package build

import (
	"bytes"
	"context"
	"embed"
	"fmt"
	"go/ast"
	"go/format"
	"go/parser"
	"go/token"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"strings"
	"text/template"
)

//go:embed stubs/*.tmpl
var stubFS embed.FS

var stubTmpl = template.Must(template.ParseFS(stubFS, "stubs/*.tmpl"))

var pluginLeaves = []string{
	"models",
	"classes",
	"controllers",
	"console",
	"jobs",
	"middleware",
	"updates",
}

type stubData struct {
	Package   string
	ID        string
	Module    string
	Framework string
	GoVersion string
	Toolchain string
	Replace   string
}

const (
	frameworkModule = "git.golem15.com/golem15/summercms"
	goVersionLine   = "go 1.27.0"
	toolchainLine   = "toolchain go1.27.0"
)

// MakePlugin scaffolds a compiling plugin module under plugins/<name>.
func MakePlugin(ctx context.Context, startDir, id string) (string, error) {
	if err := ValidatePluginID(id); err != nil {
		return "", fmt.Errorf("build: %w", err)
	}
	appDir, err := findAppDir(startDir)
	if err != nil {
		return "", err
	}
	name := pluginName(id)
	pluginDir := filepath.Join(appDir, "plugins", name)
	if !underRoot(appDir, pluginDir) {
		return "", fmt.Errorf("build: plugin path %q escapes the app root", pluginDir)
	}
	if _, err := os.Stat(pluginDir); err == nil {
		return "", fmt.Errorf("build: plugin directory %s already exists", pluginDir)
	} else if !os.IsNotExist(err) {
		return "", fmt.Errorf("build: stat %s: %w", pluginDir, err)
	}

	m, err := LoadManifest(filepath.Join(appDir, manifestName))
	if err != nil {
		return "", err
	}
	modPath := m.Module + "/plugins/" + name
	if err := validateModulePath(modPath); err != nil {
		return "", fmt.Errorf("build: plugin module: %w", err)
	}

	replace, err := frameworkReplaceFor(pluginDir, appDir)
	if err != nil {
		return "", err
	}
	data := stubData{
		Package:   name,
		ID:        id,
		Module:    modPath,
		Framework: frameworkModule,
		GoVersion: goVersionLine,
		Toolchain: toolchainLine,
		Replace:   replace,
	}
	if err := writePluginScaffold(pluginDir, data); err != nil {
		return "", err
	}
	if err := runGo(ctx, pluginDir, "mod", "tidy"); err != nil {
		return "", err
	}
	if err := ensureToolchain(filepath.Join(pluginDir, "go.mod")); err != nil {
		return "", err
	}
	return pluginDir, nil
}

// AddPlugin registers a local plugin module in summer.yaml, go.work and the app go.mod.
func AddPlugin(ctx context.Context, startDir, pluginDir string) error {
	appDir, err := findAppDir(startDir)
	if err != nil {
		return err
	}
	if pluginDir == "" {
		return fmt.Errorf("build: plugin directory is empty")
	}
	if !filepath.IsAbs(pluginDir) {
		pluginDir = filepath.Join(startDir, pluginDir)
	}
	pluginDir, err = filepath.Abs(pluginDir)
	if err != nil {
		return fmt.Errorf("build: resolve plugin directory: %w", err)
	}
	if !underRoot(appDir, pluginDir) {
		return fmt.Errorf("build: plugin directory %q is outside the app root", pluginDir)
	}

	modPath, err := readModulePath(filepath.Join(pluginDir, "go.mod"))
	if err != nil {
		return err
	}
	if err := validateModulePath(modPath); err != nil {
		return fmt.Errorf("build: plugin module: %w", err)
	}
	id, err := pluginIDFromGo(filepath.Join(pluginDir, "plugin.go"))
	if err != nil {
		return err
	}
	if err := ValidatePluginID(id); err != nil {
		return fmt.Errorf("build: %w", err)
	}

	manifestPath := filepath.Join(appDir, manifestName)
	m, err := LoadManifest(manifestPath)
	if err != nil {
		return err
	}

