/*
Copyright (c) 2019, Percona LLC.
All rights reserved.

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modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice, this
  list of conditions and the following disclaimer.

* Redistributions in binary form must reproduce the above copyright notice,
  this list of conditions and the following disclaimer in the documentation
  and/or other materials provided with the distribution.

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  contributors may be used to endorse or promote products derived from
  this software without specific prior written permission.

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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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*/

// Package query provides functions to transform queries.
package query

/*
	Fingerprint is highly-specialized and operates on a single principle:

		1. We only replace numbers, quoted strings, and value lists.

	Although we must handle a lot of details, exceptions, and special cases,
	that principle distills the problem to its essence which makes it
	possible to solve without a true SQL syntax parser (or regex). It means
	that we can simply copy and ignore the vast majority of the query because
	if it's not a number, quoted string, or value list then there's nothing
	to do. With a regex solution we can stop there and simply do transformations
	like s/\d+/?/g and s/'[^']*'/?/g but the details, exceptions, and specials
	cases make that only a partial, crude solution because, for example, with
	col = 'It\s' an escaped quote char.' now the regex needs to handle inner,
	escaped quotes so it becomes more complicated and slower. There are many
	more difficult problems like this. Consequently, neither regex nor this
	solution can be simple, but at least this solution is very fast compared
	to regex because it makes a single pass through the query whereas regex
	makes as many passes as there are regexes and, worst case, a single regex
	can make several passes due to backtracking. To handle problems like these,
	this solution is a simple state machine. In the previous example problem,
	once the first quote char (') is seen we enter the inQuote state. In this
	state, if an escape char (\) is seen, this is remembered and the next char
	is ignored. This allows us to correctly detect the real ending quote char:
	it's the first unescaped quote char. Consequently, we can simply ignore
	everything else in the quoted value. The same basic logic applies to numbers
	and value lists.

	With that principle and basic logic in mind, you'll notice three major code
	blocks:
		1. Skip parts of the query for certain states.
		2. Change state based on rune and current state.
		3. Copy a slice of the query into the fingerprint.
	The order is important because it enforces the basic logic: once we enter
	certain states we must process and finish them first because in these states
	we ignore everything but whatever ends the state. As mentioned above, the
	inQuote state is handled in the first block. When in this state, only the
	real ending quote char ends it. Consequently nothing will trick the parser;
	for example the quoted value in col="INSERT INTO t VALUES ('no problem')"
	will not be mistaken for another query and another quoted value. --
	The second block is primarily where cpFromOffset and cpToOffset are set
	which are used by the third block to copy that range of the query into the
	fingerprint. The second block stops, switches state, copies, and lets
	the code enter the first block which skips through number, quoted value, or
	value list that the second block found.
*/

import (
	"crypto/md5"
	"fmt"
	"io"
	"strings"
)

const (
	unknown             byte = iota
	inWord                   // \S+
	inNumber                 // [0-9a-fA-Fx.-]
	inSpace                  // space, tab, \r, \n
	inOp                     // [=<>!] (usually precedes a number)
	opOrNumber               // + in 2 + 2 or +3e-9
	inQuote                  // '...' or "..."
	subOrOLC                 // - or start of -- comment
	inDash                   // -- begins a one-line comment if followed by space
	inOLC                    // -- comment (at least one space after dash is required)
	divOrMLC                 // / operator or start of /* comment */
	mlcOrMySQLCode           // /* comment */ or /*! MySQL-specific code */
	inMLC                    // /* comment */
	inValues                 // VALUES (1), ..., (N)
	moreValuesOrUnknown      // , (2nd+) or ON DUPLICATE KEY or end of query
	orderBy                  // ORDER BY
	onDupeKeyUpdate          // ON DUPLICATE KEY UPDATE
	inNumberInWord           // e.g. db23
	inBackticks              // `table-1`
	inMySQLCode              // /*! MySQL-specific code */
)

var stateName map[byte]string = map[byte]string{
	0:  "unknown",
	1:  "inWord",
	2:  "inNumber",
	3:  "inSpace",
	4:  "inOp",
	5:  "opOrNumber",
	6:  "inQuote",
	7:  "subOrOLC",
	8:  "inDash",
	9:  "inOLC",
	10: "divOrMLC",
	11: "mlcOrMySQLCode",
	12: "inMLC",
	13: "inValues",
	14: "moreValuesOrUnknown",
	15: "orderBy",
	16: "onDupeKeyUpdate",
	17: "inNumberInWord",
	18: "inBackTicks",
	19: "inMySQLCode",
}

