// Package requestlog writes the lines smallwebwaf prints on stdout: one
// JSON object per request, marked "type":"request", and the process's own
// messages as JSON lines marked "type":"process".
package requestlog

import (
	"encoding/json"
	"fmt"
	"io"
	"log/slog"
	"time"
)

// The action a request line names: what smallwebwaf did with the
// request.
const (
	// ActionForward is a request passed to the app.
	ActionForward = "forward"
	// ActionTooLarge is a request or response over its size limit.
	ActionTooLarge = "too_large"
	// ActionTimedOut is a request or response that ran out of time.
	ActionTimedOut = "timed_out"
	// ActionUpstreamError is a request the app could not be reached
	// for, or whose answer could not be passed on.
	ActionUpstreamError = "upstream_error"
	// ActionRateLimited is a request refused because it took its client
	// over a rate limit, or came while the client was over one.
	ActionRateLimited = "rate_limited"
	// ActionCountryDenied is a request refused for its client's country.
	ActionCountryDenied = "country_denied"
	// ActionAdmin is a request smallwebwaf answered at one of its own
	// endpoints, under /_smallwebwaf/.
	ActionAdmin = "admin"
)

// timeLayout is RFC 3339 with milliseconds.
const timeLayout = "2006-01-02T15:04:05.000Z07:00"

// Line is one request's line in the request log. The field names are
// those of the "Request log" section of SPEC.md.
//
//nolint:tagliatelle // SPEC.md's request log names its fields in snake_case
type Line struct {
	Type           string `json:"type"`
	Time           string `json:"time"`
	ClientIP       string `json:"client_ip"`
	PeerIP         string `json:"peer_ip"`
	Country        string `json:"country"`
	Method         string `json:"method"`
	Host           string `json:"host"`
	Path           string `json:"path"`
	Query          string `json:"query"`
	Protocol       string `json:"protocol"`
	Status         int    `json:"status"`
	UpstreamStatus int    `json:"upstream_status,omitempty"`
	RequestBytes   int64  `json:"request_bytes"`
	ResponseBytes  int64  `json:"response_bytes"`
	Referer        string `json:"referer"`
	UserAgent      string `json:"user_agent"`
	Action         string `json:"action"`
	// LimitHit is the window whose rate limit the request went over:
	// minute, hour or day.
	LimitHit string `json:"limit_hit,omitempty"`
	// Aborted is true when the client went away early.
	Aborted bool `json:"aborted,omitempty"`
	// DurationTotal and DurationUpstreamTotal are in milliseconds.
	DurationTotal         float64 `json:"duration_total"`
	DurationUpstreamTotal float64 `json:"duration_upstream_total,omitempty"`
}

// Write writes line to w as one JSON line marked "type":"request".
func Write(w io.Writer, line *Line) error {
	line.Type = "request"

	encoded, err := json.Marshal(line)
	if err != nil {
		return fmt.Errorf("encode the request log line: %w", err)
	}

	_, err = w.Write(append(encoded, '\n'))
	if err != nil {
		return fmt.Errorf("write the request log line: %w", err)
	}

	return nil
}

// FormatTime formats t for a line's time field: RFC 3339 in UTC, with
// milliseconds.
func FormatTime(t time.Time) string {
	return t.UTC().Format(timeLayout)
}

// Milliseconds is d in milliseconds, to the microsecond.
func Milliseconds(d time.Duration) float64 {
	return float64(d.Microseconds()) / float64(time.Millisecond/time.Microsecond)
}

// NewProcessLogger returns the logger for the process's own messages:
// JSON lines on w, marked "type":"process", with the time in the same form
// as a request line's.
func NewProcessLogger(w io.Writer) *slog.Logger {
	handler := slog.NewJSONHandler(w, &slog.HandlerOptions{
		ReplaceAttr: func(groups []string, attr slog.Attr) slog.Attr {
			if attr.Key == slog.TimeKey && len(groups) == 0 {
				return slog.String(slog.TimeKey, FormatTime(attr.Value.Time()))
			}

			return attr
		},
	})

	return slog.New(handler).With("type", "process")
}