// Copyright 2020 lesismal. All rights reserved.
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.

package nbhttp

import (
	"fmt"
	"net"
	"net/http"
	"net/textproto"
	"strconv"
	"strings"
	"sync"

	"github.com/lesismal/nbio/mempool"
)

const (
	transferEncodingHeader = "Transfer-Encoding"
	trailerHeader          = "Trailer"
	contentLengthHeader    = "Content-Length"

	// MaxUint .
	MaxUint = ^uint(0)
	// MaxInt .
	MaxInt = int64(int(MaxUint >> 1))
)

// Parser .
type Parser struct {
	mux sync.Mutex

	cache []byte

	proto string

	statusCode int
	status     string

	headerKey   string
	headerValue string

	header  http.Header
	trailer http.Header

	contentLength int
	chunkSize     int
	chunked       bool
	headerExists  bool

	state    int8
	isClient bool

	readLimit int

	errClose error

	onClose func(p *Parser, err error)

	Processor Processor

	ConnState ReadCloser

	Engine *Engine

	Conn net.Conn

	Execute func(f func())
}

func (p *Parser) nextState(state int8) {
	switch p.state {
	case stateClose:
	default:
		p.state = state
	}
}

// OnClose .
func (p *Parser) OnClose(h func(p *Parser, err error)) {
	p.onClose = h
}

// Close .
func (p *Parser) Close(err error) {
	p.mux.Lock()
	defer p.mux.Unlock()

	if p.state == stateClose {
		return
	}

	p.state = stateClose

	p.errClose = err

	if p.ConnState != nil {
		p.ConnState.Close(p, p.errClose)
	}
	if p.Processor != nil {
		p.Processor.Close(p, p.errClose)
	}
	if len(p.cache) > 0 {
		mempool.Free(p.cache)
	}
	if p.onClose != nil {
		p.onClose(p, err)
	}
}

func parseAndValidateChunkSize(originalStr string) (int, error) {
	chunkSize, err := strconv.ParseInt(originalStr, 16, 63)
	if err != nil {
		return -1, fmt.Errorf("chunk size parse error %v: %w", originalStr, err)
	}
	if chunkSize < 0 {
		return -1, fmt.Errorf("chunk size zero")
	}
	if chunkSize > MaxInt {
		return -1, fmt.Errorf("chunk size greater than max int %d", chunkSize)
	}
	return int(chunkSize), nil
}

// Read .
func (p *Parser) Read(data []byte) error {
	p.mux.Lock()
	defer p.mux.Unlock()

	if p.state == stateClose {
		return ErrClosed
	}

	if len(data) == 0 {
		return nil
	}

	var c byte
	var start = 0
	var offset = len(p.cache)
	if offset > 0 {
		if offset+len(data) > p.readLimit {
			return ErrTooLong
		}
		p.cache = append(p.cache, data...)
		data = p.cache
	}

UPGRADER:
	if p.ConnState != nil {
		udata := data
		if start > 0 {
			udata = data[start:]
		}
		err := p.ConnState.Read(p, udata)
		if p.cache != nil {
			mempool.Free(p.cache)
			p.cache = nil
		}
		return err
	}