// Debug prints very verbose tracing information to STDOUT.
var Debug bool = false

// ReplaceNumbersInWords enables replacing numbers in words. For example:
// `SELECT c FROM org235.t` -> `SELECT c FROM org?.t`. For more examples
// look at test query_test.go/TestFingerprintWithNumberInDbName.
var ReplaceNumbersInWords = false

// Fingerprint returns the canonical form of q. The primary transformations are:
//   - Replace values with ?
//   - Collapse whitespace
//   - Remove comments
//   - Lowercase everything
//
// Additional trasnformations are performed which change the syntax of the
// original query without affecting its performance characteristics. For
// example, "ORDER BY col ASC" is the same as "ORDER BY col", so "ASC" in the
// fingerprint is removed.
func Fingerprint(q string) string {
	q += " " // need range to run off end of original query
	prevWord := ""
	f := make([]byte, len(q))
	fi := 0
	pr := rune(0) // previous rune
	s := unknown  // current state
	sqlState := unknown
	quoteChar := rune(0)
	cpFromOffset := 0
	cpToOffset := 0
	addSpace := false
	escape := false
	parOpen := 0
	parOpenTotal := 0
	valueNo := 0
	firstPar := 0

	for qi, r := range q {
		if Debug {
			fmt.Printf("\n%d:%d %s/%s [%d:%d] %x %q\n", qi, fi, stateName[s], stateName[sqlState], cpFromOffset, cpToOffset, r, r)
		}

		/**
		 * 1. Skip parts of the query for certain states.
		 */

		if s == inQuote {
			// We're in a 'quoted value' or "quoted value".  The quoted value
			// ends at the first non-escaped matching quote character (' or ").
			if r != quoteChar {
				// The only char inside a quoted value we need to track is \,
				// the escape char.  This allows us to tell that the 2nd ' in
				// '\'' is escaped, not the ending quote char.
				if escape {
					if Debug {
						fmt.Println("Ignore quoted literal")
					}
					escape = false
				} else if r == '\\' {
					if Debug {
						fmt.Println("Escape")
					}
					escape = true
				} else {
					if Debug {
						fmt.Println("Ignore quoted value")
					}
				}
			} else if escape {
				// \' or \"
				if Debug {
					fmt.Println("Quote literal")
				}
				escape = false
			} else {
				// 'foo' -> ?
				// "foo" -> ?
				if Debug {
					fmt.Println("Quote end")
				}
				escape = false

				// qi = the closing quote char, so +1 to ensure we don't copy
				// anything before this, i.e. quoted value is done, move on.
				cpFromOffset = qi + 1

				if sqlState == inValues {
					// ('Hello world!', ...) -> VALUES (, ...)
					// The inValues state uses this state to skip quoted values,
					// so we don't replace them with ?; the inValues blocks will
					// replace the entire value list with ?+.
					s = inValues
				} else {
					f[fi] = '?'
					fi++
					s = unknown
				}
			}
			continue
		} else if s == inBackticks {
			if r != '`' {
				// The only char inside a quoted value we need to track is \,
				// the escape char.  This allows us to tell that the 2nd ' in
				// '\`' is escaped, not the ending quote char.
				if escape {
					if Debug {
						fmt.Println("Ignore backtick literal")
					}
					escape = false
				} else if r == '\\' {
					if Debug {
						fmt.Println("Escape")
					}
					escape = true
				} else {
					if Debug {
						fmt.Println("Ignore quoted value")
					}
				}
			} else if escape {
				// \`
				if Debug {
					fmt.Println("Quote literal")
				}
				escape = false
			} else {
				if Debug {
					fmt.Println("Quote end")
				}
				escape = false