	already := false
	for _, p := range m.Plugins {
		if p.ID == id && p.Module == modPath {
			already = true
			continue
		}
		if p.ID == id {
			return fmt.Errorf("build: plugin id %q is already registered as %s", id, p.Module)
		}
		if p.Module == modPath {
			return fmt.Errorf("build: plugin module %q is already registered as %s", modPath, p.ID)
		}
	}
	if !already {
		m.Plugins = append(m.Plugins, Plugin{ID: id, Module: modPath})
	}

	if err := editAppModule(ctx, appDir, pluginDir, modPath); err != nil {
		return err
	}
	if err := ensureGoWork(ctx, appDir, m, pluginDir); err != nil {
		return err
	}
	if already {
		return nil
	}
	return SaveManifest(manifestPath, m)
}

func pluginName(id string) string {
	_, name, _ := strings.Cut(id, ".")
	return name
}

func writePluginScaffold(pluginDir string, data stubData) error {
	if err := os.MkdirAll(pluginDir, 0o755); err != nil {
		return fmt.Errorf("build: create plugin dir: %w", err)
	}
	pluginSrc, err := renderStub("plugin.go", data)
	if err != nil {
		return err
	}
	if err := writeFile(filepath.Join(pluginDir, "plugin.go"), pluginSrc); err != nil {
		return err
	}
	routesSrc, err := renderStub("routes.go", data)
	if err != nil {
		return err
	}
	if err := writeFile(filepath.Join(pluginDir, "routes.go"), routesSrc); err != nil {
		return err
	}
	for _, leaf := range pluginLeaves {
		src, err := renderStub(leaf+"/doc.go", data)
		if err != nil {
			return err
		}
		if err := writeFile(filepath.Join(pluginDir, leaf, "doc.go"), src); err != nil {
			return err
		}
	}
	for _, asset := range pluginAssets {
		if err := writeFile(filepath.Join(pluginDir, filepath.FromSlash(asset.rel)), []byte(asset.body)); err != nil {
			return err
		}
	}
	if err := writeRegistry(pluginDir, emptyRegistry(data.Package, data.Module)); err != nil {
		return err
	}
	modSrc, err := renderStub("go.mod", data)
	if err != nil {
		return err
	}
	return writeFile(filepath.Join(pluginDir, "go.mod"), modSrc)
}

type pluginAsset struct {
	rel  string
	body string
}

var pluginAssets = []pluginAsset{
	{rel: "config/config.yaml", body: "{}\n"},
	{rel: "lang/en/lang.yaml", body: "{}\n"},
	{rel: "views/mail/welcome.htm", body: "subject = \"Welcome\"\ndescription = \"Placeholder mail template\"\n==\nHello.\n"},
}

func renderStub(name string, data any) ([]byte, error) {
	var buf bytes.Buffer
	if err := stubTmpl.ExecuteTemplate(&buf, name, data); err != nil {
		return nil, fmt.Errorf("build: render stub %s: %w", name, err)
	}
	raw := buf.Bytes()
	if !strings.HasSuffix(name, ".go") {
		return raw, nil
	}
	formatted, err := format.Source(raw)
	if err != nil {
		return nil, fmt.Errorf("build: format stub %s: %w\n%s", name, err, raw)
	}
	return formatted, nil
}

func writeFile(path string, data []byte) error {
	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
		return fmt.Errorf("build: mkdir %s: %w", filepath.Dir(path), err)
	}
	if err := os.WriteFile(path, data, 0o644); err != nil {
		return fmt.Errorf("build: write %s: %w", path, err)
	}
	return nil
}

func frameworkReplaceFor(pluginDir, appDir string) (string, error) {
	_, replaces, err := parseGoMod(filepath.Join(appDir, "go.mod"))
	if err != nil {
		return "", err
	}
	appReplace, ok := replaces[frameworkModule]
	if !ok || appReplace == "" {
		return "", nil
	}
	target := appReplace
	if filepath.IsAbs(appReplace) {
		return filepath.ToSlash(appReplace), nil
	}
	target = filepath.Join(appDir, target)
	target, err = filepath.Abs(target)
	if err != nil {
		return "", fmt.Errorf("build: plugin replace: %w", err)
	}
	rel, err := filepath.Rel(pluginDir, target)
	if err != nil {
		return filepath.ToSlash(target), nil
	}
	return filepath.ToSlash(rel), nil
}

