// Package config loads the non-secret, local installation descriptor used by thothctl.
package config

import (
	"crypto/sha256"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"

	"gopkg.in/yaml.v3"
)

const installationFileName = "thothii-installation.yaml"

type descriptor struct {
	Profile          string   `yaml:"profile"`
	ProjectDirectory string   `yaml:"projectDirectory"`
	EnvFile          string   `yaml:"envFile"`
	Overrides        []string `yaml:"overrides"`
}

// Installation is a validated local Compose installation. It intentionally contains paths, not
// environment values or secret content.
type Installation struct {
	Path             string
	Profile          string
	ProjectDirectory string
	EnvFile          string
	Overrides        []string
}

// Load reads and validates an installation descriptor at an absolute path.
func Load(path string) (Installation, error) {
	if !filepath.IsAbs(path) {
		return Installation{}, fmt.Errorf("installation path must be absolute")
	}
	path = filepath.Clean(path)
	if filepath.Base(path) != installationFileName {
		return Installation{}, fmt.Errorf("installation file must be named %s", installationFileName)
	}
	if err := requireRegularFile(path, "installation file"); err != nil {
		return Installation{}, err
	}

	file, err := os.Open(path)
	if err != nil {
		return Installation{}, fmt.Errorf("open installation file: %w", err)
	}
	defer file.Close()

	var raw descriptor
	decoder := yaml.NewDecoder(file)
	decoder.KnownFields(true)
	if err := decoder.Decode(&raw); err != nil {
		return Installation{}, fmt.Errorf("read installation file: %w", err)
	}
	if err := ensureOnlyOneDocument(decoder); err != nil {
		return Installation{}, err
	}

	if raw.Profile != "local" && raw.Profile != "server" {
		return Installation{}, fmt.Errorf("profile must be local or server")
	}
	if err := requireDirectory(raw.ProjectDirectory, "projectDirectory"); err != nil {
		return Installation{}, err
	}
	if err := requireRegularFile(raw.EnvFile, "envFile"); err != nil {
		return Installation{}, err
	}

	installation := Installation{
		Path:             path,
		Profile:          raw.Profile,
		ProjectDirectory: filepath.Clean(raw.ProjectDirectory),
		EnvFile:          filepath.Clean(raw.EnvFile),
		Overrides:        make([]string, 0, len(raw.Overrides)),
	}
	for _, override := range raw.Overrides {
		if err := requireRegularFile(override, "override"); err != nil {
			return Installation{}, err
		}
		installation.Overrides = append(installation.Overrides, filepath.Clean(override))
	}
	for _, composeFile := range installation.ComposeFiles()[:2] {
		if err := requireRegularFile(composeFile, "Compose file"); err != nil {
			return Installation{}, err
		}
	}
	return installation, nil
}

// ComposeFiles returns the base file, selected profile file, and declared optional overrides in
// the exact order Compose applies them.
func (i Installation) ComposeFiles() []string {
	files := []string{
		filepath.Join(i.ProjectDirectory, "compose.yaml"),
		filepath.Join(i.ProjectDirectory, "deploy", "compose."+i.Profile+".yaml"),
	}
	return append(files, i.Overrides...)
}

// ProjectName is stable for one installation and avoids collisions between different checkouts.
func (i Installation) ProjectName() string {
	sum := sha256.Sum256([]byte(i.Path))
	return fmt.Sprintf("thothii-%x", sum[:6])
}

// ComposeArgs builds Docker Compose arguments without shell quoting or interpolation.
func (i Installation) ComposeArgs(command ...string) []string {
	args := []string{"compose", "--project-name", i.ProjectName(), "--project-directory", i.ProjectDirectory, "--env-file", i.EnvFile}
	for _, composeFile := range i.ComposeFiles() {
		args = append(args, "-f", composeFile)
	}
	return append(args, command...)
}

func ensureOnlyOneDocument(decoder *yaml.Decoder) error {
	var extra any
	err := decoder.Decode(&extra)
	if errors.Is(err, io.EOF) {
		return nil
	}
	if err != nil {
		return fmt.Errorf("read installation file: %w", err)
	}
	return fmt.Errorf("installation file must contain one YAML document")
}

func requireDirectory(path, field string) error {
	if !filepath.IsAbs(path) {
		return fmt.Errorf("%s must be an absolute path", field)
	}
	info, err := os.Stat(path)
	if err != nil {
		return fmt.Errorf("%s is unavailable: %w", field, err)
	}
	if !info.IsDir() {
		return fmt.Errorf("%s must be a directory", field)
	}
	return nil
}

func requireRegularFile(path, field string) error {
	if !filepath.IsAbs(path) {
		return fmt.Errorf("%s must be an absolute path", field)
	}
	info, err := os.Stat(path)
	if err != nil {
		return fmt.Errorf("%s is unavailable: %w", field, err)
	}
	if !info.Mode().IsRegular() {
		return fmt.Errorf("%s must be a regular file", field)
	}
	return nil
}