// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
// All rights reserved.

// operand-iterator.go
package expr

import (
	"fmt"
)

// -------- iterator term

func newIteratorTerm(tk *Token, dsTerm *term, args []*term) *term {
	tk.Sym = SymIterator

	children := make([]*term, 0, 1+len(args))
	children = append(children, dsTerm)
	children = append(children, args...)
	return &term{
		tk:       *tk,
		parent:   nil,
		children: children,
		position: posLeaf,
		priority: priValue,
		evalFunc: evalIterator,
	}
}

// -------- eval iterator

func evalTermArray(ctx ExprContext, a []*term) (values []any, err error) {
	values = make([]any, len(a))
	for i, t := range a {
		var value any
		if value, err = t.compute(ctx); err == nil {
			values[i] = value
		} else {
			break
		}
	}
	return
}

func getDataSourceDict(ctx ExprContext, self *term) (ds map[string]Functor, err error) {
	var value any
	if len(self.children) < 1 || self.children[0] == nil {
		err = self.Errorf("missing the data-source parameter")
		return
	}

	if value, err = self.children[0].compute(ctx); err != nil {
		return
	}

	if dictAny, ok := value.(map[any]any); ok {
		ds = make(map[string]Functor)
		for _, k := range []string{initName, currentName, nextName} {
			if item, exists := dictAny[k]; exists && item != nil {
				if functor, ok := item.(*funcDefFunctor); ok {
					ds[k] = functor
				}
			} else if k != initName {
				err = fmt.Errorf("the data-source must provide a non-nil %q operator", k)
				break
			}
		}
	} else {
		err = self.Errorf("the first param (data-source) of an iterator must be a dict, not a %T", value)
	}
	return
}

func evalIterator(ctx ExprContext, self *term) (v any, err error) {
	var ds map[string]Functor

	if ds, err = getDataSourceDict(ctx, self); err != nil {
		return
	}

	dc := &dataCursor{
		index: -1,
		ctx:   ctx.Clone(),
	}

	if initFunc, exists := ds[initName]; exists && initFunc != nil {
		var args []any
		if len(self.children) > 1 {
			if args, err = evalTermArray(ctx, self.children[1:]); err != nil {
				return
			}
		} else {
			args = []any{}
		}
		if dc.resource, err = initFunc.Invoke(dc.ctx, initName, args); err != nil {
			return
		}
	}

	dc.nextFunc, _ = ds[nextName]
	dc.currentFunc, _ = ds[currentName]
	v = dc

	return
}