package hbot

import (
	"bytes"
	"strings"
)

// Various constants used for formatting IRC messages.
const (
	tags          byte = 0x40 // Tag start indicator
	tagsEquals    byte = 0x3D // Keys and values are separated using equal signs
	tagsSeparator byte = 0x3B // Separator between multiple tags
	prefix        byte = 0x3A // Prefix or last argument
	prefixUser    byte = 0x21 // Username
	prefixHost    byte = 0x40 // Hostname
	space         byte = 0x20 // Separator

	maxLength = 510 // Maximum length is 512 - 2 for the line endings.
)

var (
	tagEscapeReplacer = strings.NewReplacer("\\:", ";", "\\s", " ", "\\r", "\r", "\\n", "\n")
)

func cutsetFunc(r rune) bool {
	// Characters to trim from prefixes/messages.
	return r == '\r' || r == '\n'
}

// Tags represents (optional) tags added to the start of each message
// See IRCv3.2 Message Tags (http://ircv3.net/specs/core/message-tags-3.2.html)
//
// <message>       ::= ['@' <tags> <SPACE>] [':' <prefix> <SPACE> ] <command> <params> <crlf>
// <tags>          ::= <tag> [';' <tag>]*
// <tag>           ::= <key> ['=' <escaped value>]
// <key>           ::= [ <vendor> '/' ] <sequence of letters, digits, hyphens (`-`)>
// <escaped value> ::= <sequence of any characters except NUL, CR, LF, semicolon (`;`) and SPACE>
// <vendor>        ::= <host>
type Tags map[string]string

// ParseTags takes a string and attempts to create a Tags struct
func ParseTags(raw string) (t Tags) {
	t = make(Tags)

	tags := strings.Split(raw, string(tagsSeparator))

	for _, val := range tags {
		replacedVal := tagEscapeReplacer.Replace(val)
		tagParts := strings.SplitN(replacedVal, string(tagsEquals), 2)
		// Tag must at least contain a key
		if len(tagParts) < 1 {
			continue
		}

		// Tag only contains key, set empty value
		if len(tagParts) == 1 {
			t[tagParts[0]] = ""
			continue
		}

		t[tagParts[0]] = tagParts[1]
	}

	return t
}

// GetTag checks whether a tag with the given key exists. The boolean return value indicates whether a value was found
func (t Tags) GetTag(key string) (string, bool) {
	if t != nil {
		if val, ok := t[key]; ok {
			return val, true
		}
	}

	return "", false
}

// writeTo is an utility function to write the tags list to a bytes.Buffer.
func (t Tags) writeTo(buffer *bytes.Buffer) {
	buffer.WriteByte(tags)

	i := 0
	mapLen := len(t)
	for k, v := range t {
		buffer.WriteString(k)
		if v != "" {
			buffer.WriteByte(tagsEquals)
			buffer.WriteString(v)
		}
		if i != mapLen-1 {
			buffer.WriteByte(tagsSeparator)
		}

		i++
	}
}

// Bytes returns the []byte representation of this collection of message tags
func (t Tags) Bytes() []byte {
	if t == nil {
		return nil
	}

	buffer := new(bytes.Buffer)
	t.writeTo(buffer)
	return buffer.Bytes()
}

// String returns the string representation of all set message tags
func (t Tags) String() (s string) {
	return string(t.Bytes())
}

// Prefix represents the prefix (sender) of an IRC message.
// See RFC1459 section 2.3.1.
//
//    <servername> | <nick> [ '!' <user> ] [ '@' <host> ]
//
type Prefix struct {
	Name string // Nick- or servername
	User string // Username
	Host string // Hostname
}

func indexByte(s string, c byte) int {
	return strings.IndexByte(s, c)
}

// ParsePrefix takes a string and attempts to create a Prefix struct.
func ParsePrefix(raw string) (p Prefix) {
	user := indexByte(raw, prefixUser)
	host := indexByte(raw, prefixHost)
	switch {
	case user > 0 && host > user:
		p.Name = raw[:user]
		p.User = raw[user+1 : host]
		p.Host = raw[host+1:]

	case user > 0:
		p.Name = raw[:user]
		p.User = raw[user+1:]

	case host > 0:
		p.Name = raw[:host]
		p.Host = raw[host+1:]

	default:
		p.Name = raw

	}
	return
}

// Empty determines whether the prefix is empty.
func (p *Prefix) Empty() bool {
	return len(p.User)+len(p.Host)+len(p.Name) == 0
}

