wizard.py

# -*- coding: utf-8 -*-
#!/usr/bin/env python
"""
<Program Name>
  wizard.py

<Author>
  Lukas Puehringer <lukas.puehringer@nyu.edu>

<Started>
  April 06, 2017

<Copyright>
  See LICENSE for licensing information.

<Purpose>
  Flask web app that provides a wizard to guide through an in-toto
  software supply chain layout creation.

<Overview of Functions>
  Utils:
      Mostly used to transform data

  NoSQL Helpers:
      The app uses MongoDB to persist user posted data for auditing and to
      improve the app. NoSQL Helpers are a couple of custom wrappers around
      common queries.

  View Decorator & Hooks:
      Currently there is one view decorator for session handling (sessions are
      used to isolate user posted data) and an after request hook to inject
      messages from the Flask's message flash framework into ajax responses.

  Views:
      Each view is an entry point for an HTTP request (c.f. paths in @app.route
      decorator). Most views correspond to a page the user surfs to and
      therefore render and return the corresponding template on a GET request.
      If a page has form postable content, the corresponding view also accepts
      a POST request which is usually sent when the user clicks NEXT as s/he
      walks through the pages. The view then handles and persists the posted
      data and in case everything went well redirects to the text view (page).
      The views in this document are ordered from top to bottom in the same
      order as the user walks from page to page.
      Some pages have additional views associated that accept ajax calls,
      e.g. to upload or remove files.

"""
import os
import uuid
import time
import io
import tarfile

from functools import wraps
from flask import (Flask, render_template, session, redirect, url_for, request,
    flash, send_file, abort, json, jsonify, get_flashed_messages)
from flask_pymongo import PyMongo
from flask_wtf.csrf import CSRFProtect

import in_toto.models.link
import in_toto.models.layout
import in_toto.models.metadata
import securesystemslib.keys

import tooldb
import create_layout

app = Flask(__name__, static_url_path="", instance_relative_config=True)
csrf = CSRFProtect(app)

app.config.update(dict(
    DEBUG=True,
    MONGO_URI="mongodb://localhost:27017/wizard",
    SECRET_KEY="do not use the development key in production!!!",
))


# Supply a config file at "instance/config.py" that carries
# e.g. your deployment secret key
app.config.from_pyfile("config.py")

mongo = PyMongo(app)

# Reload if a template has changed (only for development, i.e. in DEBUG mode)
app.jinja_env.auto_reload = app.config["DEBUG"]


# -----------------------------------------------------------------------------
# Utils
# -----------------------------------------------------------------------------
def session_to_ssc(session_data):
  """
  <Purpose>
    Takes a data from a user session, i.e. form posted data from multiple
    pages (vcs, building, qa, ...) to generate a dictionary of lists of step
    data and inspection data, i.e. a software supply chain (ssc).

  <Returns>
    Software Supply Chain data, i.e. a dictionary of step and inspection data
    Note: these are not not actual in-toto Step and Inspection objects

    e.g.:
    {
      steps: [
        {
          "name": <unique step name>,
          "cmd": <expected command>,
          "modifies": <boolean>  # whether the step modifies artifacts or not
        }, ...
      ],
      inspections: [
        {
          "name": <unique inspection name>,
          "cmd": <command to run inspection>,
          "based_on": <step name whose products are used for that inspection>
        }
      ]
    }
  """
  ssc_steps = []
  ssc_inspections = []

  for step_type in ["vcs", "building", "qa", "package"]:
    for idx, step in enumerate(session_data.get(step_type, {}).get(
        "items", [])):
      # FIXME: Come up with better auto names
      step_name = "{}-{}".format(step_type, idx + 1)
      ssc_step = {
        "name": step_name,
        "cmd" : step["cmd"],
        "modifies": True
      }

      # We create an inspection for each retval, stdout and stderr for
      # each specified QA step
      # Special treatment for QA steps:
      # If the user has specified how s/he knows if a QA step went well, e.g.
      # by looking at return value, stdout and/or stderr, we use that
      # information to suggest in-toto inspections (one per posted retval,
      # stdout, stderr per posted, QA step)
      if step_type == "qa":
        # Override modifies property set above
        # We suppose QA steps don't modify artifacts but just look at them
        ssc_step["modifies"] = False

        for inspect_type in ["retval", "stdout", "stderr"]:
          enabled = step.get(inspect_type)
          val = step.get(inspect_type + "_value")
          operator = step.get(inspect_type + "_operator")

