// Package cmd provides CLI commands for the gt tool.
package cmd

import (
	"context"
	"encoding/json"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/steveyegge/gastown/internal/state"
)

// MinBeadsVersion is the minimum required beads version for Gas Town.
// This version must include custom type support (bd-i54l).
const MinBeadsVersion = "0.44.0"

// beadsVersion represents a parsed semantic version.
type beadsVersion struct {
	major int
	minor int
	patch int
}

// parseBeadsVersion parses a version string like "0.44.0" into components.
func parseBeadsVersion(v string) (beadsVersion, error) {
	// Strip leading 'v' if present
	v = strings.TrimPrefix(v, "v")

	// Split on dots
	parts := strings.Split(v, ".")
	if len(parts) < 2 {
		return beadsVersion{}, fmt.Errorf("invalid version format: %s", v)
	}

	major, err := strconv.Atoi(parts[0])
	if err != nil {
		return beadsVersion{}, fmt.Errorf("invalid major version: %s", parts[0])
	}

	minor, err := strconv.Atoi(parts[1])
	if err != nil {
		return beadsVersion{}, fmt.Errorf("invalid minor version: %s", parts[1])
	}

	patch := 0
	if len(parts) >= 3 {
		// Handle versions like "0.44.0-dev" - take only numeric prefix
		patchStr := parts[2]
		if idx := strings.IndexFunc(patchStr, func(r rune) bool {
			return r < '0' || r > '9'
		}); idx != -1 {
			patchStr = patchStr[:idx]
		}
		if patchStr != "" {
			patch, err = strconv.Atoi(patchStr)
			if err != nil {
				return beadsVersion{}, fmt.Errorf("invalid patch version: %s", parts[2])
			}
		}
	}

	return beadsVersion{major: major, minor: minor, patch: patch}, nil
}

// compare returns -1 if v < other, 0 if equal, 1 if v > other.
func (v beadsVersion) compare(other beadsVersion) int {
	if v.major != other.major {
		if v.major < other.major {
			return -1
		}
		return 1
	}
	if v.minor != other.minor {
		if v.minor < other.minor {
			return -1
		}
		return 1
	}
	if v.patch != other.patch {
		if v.patch < other.patch {
			return -1
		}
		return 1
	}
	return 0
}

// Pre-compiled regex for beads version parsing
var beadsVersionRe = regexp.MustCompile(`bd version (\d+\.\d+(?:\.\d+)?(?:-\w+)?)`)

// versionCacheTTL is how long a cached version check remains valid.
// 24 hours is reasonable since version upgrades are infrequent.
const versionCacheTTL = 24 * time.Hour

// versionCache stores the result of a beads version check.
type versionCache struct {
	Version   string    `json:"version"`
	CheckedAt time.Time `json:"checked_at"`
	Valid     bool      `json:"valid"` // true if version meets minimum requirement
}

// versionCachePath returns the path to the version cache file.
func versionCachePath() string {
	return filepath.Join(state.CacheDir(), "beads-version.json")
}

// loadVersionCache reads the cached version check result.
func loadVersionCache() (*versionCache, error) {
	data, err := os.ReadFile(versionCachePath())
	if err != nil {
		return nil, err
	}
	var cache versionCache
	if err := json.Unmarshal(data, &cache); err != nil {
		return nil, err
	}
	return &cache, nil
}

// saveVersionCache writes the version check result to cache.
func saveVersionCache(c *versionCache) error {
	dir := state.CacheDir()
	if err := os.MkdirAll(dir, 0755); err != nil {
		return err
	}
	data, err := json.MarshalIndent(c, "", "  ")
	if err != nil {
		return err
	}
	// Atomic write via temp file
	tmp := versionCachePath() + ".tmp"
	if err := os.WriteFile(tmp, data, 0600); err != nil {
		return err
	}
	return os.Rename(tmp, versionCachePath())
}

// isCacheFresh returns true if the cache is within the TTL.
func (c *versionCache) isCacheFresh() bool {
	return time.Since(c.CheckedAt) < versionCacheTTL
}

func getBeadsVersion() (string, error) {
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()

	cmd := exec.CommandContext(ctx, "bd", "version")
	output, err := cmd.Output()
	if err != nil {
		if ctx.Err() == context.DeadlineExceeded {
			return "", fmt.Errorf("bd version check timed out")
		}
		if exitErr, ok := err.(*exec.ExitError); ok {
			return "", fmt.Errorf("bd version failed: %s", string(exitErr.Stderr))
		}
		return "", fmt.Errorf("failed to run bd: %w (is beads installed?)", err)
	}

	// Parse output like "bd version 0.44.0 (dev)"
	// or "bd version 0.44.0"
	matches := beadsVersionRe.FindStringSubmatch(string(output))
	if len(matches) < 2 {
		return "", fmt.Errorf("could not parse beads version from: %s", strings.TrimSpace(string(output)))
	}

	return matches[1], nil
}

var (
	cachedVersionCheckResult error
	versionCheckOnce         sync.Once
)

// CheckBeadsVersion verifies that the installed beads version meets the minimum requirement.
// Returns nil if the version is sufficient, or an error with details if not.
// The check is performed only once per process execution.
func CheckBeadsVersion() error {
	versionCheckOnce.Do(func() {
		cachedVersionCheckResult = checkBeadsVersionInternal()
	})
	return cachedVersionCheckResult
}

func checkBeadsVersionInternal() error {
	// Try to use cached result first to avoid subprocess spawning
	if cache, err := loadVersionCache(); err == nil && cache.isCacheFresh() {
		if cache.Valid {
			return nil // Cached successful check
		}
		// Cached failure - still need to check (version might have been upgraded)
	}

	installedStr, err := getBeadsVersion()
	if err != nil {
		// On timeout, try to use stale cache or gracefully degrade
		if strings.Contains(err.Error(), "timed out") {
			if cache, cacheErr := loadVersionCache(); cacheErr == nil && cache.Valid {
				// Use stale cache but warn
				fmt.Fprintf(os.Stderr, "Warning: bd version check timed out, using cached result (v%s)\n", cache.Version)
				return nil
			}
			// No cache available - gracefully degrade with warning
			fmt.Fprintf(os.Stderr, "Warning: bd version check timed out (high system load?), proceeding anyway\n")
			return nil
		}
		return fmt.Errorf("cannot verify beads version: %w", err)
	}

	installed, err := parseBeadsVersion(installedStr)
	if err != nil {
		return fmt.Errorf("cannot parse installed beads version %q: %w", installedStr, err)
	}

	required, err := parseBeadsVersion(MinBeadsVersion)
	if err != nil {
		// This would be a bug in our code
		return fmt.Errorf("cannot parse required beads version %q: %w", MinBeadsVersion, err)
	}

	valid := installed.compare(required) >= 0

	// Cache the result
	_ = saveVersionCache(&versionCache{
		Version:   installedStr,
		CheckedAt: time.Now(),
		Valid:     valid,
	})

	if !valid {
		return fmt.Errorf("beads version %s is required, but %s is installed\n\nPlease upgrade beads: go install github.com/steveyegge/beads/cmd/bd@latest", MinBeadsVersion, installedStr)
	}

	return nil
}