// Len calculates the length of the string representation of this prefix.
func (p *Prefix) Len() (length int) {
	length = len(p.Name)
	if len(p.User) > 0 {
		length = length + len(p.User) + 1
	}
	if len(p.Host) > 0 {
		length = length + len(p.Host) + 1
	}
	return
}

// Bytes returns a []byte representation of this prefix.
func (p *Prefix) Bytes() []byte {
	buffer := new(bytes.Buffer)
	p.writeTo(buffer)
	return buffer.Bytes()
}

// String returns a string representation of this prefix.
func (p *Prefix) String() (s string) {
	// Benchmarks revealed that in this case simple string concatenation
	// is actually faster than using a ByteBuffer as in (*Message).String()
	s = p.Name
	if len(p.User) > 0 {
		s = s + string(prefixUser) + p.User
	}
	if len(p.Host) > 0 {
		s = s + string(prefixHost) + p.Host
	}
	return
}

// IsHostmask returns true if this prefix looks like a user hostmask.
func (p *Prefix) IsHostmask() bool {
	return len(p.User) > 0 && len(p.Host) > 0
}

// IsServer returns true if this prefix looks like a server name.
func (p *Prefix) IsServer() bool {
	return len(p.User) <= 0 && len(p.Host) <= 0 // && indexByte(p.Name, '.') > 0
}

// writeTo is an utility function to write the prefix to the bytes.Buffer in Message.String().
func (p *Prefix) writeTo(buffer *bytes.Buffer) {
	buffer.WriteString(p.Name)
	if len(p.User) > 0 {
		buffer.WriteByte(prefixUser)
		buffer.WriteString(p.User)
	}
	if len(p.Host) > 0 {
		buffer.WriteByte(prefixHost)
		buffer.WriteString(p.Host)
	}
	return
}

// Message represents an IRC protocol message.
// See RFC1459 section 2.3.1.
//
//    <message>  ::= [':' <prefix> <SPACE> ] <command> <params> <crlf>
//    <prefix>   ::= <servername> | <nick> [ '!' <user> ] [ '@' <host> ]
//    <command>  ::= <letter> { <letter> } | <number> <number> <number>
//    <SPACE>    ::= ' ' { ' ' }
//    <params>   ::= <SPACE> [ ':' <trailing> | <middle> <params> ]
//
//    <middle>   ::= <Any *non-empty* sequence of octets not including SPACE
//                   or NUL or CR or LF, the first of which may not be ':'>
//    <trailing> ::= <Any, possibly *empty*, sequence of octets not including
//                   NUL or CR or LF>
//
//    <crlf>     ::= CR LF
type Message struct {
	Tags
	Prefix
	Command string
	Params  []string
}

// Param returns the i'th parameter.
// Returns the empty string if the requested parameter does not exist.
func (m *Message) Param(i int) string {
	if i < 0 || i >= len(m.Params) {
		return ""
	}
	return m.Params[i]
}

// Trailing returns the last parameter.
// Returns the empty string if there are no parameters.
func (m *Message) Trailing() string {
	if len(m.Params) > 0 {
		return m.Params[len(m.Params)-1]
	}
	return ""
}

// ParseMessage takes a string and attempts to create a Message struct.
// Returns nil if the Message is invalid.
func ParseMessage(raw string) (m *Message) {
	// Ignore empty messages.
	if raw = strings.TrimFunc(raw, cutsetFunc); len(raw) < 2 {
		return nil
	}

	i, j, k := 0, 0, 0

	m = new(Message)

	if raw[k] == tags {
		// Tags end with a space
		k = indexByte(raw, space)