          # Construct return value or byproducts inspection command
          # c.f. https://github.com/in-toto/in-toto-inspections
          if enabled:
            # Inspection commands require a link file (to inspect)
            # We use the auto name of the corresponding QA step to
            # generate the filename passed to the inspection command
            # FIXME: What about the functionary keyid in the link file name?!
            link = in_toto.models.link.FILENAME_FORMAT_SHORT.format(
                step_name=step_name)
            value = step.get(inspect_type + "_value")

            if inspect_type == "retval":
              run = ("inspect-return-value --link={link} --{operator} {value}"
                  .format(link=link, operator=operator, value=value))

            elif inspect_type in ["stdout", "stderr"]:
              if operator == "empty":
                operator = "is"
                value = ""

              run = ("inspect-byproducts"
                  " --link={link} --{inspect_type} --{operator} \"{value}\""
                  .format(link=link, inspect_type=inspect_type,
                  operator=operator, value=value))

            # FIXME: Come up with better auto names
            inspect_name = "inspection-" + str(len(ssc_inspections) + 1)
            ssc_inspections.append({
              "name": inspect_name,
              "cmd": run,
              "based_on": step_name
            })

      ssc_steps.append(ssc_step)

  ssc_data = {
    "steps": ssc_steps,
    "inspections": ssc_inspections
  }
  return ssc_data


def form_data_to_ssc(step_names, step_commands, step_modifies,
    inspection_names, inspection_commands, inspection_step_names):
  """
  <Purpose>
    Takes step and inspection properties (form posted lists) and aggregates
    them by index to step and inspection dictionaries to construct a dictionary
    of software supply chain (ssc) data.

  <Returns>
    Software Supply Chain data, i.e. a dictionary of step and inspection data
    Note: these are not not actual in-toto Step and Inspection objects

    e.g.:
    {
      steps: [
        {
          "name": <unique step name>,
          "cmd": <expected command>
          "modifies": <boolean>  # whether the step modifies artifacts or not
        }, ...
      ],
      inspections: [
        {
          "name": <unique inspection name>,
          "cmd": <command to run inspecting>,
          "based_on": <step name whose products are used for that inspection>
        }
      ]
    }

  <Exceptions>
    ValueError if step or inspection arguments have unequal lengths

  """

  if not (len(step_names) == len(step_commands) == len(step_modifies)):
    raise ValueError("The arguments 'step_names', 'step_commands' and"
      " 'step_modifies' must have equal lengths.")

  if not (len(inspection_names) == len(inspection_commands) ==
      len(inspection_step_names)):
    raise ValueError("The arguments 'inspection_names', 'inspection_commands'"
        " and 'inspection_step_names' must have equal lengths.")

  steps = []
  for i in range(len(step_names)):
    steps.append({
        "name": step_names[i],
        "cmd": step_commands[i],
        "modifies": step_modifies[i] == "true"
      })

  inspections = []
  for i in range(len(inspection_names)):
    inspections.append({
        "name": inspection_names[i],
        "cmd": inspection_commands[i],
        "based_on": inspection_step_names[i]
      })

  ssc_data = {
    "steps": steps,
    "inspections": inspections
  }
  return ssc_data


def _auth_items_to_dict(auth_items):
  """Takes a list of auth_items and returns a dictionary mapping the items
  to their respective step names, i.e..:
  [{"step_name": ..., "threshold": ..., "authorized_functionaries": ...}, ...]
  -->
  {<step name> : {"step_name": ..., "threshold": ..., "authorized_..."}, ...}
  """
  auth_dict = {}
  for auth_item in auth_items:
    auth_dict[auth_item["step_name"]] = auth_item
  return auth_dict


# -----------------------------------------------------------------------------
# NoSQL Helpers
# -----------------------------------------------------------------------------
# NOTE: Below functions rely on the current session having an id. If there is
# no id in the session, all functions redirect to `404` (page not found).
# This should never happen because all calling views should be decorated with
# @with_session_id, which ensures that the current session does have an id.
def _persist_session_subdocument(subdocument):
  """Update a subdocument (e.g. vcs, ssc, functionaries...) in session document
  identified by current session id. """
  if not session.get("id"):
    abort(404)

