package web

import (
	"bufio"
	"encoding/json"
	"os"
	"strings"
	"time"
)

// Audit-log query support for the admin-only "Audit Log" page.
//
// The server reads its own JSON-lines audit file (logs/audit.log) back to the
// browser. Records are already redacted at write time (see logger.AuditAt), so
// returning raw lines is safe as long as we never widen what is written.
//
// Only the CURRENT audit file is searched. Rotated files (audit-*.log[.gz])
// are deliberately out of scope: they need gzip support and a separate index,
// and the UI is meant for recent-window triage ("what happened just now").
const (
	auditQueryDefaultLimit = 100
	auditQueryMaxLimit     = 500
	auditQueryMaxOffset    = 10000

	// auditQueryScanBudget bounds how much of the audit file a single query
	// reads. The tail is read when the file is larger, so the newest records
	// (what operators actually triage) are always covered and a multi-GB log
	// cannot stall the WS goroutine.
	auditQueryScanBudget = 32 << 20 // 32 MB
)

// auditQueryRequest is the JSON body of the `query_audit` command.
type auditQueryRequest struct {
	From     string `json:"from"`  // RFC3339 ("2026-10-18T10:00:00Z"), optional
	To       string `json:"to"`    // RFC3339, optional
	Event    string `json:"event"` // exact ("web.login.failure"), prefix ("web." / "web.*"), or ""
	Actor    string `json:"actor"` // exact, case-insensitive
	IP       string `json:"ip"`    // exact
	DeviceID string `json:"device_id"`
	Keyword  string `json:"keyword"`   // case-insensitive substring of the raw record
	WarnOnly bool   `json:"warn_only"` // only level=warn records
	Limit    int    `json:"limit"`
	Offset   int    `json:"offset"` // skip the newest N matching records
}

// auditQueryResult is the internal result of scanning the audit file.
type auditQueryResult struct {
	Events       []map[string]any
	Total        int // matching records in the scanned window
	FileExists   bool
	FileSize     int64
	ScannedBytes int64
	Truncated    bool // the file was larger than auditQueryScanBudget
}

// handleQueryAudit implements the admin-only audit query command. The reply is
// `{cmd:"audit_result", ok, events, total, ...}`; events are newest-first.
func (h *wsHub) handleQueryAudit(c *wsClient, raw []byte) {
	const replyCmd = "audit_result"
	if !h.requireAdmin(c, raw, replyCmd) {
		return
	}
	var in auditQueryRequest
	if err := json.Unmarshal(raw, &in); err != nil {
		c.queue(mustJSON(map[string]any{"cmd": replyCmd, "ok": false, "msg": "Invalid request"}))
		return
	}
	in.Limit = clampAuditLimit(in.Limit)
	in.Offset = clampAuditOffset(in.Offset)

	path := h.log.AuditPath()
	if path == "" {
		h.audit(c, true, auditQuery, map[string]any{
			"ok":     false,
			"reason": "audit_log_disabled",
		})
		c.queue(mustJSON(map[string]any{
			"cmd": replyCmd, "ok": false,
			"msg": "Audit log file is disabled on this server (YAMA_AUDIT_LOG=off)",
		}))
		return
	}

	res, err := queryAuditLog(path, in)
	if err != nil {
		h.audit(c, true, auditQuery, map[string]any{
			"ok":     false,
			"reason": "read_failed",
			"error":  err.Error(),
		})
		c.queue(mustJSON(map[string]any{
			"cmd": replyCmd, "ok": false,
			"msg": "Failed to read audit log: " + err.Error(),
		}))
		return
	}

	// Record the query itself: an audit viewer is privileged, and reading the
	// trail is itself an auditable action. Filter terms are included so an
	// investigator can see what was searched for.
	h.audit(c, false, auditQuery, map[string]any{
		"ok":            true,
		"event_filter":  in.Event,
		"actor_filter":  in.Actor,
		"ip_filter":     in.IP,
		"device_filter": in.DeviceID,
		"keyword":       in.Keyword,
		"warn_only":     in.WarnOnly,
		"matches":       res.Total,
		"returned":      len(res.Events),
		"offset":        in.Offset,
	})

	c.queue(mustJSON(map[string]any{
		"cmd":           replyCmd,
		"ok":            true,
		"events":        res.Events,
		"total":         res.Total,
		"offset":        in.Offset,
		"limit":         in.Limit,
		"file":          path,
		"file_exists":   res.FileExists,
		"file_size":     res.FileSize,
		"scanned_bytes": res.ScannedBytes,
		"truncated":     res.Truncated,
	}))
}

func clampAuditLimit(n int) int {
	if n <= 0 {
		return auditQueryDefaultLimit
	}
	if n > auditQueryMaxLimit {
		return auditQueryMaxLimit
	}
	return n
}

func clampAuditOffset(n int) int {
	if n < 0 {
		return 0
	}
	if n > auditQueryMaxOffset {
		return auditQueryMaxOffset
	}
	return n
}

