// Copyright ©2020 The go-latex Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package ast declares the types used to represent syntax trees for
// LaTeX documents.
package ast // import "codeberg.org/go-latex/latex/ast"

import (
	"fmt"
	"io"

	"codeberg.org/go-latex/latex/token"
)

// Node is a node in a LaTeX document.
type Node interface {
	Pos() token.Pos // position of first character belonging to the node.
	End() token.Pos // position of first character immediately after the node.

	isNode()
}

// List is a collection of nodes.
type List []Node

func (x List) isNode() {}
func (x List) Pos() token.Pos {
	if len(x) == 0 {
		return -1
	}
	return x[0].Pos()
}

func (x List) End() token.Pos {
	if len(x) == 0 {
		return -1
	}
	return x[len(x)-1].End()
}

// Macro is a LaTeX macro.
// ex:
//  \sqrt{a}
//  \frac{num}{den}
type Macro struct {
	Name *Ident
	Args List
}

func (x *Macro) isNode()        {}
func (x *Macro) Pos() token.Pos { return x.Name.Pos() }
func (x *Macro) End() token.Pos {
	if len(x.Args) > 0 {
		return x.Args[len(x.Args)-1].End()
	}
	return x.Name.End()
}

// Arg is an argument of a macro.
// ex:
//  {a} in \sqrt{a}
type Arg struct {
	Lbrace token.Pos // position of '{'
	List   List      // or stmt?
	Rbrace token.Pos // position of '}'
}

func (x *Arg) Pos() token.Pos { return x.Lbrace }
func (x *Arg) End() token.Pos { return x.Rbrace }
func (x *Arg) isNode()        {}

// OptArg is an optional argument of a macro
// ex:
//  [n] in \sqrt[n]{a}
type OptArg struct {
	Lbrack token.Pos // position of '['
	List   List
	Rbrack token.Pos // position of ']'
}

func (x *OptArg) Pos() token.Pos { return x.Lbrack }
func (x *OptArg) End() token.Pos { return x.Rbrack }
func (x *OptArg) isNode()        {}

type Ident struct {
	NamePos token.Pos // identifier position
	Name    string    // identifier name
}

func (x *Ident) Pos() token.Pos { return x.NamePos }
func (x *Ident) End() token.Pos { return token.Pos(int(x.NamePos) + len(x.Name)) }
func (x *Ident) isNode()        {}

// MathExpr is a math expression.
// ex:
//  $f(x) \doteq \sqrt[n]{x}$
//  \[ x^n + y^n = z^n \]
type MathExpr struct {
	Delim string    // delimiter used for this math expression.
	Left  token.Pos // position of opening '$', '\(', '\[' or '\begin{math}'
	List  List
	Right token.Pos // position of closing '$', '\)', '\]' or '\end{math}'
}

func (x *MathExpr) isNode()        {}
func (x *MathExpr) Pos() token.Pos { return x.Left }
func (x *MathExpr) End() token.Pos { return x.Right }

type Word struct {
	WordPos token.Pos
	Text    string
}

func (x *Word) isNode()        {}
func (x *Word) Pos() token.Pos { return x.WordPos }
func (x *Word) End() token.Pos { return token.Pos(int(x.WordPos) + len(x.Text)) }

type Literal struct {
	LitPos token.Pos
	Text   string
}

func (x *Literal) isNode()        {}
func (x *Literal) Pos() token.Pos { return x.LitPos }
func (x *Literal) End() token.Pos { return token.Pos(int(x.LitPos) + len(x.Text)) }

type Symbol struct {
	SymPos token.Pos
	Text   string
}

func (x *Symbol) isNode()        {}
func (x *Symbol) Pos() token.Pos { return x.SymPos }
func (x *Symbol) End() token.Pos { return token.Pos(int(x.SymPos) + len(x.Text)) }

// Sub is a subscript node.
//
// e.g.: \sum_{i=0}
type Sub struct {
	UnderPos token.Pos
	Node     Node
}

func (x *Sub) isNode()        {}
func (x *Sub) Pos() token.Pos { return x.UnderPos }
func (x *Sub) End() token.Pos { return x.Node.End() }

// Sup is a superscript node.
//
// e.g.: \sum^{n}
type Sup struct {
	HatPos token.Pos
	Node   Node
}

func (x *Sup) isNode()        {}
func (x *Sup) Pos() token.Pos { return x.HatPos }
func (x *Sup) End() token.Pos { return x.Node.End() }

// Print prints node to w.
func Print(o io.Writer, node Node) {
	switch node := node.(type) {
	case *Arg:
		fmt.Fprintf(o, "{")
		for i, n := range node.List {
			if i > 0 {
				fmt.Fprintf(o, ", ")
			}
			Print(o, n)
		}
		fmt.Fprintf(o, "}")

	case *Ident:
		fmt.Fprintf(o, "ast.Ident{%q}", node.Name)

	case *Macro:
		fmt.Fprintf(o, "ast.Macro{%q", node.Name.Name)
		switch len(node.Args) {
		case 0:
			// no-op
		default:
			fmt.Fprintf(o, ", Args:")
			for i, n := range node.Args {
				if i > 0 {
					fmt.Fprintf(o, ", ")
				}
				Print(o, n)
			}
		}
		fmt.Fprintf(o, "}")
	case *MathExpr:
		fmt.Fprintf(o, "ast.MathExpr{")
		switch len(node.List) {
		case 0:
			// no-op
		default:
			fmt.Fprintf(o, "List:")
			for i, n := range node.List {
				if i > 0 {
					fmt.Fprintf(o, ", ")
				}
				Print(o, n)
			}
		}
		fmt.Fprintf(o, "}")
	case *OptArg:
		fmt.Fprintf(o, "[")
		for i, n := range node.List {
			if i > 0 {
				fmt.Fprintf(o, ", ")
			}
			Print(o, n)
		}
		fmt.Fprintf(o, "]")
	case *Word:
		fmt.Fprintf(o, "ast.Word{%q}", node.Text)
	case *Literal:
		fmt.Fprintf(o, "ast.Lit{%q}", node.Text)
	case List:
		fmt.Fprintf(o, "ast.List{")
		for i, n := range node {
			if i > 0 {
				fmt.Fprintf(o, ", ")
			}
			Print(o, n)
		}
		fmt.Fprintf(o, "}")

	case *Sub:
		fmt.Fprintf(o, "ast.Sub{")
		Print(o, node.Node)
		fmt.Fprintf(o, "}")

	case *Sup:
		fmt.Fprintf(o, "ast.Sup{")
		Print(o, node.Node)
		fmt.Fprintf(o, "}")

	case *Symbol:
		fmt.Fprintf(o, "ast.Symbol{%q}", node.Text)

		//	case *Op:
		//		fmt.Fprintf(o, "ast.Op{%q}", node.Text)

	case nil:
		fmt.Fprintf(o, "<nil>")

	default:
		panic(fmt.Errorf("unknown node %T", node))
	}
}

var (
	_ Node = (*List)(nil)
	_ Node = (*Arg)(nil)
	_ Node = (*Ident)(nil)
	_ Node = (*Macro)(nil)
	_ Node = (*MathExpr)(nil)
	_ Node = (*OptArg)(nil)
	_ Node = (*Word)(nil)
	_ Node = (*Literal)(nil)
	_ Node = (*Sup)(nil)
	_ Node = (*Sub)(nil)
	_ Node = (*Symbol)(nil)
)