				// qi = the closing backtick, so +1 to ensure we don't copy
				// anything before this, i.e. quoted value is done, move on.
				// cpFromOffset = qi + 1
				cpToOffset = qi + 1

				s = inWord
			}
			continue

		} else if s == inNumberInWord {
			// Replaces number in words with ?
			// e.g. `db37` to `db?`
			// Parser can fall into inNumberInWord only if
			// option ReplaceNumbersInWords is turned on
			if r >= '0' && r <= '9' {
				if Debug {
					fmt.Println("Ignore digit in word")
				}
				continue
			}
			// 123 -> ?, 0xff -> ?, 1e-9 -> ?, etc.
			if Debug {
				fmt.Println("Number in word end")
			}
			f[fi] = '?'
			fi++
			cpFromOffset = qi
			if isSpace(r) {
				s = unknown
			} else {
				s = inWord
			}
		} else if s == inNumber {
			// We're in a number which can be something simple like 123 or
			// something trickier like 1e-9 or 0xFF.  The pathological case is
			// like 12ff: this is valid hex number and a valid ident (e.g. table
			// name).  We can't detect this; the best we can do is realize that
			// 12ffz is not a number because of the z.
			if (r >= '0' && r <= '9') || (r >= 'a' && r <= 'f') || (r >= 'A' && r <= 'F') || r == '.' || r == 'x' || r == '-' {
				if Debug {
					fmt.Println("Ignore digit")
				}
				continue
			}
			if (r >= 'g' && r <= 'z') || (r >= 'G' && r <= 'Z') || r == '_' {
				if Debug {
					fmt.Println("Not a number")
				}
				cpToOffset = qi
				s = inWord
			} else if sqlState == inMySQLCode {
				// If we are in /*![version] ... */, keep the version number
				cpToOffset = qi
				s = inWord
				sqlState = unknown
			} else {
				// 123 -> ?, 0xff -> ?, 1e-9 -> ?, etc.
				if Debug {
					fmt.Println("Number end")
				}
				f[fi] = '?'
				fi++
				cpFromOffset = qi
				cpToOffset = qi
				s = unknown
			}
		} else if s == inValues {
			// We're in the (val1),...,(valN) after IN or VALUE[S].  A single
			// () value ends when the parenthesis are balanced, but...
			if r == ')' {
				parOpen--
				parOpenTotal++
				if Debug {
					fmt.Println("Close parenthesis", parOpen)
				}
			} else if r == '(' {
				parOpen++
				if Debug {
					fmt.Println("Open parenthesis", parOpen)
				}
				if parOpen == 1 {
					firstPar = qi
				}
			} else if r == '\'' || r == '"' {
				// VALUES ('Hello world!') -> enter inQuote state to skip
				// the quoted value so ')' in 'This ) is a trick' doesn't
				// balance an outer parenthesis.
				if Debug {
					fmt.Println("Quote begin")
				}
				s = inQuote
				quoteChar = r
				continue
			} else if isSpace(r) {
				if Debug {
					fmt.Println("Space")
				}
				continue
			}
			if parOpen > 0 {
				// Parenthesis are not balanced yet; i.e. haven't reached
				// closing ) for this value.
				continue
			}
			if parOpenTotal == 0 {
				// SELECT value FROM t
				if Debug {
					fmt.Println("Literal values not VALUES()")
				}
				s = inWord
				continue
			}
			// (<anything>) -> (?+) only for first value, but check for subqueries
			if Debug {
				fmt.Println("Values end")
			}
			valueNo++
			if valueNo == 1 {
				if qi-firstPar > 1 {
					// Check if this is a subquery by looking for SELECT keyword
					content := strings.ToLower(strings.TrimSpace(q[firstPar+1 : qi]))
					if strings.HasPrefix(content, "select") {
						// This is a subquery, fingerprint it recursively
