// Mgmt
// Copyright (C) 2013-2023+ James Shubin and the project contributors
// Written by James Shubin <james@shubin.ca> and the project contributors
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package funcs

import (
	"fmt"

	"github.com/purpleidea/mgmt/lang/interfaces"
	"github.com/purpleidea/mgmt/lang/types"
	"github.com/purpleidea/mgmt/util/errwrap"
)

const (
	// ContainsFuncName is the name this function is registered as. This
	// starts with an underscore so that it cannot be used from the lexer.
	// XXX: change to _contains and add syntax in the lexer/parser
	ContainsFuncName = "contains"

	// arg names...
	containsArgNameNeedle   = "needle"
	containsArgNameHaystack = "haystack"
)

func init() {
	Register(ContainsFuncName, func() interfaces.Func { return &ContainsPolyFunc{} }) // must register the func and name
}

// ContainsPolyFunc returns true if a value is found in a list. Otherwise false.
type ContainsPolyFunc struct {
	Type *types.Type // this is the type of value stored in our list

	init *interfaces.Init
	last types.Value // last value received to use for diff

	result types.Value // last calculated output

	closeChan chan struct{}
}

// String returns a simple name for this function. This is needed so this struct
// can satisfy the pgraph.Vertex interface.
func (obj *ContainsPolyFunc) String() string {
	return ContainsFuncName
}

// ArgGen returns the Nth arg name for this function.
func (obj *ContainsPolyFunc) ArgGen(index int) (string, error) {
	seq := []string{containsArgNameNeedle, containsArgNameHaystack}
	if l := len(seq); index >= l {
		return "", fmt.Errorf("index %d exceeds arg length of %d", index, l)
	}
	return seq[index], nil
}

// Unify returns the list of invariants that this func produces.
func (obj *ContainsPolyFunc) Unify(expr interfaces.Expr) ([]interfaces.Invariant, error) {
	var invariants []interfaces.Invariant
	var invar interfaces.Invariant

	// func(needle variant, haystack variant) bool
	// func(needle %s, haystack []%s) bool

	needleName, err := obj.ArgGen(0)
	if err != nil {
		return nil, err
	}
	haystackName, err := obj.ArgGen(1)
	if err != nil {
		return nil, err
	}

	dummyNeedle := &interfaces.ExprAny{}   // corresponds to the needle type
	dummyHaystack := &interfaces.ExprAny{} // corresponds to the haystack type
	//dummyHaystackValue := &interfaces.ExprAny{} // corresponds to the haystack list type
	dummyOut := &interfaces.ExprAny{} // corresponds to the out boolean

	//invar = &unification.EqualityInvariant{
	//	Expr1: dummyNeedle,
	//	Expr2: dummyHaystackValue,
	//}
	//invariants = append(invariants, invar)

	// list relationship between needle and haystack
	// TODO: did I get this equality backwards?
	invar = &interfaces.EqualityWrapListInvariant{
		Expr1:    dummyHaystack,
		Expr2Val: dummyNeedle,
	}
	invariants = append(invariants, invar)

	// full function
	mapped := make(map[string]interfaces.Expr)
	ordered := []string{needleName, haystackName}
	mapped[needleName] = dummyNeedle
	mapped[haystackName] = dummyHaystack

	invar = &interfaces.EqualityWrapFuncInvariant{
		Expr1:    expr, // maps directly to us!
		Expr2Map: mapped,
		Expr2Ord: ordered,
		Expr2Out: dummyOut,
	}
	invariants = append(invariants, invar)

	// return type of bool
	invar = &interfaces.EqualsInvariant{
		Expr: dummyOut,
		Type: types.TypeBool,
	}
	invariants = append(invariants, invar)

	// generator function to link this to the right type
	fn := obj.fnBuilder(false, expr, dummyNeedle, dummyHaystack, dummyOut)
	invar = &interfaces.GeneratorInvariant{
		Func: fn,
	}
	invariants = append(invariants, invar)

