/*
	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 (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"github.com/alecthomas/participle/lexer"
)

var loopRunning bool
var breakLoop bool
var funcRunning bool
var retValue interface{} = nil

// 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
}

func (ast *AST) Dump() ([]byte, error) {
	return json.Marshal(ast)
}

func (ast *AST) DumpPretty() ([]byte, error) {
	buf := bytes.NewBuffer([]byte{})
	enc := json.NewEncoder(buf)
	enc.SetIndent("", "    ")
	err := enc.Encode(ast)
	if err != nil {
		return buf.Bytes(), err
	}
	return buf.Bytes(), nil
}

func LoadAST(data []byte) (*AST, error) {
	var ast AST
	err := json.Unmarshal(data, &ast)
	if err != nil {
		return nil, err
	}
	return &ast, nil
}

// Execute a variable declaration
func executeVarCmd(Var *Var) error {
	// 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 Var.Index != nil {
		// If variable definition has an associated index, get index value
		index, err := callIfFunc(ParseValue(Var.Index))
		if err != nil {
			return fmt.Errorf("%s: %s", Var.Index.Pos, err)
		}
		// Attempt to get the variable from Vars and assert it as a []interface{}
		slc, ok := Vars[Var.Key].([]interface{})
		// If assertion successful
		if ok {
			// Assert index value as a 64-bit float
			indexInt, ok := index.(float64)
			if !ok {
				return fmt.Errorf("%s: %s", Var.Pos, "variable "+Var.Key+" does not exist or is not an array")
			}
			// Set integer index of interface{} slice to value
			slc[int64(indexInt)] = val
		} else {
			// If slice assertion unsuccessful, attempt to assert as map[interface{}]interface{}
			iMap, ok := Vars[Var.Key].(map[interface{}]interface{})
			if !ok {
				return fmt.Errorf("%s: %s", Var.Pos, "variable "+Var.Key+" does not exist or is not a map")
			}
			// Set index of interface{} to interface{} map to value
			iMap[index] = val
		}
	} else {
		// If value is not a function call, set variable to parsed value
		Vars[Var.Key] = val
	}
	return nil
}

// Execute an if statement
func executeIfCmd(If *If) error {
	// 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)
			}
		}
	}
	return nil
}

// Execute a repeat loop
func executeRptLoop(rptLoop *RptLoop) error {
	// Set loopRunning to true to allow break
	loopRunning = true
	// Run for loop with correct amount of iterations
rpt:
	for i := 0; i < *rptLoop.Times; i++ {
		// If user requested index variable via "{ var in ... }"
		if rptLoop.IndexVar != nil {
			// Set requested variable name to index
			Vars[*rptLoop.IndexVar] = i
		}
		// For each command within the loop
		for _, InnerCmd := range rptLoop.InnerCmds {
			// Execute command recursively
			err := executeCmd(InnerCmd)
			if err != nil {
				return fmt.Errorf("%s: %s", InnerCmd.Pos, err)
			}
			// If breakLoop set to true
			if breakLoop {
				// Reset breakLoop
				breakLoop = false
				break rpt
			}
		}
	}
	// Remove index variable if existent
	delete(Vars, *rptLoop.IndexVar)
	// Reset loopRunning
	loopRunning = false
	return nil
}

// Execute a while loop
func executeWhlLoop(whlLoop *WhlLoop) error {
	loopRunning = true
	// Get condition value
	condVal, err := callIfFunc(ParseValue(whlLoop.Condition))
	if err != nil {
		return fmt.Errorf("%s: %s", whlLoop.Condition.Pos, err)
	}
	// Attempt to assert condition type as bool
	condBool, ok := condVal.(bool)
	if !ok {
		return errors.New("condition must be a boolean")
	}
	// Run for loop if condition is true
whl:
	for condBool {
		// For each inner command
		for _, InnerCmd := range whlLoop.InnerCmds {
			// Execute command recursively
			err := executeCmd(InnerCmd)
			if err != nil {
				return fmt.Errorf("%s: %s", InnerCmd.Pos, err)
			}
			// If breakLoop set to true
			if breakLoop {
				// Reset breakLoop
				breakLoop = false
				break whl
			}
			// Get condition value
			condVal, err = callIfFunc(ParseValue(whlLoop.Condition))
			if err != nil {
				return fmt.Errorf("%s: %s", whlLoop.Condition.Pos, err)
			}
			// Attempt to assert condition type as bool and update its value
			condBool, ok = condVal.(bool)
			if !ok {
				return errors.New("condition must be a boolean")
			}
		}
	}
	loopRunning = false
	return nil
}