						subqueryFingerprint := Fingerprint(q[firstPar+1 : qi])
						subqueryResult := "(" + subqueryFingerprint + ")"
						if Debug {
							fmt.Printf("Subquery detected: %s -> %s\n", q[firstPar+1:qi], subqueryFingerprint)
						}
						copy(f[fi:fi+len(subqueryResult)], subqueryResult)
						fi += len(subqueryResult)
					} else {
						// Regular value list
						copy(f[fi:fi+4], "(?+)")
						fi += 4
					}
				} else {
					// INSERT INTO t VALUES ()
					copy(f[fi:fi+2], "()")
					fi += 2
				}
				firstPar = 0
			}
			// ... the difficult part is that there may be other values, e.g.
			// (1), (2), (3).  So we enter the following state.  The values list
			// ends when the next char is not a comma.
			s = moreValuesOrUnknown
			pr = r
			cpFromOffset = qi + 1
			parOpenTotal = 0
			continue
		} else if s == inMLC {
			// We're in a /* mutli-line comments */.  Skip and ignore it all.
			if pr == '*' && r == '/' {
				// /* foo */ -> (nothing)
				if Debug {
					fmt.Printf("Multi-line comment end. pr: %s\n", string(pr))
				}
				s = unknown
			} else {
				pr = r
				if Debug {
					fmt.Println("Ignore multi-line comment content")
				}
			}
			continue
		} else if s == mlcOrMySQLCode {
			// We're at the start of either a /* multi-line comment */ or some
			// /*![version] some MySQL-specific code */.  The ! after the /*
			// determines which one.
			if r != '!' {
				if Debug {
					fmt.Println("Multi-line comment")
				}
				pr = r
				s = inMLC
				continue
			} else {
				// /*![version] SQL_NO_CACHE */ -> /*![version] SQL_NO_CACHE */ (no change)
				if Debug {
					fmt.Println("MySQL-specific code")
				}
				s = inWord
				sqlState = inMySQLCode
			}
		} else if s == inOLC {
			// We're in a -- one line comment.  A space after -- is required.
			// It ends at the end of the line, but there can be more query after
			// it like:
			//   SELECT * -- comment
			//   FROM t
			// is really "SELECT * FROM t".
			if r == 0x0A { // newline
				if Debug {
					fmt.Println("One-line comment end")
				}
				s = unknown
			}
			continue
		} else if isSpace(r) && isSpace(pr) {
			// All space is collapsed into a single space, so if this char is
			// a space and the previous was too, then skip the extra space.
			if Debug {
				fmt.Println("Skip space")
			}
			// +1 here ensures we actually skip the extra space in certain
			// cases like "select \n-- bar\n foo".  When a part of the query
			// triggers a copy of preceding chars, if the only preceding char
			// is a space then it's incorrectly copied, but +1 sets cpFromOffset
			// to the same offset as the trigger char, thus avoiding the copy.
			// For example in that ^ query, the offsets are:
			//   0 's'
			//   1 'e'
			//   2 'l'
			//   3 'e'
			//   4 'c'
			//   5 't'
			//   6 ' '
			//   7 '\n'
			//   8 '-'
			// After copying 'select ', we are here @ 7 and intend to skip the
			// newline.  Next, the '-' @ 8 triggers a copy of any preceding
			// chars.  So here if we set cpFromOffset = 7 then 7:8 is copied,
			// the newline, but setting cpFromOffset = 7 + 1 is 8:8 and so
			// nothing is copied as we want.  Actually, cpToOffset is still 6
			// in this case, but 8:6 avoids the copy too.
			cpFromOffset = qi + 1
			pr = r
			continue
		}