  # Search session document by session ID in DB and update (replace)
  # subdocument. If the entire document does not exist it is inserted
  mongo.db.session_collection.update_one(
    {"_id": session["id"]},
    {"$set": subdocument},
    upsert=True)


def _persist_session_subdocument_ts(subdocument):
  """Updates/adds last_modified to the subdocument before persisting it. """

  for key in subdocument.keys():
    subdocument[key]["last_modified"] = time.time()
  _persist_session_subdocument(subdocument)


def _get_session_subdocument(key):
  """Returns a subdocument (e.g. vcs, ssc, functionaries...) identified by
  passed key from session document identified by current session id.
  Returns an empty dict if document or subdocument are not found.  """
  if not session.get("id"):
    abort(404)

    # Get session document (use short circuit for default empty dict)
  session_doc = mongo.db.session_collection.find_one(
      {"_id": session["id"]})

  if not session_doc:
    return {}

  # Get vcs data from session document or empty dict
  return session_doc.get(key, {})


def _get_session_document():
  """Returns the entire session document.
  Returns an empty dict if document or subdocument are not found.  """

  if not session.get("id"):
    abort(404)

  session_doc = mongo.db.session_collection.find_one(
    {"_id": session["id"]})

  if not session_doc:
    return {}

  return session_doc


# -----------------------------------------------------------------------------
# View Decorator & Hooks
# -----------------------------------------------------------------------------
def with_session_id(wrapped_func):
  """
  Generate new session id if it does not exist.

  For now, a user could start a new session on any page
  TODO: Should we redirect to the start page if the session is new?
  """
  @wraps(wrapped_func)
  def decorated_function(*args, **kwargs):
    if not session.get("id"):
      # Security is not paramount, we don't store sensitive data, right?
      session["id"] = uuid.uuid4()
      app.logger.info("New session ID '{}'".format(session["id"]))

    return wrapped_func(*args, **kwargs)
  return decorated_function


@app.after_request
def ajax_flash_messages(response):
  """ This function intercepts JSON responses to ajax requests and injects
  a "messages" field containing flashed messages.
  To display them the JS callback that receives the response can call
  show_messages(repsonse.messages).
  """

  if (request.headers.get("X-Requested-With") == "XMLHttpRequest"  and
      response.headers.get("Content-Type") == "application/json"):
    response_data = json.loads(response.get_data())
    response_data["messages"] = get_flashed_messages(with_categories=True)
    response.set_data(json.dumps(response_data))

  return response


# -----------------------------------------------------------------------------
# Views
# -----------------------------------------------------------------------------
@app.route("/")
@with_session_id
def start():
  """Step 0.
  Wizard entry point, static landing page. """
  return render_template("start.html")


@app.route("/vcs", methods=["GET", "POST"])
@with_session_id
def vcs():
  """Step 1.
  Enter information about version control system. """
  options = tooldb.COLLECTION["vcs"]

  if request.method == "POST":
    # Grab the form posted vcs commands and persist
    # FIXME: Needs sanitizing
    vcs_data = {
      "items": [{"cmd": cmd} for cmd in request.form.getlist("vcs_cmd[]")],
      "comment": request.form.get("comment", "")
    }
    _persist_session_subdocument_ts({"vcs": vcs_data})

    flash("Now let's see how you build your software...",
        "alert-success")
    return redirect(url_for("building"))

  user_data = _get_session_subdocument("vcs")
  return render_template("vcs.html", options=options,
      user_data=user_data)


@app.route("/building", methods=["GET", "POST"])
@with_session_id
def building():
  """Step 2.
  Enter information about building. """
  options = tooldb.COLLECTION["building"]

  if request.method == "POST":
    # Grab the form posted building commands and persist
    # FIXME: Needs sanitizing
    building_data = {
      "items": [{"cmd": cmd} for cmd in request.form.getlist("build_cmd[]")],
      "comment": request.form.get("comment", "")
    }
    _persist_session_subdocument_ts({"building": building_data})

    flash("Let's talk about quality management next...",
        "alert-success")
    return redirect(url_for("quality_management"))

  user_data = _get_session_subdocument("building")
  return render_template("building.html", options=options, user_data=user_data)


