// Package project finds a ThothII source checkout from a directory within it.
package project

import (
	"errors"
	"fmt"
	"os"
	"path/filepath"
)

// Root identifies one ThothII checkout. Path is resolved for stable identity across symlinks.
type Root struct {
	Path       string
	IsWorktree bool
}

// Discover walks from start towards the filesystem root until it finds the ThothII source-layout
// contract. A regular .git file identifies a linked Git worktree; a .git directory identifies a
// main checkout.
func Discover(start string) (Root, error) {
	if start == "" {
		return Root{}, errors.New("ThothII project root could not be discovered from an empty directory")
	}
	abs, err := filepath.Abs(start)
	if err != nil {
		return Root{}, errors.New("ThothII project root could not resolve the current directory")
	}
	resolved, err := filepath.EvalSymlinks(abs)
	if err != nil {
		return Root{}, fmt.Errorf("ThothII project root could not resolve %s", filepath.Clean(abs))
	}
	info, err := os.Stat(resolved)
	if err != nil || !info.IsDir() {
		return Root{}, fmt.Errorf("ThothII project root could not read %s", filepath.Clean(abs))
	}

	for directory := filepath.Clean(resolved); ; directory = filepath.Dir(directory) {
		if isRoot(directory) {
			return Root{Path: directory, IsWorktree: isLinkedWorktree(directory)}, nil
		}
		parent := filepath.Dir(directory)
		if parent == directory {
			break
		}
	}
	return Root{}, fmt.Errorf("ThothII project root not found from %s", filepath.Clean(abs))
}

func isRoot(directory string) bool {
	if !isGitMarker(filepath.Join(directory, ".git")) || !isRegularFile(filepath.Join(directory, "compose.yaml")) || !isDirectory(filepath.Join(directory, "deploy")) {
		return false
	}
	for _, name := range []string{"backend", "frontend", "harness", "tools"} {
		if !isDirectory(filepath.Join(directory, name)) {
			return false
		}
	}
	return true
}

func isLinkedWorktree(directory string) bool {
	info, err := os.Lstat(filepath.Join(directory, ".git"))
	return err == nil && info.Mode().IsRegular()
}

func isGitMarker(path string) bool {
	info, err := os.Lstat(path)
	return err == nil && (info.IsDir() || info.Mode().IsRegular())
}

func isRegularFile(path string) bool {
	info, err := os.Stat(path)
	return err == nil && info.Mode().IsRegular()
}

func isDirectory(path string) bool {
	info, err := os.Stat(path)
	return err == nil && info.IsDir()
}