		/**
		 * 2. Change state based on rune and current state.
		 */

		switch {
		case r >= 0x30 && r <= 0x39: // 0-9
			switch s {
			case opOrNumber:
				if Debug {
					fmt.Println("+/-First digit")
				}
				cpToOffset = qi - 1
				s = inNumber
			case inOp:
				if Debug {
					fmt.Println("First digit after operator")
				}
				cpToOffset = qi
				s = inNumber
			case inWord:
				if pr == '(' {
					if Debug {
						fmt.Println("Number in function")
					}
					cpToOffset = qi
					s = inNumber
				} else if pr == ',' {
					// foo,4 -- 4 may be a number literal or a word/ident
					if Debug {
						fmt.Println("Number or word")
					}
					s = inNumber
					cpToOffset = qi
				} else {
					if Debug {
						fmt.Println("Number in word")
					}
					if ReplaceNumbersInWords {
						s = inNumberInWord
						cpToOffset = qi
					}
				}
			default:
				if Debug {
					fmt.Println("Number literal")
				}
				s = inNumber
				cpToOffset = qi
			}
		case isSpace(r):
			if s == unknown {
				if Debug {
					fmt.Println("Lost in space")
				}
				if fi > 0 && !isSpace(rune(f[fi-1])) {
					if Debug {
						fmt.Println("Add space")
					}
					f[fi] = ' '
					fi++
					// This is a common case: a space after skipping something,
					// e.g. col = 'foo'<space>. We want only the first space,
					// so advance cpFromOffset to whatever is after the space
					// and if it's more space then space skipping block will
					// handle it.
				}
				cpFromOffset = qi + 1
			} else if s == inDash {
				if Debug {
					fmt.Println("One-line comment begin")
				}
				s = inOLC
				if cpToOffset > 2 {
					cpToOffset = qi - 2
				}
			} else if s == moreValuesOrUnknown {
				if Debug {
					fmt.Println("Space after values")
				}
				if valueNo == 1 {
					f[fi] = ' '
					fi++
				}
			} else {
				if Debug {
					fmt.Println("Word end")
				}
				word := strings.ToLower(q[cpFromOffset:qi])
				// Only match USE if it is the first word in the query, otherwise,
				// it could be a USE INDEX
				if word == "use" && prevWord == "" {
					return "use ?"
				} else if (word == "null" && (prevWord != "is" && prevWord != "not")) || word == "null," {
					if Debug {
						fmt.Println("NULL as value")
					}
					f[fi] = '?'
					fi++
					if word[len(word)-1] == ',' {
						f[fi] = ','
						fi++
					}
					f[fi] = ' '
					fi++
					cpFromOffset = qi + 1
				} else if prevWord == "order" && word == "by" {
					if Debug {
						fmt.Println("ORDER BY begin")
					}
					sqlState = orderBy
				} else if sqlState == orderBy && wordIn(word, "asc", "asc,", "asc ") {
					if Debug {
						fmt.Println("ORDER BY ASC")
					}
					cpFromOffset = qi
					if word[len(word)-1] == ',' {
						fi--
						f[fi] = ','
						f[fi+1] = ' '
						fi += 2
					}
				} else if prevWord == "key" && word == "update" {
					if Debug {
						fmt.Println("ON DUPLICATE KEY UPDATE begin")
					}
					sqlState = onDupeKeyUpdate
				}
				s = inSpace
				cpToOffset = qi
				addSpace = true
			}
		case r == '\'' || r == '"':
			if pr != '\\' {
				if s != inQuote {
					if Debug {
						fmt.Println("Quote begin")
					}
					s = inQuote
					quoteChar = r
					cpToOffset = qi
					if pr == 'x' || pr == 'b' {
						if Debug {
							fmt.Println("Hex/binary value")
						}
						// We're at the first quote char of x'0F'
						// (or b'0101', etc.), so -2 for the quote char and
						// the x or b char to copy anything before and up to
						// this value.
						cpToOffset = -2
					}
				}
			}
		case r == '`':
			if pr != '\\' {
				if s != inBackticks {
					if Debug {
						fmt.Println("Beckticks begin")
					}
					s = inBackticks
				}
			}
		case r == '=' || r == '<' || r == '>' || r == '!':
			if Debug {
				fmt.Println("Operator")
			}
			if s != inWord && s != inOp {
				cpFromOffset = qi
			}
			s = inOp
		case r == '/':
			if Debug {
				fmt.Println("Op or multi-line comment")
			}
			s = divOrMLC
		case r == '*' && s == divOrMLC:
			if Debug {
				fmt.Println("Multi-line comment or MySQL-specific code")
			}
			s = mlcOrMySQLCode
		case r == '+':
			if Debug {
				fmt.Println("Operator or number")
			}
			s = opOrNumber
		case r == '-':
			if pr == '-' {
				if Debug {
					fmt.Println("Dash")
				}
				s = inDash
			} else {
				if Debug {
					fmt.Println("Operator or number")
				}
				s = opOrNumber
			}
		case r == '.':
			if s == inNumber || s == inOp {
				if Debug {
					fmt.Println("Floating point number")
				}
				s = inNumber
				cpToOffset = qi
			}
		case r == '(':
			if prevWord == "call" {
				// 'CALL foo(...)' -> 'call foo'
				if Debug {
					fmt.Println("CALL sp_name")
				}
				return "call " + q[cpFromOffset:qi]
			} else if sqlState != onDupeKeyUpdate && (((s == inSpace || s == moreValuesOrUnknown) && (prevWord == "value" || prevWord == "values" || prevWord == "in")) || wordIn(q[cpFromOffset:qi], "value", "values", "in")) {
				// VALUE(, VALUE (, VALUES(, VALUES (, IN(, or IN(
				// but not after ON DUPLICATE KEY UPDATE
				if Debug {
					fmt.Println("Values begin")
				}
				s = inValues
				sqlState = inValues
				parOpen = 1
				firstPar = qi
				if valueNo == 0 {
					cpToOffset = qi
				}
			} else if s != inWord {
				if Debug {
					fmt.Println("Random (")
				}
				valueNo = 0
				cpFromOffset = qi
				s = inWord
			}
		case r == ',' && s == moreValuesOrUnknown:
			if Debug {
				fmt.Println("More values")
			}
		case r == ':' && prevWord == "administrator":
			// 'administrator command: Init DB' -> 'administrator command: Init DB' (no change)
			if Debug {
				fmt.Println("Admin cmd")
			}
			return q[0 : len(q)-1] // original query minus the trailing space we added
		case r == '#':
			if Debug {
				fmt.Println("One-line comment begin")
			}
			addSpace = false
			s = inOLC
		default:
			if s != inWord && s != inOp {
				// If in a word or operator then keep copying the query, else
				// previous chars were being ignored for some reason, but now
				// we should start copying again, so set cpFromOffset.  Example:
				// col=NOW(). 'col' will be set to copy, but then '=' will put
				// us in inOp state which, if a value follows, will trigger a
				// copy of "col=", but "NOW()" is not a value so "N" is caught
				// here and since s=inOp still we do not copy yet (this block is
				//  not entered).
				if Debug {
					fmt.Println("Random character")
				}
				valueNo = 0
				cpFromOffset = qi

