// Package audit records who changed what: every change made through the
// admin API and the administration pages, written to the store with the
// request's fields — anything secret taken out — and how it ended.
package audit

import (
	"bytes"
	"context"
	"encoding/json"
	"io"
	"log/slog"
	"net/http"
	"net/url"
	"regexp"
	"sort"
	"strings"
	"time"

	"gitea.mynodes.xyz/ilker/llmgw/internal/store"
)

// Sink is where events go: the store.
type Sink interface {
	WriteAudit(ctx context.Context, e store.AuditEvent) error
}

// secretName is a field whose value is never recorded.
// The password form's fields are current and new.
var secretName = regexp.MustCompile(`(?i)(pass|secret|token|api_?key|^key$|dsn|private|credential|csrf|cookie|^current$|^new$|^confirm)`)

// Redact is a request's fields with secrets replaced, as JSON.
func Redact(fields map[string]any) string {
	clean := redactValue(fields)
	b, _ := json.Marshal(clean)
	if len(b) > 8192 {
		b = append(b[:8192], []byte("…")...)
	}
	return string(b)
}

func redactValue(v any) any {
	switch t := v.(type) {
	case map[string]any:
		out := make(map[string]any, len(t))
		for k, val := range t {
			if secretName.MatchString(k) {
				out[k] = "***"
				continue
			}
			out[k] = redactValue(val)
		}
		return out
	case []any:
		out := make([]any, len(t))
		for i, val := range t {
			out[i] = redactValue(val)
		}
		return out
	case string:
		// A secret pasted where a name was expected.
		if strings.HasPrefix(t, "sk-") || strings.Contains(t, "PRIVATE KEY") {
			return "***"
		}
		return t
	}
	return v
}

// FormFields is a form as fields, for Redact.
func FormFields(v url.Values) map[string]any {
	out := map[string]any{}
	keys := make([]string, 0, len(v))
	for k := range v {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	for _, k := range keys {
		if len(v[k]) == 1 {
			out[k] = v[k][0]
		} else {
			out[k] = v[k]
		}
	}
	return out
}

// statusWriter keeps the status a handler answered with.
type statusWriter struct {
	http.ResponseWriter
	status int
}

func (w *statusWriter) WriteHeader(code int) {
	if w.status == 0 {
		w.status = code
	}
	w.ResponseWriter.WriteHeader(code)
}

func (w *statusWriter) Write(b []byte) (int, error) {
	if w.status == 0 {
		w.status = http.StatusOK
	}
	return w.ResponseWriter.Write(b)
}

func (w *statusWriter) Flush() {
	if f, ok := w.ResponseWriter.(http.Flusher); ok {
		f.Flush()
	}
}

// API records every change to the admin API: a request that is not a GET or
// HEAD, under /api/. actor says who made it.
func API(sink Sink, actor func(*http.Request) string, log *slog.Logger, next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.Method == http.MethodGet || r.Method == http.MethodHead || !strings.HasPrefix(r.URL.Path, "/api/") {
			next.ServeHTTP(w, r)
			return
		}
		var body []byte
		if r.Body != nil {
			// The first 64 KiB are what is recorded; the handler is given the
			// whole body, or a larger one — a quality suite sent whole — would
			// reach it cut off.
			body, _ = io.ReadAll(io.LimitReader(r.Body, 64<<10))
			r.Body = struct {
				io.Reader
				io.Closer
			}{io.MultiReader(bytes.NewReader(body), r.Body), r.Body}
		}
		sw := &statusWriter{ResponseWriter: w}
		next.ServeHTTP(sw, r)
		e := store.AuditEvent{At: time.Now(), Actor: actor(r), Source: "api",
			Action: r.Method + " " + r.URL.Path, Status: sw.status}
		var fields map[string]any
		if json.Unmarshal(body, &fields) == nil {
			e.Detail = Redact(fields)
		}
		for _, k := range []string{"name", "target", "scope", "model"} {
			if s, ok := fields[k].(string); ok && e.Target == "" {
				e.Target = s
			}
		}
		Write(r.Context(), sink, log, e)
	})
}

// Write records an event, saying so in the log when the store will not take
// it: a change that happened and is not in the audit is worth a warning.
func Write(ctx context.Context, sink Sink, log *slog.Logger, e store.AuditEvent) {
	if sink == nil {
		return
	}
	if err := sink.WriteAudit(context.WithoutCancel(ctx), e); err != nil && log != nil {
		log.Warn("a change could not be written to the audit log", "action", e.Action, "actor", e.Actor, "err", err)
	}
}