Dragon-Knight/internal/template/template.go

package template

import (
	"fmt"
	"maps"
	"os"
	"path/filepath"
	"reflect"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/valyala/fasthttp"
)

// Cache is the global singleton instance
var Cache *TemplateCache

type TemplateCache struct {
	mu        sync.RWMutex
	templates map[string]*Template
	basePath  string
}

type Template struct {
	name     string
	content  string
	modTime  time.Time
	filePath string
	cache    *TemplateCache
}

func NewCache(basePath string) *TemplateCache {
	if basePath == "" {
		exe, err := os.Executable()
		if err != nil {
			basePath = "."
		} else {
			basePath = filepath.Dir(exe)
		}
	}

	return &TemplateCache{
		templates: make(map[string]*Template),
		basePath:  basePath,
	}
}

// InitializeCache initializes the global Cache singleton
func InitializeCache(basePath string) {
	Cache = NewCache(basePath)
}

func (c *TemplateCache) Load(name string) (*Template, error) {
	c.mu.RLock()
	tmpl, exists := c.templates[name]
	c.mu.RUnlock()

	if exists {
		if err := c.checkAndReload(tmpl); err != nil {
			return nil, err
		}
		return tmpl, nil
	}

	return c.loadFromFile(name)
}

func (c *TemplateCache) loadFromFile(name string) (*Template, error) {
	filePath := filepath.Join(c.basePath, "templates", name)

	info, err := os.Stat(filePath)
	if err != nil {
		return nil, fmt.Errorf("template file not found: %s", name)
	}

	content, err := os.ReadFile(filePath)
	if err != nil {
		return nil, fmt.Errorf("failed to read template: %w", err)
	}

	tmpl := &Template{
		name:     name,
		content:  string(content),
		modTime:  info.ModTime(),
		filePath: filePath,
		cache:    c,
	}

	c.mu.Lock()
	c.templates[name] = tmpl
	c.mu.Unlock()

	return tmpl, nil
}

func (c *TemplateCache) checkAndReload(tmpl *Template) error {
	info, err := os.Stat(tmpl.filePath)
	if err != nil {
		return err
	}

	if info.ModTime().After(tmpl.modTime) {
		content, err := os.ReadFile(tmpl.filePath)
		if err != nil {
			return err
		}

		c.mu.Lock()
		tmpl.content = string(content)
		tmpl.modTime = info.ModTime()
		c.mu.Unlock()
	}

	return nil
}

func (t *Template) RenderPositional(args ...any) string {
	result := t.content
	for i, arg := range args {
		placeholder := fmt.Sprintf("{%d}", i)
		result = strings.ReplaceAll(result, placeholder, fmt.Sprintf("%v", arg))
	}
	result = t.processIncludes(result, nil)
	return result
}

func (t *Template) RenderNamed(data map[string]any) string {
	result := t.content

	// Process blocks first to extract them
	blocks := make(map[string]string)
	result = t.processBlocks(result, blocks)

	// Process includes
	result = t.processIncludes(result, data)

	// Process loops and conditionals
	result = t.processLoops(result, data)
	result = t.processConditionals(result, data)

	// Process yield with conditionals in blocks
	result = t.processYield(result, blocks, data)

	// Apply data substitutions
	for key, value := range data {
		placeholder := fmt.Sprintf("{%s}", key)
		result = strings.ReplaceAll(result, placeholder, fmt.Sprintf("%v", value))
	}

	result = t.replaceDotNotation(result, data)

	return result
}

func (t *Template) replaceDotNotation(content string, data map[string]any) string {
	result := content

	start := 0
	for {
		startIdx := strings.Index(result[start:], "{")
		if startIdx == -1 {
			break
		}
		startIdx += start

		endIdx := strings.Index(result[startIdx:], "}")
		if endIdx == -1 {
			break
		}
		endIdx += startIdx

		placeholder := result[startIdx+1 : endIdx]

		if strings.Contains(placeholder, ".") {
			value := t.getNestedValue(data, placeholder)
			if value != nil {
				result = result[:startIdx] + fmt.Sprintf("%v", value) + result[endIdx+1:]
				start = startIdx + len(fmt.Sprintf("%v", value))
				continue
			}
		}

		start = endIdx + 1
	}

	return result
}

func (t *Template) getNestedValue(data map[string]any, path string) any {
	keys := strings.Split(path, ".")
	var current any = data

	for i, key := range keys {
		if i == len(keys)-1 {
			// Final key - handle both maps and structs
			switch v := current.(type) {
			case map[string]any:
				return v[key]
			default:
				return t.getStructField(current, key)
			}
		}

