package main

import (
	"fmt"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"unicode"
)

// An issue report in hq, `04-ISSUES/NNN-slug/00-report.md`, as the import of slice 3 reads it (novox/hq
// to-be 53 §8): a YAML frontmatter of a few keys, a heading that is the title, and the report. The
// frontmatter is read as hq's own checks read it (00-META/checks/cycle.py), a little more carefully: a
// list in brackets may run over lines and hold commas inside parentheses or quotes, a block list's items
// may be quoted, and a long value may wrap onto an indented line.

// Report is one issue report as read from its folder.
type Report struct {
	Number uint64
	// Folder is the issue's folder, `04-ISSUES/NNN-slug`.
	Folder string
	// Path is the report, `<Folder>/00-report.md`.
	Path   string
	Title  string
	Status string
	// Opened and Closed are dates as the frontmatter gives them, YYYY-MM-DD, or empty.
	Opened        string
	Closed        string
	LocatedIn     []string
	FixedBy       []string
	AmendedDesign []string
	Replay        string
	ReplayNone    string
	// Body is the report without its frontmatter and its title.
	Body string
	// Issues and Decisions are the other issues and the decision records the report names.
	Issues    []uint64
	Decisions []string
	// Odd is what was odd about the report and did not stop it from being read.
	Odd []string
}

var (
	issueFolder = regexp.MustCompile(`^([0-9]{1,4})-([a-z0-9]+(?:-[a-z0-9]+)*)$`)
	frontKey    = regexp.MustCompile(`^([A-Za-z][A-Za-z0-9-]*):(.*)$`)
	blockItem   = regexp.MustCompile(`^\s+-\s*(.*)$`)
	continued   = regexp.MustCompile(`^\s+(\S.*)$`)
	heading     = regexp.MustCompile(`(?m)^#\s+(.+?)\s*$`)
	numbered    = regexp.MustCompile(`^([0-9]{1,4})\s*([.:]|—|–|-)?\s*(.*)$`)
	dateShape   = regexp.MustCompile(`^[0-9]{4}-[0-9]{2}-[0-9]{2}$`)
	namesIssue  = regexp.MustCompile(`(?i)\bissue ([0-9]{1,4})\b|04-ISSUES/([0-9]{1,4})-`)
	namesRecord = regexp.MustCompile(`\bADR ([0-9]{4})\b|02-DECISIONS/([0-9]{4})-`)
)

// folderNumber is the number an issue folder's name carries, or false for a name that is not one.
func folderNumber(name string) (uint64, bool) {
	m := issueFolder.FindStringSubmatch(name)
	if m == nil || len(m[2]) > 120 {
		return 0, false
	}
	n, err := strconv.ParseUint(m[1], 10, 64)
	if err != nil || n == 0 {
		return 0, false
	}
	return n, true
}

// frontmatter is the YAML block between the first two `---` lines as {key: values}, and the text after
// it. A scalar is one value; a list, in brackets or as block items, its items; an empty value no values.
// A key given twice keeps the last. False when the text has no frontmatter.
func frontmatter(text string) (map[string][]string, string, bool) {
	text = strings.ReplaceAll(text, "\r\n", "\n")
	if !strings.HasPrefix(text, "---\n") {
		return nil, "", false
	}
	rest := text[4:]
	end := -1
	if strings.HasPrefix(rest, "---\n") || rest == "---" {
		end = 0
	} else if i := strings.Index(rest, "\n---\n"); i >= 0 {
		end = i + 1
	} else if strings.HasSuffix(rest, "\n---") {
		end = len(rest) - 3
	}
	if end < 0 {
		return nil, "", false
	}
	block := rest[:end]
	body := strings.TrimPrefix(rest[end:], "---")
	body = strings.TrimPrefix(body, "\n")

