package main

import (
	"fmt"
	"log"
	"os"
	"strings"
	"sort"
	"io"
)

const (
	bufsize = 512
	prefix  = `.\"s `
	end = `.\"e`
	section = `.\"§`
	//tableHead = ".TS\nexpand;\nl1w(1.5i) l1w(4.5i)."
	//tableFoot = ".TE"
	mac = ".ref"
	//delim = "()"
)

var tableHead, tableFoot, delim, extraPrefix, extraSuffix string

type Reference struct {
	name  string
	contents string
	index int
}

func interpEscape(str string) string {
	var rt string
	for i := 0; i < len(str); i++ {
		if str[i] == '\\' {
			i++
			if str[i] == 'n' {
				rt += "\n"
			} else {
				rt += "\\n"
			}
		} else {
			rt += string(str[i])
		}
	}
	return rt + "\n"
}

func getRefTxt(lines []string) string {
	var txt string
	for _, line := range lines {
		if strings.HasPrefix(line, end) {
			break
		}
		txt += line + "\n"
	}
	return string(txt)
}

func findIndex(refs []Reference, name string) int {
	for _, ref := range refs {
		if ref.name == name {
			return ref.index
		}
	}
	return -1
}

func checkLetter(ch rune) bool {
	if ch >= 'A' && ch <= 'Z' ||
		ch >= 'a' && ch <= 'z' {
		return true
	}
	return false
}

func checkAllCaps(word string) bool {
	for _, ch := range word {
		if !checkLetter(ch) {
			continue
		}
		if ch < 'A' || ch > 'Z' {
			return false
		}
	}
	return true
}
// Typographic niceties.
func extraFmt(ref string) string {
	words := strings.Split(ref, " ")
	if checkAllCaps(words[0]) {
		words[0] = extraPrefix + words[0] + extraSuffix
	}
	words[1] = extraPrefix + words[1] + extraSuffix

	return words[0] + " " + words[1]
}

func main() {
	in := os.Stdin
	if len(os.Args) > 1 {
		var err error
		in, err = os.Open(os.Args[1])
		if err != nil {
			log.Fatal(err)
		}
	}

	bytes, err := io.ReadAll(in)
	if err != nil {
		log.Fatal(err)
	}
	contents := string(bytes)

	/* Iterate through the contents of the file twice:
	Once to find and index all references.
	Again to refer to each reference. */
	var refs []Reference
	div := -1
	lines := strings.Split(contents, "\n")
	for i, line := range lines {
		if strings.HasPrefix(line, section) {
			div = i
			words := strings.Split(line, "#")
			wc := len(words)
			if wc < 4 {
				log.Fatal(`Provide 3 arguments in the § split, delimited by #.
• A tbl(7) header
• A tbl(7) footer
• A pair of delimiters for references, such as "()"
Below is an example.
.\"§#.TS\nexpand;\nl1w(1.5i) l1w(4.5i).#.TE#()#\fC#\fP
The final two arguments in that example are optional.`)
			}
			tableHead = interpEscape(words[1])
			tableFoot = interpEscape(words[2])
			delim = words[3]
			if wc > 4 {
				extraPrefix = words[4]
			}
			if wc > 5 {
				extraSuffix = words[5]
			}
		}
	}
	// If no split, quietly return contents.
	if div == -1 {
		fmt.Print(contents)
		return
	}

	for i, line := range lines[div:] {
		if strings.HasPrefix(line, prefix) {
			var ref Reference
			ref.name = line[len(prefix):]
			// i is relative to the lines after div.
			ref.contents = getRefTxt(lines[div+i+1:])
			refs = append(refs, ref)
		}
	}

	/* Sort references alphabetically. */
	sort.Slice(refs, func(i, j int) bool {
		return strings.Compare(refs[i].name, refs[j].name) < 0
	})

	for i := range refs {
		refs[i].index = i
	}

	// Second pass.
	for _, line := range lines[:div] {
		if strings.HasPrefix(line, mac) {
			var name string
			var start, end int
			for i := range line {
				if line[i] == delim[0] {
					start = i+1
				}
				if line[i] == delim[1] {
					end = i
					break
				}
			}
			name = line[start:end]
			index := findIndex(refs, name)
			fmt.Printf(".post.url #%d \"%s\"\n\n", index,
				extraFmt(line[start-1:]))
		} else {
			fmt.Println(line)
		}
	}

	// Format References into AMS Style bibiography.
	/* As it turns out, in order to be referenced individually,
	each reference needs its own table. */
	for _, ref := range refs {
		fmt.Printf(".post.name %d\n", ref.index)
		fmt.Printf(tableHead)
		fmt.Printf("T{\n%c%s%c\nT}", delim[0], extraFmt(ref.name),
			delim[1])
		fmt.Printf("\tT{\n%sT}\n", ref.contents)
		fmt.Println(tableFoot)
	}
}