func pluginIDFromGo(path string) (string, error) {
	fset := token.NewFileSet()
	file, err := parser.ParseFile(fset, path, nil, 0)
	if err != nil {
		return "", fmt.Errorf("build: parse %s: %w", path, err)
	}
	var id string
	ast.Inspect(file, func(n ast.Node) bool {
		fn, ok := n.(*ast.FuncDecl)
		if !ok || fn.Name == nil || fn.Name.Name != "ID" || fn.Recv == nil || fn.Body == nil {
			return true
		}
		for _, stmt := range fn.Body.List {
			ret, ok := stmt.(*ast.ReturnStmt)
			if !ok || len(ret.Results) != 1 {
				continue
			}
			lit, ok := ret.Results[0].(*ast.BasicLit)
			if !ok || lit.Kind != token.STRING {
				continue
			}
			s, err := strconv.Unquote(lit.Value)
			if err == nil {
				id = s
			}
		}
		return true
	})
	if id == "" {
		return "", fmt.Errorf("build: %s does not return a plugin id", path)
	}
	return id, nil
}

func editAppModule(ctx context.Context, appDir, pluginDir, modPath string) error {
	if err := runGo(ctx, appDir, "mod", "edit", "-require="+modPath+"@v0.0.0"); err != nil {
		return err
	}
	rel, err := filepath.Rel(appDir, pluginDir)
	if err != nil {
		return fmt.Errorf("build: plugin replace: %w", err)
	}
	rel = filepath.ToSlash(rel)
	if rel != ".." && !strings.HasPrefix(rel, "../") && !filepath.IsAbs(rel) && !strings.HasPrefix(rel, "./") {
		rel = "./" + rel
	}
	if err := runGo(ctx, appDir, "mod", "edit", "-replace="+modPath+"="+rel); err != nil {
		return err
	}
	return ensureToolchain(filepath.Join(appDir, "go.mod"))
}

func ensureGoWork(ctx context.Context, appDir string, m Manifest, pluginDir string) error {
	gw := findGoWork(appDir)
	if gw == "" {
		if err := writeGoWork(filepath.Join(appDir, "go.work")); err != nil {
			return err
		}
		gw = filepath.Join(appDir, "go.work")
		for _, p := range m.Plugins {
			if dir := localModuleDir(appDir, p.Module); dir != "" && dir != pluginDir {
				if err := runGoWorkUse(ctx, appDir, gw, dir); err != nil {
					return err
				}
			}
		}
	}
	return runGoWorkUse(ctx, appDir, gw, pluginDir)
}

func writeGoWork(path string) error {
	body := goVersionLine + "\n\n" + toolchainLine + "\n\nuse (\n\t.\n)\n"
	if err := os.WriteFile(path, []byte(body), 0o644); err != nil {
		return fmt.Errorf("build: write go.work: %w", err)
	}
	return nil
}

func runGoWorkUse(ctx context.Context, appDir, goWork, dir string) error {
	cmd := exec.CommandContext(ctx, "go", "work", "use", dir)
	cmd.Dir = appDir
	applyGoWorkFile(cmd, goWork)
	out, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("build: go work use: %w\n%s", err, out)
	}
	return ensureToolchain(goWork)
}

func localModuleDir(appDir, module string) string {
	_, replaces, err := parseGoMod(filepath.Join(appDir, "go.mod"))
	if err != nil {
		return ""
	}
	r, ok := replaces[module]
	if !ok || r == "" {
		return ""
	}
	if filepath.IsAbs(r) {
		return r
	}
	return filepath.Clean(filepath.Join(appDir, r))
}

func readModulePath(path string) (string, error) {
	module, _, err := parseGoMod(path)
	if err != nil {
		return "", err
	}
	if module == "" {
		return "", fmt.Errorf("build: %s has no module path", path)
	}
	return module, nil
}