@app.route("/quality", methods=["GET", "POST"])
@with_session_id
def quality_management():
  """Step 3.
  Enter information about quality management. """
  options = tooldb.COLLECTION["qa"]

  if request.method == "POST":
    # Grab the form posted quality management data and persist
    # FIXME: Needs sanitizing
    cmd_list = request.form.getlist("cmd[]")

    retval_include_list = request.form.getlist("retval_include[]")
    retval_operator_list = request.form.getlist("retval_operator[]")
    retval_value_list = request.form.getlist("retval_value[]")

    stdout_include_list = request.form.getlist("stdout_include[]")
    stdout_operator_list = request.form.getlist("stdout_operator[]")
    stdout_value_list = request.form.getlist("stdout_value[]")

    stderr_include_list = request.form.getlist("stderr_include[]")
    stderr_operator_list = request.form.getlist("stderr_operator[]")
    stderr_value_list = request.form.getlist("stderr_value[]")

    # Values of a step are related by the same index
    # All lists must be equally long
    # FIXME: Don't assert, try!
    assert(len(cmd_list) ==
        len(retval_include_list) == len(retval_operator_list) ==
        len(retval_value_list) == len(stdout_include_list) ==
        len(stdout_operator_list) == len(stdout_value_list) ==
        len(stderr_include_list) == len(stderr_operator_list) ==
        len(stderr_value_list))

    # Pick any one (they all must have the same length any way)
    qa_steps_cnt = len(cmd_list)

    # There can only be one comment
    posted_coment = request.form.get("comment", "")

    posted_items = []
    for i in range(qa_steps_cnt):
      posted_items.append({
          "cmd": cmd_list[i],
          "retval": retval_include_list[i] == "true",
          "retval_operator": retval_operator_list[i],
          "retval_value": retval_value_list[i],
          "stdout": stdout_include_list[i] == "true",
          "stdout_operator": stdout_operator_list[i],
          "stdout_value": stdout_value_list[i],
          "stderr": stderr_include_list[i] == "true",
          "stderr_operator": stderr_operator_list[i],
          "stderr_value": stderr_value_list[i],
        })

    # Note: We store the data as posted. Only in the software supply chain
    # view do we transform this data, e.g. create inspection commands, etc.
    qa_data = {
      "items": posted_items,
      "comment": posted_coment
    }
    _persist_session_subdocument_ts({"qa": qa_data})

    flash("Nice quality management, but how do you package your software?",
        "alert-success")
    return redirect(url_for("packaging"))

  user_data = _get_session_subdocument("qa")
  return render_template("quality.html", options=options, user_data=user_data)


@app.route("/packaging", methods=["GET", "POST"])
@with_session_id
def packaging():
  """Step 4.
  Enter information about packaging. """
  options = tooldb.COLLECTION["package"]

  if request.method == "POST":
    # Grab the form posted building commands and persist
    # FIXME: Needs sanitizing
    package_data = {
      "items": [{"cmd": cmd} for cmd in request.form.getlist("cmd[]")],
      "comment": request.form.get("comment", "")
    }
    _persist_session_subdocument_ts({"package": package_data})

    flash("Now let's see if we got your software supply chain right...",
        "alert-success")
    return redirect(url_for("software_supply_chain"))

  user_data = _get_session_subdocument("package")
  return render_template("packaging.html", options=options, user_data=user_data)


@app.route("/software-supply-chain", methods=["GET", "POST"])
@with_session_id
def software_supply_chain():
  """Step 5.
  On get generate and serve software supply chain data (ssc graph) based
  on form data posted from previous pages and stored to session
  (c.f. helper `session_to_graph`).

  On post we override the generated software supply chain using the posted
  form data (c.f. helper `form_data_to_graph`).

  Latter will be used for subsequent get queries and on subsequent pages.
  """

  if request.method == "POST":
    # Grab the form posted software supply chain data and persist
    # FIXME: Needs sanitizing, e.g.
    # restrict step and inspection names (must be unique) and inspection
    # step names (must reference an existing step)
    step_names = request.form.getlist("step_name[]")
    step_commands = request.form.getlist("step_cmd[]")
    step_modifies = request.form.getlist("step_modifies[]")
    inspection_names = request.form.getlist("inspection_name[]")
    inspection_commands = request.form.getlist("inspection_cmd[]")
    inspection_step_names = request.form.getlist("inspection_step_name[]")

    comment = request.form.get("comment", "")

