package log

import (
	"bytes"
	"context"
	"encoding/json"
	"io"
	"log/slog"
	"net/http"
	"time"

	"github.com/c2h5oh/datasize"
)

type RoundTripCollector struct {
	Request *http.Request
	// HTTP Response. May be nil.
	Response     *http.Response
	Start        time.Time
	End          time.Time
	RequestBody  *bytes.Buffer
	ResponseBody *bytes.Buffer
}

func (ht RoundTripCollector) LogValue() slog.Value {
	values := make([]slog.Attr, 0, 4)
	if !ht.Start.IsZero() {
		values = append(values, slog.Time("start", ht.Start))
	}
	if !ht.End.IsZero() {
		values = append(values, slog.Time("end", ht.End))
	}
	if !ht.Start.IsZero() && !ht.End.IsZero() {
		values = append(values, slog.Duration("duration", ht.End.Sub(ht.Start)))
	}
	if ht.Request != nil {
		vals := make([]slog.Attr, 0, 5)
		vals = append(vals, slog.String("url", ht.Request.URL.String()))
		vals = append(vals, slog.String("method", ht.Request.Method))
		headers := []slog.Attr{}
		for k := range ht.Request.Header {
			headers = append(headers, slog.String(k, ht.Request.Header.Get(k)))
		}
		if len(headers) > 0 {
			vals = append(vals, slog.Attr{Key: "headers", Value: slog.GroupValue(headers...)})
		}
		if ht.RequestBody.Len() > 0 {
			cl := datasize.ByteSize(ht.RequestBody.Len())
			vals = append(vals, slog.String("content_length", cl.HumanReadable()))
			if ht.Request.Header.Get("Content-Type") == "application/json" {
				vals = append(vals, slog.Any("body", json.RawMessage(ht.RequestBody.Bytes())))
			} else {
				vals = append(vals, slog.String("body", ht.RequestBody.String()))
			}
		}
		values = append(values, slog.Attr{Key: "request", Value: slog.GroupValue(vals...)})
	}
	if ht.Response != nil {
		vals := make([]slog.Attr, 0, 4)
		vals = append(vals, slog.Int("code", ht.Response.StatusCode))
		cl := datasize.ByteSize(ht.Response.ContentLength)
		vals = append(vals, slog.String("content_length", cl.HumanReadable()))
		headers := []slog.Attr{}
		for k := range ht.Response.Header {
			headers = append(headers, slog.String(k, ht.Response.Header.Get(k)))
		}
		if ht.ResponseBody.Len() > 0 {
			if ht.Response.Header.Get("Content-Type") == "application/json" {
				vals = append(vals, slog.Any("body", json.RawMessage(ht.ResponseBody.Bytes())))
			} else {
				vals = append(vals, slog.String("body", ht.ResponseBody.String()))
			}
		}
		values = append(values, slog.Attr{Key: "response", Value: slog.GroupValue(vals...)})
	}
	return slog.GroupValue(values...)
}

type httpLogCollectorKey struct{}

// ContextWithRoundTripCollector injects an *HTTPLogCollector into given context.
func ContextWithRoundTripCollector(ctx context.Context) (context.Context, *RoundTripCollector) {
	coll := &RoundTripCollector{}
	return context.WithValue(ctx, httpLogCollectorKey{}, coll), coll
}

// RoundTripCollectorFromContext gets an *HTTPLogCollector instance.
//
// Returns nil if not found.
func RoundTripCollectorFromContext(ctx context.Context) *RoundTripCollector {
	coll, _ := ctx.Value(httpLogCollectorKey{}).(*RoundTripCollector)
	return coll
}

type RoundTripper struct {
	Next http.RoundTripper
}

// NewRoundTripper creates a new http log collector round tripper.
//
// If next is nil, uses http.DefaultTransport instead.
func NewRoundTripper(next http.RoundTripper) *RoundTripper {
	if next == nil {
		next = http.DefaultTransport
	}
	return &RoundTripper{next}
}

type bodyCloser struct {
	io.Reader
	close func() error
}

func (b bodyCloser) Close() error {
	return b.close()
}

// RoundTrip implements http.RoundTripper
func (ht *RoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
	coll := RoundTripCollectorFromContext(req.Context())
	if coll == nil {
		return ht.Next.RoundTrip(req)
	}
	coll.RequestBody = new(bytes.Buffer)
	coll.ResponseBody = new(bytes.Buffer)
	coll.Request = req
	if coll.Request.Body != nil {
		tee := io.TeeReader(coll.Request.Body, coll.RequestBody)
		req.Body = bodyCloser{tee, req.Body.Close}
	}
	coll.Start = time.Now()
	resp, err := ht.Next.RoundTrip(req)
	coll.End = time.Now()
	coll.Response = resp
	if resp != nil {
		coll.Request = resp.Request
		tee := io.TeeReader(resp.Body, coll.ResponseBody)
		resp.Body = bodyCloser{tee, resp.Body.Close}
	}
	return resp, err
}