package eval

// TODO: a lot of code duplication that can be solved by a type checking helper

import (
	"fmt"
	"strings"

	"github.com/cevaris/ordered_map"

	"github.com/hellerve/argos/ast"
)

var trueVal = ast.AST{ast.Bool, true}
var falseVal = ast.AST{ast.Bool, false}
var nilVal = ast.AST{ast.List, []*ast.AST{}}

func RootEnv() ast.Env {
	e := ast.ParentEnv()

	prims := map[string]ast.PrimFn{
		"cons":  evalCons,
		"car":   evalCar,
		"cdr":   evalCdr,
		"null?": evalNull,
		"pr":    evalPr,
		"table": evalTable,
		"type":  evalType,
	}

	for k, v := range prims {
		prim := ast.AST{ast.Prim, ast.Primitive{k, v}}
		e.Values[k] = &prim
	}

	return e
}

func checkArity(input []*ast.AST, arity int, name string) error {
	ilen := len(input)
	if ilen != arity {
		return fmt.Errorf("Argument count to '%s' must be %d, was %d", name, arity, ilen)
	}

	return nil
}

func evalDef(input []*ast.AST, e ast.Env) (*ast.AST, error) {
	err := checkArity(input, 2, "=")

	if err != nil {
		return nil, err
	}

	variable := input[0]

	if variable.Tag != ast.Symbol {
		// TODO destructuring assignment
		variable, err = Eval(variable, e)

		if err != nil {
			return nil, err
		}

		if variable.Tag != ast.Symbol {
			variable, err = Eval(input[1], e)
			return variable, err
		}
	}

	if err != nil {
		return nil, err
	}

	sym := variable.Val.(string)

	evald, err := Eval(input[1], e)

	if err != nil {
		return nil, err
	}

	e.Values[sym] = evald

	return evald, nil
}

func arithCast(input *ast.AST, e ast.Env) (float64, error) {
	evald, err := Eval(input, e)
	if err != nil {
		return 0, err
	}

	if evald.Tag != ast.Num {
		return 0, fmt.Errorf("Cannot perform arithmetic on ", evald.Pretty())
	}

	return evald.Val.(float64), nil
}

func evalArith(input []*ast.AST, e ast.Env, fn func(float64, float64) float64) (*ast.AST, error) {
	ilen := len(input)
	if ilen < 2 {
		return nil, fmt.Errorf("Arithmetic functions take at least 2 arguments, got %d", ilen)
	}

	acc, err := arithCast(input[0], e)

	if err != nil {
		return nil, err
	}

	for _, elem := range input[1:] {
		val, err := arithCast(elem, e)

		if err != nil {
			return nil, err
		}
		acc = fn(acc, val)
	}

	res := ast.AST{ast.Num, acc}
	return &res, nil
}

func evalLog(input []*ast.AST, e ast.Env, fn func(float64, float64) bool) (*ast.AST, error) {
	ilen := len(input)
	if ilen < 2 {
		return nil, fmt.Errorf("Logic functions take at least 2 arguments, got %d", ilen)
	}

	old, err := arithCast(input[0], e)

	if err != nil {
		return nil, err
	}

	acc := true
	for _, elem := range input[1:] {
		val, err := arithCast(elem, e)

		if err != nil {
			return nil, err
		}
		acc = acc && fn(old, val)
		old = val
	}

	if acc {
		return &trueVal, nil
	}
	return &falseVal, nil
}

func evalEq(input []*ast.AST, e ast.Env) (*ast.AST, error) {
	err := checkArity(input, 2, "is")

	if err != nil {
		return nil, err
	}

	x, err := Eval(input[0], e)

	if err != nil {
		return nil, err
	}

	y, err := Eval(input[1], e)

	if err != nil {
		return nil, err
	}

	if x.Tag != y.Tag {
		return &falseVal, nil
	}

	if x.Val == y.Val {
		return &trueVal, nil
	}
	return &falseVal, nil
}

func evalCons(input []*ast.AST) (*ast.AST, error) {
	err := checkArity(input, 2, "cons")

