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TU_Assignment/main.py

160 lines
4.7 KiB

import json, os
from flask import Flask, jsonify, request, render_template, escape
app = Flask(__name__)
app.template_folder = "frontend/"
app.static_folder = "frontend/assets/"
PATH = "graph.json"
graph = {}
def bellmann_ford(graph, node_a):
"""
Calculate distance from node_a to all other nodes assuming no negative
cycles.
Kommentar:
Auch wenn Dijkstra der effizientere Algorithmus in diesem Falle wäre,
habe mich dazu entschieden Bellmann Ford zu implementieren.
Dijkstra musste ich schon mindestens 4 mal in meiner Ausbildung
implementieren. Ich hatte mal wieder Lust auf Dynamische Programmierung.
"""
# weights
from_a_to = {node: float("inf") for node in graph}
from_a_to[node_a] = 0
# save path so we dont have to backtrace later
path_from_a_to = {node: [] for node in graph}
path_from_a_to[node_a] = [node_a]
for i in range(len(graph.keys())-1):
for s,e in [(s,e) for s in graph for e in graph[s]]:
if from_a_to[s] + graph[s][e] < from_a_to[e]:
path_from_a_to[e] = path_from_a_to[s] + [e]
from_a_to[e] = from_a_to[s] + graph[s][e]
return path_from_a_to
def error(message):
return jsonify({"error": message})
def edges_to_json(graph):
return_list = []
done = []
for s in graph:
for e in graph[s]:
if (e,s) not in done:
return_list.append({"start":s,"end":e,"weight":graph[s][e]})
done.append((s,e))
return return_list
# -----------------------------------------------------------------------------
# ------------------------------API--------------------------------------------
# -----------------------------------------------------------------------------
@app.route('/api/paths/<start>/<end>', methods=['GET'])
def get_path(start, end):
if start == end:
return error("Start and end node must be different."), 400
if start not in graph:
return error("Start node does not exist."), 400
if end not in graph:
return error("End node does not exist."), 400
path = bellmann_ford(graph, start)[end]
if len(path) == 0:
return error("There exists no path."), 400
return jsonify({'path': path})
@app.route('/api/nodes', methods=['POST'])
def create_node():
if not request.json:
return error("Request needs to be JSON."), 400
if 'name' not in request.json:
return error("Name must be set."), 400
name = request.json['name']
if name == "":
return error("Name cannot be empty."), 400
if name in graph:
return error(f'Node with name "{escape(name)}" already exist.'), 400
graph[name] = {}
return jsonify(name), 201
@app.route('/api/edges', methods=['POST'])
def create_edge():
if not request.json:
return error("Request needs to be JSON."), 400
if 'start' not in request.json:
return error("Start node must be set."), 400
if 'end' not in request.json:
return error("End node must be set."), 400
if 'weight' not in request.json:
return error("Edge weight must be set."), 400
start = request.json['start']
end = request.json['end']
weight = request.json['weight']
try:
weight = float(weight)
except ValueError:
return error("Weight must be a number."), 400
if weight < 0:
return error("Weight must be positive."), 400
if start == end:
return error("Start and end node must be different."), 400
if start not in graph:
return error("Start node does not exist."), 400
if end not in graph:
return error("End node does not exist."), 400
if start in graph and end in graph[start]:
return error("Edge already exists."), 400
edge = {"start":start,"end":end, "weight": weight}
graph[start][end] = weight
graph[end][start] = weight
return jsonify(edge), 201
@app.route('/api/edges/<start>/<end>', methods=['DELETE'])
def delete_edge(start, end):
if start in graph and end in graph[start]:
del graph[start][end]
del graph[end][start]
return jsonify({"start":start,"end":end}), 200
@app.route("/save")
def save():
try:
with open(PATH, 'w') as f:
json.dump(graph, f)
return jsonify({"info":"Saved graph",**graph}), 200
except Exception:
return error("Internal Server Error"), 500
@app.route("/clear")
def clear():
global graph
graph = {}
return "", 204
@app.route("/")
def index():
return render_template("index.html", nodes=list(graph.keys()), edges=edges_to_json(graph))
if __name__ == '__main__':
if os.path.isfile(PATH) and os.access(PATH, os.R_OK):
with open(PATH, 'r') as f:
graph = json.load(f)
app.run(host="127.0.0.1", debug= True, port=5000)