(ns query-1
  (:require [clojure.java.io :as io]
            [clojure.string :as string]
        ))
; check if the city has more than 0.5E6 people
(def csv-file "data/ca.csv")

;;reading csv file into hashmap clojure

(defn parse-record [line]
    (let [x line
          [city lat long country iso2 admin capital pop poppropper]
          (string/split x #",")]
    {:city city
     :lat  (read-string lat)
     :long (read-string long)
     :country country
     :iso2  iso2
     :admin  admin
     :capital capital
     :pop   (read-string pop)
     :popproper poppropper}))

(defn cities []
  (with-open [rdr (io/reader csv-file)]
    (vec
     (for [line (drop 1 (line-seq rdr))]
       (parse-record line)))))

(defn city
  ([name xs]
   (->> xs
        (filter #(= (:city %) name))
        first))
  ([name] (city (cities))))

(defn distance [record1 record2]
  (let [R 6371
        dlat (Math/toRadians (- (:lat record2) (:lat record1)))
        dlon (Math/toRadians (- (:long record2) (:long record1)))
        lolnice (Math/toRadians (:lat record1))
        dnice (Math/toRadians (:lat record2))
        a (+ (* (Math/sin (/ dlat 2))
                (Math/sin (/ dlat 2)))
             (* (Math/sin (/ dlon 2))
                (Math/sin (/ dlon 2))
                (Math/cos lolnice)
                (Math/cos dnice)))]
    (* R 2 (Math/asin (Math/sqrt a)))))

(defn large [city-record]
  (> (:pop city-record)  0.5E6))

(defn close [c1 c2]
  (< (distance c1 c2) 600))

(defn closest-city-pairs []
  (let [large-cities (->> (cities) (filter large) vec)]
    (for [x (butlast large-cities)
          y (rest    large-cities)
          :when (and (not= x y)
                     (close x y))]
      [(:city x) (:city y)])))