func parseGoMod(path string) (string, map[string]string, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return "", nil, fmt.Errorf("build: read %s: %w", path, err)
	}
	module := ""
	replaces := make(map[string]string)
	inReplace := false
	for _, raw := range strings.Split(string(data), "\n") {
		line := strings.TrimSpace(raw)
		if i := strings.Index(line, "//"); i >= 0 {
			line = strings.TrimSpace(line[:i])
		}
		if line == "" {
			continue
		}
		if module == "" && strings.HasPrefix(line, "module ") {
			module = strings.TrimSpace(strings.TrimPrefix(line, "module "))
			continue
		}
		if line == "replace (" {
			inReplace = true
			continue
		}
		if inReplace {
			if line == ")" {
				inReplace = false
				continue
			}
			if old, new, ok := splitReplace(line); ok {
				replaces[old] = new
			}
			continue
		}
		if strings.HasPrefix(line, "replace ") {
			if old, new, ok := splitReplace(strings.TrimPrefix(line, "replace ")); ok {
				replaces[old] = new
			}
		}
	}
	return module, replaces, nil
}

func splitReplace(s string) (old, new string, ok bool) {
	parts := strings.SplitN(s, "=>", 2)
	if len(parts) != 2 {
		return "", "", false
	}
	oldFields := strings.Fields(strings.TrimSpace(parts[0]))
	newFields := strings.Fields(strings.TrimSpace(parts[1]))
	if len(oldFields) == 0 || len(newFields) == 0 {
		return "", "", false
	}
	return oldFields[0], newFields[0], true
}

func ensureToolchain(path string) error {
	data, err := os.ReadFile(path)
	if err != nil {
		return fmt.Errorf("build: read %s: %w", path, err)
	}
	if bytes.Contains(data, []byte(toolchainLine)) {
		return nil
	}
	lines := strings.Split(string(data), "\n")
	out := make([]string, 0, len(lines)+2)
	inserted := false
	for _, line := range lines {
		out = append(out, line)
		if !inserted && strings.HasPrefix(strings.TrimSpace(line), "go ") {
			out = append(out, "", toolchainLine)
			inserted = true
		}
	}
	if !inserted {
		out = append([]string{toolchainLine, ""}, out...)
	}
	if err := os.WriteFile(path, []byte(strings.Join(out, "\n")), 0o644); err != nil {
		return fmt.Errorf("build: write %s: %w", path, err)
	}
	return nil
}

func underRoot(root, path string) bool {
	rel, err := filepath.Rel(root, path)
	if err != nil {
		return false
	}
	if rel == ".." || strings.HasPrefix(rel, ".."+string(os.PathSeparator)) {
		return false
	}
	return true
}

func findGoWork(start string) string {
	dir := start
	for {
		candidate := filepath.Join(dir, "go.work")
		if st, err := os.Stat(candidate); err == nil && !st.IsDir() {
			return candidate
		}
		parent := filepath.Dir(dir)
		if parent == dir {
			return ""
		}
		dir = parent
	}
}

func runGo(ctx context.Context, dir string, args ...string) error {
	cmd := exec.CommandContext(ctx, "go", args...)
	cmd.Dir = dir
	applyGoWork(cmd, dir)
	out, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("build: go %s: %w\n%s", strings.Join(args, " "), err, out)
	}
	return nil
}

func applyGoWork(cmd *exec.Cmd, dir string) {
	if gw := findGoWork(dir); gw != "" {
		applyGoWorkFile(cmd, gw)
		return
	}
	applyGoWorkFile(cmd, "off")
}

func applyGoWorkFile(cmd *exec.Cmd, goWork string) {
	env := os.Environ()
	filtered := make([]string, 0, len(env)+2)
	for _, e := range env {
		if strings.HasPrefix(e, "GOWORK=") || strings.HasPrefix(e, "GOFLAGS=") {
			continue
		}
		filtered = append(filtered, e)
	}
	filtered = append(filtered, "GOWORK="+goWork)
	if goWork == "off" {
		filtered = append(filtered, "GOFLAGS=-mod=mod")
	}
	cmd.Env = filtered
}