    # Names and Commands of a step or inspection are related by the same index
    # All lists should be equally long
    # FIXME: Don't assert, try!
    assert(len(step_names) == len(step_commands) == len(step_modifies))
    assert(len(inspection_names) == len(inspection_commands) ==
        len(inspection_step_names))

    # Create and persist software supply chain data from posted form
    ssc_data = form_data_to_ssc(step_names, step_commands, step_modifies,
        inspection_names, inspection_commands, inspection_step_names)
    # Add posted comment to ssc_data
    ssc_data["comment"] = comment

    # Persist and redirect to next page
    _persist_session_subdocument_ts({"ssc": ssc_data})
    return redirect(url_for("functionaries"))



  # Query all session data (posted on vcs, building, qa, ... pages)
  session_data = _get_session_document()

  # Query any existing software supply chain data (posted on this page)
  ssc_data = session_data.get("ssc", {})
  ssc_last_modified = ssc_data.get("last_modified", 0)

  # Assume we don't have to show the refresh dialog (explained below)
  show_refresh_dialog = False

  # Only (re)generate software supply chain graph from data the user has posted
  # on previous pages, if there is no ssc data from this page in the db or the
  # user has sent he `refresh` parameter
  if not ssc_data or request.args.get("refresh"):
    ssc_data = session_to_ssc(session_data)

  # Otherwise we serve existing ssc data
  else:
    # If existing ssc data is older than any of stored vcs/building/qa/package
    # data we still serve the stored ssc data but additionally show a
    # "Do you want to re-generate the software supply chain?" dialog with a
    # link that includes the `refresh` get parameter
    for subdocument in ["vcs", "building", "qa", "package"]:
      data_last_modified = session_data.get(subdocument,
          {}).get("last_modified", 0)

      if ssc_last_modified < data_last_modified:
        show_refresh_dialog = True
        break

  return render_template("software_supply_chain.html",
      ssc_data=ssc_data, show_refresh=show_refresh_dialog)


@app.route("/functionaries", methods=["GET", "POST"])
@with_session_id
def functionaries():
  """Step 6.
  On get serve functionary keys upload and keys dropzone.
  On post store comment and redirect to next page.

  The actual functionary public key upload uses a different view queried
  with ajax (ajax_upload_key).

  """
  functionaries = _get_session_subdocument("functionaries")
  if request.method == "POST":
    functionaries["comment"] = request.form.get("comment", "")
    _persist_session_subdocument({"functionaries": functionaries})

    flash("Now tell us who is authorized to do what...",
        "alert-success")
    return redirect(url_for("authorizing"))

  return render_template("functionaries.html", functionaries=functionaries)


@app.route("/functionaries/upload", methods=["POST"])
@with_session_id
def ajax_upload_key():
  """Ajax upload a functionary key. Key files are stored to the db in their
  dictionary representation. """
  functionary_key = request.files.get("functionary_key", None)
  functionary_name = request.form.get("functionary_name", None)

  if not functionary_name:
    flash("Something went wrong: We don't know which functionary,"
              " this key belongs to", "alert-danger")

    return jsonify({"error": True})

  if not functionary_key:
    flash("Something went wrong: No file uploaded", "alert-danger")
    return jsonify({"error": True})

  if functionary_key.filename == "":
    flash("Something went wrong: No file selected", "alert-danger")
    return jsonify({"error": True})

  try:
    # We try to load the public key to check the format
    key = securesystemslib.keys.import_rsakey_from_public_pem(
        functionary_key.read())

    securesystemslib.formats.PUBLIC_KEY_SCHEMA.check_match(key)
    file_name = functionary_key.filename

    functionary_db_item = {
      "functionary_name": functionary_name,
      "file_name": file_name,
      "key_dict": key
    }

