package pp

import (
	"github.com/d5/tengo/v2"
	"github.com/d5/tengo/v2/stdlib"
	"context"
	"strings"
	"fmt"
)

type Preprocessor struct {
	// The string will be inserted in the
	// beginning of processed files.
	head string

	tags [2]string
	modules *tengo.ModuleMap
}

// Evaluate the expression and return the value
// it would print.
func (pp *Preprocessor) Eval(data string) (string, error) {
	const retHead = `
		printf := func(format, ...vals) {
			__ret__ += __Sprintf(format, vals...)
		}
	`
	script := tengo.NewScript([]byte(retHead + pp.head + "\n" + data))
	err := script.Add("__Sprintf", &tengo.UserFunction{
			Value: func(args ...tengo.Object) (tengo.Object, error){
				if len(args) < 1 {
					return nil, tengo.ErrWrongNumArguments
				}
				format, ok := tengo.ToString(args[0])
				if !ok {
					return nil, tengo.ErrInvalidArgumentType{
						Expected: "string",
					}
				}
				gargs := make([]any, len(args) - 1)
				for i := range gargs {
					gargs[i] = tengo.ToInterface(args[i+1])
					//fmt.Printf("shit: %q\n", gargs[i])
				}
				str := fmt.Sprintf(format, gargs...)
				return tengo.FromInterface(str)
			},
		},
	)
	if err != nil {
		return "", err
	}
	err = script.Add("__ret__", "")
	if err != nil{ 
		return "", err
	}
	compiled, err := script.RunContext(context.Background())
	if err != nil {
		return "", err
	}

	return compiled.Get("__ret__").String(), nil
}

// Get the new preprocessor with default options.
func NewPp() *Preprocessor {
	pp := &Preprocessor{
		tags: [2]string{
			"<?tengo",
			"?>",
		},
		modules: stdlib.GetModuleMap(stdlib.AllModuleNames()...)
	}
	return pp
}

func (pp *Preprocessor) Process(data string) (string, error) {
	var b strings.Builder
	last := 0
	for {
		idxStart := strings.Index(data[last:], pp.tags[0])
		idxEnd := strings.Index(data[last:], pp.tags[1])
		//fmt.Printf("cock %d %d %d\n", last, idxStart, idxEnd)
		if idxStart < 0 {
			if idxEnd >= 0 {
				return "", UnexpectedError{
					What: "end tag",
				}
			}
			fmt.Fprint(&b, data[last:])
			break
		} else if idxEnd < 0 {
			return "", UnexpectedError{
				What: "start tag",
			}
		}
		fmt.Fprint(&b, data[last:idxStart])
		code := data[idxStart+len(pp.tags[0]):idxEnd]
		str, err := pp.Eval(code)
		if err != nil {
			return "", err
		}
		fmt.Fprint(&b, str)
		data = data[idxEnd + len(pp.tags[1])+1:]
	}

	return b.String(), nil
}