		// Intermediate key - get the next value
		var next any
		switch v := current.(type) {
		case map[string]any:
			var ok bool
			next, ok = v[key]
			if !ok {
				return nil
			}
		default:
			next = t.getStructField(current, key)
			if next == nil {
				return nil
			}
		}

		// Prepare for next iteration
		switch v := next.(type) {
		case map[string]any:
			current = v
		case map[any]any:
			newMap := make(map[string]any)
			for k, val := range v {
				newMap[fmt.Sprintf("%v", k)] = val
			}
			current = newMap
		default:
			rv := reflect.ValueOf(next)
			if rv.Kind() == reflect.Map {
				newMap := make(map[string]any)
				for _, k := range rv.MapKeys() {
					newMap[fmt.Sprintf("%v", k.Interface())] = rv.MapIndex(k).Interface()
				}
				current = newMap
			} else {
				// For structs, keep the struct value for the next iteration
				current = next
			}
		}
	}

	return nil
}

// getStructField gets a field value from a struct using reflection
func (t *Template) getStructField(obj any, fieldName string) any {
	if obj == nil {
		return nil
	}

	rv := reflect.ValueOf(obj)
	if rv.Kind() == reflect.Ptr {
		if rv.IsNil() {
			return nil
		}
		rv = rv.Elem()
	}

	if rv.Kind() != reflect.Struct {
		return nil
	}

	field := rv.FieldByName(fieldName)
	if !field.IsValid() {
		return nil
	}

	return field.Interface()
}

func (t *Template) getLength(value any) int {
	if value == nil {
		return 0
	}

	rv := reflect.ValueOf(value)
	switch rv.Kind() {
	case reflect.Slice, reflect.Array, reflect.Map, reflect.String:
		return rv.Len()
	default:
		return 0
	}
}

func (t *Template) WriteTo(ctx *fasthttp.RequestCtx, data any) {
	var result string

	switch v := data.(type) {
	case map[string]any:
		result = t.RenderNamed(v)
	case []any:
		result = t.RenderPositional(v...)
	default:
		rv := reflect.ValueOf(data)
		if rv.Kind() == reflect.Slice {
			args := make([]any, rv.Len())
			for i := 0; i < rv.Len(); i++ {
				args[i] = rv.Index(i).Interface()
			}
			result = t.RenderPositional(args...)
		} else {
			result = t.RenderPositional(data)
		}
	}

	ctx.SetContentType("text/html; charset=utf-8")
	ctx.WriteString(result)
}

// processIncludes handles {include "template.html"} directives
func (t *Template) processIncludes(content string, data map[string]any) string {
	result := content

	for {
		start := strings.Index(result, "{include ")
		if start == -1 {
			break
		}

		end := strings.Index(result[start:], "}")
		if end == -1 {
			break
		}
		end += start

		directive := result[start+9 : end] // Skip "{include "
		templateName := strings.Trim(directive, "\" ")

		if includedTemplate, err := t.cache.Load(templateName); err == nil {
			var includedContent string
			if data != nil {
				includedContent = includedTemplate.RenderNamed(data)
			} else {
				includedContent = includedTemplate.content
			}
			result = result[:start] + includedContent + result[end+1:]
		} else {
			// Remove the include directive if template not found
			result = result[:start] + result[end+1:]
		}
	}

	return result
}

// processBlocks extracts {block "name"}...{/block} sections
func (t *Template) processBlocks(content string, blocks map[string]string) string {
	result := content

	for {
		start := strings.Index(result, "{block ")
		if start == -1 {
			break
		}

		nameEnd := strings.Index(result[start:], "}")
		if nameEnd == -1 {
			break
		}
		nameEnd += start

		blockName := strings.Trim(result[start+7:nameEnd], "\" ")

		contentStart := nameEnd + 1
		endTag := "{/block}"
		contentEnd := strings.Index(result[contentStart:], endTag)
		if contentEnd == -1 {
			break
		}
		contentEnd += contentStart

		blockContent := result[contentStart:contentEnd]
		blocks[blockName] = blockContent