    # Clumsy update or insert for functionary array embedded subdocument
    # NOTE: Unfortunately we can't "upsert" on arrays but must first try to
    # update and if that does not work insert.
    # https://docs.mongodb.com/manual/reference/operator/update/positional/#upsert
    # https://stackoverflow.com/questions/23470658/mongodb-upsert-sub-document
    query_result = mongo.db.session_collection.update_one(
        {
          "_id": session["id"],
          "functionaries.items.functionary_name": functionary_name
        },
        {
          "$set": {"functionaries.items.$": functionary_db_item}
        })

    if not query_result.matched_count:
      query_result = mongo.db.session_collection.update_one(
          {
            "_id": session["id"],
            # This query part should deal with concurrent requests
            "functionaries.items.functionary_name": {"$ne": functionary_name}
          },
          {
            "$push": {"functionaries.items": functionary_db_item}
          }, upsert=True)

      flash("Added key '{fn}' for functionary '{functionary}'"
          .format(fn=file_name, functionary=functionary_name),
          "alert-success")
    else:
      flash("Updated key '{fn}' for functionary ""'{functionary}'"
          .format(fn=file_name, functionary=functionary_name),
          "alert-success")

    # TODO: Throw more rocks at query_result

  except Exception as e:
    flash("Could not store uploaded file. Error: {}".format(e),
        "alert-danger")
    return jsonify({"error": True})

  return jsonify({"error": False})


@app.route("/functionaries/remove", methods=["POST"])
@with_session_id
def ajax_remove_functionary():
  """Remove the posted functionary (by name) from the functionary session
  subdocument, which also removes the key. """
  functionary_name = request.form.get("functionary_name")

  try:
    # Remove the link entry with posted file name in the session
    # document's functionaries.items list
    query_result = mongo.db.session_collection.update_one(
        {"_id": session["id"]},
        {"$pull": {"functionaries.items":
          {"functionary_name": functionary_name}}})
    # TODO: Throw rocks at query_result

  except Exception as e:
    flash("Could not remove functionary '{name}': {e}".format(
        name=functionary_name, e=e), "alert-danger")
    return jsonify({"error": True})

  else:
    flash("Removed functionary '{name}'.".format(
        name=functionary_name), "alert-success")
    return jsonify({"error": False})


@app.route("/authorizing", methods=["GET", "POST"])
@with_session_id
def authorizing():
  """Step 7.
  Authorize functionaries to carry out software supply chain steps. """

  if request.method == "POST":
    # Grab the form posted authorizing data and persist
    # FIXME: Some sanitizing/validation already done below but might need more
    step_names = request.form.getlist("step_name[]")
    thresholds = request.form.getlist("threshold[]")
    comment = request.form.get("comment", "")

    # Steps names, commands and thresholds are related by the same index
    # These lists should be equally long
    # FIXME: Don't assert, try!
    assert(len(step_names) == len(thresholds))

    # The authorized functionaries multi select form element has the
    # respective step name in its name, e.g. for building step:
    # <select name="functionary_name_building[]" ...>
    # (c.f authorizing_functionaries.html)
    auth_items = []
    for idx, step_name in enumerate(step_names):
      functionaries_for_step = request.form.getlist(
          "functionary_name_" + step_name + "[]")

      auth_data = {
        "step_name": step_name,
        "threshold": int(thresholds[idx]),
        "authorized_functionaries": functionaries_for_step
      }
      auth_items.append(auth_data)

    # We validate here (after above processing) so that we can return
    # consistent data in case of invalidity
    valid = True
    for auth_item in auth_items:
      if not auth_item["authorized_functionaries"]:
        valid = False
        flash("Step '{name}': Authorize at least one functionary".format(
            name=auth_item["step_name"]), "alert-warning")

      elif auth_item["threshold"] > len(auth_item["authorized_functionaries"]):
        valid = False
        flash("Step '{name}': Threshold can't be higher than the "
            " number of authorized functionaries".format(
            name=auth_item["step_name"]), "alert-warning")

    # Only persist and go to the next page if valid, else go back to this page
    if valid:
      flash("It's time to do a test run of your software supply chain",
          "alert-success")

      query_result = mongo.db.session_collection.update_one(
          { "_id": session["id"]},
          {"$set": {"authorizing.items": auth_items,
            "authorizing.comment": comment}})
      return redirect(url_for("chaining"))

  else: # request not POST
    authorizing = _get_session_subdocument("authorizing")
    auth_items = authorizing.get("items", [])
    comment = authorizing.get("comment", "")

  # We store auth data items to db as list but in the templates we need a
  # mapping between auth items and steps
  auth_dict = _auth_items_to_dict(auth_items)

  session_functionaries = _get_session_subdocument("functionaries")
  session_steps = _get_session_subdocument("ssc").get("steps", [])
  return render_template("authorizing_functionaries.html",
      functionaries=session_functionaries, steps=session_steps,
      auth_dict=auth_dict, comment=comment)


@app.route("/chaining", methods=["GET", "POST"])
@with_session_id
def chaining():
  """Step 8.
  On get serve dry run snippet and link metadata upload.
  On post store comment and redirect to next page.