		// Tags must not be empty if the indicator is present
		if k < 2 {
			return nil
		}

		m.Tags = ParseTags(raw[1:k])
		// Skip space at the end of the tags
		k++
	}

	if raw[k] == prefix {
		// Prefix ends with a space.
		i = k + indexByte(raw[k:], space)

		// Prefix string must not be empty if the indicator is present.
		if i < 2 {
			return nil
		}

		m.Prefix = ParsePrefix(raw[k+1 : i])

		// Skip space at the end of the prefix
		i++
	} else {
		i = k
	}
	// Find end of command
	j = i + indexByte(raw[i:], space)

	// Extract command
	if j > i {
		m.Command = strings.ToUpper(raw[i:j])
	} else {
		m.Command = strings.ToUpper(raw[i:])

		// We're done here!
		return m
	}

	// Find prefix for trailer. Note that because we need to match the trailing
	// argument even if it's the only one, we can't skip the space until we've
	// searched for it.
	i = strings.Index(raw[j:], " :")

	// Skip the space
	j++

	if i < 0 {

		// There is no trailing argument!
		m.Params = strings.Split(raw[j:], string(space))

		// We're done here!
		return m
	}

	// Compensate for index on substring. Note that we skipped the space after
	// looking for i, so we need to subtract 1 to account for that.
	i = i + j - 1

	// Check if we need to parse arguments.
	if i > j {
		m.Params = strings.Split(raw[j:i], string(space))
	}

	m.Params = append(m.Params, raw[i+2:])

	return m
}

// Len calculates the length of the string representation of this message.
func (m *Message) Len() (length int) {
	if !m.Prefix.Empty() {
		length = m.Prefix.Len() + 2 // Include prefix and trailing space
	}

	length = length + len(m.Command)

	if len(m.Params) > 0 {
		length = length + len(m.Params)
		for _, param := range m.Params {
			length = length + len(param)
		}

		if trailing := m.Trailing(); len(trailing) < 1 || strings.Contains(trailing, " ") || trailing[0] == ':' {
			// Add one for the colon in the trailing parameter
			length++
		}
	}

	return
}

// Bytes returns a []byte representation of this message.
//
// As noted in rfc2812 section 2.3, messages should not exceed 512 characters
// in length. This method forces that limit by discarding any characters
// exceeding the length limit.
func (m *Message) Bytes() []byte {
	buffer := new(bytes.Buffer)

	// Message tags
	if m.Tags != nil {
		buffer.WriteByte(tags)
		m.Tags.writeTo(buffer)
		buffer.WriteByte(space)
	}

	// Message prefix
	if !m.Prefix.Empty() {
		buffer.WriteByte(prefix)
		m.Prefix.writeTo(buffer)
		buffer.WriteByte(space)
	}

	// Command is required
	buffer.WriteString(m.Command)

	// Space separated list of arguments
	if len(m.Params) > 1 {
		buffer.WriteByte(space)
		buffer.WriteString(strings.Join(m.Params[:len(m.Params)-1], string(space)))
	}

	if len(m.Params) > 0 {
		buffer.WriteByte(space)
		trailing := m.Trailing()
		if len(trailing) < 1 || strings.Contains(trailing, " ") || trailing[0] == ':' {
			buffer.WriteByte(prefix)
		}
		buffer.WriteString(trailing)
	}

	// We need the limit the buffer length.
	if buffer.Len() > (maxLength) {
		buffer.Truncate(maxLength)
	}

	return buffer.Bytes()
}

// String returns a string representation of this message.
//
// As noted in rfc2812 section 2.3, messages should not exceed 512 characters
// in length. This method forces that limit by discarding any characters
// exceeding the length limit.
func (m *Message) String() string {
	return string(m.Bytes())
}