		// Remove the block definition from the template
		result = result[:start] + result[contentEnd+len(endTag):]
	}

	return result
}

// processYield handles {yield} directives for template inheritance
func (t *Template) processYield(content string, blocks map[string]string, data map[string]any) string {
	result := content

	for blockName, blockContent := range blocks {
		// Process conditionals and loops in block content before yielding
		processedBlock := t.processLoops(blockContent, data)
		processedBlock = t.processConditionals(processedBlock, data)

		yieldPlaceholder := fmt.Sprintf("{yield \"%s\"}", blockName)
		result = strings.ReplaceAll(result, yieldPlaceholder, processedBlock)
	}

	// Replace any remaining {yield} with empty string
	result = strings.ReplaceAll(result, "{yield}", "")

	return result
}

// processLoops handles {for item in items}...{/for} and {for key,value in map}...{/for}
func (t *Template) processLoops(content string, data map[string]any) string {
	result := content

	for {
		start := strings.Index(result, "{for ")
		if start == -1 {
			break
		}

		headerEnd := strings.Index(result[start:], "}")
		if headerEnd == -1 {
			break
		}
		headerEnd += start

		header := result[start+5 : headerEnd] // Skip "{for "

		contentStart := headerEnd + 1
		endTag := "{/for}"
		contentEnd := strings.Index(result[contentStart:], endTag)
		if contentEnd == -1 {
			break
		}
		contentEnd += contentStart

		loopContent := result[contentStart:contentEnd]
		expanded := t.expandLoop(header, loopContent, data)

		result = result[:start] + expanded + result[contentEnd+len(endTag):]
	}

	return result
}

// expandLoop processes a single loop construct
func (t *Template) expandLoop(header, content string, data map[string]any) string {
	parts := strings.Split(strings.TrimSpace(header), " in ")
	if len(parts) != 2 {
		return ""
	}

	varPart := strings.TrimSpace(parts[0])
	sourcePart := strings.TrimSpace(parts[1])

	source := t.getNestedValue(data, sourcePart)
	if source == nil {
		return ""
	}

	var result strings.Builder

	// Handle key,value pairs
	if strings.Contains(varPart, ",") {
		keyVar, valueVar := strings.TrimSpace(varPart[:strings.Index(varPart, ",")]), strings.TrimSpace(varPart[strings.Index(varPart, ",")+1:])

		rv := reflect.ValueOf(source)
		switch rv.Kind() {
		case reflect.Map:
			for _, key := range rv.MapKeys() {
				iterData := make(map[string]any)
				maps.Copy(iterData, data)
				iterData[keyVar] = key.Interface()
				iterData[valueVar] = rv.MapIndex(key).Interface()

				iterResult := content
				iterResult = t.processLoops(iterResult, iterData)
				iterResult = t.processConditionals(iterResult, iterData)
				for k, v := range iterData {
					placeholder := fmt.Sprintf("{%s}", k)
					iterResult = strings.ReplaceAll(iterResult, placeholder, fmt.Sprintf("%v", v))
				}
				iterResult = t.replaceDotNotation(iterResult, iterData)
				result.WriteString(iterResult)
			}
		case reflect.Slice, reflect.Array:
			for i := 0; i < rv.Len(); i++ {
				iterData := make(map[string]any)
				maps.Copy(iterData, data)
				iterData[keyVar] = i
				iterData[valueVar] = rv.Index(i).Interface()

				iterResult := content
				iterResult = t.processLoops(iterResult, iterData)
				iterResult = t.processConditionals(iterResult, iterData)
				for k, v := range iterData {
					placeholder := fmt.Sprintf("{%s}", k)
					iterResult = strings.ReplaceAll(iterResult, placeholder, fmt.Sprintf("%v", v))
				}
				iterResult = t.replaceDotNotation(iterResult, iterData)
				result.WriteString(iterResult)
			}
		}
	} else {
		// Single variable iteration
		rv := reflect.ValueOf(source)
		switch rv.Kind() {
		case reflect.Slice, reflect.Array:
			for i := 0; i < rv.Len(); i++ {
				iterData := make(map[string]any)
				maps.Copy(iterData, data)
				iterData[varPart] = rv.Index(i).Interface()

