transform content.
 *
 * @typeParam P Processor settings. Useful when packaging unified with a preset parser and compiler.
 */
declare function unified<P = unified.Settings>(): unified.Processor<P>
export = unified