// queryAuditLog scans path for audit records matching q. The returned events
// are the newest limit records after skipping offset, in newest-first order.
func queryAuditLog(path string, q auditQueryRequest) (auditQueryResult, error) {
	res := auditQueryResult{Events: []map[string]any{}}

	f, err := os.Open(path)
	if err != nil {
		if os.IsNotExist(err) {
			// No audit record has been written yet (lumberjack creates the file
			// lazily). An empty result is correct, not an error.
			return res, nil
		}
		return res, err
	}
	defer f.Close()

	info, err := f.Stat()
	if err != nil {
		return res, err
	}
	res.FileExists = true
	res.FileSize = info.Size()

	// For very large files, scan only the tail; the newest matches live there.
	start := int64(0)
	if info.Size() > auditQueryScanBudget {
		start = info.Size() - auditQueryScanBudget
		if _, err := f.Seek(start, 0); err != nil {
			return res, err
		}
		res.Truncated = true
	}

	from, hasFrom := parseAuditTime(q.From)
	to, hasTo := parseAuditTime(q.To)

	keep := q.Offset + q.Limit
	ring := make([]map[string]any, keep)
	filled := 0

	sc := bufio.NewScanner(f)
	// Sanitized values are capped at 4096 bytes each; a record with many
	// fields stays well under 1 MB. Allow headroom rather than aborting the
	// whole query on one long line.
	sc.Buffer(make([]byte, 64*1024), 4*1024*1024)

	first := true
	for sc.Scan() {
		line := sc.Text()
		if start > 0 && first {
			// Seeking into the middle of the file lands mid-line. Drop that
			// partial record.
			first = false
			continue
		}
		first = false
		res.ScannedBytes += int64(len(line)) + 1

		line = strings.TrimSpace(line)
		if line == "" {
			continue
		}
		var rec map[string]any
		if err := json.Unmarshal([]byte(line), &rec); err != nil {
			continue // tolerate a torn line instead of failing the page
		}
		if _, ok := rec["event"].(string); !ok {
			continue
		}
		// Only audit records belong on the page. The dedicated file contains
		// nothing else, but a hand-edited or mixed file must not surface
		// ordinary operational lines here.
		if rec["audit"] != true {
			continue
		}
		if !auditRecordMatches(rec, line, q, from, hasFrom, to, hasTo) {
			continue
		}
		// Ring buffer of the last `keep` matches (file order is chronological).
		ring[res.Total%keep] = rec
		if filled < keep {
			filled++
		}
		res.Total++
	}
	if err := sc.Err(); err != nil {
		return res, err
	}

	// Newest first, skipping Offset. The match with 0-based index i lives at
	// ring[i%keep] as long as i >= Total-filled.
	for i := res.Total - 1 - q.Offset; i >= 0 && i >= res.Total-filled; i-- {
		res.Events = append(res.Events, ring[i%keep])
		if len(res.Events) >= q.Limit {
			break
		}
	}
	return res, nil
}

// auditRecordMatches applies the non-time and time filters to one record.
// line is the raw JSON line, used for the keyword substring search.
func auditRecordMatches(rec map[string]any, line string, q auditQueryRequest, from time.Time, hasFrom bool, to time.Time, hasTo bool) bool {
	if q.Event != "" && !auditEventFilterMatches(q.Event, auditStringField(rec, "event")) {
		return false
	}
	if q.Actor != "" && !strings.EqualFold(auditStringField(rec, "actor"), q.Actor) {
		return false
	}
	if q.IP != "" && auditStringField(rec, "ip") != q.IP {
		return false
	}
	if q.DeviceID != "" && auditStringField(rec, "device_id") != q.DeviceID {
		return false
	}
	if q.WarnOnly && auditStringField(rec, "level") != "warn" {
		return false
	}
	if q.Keyword != "" && !strings.Contains(strings.ToLower(line), strings.ToLower(q.Keyword)) {
		return false
	}
	if hasFrom || hasTo {
		t, ok := parseAuditTime(auditStringField(rec, "time"))
		if !ok {
			return false // cannot prove it is in range
		}
		if hasFrom && t.Before(from) {
			return false
		}
		if hasTo && t.After(to) {
			return false
		}
	}
	return true
}

// auditEventFilterMatches supports three forms so the UI stays simple:
//
//	"web.login.failure" exact
//	"web.*"             prefix (trailing "*")
//	"web."              prefix (trailing ".")
func auditEventFilterMatches(filter, event string) bool {
	switch {
	case strings.HasSuffix(filter, "*"):
		return strings.HasPrefix(event, strings.TrimSuffix(filter, "*"))
	case strings.HasSuffix(filter, "."):
		return strings.HasPrefix(event, filter)
	default:
		return event == filter
	}
}

func auditStringField(rec map[string]any, key string) string {
	s, _ := rec[key].(string)
	return s
}

// parseAuditTime accepts the formats operators and browsers realistically send.
// Layouts without an explicit zone are parsed as UTC; the frontend always sends
// Date.toISOString(), so the RFC3339 path is what production uses.
func parseAuditTime(s string) (time.Time, bool) {
	s = strings.TrimSpace(s)
	if s == "" {
		return time.Time{}, false
	}
	layouts := []string{
		time.RFC3339Nano,
		time.RFC3339,
		"2006-01-02T15:04:05",
		"2006-01-02T15:04",
		"2006-01-02 15:04:05",
		"2006-01-02",
	}
	for _, layout := range layouts {
		if t, err := time.Parse(layout, s); err == nil {
			return t, true
		}
	}
	return time.Time{}, false
}