				iterResult := content
				iterResult = t.processLoops(iterResult, iterData)
				iterResult = t.processConditionals(iterResult, iterData)
				for k, v := range iterData {
					placeholder := fmt.Sprintf("{%s}", k)
					iterResult = strings.ReplaceAll(iterResult, placeholder, fmt.Sprintf("%v", v))
				}
				iterResult = t.replaceDotNotation(iterResult, iterData)
				result.WriteString(iterResult)
			}
		case reflect.Map:
			for _, key := range rv.MapKeys() {
				iterData := make(map[string]any)
				maps.Copy(iterData, data)
				iterData[varPart] = rv.MapIndex(key).Interface()

				iterResult := content
				iterResult = t.processLoops(iterResult, iterData)
				iterResult = t.processConditionals(iterResult, iterData)
				for k, v := range iterData {
					placeholder := fmt.Sprintf("{%s}", k)
					iterResult = strings.ReplaceAll(iterResult, placeholder, fmt.Sprintf("%v", v))
				}
				iterResult = t.replaceDotNotation(iterResult, iterData)
				result.WriteString(iterResult)
			}
		}
	}

	return result.String()
}

// processConditionals handles {if condition}...{/if} and {if condition}...{else}...{/if}
func (t *Template) processConditionals(content string, data map[string]any) string {
	result := content

	for {
		start := strings.Index(result, "{if ")
		if start == -1 {
			break
		}

		headerEnd := strings.Index(result[start:], "}")
		if headerEnd == -1 {
			break
		}
		headerEnd += start

		condition := strings.TrimSpace(result[start+4 : headerEnd]) // Skip "{if "

		contentStart := headerEnd + 1

		// Find matching {/if} by tracking nesting level
		nestLevel := 1
		pos := contentStart
		contentEnd := -1

		for pos < len(result) && nestLevel > 0 {
			ifStart := strings.Index(result[pos:], "{if ")
			endStart := strings.Index(result[pos:], "{/if}")

			if ifStart != -1 && (endStart == -1 || ifStart < endStart) {
				// Found nested {if}
				nestLevel++
				pos += ifStart + 4
			} else if endStart != -1 {
				// Found {/if}
				nestLevel--
				if nestLevel == 0 {
					contentEnd = pos + endStart
					break
				}
				pos += endStart + 5
			} else {
				break
			}
		}

		if contentEnd == -1 {
			break
		}

		ifContent := result[contentStart:contentEnd]

		// Check for else clause at the same nesting level
		elseStart := t.findElseAtLevel(ifContent)
		var trueContent, falseContent string
		if elseStart != -1 {
			trueContent = ifContent[:elseStart]
			falseContent = ifContent[elseStart+6:] // Skip "{else}"
		} else {
			trueContent = ifContent
			falseContent = ""
		}

		var selectedContent string
		if t.evaluateCondition(condition, data) {
			selectedContent = trueContent
		} else {
			selectedContent = falseContent
		}

		// Recursively process the selected content
		selectedContent = t.processLoops(selectedContent, data)
		selectedContent = t.processConditionals(selectedContent, data)

		result = result[:start] + selectedContent + result[contentEnd+5:] // +5 for "{/if}"
	}

	return result
}

// findElseAtLevel finds {else} at the top level (not nested)
func (t *Template) findElseAtLevel(content string) int {
	nestLevel := 0
	pos := 0

	for pos < len(content) {
		ifStart := strings.Index(content[pos:], "{if ")
		elseStart := strings.Index(content[pos:], "{else}")
		endStart := strings.Index(content[pos:], "{/if}")

		// Find the earliest occurrence
		earliest := -1
		var tag string

		if ifStart != -1 && (earliest == -1 || ifStart < earliest-pos) {
			earliest = pos + ifStart
			tag = "if"
		}
		if elseStart != -1 && (earliest == -1 || elseStart < earliest-pos) {
			earliest = pos + elseStart
			tag = "else"
		}
		if endStart != -1 && (earliest == -1 || endStart < earliest-pos) {
			earliest = pos + endStart
			tag = "end"
		}

		if earliest == -1 {
			break
		}

		switch tag {
		case "if":
			nestLevel++
			pos = earliest + 4
		case "else":
			if nestLevel == 0 {
				return earliest
			}
			pos = earliest + 6
		case "end":
			nestLevel--
			pos = earliest + 5
		}
	}

	return -1
}

// evaluateCondition evaluates simple conditions like "user.name", "count > 0", "items"
func (t *Template) evaluateCondition(condition string, data map[string]any) bool {
	condition = strings.TrimSpace(condition)

