package build

import (
	"bytes"
	"context"
	"crypto/rand"
	"encoding/base64"
	"errors"
	"fmt"
	"go/token"
	"io"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"runtime"
	"strings"
)

// appNameRe is the public `summer new <name>` rule: lower-case letters and
// digits, starting with a letter. The name is also the second part of the
// starter plugin ID golem15.<name>.
var appNameRe = regexp.MustCompile(`^[a-z][a-z0-9]*$`)

// NewOptions configures NewApp.
type NewOptions struct {
	// Name is the application name; the app is written to sm-<Name>-app.
	Name string
	// Parent is the directory that receives sm-<Name>-app. Empty means the
	// current directory.
	Parent string
	// Framework is the path to the framework checkout, resolved against
	// Parent when relative. Empty means auto-detection: a sibling
	// summercms or summercms.go checkout, then the source tree this binary
	// was built from.
	Framework string
	// NoPlugin skips the starter plugin; summer.yaml then lists no plugins.
	NoPlugin bool
	// AppKey is written to .env as SUMMER_APP__KEY. It must be the base64
	// (standard encoding) of 32 bytes; the CLI passes lagoon.GenerateAppKey.
	AppKey string
	// AdminSecret is written to .env as SUMMER_ADMIN__JWT__SECRET, the HMAC
	// secret of admin tokens (admin.jwt.secret). Empty means NewApp
	// generates the base64 of 32 crypto/rand bytes.
	AdminSecret string
	// NoGit skips git init and the first commit.
	NoGit bool
}

// Local development database written to compose.yaml and .env. The port is
// not 5432 so it does not clash with a PostgreSQL already on the host, and
// it is published on the loopback address only.
const (
	devDBUser     = "summer"
	devDBPassword = "summer"
	devDBHostPort = "127.0.0.1:54320"
)

// Fallback identity for the first commit when git has none configured.
const (
	fallbackGitName  = "SummerCMS"
	fallbackGitEmail = "summer@localhost"
)

// frameworkSiblings are the directory names auto-detection tries next to
// the new application. A candidate counts only when its go.mod declares the
// framework module.
var frameworkSiblings = []string{"summercms", "summercms.go"}

// frameworkFromBinary returns the framework checkout this binary was built
// from, or "" when unknown. Tests replace it.
var frameworkFromBinary = binarySourceFramework

// genFile is one file NewApp writes itself, relative to the app root. A
// non-empty Link makes it a symlink to Link (relative to the file) instead.
type genFile struct {
	Rel  string
	Body []byte
	Mode os.FileMode
	Link string
}

// newData feeds the new/* templates.
type newData struct {
	Name        string
	Module      string
	Framework   string
	GoVersion   string
	Toolchain   string
	Replace     string
	DSN         string
	AppKey      string
	AdminSecret string
	NoPlugin    bool
}

// ValidateAppName reports whether name is usable as `summer new <name>`.
func ValidateAppName(name string) error {
	if !appNameRe.MatchString(name) {
		return fmt.Errorf("build: app name %q must be lower-case letters and digits, starting with a letter", name)
	}
	if token.IsKeyword(name) {
		return fmt.Errorf("build: app name %q is a Go keyword; the starter plugin package would not compile", name)
	}
	switch name {
	case "main":
		return fmt.Errorf("build: app name %q is reserved: plugins/main would be a program, not an importable package", name)
	case "internal":
		return fmt.Errorf("build: app name %q is reserved: Go forbids importing plugins/internal from the app", name)
	}
	return nil
}

// appModulePath is the module path of a generated application.
func appModulePath(name string) string {
	return "git.golem15.com/golem15/sm-" + name + "-app"
}

// appDirName is the directory a generated application lives in.
func appDirName(name string) string {
	return "sm-" + name + "-app"
}

