package parse

import (
	"fmt"
	"strconv"
	"strings"
	"time"
)

type Result struct {
	Body          string
	Glyph         string
	Title         *string
	Description   *string
	TimeAnchor    *string
	Tags          []string
	FilterTags    []string
	CardSuffix    *string
	Pin           bool
	Query         bool
	QueryDateFrom *string
	QueryDateTo   *string
	QueryCardType *string
}

var validCardTypes = map[string]string{
	"card":      "snippet",
	"c":         "snippet",
	"snippet":   "snippet",
	"template":  "template",
	"checklist": "checklist",
	"decision":  "decision",
	"link":      "link",
	"note":      "note",
	"n":         "note",
}

func Parse(input string) (*Result, error) {
	input = strings.TrimSpace(input)
	if input == "" {
		return nil, fmt.Errorf("empty input")
	}

	r := &Result{
		Glyph: "note",
		Tags:  []string{},
	}

	remaining := input

	// Step 1: Escape check — `\` prefix → thought, no prefix detection
	if strings.HasPrefix(remaining, `\`) {
		remaining = remaining[1:]
		r.Glyph = "note"
		clean, err := extractModifiers(r, remaining, false)
		if err != nil {
			return nil, err
		}
		r.Body = clean
		if r.Body == "" && r.Title == nil {
			return nil, fmt.Errorf("empty body after extracting modifiers")
		}
		return r, nil
	}

	// Step 2: Query check — `?` prefix → search mode
	if strings.HasPrefix(remaining, "?") {
		remaining = strings.TrimSpace(remaining[1:])
		r.Query = true
		r.Glyph = ""
		tokens := strings.Fields(remaining)
		var bodyParts []string
		now := time.Now()
		for _, tok := range tokens {
			switch {
			case strings.HasPrefix(tok, "#") && len(tok) > 1 && !strings.HasPrefix(tok, "##"):
				tag := strings.ToLower(tok[1:])
				r.FilterTags = append(r.FilterTags, tag)
			case tok == "@today":
				d := now.Format("2006-01-02")
				r.QueryDateFrom = &d
				r.QueryDateTo = &d
			case tok == "@yesterday":
				d := now.AddDate(0, 0, -1).Format("2006-01-02")
				r.QueryDateFrom = &d
				r.QueryDateTo = &d
			case tok == "@week":
				d := now.AddDate(0, 0, -7).Format("2006-01-02")
				r.QueryDateFrom = &d
			case tok == "@month":
				d := now.AddDate(0, -1, 0).Format("2006-01-02")
				r.QueryDateFrom = &d
			case strings.HasPrefix(tok, ">") && strings.HasSuffix(tok, "d"):
				if n, err := strconv.Atoi(tok[1 : len(tok)-1]); err == nil && n > 0 {
					d := now.AddDate(0, 0, -n).Format("2006-01-02")
					r.QueryDateTo = &d
				} else {
					bodyParts = append(bodyParts, tok)
				}
			case strings.HasPrefix(tok, "<") && strings.HasSuffix(tok, "d"):
				if n, err := strconv.Atoi(tok[1 : len(tok)-1]); err == nil && n > 0 {
					d := now.AddDate(0, 0, -n).Format("2006-01-02")
					r.QueryDateFrom = &d
				} else {
					bodyParts = append(bodyParts, tok)
				}
			case strings.HasPrefix(tok, "^") && len(tok) > 1:
				suffix := tok[1:]
				if ct, ok := validCardTypes[suffix]; ok {
					r.QueryCardType = &ct
				} else {
					bodyParts = append(bodyParts, tok)
				}
			default:
				bodyParts = append(bodyParts, tok)
			}
		}
		r.Body = strings.Join(bodyParts, " ")
		return r, nil
	}

	// Step 3: Kind prefix — `-`, `@time`, `!time`
	// `@` and `!` are kind prefixes ONLY if followed by a valid time token.
	// Otherwise the input is treated as a plain note.
	if strings.HasPrefix(remaining, "- ") {
		r.Glyph = "todo"
		remaining = strings.TrimSpace(remaining[2:])
	} else if remaining == "-" {
		r.Glyph = "todo"
		remaining = ""
	} else if strings.HasPrefix(remaining, "@") {
		if rest, ok := tryPrefixTime(r, remaining[1:]); ok {
			r.Glyph = "event"
			remaining = rest
		}
	} else if strings.HasPrefix(remaining, "!") {
		afterBang := remaining[1:]
		// `!pin` is a flag, not a reminder prefix
		firstWord := ""
		if fields := strings.Fields(afterBang); len(fields) > 0 {
			firstWord = fields[0]
		}
		if !strings.EqualFold(firstWord, "pin") {
			if rest, ok := tryPrefixTime(r, afterBang); ok {
				r.Glyph = "reminder"
				remaining = rest
			}
		}
	}

