'use strict'

var extend = require('extend')
var bail = require('bail')
var vfile = require('vfile')
var trough = require('trough')
var plain = require('is-plain-obj')

// Expose a frozen processor.
module.exports = unified().freeze()

var slice = [].slice
var own = {}.hasOwnProperty

// Process pipeline.
var pipeline = trough()
  .use(pipelineParse)
  .use(pipelineRun)
  .use(pipelineStringify)

function pipelineParse(p, ctx) {
  ctx.tree = p.parse(ctx.file)
}

function pipelineRun(p, ctx, next) {
  p.run(ctx.tree, ctx.file, done)

  function done(err, tree, file) {
    if (err) {
      next(err)
    } else {
      ctx.tree = tree
      ctx.file = file
      next()
    }
  }
}

function pipelineStringify(p, ctx) {
  ctx.file.contents = p.stringify(ctx.tree, ctx.file)
}

// Function to create the first processor.
function unified() {
  var attachers = []
  var transformers = trough()
  var namespace = {}
  var frozen = false
  var freezeIndex = -1

  // Data management.
  processor.data = data

  // Lock.
  processor.freeze = freeze

  // Plugins.
  processor.attachers = attachers
  processor.use = use

  // API.
  processor.parse = parse
  processor.stringify = stringify
  processor.run = run
  processor.runSync = runSync
  processor.process = process
  processor.processSync = processSync

  // Expose.
  return processor

  // Create a new processor based on the processor in the current scope.
  function processor() {
    var destination = unified()
    var length = attachers.length
    var index = -1

    while (++index < length) {
      destination.use.apply(null, attachers[index])
    }

    destination.data(extend(true, {}, namespace))

    return destination
  }

  // Freeze: used to signal a processor that has finished configuration.
  //
  // For example, take unified itself: it’s frozen.
  // Plugins should not be added to it.
  // Rather, it should be extended, by invoking it, before modifying it.
  //
  // In essence, always invoke this when exporting a processor.
  function freeze() {
    var values
    var plugin
    var options
    var transformer

    if (frozen) {
      return processor
    }

    while (++freezeIndex < attachers.length) {
      values = attachers[freezeIndex]
      plugin = values[0]
      options = values[1]
      transformer = null

      if (options === false) {
        continue
      }

      if (options === true) {
        values[1] = undefined
      }

      transformer = plugin.apply(processor, values.slice(1))

      if (typeof transformer === 'function') {
        transformers.use(transformer)
      }
    }

    frozen = true
    freezeIndex = Infinity

    return processor
  }

  // Data management.
  // Getter / setter for processor-specific informtion.
  function data(key, value) {
    if (typeof key === 'string') {
      // Set `key`.
      if (arguments.length === 2) {
        assertUnfrozen('data', frozen)

        namespace[key] = value

        return processor
      }

      // Get `key`.
      return (own.call(namespace, key) && namespace[key]) || null
    }

    // Set space.
    if (key) {
      assertUnfrozen('data', frozen)
      namespace = key
      return processor
    }

    // Get space.
    return namespace
  }

  // Plugin management.
  //
  // Pass it:
  // *   an attacher and options,
  // *   a preset,
  // *   a list of presets, attachers, and arguments (list of attachers and
  //     options).
  function use(value) {
    var settings

    assertUnfrozen('use', frozen)

    if (value === null || value === undefined) {
      // Empty.
    } else if (typeof value === 'function') {
      addPlugin.apply(null, arguments)
    } else if (typeof value === 'object') {
      if ('length' in value) {
        addList(value)
      } else {
        addPreset(value)
      }
    } else {
      throw new Error('Expected usable value, not `' + value + '`')
    }

    if (settings) {
      namespace.settings = extend(namespace.settings || {}, settings)
    }

    return processor

    function addPreset(result) {
      addList(result.plugins)

      if (result.settings) {
        settings = extend(settings || {}, result.settings)
      }
    }

    function add(value) {
      if (typeof value === 'function') {
        addPlugin(value)
      } else if (typeof value === 'object') {
        if ('length' in value) {
          addPlugin.apply(null, value)
        } else {
          addPreset(value)
        }
      } else {
        throw new Error('Expected usable value, not `' + value + '`')
      }
    }

    function addList(plugins) {
      var length
      var index

      if (plugins === null || plugins === undefined) {
        // Empty.
      } else if (typeof plugins === 'object' && 'length' in plugins) {
        length = plugins.length
        index = -1

        while (++index < length) {
          add(plugins[index])
        }
      } else {
        throw new Error('Expected a list of plugins, not `' + plugins + '`')
      }
    }

    function addPlugin(plugin, value) {
      var entry = find(plugin)

      if (entry) {
        if (plain(entry[1]) && plain(value)) {
          value = extend(entry[1], value)
        }

