mcp/internal/tools/validate_snippet.go

package tools

import (
	"context"

	"code.nochebuena.dev/einherjar/mcp/internal/envspec"
	"code.nochebuena.dev/einherjar/mcp/internal/index"
	"code.nochebuena.dev/einherjar/mcp/internal/rules"
	"github.com/modelcontextprotocol/go-sdk/mcp"
)

type validateSnippetInput struct {
	Code string `json:"code" jsonschema:"Go source code to validate against Einherjar conventions. A full file is preferred; a partial body will be wrapped automatically."`
}

type validateSnippetOutput struct {
	Findings []rules.Finding `json:"findings"`
	Summary  string          `json:"summary"`
}

func registerValidateSnippet(s *mcp.Server, idx *index.Index) {
	// Inject the real framework env-var names so config.unknown-env-var can reject
	// invented/misspelled EINHERJAR_* tags instead of guessing.
	rules.SetKnownEnvVars(envspec.KnownNames(idx))
	mcp.AddTool(s, &mcp.Tool{
		Name:        "validate_snippet",
		Description: "Validate a Go snippet against Einherjar wiring conventions: lifecycle setup, logger configuration, env-var handling, server registration. Findings are advisory, not a substitute for go vet or the project's tests.",
	}, func(ctx context.Context, req *mcp.CallToolRequest, args validateSnippetInput) (*mcp.CallToolResult, validateSnippetOutput, error) {
		findings := rules.Run(args.Code)
		if findings == nil {
			findings = []rules.Finding{}
		}
		summary := summarise(findings)
		out := validateSnippetOutput{Findings: findings, Summary: summary}
		return jsonText(out), out, nil
	})
}

func summarise(fs []rules.Finding) string {
	if len(fs) == 0 {
		return "No issues found — snippet follows Einherjar conventions."
	}
	var errs, warns, infos int
	for _, f := range fs {
		switch f.Severity {
		case rules.SeverityError:
			errs++
		case rules.SeverityWarning:
			warns++
		case rules.SeverityInfo:
			infos++
		}
	}
	return pluralise(errs, "error", "errors") + ", " +
		pluralise(warns, "warning", "warnings") + ", " +
		pluralise(infos, "note", "notes")
}

func pluralise(n int, singular, plural string) string {
	if n == 1 {
		return "1 " + singular
	}
	return itoa(n) + " " + plural
}

func itoa(n int) string {
	if n == 0 {
		return "0"
	}
	neg := n < 0
	if neg {
		n = -n
	}
	var buf [20]byte
	i := len(buf)
	for n > 0 {
		i--
		buf[i] = byte('0' + n%10)
		n /= 10
	}
	if neg {
		i--
		buf[i] = '-'
	}
	return string(buf[i:])
}