// Copyright (C) 2017 Keelan Lightfoot
// Copyright (C) 2007-2008 Board of Regents of the University of Wisconsin
//             System (Univ. of Wisconsin-Madison, Trace R&D Center)
// Copyright (C) 2007-2008 Omnitor AB
// Copyright (C) 2007-2008 Voiceriver Inc
//
// This library is free software; you can redistribute it and/or modify it
// under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation; either version 2.1 of the License, or (at
// your option) any later version.

package gortty

import (
	"fmt"
	"unicode"
)

const (
	shiftUnknown = iota
	shiftLetter
	shiftFigure
	shiftWhitespace
)

var (
	defaultSubstitutes = map[rune]rune{
		'{': '(',
		'}': ')',
		'[': '(',
		']': ')',
	}

	codeSets = map[string]CodeSet{
		// TDD Telecommunications Device for the Deaf standard
		"TDD": CodeSet{
			Codes: [2][]rune{
				{'\b', 'E', '\n', 'A', ' ', 'S', 'I', 'U', '\r', 'D', 'R', 'J', 'N', 'F', 'C', 'K', 'T', 'Z', 'L', 'W', 'H', 'Y', 'P', 'Q', 'O', 'B', 'G', '\x0e', 'M', 'X', 'V', '\x0f'},
				{'\b', '3', '\n', '-', ' ', ',', '8', '7', '\r', '$', '4', '\'', ',', '!', ':', '(', '5', '"', ')', '2', '=', '6', '0', '1', '9', '?', '+', '\x0e', '.', '/', ';', '\x0f'},
			},
			Substitutes: defaultSubstitutes,
			Fallback:    '\'',
			ShiftCode:   0x1b,
			UnshiftCode: 0x1f,
		},
		// USTTY US Teletype Corporation
		"USTTY": CodeSet{
			Codes: [2][]rune{
				{'\x00', 'E', '\n', 'A', ' ', 'S', 'I', 'U', '\r', 'D', 'R', 'J', 'N', 'F', 'C', 'K', 'T', 'Z', 'L', 'W', 'H', 'Y', 'P', 'Q', 'O', 'B', 'G', '\x0e', 'M', 'X', 'V', '\x0f'},
				{'\x00', '3', '\n', '-', ' ', '\a', '8', '7', '\r', '$', '4', '\'', ',', '!', ':', '(', '5', '"', ')', '2', '#', '6', '0', '1', '9', '?', '&', '\x0e', '.', '/', ';', '\x0f'},
			},
			Substitutes: defaultSubstitutes,
			Fallback:    '-',
			ShiftCode:   0x1b,
			UnshiftCode: 0x1f,
		},
		// USITA2 USITA2
		"USITA2": CodeSet{
			Codes: [2][]rune{
				{'\x00', 'E', '\n', 'A', ' ', 'S', 'I', 'U', '\r', 'D', 'R', 'J', 'N', 'F', 'C', 'K', 'T', 'Z', 'L', 'W', 'H', 'Y', 'P', 'Q', 'O', 'B', 'G', '\x0e', 'M', 'X', 'V', '\x0f'},
				{'\x00', '3', '\n', '-', ' ', '\'', '8', '7', '\r', '$', '4', '\a', ',', '!', ':', '(', '5', '"', ')', '2', '=', '6', '0', '1', '9', '?', '&', '\x0e', '.', '/', '=', '\x0f'},
			},
			Substitutes: defaultSubstitutes,
			Fallback:    '-',
			ShiftCode:   0x1b,
			UnshiftCode: 0x1f,
		},
		// Weather US Weather
		"Weather": CodeSet{
			Codes: [2][]rune{
				{'\x00', 'E', '\n', 'A', ' ', 'S', 'I', 'U', '\r', 'D', 'R', 'J', 'N', 'F', 'C', 'K', 'T', 'Z', 'L', 'W', 'H', 'Y', 'P', 'Q', 'O', 'B', 'G', '\x0e', 'M', 'X', 'V', '\x0f'},
				{'\x00', '3', '\n', '↑', ' ', '\a', '8', '7', '\r', '↗', '4', '↙', '⦷', '→', '○', '←', '5', '+', '↖', '2', '↓', '6', '0', '1', '9', '⊕', '↘', '\x0e', '.', '/', '⦶', '\x0f'},
			},
			Substitutes: defaultSubstitutes,
			Fallback:    '-',
			ShiftCode:   0x1b,
			UnshiftCode: 0x1f,
		},
		// Fractions US Fractions
		"Fractions": CodeSet{
			Codes: [2][]rune{
				{'\x00', 'E', '\n', 'A', ' ', 'S', 'I', 'U', '\r', 'D', 'R', 'J', 'N', 'F', 'C', 'K', 'T', 'Z', 'L', 'W', 'H', 'Y', 'P', 'Q', 'O', 'B', 'G', '\x0e', 'M', 'X', 'V', '\x0f'},
				{'\x00', '3', '\n', '↑', ' ', '\a', '8', '7', '\r', '$', '4', '\'', '⅞', '¼', '⅛', '½', '5', '"', '¾', '2', ' ', '6', '0', '1', '9', '⅝', '&', '\x0e', '.', '/', '⅜', '\x0f'},
			},
			Substitutes: defaultSubstitutes,
			Fallback:    '-',
			ShiftCode:   0x1b,
			UnshiftCode: 0x1f,
		},
	}
)