  The link file upload uses a different view queried
  with ajax (ajax_upload_link).
  """

  chaining = _get_session_subdocument("chaining")
  steps = _get_session_subdocument("ssc").get("steps", [])

  if request.method == "POST":
    chaining["comment"] = request.form.get("comment", "")
    _persist_session_subdocument({"chaining": chaining})

    flash("And that's basically it... :)", "alert-success")
    return redirect(url_for("wrap_up"))

  return render_template("chaining.html", steps=steps, chaining=chaining)


@app.route("/chaining/upload", methods=["POST"])
@with_session_id
def ajax_upload_link():
  """Ajax upload link metadata file either individually or as tar archive.
  Link files are stored to the db as canonical json string dump. """

  uploaded_file = request.files.get("step_link", None)

  if not uploaded_file:
    flash("Something went wrong: No file uploaded", "alert-danger")
    return jsonify()

  if uploaded_file.filename == "":
    flash("Something went wrong: No file selected", "alert-danger")
    return jsonify()

  # The uploaded file might be a tar archive so let's try to unpack it
  link_file_tuples = []
  try:
    link_archive = tarfile.open(fileobj=uploaded_file)
    for tar_info in link_archive.getmembers():
      link_file = link_archive.extractfile(tar_info)
      link_file_tuples.append((tar_info.name, link_file))

  except tarfile.TarError as e:
    # If that does not work we assume the uploaded file was a link
    link_file_tuples.append((uploaded_file.filename, uploaded_file))


  added_files = []
  msg_type = "alert-success"
  # Now iterate over all files we have, try to load them as link and
  # store them to database
  for link_filename, link_file in link_file_tuples:
    try:
      link_metadata_dict = json.loads(link_file.read())
      link_dict = link_metadata_dict.get("signed")
      if not isinstance(link_dict, dict):
        raise ValueError("Wrong metadata format")

      # FIXME: There is a bug in in_toto_mock that causes the returned link
      # be wrapped twice in a Metablock. The bug is fixed but not yet merged
      # github.com/in-toto/in-toto/commit/4d34fd914d0a0dfac30eaa7af1590ff53161477e
      # Let's work around this bug by unwrapping a second time. If it is not
      # double wrapped we default to parsing a valid Link, as returned e.g. by
      # in_toto_run
      link_dict = link_dict.get("signed", link_dict)

      # Instantiate a link object form the link dictionary
      link = in_toto.models.link.Link.read(link_dict)

      link_db_item = {
        "step_name": link.name,
        "file_name": link_filename,
        # NOTE: We can't store the dict representation of the link, because
        # MongoDB does not allow dotted keys, e.g. "materials": {"foo.py": {...
        # hence we store it as canonical json string dump (c.f. Link __repr__)
        # NOTE: I wonder if we are prone to exceed the max document size
        # (16 MB) if we store all the session info in one document? Unlikely.
        "link_str": repr(link)
      }

      # Push link item to the chaining.items array in the session document
      query_result = mongo.db.session_collection.update_one(
          {"_id": session["id"]},
          {"$push": {"chaining.items": link_db_item}},
          upsert=True)

      # TODO: Throw more rocks at query_result

    except Exception as e:
      msg_type = "alert-danger"
      flash("Could not store link '{}': {}".format(link_filename, e),
          "alert-danger")

    else:
      added_files.append(link_filename)
      flash("Stored link '{file_name}' for step '{name}'!"
          .format(file_name=link_filename, name=link.name), "alert-success")

  return jsonify({"files": added_files})



@app.route("/chaining/remove", methods=["POST"])
@with_session_id
def ajax_remove_link():
  """ Remove the posted link by step name from the chaining session
  subdocument.
  """
  link_filename = request.form.get("link_filename")
  try:
    # Remove the link entry with posted file name in the session
    # document's chaining.items list
    res = mongo.db.session_collection.update_one(
        {"_id": session["id"]},
        {"$pull": {"chaining.items": {"file_name": link_filename}}})
    # TODO: Throw rocks at query_result

  except Exception as e:
    flash("Could not remove link file '{link}': '{e}'".format(
          link=link_filename, e=e), "alert-danger")
    return jsonify({"error": True})

  else:
    flash("Removed link file '{link}'".format(
          link=link_filename), "alert-success")

  return jsonify({"error": False})


