package main

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"golang.org/x/mod/modfile"
)

type pluginGoModViolation struct {
	file   string
	line   int
	rule   string
	detail string
}

func currentCMSCoreSDKVersion() (string, error) {
	return readRequiredModuleVersion(filepath.Join(blockNinjaRepoRoot(), "backend", "go.mod"), blockCoreImportPrefix)
}

func parseGoModForSafety(goModPath string) (*modfile.File, []pluginGoModViolation) {
	if !fileExists(goModPath) {
		return nil, []pluginGoModViolation{{
			file:   filepath.Base(goModPath),
			rule:   "missing-go-mod",
			detail: fmt.Sprintf("missing %s", filepath.Base(goModPath)),
		}}
	}

	data, err := os.ReadFile(goModPath)
	if err != nil {
		return nil, []pluginGoModViolation{{
			file:   filepath.Base(goModPath),
			rule:   "read-go-mod",
			detail: fmt.Sprintf("failed to read go.mod: %v", err),
		}}
	}

	parsed, err := modfile.Parse(goModPath, data, nil)
	if err != nil {
		return nil, []pluginGoModViolation{{
			file:   filepath.Base(goModPath),
			rule:   "parse-go-mod",
			detail: fmt.Sprintf("failed to parse go.mod: %v", err),
		}}
	}

	return parsed, nil
}

func newGoModReplaceViolation(parsed *modfile.File, replace *modfile.Replace, rule string) pluginGoModViolation {
	detail := fmt.Sprintf("replace directive present for %s", replace.Old.Path)
	if replace.New.Path != "" {
		detail += fmt.Sprintf(" -> %s", replace.New.Path)
	}
	if replace.New.Version != "" {
		detail += fmt.Sprintf(" %s", replace.New.Version)
	}

	line := 0
	if replace.Syntax != nil {
		line = replace.Syntax.Start.Line
	}

	return pluginGoModViolation{
		file:   filepath.Base(parsed.Syntax.Name),
		line:   line,
		rule:   rule,
		detail: detail,
	}
}

func checkGoModForAnyReplaceDirectives(goModPath string) []pluginGoModViolation {
	parsed, violations := parseGoModForSafety(goModPath)
	if parsed == nil {
		return violations
	}

	for _, replace := range parsed.Replace {
		violations = append(violations, newGoModReplaceViolation(parsed, replace, "no-replace-directives"))
	}

	return violations
}

func checkGoModForModuleReplaceDirective(goModPath, modulePath string) []pluginGoModViolation {
	parsed, violations := parseGoModForSafety(goModPath)
	if parsed == nil {
		return violations
	}

	for _, replace := range parsed.Replace {
		if replace.Old.Path != modulePath {
			continue
		}
		violations = append(violations, newGoModReplaceViolation(parsed, replace, "no-local-block-core-replace"))
	}

	return violations
}

func readRequiredModuleVersion(goModPath, modulePath string) (string, error) {
	data, err := os.ReadFile(goModPath)
	if err != nil {
		return "", err
	}
	parsed, err := modfile.Parse(goModPath, data, nil)
	if err != nil {
		return "", err
	}
	for _, req := range parsed.Require {
		if req.Mod.Path == modulePath {
			return req.Mod.Version, nil
		}
	}
	return "", fmt.Errorf("%s does not require %s", goModPath, modulePath)
}

func checkCMSCoreSDKGoMod(root string) []pluginGoModViolation {
	return checkGoModForModuleReplaceDirective(filepath.Join(root, "go.mod"), blockCoreImportPrefix)
}

// isCodelessPluginRepo mirrors the ninja CLI classifier (core
// cmd/ninja/internal/bnp.IsCodelessRepo): a plugin.mod with no Go source at
// the repo root is a codeless plugin (WO-WZ-020) — declarative-only, no
// go.mod and no SDK version to pin.
func isCodelessPluginRepo(root string) bool {
	if !fileExists(filepath.Join(root, "plugin.mod")) {
		return false
	}
	entries, err := os.ReadDir(root)
	if err != nil {
		return false
	}
	for _, e := range entries {
		if !e.IsDir() && strings.HasSuffix(e.Name(), ".go") {
			return false
		}
	}
	return true
}

func checkStandalonePluginGoMod(root, requiredSDKVersion string) []pluginGoModViolation {
	if isCodelessPluginRepo(root) {
		return nil
	}
	goModPath := filepath.Join(root, "go.mod")
	parsed, violations := parseGoModForSafety(goModPath)
	if parsed == nil {
		if len(violations) == 1 && violations[0].rule == "missing-go-mod" {
			violations[0].detail = "standalone plugins must be standalone Go modules with a repo-root go.mod"
		}
		return violations
	}

	violations = append(violations, checkGoModForAnyReplaceDirectives(goModPath)...)

	currentSDKVersion := ""
	for _, req := range parsed.Require {
		if req.Mod.Path == blockCoreImportPrefix {
			currentSDKVersion = req.Mod.Version
			break
		}
	}
	if currentSDKVersion == "" {
		violations = append(violations, pluginGoModViolation{
			file:   "go.mod",
			rule:   "missing-block-core-require",
			detail: fmt.Sprintf("missing required module %s", blockCoreImportPrefix),
		})
		return violations
	}

	if requiredSDKVersion != "" && currentSDKVersion != requiredSDKVersion {
		violations = append(violations, pluginGoModViolation{
			file:   "go.mod",
			rule:   "block-core-version-mismatch",
			detail: fmt.Sprintf("requires %s, want %s", currentSDKVersion, requiredSDKVersion),
		})
	}

	return violations
}