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

// parser.go
package expr

import (
	"fmt"
)

//-------- parser

type parser struct {
	ctx exprContext
}

func NewParser(ctx exprContext) (p *parser) {
	p = &parser{
		ctx: ctx,
	}
	return p
}

func (self *parser) parseFunction(scanner *scanner, tk *Token) (tree *term, err error) {
	name, _ := tk.Value.(string)
	funcObj := self.ctx.GetFuncInfo(name)
	if funcObj == nil {
		err = fmt.Errorf("unknown function %s()", name)
		return
	}
	maxArgs := funcObj.MaxArgs()
	if maxArgs < 0 {
		maxArgs = funcObj.MinArgs() + 10
	}
	args := make([]*term, 0, maxArgs)
	lastSym := SymUnknown
	for lastSym != SymClosedRound && lastSym != SymEos {
		var subTree *ast
		if subTree, err = self.parse(scanner, SymComma, SymClosedRound); err == nil {
			if subTree.root != nil {
				args = append(args, subTree.root)
			}
		} else {
			break
		}
		lastSym = scanner.Previous().Sym
	}
	if err == nil {
		// TODO Check arguments
		tree = newFuncTerm(tk, args)
	}
	return
}

func (self *parser) parseList(scanner *scanner) (tree *term, err error) {
	args := make([]*term, 0)
	lastSym := SymUnknown
	for lastSym != SymClosedSquare && lastSym != SymEos {
		var subTree *ast
		if subTree, err = self.parse(scanner, SymComma, SymClosedSquare); err == nil {
			if subTree.root != nil {
				args = append(args, subTree.root)
			}
		} else {
			break
		}
		lastSym = scanner.Previous().Sym
	}
	if err == nil {
		// TODO Check arguments
		tree = newListTerm(args)
	}
	return
}

func (self *parser) parse(scanner *scanner, termSymbols ...Symbol) (tree *ast, err error) {
	tree = NewAst()
	firstToken := true
	lastSym := SymUnknown
	for tk := scanner.Next(); err == nil && tk != nil && !tk.IsTerm(termSymbols); tk = scanner.Next() {
		if tk.Sym == SymComment {
			continue
		}

		if tk.Sym == SymSemiColon {
			tree.ToForest()
			continue
		}

		//fmt.Println("Token:", tk)
		if firstToken && (tk.Sym == SymMinus || tk.Sym == SymPlus) {
			if tk.Sym == SymMinus {
				tk.Sym = SymChangeSign
			} else {
				tk.Sym = SymUnchangeSign
			}
		}
		firstToken = false
		switch tk.Sym {
		case SymOpenRound:
			var subTree *ast
			if subTree, err = self.parse(scanner, SymClosedRound); err == nil {
				subTree.root.priority = priValue
				tree.addTerm(subTree.root)
			}
		case SymFunction:
			var funcTerm *term
			if funcTerm, err = self.parseFunction(scanner, tk); err == nil {
				err = tree.addTerm(funcTerm)
			}
		case SymOpenSquare:
			var listTerm *term
			if listTerm, err = self.parseList(scanner); err == nil {
				err = tree.addTerm(listTerm)
			}
		case SymEqual:
			if lastSym == SymIdentifier {
				err = tree.addToken(tk)
			} else {
				err = fmt.Errorf(`assign operator (%q) must be preceded by a variable`, tk.source)
			}
		default:
			err = tree.addToken(tk)
		}
		lastSym = tk.Sym
	}
	return
}