package generate

import (
	"bytes"
	"errors"
	"fmt"
	"go/format"
	"go/token"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"

	"gitea.lclr.dev/AI/mcp-framework/manifest"
)

var ErrGeneratedFilesOutdated = errors.New("generated files are not up to date")

type Options struct {
	ProjectDir   string
	ManifestPath string
	PackageDir   string
	PackageName  string
	Check        bool
}

type Result struct {
	Root  string
	Files []string
}

func Generate(options Options) (Result, error) {
	normalized, err := normalizeOptions(options)
	if err != nil {
		return Result{}, err
	}

	if _, err := manifest.Load(normalized.ManifestPath); err != nil {
		return Result{}, err
	}

	manifestContent, err := os.ReadFile(normalized.ManifestPath)
	if err != nil {
		return Result{}, fmt.Errorf("read manifest %s: %w", normalized.ManifestPath, err)
	}

	content, err := renderManifestLoader(normalized.PackageName, string(manifestContent))
	if err != nil {
		return Result{}, err
	}

	files := []generatedFile{
		{
			Path:    filepath.Join(normalized.PackageDir, "manifest.go"),
			Content: content,
			Mode:    0o644,
		},
	}

	written := make([]string, 0, len(files))
	for _, file := range files {
		target := filepath.Join(normalized.ProjectDir, file.Path)
		if normalized.Check {
			current, err := os.ReadFile(target)
			if err != nil {
				if errors.Is(err, os.ErrNotExist) {
					return Result{}, fmt.Errorf("%w: %s", ErrGeneratedFilesOutdated, file.Path)
				}
				return Result{}, fmt.Errorf("read generated file %q: %w", target, err)
			}
			if !bytes.Equal(current, []byte(file.Content)) {
				return Result{}, fmt.Errorf("%w: %s", ErrGeneratedFilesOutdated, file.Path)
			}
			written = append(written, file.Path)
			continue
		}

		if err := writeGeneratedFile(target, file.Content, file.Mode); err != nil {
			return Result{}, err
		}
		written = append(written, file.Path)
	}

	sort.Strings(written)
	return Result{
		Root:  normalized.ProjectDir,
		Files: written,
	}, nil
}

type normalizedOptions struct {
	ProjectDir   string
	ManifestPath string
	PackageDir   string
	PackageName  string
	Check        bool
}

type generatedFile struct {
	Path    string
	Content string
	Mode    os.FileMode
}

func normalizeOptions(options Options) (normalizedOptions, error) {
	manifestPath := strings.TrimSpace(options.ManifestPath)
	projectDir := strings.TrimSpace(options.ProjectDir)

	if manifestPath == "" {
		baseDir := projectDir
		if baseDir == "" {
			wd, err := os.Getwd()
			if err != nil {
				return normalizedOptions{}, fmt.Errorf("resolve working directory: %w", err)
			}
			baseDir = wd
		}
		manifestPath = filepath.Join(baseDir, manifest.DefaultFile)
	} else if !filepath.IsAbs(manifestPath) {
		baseDir := projectDir
		if baseDir == "" {
			wd, err := os.Getwd()
			if err != nil {
				return normalizedOptions{}, fmt.Errorf("resolve working directory: %w", err)
			}
			baseDir = wd
		}
		manifestPath = filepath.Join(baseDir, manifestPath)
	}

	resolvedManifest, err := filepath.Abs(manifestPath)
	if err != nil {
		return normalizedOptions{}, fmt.Errorf("resolve manifest path %q: %w", manifestPath, err)
	}

	if projectDir == "" {
		projectDir = filepath.Dir(resolvedManifest)
	}
	resolvedProjectDir, err := filepath.Abs(projectDir)
	if err != nil {
		return normalizedOptions{}, fmt.Errorf("resolve project dir %q: %w", projectDir, err)
	}

	packageDir := filepath.Clean(strings.TrimSpace(options.PackageDir))
	if packageDir == "." || packageDir == "" {
		packageDir = "mcpgen"
	}
	if filepath.IsAbs(packageDir) || packageDir == ".." || strings.HasPrefix(packageDir, ".."+string(filepath.Separator)) {
		return normalizedOptions{}, fmt.Errorf("package dir %q must be relative to the project", options.PackageDir)
	}

	packageName := strings.TrimSpace(options.PackageName)
	if packageName == "" {
		packageName = filepath.Base(packageDir)
	}
	if !token.IsIdentifier(packageName) {
		return normalizedOptions{}, fmt.Errorf("package name %q is not a valid Go identifier", packageName)
	}

	return normalizedOptions{
		ProjectDir:   resolvedProjectDir,
		ManifestPath: resolvedManifest,
		PackageDir:   packageDir,
		PackageName:  packageName,
		Check:        options.Check,
	}, nil
}

func renderManifestLoader(packageName, manifestContent string) (string, error) {
	source := fmt.Sprintf(`// Code generated by mcp-framework generate. DO NOT EDIT.

package %s

import fwmanifest "gitea.lclr.dev/AI/mcp-framework/manifest"

const embeddedManifest = %s

func LoadManifest(startDir string) (fwmanifest.File, string, error) {
	return fwmanifest.LoadDefaultOrEmbedded(startDir, embeddedManifest)
}
`, packageName, strconv.Quote(manifestContent))

	formatted, err := format.Source([]byte(source))
	if err != nil {
		return "", fmt.Errorf("format generated manifest loader: %w", err)
	}

	return string(formatted), nil
}

func writeGeneratedFile(path, content string, mode os.FileMode) error {
	current, err := os.ReadFile(path)
	if err == nil && bytes.Equal(current, []byte(content)) {
		return nil
	}
	if err != nil && !errors.Is(err, os.ErrNotExist) {
		return fmt.Errorf("read generated file %q: %w", path, err)
	}

	dir := filepath.Dir(path)
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return fmt.Errorf("create generated directory %q: %w", dir, err)
	}

	if mode == 0 {
		mode = 0o644
	}
	if err := os.WriteFile(path, []byte(content), mode); err != nil {
		return fmt.Errorf("write generated file %q: %w", path, err)
	}

	return nil
}