// Package debug provides helpers for the structured debug-mode plumbing:
// request IDs, baseline argument/result redaction, and result-preview
// truncation. See issue #13.
//
// Redaction here is intentionally a thin baseline. Issue #5 will introduce a
// shared redactor; once that lands the helpers in this file should defer to
// it instead of doing their own key-name matching.
package debug

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"net/url"
	"strings"
	"unicode/utf8"

	mcpContext "gitea.com/gitea/gitea-mcp/pkg/context"
)

// MaxResultPreview caps the size of result snippets in debug logs so a huge
// response body doesn't dominate the log file.
const MaxResultPreview = 1024

// NewRequestID returns a short hex-encoded identifier used to correlate
// log lines for a single tool invocation across the middleware, the result
// formatter, and the HTTP RoundTripper.
func NewRequestID() string {
	var b [6]byte
	if _, err := rand.Read(b[:]); err != nil {
		// crypto/rand failing is exceptional; fall back to a fixed marker
		// rather than panicking inside an observability-only code path.
		return "req-unknown"
	}
	return hex.EncodeToString(b[:])
}

// RequestIDFromContext returns the request ID from ctx, or "" if absent.
func RequestIDFromContext(ctx context.Context) string {
	if ctx == nil {
		return ""
	}
	if v, ok := ctx.Value(mcpContext.RequestIDContextKey).(string); ok {
		return v
	}
	return ""
}

// ToolNameFromContext returns the tool name recorded by the logging
// middleware, or "" if the call wasn't routed through it (e.g. direct REST
// helper calls in tests).
func ToolNameFromContext(ctx context.Context) string {
	if ctx == nil {
		return ""
	}
	if v, ok := ctx.Value(mcpContext.ToolNameContextKey).(string); ok {
		return v
	}
	return ""
}

// sensitiveKeys are argument names that should never appear verbatim in logs.
// Match is case-insensitive and substring-based to catch variants like
// "access_token", "api_key", "client_secret".
var sensitiveKeys = []string{
	"token", "password", "passwd", "secret", "api_key", "apikey",
	"authorization", "auth", "credential",
}

// RedactArgs walks a tool-argument value and returns a copy with sensitive
// fields masked. Non-map / non-slice values are returned as-is. The input is
// not mutated.
func RedactArgs(v any) any {
	switch t := v.(type) {
	case map[string]any:
		out := make(map[string]any, len(t))
		for k, val := range t {
			if isSensitiveKey(k) {
				out[k] = "[REDACTED]"
				continue
			}
			out[k] = RedactArgs(val)
		}
		return out
	case []any:
		out := make([]any, len(t))
		for i, val := range t {
			out[i] = RedactArgs(val)
		}
		return out
	default:
		return v
	}
}

func isSensitiveKey(k string) bool {
	lower := strings.ToLower(k)
	for _, s := range sensitiveKeys {
		if strings.Contains(lower, s) {
			return true
		}
	}
	return false
}

// StripQueryTokens removes query parameters whose names look sensitive so
// they don't end up in HTTP-level URL logs. Returns the input unchanged if
// it can't be parsed.
func StripQueryTokens(rawURL string) string {
	u, err := url.Parse(rawURL)
	if err != nil {
		return rawURL
	}
	q := u.Query()
	changed := false
	for k := range q {
		if isSensitiveKey(k) {
			q.Set(k, "REDACTED")
			changed = true
		}
	}
	if !changed {
		return rawURL
	}
	u.RawQuery = q.Encode()
	return u.String()
}

// TruncatePreview returns s clipped to MaxResultPreview runes, with an
// ellipsis suffix if anything was dropped. Operates on runes (not bytes) so
// we don't slice through the middle of a UTF-8 sequence.
func TruncatePreview(s string) string {
	if utf8.RuneCountInString(s) <= MaxResultPreview {
		return s
	}
	var b strings.Builder
	b.Grow(MaxResultPreview + 4)
	count := 0
	for _, r := range s {
		if count >= MaxResultPreview {
			break
		}
		b.WriteRune(r)
		count++
	}
	b.WriteString("...")
	return b.String()
}