// NewApp writes a ready-to-run application to <Parent>/sm-<Name>-app and
// returns its path. It refuses a target that exists in any form.
func NewApp(ctx context.Context, opts NewOptions, out io.Writer) (string, error) {
	if out == nil {
		out = io.Discard
	}
	if err := ValidateAppName(opts.Name); err != nil {
		return "", err
	}
	if err := validateAppKey(opts.AppKey); err != nil {
		return "", err
	}
	if opts.AdminSecret == "" {
		secret, err := generateAdminSecret()
		if err != nil {
			return "", fmt.Errorf("build: generate admin secret: %w", err)
		}
		opts.AdminSecret = secret
	}
	if err := validateAdminSecret(opts.AdminSecret); err != nil {
		return "", err
	}
	parent := opts.Parent
	if parent == "" {
		parent = "."
	}
	parent, err := filepath.Abs(parent)
	if err != nil {
		return "", fmt.Errorf("build: resolve parent directory: %w", err)
	}
	if st, err := os.Stat(parent); err != nil {
		return "", fmt.Errorf("build: parent directory: %w", err)
	} else if !st.IsDir() {
		return "", fmt.Errorf("build: parent %s is not a directory", parent)
	}
	target := filepath.Join(parent, appDirName(opts.Name))
	if _, err := os.Lstat(target); err == nil {
		return "", fmt.Errorf("build: %s already exists; choose another name or remove it", target)
	} else if !errors.Is(err, os.ErrNotExist) {
		return "", fmt.Errorf("build: stat %s: %w", target, err)
	}
	framework, err := resolveFramework(parent, opts.Framework)
	if err != nil {
		return "", err
	}
	if underRoot(framework, target) {
		return "", fmt.Errorf("build: %s is inside the framework checkout %s; run summer new in the directory next to the checkout", target, framework)
	}

	files, err := planNewApp(opts, target, framework)
	if err != nil {
		return "", err
	}
	if err := os.Mkdir(target, 0o755); err != nil {
		return "", fmt.Errorf("build: create %s: %w", target, err)
	}
	// target did not exist before this run, so a failure removes it and a
	// re-run with the same name is not blocked.
	if err := populateApp(ctx, opts, target, files); err != nil {
		if rmErr := os.RemoveAll(target); rmErr != nil {
			return "", fmt.Errorf("build: create %s: %w (removing it failed: %v)", target, err, rmErr)
		}
		return "", fmt.Errorf("build: create %s (removed it): %w", target, err)
	}
	if !opts.NoGit {
		initGit(ctx, target, opts.Name, out)
	}
	fmt.Fprintf(out, "created %s\n", target)
	next, err := renderStub("new/next-steps", newData{Name: opts.Name, NoPlugin: opts.NoPlugin})
	if err != nil {
		return target, err
	}
	_, _ = out.Write(next)
	return target, nil
}

// validateAppKey requires the base64 (standard encoding) of 32 bytes, the
// form lagoon accepts for app.key.
func validateAppKey(key string) error {
	raw, err := base64.StdEncoding.DecodeString(key)
	if key == "" || err != nil || len(raw) != 32 {
		return fmt.Errorf("build: application key must be the base64 of 32 bytes")
	}
	return nil
}

// adminSecretRe is the character set an admin secret may use: it is written
// unquoted into .env, whose reader trims whitespace and strips quotes.
var adminSecretRe = regexp.MustCompile(`^[A-Za-z0-9+/=_-]{32,}$`)

// generateAdminSecret returns the base64 (standard encoding) of 32
// crypto/rand bytes.
func generateAdminSecret() (string, error) {
	raw := make([]byte, 32)
	if _, err := rand.Read(raw); err != nil {
		return "", err
	}
	return base64.StdEncoding.EncodeToString(raw), nil
}

// validateAdminSecret requires at least 32 characters that are safe to
// write unquoted into .env.
func validateAdminSecret(s string) error {
	if !adminSecretRe.MatchString(s) {
		return fmt.Errorf("build: admin secret must be at least 32 characters of letters, digits, +, /, =, _ or -")
	}
	return nil
}

// devDSN is the .env database DSN matching compose.yaml.
func devDSN(name string) string {
	return "postgres://" + devDBUser + ":" + devDBPassword + "@" + devDBHostPort + "/" + name + "?sslmode=disable"
}