	for i := offset; i < len(data); i++ {
		if p.ConnState != nil {
			goto UPGRADER
		}
		c = data[i]
		switch p.state {
		case stateClose:
			return ErrClosed
		case stateMethodBefore:
			if isValidMethodChar(c) {
				start = i
				p.nextState(stateMethod)
				continue
			}
			return ErrInvalidMethod
		case stateMethod:
			if c == ' ' {
				var method = strings.ToUpper(string(data[start:i]))
				if !isValidMethod(method) {
					return ErrInvalidMethod
				}
				p.Processor.OnMethod(method)
				start = i + 1
				p.nextState(statePathBefore)
				continue
			}
			if !isAlpha(c) {
				return ErrInvalidMethod
			}
		case statePathBefore:
			switch c {
			case '/', '*':
				start = i
				p.nextState(statePath)
				continue
			}
			switch c {
			case ' ':
			default:
				return ErrInvalidRequestURI
			}
		case statePath:
			if c == ' ' {
				var uri = string(data[start:i])
				if err := p.Processor.OnURL(uri); err != nil {
					return err
				}
				start = i + 1
				p.nextState(stateProtoBefore)
			}
		case stateProtoBefore:
			if c != ' ' {
				start = i
				p.nextState(stateProto)
			}
		case stateProto:
			switch c {
			case ' ':
				if p.proto == "" {
					p.proto = string(data[start:i])
				}
			case '\r':
				if p.proto == "" {
					p.proto = string(data[start:i])
				}
				if err := p.Processor.OnProto(p.proto); err != nil {
					p.proto = ""
					return err
				}
				p.proto = ""
				p.nextState(stateProtoLF)
			}
		case stateClientProtoBefore:
			if c == 'H' {
				start = i
				p.nextState(stateClientProto)
				continue
			}
			return ErrInvalidMethod
		case stateClientProto:
			switch c {
			case ' ':
				if p.proto == "" {
					p.proto = string(data[start:i])
				}
				if err := p.Processor.OnProto(p.proto); err != nil {
					p.proto = ""
					return err
				}
				p.proto = ""
				p.nextState(stateStatusCodeBefore)
			}
		case stateStatusCodeBefore:
			switch c {
			case ' ':
			default:
				if isNum(c) {
					start = i
					p.nextState(stateStatusCode)
				}
				continue
			}
			return ErrInvalidHTTPStatusCode
		case stateStatusCode:
			if c == ' ' {
				cs := string(data[start:i])
				code, err := strconv.Atoi(cs)
				if err != nil {
					return err
				}
				p.statusCode = code
				p.nextState(stateStatusBefore)
				continue
			}
			if !isNum(c) {
				return ErrInvalidHTTPStatusCode
			}
		case stateStatusBefore:
			switch c {
			case ' ':
			default:
				if isAlpha(c) {
					start = i
					p.nextState(stateStatus)
				}
				continue
			}
			return ErrInvalidHTTPStatus
		case stateStatus:
			switch c {
			case ' ':
				if p.status == "" {
					p.status = string(data[start:i])
				}
			case '\r':
				if p.status == "" {
					p.status = string(data[start:i])
				}
				p.Processor.OnStatus(p.statusCode, p.status)
				p.statusCode = 0
				p.status = ""
				p.nextState(stateStatusLF)
			}
		case stateStatusLF:
			if c == '\n' {
				p.nextState(stateHeaderKeyBefore)
				continue
			}
			return ErrLFExpected
		case stateProtoLF:
			if c == '\n' {
				start = i + 1
				p.nextState(stateHeaderKeyBefore)
				continue
			}
			return ErrLFExpected
		case stateHeaderValueLF:
			if c == '\n' {
				start = i + 1
				p.nextState(stateHeaderKeyBefore)
				continue
			}
			return ErrLFExpected
		case stateHeaderKeyBefore:
			switch c {
			case ' ':
				if !p.headerExists {
					return ErrInvalidCharInHeader
				}
			case '\r':
				err := p.parseTransferEncoding()
				if err != nil {
					return err
				}
				err = p.parseContentLength()
				if err != nil {
					return err
				}
				p.Processor.OnContentLength(p.contentLength)
				err = p.parseTrailer()
				if err != nil {
					return err
				}
				start = i + 1
				p.nextState(stateHeaderOverLF)
			case '\n':
				return ErrInvalidCharInHeader
			default:
				if isAlpha(c) {
					start = i
					p.nextState(stateHeaderKey)
					p.headerExists = true
					continue
				}
				return ErrInvalidCharInHeader
			}
		case stateHeaderKey:
			switch c {
			case ' ':
				if p.headerKey == "" {
					p.headerKey = http.CanonicalHeaderKey(string(data[start:i]))
				}
			case ':':
				if p.headerKey == "" {
					p.headerKey = http.CanonicalHeaderKey(string(data[start:i]))
				}
				start = i + 1
				p.nextState(stateHeaderValueBefore)
			case '\r', '\n':
				return ErrInvalidCharInHeader
			default:
				if !isToken(c) {
					return ErrInvalidCharInHeader
				}
			}
		case stateHeaderValueBefore:
			switch c {
			case ' ':
			case '\r':
				if p.headerValue == "" {
					p.headerValue = string(data[start:i])
				}
				switch p.headerKey {
				case transferEncodingHeader, trailerHeader, contentLengthHeader:
					if p.header == nil {
						p.header = http.Header{}
					}
					p.header.Add(p.headerKey, p.headerValue)
				default:
				}

				p.Processor.OnHeader(p.headerKey, p.headerValue)
				p.headerKey = ""
				p.headerValue = ""

				start = i + 1
				p.nextState(stateHeaderValueLF)
			case '\n':
				return ErrInvalidCharInHeader
			default:
				// if !isToken(c) {
				// 	return ErrInvalidCharInHeader
				// }
				start = i
				p.nextState(stateHeaderValue)
			}
		case stateHeaderValue:
			switch c {
			case '\r':
				if p.headerValue == "" {
					p.headerValue = string(data[start:i])
				}
				switch p.headerKey {
				case transferEncodingHeader, trailerHeader, contentLengthHeader:
					if p.header == nil {
						p.header = http.Header{}
					}
					p.header.Add(p.headerKey, p.headerValue)
				default:
				}

				p.Processor.OnHeader(p.headerKey, p.headerValue)
				p.headerKey = ""
				p.headerValue = ""

