scpt/ast.go

/*
	Copyright (c) 2021 Arsen Musayelyan

	Permission is hereby granted, free of charge, to any person obtaining a copy
	of this software and associated documentation files (the "Software"), to deal
	in the Software without restriction, including without limitation the rights
	to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	copies of the Software, and to permit persons to whom the Software is
	furnished to do so, subject to the following conditions:

	The above copyright notice and this permission notice shall be included in all
	copies or substantial portions of the Software.
*/

package scpt

import (
	"errors"
	"fmt"
	"github.com/alecthomas/participle/lexer"
)

// AST stores the root of the Abstract Syntax Tree for scpt
type AST struct {
	Pos      lexer.Position
	Commands []*Command `@@*`
}

// Execute traverses the AST and executes any commands, it returns an error
// containing the position at which the error was encountered and the error
// itself
func (ast *AST) Execute() error {
	// For each command in AST
	for _, cmd := range ast.Commands {
		// Execute current command
		err := executeCmd(cmd)
		if err != nil {
			return err
		}
	}
	return nil
}

// Parse and execute command
func executeCmd(cmd *Command) error {
	// If parsing variables
	if cmd.Vars != nil {
		// For each variable
		for _, Var := range cmd.Vars {
			// Parse value of variable
			val, err := ParseValue(Var.Value)
			if err != nil {
				return fmt.Errorf("%s: %s", Var.Value.Pos, err)
			}
			// If value of variable is a function call
			if IsFuncCall(val) {
				// Assert type of val as *FuncCall
				Call := val.(*FuncCall)
				// Set variable value to function return value
				Vars[Var.Key], err = CallFunction(Call)
				if err != nil {
					return fmt.Errorf("%s: %s", Var.Value.Pos, err)
				}
			} else {
				// If value is not a function call, set variable value to parsed value
				Vars[Var.Key] = val
			}
		}
	} else if cmd.Calls != nil {
		// For each function call
		for _, Call := range cmd.Calls {
			// Attempt to call function
			_, err := CallFunction(Call)
			if err != nil {
				return fmt.Errorf("%s: %s", Call.Pos, err)
			}
		}
	} else if cmd.Ifs != nil {
		// For each if statement
		for _, If := range cmd.Ifs {
			// Get condition value
			condVal, err := callIfFunc(ParseValue(If.Condition))
			if err != nil {
				return fmt.Errorf("%s: %s", If.Condition.Pos, err)
			}
			// Attempt to assert condition type as bool
			condBool, ok := condVal.(bool)
			if !ok {
				return errors.New("condition must be a boolean")
			}
			// If condition is true
			if condBool {
				// For each inner command
				for _, InnerCmd := range If.InnerCmds {
					// Execute command recursively
					err := executeCmd(InnerCmd)
					if err != nil {
						return fmt.Errorf("%s: %s", InnerCmd.Pos, err)
					}
				}
			}
		}
	} else if cmd.RptLoops != nil {
		// For each repeat loop
		for _, RptLoop := range cmd.RptLoops {
			for i:=0;i<*RptLoop.Times;i++ {
				if RptLoop.IndexVar != nil {
					Vars[*RptLoop.IndexVar] = i
				}
				for _, InnerCmd := range RptLoop.InnerCmds {
					// Execute command recursively
					err := executeCmd(InnerCmd)
					if err != nil {
						return fmt.Errorf("%s: %s", InnerCmd.Pos, err)
					}
				}
			}
			delete(Vars, *RptLoop.IndexVar)
		}
	}
	return nil
}

// Command stores any commands encountered while parsing a script
type Command struct {
	Pos    lexer.Position
	Tokens []lexer.Token
	Vars   []*Var      `( @@`
	Ifs    []*If       `| @@`
	RptLoops []*RptLoop`| @@`
	Calls  []*FuncCall `| @@)`
}

// If stores any if statements encountered while parsing a script
type If struct {
	Pos       lexer.Position
	Condition *Value     `"if" @@ "{"`
	InnerCmds []*Command `@@* "}"`
}

type RptLoop struct {
	Pos       lexer.Position
	Times     *int     `"repeat" @Number "times" "{"`
	IndexVar *string `(@Ident "in")?`
	InnerCmds []*Command `@@* "}"`
}

// FuncCall stores any function calls encountered while parsing a script
type FuncCall struct {
	Pos  lexer.Position
	Name string `@Ident @("-" Ident)*`
	Args []*Arg `@@*`
}

// Arg stores arguments for function calls
type Arg struct {
	Pos   lexer.Position
	Key   string `("with" @Ident)?`
	Value *Value `@@`
}

// Var stores any variables encountered while parsing a script
type Var struct {
	Pos   lexer.Position
	Key   string `"set" @Ident "to"`
	Value *Value `@@`
}

// Value stores any literal values encountered while parsing a script
type Value struct {
	Pos    lexer.Position
	String *string     `  @String`
	Number *float64    `| @Number`
	Bool   *Bool       `| @("true" | "false")`
	SubCmd *FuncCall   `| "(" @@ ")"`
	VarVal *string     `| "$" @Ident`
	Expr   *Expression `| "{" @@ "}"`
}

// Bool stores boolean values encountered while parsing a script.
// It is required for the Capture method
type Bool bool

// Capture parses a boolean literal encountered in the script into
// a Go boolean value
func (b *Bool) Capture(values []string) error {
	// Convert string to boolean
	*b = values[0] == "true"
	return nil
}

// Expression stores any expressions encountered while parsing a
// script for later evaluation
type Expression struct {
	Pos       lexer.Position
	Left      *Value          `@@`
	RightSegs []*ExprRightSeg `@@*`
}

// ExprRightSeg stores segments of the right side of an expression
type ExprRightSeg struct {
	Op    string `@Operator`
	Right *Value `@@`
}