path: root/db_query_interface.go

package main

import (
  "fmt"
  "bufio"
  "strings"
  "os"
  "errors"
  "encoding/hex"
)

type DbInterface struct {
  db *MemDatabase
  trie *Trie
}

func NewDBInterface() *DbInterface {
  db, _ := NewMemDatabase()
  trie := NewTrie(db, "")

  return &DbInterface{db: db, trie: trie}
}

func (i *DbInterface) ValidateInput(action string, argumentLength int) error {
  err := false
  var expArgCount int

  switch {
  case action == "update" && argumentLength != 2:
    err = true
    expArgCount = 2
  case action == "get" && argumentLength != 1:
    err = true
    expArgCount = 1
  case (action == "quit" || action == "exit") && argumentLength != 0:
    err = true
    expArgCount = 0
  }

  if err {
    return errors.New(fmt.Sprintf("'%s' requires %d args, got %d", action, expArgCount, argumentLength))
  } else {
    return nil
  }
}

func (i *DbInterface) ParseInput(input string) bool {
  scanner := bufio.NewScanner(strings.NewReader(input))
  scanner.Split(bufio.ScanWords)

  count := 0
  var tokens []string
  for scanner.Scan() {
    count++
    tokens = append(tokens, scanner.Text())
  }
  if err := scanner.Err(); err != nil {
    fmt.Fprintln(os.Stderr, "reading input:", err)
  }

  if len(tokens) == 0 { return true }

  err := i.ValidateInput(tokens[0], count-1)
  if err != nil {
    fmt.Println(err)
  } else  {
    switch tokens[0] {
    case "update":
      i.trie.Update(tokens[1], tokens[2])

      fmt.Println(hex.EncodeToString([]byte(i.trie.root)))
    case "get":
      fmt.Println(i.trie.Get(tokens[1]))
    case "exit", "quit", "q":
      return false
    default:
      fmt.Println("Unknown command:", tokens[0])
    }
  }

  return true
}

func (i *DbInterface) Start() {
  reader := bufio.NewReader(os.Stdin)
  for {
    fmt.Printf("db >>> ")
    str, _, err := reader.ReadLine()
    if err != nil {
      fmt.Println("Error reading input", err)
    } else {
      if !i.ParseInput(string(str)) {
        return
      }
    }
  }
}