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package main

import (
	"database/sql"
	"flag"
	"fmt"
	"math/rand"
	"os"
	"os/exec"

	_ "modernc.org/sqlite"
)

var verbose = flag.Bool("v", false, "debug output")
var file = flag.String("f", "cards", "cards file")

type segmentTree struct {
	N   int
	seg []int
}

// Build segment tree
func (s segmentTree) build(a *sql.Rows, l, r, n int) {
	if l == r {
		a.Next()
		a.Scan(&s.seg[n])
		return
	}
	m := (l + r) >> 1
	s.build(a, l, m, n<<1)
	s.build(a, m+1, r, n<<1|1)
	s.seg[n] = s.seg[n<<1] + s.seg[n<<1|1]
}

// Update value at index x
func (s segmentTree) update(x, v, l, r, n int) {
	if l == r {
		s.seg[n] = v
		return
	}
	m := (l + r) >> 1
	if x <= m {
		s.update(x, v, l, m, n<<1)
	} else {
		s.update(x, v, m+1, r, n<<1|1)
	}
	s.seg[n] = s.seg[n<<1] + s.seg[n<<1|1]
}

// Find element with prefix sum v
func (s segmentTree) query(v, l, r, n int) (int, int) {
	if l == r {
		return s.seg[n], l
	}
	m := (l + r) >> 1
	if s.seg[n<<1] >= v {
		return s.query(v, l, m, n<<1)
	} else {
		return s.query(v-s.seg[n<<1], m+1, r, n<<1|1)
	}
}

func main() {
	flag.Parse()

	db, err := sql.Open("sqlite", *file)
	if err != nil {
		panic(err)
	}

	// Get number of cards
	var N int
	_ = db.QueryRow("SELECT COUNT(*) FROM cards").Scan(&N)
	s := segmentTree{N, make([]int, 4*N)}

	// Build segment tree
	rows, err := db.Query("SELECT weight FROM cards")
	if err != nil {
		panic(err)
	}
	s.build(rows, 0, N-1, 1)
	rows.Close()

	if *verbose {
		fmt.Println(s)
	}

	// https://stackoverflow.com/questions/14094190/function-similar-to-getchar
	// disable input buffering
	exec.Command("stty", "-F", "/dev/tty", "cbreak", "min", "1").Run()
	// do not display entered characters on the screen
	exec.Command("stty", "-F", "/dev/tty", "-echo").Run()
	// restore the echoing state when exiting
	defer exec.Command("stty", "-F", "/dev/tty", "echo").Run()

	for {
		// Choose a random card
		x := rand.Intn(s.seg[1])
		w, i := s.query(x, 0, N-1, 1)

		if *verbose {
			fmt.Println(x)
			fmt.Println(w)
			fmt.Println(i)
		}

		// Get card contents from database
		var key, val string
		db.QueryRow("SELECT key, val FROM cards WHERE idx=?", i).Scan(&key, &val)
		fmt.Println(key)

		// Wait for confirmation
		var b []byte = make([]byte, 1)
		os.Stdin.Read(b)
		fmt.Println(val)

		// Read user input
		os.Stdin.Read(b)
		if b[0] == byte('y') {
			w >>= 1
		} else if b[0] == byte('n') {
			w <<= 1
		} else {
			os.Exit(0)
		}

		// Update segment tree and database
		s.update(i, w, 0, N-1, 1)
		_, err = db.Exec("UPDATE cards SET weight=? WHERE idx=?", w, i)
		if err != nil {
			panic(err)
		}
	}
}