	return invariants, nil
}

// fnBuilder builds the function for the generator invariant. It is unique in
// that it can recursively call itself to build a second generation generator
// invariant. This can only happen once, because by then we'll have given all
// the new information we can, and falsely producing redundant information is a
// good way to stall the solver if it thinks it keeps learning more things!
func (obj *ContainsPolyFunc) fnBuilder(recurse bool, expr, dummyNeedle, dummyHaystack, dummyOut interfaces.Expr) func(fnInvariants []interfaces.Invariant, solved map[interfaces.Expr]*types.Type) ([]interfaces.Invariant, error) {
	return func(fnInvariants []interfaces.Invariant, solved map[interfaces.Expr]*types.Type) ([]interfaces.Invariant, error) {
		for _, invariant := range fnInvariants {
			// search for this special type of invariant
			cfavInvar, ok := invariant.(*interfaces.CallFuncArgsValueInvariant)
			if !ok {
				continue
			}
			// did we find the mapping from us to ExprCall ?
			if cfavInvar.Func != expr {
				continue
			}
			// cfavInvar.Expr is the ExprCall! (the return pointer)
			// cfavInvar.Args are the args that ExprCall uses!
			if l := len(cfavInvar.Args); l != 2 {
				return nil, fmt.Errorf("unable to build function with %d args", l)
			}

			var invariants []interfaces.Invariant
			var invar interfaces.Invariant

			if !recurse { // only do this once!
				// add the relationship to the returned value
				invar = &interfaces.EqualityInvariant{
					Expr1: dummyOut,
					Expr2: cfavInvar.Expr,
				}
				invariants = append(invariants, invar)

				// add the relationships to the called args
				invar = &interfaces.EqualityInvariant{
					Expr1: dummyNeedle,
					Expr2: cfavInvar.Args[0],
				}
				invariants = append(invariants, invar)

				invar = &interfaces.EqualityInvariant{
					Expr1: dummyHaystack,
					Expr2: cfavInvar.Args[1],
				}
				invariants = append(invariants, invar)

				// TODO: do we return this relationship with ExprCall?
				invar = &interfaces.EqualityWrapCallInvariant{
					// TODO: should Expr1 and Expr2 be reversed???
					Expr1: cfavInvar.Expr,
					//Expr2Func: cfavInvar.Func, // same as below
					Expr2Func: expr,
				}
				invariants = append(invariants, invar)
			}

			var needleTyp *types.Type

			// Instead of using cfavInvar.Args[*].Type() I think we
			// can probably rely on the solved to find this for us!
			if typ, exists := solved[cfavInvar.Args[1]]; exists {
				if k := typ.Kind; k == types.KindList {
					needleTyp = typ.Val // contained element type
				}
			}

			if typ, exists := solved[cfavInvar.Args[0]]; exists {
				if err := needleTyp.Cmp(typ); needleTyp != nil && err != nil {
					// inconsistent types!
					return nil, errwrap.Wrapf(err, "inconsistent type")
				}

				needleTyp = typ
			}

			// We only want to recurse once.
			if recurse && needleTyp == nil {
				// nothing new we can do
				return nil, fmt.Errorf("couldn't generate new invariants")
			}

			if needleTyp == nil {
				// recurse-- we build a new one!
				fn := obj.fnBuilder(true, expr, dummyNeedle, dummyHaystack, dummyOut)
				invar = &interfaces.GeneratorInvariant{
					Func: fn,
				}
				invariants = append(invariants, invar)
			}

			invar = &interfaces.EqualsInvariant{
				Expr: dummyNeedle,
				Type: needleTyp,
			}
			invariants = append(invariants, invar)

			return invariants, nil // generator return
		}
		// We couldn't tell the solver anything it didn't already know!
		return nil, fmt.Errorf("couldn't generate new invariants")
	}
}

// Polymorphisms returns the list of possible function signatures available for
// this static polymorphic function. It relies on type and value hints to limit
// the number of returned possibilities.
func (obj *ContainsPolyFunc) Polymorphisms(partialType *types.Type, partialValues []types.Value) ([]*types.Type, error) {
	// TODO: return `variant` as arg for now -- maybe there's a better way?
	variant := []*types.Type{types.NewType("func(needle variant, haystack variant) bool")}

	if partialType == nil {
		return variant, nil
	}

	var typ *types.Type

	ord := partialType.Ord
	if partialType.Map != nil {
		if len(ord) != 2 {
			return nil, fmt.Errorf("must have exactly three args in contains func")
		}
		if tNeedle, exists := partialType.Map[ord[0]]; exists && tNeedle != nil {
			typ = tNeedle // solved
		}
		if tHaystack, exists := partialType.Map[ord[1]]; exists && tHaystack != nil {
			if tHaystack.Kind != types.KindList {
				return nil, fmt.Errorf("second arg must be of kind list")
			}
			if typ != nil && typ.Cmp(tHaystack.Val) != nil {
				return nil, fmt.Errorf("list contents in second arg for contains must match search type")
			}
			typ = tHaystack.Val // solved
		}
	}

	if tOut := partialType.Out; tOut != nil {
		if tOut.Kind != types.KindBool {
			return nil, fmt.Errorf("return type must be a bool")
		}
	}

	if typ == nil {
		return variant, nil
	}

	typFunc := types.NewType(fmt.Sprintf("func(needle %s, haystack []%s) bool", typ.String(), typ.String()))

