// Audit exports: CSV downloads of the evidence tables an auditor needs —
// user accounts (with last-login), API keys (with last-use), and the ring
// operation log. All read-level: exporting is exactly what a viewer/auditor
// role exists for. CSV cells are RFC4180-escaped; timestamps are ISO8601 UTC
// so spreadsheets sort them correctly.
package httpapi

import (
	"bytes"
	"encoding/json"
	"fmt"
	"net/http"
	"strconv"
	"strings"
	"time"

	"webui4frpc/internal/cluster"
)

// csvEscape quotes a cell per RFC4180: wrap in double quotes when the value
// contains quote/comma/newline, doubling embedded quotes. Prefixing a leading
// '=' '+' '@' '\t' with an apostrophe defuses spreadsheet formula injection
// (CSV cells are data, not formulas — auditors open these in Excel).
func csvEscape(v string) string {
	if v == "" {
		return ""
	}
	if strings.ContainsAny(v, ",\"\n\r") {
		v = `"` + strings.ReplaceAll(v, `"`, `""`) + `"`
	}
	if len(v) > 0 && (v[0] == '=' || v[0] == '+' || v[0] == '@' || v[0] == '\t' || v[0] == '-') {
		return "'" + v
	}
	return v
}

// isoTime renders unix seconds as ISO8601 UTC ("2026-08-24T12:00:00Z"); 0 →
// empty (never logged / never used).
func isoTime(unix int64) string {
	if unix <= 0 {
		return ""
	}
	return time.Unix(unix, 0).UTC().Format(time.RFC3339)
}

// writeCSV sets attachment headers and streams the header row + rows.
func writeCSV(w http.ResponseWriter, filename string, header []string, rows [][]string) {
	var b strings.Builder
	writeRow := func(cells []string) {
		for i, c := range cells {
			if i > 0 {
				b.WriteByte(',')
			}
			b.WriteString(csvEscape(c))
		}
		b.WriteString("\r\n")
	}
	writeRow(header)
	for _, r := range rows {
		writeRow(r)
	}
	w.Header().Set("Content-Type", "text/csv; charset=utf-8")
	w.Header().Set("Content-Disposition", fmt.Sprintf(`attachment; filename=%q`, filename))
	_, _ = w.Write([]byte(b.String()))
}

// handleAuditUsersCsv serves GET /audit/users.csv: the account inventory with
// last-login timestamps. Admin-only? No — read-level: auditors (viewer role)
// are precisely the people who need this; password hashes were never part of
// the User JSON shape and are not included here either.
func (h *Handler) handleAuditUsersCsv(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		methodNotAllowed(w)
		return
	}
	users, err := h.Store.ListUsers()
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	rows := make([][]string, 0, len(users))
	for _, u := range users {
		rows = append(rows, []string{
			strconv.FormatInt(u.ID, 10),
			u.Username,
			u.Role,
			strconv.FormatBool(u.Enabled),
			strconv.FormatBool(u.System),
			isoTime(u.CreatedAt),
			isoTime(u.LastLoginAt),
		})
	}
	writeCSV(w,
		fmt.Sprintf("audit-users-%s.csv", time.Now().UTC().Format("20060102-150405")),
		[]string{"id", "username", "role", "enabled", "system", "created_at", "last_login_at"},
		rows)
}

// handleAuditApiKeysCsv serves GET /audit/apikeys.csv: key inventory with
// scope, last-use and expiry. The plaintext key is unrecoverable by design;
// only the display prefix is exported.
func (h *Handler) handleAuditApiKeysCsv(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		methodNotAllowed(w)
		return
	}
	keys, err := h.Store.ListApiKeys()
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	// Resolve owning username for readability.
	nameOf := map[int64]string{}
	if users, err := h.Store.ListUsers(); err == nil {
		for _, u := range users {
			nameOf[u.ID] = u.Username
		}
	}
	rows := make([][]string, 0, len(keys))
	for _, k := range keys {
		expires := ""
		if k.ExpiresAt != 0 {
			expires = isoTime(k.ExpiresAt)
		}
		rows = append(rows, []string{
			strconv.FormatInt(k.ID, 10),
			k.Prefix + "…",
			nameOf[k.UserID],
			k.Label,
			k.Scope,
			isoTime(k.CreatedAt),
			isoTime(k.LastUsedAt),
			expires,
		})
	}
	writeCSV(w,
		fmt.Sprintf("audit-apikeys-%s.csv", time.Now().UTC().Format("20060102-150405")),
		[]string{"id", "key_prefix", "owner", "label", "scope", "created_at", "last_used_at", "expires_at"},
		rows)
}

// handleAuditClusterLogCsv serves GET /audit/cluster-log.csv: this node's ring
// operation log (forward add/remove, join/leave, leader changes, claims) as
// one flat CSV sorted by seq — the "who did what to the cluster" timeline.
// Data payloads are flattened into a human-readable detail column plus raw
// JSON for lossless reprocessing.
func (h *Handler) handleAuditClusterLogCsv(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		methodNotAllowed(w)
		return
	}
	if h.Ring == nil {
		http.Error(w, "ring engine not enabled", http.StatusNotFound)
		return
	}
	snap := h.Ring.Snapshot()
	entries := snap.Log
	rows := make([][]string, 0, len(entries))
	for _, e := range entries {
		rows = append(rows, []string{
			strconv.FormatInt(e.Seq, 10),
			isoTime(e.At),
			e.Node,
			e.Kind,
			cluster.DetailOf(e),
			rawJSON(e.Data),
		})
	}
	writeCSV(w,
		fmt.Sprintf("audit-cluster-log-%s.csv", time.Now().UTC().Format("20060102-150405")),
		[]string{"seq", "time_utc", "node", "kind", "detail", "data_json"},
		rows)
}

// rawJSON renders the log entry's payload as compact JSON (empty when absent)
// for the lossless audit column.
func rawJSON(data json.RawMessage) string {
	if len(data) == 0 {
		return ""
	}
	var buf bytes.Buffer
	if err := json.Compact(&buf, data); err != nil {
		return string(data)
	}
	return buf.String()
}