package logging

import (
	"fmt"
	"log"
	"net"
	"net/http"
	"strconv"
	"strings"
	"time"
)

// ---------- Access logging ----------

// statusRecorder captures the status code and body size for the access log.
type statusRecorder struct {
	http.ResponseWriter
	status int
	bytes  int
}

func (r *statusRecorder) WriteHeader(code int) {
	if r.status == 0 {
		r.status = code
	}
	r.ResponseWriter.WriteHeader(code)
}

func (r *statusRecorder) Write(b []byte) (int, error) {
	if r.status == 0 {
		r.status = http.StatusOK
	}
	n, err := r.ResponseWriter.Write(b)
	r.bytes += n
	return n, err
}

// logField escapes a value for a quoted log field the way nginx does
// (quotes, backslashes and control characters become \xHH) and uses "-"
// for empty values.
func logField(s string) string {
	if s == "" {
		return "-"
	}
	var b strings.Builder
	for i := 0; i < len(s); i++ {
		c := s[i]
		if c == '"' || c == '\\' || c < 0x20 || c == 0x7f {
			fmt.Fprintf(&b, "\\x%02X", c)
		} else {
			b.WriteByte(c)
		}
	}
	return b.String()
}

// clientKey attempts to produce a client host name as a key identifier to split
// requests in the log between sources. Could be extended to also check
// Forwarded-For or other proxy headers
func clientKey(req *http.Request) string {
	host, _, err := net.SplitHostPort(req.RemoteAddr)
	if err != nil {
		return req.RemoteAddr
	}
	return host
}

// AccessLog wraps next, writing a line to logger for each request in the
// Apache/nginx Common Log Format, or the Combined Log Format (which adds the
// referer and user agent) if combined is true.
func AccessLog(logger *log.Logger, combined bool, next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
		start := time.Now()
		rec := &statusRecorder{ResponseWriter: w}
		next.ServeHTTP(rec, req)
		if rec.status == 0 {
			rec.status = http.StatusOK
		}

		user := "-"
		if u, _, ok := req.BasicAuth(); ok && u != "" {
			user = logField(u)
		}
		size := "-" // CLF uses "-" for an empty body
		if rec.bytes > 0 {
			size = strconv.Itoa(rec.bytes)
		}
		line := fmt.Sprintf(`%s - %s [%s] "%s" %d %s`,
			clientKey(req),
			user,
			start.Format("02/Jan/2006:15:04:05 -0700"),
			logField(req.Method+" "+req.RequestURI+" "+req.Proto),
			rec.status,
			size,
		)
		if combined {
			line += fmt.Sprintf(
				` "%s" "%s"`, logField(req.Referer()), logField(req.UserAgent()),
			)
		}
		logger.Println(line)
	})
}