package pgsql

import (
	"fmt"
	"regexp"
	"strings"
	"unicode"
)

// TemplateFunctions returns a map of custom template functions
func TemplateFunctions() map[string]interface{} {
	return map[string]interface{}{
		// String manipulation
		"upper":      strings.ToUpper,
		"lower":      strings.ToLower,
		"snake_case": toSnakeCase,
		"camelCase":  toCamelCase,

		// SQL formatting
		"indent":          indent,
		"quote":           quote,
		"escape":          escape,
		"safe_identifier": safeIdentifier,

		// Type conversion
		"goTypeToSQL": goTypeToSQL,
		"sqlTypeToGo": sqlTypeToGo,
		"isNumeric":   isNumeric,
		"isText":      isText,

		// Collection helpers
		"first":     first,
		"last":      last,
		"filter":    filter,
		"mapFunc":   mapFunc,
		"join_with": joinWith,

		// Built-in Go template function (for convenience)
		"join": strings.Join,
	}
}

// String manipulation functions

// toSnakeCase converts a string to snake_case
func toSnakeCase(s string) string {
	// Insert underscore before uppercase letters
	var result strings.Builder
	for i, r := range s {
		if unicode.IsUpper(r) {
			if i > 0 {
				result.WriteRune('_')
			}
			result.WriteRune(unicode.ToLower(r))
		} else {
			result.WriteRune(r)
		}
	}
	return result.String()
}

// toCamelCase converts a string to camelCase
func toCamelCase(s string) string {
	// Split by underscore
	parts := strings.Split(s, "_")
	if len(parts) == 0 {
		return s
	}

	// First part stays lowercase
	result := strings.ToLower(parts[0])

	// Capitalize first letter of remaining parts
	for _, part := range parts[1:] {
		if len(part) > 0 {
			result += strings.ToUpper(part[0:1]) + strings.ToLower(part[1:])
		}
	}

	return result
}

// SQL formatting functions

// indent indents each line of text by the specified number of spaces
func indent(spaces int, text string) string {
	prefix := strings.Repeat(" ", spaces)
	lines := strings.Split(text, "\n")
	for i, line := range lines {
		if line != "" {
			lines[i] = prefix + line
		}
	}
	return strings.Join(lines, "\n")
}

// quote quotes a string value for SQL (escapes single quotes)
func quote(s string) string {
	return "'" + strings.ReplaceAll(s, "'", "''") + "'"
}

// escape escapes a string for SQL (escapes single quotes and backslashes)
func escape(s string) string {
	s = strings.ReplaceAll(s, "\\", "\\\\")
	s = strings.ReplaceAll(s, "'", "''")
	return s
}

// safeIdentifier makes a string safe to use as a SQL identifier
func safeIdentifier(s string) string {
	// Remove or replace dangerous characters
	// Allow: letters, numbers, underscore
	reg := regexp.MustCompile(`[^a-zA-Z0-9_]`)
	safe := reg.ReplaceAllString(s, "_")

	// Ensure it doesn't start with a number
	if len(safe) > 0 && unicode.IsDigit(rune(safe[0])) {
		safe = "_" + safe
	}

	// Convert to lowercase (PostgreSQL convention)
	return strings.ToLower(safe)
}

// Type conversion functions

// goTypeToSQL converts Go type to PostgreSQL type
func goTypeToSQL(goType string) string {
	typeMap := map[string]string{
		"string":    "text",
		"int":       "integer",
		"int32":     "integer",
		"int64":     "bigint",
		"float32":   "real",
		"float64":   "double precision",
		"bool":      "boolean",
		"time.Time": "timestamp",
		"[]byte":    "bytea",
	}

	if sqlType, ok := typeMap[goType]; ok {
		return sqlType
	}
	return "text" // Default
}

// sqlTypeToGo converts PostgreSQL type to Go type
func sqlTypeToGo(sqlType string) string {
	sqlType = strings.ToLower(sqlType)

	typeMap := map[string]string{
		"text":             "string",
		"varchar":          "string",
		"char":             "string",
		"integer":          "int",
		"int":              "int",
		"bigint":           "int64",
		"smallint":         "int16",
		"serial":           "int",
		"bigserial":        "int64",
		"real":             "float32",
		"double precision": "float64",
		"numeric":          "float64",
		"decimal":          "float64",
		"boolean":          "bool",
		"timestamp":        "time.Time",
		"timestamptz":      "time.Time",
		"date":             "time.Time",
		"time":             "time.Time",
		"bytea":            "[]byte",
		"json":             "json.RawMessage",
		"jsonb":            "json.RawMessage",
		"uuid":             "string",
	}

	if goType, ok := typeMap[sqlType]; ok {
		return goType
	}
	return "string" // Default
}

// isNumeric checks if a SQL type is numeric
func isNumeric(sqlType string) bool {
	sqlType = strings.ToLower(sqlType)
	numericTypes := []string{
		"integer", "int", "bigint", "smallint", "serial", "bigserial",
		"real", "double precision", "numeric", "decimal", "float",
	}
	for _, t := range numericTypes {
		if strings.Contains(sqlType, t) {
			return true
		}
	}
	return false
}

// isText checks if a SQL type is text-based
func isText(sqlType string) bool {
	sqlType = strings.ToLower(sqlType)
	textTypes := []string{
		"text", "varchar", "char", "character", "string",
	}
	for _, t := range textTypes {
		if strings.Contains(sqlType, t) {
			return true
		}
	}
	return false
}

// Collection helper functions

// first returns the first element of a slice, or nil if empty
func first(slice interface{}) interface{} {
	switch v := slice.(type) {
	case []string:
		if len(v) > 0 {
			return v[0]
		}
	case []int:
		if len(v) > 0 {
			return v[0]
		}
	case []interface{}:
		if len(v) > 0 {
			return v[0]
		}
	}
	return nil
}

// last returns the last element of a slice, or nil if empty
func last(slice interface{}) interface{} {
	switch v := slice.(type) {
	case []string:
		if len(v) > 0 {
			return v[len(v)-1]
		}
	case []int:
		if len(v) > 0 {
			return v[len(v)-1]
		}
	case []interface{}:
		if len(v) > 0 {
			return v[len(v)-1]
		}
	}
	return nil
}

// filter filters a slice based on a predicate (simplified version)
// Usage in template: {{filter .Columns "NotNull"}}
func filter(slice interface{}, fieldName string) interface{} {
	// This is a simplified implementation
	// In templates, you'd use: {{range $col := .Columns}}{{if $col.NotNull}}...{{end}}{{end}}
	// This function is mainly for documentation purposes
	return slice
}

// mapFunc maps a function over a slice (simplified version)
// Usage in template: {{range .Columns}}{{mapFunc .Name "upper"}}{{end}}
func mapFunc(value interface{}, funcName string) interface{} {
	// This is a simplified implementation
	// In templates, you'd directly call: {{upper .Name}}
	// This function is mainly for documentation purposes
	return value
}

// joinWith joins a slice of strings with a separator
func joinWith(slice []string, separator string) string {
	return strings.Join(slice, separator)
}

// Additional helper functions

// formatType formats a SQL type with length/precision
func formatType(baseType string, length, precision int) string {
	if length > 0 && precision > 0 {
		return fmt.Sprintf("%s(%d,%d)", baseType, length, precision)
	}
	if length > 0 {
		return fmt.Sprintf("%s(%d)", baseType, length)
	}
	return baseType
}