package gateway

import (
	"log/slog"
	"net/http"
	"strconv"
	"strings"
	"time"

	apperr "git.yeij.top/AskaEth/Cyrene_v2/internal/errors"
	"git.yeij.top/AskaEth/Cyrene_v2/internal/logger"
)

// Log-tail endpoint tuning. Compile-time constants (project rule §10).
const (
	defaultLogLimit = 200
	maxLogLimit     = 1000
)

// AdminLogEntry is the wire shape of one entry in
// GET /api/v1/admin/observability/logs: {time,level,source,msg}. `time` is
// RFC3339 UTC (matching trace/audit); `level` ∈ debug|info|warn|error; `source`
// is the record's provenance tag, empty when the record carried none.
type AdminLogEntry struct {
	Time   string `json:"time"`
	Level  string `json:"level"`
	Source string `json:"source"`
	Msg    string `json:"msg"`
}

// SetLogBuffer injects the process-wide log ring buffer behind
// GET /api/v1/admin/observability/logs. The composition root calls it once the
// gateway exists (the logger is built before the gateway); until then the
// endpoint answers 501. It is safe to call concurrently.
func (s *Server) SetLogBuffer(buf *logger.RingBuffer) {
	if s == nil || s.obs == nil {
		return
	}
	s.obs.logBuf.Store(buf)
}

// logBuffer returns the injected log ring buffer, or nil when none was injected.
func (s *Server) logBuffer() *logger.RingBuffer {
	if s == nil || s.obs == nil {
		return nil
	}
	return s.obs.logBuf.Load()
}

// adminObservabilityLogs returns the most recent backend log records, newest
// first, optionally filtered to a minimum level (admin read). It is the backend
// behind the panel's log tail: the records come from the logger's own ring
// buffer and nothing is re-rendered or fabricated.
func (s *Server) adminObservabilityLogs(w http.ResponseWriter, r *http.Request) {
	minLevel, filtered, ok := parseLogLevel(r.URL.Query().Get("level"))
	if !ok {
		writeError(w, &apperr.AppError{
			Code:     "invalid_level",
			Message:  "level 只能为 debug/info/warn/error 或留空",
			HTTPCode: http.StatusBadRequest,
		})
		return
	}
	buf := s.logBuffer()
	if buf == nil {
		writeError(w, &apperr.AppError{
			Code:     "not_implemented",
			Message:  "日志环形缓冲未注入（组合根未挂载 logger.RingBuffer）",
			HTTPCode: http.StatusNotImplemented,
		})
		return
	}
	limit := parseLogLimit(r)
	entries := buf.Snapshot(0)
	out := make([]AdminLogEntry, 0, min(len(entries), limit))
	for _, e := range entries {
		if filtered && logger.ParseLevel(e.Level) < minLevel {
			continue
		}
		out = append(out, adminLogOf(e))
		if len(out) == limit {
			break
		}
	}
	writeJSON(w, http.StatusOK, out)
}

// adminLogOf maps a captured log entry to the camelCase admin wire shape.
func adminLogOf(e logger.Entry) AdminLogEntry {
	return AdminLogEntry{
		Time:   e.Time.UTC().Format(time.RFC3339),
		Level:  e.Level,
		Source: e.Source,
		Msg:    e.Msg,
	}
}

// parseLogLevel resolves the ?level= filter. An empty value disables filtering
// (filtered=false); debug/info/warn/error select that level and above; anything
// else is rejected with ok=false so the handler answers 400.
func parseLogLevel(raw string) (min slog.Level, filtered, ok bool) {
	switch strings.ToLower(strings.TrimSpace(raw)) {
	case "":
		return 0, false, true
	case "debug":
		return slog.LevelDebug, true, true
	case "info":
		return slog.LevelInfo, true, true
	case "warn":
		return slog.LevelWarn, true, true
	case "error":
		return slog.LevelError, true, true
	default:
		return 0, false, false
	}
}

// parseLogLimit parses the ?limit= query param, clamping to [1, maxLogLimit] and
// selecting defaultLogLimit when absent or invalid.
func parseLogLimit(r *http.Request) int {
	n, err := strconv.Atoi(r.URL.Query().Get("limit"))
	if err != nil || n <= 0 {
		return defaultLogLimit
	}
	if n > maxLogLimit {
		return maxLogLimit
	}
	return n
}