	if err != nil {
		return nil, err
	}

	lst := input[1]

	if lst.Tag != ast.Quoted {
		return nil, fmt.Errorf("Cannot cons to non-list %s", lst.Pretty())
	}

	fst := input[0]

	res := ast.AST{ast.List, append([]*ast.AST{fst}, lst.Val.(*ast.AST).Val.([]*ast.AST)...)}

	return &res, nil
}

func evalCar(input []*ast.AST) (*ast.AST, error) {
	err := checkArity(input, 1, "car")

	if err != nil {
		return nil, err
	}

	lst := input[0]

	if lst.Tag != ast.Quoted {
		return nil, fmt.Errorf("Cannot car from non-list %s", lst.Pretty())
	}

	res := lst.Val.(*ast.AST).Val.([]*ast.AST)[0]
	return res, nil
}

func evalCdr(input []*ast.AST) (*ast.AST, error) {
	err := checkArity(input, 1, "cdr")

	if err != nil {
		return nil, err
	}

	lst := input[0]

	if lst.Tag != ast.Quoted {
		return nil, fmt.Errorf("Cannot cdr from non-list %s", lst.Pretty())
	}

	res := ast.AST{ast.List, lst.Val.(*ast.AST).Val.([]*ast.AST)[1:]}
	return &res, nil
}

func evalNull(input []*ast.AST) (*ast.AST, error) {
	err := checkArity(input, 1, "null")

	if err != nil {
		return nil, err
	}

	lst := input[0]

	if lst.Tag != ast.Quoted {
		return nil, fmt.Errorf("Cannot call null? on non-list %s", lst.Pretty())
	}

	res := ast.AST{ast.Bool, len(lst.Val.(*ast.AST).Val.([]*ast.AST)) == 0}
	return &res, nil
}

func evalFn(input []*ast.AST, e ast.Env) (*ast.AST, error) {
	err := checkArity(input, 2, "fn")

	if err != nil {
		return nil, err
	}

	args := input[0]

	if args.Tag != ast.List {
		return nil, fmt.Errorf("Cannot call fn with argument list %s", args.Pretty())
	}

	var argsStr []string
	var rest *string = nil
	opt := ordered_map.NewOrderedMap()

	argslst := args.Val.([]*ast.AST)
	for i, a := range argslst {
		if a.Tag != ast.Symbol && a.Tag != ast.List {
			return nil, fmt.Errorf("Argument list cannot contain %s", a.Pretty())
		}

		if a.Tag == ast.List {
			argv := a.Val.([]*ast.AST)
			argvln := len(argv)
			if (argvln != 3 && argvln != 2) || argv[0].Tag != ast.Symbol || argv[0].Val.(string) != "o" || argv[0].Tag != ast.Symbol {
				return nil, fmt.Errorf("Argument list cannot contain %s", a.Pretty())
			}
			if argvln == 2 {
				opt.Set(argv[1].Val.(string), nil)
			} else if argvln == 3 {
				opt.Set(argv[1].Val.(string), argv[2])
			}
			continue
		}

		val := a.Val.(string)
		// TODO: error handling
		if val == "." {
			str := argslst[i+1].Val.(string)
			rest = &str
			break
		}

		argsStr = append(argsStr, val)
	}

	body := input[1]

  fe := ast.NewEnv(&e)

	res := ast.AST{ast.Fn, ast.Func{argsStr, rest, opt, body, fe}}
	return &res, nil
}

func funcApply(f ast.Func, args []*ast.AST, e ast.Env) (*ast.AST, error) {
	plen := len(f.Params)
	alen := len(args)

	if plen != alen && !f.HasRest() && !f.HasOpt() {
		return nil, fmt.Errorf("Function expected %d arguments, was called with %d.", plen, alen)
	}

