/*
Package proto provides byte-level interaction with HTTP request payload.

Example of HTTP payload for future references, new line symbols escaped:

	POST /upload HTTP/1.1\r\n
	User-Agent: Gor\r\n
	Content-Length: 11\r\n
	\r\n
	Hello world

	GET /index.html HTTP/1.1\r\n
	User-Agent: Gor\r\n
	\r\n
	\r\n
*/
package proto

import (
	"bytes"
	"github.com/buger/gor/byteutils"
)

// In HTTP newline defined by 2 bytes (for both windows and *nix support)
var CLRF = []byte("\r\n")

// New line acts as separator: end of Headers or Body (in some cases)
var EmptyLine = []byte("\r\n\r\n")

// Separator for Header line. Header looks like: `HeaderName: value`
var HeaderDelim = []byte(": ")

// MIMEHeadersEndPos finds end of the Headers section, which should end with empty line.
func MIMEHeadersEndPos(payload []byte) int {
	return bytes.Index(payload, EmptyLine)
}

// MIMEHeadersStartPos finds start of Headers section
// It just finds position of second line (first contains location and method).
func MIMEHeadersStartPos(payload []byte) int {
	return bytes.Index(payload, CLRF) + 2 // Find first line end
}

// header return value and positions of header/value start/end.
// If not found, value will be blank, and headerStart will be -1
// Do not support multi-line headers.
func header(payload []byte, name []byte) (value []byte, headerStart, valueStart, headerEnd int) {
	headerStart = bytes.Index(payload, name)

	if headerStart == -1 {
		return
	}

	valueStart = headerStart + len(name) + 1 // Skip ":" after header name
	if payload[valueStart] == ' ' {          // Ignore empty space after ':'
		valueStart++
	}

	headerEnd = valueStart + bytes.IndexByte(payload[valueStart:], '\n')

	if payload[headerEnd-1] == '\r' {
		headerEnd -= 1
	}

	value = payload[valueStart:headerEnd]

	return
}

// Header returns header value, if header not found, value will be blank
func Header(payload, name []byte) []byte {
	val, _, _, _ := header(payload, name)

	return val
}

// SetHeader sets header value. If header not found it creates new one.
// Returns modified request payload
func SetHeader(payload, name, value []byte) []byte {
	_, hs, vs, he := header(payload, name)

	if hs != -1 {
		// If header found we just repace its value
		return byteutils.Replace(payload, vs, he, value)
	}

	return AddHeader(payload, name, value)
}

// AddHeader takes http payload and appends new header to the start of headers section
// Returns modified request payload
func AddHeader(payload, name, value []byte) []byte {
	header := make([]byte, len(name)+2+len(value)+2)
	copy(header[0:], name)
	copy(header[len(name):], HeaderDelim)
	copy(header[len(name)+2:], value)
	copy(header[len(header)-2:], CLRF)

	mimeStart := MIMEHeadersStartPos(payload)

	return byteutils.Insert(payload, mimeStart, header)
}

// Body returns request/response body
func Body(payload []byte) []byte {
	// 4 -> len(EMPTY_LINE)
	return payload[MIMEHeadersEndPos(payload)+4:]
}

// Path takes payload and retuns request path: Split(firstLine, ' ')[1]
func Path(payload []byte) []byte {
	start := bytes.IndexByte(payload, ' ') + 1
	end := bytes.IndexByte(payload[start:], ' ')

	return payload[start : start+end]
}

// SetPath takes payload, sets new path and returns modified payload
func SetPath(payload, path []byte) []byte {
	start := bytes.IndexByte(payload, ' ') + 1
	end := bytes.IndexByte(payload[start:], ' ')

	return byteutils.Replace(payload, start, start+end, path)
}

// PathParam returns URL query attribute by given name, if no found: valueStart will be -1
func PathParam(payload, name []byte) (value []byte, valueStart, valueEnd int) {
	path := Path(payload)

	if paramStart := bytes.Index(path, append(name, '=')); paramStart != -1 {
		valueStart := paramStart + len(name) + 1
		paramEnd := bytes.IndexByte(path[valueStart:], '&')

		// Param can end with '&' (another param), or end of line
		if paramEnd == -1 { // It is final param
			paramEnd = len(path)
		} else {
			paramEnd += valueStart
		}

		return path[valueStart:paramEnd], valueStart, paramEnd
	}

	return []byte(""), -1, -1
}

// SetPathParam takes payload and updates path Query attribute
// If query param not found, it will append new
// Returns modified payload
func SetPathParam(payload, name, value []byte) []byte {
	path := Path(payload)
	_, vs, ve := PathParam(payload, name)

	if vs != -1 { // If param found, replace its value and set new Path
		newPath := make([]byte, len(path))
		copy(newPath, path)
		newPath = byteutils.Replace(newPath, vs, ve, value)

		return SetPath(payload, newPath)
	}

	// if param not found append to end of url
	// Adding 2 because of '?' or '&' at start, and '=' in middle
	newParam := make([]byte, len(name)+len(value)+2)

	if bytes.IndexByte(path, '?') == -1 {
		newParam[0] = '?'
	} else {
		newParam[0] = '&'
	}

	// Copy "param=value" into buffer, after it looks like "?param=value"
	copy(newParam[1:], name)
	newParam[1+len(name)] = '='
	copy(newParam[2+len(name):], value)

	// Append param to the end of path
	newPath := make([]byte, len(path)+len(newParam))
	copy(newPath, path)
	copy(newPath[len(path):], newParam)

	return SetPath(payload, newPath)
}

// SetHost updates Host header for HTTP/1.1 or updates host in path for HTTP/1.0 or Proxy requests
// Returns modified payload
func SetHost(payload, url, host []byte) []byte {
	// If this is HTTP 1.0 traffic or proxy traffic it may include host right into path variable, so instead of setting Host header we rewrite Path
	// Fix for https://github.com/buger/gor/issues/156
	if path := Path(payload); bytes.HasPrefix(path, []byte("http")) {
		hostStart := bytes.IndexByte(path, ':') // : position "https?:"
		hostStart += 3                          // Skip 1 ':' and 2 '\'
		hostEnd := hostStart + bytes.IndexByte(path[hostStart:], '/')

		newPath := make([]byte, len(path))
		copy(newPath, path)
		newPath = byteutils.Replace(newPath, 0, hostEnd, url)

		return SetPath(payload, newPath)
	}

	return SetHeader(payload, []byte("Host"), host)
}

// Method returns HTTP method
func Method(payload []byte) []byte {
	end := bytes.IndexByte(payload, ' ')

	return payload[:end]
}

// Status returns response status.
// It happend to be in same position as request payload path
func Status(payload []byte) []byte {
	return Path(payload)
}

var httpMethods []string = []string{
	"GET ", "OPTI", "HEAD", "POST", "PUT ", "DELE", "TRAC", "CONN",
}

func IsHTTPPayload(payload []byte) bool {
	if len(payload) < 4 {
		return false
	}

	method := string(payload[0:4])

	for _, m := range httpMethods {
		if method == m {
			return true
		}
	}
	return false
}