        entry[1] = value
      } else {
        attachers.push(slice.call(arguments))
      }
    }
  }

  function find(plugin) {
    var length = attachers.length
    var index = -1
    var entry

    while (++index < length) {
      entry = attachers[index]

      if (entry[0] === plugin) {
        return entry
      }
    }
  }

  // Parse a file (in string or vfile representation) into a unist node using
  // the `Parser` on the processor.
  function parse(doc) {
    var file = vfile(doc)
    var Parser

    freeze()
    Parser = processor.Parser
    assertParser('parse', Parser)

    if (newable(Parser, 'parse')) {
      return new Parser(String(file), file).parse()
    }

    return Parser(String(file), file) // eslint-disable-line new-cap
  }

  // Run transforms on a unist node representation of a file (in string or
  // vfile representation), async.
  function run(node, file, cb) {
    assertNode(node)
    freeze()

    if (!cb && typeof file === 'function') {
      cb = file
      file = null
    }

    if (!cb) {
      return new Promise(executor)
    }

    executor(null, cb)

    function executor(resolve, reject) {
      transformers.run(node, vfile(file), done)

      function done(err, tree, file) {
        tree = tree || node
        if (err) {
          reject(err)
        } else if (resolve) {
          resolve(tree)
        } else {
          cb(null, tree, file)
        }
      }
    }
  }

  // Run transforms on a unist node representation of a file (in string or
  // vfile representation), sync.
  function runSync(node, file) {
    var complete = false
    var result

    run(node, file, done)

    assertDone('runSync', 'run', complete)

    return result

    function done(err, tree) {
      complete = true
      bail(err)
      result = tree
    }
  }

  // Stringify a unist node representation of a file (in string or vfile
  // representation) into a string using the `Compiler` on the processor.
  function stringify(node, doc) {
    var file = vfile(doc)
    var Compiler

    freeze()
    Compiler = processor.Compiler
    assertCompiler('stringify', Compiler)
    assertNode(node)

    if (newable(Compiler, 'compile')) {
      return new Compiler(node, file).compile()
    }

    return Compiler(node, file) // eslint-disable-line new-cap
  }

  // Parse a file (in string or vfile representation) into a unist node using
  // the `Parser` on the processor, then run transforms on that node, and
  // compile the resulting node using the `Compiler` on the processor, and
  // store that result on the vfile.
  function process(doc, cb) {
    freeze()
    assertParser('process', processor.Parser)
    assertCompiler('process', processor.Compiler)

    if (!cb) {
      return new Promise(executor)
    }

    executor(null, cb)

    function executor(resolve, reject) {
      var file = vfile(doc)

      pipeline.run(processor, {file: file}, done)

      function done(err) {
        if (err) {
          reject(err)
        } else if (resolve) {
          resolve(file)
        } else {
          cb(null, file)
        }
      }
    }
  }

  // Process the given document (in string or vfile representation), sync.
  function processSync(doc) {
    var complete = false
    var file

    freeze()
    assertParser('processSync', processor.Parser)
    assertCompiler('processSync', processor.Compiler)
    file = vfile(doc)

    process(file, done)

    assertDone('processSync', 'process', complete)

    return file

    function done(err) {
      complete = true
      bail(err)
    }
  }
}

// Check if `value` is a constructor.
function newable(value, name) {
  return (
    typeof value === 'function' &&
    value.prototype &&
    // A function with keys in its prototype is probably a constructor.
    // Classes’ prototype methods are not enumerable, so we check if some value
    // exists in the prototype.
    (keys(value.prototype) || name in value.prototype)
  )
}

// Check if `value` is an object with keys.
function keys(value) {
  var key
  for (key in value) {
    return true
  }

  return false
}

// Assert a parser is available.
function assertParser(name, Parser) {
  if (typeof Parser !== 'function') {
    throw new Error('Cannot `' + name + '` without `Parser`')
  }
}

// Assert a compiler is available.
function assertCompiler(name, Compiler) {
  if (typeof Compiler !== 'function') {
    throw new Error('Cannot `' + name + '` without `Compiler`')
  }
}

// Assert the processor is not frozen.
function assertUnfrozen(name, frozen) {
  if (frozen) {
    throw new Error(
      'Cannot invoke `' +
        name +
        '` on a frozen processor.\nCreate a new processor first, by invoking it: use `processor()` instead of `processor`.'
    )
  }
}

// Assert `node` is a unist node.
function assertNode(node) {
  if (!node || typeof node.type !== 'string') {
    throw new Error('Expected node, got `' + node + '`')
  }
}

// Assert that `complete` is `true`.
function assertDone(name, asyncName, complete) {
  if (!complete) {
    throw new Error(
      '`' + name + '` finished async. Use `' + asyncName + '` instead'
    )
  }
}