// Copyright 2014 The Chihaya Authors. All rights reserved.
// Use of this source code is governed by the BSD 2-Clause license,
// which can be found in the LICENSE file.

// Package query implements a faster single-purpose URL Query parser.
package query

import (
	"errors"
	"net"
	"net/http"
	"net/url"
	"strconv"
	"strings"

	"github.com/chihaya/chihaya/config"
)

// Query represents a parsed URL.Query.
type Query struct {
	Infohashes []string
	Params     map[string]string
}

// New parses a raw url query.
func New(query string) (*Query, error) {
	var (
		keyStart, keyEnd int
		valStart, valEnd int
		firstInfohash    string

		onKey       = true
		hasInfohash = false

		q = &Query{
			Infohashes: nil,
			Params:     make(map[string]string),
		}
	)

	for i, length := 0, len(query); i < length; i++ {
		separator := query[i] == '&' || query[i] == ';' || query[i] == '?'
		if separator || i == length-1 {
			if onKey {
				keyStart = i + 1
				continue
			}

			if i == length-1 && !separator {
				if query[i] == '=' {
					continue
				}
				valEnd = i
			}

			keyStr, err := url.QueryUnescape(query[keyStart : keyEnd+1])
			if err != nil {
				return nil, err
			}

			valStr, err := url.QueryUnescape(query[valStart : valEnd+1])
			if err != nil {
				return nil, err
			}

			q.Params[strings.ToLower(keyStr)] = valStr

			if keyStr == "info_hash" {
				if hasInfohash {
					// Multiple infohashes
					if q.Infohashes == nil {
						q.Infohashes = []string{firstInfohash}
					}
					q.Infohashes = append(q.Infohashes, valStr)
				} else {
					firstInfohash = valStr
					hasInfohash = true
				}
			}

			onKey = true
			keyStart = i + 1

		} else if query[i] == '=' {
			onKey = false
			valStart = i + 1
		} else if onKey {
			keyEnd = i
		} else {
			valEnd = i
		}
	}

	return q, nil
}

// Uint64 is a helper to obtain a uints of any base from a Query. After being
// called, you can safely cast the uint64 to your desired base.
func (q *Query) Uint64(key string) (uint64, error) {
	str, exists := q.Params[key]
	if !exists {
		return 0, errors.New("value does not exist for key: " + key)
	}

	val, err := strconv.ParseUint(str, 10, 64)
	if err != nil {
		return 0, err
	}

	return val, nil
}

// RequestedPeerCount returns the request peer count or the provided fallback.
func (q Query) RequestedPeerCount(fallback int) int {
	if numWantStr, exists := q.Params["numwant"]; exists {
		numWant, err := strconv.Atoi(numWantStr)
		if err != nil {
			return fallback
		}
		return numWant
	}

	return fallback
}

func getIPs(ipstr string, ipv4, ipv6 net.IP, cfg *config.NetConfig) (net.IP, net.IP, bool) {
	var done bool

	if ip := net.ParseIP(ipstr); ip != nil {
		newIPv4 := ip.To4()

		if ipv4 == nil && newIPv4 != nil {
			ipv4 = newIPv4
		} else if ipv6 == nil && newIPv4 == nil {
			ipv6 = ip
		}
	}

	if cfg.DualStackedPeers {
		done = ipv4 != nil && ipv6 != nil
	} else {
		done = ipv4 != nil || ipv6 != nil
	}

	return ipv4, ipv6, done
}

// RequestedIP returns the requested IP address from a Query.
func (q Query) RequestedIP(r *http.Request, cfg *config.NetConfig) (v4, v6 net.IP, err error) {
	var done bool

	if cfg.AllowIPSpoofing {
		if str, ok := q.Params["ip"]; ok {
			if v4, v6, done = getIPs(str, v4, v6, cfg); done {
				return
			}
		}

		if str, ok := q.Params["ipv4"]; ok {
			if v4, v6, done = getIPs(str, v4, v6, cfg); done {
				return
			}
		}

		if str, ok := q.Params["ipv6"]; ok {
			if v4, v6, done = getIPs(str, v4, v6, cfg); done {
				return
			}
		}
	}

	if cfg.RealIPHeader != "" {
		if xRealIPs, ok := q.Params[cfg.RealIPHeader]; ok {
			if v4, v6, done = getIPs(string(xRealIPs[0]), v4, v6, cfg); done {
				return
			}
		}
	} else {
		if r.RemoteAddr == "" {
			if v4 == nil {
				v4 = net.ParseIP("127.0.0.1")
			}
			return
		}

		if idx := strings.LastIndex(r.RemoteAddr, ":"); idx != -1 {
			if v4, v6, done = getIPs(r.RemoteAddr[0:idx], v4, v6, cfg); done {
				return
			}
		}
	}

	if v4 == nil && v6 == nil {
		err = errors.New("failed to parse IP address")
	}
	return
}