// initGit creates the repository with one commit on main. Every failure is a
// warning: the application is usable without git.
func initGit(ctx context.Context, dir, name string, out io.Writer) {
	if _, err := exec.LookPath("git"); err != nil {
		fmt.Fprintf(out, "warning: git not found on PATH; skipped git init\n")
		return
	}
	if res, err := runGit(ctx, dir, "init", "--quiet", "--initial-branch=main"); err != nil {
		fmt.Fprintf(out, "warning: git init failed, the app has no repository: %v\n%s", err, res)
		return
	}
	if res, err := runGit(ctx, dir, "add", "-A"); err != nil {
		fmt.Fprintf(out, "warning: git add failed, nothing committed: %v\n%s", err, res)
		return
	}
	var args []string
	var missing []string
	if gitIdentityMissing(ctx, dir, "user.name", "GIT_AUTHOR_NAME", "GIT_COMMITTER_NAME") {
		args = append(args, "-c", "user.name="+fallbackGitName)
		missing = append(missing, "user.name")
	}
	if gitIdentityMissing(ctx, dir, "user.email", "GIT_AUTHOR_EMAIL", "GIT_COMMITTER_EMAIL") {
		args = append(args, "-c", "user.email="+fallbackGitEmail)
		missing = append(missing, "user.email")
	}
	if len(missing) > 0 {
		fmt.Fprintf(out, "warning: git %s not configured; the first commit uses %s <%s>\n",
			strings.Join(missing, " and "), fallbackGitName, fallbackGitEmail)
	}
	args = append(args, "commit", "--quiet", "-m", "Create "+appDirName(name)+" with summer new")
	if res, err := runGit(ctx, dir, args...); err != nil {
		fmt.Fprintf(out, "warning: git commit failed; the files are staged but not committed: %v\n%s", err, res)
	}
}

// gitIdentityMissing reports whether key is unset in git config and none of
// the environment variables that supply it are set.
func gitIdentityMissing(ctx context.Context, dir, key string, envs ...string) bool {
	for _, e := range envs {
		if os.Getenv(e) != "" {
			return false
		}
	}
	res, err := runGit(ctx, dir, "config", key)
	return err != nil || len(bytes.TrimSpace(res)) == 0
}

// runGit runs git in dir with stdin closed and terminal prompts disabled.
func runGit(ctx context.Context, dir string, args ...string) ([]byte, error) {
	cmd := exec.CommandContext(ctx, "git", args...)
	cmd.Dir = dir
	cmd.Stdin = nil
	cmd.Env = append(os.Environ(), "GIT_TERMINAL_PROMPT=0")
	return cmd.CombinedOutput()
}

// resolveFramework picks the framework checkout: the explicit flag (never
// falling through when it is wrong), then a sibling of parent whose go.mod
// declares the framework module, then the source tree of this binary. Paths
// stay lexical so a symlinked sibling yields a ../<sibling> replace.
func resolveFramework(parent, flag string) (string, error) {
	if flag != "" {
		dir := flag
		if !filepath.IsAbs(dir) {
			dir = filepath.Join(parent, dir)
		}
		dir = filepath.Clean(dir)
		if err := checkFramework(dir); err != nil {
			return "", fmt.Errorf("build: --framework %s: %w", flag, err)
		}
		return dir, nil
	}
	for _, name := range frameworkSiblings {
		dir := filepath.Join(parent, name)
		if checkFramework(dir) == nil {
			return dir, nil
		}
	}
	if dir := frameworkFromBinary(); dir != "" && checkFramework(dir) == nil {
		return dir, nil
	}
	return "", fmt.Errorf("build: no framework checkout found: looked for %s next to %s; pass --framework <path>",
		strings.Join(frameworkSiblings, " and "), parent)
}

// binarySourceFramework returns the repository root this file was compiled
// from. A -trimpath build records a module-relative path, which is ignored.
func binarySourceFramework() string {
	_, file, _, ok := runtime.Caller(0)
	if !ok || !filepath.IsAbs(file) {
		return ""
	}
	// file is <root>/internal/build/new.go.
	root := filepath.Dir(filepath.Dir(filepath.Dir(file)))
	if checkFramework(root) != nil {
		return ""
	}
	return root
}

// checkFramework requires dir/go.mod to declare the framework module.
func checkFramework(dir string) error {
	module, _, err := parseGoMod(filepath.Join(dir, "go.mod"))
	if err != nil {
		return fmt.Errorf("framework checkout %s: %w", dir, err)
	}
	if module != frameworkModule {
		return fmt.Errorf("%s declares module %q, not the framework %s", dir, module, frameworkModule)
	}
	return nil
}

