package session

import (
	"crypto/sha256"
	"encoding/hex"
	"path/filepath"
	"runtime"
	"strings"
)

// SessionName returns a stable tmux session name for the given workspace.
// Format: ctask-<category>-<slug>-<hash6>.
//
// category and slug are sanitized to [A-Za-z0-9_-]; characters outside that
// set become '_'; runs of '_' collapse; both are lowercased. slug is
// truncated to 30 characters maximum (after sanitization). hash6 is the
// first six lowercase-hex characters of sha256(canonical absolute path).
//
// On Windows the path is lowercased before hashing to match
// config.searchRootKey conventions for case-insensitive filesystems.
func SessionName(category, slug, absWsPath string) string {
	cat := sanitizeNameComponent(category)
	sl := sanitizeNameComponent(slug)
	if len(sl) > 30 {
		sl = sl[:30]
		sl = strings.TrimRight(sl, "_")
	}
	clean := filepath.Clean(absWsPath)
	if runtime.GOOS == "windows" {
		clean = strings.ToLower(clean)
	}
	sum := sha256.Sum256([]byte(clean))
	hash := hex.EncodeToString(sum[:])[:6]
	return "ctask-" + cat + "-" + sl + "-" + hash
}

// sanitizeNameComponent replaces every char outside [A-Za-z0-9_-] with '_',
// collapses runs of '_', trims leading/trailing '_' and '-', and lowercases.
func sanitizeNameComponent(s string) string {
	if s == "" {
		return "_"
	}
	var b strings.Builder
	b.Grow(len(s))
	for _, r := range s {
		switch {
		case r >= 'a' && r <= 'z':
			b.WriteRune(r)
		case r >= 'A' && r <= 'Z':
			b.WriteRune(r + ('a' - 'A'))
		case r >= '0' && r <= '9':
			b.WriteRune(r)
		case r == '_' || r == '-':
			b.WriteRune(r)
		default:
			b.WriteByte('_')
		}
	}
	out := b.String()
	for strings.Contains(out, "__") {
		out = strings.ReplaceAll(out, "__", "_")
	}
	out = strings.Trim(out, "_-")
	if out == "" {
		return "_"
	}
	return out
}