// CodeSet represents a teletype character set.
type CodeSet struct {
	// Codes specifies a mapping of runes to codes. There are two tables, 0 for ltrs, 1 for figs
	Codes [2][]rune
	// Substitutes specifies what characters to re-map to existing table entries
	Substitutes map[rune]rune
	// Fallback specifies what rune to use when a table entry or substitution cant be found
	Fallback rune
	// ShiftRune is fun
	ShiftCode byte
	// UnshiftRune is fun
	UnshiftCode byte

	runeToCodeSet map[rune]code
	initialized   bool
}

type code struct {
	shift int
	v     byte
}

//LoadCodeSet is fun
func LoadCodeSet(n string) (*CodeSet, error) {
	cs, ok := codeSets[n]

	if !ok {
		return nil, fmt.Errorf("Attempt to load nonexistent codeset: %s", n)
	}

	cs.initialize()

	return &cs, nil
}

func (cs *CodeSet) initialize() *CodeSet {

	cs.runeToCodeSet = make(map[rune]code)

	for i, runes := range cs.Codes {

		var shift int

		switch i {
		case 0:
			shift = shiftLetter
		case 1:
			shift = shiftFigure
		}

		for v, r := range runes {
			if c, exists := cs.runeToCodeSet[r]; exists {
				c.shift = shiftWhitespace
				cs.runeToCodeSet[r] = c
			} else {
				cs.runeToCodeSet[r] = code{
					shift: shift,
					v:     byte(v),
				}
			}

		}
	}

	for in, out := range cs.Substitutes {
		if _, ok := cs.runeToCodeSet[in]; ok {
			// dont load a translation if it overlaps an existing table entry
			continue
		}
		if b, ok := cs.runeToCodeSet[out]; ok {
			// only set the translation if the output exists in table
			cs.runeToCodeSet[in] = b
		}
	}
	return cs
}

func (cs *CodeSet) toCode(r rune) code {

	if c, ok := cs.runeToCodeSet[unicode.ToUpper(r)]; ok {
		return c
	}

	return cs.runeToCodeSet[cs.Fallback]
}

func (cs *CodeSet) toByte(r rune) byte {

	if c, ok := cs.runeToCodeSet[unicode.ToUpper(r)]; ok {
		return c.v
	}

	return cs.runeToCodeSet[cs.Fallback].v
}

func (c code) toByte() byte {
	return c.v
}

func (cs *CodeSet) shift() byte {
	return cs.ShiftCode
}

func (cs *CodeSet) unshift() byte {
	return cs.UnshiftCode
}

func (cs *CodeSet) toRune(shift int, b byte) rune {
	var i int
	switch shift {
	case shiftLetter:
		i = 0
	case shiftFigure:
		i = 1
	}
	if int(b) < len(cs.Codes[i]) {
		return cs.Codes[i][int(b)]
	}
	return '�'
}