package engine

import (
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"time"

	"github.com/h2non/filetype"

	"github.com/alexandrev/homeflow/internal/config"
	"github.com/alexandrev/homeflow/internal/state"
)

// ActionContext is passed to each action in the pipeline.
// Actions that rename or move the file must update CurrentPath.
type ActionContext struct {
	CurrentPath  string
	OriginalPath string
	RuleName     string
	Vars         map[string]string // pre-computed template variables
	Services     map[string]config.ServiceConfig
	State        *state.DB
}

// RenderTemplate replaces {key} and {key:format} placeholders.
// Supported keys: filename, stem, ext, hash8, size_kb, seq, date, mtime.
func RenderTemplate(tmpl string, ctx *ActionContext) string {
	var sb strings.Builder
	i := 0
	for i < len(tmpl) {
		if tmpl[i] == '{' {
			j := strings.Index(tmpl[i:], "}")
			if j == -1 {
				sb.WriteByte(tmpl[i])
				i++
				continue
			}
			token := tmpl[i+1 : i+j]
			i += j + 1
			sb.WriteString(resolveToken(token, ctx))
		} else {
			sb.WriteByte(tmpl[i])
			i++
		}
	}
	return sb.String()
}

func resolveToken(token string, ctx *ActionContext) string {
	key, format, hasFormat := strings.Cut(token, ":")

	switch key {
	case "filename":
		return filepath.Base(ctx.CurrentPath)
	case "stem":
		base := filepath.Base(ctx.CurrentPath)
		ext := filepath.Ext(base)
		return strings.TrimSuffix(base, ext)
	case "ext":
		return filepath.Ext(ctx.CurrentPath)
	case "hash8":
		if h, ok := ctx.Vars["hash8"]; ok {
			return h
		}
		return ""
	case "size_kb":
		if s, ok := ctx.Vars["size_kb"]; ok {
			return s
		}
		return "0"
	case "seq":
		if s, ok := ctx.Vars["seq"]; ok {
			return s
		}
		return "0"
	case "date":
		if hasFormat {
			return time.Now().Format(format)
		}
		return time.Now().Format("2006-01-02")
	case "mtime":
		if ts, ok := ctx.Vars["mtime"]; ok {
			if hasFormat {
				t, err := time.Parse(time.RFC3339, ts)
				if err == nil {
					return t.Format(format)
				}
			}
			return ts
		}
		return ""
	}

	// fall back to Vars map
	if v, ok := ctx.Vars[key]; ok {
		return v
	}
	return "{" + token + "}"
}

// MatchFile checks if a file matches a rule's conditions.
func MatchFile(path string, rule *config.RuleConfig) (bool, error) {
	info, err := os.Stat(path)
	if err != nil {
		return false, err
	}
	m := &rule.Match

	// Extension check
	if len(m.Extensions) > 0 {
		ext := strings.ToLower(filepath.Ext(path))
		found := false
		for _, e := range m.Extensions {
			if strings.ToLower(e) == ext {
				found = true
				break
			}
		}
		if !found {
			return false, nil
		}
	}

	// Name pattern (glob)
	if m.NamePattern != "" {
		matched, err := filepath.Match(m.NamePattern, filepath.Base(path))
		if err != nil {
			return false, fmt.Errorf("invalid name_pattern: %w", err)
		}
		if !matched {
			return false, nil
		}
	}

	// Name regex
	if m.NameRegex != "" {
		re, err := regexp.Compile(m.NameRegex)
		if err != nil {
			return false, fmt.Errorf("invalid name_regex: %w", err)
		}
		if !re.MatchString(filepath.Base(path)) {
			return false, nil
		}
	}

	// Size checks
	sizeKB := info.Size() / 1024
	if m.MinSizeKB > 0 && sizeKB < m.MinSizeKB {
		return false, nil
	}
	if m.MaxSizeKB > 0 && sizeKB > m.MaxSizeKB {
		return false, nil
	}

	// Age checks
	ageSecs := int64(time.Since(info.ModTime()).Seconds())
	if m.AgeSecsMin > 0 && ageSecs < m.AgeSecsMin {
		return false, nil
	}
	if m.AgeSecsMax > 0 && ageSecs > m.AgeSecsMax {
		return false, nil
	}

	// MIME type check (uses magic bytes — relatively expensive, do last)
	if len(m.MimeTypes) > 0 {
		mime, err := detectMIME(path)
		if err != nil {
			return false, err
		}
		found := false
		for _, mt := range m.MimeTypes {
			if strings.EqualFold(mt, mime) {
				found = true
				break
			}
		}
		if !found {
			return false, nil
		}
	}

	return true, nil
}

func detectMIME(path string) (string, error) {
	f, err := os.Open(path)
	if err != nil {
		return "", err
	}
	defer f.Close()

	buf := make([]byte, 261)
	n, err := f.Read(buf)
	if err != nil && err != io.EOF {
		return "", err
	}
	kind, _ := filetype.Match(buf[:n])
	if kind == filetype.Unknown {
		return "application/octet-stream", nil
	}
	return kind.MIME.Value, nil
}

// BuildContext creates an ActionContext for a matched file + rule.
func BuildContext(path string, rule *config.RuleConfig, services map[string]config.ServiceConfig, st *state.DB) (*ActionContext, error) {
	info, err := os.Stat(path)
	if err != nil {
		return nil, err
	}

	vars := map[string]string{
		"mtime":   info.ModTime().UTC().Format(time.RFC3339),
		"size_kb": strconv.FormatInt(info.Size()/1024, 10),
	}

	// Compute hash8 lazily by doing it once here
	if h, err := fileHash8(path); err == nil {
		vars["hash8"] = h
	}

	// Get seq for this rule
	var seqStr string
	if st != nil {
		if seq, err := st.NextSeq(rule.Name); err == nil {
			seqStr = strconv.FormatInt(seq, 10)
		}
	}
	vars["seq"] = seqStr

	return &ActionContext{
		CurrentPath:  path,
		OriginalPath: path,
		RuleName:     rule.Name,
		Vars:         vars,
		Services:     services,
		State:        st,
	}, nil
}

func fileHash8(path string) (string, error) {
	f, err := os.Open(path)
	if err != nil {
		return "", err
	}
	defer f.Close()
	h := sha256.New()
	if _, err := io.Copy(h, f); err != nil {
		return "", err
	}
	return hex.EncodeToString(h.Sum(nil))[:8], nil
}

// FileSHA256 returns the full hex SHA256 of a file (used for dedup in state).
func FileSHA256(path string) (string, error) {
	f, err := os.Open(path)
	if err != nil {
		return "", err
	}
	defer f.Close()
	h := sha256.New()
	if _, err := io.Copy(h, f); err != nil {
		return "", err
	}
	return hex.EncodeToString(h.Sum(nil)), nil
}