package infra

import (
	"crypto/sha256"
	"database/sql"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"regexp"
	"strings"

	_ "github.com/mattn/go-sqlite3"
)

// CopiedCodeEntry represents a function body in an app file that matches
// the normalized body of a registry function. MVP only emits exact_copy.
type CopiedCodeEntry struct {
	AppFile     string  `json:"app_file"`
	AppFunction string  `json:"app_function"`
	RegistryID  string  `json:"registry_id"`
	BodyHash    string  `json:"body_hash"`
	Similarity  float64 `json:"similarity"`
	Kind        string  `json:"kind"` // exact_copy | near_copy | partial_match
}

// AuditCopiedCode walks apps/ and projects/*/apps/, extracts function
// declarations per language, computes a normalized body hash (strip
// comments + collapse whitespace), and matches against fingerprints
// built from registry.db.functions.code.
//
// MVP scope:
//   - Languages: go, py, bash, ts, cpp
//   - Match level: exact_copy only (similarity = 1.0)
//   - Skips paths whose own file_path is the registry function (a function
//     is not a copy of itself).
//
// Returns the list of suspected copies. Does NOT write to any DB.
// Persistence is the caller's responsibility (e.g. call_monitor).
func AuditCopiedCode(registryRoot string) ([]CopiedCodeEntry, error) {
	dbPath := filepath.Join(registryRoot, "registry.db")
	db, err := sql.Open("sqlite3", dbPath+"?_journal_mode=WAL")
	if err != nil {
		return nil, fmt.Errorf("audit_copied_code: open db: %w", err)
	}
	defer db.Close()

	// Build fingerprint index: normalized_hash -> [registry_id ...]
	// and skip-set: file_path -> registry_id (so we don't flag the function
	// as a copy of itself).
	rows, err := db.Query("SELECT id, name, lang, code, file_path FROM functions WHERE code != ''")
	if err != nil {
		return nil, fmt.Errorf("audit_copied_code: query functions: %w", err)
	}
	defer rows.Close()

	fpIndex := map[string][]string{}
	registryFilePaths := map[string]struct{}{}
	for rows.Next() {
		var id, name, lang, code, filePath string
		if err := rows.Scan(&id, &name, &lang, &code, &filePath); err != nil {
			return nil, err
		}
		if filePath != "" {
			registryFilePaths[filePath] = struct{}{}
		}
		// If the `code` column contains a whole module (e.g. Python file
		// with multiple defs), only index the function declaration whose
		// name matches the registry entry. Otherwise (single-fn files
		// like Go), hash the whole body. Both paths yield a single
		// normalized hash mapped to this id.
		decls := extractFunctions(code, lang)
		var fnBody string
		if len(decls) > 1 {
			for _, d := range decls {
				if d.Name == name {
					fnBody = d.Body
					break
				}
			}
		} else if len(decls) == 1 {
			fnBody = decls[0].Body
		} else {
			fnBody = code
		}
		if fnBody == "" {
			continue
		}
		h := normalizedBodyHash(fnBody, lang)
		if h == "" {
			continue
		}
		fpIndex[h] = append(fpIndex[h], id)
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}

	// Walk app trees
	scanDirs := []string{filepath.Join(registryRoot, "apps")}
	if entries, err := os.ReadDir(filepath.Join(registryRoot, "projects")); err == nil {
		for _, p := range entries {
			if !p.IsDir() {
				continue
			}
			scanDirs = append(scanDirs, filepath.Join(registryRoot, "projects", p.Name(), "apps"))
		}
	}

	var out []CopiedCodeEntry
	for _, d := range scanDirs {
		_ = filepath.WalkDir(d, func(path string, dirent fs.DirEntry, err error) error {
			if err != nil {
				return nil
			}
			if dirent.IsDir() {
				if shouldSkipDir(dirent.Name()) {
					return filepath.SkipDir
				}
				return nil
			}
			lang := langFromExt(path)
			if lang == "" {
				return nil
			}
			rel, _ := filepath.Rel(registryRoot, path)
			// Don't audit the registry function file itself
			if _, isRegistry := registryFilePaths[rel]; isRegistry {
				return nil
			}
			data, err := os.ReadFile(path)
			if err != nil {
				return nil
			}
			funcs := extractFunctions(string(data), lang)
			for _, fn := range funcs {
				h := normalizedBodyHash(fn.Body, lang)
				if h == "" {
					continue
				}
				if matches, ok := fpIndex[h]; ok {
					for _, rid := range matches {
						out = append(out, CopiedCodeEntry{
							AppFile:     rel,
							AppFunction: fn.Name,
							RegistryID:  rid,
							BodyHash:    h,
							Similarity:  1.0,
							Kind:        "exact_copy",
						})
					}
				}
			}
			return nil
		})
	}
	return out, nil
}