@app.route("/wrap-up")
@with_session_id
def wrap_up():
  """Step 9.
  Serves link to download layout and further instructions
   - Download layout
   - Create project owner key (keygen snippet)
   - Sign layout (signing snippet)
   - Per functionary commands (in-toto-run snippet)
   - FIXME: More release instructions
  """
  functionaries = _get_session_subdocument("functionaries")
  auth_items = _get_session_subdocument("authorizing").get("items", [])
  auth_dict = _auth_items_to_dict(auth_items)

  steps = _get_session_subdocument("ssc").get("steps", [])
  return render_template("wrap_up.html", steps=steps, auth_dict=auth_dict,
      functionaries=functionaries)


@app.route("/download-layout")
@with_session_id
def download_layout():
  """Creates in-toto layout based on session data and uploaded links and
  serves it as file download with a timestamped name.


  FIXME:
    - Enhance layout creation
    - Factor out layout creation functionality that's implemented here, e.g. to
      create_layout.py
  """
  # Iterate over items in ssc session subdocument and create an ordered list
  # of related link objects retrieved from the chaining session subdocument
  session_ssc = _get_session_subdocument("ssc")
  session_chaining = _get_session_subdocument("chaining")
  links = []
  for step in session_ssc.get("steps", []):
    for link_data in session_chaining.get("items", []):
      if link_data["step_name"] == step["name"]:
        link_str = json.loads(link_data["link_str"])
        link = in_toto.models.link.Link.read(link_str)

        links.append(link)

  # Create basic layout with steps based on links and simple artifact rules
  layout = create_layout.create_layout_from_ordered_links(links)

  # Add pubkeys to layout
  functionary_keyids = {}
  for functionary in _get_session_subdocument("functionaries").get("items", []):
    key = functionary.get("key_dict")
    functionary_name = functionary.get("functionary_name")

    # Check the format of the uploaded public key
    # TODO: Handle invalid key
    securesystemslib.formats.PUBLIC_KEY_SCHEMA.check_match(key)

    # Add keys to layout's key store
    layout.keys[key["keyid"]] = key

    # Add keys to functionary name-keyid map needed below
    functionary_keyids[functionary_name] = key["keyid"]

  auth_items = _get_session_subdocument("authorizing").get("items", [])
  auth_dict = _auth_items_to_dict(auth_items)

  # Add authorized functionaries to steps and set functionary threshold
  for idx in range(len(layout.steps)):
    step_name = layout.steps[idx].name
    auth_data = auth_dict.get(step_name)

    for functionary_name in auth_data.get("authorized_functionaries", []):
      keyid = functionary_keyids.get(functionary_name)
      if keyid:
        layout.steps[idx].pubkeys.append(keyid)

    layout.steps[idx].threshold = auth_data.get("threshold")

  # Add inspections to layout
  inspections = session_ssc.get("inspections", [])
  for inspection_data in inspections:
    inspection = in_toto.models.layout.Inspection(
        name=inspection_data["name"],
        expected_materials=[
          ["MATCH", "*", "WITH", "PRODUCTS", "FROM", inspection_data["based_on"]]
        ])
    inspection.set_run_from_string(inspection_data["cmd"])

    layout.inspect.append(inspection)

  layout.validate()
  layout_name = "untitled-" + str(time.time()).replace(".", "") + ".layout"

  layout_metadata = in_toto.models.metadata.Metablock(signed=layout)

  # Dump layout to memory file and server to user
  layout_fp = io.BytesIO()
  layout_fp.write("{}".format(layout_metadata).encode("utf-8"))
  layout_fp.seek(0)
  return send_file(layout_fp,
      mimetype="application/json", as_attachment=True,
      attachment_filename=layout_name)


@app.route("/guarantees")
@with_session_id
def guarantees():
  """ Show what the software supply chain protects against and give advice for
  more guarantees.

  FIXME: Not yet implemented
  """
  return render_template("guarantees.html")

if __name__ == "__main__":
  app.run()