package releaseprep

import (
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"strings"
)

var versionPattern = regexp.MustCompile(`const String = "[^"]+"`)

func Prepare(rootDir, version, releaseDate string) error {
	normalizedVersion := strings.TrimPrefix(strings.TrimSpace(version), "v")
	if normalizedVersion == "" {
		return fmt.Errorf("version must not be empty")
	}

	releaseDate = strings.TrimSpace(releaseDate)
	if releaseDate == "" {
		return fmt.Errorf("release date must not be empty")
	}

	if err := updateVersionFile(rootDir, normalizedVersion); err != nil {
		return err
	}

	if err := updateChangelog(rootDir, normalizedVersion, releaseDate); err != nil {
		return err
	}

	return nil
}

func updateVersionFile(rootDir, version string) error {
	path := filepath.Join(rootDir, "internal", "homesick", "version", "version.go")
	contents, err := os.ReadFile(path)
	if err != nil {
		return fmt.Errorf("read version file: %w", err)
	}

	updated := versionPattern.ReplaceAllString(string(contents), fmt.Sprintf(`const String = %q`, version))
	if updated == string(contents) {
		return fmt.Errorf("version constant not found in %s", path)
	}

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

	return nil
}

func updateChangelog(rootDir, version, releaseDate string) error {
	path := filepath.Join(rootDir, "changelog.md")
	contents, err := os.ReadFile(path)
	if err != nil {
		return fmt.Errorf("read changelog: %w", err)
	}

	text := string(contents)
	unreleasedHeader := "## [Unreleased]\n"
	start := strings.Index(text, unreleasedHeader)
	if start == -1 {
		return fmt.Errorf("unreleased section not found in changelog")
	}

	afterHeader := start + len(unreleasedHeader)
	nextSectionRelative := strings.Index(text[afterHeader:], "\n## [")
	if nextSectionRelative == -1 {
		nextSectionRelative = len(text[afterHeader:])
	}
	nextSectionStart := afterHeader + nextSectionRelative
	unreleasedBody := strings.TrimLeft(text[afterHeader:nextSectionStart], "\n")

	newSection := fmt.Sprintf("## [%s] - %s\n", version, releaseDate)
	if strings.TrimSpace(unreleasedBody) != "" {
		newSection += "\n" + unreleasedBody
		if !strings.HasSuffix(newSection, "\n") {
			newSection += "\n"
		}
	}

	updated := text[:afterHeader] + "\n" + newSection + text[nextSectionStart:]
	if err := os.WriteFile(path, []byte(updated), 0o644); err != nil {
		return fmt.Errorf("write changelog: %w", err)
	}

	return nil
}