// planNewApp renders every file NewApp writes from its own templates. It
// reads nothing but the framework go.mod, so the output can be compared
// byte for byte.
func planNewApp(opts NewOptions, target, framework string) ([]genFile, error) {
	if err := ValidateAppName(opts.Name); err != nil {
		return nil, err
	}
	if err := validateAppKey(opts.AppKey); err != nil {
		return nil, err
	}
	if err := validateAdminSecret(opts.AdminSecret); err != nil {
		return nil, err
	}
	if err := checkFramework(framework); err != nil {
		return nil, fmt.Errorf("build: %w", err)
	}
	replace, err := relModulePath(target, framework)
	if err != nil {
		return nil, fmt.Errorf("build: framework replace: %w", err)
	}
	data := newData{
		Name:        opts.Name,
		Module:      appModulePath(opts.Name),
		Framework:   frameworkModule,
		GoVersion:   goVersionLine,
		Toolchain:   toolchainLine,
		Replace:     replace,
		DSN:         devDSN(opts.Name),
		AppKey:      opts.AppKey,
		AdminSecret: opts.AdminSecret,
		NoPlugin:    opts.NoPlugin,
	}
	plan := []struct {
		rel  string
		tmpl string
		mode os.FileMode
	}{
		{"go.mod", "new/go.mod", 0o644},
		{"config/app.yaml", "new/config/app.yaml", 0o644},
		{"config/database.yaml", "new/config/database.yaml", 0o644},
		{"config/http.yaml", "new/config/http.yaml", 0o644},
		{"config/storage.yaml", "new/config/storage.yaml", 0o644},
		{".env", "new/env", 0o600},
		{".env.example", "new/env.example", 0o644},
		{"compose.yaml", "new/compose.yaml", 0o644},
		{".gitignore", "new/gitignore", 0o644},
		{"CLAUDE.md", "new/CLAUDE.md", 0o644},
	}
	files := make([]genFile, 0, len(plan))
	for _, p := range plan {
		body, err := renderStub(p.tmpl, data)
		if err != nil {
			return nil, err
		}
		files = append(files, genFile{Rel: p.rel, Body: body, Mode: p.mode})
	}
	// One source for agent instructions; a relative symlink survives git
	// clone on Linux and macOS.
	files = append(files, genFile{Rel: "AGENTS.md", Link: "CLAUDE.md"})
	return files, nil
}

// populateApp writes the planned files, the workspace, the manifest and the
// starter plugin into target, then generates main.go and plugins.gen.go.
func populateApp(ctx context.Context, opts NewOptions, target string, files []genFile) error {
	for _, f := range files {
		path := filepath.Join(target, filepath.FromSlash(f.Rel))
		if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
			return fmt.Errorf("build: mkdir %s: %w", filepath.Dir(path), err)
		}
		if f.Link != "" {
			if err := os.Symlink(f.Link, path); err != nil {
				return fmt.Errorf("build: symlink %s: %w", path, err)
			}
			continue
		}
		if err := os.WriteFile(path, f.Body, f.Mode); err != nil {
			return fmt.Errorf("build: write %s: %w", path, err)
		}
		// WriteFile honours the umask; set the mode exactly (.env is 0600).
		if err := os.Chmod(path, f.Mode); err != nil {
			return fmt.Errorf("build: chmod %s: %w", path, err)
		}
	}
	// The app's own go.work comes before the plugin step so a go.work in an
	// ancestor directory is never picked up.
	if err := writeGoWork(filepath.Join(target, "go.work")); err != nil {
		return err
	}
	manifestPath := filepath.Join(target, manifestName)
	if err := SaveManifest(manifestPath, Manifest{Module: appModulePath(opts.Name), Binary: opts.Name}); err != nil {
		return err
	}
	if !opts.NoPlugin {
		if err := addStarterPlugin(ctx, opts.Name, target); err != nil {
			return err
		}
	}
	m, err := LoadManifest(manifestPath)
	if err != nil {
		return err
	}
	return generate(target, m)
}

// addStarterPlugin creates golem15.<name> through the make:plugin and
// plugin:add code paths, with the starter route.
func addStarterPlugin(ctx context.Context, name, target string) error {
	if _, err := makePlugin(ctx, target, "golem15."+name, pluginOptions{StarterRoute: true}); err != nil {
		return err
	}
	return AddPlugin(ctx, target, filepath.Join("plugins", name))
}