// ---- Helpers (unexported) ----

func shouldSkipDir(name string) bool {
	switch name {
	case ".git", ".venv", "node_modules", "__pycache__", "build", "dist", "vendor", ".pytest_cache", ".cache", "_vendored":
		return true
	}
	return false
}

func langFromExt(path string) string {
	switch strings.ToLower(filepath.Ext(path)) {
	case ".go":
		return "go"
	case ".py":
		return "py"
	case ".sh":
		return "bash"
	case ".ts", ".tsx":
		return "ts"
	case ".cpp", ".cc", ".cxx":
		return "cpp"
	}
	return ""
}

func normalizedBodyHash(code, lang string) string {
	norm := stripCommentsAndWhitespace(code, lang)
	if len(norm) < 20 {
		// Skip trivial bodies: too short to be meaningful match.
		return ""
	}
	h := sha256.Sum256([]byte(norm))
	return fmt.Sprintf("%x", h)[:16]
}

func stripCommentsAndWhitespace(s, lang string) string {
	switch lang {
	case "go", "ts", "cpp":
		s = stripCStyleComments(s)
	case "py":
		s = stripPythonDocstrings(s)
		s = stripHashComments(s)
	case "bash":
		s = stripHashComments(s)
	}
	return collapseWhitespace(s)
}

var (
	reCStyleSingle = regexp.MustCompile(`//[^\n]*`)
	reCStyleMulti  = regexp.MustCompile(`(?s)/\*.*?\*/`)
	reHashLine     = regexp.MustCompile(`(?m)#.*$`)
	reTripleQuote  = regexp.MustCompile(`(?s)"""[\s\S]*?"""|'''[\s\S]*?'''`)
	reWS           = regexp.MustCompile(`\s+`)
)

func stripCStyleComments(s string) string {
	s = reCStyleMulti.ReplaceAllString(s, " ")
	s = reCStyleSingle.ReplaceAllString(s, " ")
	return s
}

func stripHashComments(s string) string {
	return reHashLine.ReplaceAllString(s, "")
}

func stripPythonDocstrings(s string) string {
	return reTripleQuote.ReplaceAllString(s, " ")
}

func collapseWhitespace(s string) string {
	return strings.TrimSpace(reWS.ReplaceAllString(s, " "))
}

type fnDecl struct {
	Name string
	Body string
}

// extractFunctions extracts function declarations from source.
// MVP: regex-based, naive brace matching. Misses nested closures, methods
// with complex receivers, multi-line signatures with embedded {.
func extractFunctions(src, lang string) []fnDecl {
	switch lang {
	case "go":
		return extractBracedFunctions(src, regexp.MustCompile(`(?m)^func\s+(?:\([^)]*\)\s+)?(\w+)\s*\(`))
	case "bash":
		return extractBracedFunctions(src, regexp.MustCompile(`(?m)^(\w[\w_]*)\s*\(\s*\)\s*\{`))
	case "ts":
		return extractBracedFunctions(src, regexp.MustCompile(`(?m)(?:export\s+)?(?:async\s+)?function\s+(\w+)\s*\(`))
	case "cpp":
		return extractBracedFunctions(src, regexp.MustCompile(`(?m)^[\w:][\w:\s\*&<>,]*\s+(\w+)\s*\([^)]*\)\s*(?:const\s*)?(?:noexcept\s*)?\{`))
	case "py":
		return extractPythonFunctions(src)
	}
	return nil
}

// extractBracedFunctions matches a name via regex, then finds the body by
// scanning to the next '{' and balancing braces. Crude: ignores strings,
// comments, and char literals — false positives possible on weird code.
func extractBracedFunctions(src string, re *regexp.Regexp) []fnDecl {
	var out []fnDecl
	matches := re.FindAllStringSubmatchIndex(src, -1)
	for _, m := range matches {
		name := src[m[2]:m[3]]
		// Find first '{' after match end
		start := -1
		for i := m[1]; i < len(src); i++ {
			if src[i] == '{' {
				start = i
				break
			}
			// Bail out if newline-newline encountered (not a function with body)
			if i+1 < len(src) && src[i] == '\n' && src[i+1] == '\n' {
				break
			}
		}
		if start == -1 {
			continue
		}
		depth := 0
		end := -1
		for i := start; i < len(src); i++ {
			switch src[i] {
			case '{':
				depth++
			case '}':
				depth--
				if depth == 0 {
					end = i + 1
				}
			}
			if end != -1 {
				break
			}
		}
		if end == -1 {
			continue
		}
		out = append(out, fnDecl{Name: name, Body: src[start:end]})
	}
	return out
}

// extractPythonFunctions uses indentation: def name(...): ... until dedent.
func extractPythonFunctions(src string) []fnDecl {
	var out []fnDecl
	lines := strings.Split(src, "\n")
	re := regexp.MustCompile(`^(\s*)def\s+(\w+)\s*\(`)
	for i, line := range lines {
		m := re.FindStringSubmatch(line)
		if m == nil {
			continue
		}
		defIndent := len(m[1])
		name := m[2]
		bodyLines := []string{line}
		for j := i + 1; j < len(lines); j++ {
			l := lines[j]
			if strings.TrimSpace(l) == "" {
				bodyLines = append(bodyLines, l)
				continue
			}
			indent := 0
			for _, c := range l {
				if c == ' ' || c == '\t' {
					indent++
				} else {
					break
				}
			}
			if indent <= defIndent {
				break
			}
			bodyLines = append(bodyLines, l)
		}
		out = append(out, fnDecl{Name: name, Body: strings.Join(bodyLines, "\n")})
	}
	return out
}