	out := map[string][]string{}
	key := ""
	const (
		none = iota
		scalar
		list
		flow
	)
	mode := none
	flowText := ""
	closeFlow := func() {
		out[key] = splitFlow(flowText)
		mode = list
	}
	for _, line := range strings.Split(block, "\n") {
		if strings.TrimSpace(line) == "" || strings.HasPrefix(strings.TrimSpace(line), "#") {
			continue
		}
		if mode == flow {
			flowText += " " + strings.TrimSpace(line)
			if flowClosed(flowText) {
				closeFlow()
			}
			continue
		}
		if m := frontKey.FindStringSubmatch(line); m != nil && !strings.HasPrefix(line, " ") {
			key = m[1]
			value := strings.TrimSpace(m[2])
			switch {
			case value == "":
				out[key] = nil
				mode = list
			case strings.HasPrefix(value, "["):
				flowText = value
				mode = flow
				if flowClosed(flowText) {
					closeFlow()
				}
			default:
				out[key] = []string{unquote(value)}
				mode = scalar
			}
			continue
		}
		if key == "" {
			continue
		}
		if m := blockItem.FindStringSubmatch(line); m != nil && mode == list {
			out[key] = append(out[key], unquote(strings.TrimSpace(m[1])))
			continue
		}
		if m := continued.FindStringSubmatch(line); m != nil && len(out[key]) > 0 {
			last := len(out[key]) - 1
			out[key][last] = strings.TrimSpace(out[key][last] + " " + strings.TrimSpace(m[1]))
		}
	}
	if mode == flow {
		// Never closed: what was read of it, without the bracket.
		out[key] = splitFlow(flowText + "]")
	}
	return out, body, true
}

// flowClosed says whether a bracketed list has its closing bracket, outside quotes. A quote opens an item
// only at the item's start: an apostrophe inside prose ("the provisioner's ACL") is no quote.
func flowClosed(s string) bool {
	depth, quote, atStart := 0, rune(0), true
	for _, r := range s {
		switch {
		case quote != 0:
			if r == quote {
				quote = 0
			}
			continue
		case (r == '"' || r == '\'') && atStart:
			quote = r
		case r == '[':
			depth++
		case r == ']':
			depth--
			if depth == 0 {
				return true
			}
		}
		atStart = r == '[' || r == ',' || atStart && unicode.IsSpace(r)
	}
	return false
}

// splitFlow is a bracketed list's items: split on the commas outside parentheses, brackets and quotes,
// a quote opening an item only at its start.
func splitFlow(s string) []string {
	s = strings.TrimSpace(s)
	s = strings.TrimPrefix(s, "[")
	s = strings.TrimSuffix(s, "]")
	var items []string
	var cur strings.Builder
	depth, quote, atStart := 0, rune(0), true
	flush := func() {
		if v := unquote(strings.TrimSpace(cur.String())); v != "" {
			items = append(items, v)
		}
		cur.Reset()
	}
	for _, r := range s {
		switch {
		case quote != 0:
			if r == quote {
				quote = 0
			}
		case (r == '"' || r == '\'') && atStart:
			quote = r
		case r == '(' || r == '[':
			depth++
		case r == ')' || r == ']':
			if depth > 0 {
				depth--
			}
		case r == ',' && depth == 0:
			flush()
			atStart = true
			continue
		}
		cur.WriteRune(r)
		atStart = atStart && unicode.IsSpace(r)
	}
	flush()
	return items
}

// unquote strips one pair of matching quotes around a value, and the escapes a double-quoted YAML
// scalar uses for its own quote.
func unquote(v string) string {
	if len(v) >= 2 && (v[0] == '"' && v[len(v)-1] == '"' || v[0] == '\'' && v[len(v)-1] == '\'') {
		inner := v[1 : len(v)-1]
		if v[0] == '"' {
			inner = strings.ReplaceAll(inner, `\"`, `"`)
		} else {
			inner = strings.ReplaceAll(inner, `''`, `'`)
		}
		return strings.TrimSpace(inner)
	}
	return v
}

