package cnp

import (
	"bytes"
	"io"
	"strings"
	"time"
)

// Response represents a CNP response message.
type Response struct {
	Message
}

// NewResponse creates a new Response from a response intent and optional body
// data.
func NewResponse(intent string, body []byte) (resp *Response, err error) {
	var r io.Reader
	if body != nil {
		r = bytes.NewReader(body)
	}
	resp = &Response{*NewMessage("", r)}
	err = resp.SetResponseIntent(intent)
	return
}

var responseIntents = map[string]bool{
	IntentOK:          true,
	IntentNotModified: true,
	IntentRedirect:    true,
	IntentError:       true,
}

// ParseResponse parses a response message.
func ParseResponse(r io.Reader) (*Response, error) {
	msg, err := ParseMessage(r)
	if msg == nil {
		return nil, err
	}
	return &Response{*msg}, err
}

// ResponseIntent retrieves the response intent.
// If the intent is unknown, the "error" intent is returned.
func (r *Response) ResponseIntent() string {
	s := r.Intent()
	if !responseIntents[s] {
		return IntentError
	}
	return s
}

// SetResponseIntent sets the response intent.
// If the provided intent is not a known response intent, an error is returned
// and the intent is set to "error".
func (r *Response) SetResponseIntent(intent string) error {
	if !responseIntents[intent] {
		r.SetIntent(IntentError)
		return ErrorInvalid{"invalid response: unknown response intent"}
	}
	r.SetIntent(intent)
	return nil
}

// Name retrieves the name response parameter.
//
// If the name response parameter is not a valid filename, an empty string is
// returned.
func (r *Response) Name() string {
	name, err := getFilename(&r.Message, "name")
	if err != nil {
		return ""
	}
	return name
}

// SetName sets the name response parameter.
//
// An error is raised if the name includes characters not valid in a filename
// (slash, null byte).
func (r *Response) SetName(name string) error {
	return setFilename(&r.Message, "name", name)
}

// Type retrieves the type response parameter.
//
// If the type response parameter is invalid or empty, the default value
// "application/octet-stream" is returned.
func (r *Response) Type() string {
	typ, _ := getType(&r.Message, "type")
	return typ
}

// SetType sets the type response parameter.
//
// An error is raised if typ is not a valid format for a MIME type.
func (r *Response) SetType(typ string) error {
	return setType(&r.Message, "type", typ)
}

// Time retrieves the time response parameter.
//
// If the parameter isn't a valid RFC3339 timestamp, a zero time.Time is
// returned.
func (r *Response) Time() time.Time {
	t, err := getTime(&r.Message, "time")
	if err != nil {
		return time.Time{}
	}
	return t
}

// SetTime sets the time response parameter.
//
// If t is the zero time value, the time parameter is unset.
func (r *Response) SetTime(t time.Time) {
	setTime(&r.Message, "time", t)
}

// Modified retrieves the modified Response parameter.
//
// If the parameter isn't a valid RFC3339 timestamp, a zero time.Time is
// returned.
func (r *Response) Modified() time.Time {
	t, err := getTime(&r.Message, "modified")
	if err != nil {
		return time.Time{}
	}
	return t
}

// SetModified sets the modified response parameter.
//
// If the time response parameter is empty, it's set to the current time.
// If t is the zero time value, the modified parameter is unset.
func (r *Response) SetModified(t time.Time) {
	setTime(&r.Message, "modified", t)
	if r.Time().IsZero() {
		r.SetTime(time.Now())
	}
}

// Location retrieves the host and path from the location response
// parameter.
//
// If the location parameter is empty, it returns empty host and path. If the
// location parameter is invalid, an error is returned.
func (r *Response) Location() (host, path string, err error) {
	l := r.Param("location")
	if l == "" {
		return "", "", nil
	}
	if err := validateRequestIntent(l); err != nil {
		return "", "", err
	}
	ss := strings.SplitN(l, "/", 2)
	return ss[0], "/" + ss[1], nil
}

// SetLocation sets the location response parameter to host and path.
//
// If the host or path are invalid
func (r *Response) SetLocation(host, path string) error {
	if strings.ContainsRune(host, '/') {
		return ErrorInvalid{"invalid response: invalid location parameter"}
	}
	l := host + path
	if err := validateRequestIntent(l); err != nil {
		return ErrorInvalid{"invalid response: invalid location parameter"}
	}
	r.SetParam("location", l)
	return nil
}

var responseErrorReasons = map[string]bool{
	ReasonSyntax:       true,
	ReasonVersion:      true,
	ReasonInvalid:      true,
	ReasonNotSupported: true,
	ReasonTooLarge:     true,
	ReasonNotFound:     true,
	ReasonDenied:       true,
	ReasonRejected:     true,
	ReasonServerError:  true,
	"":                 true,
}

// Reason retrieves the reason response parameter.
//
// If the reason is nonempty and unknown, "server_error" is returned.
func (r *Response) Reason() string {
	reason := r.Param("reason")
	if _, ok := responseErrorReasons[reason]; ok {
		return reason
	}
	return ReasonServerError
}

// SetReason sets the reason response parameter.
//
// If the reason is nonempty and unknown, it sets "server_error" instead.
func (r *Response) SetReason(reason string) error {
	if _, ok := responseErrorReasons[reason]; !ok {
		r.SetParam("reason", ReasonServerError)
		return ErrorInvalid{"invalid response: unknown error reason"}
	}
	r.SetParam("reason", reason)
	return nil
}

// Validate validates the response intent and header parameter value format
// (length, name, type, time, modified, location, reason)
func (r *Response) Validate() error {
	if !responseIntents[r.Intent()] {
		return ErrorInvalid{"invalid response: unknown response intent"}
	}
	if err := r.Message.Validate(); err != nil {
		return err
	}
	if _, err := getFilename(&r.Message, "name"); err != nil {
		return err
	}
	if _, err := getType(&r.Message, "type"); err != nil {
		return err
	}
	if _, err := getTime(&r.Message, "time"); err != nil {
		return err
	}
	if _, err := getTime(&r.Message, "modified"); err != nil {
		return err
	}
	if h, p, err := r.Location(); err != nil {
		return err
	} else if r.ResponseIntent() == IntentRedirect && h == "" && p == "" {
		return ErrorInvalid{"invalid response: redirect response needs location parameter"}
	}
	if !responseErrorReasons[r.Param("reason")] {
		return ErrorInvalid{"invalid response: unknown error reason"}
	}
	return nil
}

// Write writes the response to w.
func (r *Response) Write(w io.Writer) error {
	if _, ok := r.Header.Parameters["length"]; !ok {
		r.TryComputeLength()
	}
	return r.Message.Write(w)
}