	for i, a := range f.Params {
		f.Env.Values[a] = args[i]
	}

	if f.HasRest() {
		lst := ast.AST{ast.List, args[plen:]}
		quoted := ast.AST{ast.Quoted, &lst}
		f.Env.Values[*f.Rest] = &quoted
	} else {
		iter := f.Opt.IterFunc()
		i := plen
		for kv, ok := iter(); ok; kv, ok = iter() {
			if i < alen {
				f.Env.Values[kv.Key.(string)] = args[i]
			} else {
				f.Env.Values[kv.Key.(string)] = kv.Value.(*ast.AST)
			}
			i++
		}
	}

	return Eval(f.Body, f.Env)
}

func evalPr(l []*ast.AST) (*ast.AST, error) {
	var toPrint []string
	for _, elem := range l {
		toPrint = append(toPrint, elem.Pretty())
	}
	fmt.Print(strings.Join(toPrint, " "))
	return &nilVal, nil
}

func evalIf(l []*ast.AST, e ast.Env) (*ast.AST, error) {
	i := 0
	for i < len(l) {
		if i == len(l)-1 {
			return Eval(l[i], e)
		}
		cond, err := Eval(l[i], e)

		if err != nil {
			return nil, err
		}

		if cond == &trueVal {
			return Eval(l[i+1], e)
		}
		i += 2
	}
	return &nilVal, nil
}

func evalDo(l []*ast.AST, e ast.Env) (*ast.AST, error) {
	var res *ast.AST
	var err error
	for _, elem := range l {
		res, err = Eval(elem, e)

		if err != nil {
			return nil, err
		}
	}
	return res, nil
}

func evalApply(l []*ast.AST, e ast.Env) (*ast.AST, error) {
	err := checkArity(l, 2, "apply")

	if err != nil {
		return nil, err
	}

	// TODO: error handling
	args, err := Eval(l[1], e)

	if err != nil {
		return nil, err
	}

	if args.Tag != ast.Quoted {
		return nil, fmt.Errorf("Argument 2 to apply must be a list, got %s", args.Pretty())
	}

	argslst := args.Val.(*ast.AST).Val.([]*ast.AST)
	return evalList(append([]*ast.AST{l[0]}, argslst...), e)
}

func evalWhile(l []*ast.AST, e ast.Env) (*ast.AST, error) {
	err := checkArity(l, 2, "while")

	if err != nil {
		return nil, err
	}

	var res *ast.AST

	for {
		cond, err := Eval(l[0], e)

		if err != nil {
			return nil, err
		}

		if cond == &falseVal {
			break
		}
		res, err = Eval(l[1], e)

		if err != nil {
			return nil, err
		}
	}
	return res, nil
}

func evalTable(l []*ast.AST) (*ast.AST, error) {
	err := checkArity(l, 0, "table")

	if err != nil {
		return nil, err
	}

	res := ast.AST{ast.Table, make(map[*ast.AST]*ast.AST)}
	return &res, nil
}

func evalType(l []*ast.AST) (*ast.AST, error) {
	err := checkArity(l, 1, "type")

	if err != nil {
		return nil, err
	}

	return l[0].Type(), nil
}

func evalSymbolList(l []*ast.AST, e ast.Env) (*ast.AST, error) {
	sym := l[0].Val.(string)

	l = l[1:]
	// TODO: make more of these primitives
	switch sym {
	case "=":
		return evalDef(l, e)
	case "is":
		return evalEq(l, e)
	case "apply":
		return evalApply(l, e)
	case "quote":
		lst := l[0]
		res := ast.AST{ast.Quoted, lst}
		return &res, nil
	case "fn":
		return evalFn(l, e)
	case "if":
		return evalIf(l, e)
	case "do":
		return evalDo(l, e)
	case "while":
		return evalWhile(l, e)
	case "+":
		return evalArith(l, e, func(x float64, y float64) float64 { return x + y })
	case "-":
		return evalArith(l, e, func(x float64, y float64) float64 { return x - y })
	case "*":
		return evalArith(l, e, func(x float64, y float64) float64 { return x * y })
	case "/":
		return evalArith(l, e, func(x float64, y float64) float64 { return x / y })
	case "%":
		return evalArith(l, e, func(x float64, y float64) float64 { return float64(int64(x) % int64(y)) })
	case "<":
		return evalLog(l, e, func(x float64, y float64) bool { return x < y })
	case ">":
		return evalLog(l, e, func(x float64, y float64) bool { return x > y })
	}
	res, err := e.Lookup(sym)