				start = i + 1
				p.nextState(stateHeaderValueLF)
			case '\n':
				return ErrInvalidCharInHeader
			default:
			}
		case stateHeaderOverLF:
			if c == '\n' {
				p.headerExists = false
				if p.chunked {
					start = i + 1
					p.nextState(stateBodyChunkSizeBefore)
				} else {
					start = i + 1
					if p.contentLength > 0 {
						p.nextState(stateBodyContentLength)
					} else {
						p.handleMessage()
					}
				}
				continue
			}
			return ErrLFExpected
		case stateBodyContentLength:
			cl := p.contentLength
			left := len(data) - start
			if left >= cl {
				p.Processor.OnBody(data[start : start+cl])
				p.handleMessage()
				start += cl
				i = start - 1
			} else {
				goto Exit
			}
		case stateBodyChunkSizeBefore:
			if isHex(c) {
				p.chunkSize = -1
				start = i
				p.nextState(stateBodyChunkSize)
				continue
			}
			return ErrInvalidChunkSize
		case stateBodyChunkSize:
			switch c {
			case ' ':
				if p.chunkSize < 0 {
					chunkSize, err := parseAndValidateChunkSize(string(data[start:i]))
					if err != nil {
						return err
					}
					p.chunkSize = chunkSize
				}
			case '\r':
				if p.chunkSize < 0 {
					chunkSize, err := parseAndValidateChunkSize(string(data[start:i]))
					if err != nil {
						return err
					}
					p.chunkSize = chunkSize
				}
				start = i + 1
				p.nextState(stateBodyChunkSizeLF)
			default:
				if !isHex(c) && p.chunkSize < 0 {
					chunkSize, err := parseAndValidateChunkSize(string(data[start:i]))
					if err != nil {
						return err
					}
					p.chunkSize = chunkSize
				}
			}
		case stateBodyChunkSizeLF:
			if c == '\n' {
				start = i + 1
				if p.chunkSize > 0 {
					p.nextState(stateBodyChunkData)
				} else {
					// chunk size is 0

					if len(p.trailer) > 0 {
						// read trailer headers
						p.nextState(stateBodyTrailerHeaderKeyBefore)
					} else {
						// read tail cr lf
						p.nextState(stateTailCR)
					}
				}
				continue
			}
			return ErrLFExpected
		case stateBodyChunkData:
			cl := p.chunkSize
			left := len(data) - start
			if left >= cl {
				p.Processor.OnBody(data[start : start+cl])
				start += cl
				i = start - 1
				p.nextState(stateBodyChunkDataCR)
			} else {
				goto Exit
			}
		case stateBodyChunkDataCR:
			if c == '\r' {
				p.nextState(stateBodyChunkDataLF)
				continue
			}
			return ErrCRExpected
		case stateBodyChunkDataLF:
			if c == '\n' {
				p.nextState(stateBodyChunkSizeBefore)
				continue
			}
			return ErrLFExpected
		case stateBodyTrailerHeaderValueLF:
			if c == '\n' {
				start = i
				p.nextState(stateBodyTrailerHeaderKeyBefore)
				continue
			}
			return ErrLFExpected
		case stateBodyTrailerHeaderKeyBefore:
			if isAlpha(c) {
				start = i
				p.nextState(stateBodyTrailerHeaderKey)
				continue
			}

			// all trailer header readed
			if c == '\r' {
				if len(p.trailer) > 0 {
					return ErrTrailerExpected
				}
				start = i + 1
				p.nextState(stateTailLF)
				continue
			}
		case stateBodyTrailerHeaderKey:
			switch c {
			case ' ':
				if p.headerKey == "" {
					p.headerKey = http.CanonicalHeaderKey(string(data[start:i]))
				}
				continue
			case ':':
				if p.headerKey == "" {
					p.headerKey = http.CanonicalHeaderKey(string(data[start:i]))
				}
				start = i + 1
				p.nextState(stateBodyTrailerHeaderValueBefore)
				continue
			}
			if !isToken(c) {
				return ErrInvalidCharInHeader
			}
		case stateBodyTrailerHeaderValueBefore:
			switch c {
			case ' ':
			case '\r':
				if p.headerValue == "" {
					p.headerValue = string(data[start:i])
				}
				p.Processor.OnTrailerHeader(p.headerKey, p.headerValue)
				p.headerKey = ""
				p.headerValue = ""

				start = i + 1
				p.nextState(stateBodyTrailerHeaderValueLF)
			default:
				// if !isToken(c) {
				// 	return ErrInvalidCharInHeader
				// }
				start = i
				p.nextState(stateBodyTrailerHeaderValue)
			}
		case stateBodyTrailerHeaderValue:
			switch c {
			case ' ':
				if p.headerValue == "" {
					p.headerValue = string(data[start:i])
				}
			case '\r':
				if p.headerValue == "" {
					p.headerValue = string(data[start:i])
				}
				if len(p.trailer) == 0 {
					return fmt.Errorf("invalid trailer '%v'", p.headerKey)
				}
				delete(p.trailer, p.headerKey)