	// TODO: type check that the partialValues are compatible

	return []*types.Type{typFunc}, nil // solved!
}

// Build is run to turn the polymorphic, undetermined function, into the
// specific statically typed version. It is usually run after Unify completes,
// and must be run before Info() and any of the other Func interface methods are
// used. This function is idempotent, as long as the arg isn't changed between
// runs.
func (obj *ContainsPolyFunc) Build(typ *types.Type) error {
	// typ is the KindFunc signature we're trying to build...
	if typ.Kind != types.KindFunc {
		return fmt.Errorf("input type must be of kind func")
	}

	if len(typ.Ord) != 2 {
		return fmt.Errorf("the contains function needs exactly two args")
	}
	if typ.Out == nil {
		return fmt.Errorf("return type of function must be specified")
	}
	if typ.Map == nil {
		return fmt.Errorf("invalid input type")
	}

	tNeedle, exists := typ.Map[typ.Ord[0]]
	if !exists || tNeedle == nil {
		return fmt.Errorf("first arg must be specified")
	}

	tHaystack, exists := typ.Map[typ.Ord[1]]
	if !exists || tHaystack == nil {
		return fmt.Errorf("second arg must be specified")
	}

	if tHaystack.Kind != types.KindList {
		return fmt.Errorf("second argument must be of kind list")
	}

	if err := tHaystack.Val.Cmp(tNeedle); err != nil {
		return errwrap.Wrapf(err, "type of first arg must match type of list elements in second arg")
	}

	if err := typ.Out.Cmp(types.TypeBool); err != nil {
		return errwrap.Wrapf(err, "return type must be a boolean")
	}

	obj.Type = tNeedle // type of value stored in our list
	return nil
}

// Validate tells us if the input struct takes a valid form.
func (obj *ContainsPolyFunc) Validate() error {
	if obj.Type == nil { // build must be run first
		return fmt.Errorf("type is still unspecified")
	}
	return nil
}

// Info returns some static info about itself. Build must be called before this
// will return correct data.
func (obj *ContainsPolyFunc) Info() *interfaces.Info {
	var sig *types.Type
	if obj.Type != nil { // don't panic if called speculatively
		s := obj.Type.String()
		sig = types.NewType(fmt.Sprintf("func(needle %s, haystack []%s) bool", s, s))
	}
	return &interfaces.Info{
		Pure: true,
		Memo: false,
		Sig:  sig, // func kind
		Err:  obj.Validate(),
	}
}

// Init runs some startup code for this function.
func (obj *ContainsPolyFunc) Init(init *interfaces.Init) error {
	obj.init = init
	obj.closeChan = make(chan struct{})
	return nil
}

// Stream returns the changing values that this func has over time.
func (obj *ContainsPolyFunc) Stream() error {
	defer close(obj.init.Output) // the sender closes
	for {
		select {
		case input, ok := <-obj.init.Input:
			if !ok {
				return nil // can't output any more
			}
			//if err := input.Type().Cmp(obj.Info().Sig.Input); err != nil {
			//	return errwrap.Wrapf(err, "wrong function input")
			//}

			if obj.last != nil && input.Cmp(obj.last) == nil {
				continue // value didn't change, skip it
			}
			obj.last = input // store for next

			needle := input.Struct()[containsArgNameNeedle]
			haystack := (input.Struct()[containsArgNameHaystack]).(*types.ListValue)

			_, exists := haystack.Contains(needle)
			var result types.Value = &types.BoolValue{V: exists}

			// if previous input was `2 + 4`, but now it
			// changed to `1 + 5`, the result is still the
			// same, so we can skip sending an update...
			if obj.result != nil && result.Cmp(obj.result) == nil {
				continue // result didn't change
			}
			obj.result = result // store new result

		case <-obj.closeChan:
			return nil
		}

		select {
		case obj.init.Output <- obj.result: // send
		case <-obj.closeChan:
			return nil
		}
	}
}

// Close runs some shutdown code for this function and turns off the stream.
func (obj *ContainsPolyFunc) Close() error {
	close(obj.closeChan)
	return nil
}