	// Steps 4-5: Title and description extraction
	var titleRaw, descRaw string
	hasTitle := false

	lines := strings.SplitN(remaining, "\n", 2)
	firstLine := strings.TrimSpace(lines[0])

	if strings.HasPrefix(firstLine, "|") {
		hasTitle = true
		titleContent := firstLine[1:]
		if idx := strings.Index(titleContent, " // "); idx >= 0 {
			titleRaw = strings.TrimSpace(titleContent[:idx])
			descRaw = strings.TrimSpace(titleContent[idx+4:])
		} else {
			titleRaw = strings.TrimSpace(titleContent)
		}
		if len(lines) > 1 {
			remaining = lines[1]
		} else {
			remaining = ""
		}
	} else {
		allLines := strings.Split(remaining, "\n")
		var descParts []string
		startBody := 0
		for i, line := range allLines {
			trimmed := strings.TrimSpace(line)
			if strings.HasPrefix(trimmed, "// ") || trimmed == "//" {
				descParts = append(descParts, strings.TrimSpace(trimmed[2:]))
				startBody = i + 1
			} else {
				break
			}
		}
		if len(descParts) > 0 {
			descRaw = strings.Join(descParts, " ")
			remaining = strings.Join(allLines[startBody:], "\n")
		} else if !strings.Contains(firstLine, "://") {
			if idx := strings.Index(firstLine, " // "); idx >= 0 {
				descRaw = strings.TrimSpace(firstLine[idx+4:])
				remaining = strings.TrimSpace(firstLine[:idx])
				if len(lines) > 1 {
					remaining += "\n" + lines[1]
				}
			}
		}
	}

	// Steps 6-8: Extract flags, tags, time, card suffix from title/desc/body
	if hasTitle {
		clean, err := extractModifiers(r, titleRaw, false)
		if err != nil {
			return nil, err
		}
		if clean != "" {
			r.Title = &clean
		}
	}
	if descRaw != "" {
		clean, err := extractModifiers(r, descRaw, false)
		if err != nil {
			return nil, err
		}
		if clean != "" {
			r.Description = &clean
		}
	}

	clean, err := extractModifiers(r, remaining, true)
	if err != nil {
		return nil, err
	}
	r.Body = clean

	if r.Body == "" && r.Title == nil {
		return nil, fmt.Errorf("empty body after extracting modifiers")
	}

	return r, nil
}

// tryPrefixTime attempts to extract a time token from the start of text.
// Returns (remaining text, true) on success, or ("", false) if no valid time found.
func tryPrefixTime(r *Result, text string) (string, bool) {
	text = strings.TrimSpace(text)
	if text == "" {
		return "", false
	}
	sp := strings.IndexByte(text, ' ')
	var timeStr, rest string
	if sp >= 0 {
		timeStr = text[:sp]
		rest = strings.TrimSpace(text[sp+1:])
	} else {
		timeStr = text
		rest = ""
	}
	if validateTime(timeStr) != nil {
		return "", false
	}
	r.TimeAnchor = &timeStr
	return rest, true
}

// extractModifiers extracts tags, flags, time anchors, and card suffixes from text.
// handleFlags controls whether !pin is extracted (true for body, false for title/desc in some contexts).
func extractModifiers(r *Result, text string, handleFlags bool) (string, error) {
	seen := map[string]bool{}
	for _, t := range r.Tags {
		seen[strings.ToLower(t)] = true
	}

	var outLines []string
	for _, line := range strings.Split(text, "\n") {
		tokens := strings.Fields(line)
		var lineParts []string
		for _, tok := range tokens {
			switch {
			case handleFlags && strings.EqualFold(tok, "!pin"):
				r.Pin = true

			case strings.HasPrefix(tok, "##") && len(tok) > 2:
				lineParts = append(lineParts, "#"+tok[2:])

			case strings.HasPrefix(tok, "@") && len(tok) > 1:
				timeStr := tok[1:]
				if validateTime(timeStr) != nil {
					lineParts = append(lineParts, tok)
				} else if r.TimeAnchor != nil {
					return "", fmt.Errorf("multiple time anchors")
				} else {
					r.TimeAnchor = &timeStr
				}

			case strings.HasPrefix(tok, "#") && len(tok) > 1:
				tag := strings.ToLower(tok[1:])
				if !seen[tag] {
					r.Tags = append(r.Tags, tag)
					seen[tag] = true
				}

			case strings.HasPrefix(tok, "^") && len(tok) > 1:
				suffix := tok[1:]
				cardType, ok := validCardTypes[suffix]
				if !ok {
					return "", fmt.Errorf("invalid card type %q", suffix)
				}
				if r.CardSuffix != nil {
					return "", fmt.Errorf("multiple card suffixes")
				}
				r.CardSuffix = &cardType

			default:
				lineParts = append(lineParts, tok)
			}
		}
		outLines = append(outLines, strings.Join(lineParts, " "))
	}
	return strings.Join(outLines, "\n"), nil
}

func validateTime(s string) error {
	parts := strings.SplitN(s, ":", 2)
	if len(parts) != 2 {
		return fmt.Errorf("expected HH:MM format")
	}
	h, err := strconv.Atoi(parts[0])
	if err != nil || h < 0 || h > 23 {
		return fmt.Errorf("hours must be 0-23")
	}
	m, err := strconv.Atoi(parts[1])
	if err != nil || m < 0 || m > 59 {
		return fmt.Errorf("minutes must be 0-59")
	}
	return nil
}