package logging

import (
	"context"
	"errors"
	"io"
	"time"

	sr "tildegit.org/tjp/sliderule"
)

func LogRequests(logger Logger) sr.Middleware {
	return func(inner sr.Handler) sr.Handler {
		return sr.HandlerFunc(func(ctx context.Context, request *sr.Request) *sr.Response {
			start := time.Now()
			response := inner.Handle(ctx, request)
			if response != nil {
				response.Body = loggingBody(logger, request, response, start)
			}

			return response
		})
	}
}

type loggedResponseBody struct {
	request  *sr.Request
	response *sr.Response
	body     io.Reader

	start time.Time

	written int
	logger  Logger
}

func (lr *loggedResponseBody) log() {
	end := time.Now()
	_ = lr.logger.Log(
		"msg", "request",
		"ts", end.UTC(),
		"dur", end.Sub(lr.start),
		"url", lr.request.URL,
		"status", lr.response.Status,
		"bodylen", lr.written,
	)
}

func (lr *loggedResponseBody) Read(b []byte) (int, error) {
	if lr.body == nil {
		lr.log()
		return 0, io.EOF
	}

	wr, err := lr.body.Read(b)
	lr.written += wr

	if errors.Is(err, io.EOF) {
		lr.log()
	}

	return wr, err
}

func (lr *loggedResponseBody) Close() error {
	if cl, ok := lr.body.(io.Closer); ok {
		return cl.Close()
	}
	return nil
}

type loggedWriteToResponseBody struct {
	*loggedResponseBody
}

func (lwtr loggedWriteToResponseBody) WriteTo(dst io.Writer) (int64, error) {
	n, err := lwtr.body.(io.WriterTo).WriteTo(dst)
	if err == nil {
		lwtr.written += int(n)
		lwtr.log()
	}
	return n, err
}

func loggingBody(logger Logger, request *sr.Request, response *sr.Response, start time.Time) io.Reader {
	body := &loggedResponseBody{
		request:  request,
		response: response,
		body:     response.Body,
		start:    start,
		written:  0,
		logger:   logger,
	}

	if _, ok := response.Body.(io.WriterTo); ok {
		return loggedWriteToResponseBody{body}
	}

	return body
}