				p.Processor.OnTrailerHeader(p.headerKey, p.headerValue)
				start = i + 1
				p.headerKey = ""
				p.headerValue = ""
				p.nextState(stateBodyTrailerHeaderValueLF)
			default:
				// if !isToken(c) {
				// 	return ErrInvalidCharInHeader
				// }
			}
		case stateTailCR:
			if c == '\r' {
				p.nextState(stateTailLF)
				continue
			}
			return ErrCRExpected
		case stateTailLF:
			if c == '\n' {
				start = i + 1
				p.handleMessage()
				continue
			}
			return ErrLFExpected
		default:
		}
	}

Exit:
	left := len(data) - start
	if left > 0 {
		if p.cache == nil {
			p.cache = mempool.Malloc(left)
			copy(p.cache, data[start:])
		} else if start > 0 {
			oldCache := p.cache
			p.cache = mempool.Malloc(left)
			copy(p.cache, data[start:])
			mempool.Free(oldCache)
		}
	} else if len(p.cache) > 0 {
		mempool.Free(p.cache)
		p.cache = nil
	}

	return nil
}

func (p *Parser) parseTransferEncoding() error {
	raw, present := p.header[transferEncodingHeader]
	if !present {
		return nil
	}
	delete(p.header, transferEncodingHeader)

	if len(raw) != 1 {
		return fmt.Errorf("too many transfer encodings: %q", raw)
	}
	if strings.ToLower(textproto.TrimString(raw[0])) != "chunked" {
		return fmt.Errorf("unsupported transfer encoding: %q", raw[0])
	}
	delete(p.header, contentLengthHeader)
	p.chunked = true

	return nil
}

func (p *Parser) parseContentLength() (err error) {
	if cl := p.header.Get(contentLengthHeader); cl != "" {
		if p.chunked {
			return ErrUnexpectedContentLength
		}
		end := len(cl) - 1
		for i := end; i >= 0; i-- {
			if cl[i] != ' ' {
				if i != end {
					cl = cl[:i+1]
				}
				break
			}
		}
		l, err := strconv.ParseInt(cl, 10, 63)
		if err != nil {
			return fmt.Errorf("%s %q", "bad Content-Length", cl)
		}
		if l < 0 {
			return fmt.Errorf("length less than zero (%d): %w", l, ErrInvalidContentLength)
		}
		if l > MaxInt {
			return fmt.Errorf("length greater than maxint (%d): %w", l, ErrInvalidContentLength)
		}
		p.contentLength = int(l)
	} else {
		p.contentLength = -1
	}
	return nil
}

func (p *Parser) parseTrailer() error {
	if !p.chunked {
		return nil
	}
	header := p.header

	trailers, ok := header[trailerHeader]
	if !ok {
		return nil
	}

	header.Del(trailerHeader)

	trailer := http.Header{}
	for _, key := range trailers {
		key = textproto.TrimString(key)
		if key == "" {
			continue
		}
		if !strings.Contains(key, ",") {
			key = http.CanonicalHeaderKey(key)
			switch key {
			case transferEncodingHeader, trailerHeader, contentLengthHeader:
				return fmt.Errorf("%s %q", "bad trailer key", key)
			default:
				trailer[key] = nil
			}
			continue
		}
		for _, k := range strings.Split(key, ",") {
			if k = textproto.TrimString(k); k != "" {
				k = http.CanonicalHeaderKey(k)
				switch k {
				case transferEncodingHeader, trailerHeader, contentLengthHeader:
					return fmt.Errorf("%s %q", "bad trailer key", k)
				default:
					trailer[k] = nil
				}
			}
		}
	}
	if len(trailer) > 0 {
		p.trailer = trailer
	}
	return nil
}

func (p *Parser) handleMessage() {
	p.Processor.OnComplete(p)
	p.header = nil

	if !p.isClient {
		p.nextState(stateMethodBefore)
	} else {
		p.nextState(stateClientProtoBefore)
	}
}

// NewParser .
func NewParser(processor Processor, isClient bool, readLimit int, executor func(f func())) *Parser {
	if processor == nil {
		processor = NewEmptyProcessor()
	}
	state := stateMethodBefore
	if isClient {
		state = stateClientProtoBefore
	}
	if readLimit <= 0 {
		readLimit = DefaultHTTPReadLimit
	}
	if executor == nil {
		executor = func(f func()) {
			f()
		}
	}
	p := &Parser{
		state:     state,
		readLimit: readLimit,
		isClient:  isClient,
		Execute:   executor,
		Processor: processor,
	}
	return p
}