	if err != nil {
		return nil, err
	}

	return evalList(append([]*ast.AST{res}, l...), e)
}

func evalIdx(l []*ast.AST, e ast.Env) (*ast.AST, error) {
	head := l[0]

	err := checkArity(l, 2, "indexing")

	if err != nil {
		return nil, err
	}

	arg, err := Eval(l[1], e)

	if err != nil {
		return nil, err
	}

	switch head.Tag {
	case ast.Quoted:
		if arg.Tag != ast.Num {
			return nil, fmt.Errorf("Cannot index using %s", arg.Pretty())
		}

		idx := int64(arg.Val.(float64))
		var actualLen int64
		val := head.Val.(*ast.AST).Val.([]*ast.AST)
		actualLen = int64(len(val))
		actualIdx := idx
		if idx < 0 {
			actualIdx = actualLen + idx
		}
		if actualLen > actualIdx && actualIdx > 0 {
			return val[actualIdx], nil
		}
		return nil, fmt.Errorf("Out of bounds access (idx %d at %s)", idx, head.Pretty())
	case ast.String:
		if arg.Tag != ast.Num {
			return nil, fmt.Errorf("Cannot index using %s", arg.Pretty())
		}

		idx := int64(arg.Val.(float64))
		var actualLen int64
		val := []rune(head.Val.(string))
		actualLen = int64(len(val))
		actualIdx := idx
		if idx < 0 {
			actualIdx = actualLen + idx
		}
		if actualLen > actualIdx && actualIdx > 0 {
			res := ast.AST{ast.Char, val[actualIdx]}
			return &res, nil
		}
		return nil, fmt.Errorf("Out of bounds access (idx %d at %s)", idx, head.Pretty())
	case ast.Table:
		val := head.Val.(map[*ast.AST]*ast.AST)
		res, ok := val[arg]
		if !ok {
			return &nilVal, nil
		}
		return res, nil
	}
	return nil, fmt.Errorf("Cannot index %s", head.Pretty())
}

func primCall(f ast.Primitive, l []*ast.AST, e ast.Env) (*ast.AST, error) {
	var args []*ast.AST

	for _, a := range l {
		res, err := Eval(a, e)
		if err != nil {
			return nil, err
		}
		args = append(args, res)
	}

	return f.Fn(args)
}

func evalList(l []*ast.AST, e ast.Env) (*ast.AST, error) {
	head := l[0]
	var err error

	if head.Tag == ast.List {
		head, err = Eval(head, e)

		if err != nil {
			return nil, err
		}
	}

	switch head.Tag {
	case ast.Symbol:
		return evalSymbolList(l, e)
	case ast.Fn:
		return funcApply(head.Val.(ast.Func), l[1:], e)
	case ast.Prim:
		return primCall(head.Val.(ast.Primitive), l[1:], e)
	case ast.String, ast.Quoted, ast.Table:
		return evalIdx(append([]*ast.AST{head}, l[1:]...), e)
	}
	return nil, fmt.Errorf("Cannot perform call on %s", head.Pretty())
}

func Eval(input *ast.AST, e ast.Env) (*ast.AST, error) {
	if input.Tag == ast.List {
		l := input.Val.([]*ast.AST)
		return evalList(l, e)
	}
	if input.Tag == ast.Symbol {
		val := input.Val.(string)

		var err error
		var res *ast.AST
		switch val {
		case "true":
			res = &trueVal
		case "false":
			res = &falseVal
		case "nil":
			res = &nilVal
		default:
			res, err = e.Lookup(val)
		}
		return res, err
	}
	return input, nil
}