// Execute a function definition
func executeFuncDef(def *FuncDef) error {
	// Set requested function name in Funcs
	Funcs[*def.Name] = func(args map[string]interface{}) (interface{}, error) {
		funcRunning = true
		// Create new empty map[interface{}]interface{}
		argIMap := map[interface{}]interface{}{}
		// Convert args map[string]interface{} to map[interface{}]interface{}
		for key, value := range args {
			argIMap[key] = value
		}
		// Set variable _args to the args map[interface{}]interface{}
		Vars["_args"] = argIMap
		// For each command within the definition
		for _, InnerCmd := range def.InnerCmds {
			// Execute command recursively
			err := executeCmd(InnerCmd)
			if err != nil {
				return nil, fmt.Errorf("%s: %s", InnerCmd.Pos, err)
			}
			if retValue != nil {
				ret := retValue
				retValue = nil
				funcRunning = false
				return ret, nil
			}
		}
		// Remove args variable from Vars
		delete(Vars, "_args")
		funcRunning = false
		return nil, nil
	}
	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 {
			// Attempt to execute the variable command
			err := executeVarCmd(Var)
			if err != nil {
				return err
			}
		}
	} 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 {
			// Attempt to execute the if command
			err := executeIfCmd(If)
			if err != nil {
				return err
			}
		}
	} else if cmd.RptLoops != nil {
		// For each repeat loop
		for _, RptLoop := range cmd.RptLoops {
			// Attempt to execute the repeat loop
			err := executeRptLoop(RptLoop)
			if err != nil {
				return err
			}
		}
	} else if cmd.WhlLoops != nil {
		// For each while loop
		for _, WhlLoop := range cmd.WhlLoops {
			// Attempt to execute the while loop
			err := executeWhlLoop(WhlLoop)
			if err != nil {
				return err
			}
		}
	} else if cmd.Defs != nil {
		// For each function definition
		for _, Def := range cmd.Defs {
			// Attempt to execute the function definition
			err := executeFuncDef(Def)
			if err != nil {
				return err
			}
		}
	}
	return nil
}

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

// 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 *VarVal      `| @@`
	Expr   *Expression  `| "{" @@ "}"`
	Map    []*MapKVPair `| "[" (@@ ("," @@)* )? "]"`
	Array  []*Value     `| "[" (@@ ("," @@)* )? "]"`
	Opposite *Value `| "!" @@`
}

// 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
}

// 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 `@@`
}

// VarVal stores any references to a variable encountered while parsing a script
type VarVal struct {
	Name  *string `"$" @Ident`
	Index *Value  `("[" @@ "]")?`
}

// 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 `@@`
}

// MapKVPair stores any key/value pairs encountered while parsing map literals
type MapKVPair struct {
	Key   *Value `@@`
	Value *Value `":" @@`
}

// FuncDef stores any function definitions encountered while parsing a script
type FuncDef struct {
	Pos       lexer.Position
	Name      *string    `"define" @Ident "{"`
	InnerCmds []*Command `@@* "}"`
}

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

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

// RptLoop stores any repeat loops encountered while parsing a script
type RptLoop struct {
	Pos       lexer.Position
	Times     *int       `"repeat" @Number "times" "{"`
	IndexVar  *string    `(@Ident "in")?`
	InnerCmds []*Command `@@* "}"`
}

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