	// Handle 'and' operator
	if strings.Contains(condition, " and ") {
		parts := strings.SplitSeq(condition, " and ")
		for part := range parts {
			if !t.evaluateCondition(strings.TrimSpace(part), data) {
				return false
			}
		}
		return true
	}

	// Handle comparison operators
	for _, op := range []string{">=", "<=", "!=", "==", ">", "<"} {
		if strings.Contains(condition, op) {
			parts := strings.Split(condition, op)
			if len(parts) == 2 {
				left := strings.TrimSpace(parts[0])
				right := strings.TrimSpace(parts[1])
				return t.compareValues(t.getConditionValue(left, data), t.getConditionValue(right, data), op)
			}
		}
	}

	// Simple existence check
	value := t.getConditionValue(condition, data)
	return t.isTruthy(value)
}

// getConditionValue gets a value for condition evaluation
func (t *Template) getConditionValue(expr string, data map[string]any) any {
	expr = strings.TrimSpace(expr)

	// Handle length operator
	if strings.HasPrefix(expr, "#") {
		varName := expr[1:] // Remove the #
		value := t.getNestedValue(data, varName)
		return t.getLength(value)
	}

	// Try to parse as number
	if num, err := strconv.ParseFloat(expr, 64); err == nil {
		return num
	}

	// Try to parse as string literal
	if strings.HasPrefix(expr, "\"") && strings.HasSuffix(expr, "\"") {
		return expr[1 : len(expr)-1]
	}

	// Try as variable reference
	if strings.Contains(expr, ".") {
		return t.getNestedValue(data, expr)
	}

	if value, ok := data[expr]; ok {
		return value
	}

	return expr
}

// compareValues compares two values with the given operator
func (t *Template) compareValues(left, right any, op string) bool {
	switch op {
	case "==":
		return fmt.Sprintf("%v", left) == fmt.Sprintf("%v", right)
	case "!=":
		return fmt.Sprintf("%v", left) != fmt.Sprintf("%v", right)
	case ">", ">=", "<", "<=":
		leftNum, leftOk := t.toFloat(left)
		rightNum, rightOk := t.toFloat(right)
		if !leftOk || !rightOk {
			return false
		}
		switch op {
		case ">":
			return leftNum > rightNum
		case ">=":
			return leftNum >= rightNum
		case "<":
			return leftNum < rightNum
		case "<=":
			return leftNum <= rightNum
		}
	}
	return false
}

// toFloat converts a value to float64 if possible
func (t *Template) toFloat(value any) (float64, bool) {
	switch v := value.(type) {
	case int:
		return float64(v), true
	case int64:
		return float64(v), true
	case float32:
		return float64(v), true
	case float64:
		return v, true
	case string:
		if f, err := strconv.ParseFloat(v, 64); err == nil {
			return f, true
		}
	}
	return 0, false
}

// isTruthy determines if a value is truthy
func (t *Template) isTruthy(value any) bool {
	if value == nil {
		return false
	}

	switch v := value.(type) {
	case bool:
		return v
	case int:
		return v != 0
	case float64:
		return v != 0
	case string:
		return v != ""
	default:
		rv := reflect.ValueOf(value)
		switch rv.Kind() {
		case reflect.Slice, reflect.Array, reflect.Map:
			return rv.Len() > 0
		case reflect.Ptr:
			return !rv.IsNil()
		}
		return true
	}
}

// RenderToContext is a simplified helper that renders a template and writes it to the request context
// with error handling. Returns true if successful, false if an error occurred (error is written to response).
func RenderToContext(ctx *fasthttp.RequestCtx, templateName string, data map[string]any) bool {
	tmpl, err := Cache.Load(templateName)
	if err != nil {
		ctx.SetStatusCode(fasthttp.StatusInternalServerError)
		fmt.Fprintf(ctx, "Template error: %v", err)
		return false
	}

	tmpl.WriteTo(ctx, data)
	return true
}

// RenderNamed is a simplified helper that loads and renders a template with the given data,
// returning the rendered content or an error.
func RenderNamed(templateName string, data map[string]any) (string, error) {
	tmpl, err := Cache.Load(templateName)
	if err != nil {
		return "", fmt.Errorf("failed to load template %s: %w", templateName, err)
	}

	return tmpl.RenderNamed(data), nil
}