// ParseReport reads one issue report. The folder is its name, `NNN-slug`; the text is the report whole.
// What makes a report unreadable is an error: no frontmatter, no title, no status, or a status that
// is not one of the six. What is odd but readable is said in Odd.
func ParseReport(folder, text string) (*Report, error) {
	n, ok := folderNumber(folder)
	if !ok {
		return nil, fmt.Errorf("%q is not an issue folder's name: NNN-slug, lower-case words joined by hyphens", folder)
	}
	front, body, ok := frontmatter(text)
	if !ok {
		return nil, fmt.Errorf("%s/00-report.md has no frontmatter", folder)
	}
	r := &Report{Number: n, Folder: "04-ISSUES/" + folder, Path: "04-ISSUES/" + folder + "/00-report.md"}
	one := func(key string) string {
		if v := front[key]; len(v) > 0 {
			if len(v) > 1 {
				r.Odd = append(r.Odd, fmt.Sprintf("%s: is a list of %d; one value was expected, and they were joined", key, len(v)))
				return strings.Join(v, "; ")
			}
			return v[0]
		}
		return ""
	}
	r.Status = one("status")
	if r.Status == "" {
		return nil, fmt.Errorf("%s/00-report.md has no status", folder)
	}
	if !known(r.Status) {
		return nil, fmt.Errorf("%s/00-report.md has the status %q, not one of %s", folder, r.Status, strings.Join(Statuses, ", "))
	}
	r.Opened = one("opened")
	if r.Opened != "" && !dateShape.MatchString(r.Opened) {
		r.Odd = append(r.Odd, fmt.Sprintf("opened: %q is not a date", r.Opened))
		r.Opened = ""
	}
	for _, key := range []string{"resolved", "closed"} {
		if v := one(key); v != "" {
			if dateShape.MatchString(v) {
				r.Closed = v
			} else {
				r.Odd = append(r.Odd, fmt.Sprintf("%s: %q is not a date", key, v))
			}
		}
	}
	r.LocatedIn = front["located-in"]
	r.FixedBy = front["fixed-by"]
	r.AmendedDesign = front["amended-design"]
	r.Replay = one("replay")
	r.ReplayNone = one("replay-none")
	imported := map[string]bool{"status": true, "opened": true, "resolved": true, "closed": true, "located-in": true,
		"fixed-by": true, "amended-design": true, "replay": true, "replay-none": true}
	var unknown []string
	for k := range front {
		if !imported[k] {
			unknown = append(unknown, k)
		}
	}
	if len(unknown) > 0 {
		sort.Strings(unknown)
		r.Odd = append(r.Odd, "frontmatter keys not imported: "+strings.Join(unknown, ", "))
	}

	m := heading.FindStringSubmatchIndex(body)
	if m == nil {
		return nil, fmt.Errorf("%s/00-report.md has no title: no `# ` heading", folder)
	}
	title := body[m[2]:m[3]]
	// "362. The title", "043 — The title": the number and its separator are the folder's, not the title's. A
	// title that starts with a bare number ("2 nodes …") keeps it, unless the number is the folder's.
	if nm := numbered.FindStringSubmatch(title); nm != nil {
		heads, _ := strconv.ParseUint(nm[1], 10, 64)
		if nm[2] != "" || heads == n {
			title = nm[3]
			if heads != n && title != "" {
				r.Odd = append(r.Odd, fmt.Sprintf("the title is numbered %s; the folder is %d", nm[1], n))
			}
		}
	}
	r.Title = strings.TrimSpace(title)
	if r.Title == "" {
		return nil, fmt.Errorf("%s/00-report.md has an empty title", folder)
	}
	r.Body = strings.TrimSpace(body[:m[0]] + body[m[1]:])

	seen := map[uint64]bool{n: true}
	for _, mm := range namesIssue.FindAllStringSubmatch(text, -1) {
		if other, err := strconv.ParseUint(mm[1]+mm[2], 10, 64); err == nil && !seen[other] {
			seen[other] = true
			r.Issues = append(r.Issues, other)
		}
	}
	sort.Slice(r.Issues, func(i, j int) bool { return r.Issues[i] < r.Issues[j] })
	records := map[string]bool{}
	for _, mm := range namesRecord.FindAllStringSubmatch(text, -1) {
		if d := mm[1] + mm[2]; !records[d] {
			records[d] = true
			r.Decisions = append(r.Decisions, d)
		}
	}
	sort.Strings(r.Decisions)
	return r, nil
}