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

// operand-iterator.go
package expr

import (
	"fmt"
	"slices"
	"strings"
)

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

	requiredFields := []string{currentName, nextName}
	fieldsMask := 0b11
	foundFields := 0
	if dictAny, ok := value.(map[any]any); ok {
		ds = make(map[string]Functor)
		for keyAny, item := range dictAny {
			if key, ok := keyAny.(string); ok {
				if functor, ok := item.(*funcDefFunctor); ok {
					ds[key] = functor
					if index := slices.Index(requiredFields, key); index >= 0 {
						foundFields |= 1 << index
					}
				}
			}
		}
		// check required functions
		if foundFields != fieldsMask {
			missingFields := make([]string, 0, len(requiredFields))
			for index, field := range requiredFields {
				if (foundFields & (1 << index)) == 0 {
					missingFields = append(missingFields, field)
				}
			}
			err = fmt.Errorf("the data-source must provide a non-nil %q operator(s)", strings.Join(missingFields, ", "))
		}
	} 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 := newDataCursor(ctx, ds)

	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{}
		}

		initCtx := dc.ctx.Clone()
		if dc.resource, err = initFunc.Invoke(initCtx, initName, args); err != nil {
			return
		}
		exportObjects(dc.ctx, initCtx)
	}

	dc.nextFunc, _ = ds[nextName]
	dc.currentFunc, _ = ds[currentName]
	dc.cleanFunc, _ = ds[cleanName]
	dc.resetFunc, _ = ds[resetName]

	v = dc

	return
}