				if sqlState == inValues {
					// Values are comma-separated, so the first random char
					// marks the end of the VALUE() or IN() list.
					if Debug {
						fmt.Println("No more values")
					}
					sqlState = unknown
				}
			}
			s = inWord
		}

		/**
		 * 3. Copy a slice of the query into the fingerprint.
		 */

		if cpToOffset > cpFromOffset {
			l := cpToOffset - cpFromOffset
			prevWord = strings.ToLower(q[cpFromOffset:cpToOffset])
			if Debug {
				fmt.Printf("copy '%s' (%d:%d, %d:%d) %d\n", prevWord, fi, fi+l, cpFromOffset, cpToOffset, l)
			}
			copy(f[fi:fi+l], prevWord)
			fi += l
			cpFromOffset = cpToOffset
			valueKeywords := []string{"in", "value", "values"}
			if wordIn(prevWord, valueKeywords...) && sqlState != onDupeKeyUpdate {
				addSpace = false
				// since we only consider the keywords if it exists at a top-level (except onDupeKeyUpdate),
				// we only do the conversion below if the "keywords" actually open a value list (i.e., before opening a parenthesis).
				if r == '(' || (isSpace(r) && qi+1 < len(q) && ((q[qi+1] == '(') || (q[qi+1] == ' '))) {
					// IN ()     -> in(?+)
					// VALUES () -> values(?+)
					s = inValues
					sqlState = inValues
				} else {
					f[fi] = ' '
					fi++
					cpFromOffset++
				}
			} else if addSpace {
				if Debug {
					fmt.Println("Add space")
				}
				f[fi] = ' '
				fi++
				cpFromOffset++
				addSpace = false
			}
		}
		pr = r
	}

	// Remove trailing spaces.
	for fi > 0 && isSpace(rune(f[fi-1])) {
		fi--
	}

	// Clean up control characters, and return the fingerprint
	return strings.Replace(string(f[0:fi]), "\x00", "", -1)
}

func isSpace(r rune) bool {
	return r == 0x20 || r == 0x09 || r == 0x0D || r == 0x0A
}

func wordIn(q string, words ...string) bool {
	q = strings.ToLower(q)
	for _, word := range words {
		if q == word {
			return true
		}
	}
	return false
}

// Id returns the right-most 16 characters of the MD5 checksum of fingerprint.
// Query IDs are the shortest way to uniquely identify queries.
func Id(fingerprint string) string {
	id := md5.New()
	io.WriteString(id, fingerprint)
	h := fmt.Sprintf("%x", id.Sum(nil))
	return strings.ToUpper(h[16:32])
}