package pdfdoc

import (
	"fmt"
	"regexp"
	"strconv"
	"strings"
	"unicode/utf8"

	"git.wntrmute.dev/kyle/sift/internal/pdftext"
)

// maxGrepMatches bounds how many match blocks are shown; the count reported is
// always the true total.
const maxGrepMatches = 100

// maxGrepPatternBytes bounds a grep pattern; a longer one is rejected before it
// can compile.
const maxGrepPatternBytes = 200

// hit is one match: the 1-based page and the 0-based line index within it.
type hit struct{ page, line int }

// renderGrep searches every line of every page in the range (all pages when no
// range is given) and returns the matches with their page numbers.
func renderGrep(doc *pdftext.Doc, opt Options) (Rendered, error) {
	pattern := opt.Grep
	if len(pattern) > maxGrepPatternBytes {
		return Rendered{}, fmt.Errorf("%w: pattern over %d bytes", ErrBadGrep, maxGrepPatternBytes)
	}
	re, err := regexp.Compile(grepPattern(pattern))
	if err != nil {
		return Rendered{}, fmt.Errorf("%w: %v", ErrBadGrep, err)
	}

	start, end := 1, len(doc.Text)
	if opt.Pages != "" {
		s, e, err := parsePages(opt.Pages, len(doc.Text))
		if err != nil {
			return Rendered{}, err
		}
		start, end = s, e
	}

	var hits []hit
	linesByPage := make(map[int][]string, end-start+1)
	for p := start; p <= end; p++ {
		lines := splitLines(doc.Text[p-1])
		linesByPage[p] = lines
		for j := range lines {
			if re.MatchString(lines[j]) {
				hits = append(hits, hit{p, j})
			}
		}
	}

	n := len(hits)
	var header string
	switch {
	case n == 0:
		header = `grep "` + pattern + `": no matches`
	case n == 1:
		header = `grep "` + pattern + `": 1 match`
	default:
		header = fmt.Sprintf(`grep "%s": %d matches`, pattern, n)
	}
	if n > maxGrepMatches {
		header += ", showing the first " + strconv.Itoa(maxGrepMatches)
	}

	maxBlocks := n
	if maxBlocks > maxGrepMatches {
		maxBlocks = maxGrepMatches
	}

	outLines := make([]string, 0, 16+len(hits))
	outLines = append(outLines, header)
	running := utf8.RuneCountInString(header)
	shown := 0
	for i := 0; i < maxBlocks; i++ {
		block := matchBlock(hits[i], linesByPage)
		add := utf8.RuneCountInString(strings.Join(block, "\n"))
		if i == 0 {
			if running+add > opt.OutCap {
				break
			}
		} else if running+1+add > opt.OutCap {
			break
		}
		outLines = append(outLines, block...)
		running += add
		if i > 0 {
			running++
		}
		shown++
	}
	content := strings.Join(outLines, "\n")
	if utf8.RuneCountInString(content) > opt.OutCap {
		content = truncateRunes(content, opt.OutCap)
	}

	note := ""
	if shown < maxBlocks {
		note = fmt.Sprintf("showing %d of %d matches", shown, n)
	}
	return Rendered{Content: content, GrepHits: n, Note: note}, nil
}

// grepPattern applies smart case: it lowercases-sensitively prefixes "(?i)"
// unless the pattern already contains an upper-case letter, which asks for a
// case-sensitive search.
func grepPattern(pattern string) string {
	if hasUpper(pattern) {
		return pattern
	}
	return "(?i)" + pattern
}

// hasUpper reports whether s contains an upper-case ASCII letter.
func hasUpper(s string) bool {
	for _, r := range s {
		if r >= 'A' && r <= 'Z' {
			return true
		}
	}
	return false
}

// matchBlock renders one hit as its previous line, the matching line, the next
// line and a separator. Context lines that do not exist (the match is on the
// first or last line) are omitted.
func matchBlock(h hit, linesByPage map[int][]string) []string {
	lines := linesByPage[h.page]
	var b []string
	if h.line > 0 {
		b = append(b, fmt.Sprintf("p. %d- %s", h.page, strings.TrimSpace(lines[h.line-1])))
	}
	b = append(b, fmt.Sprintf("p. %d: %s", h.page, strings.TrimSpace(lines[h.line])))
	if h.line+1 < len(lines) {
		b = append(b, fmt.Sprintf("p. %d- %s", h.page, strings.TrimSpace(lines[h.line+1])))
	}
	return append(b, "--")
}

// splitLines splits a page into its lines, dropping the single empty line a
// trailing newline would otherwise introduce.
func splitLines(s string) []string {
	lines := strings.Split(s, "\n")
	if len(lines) > 1 && lines[len(lines)-1] == "" && strings.HasSuffix(s, "\n") {
		lines = lines[:len(lines)-1]
	}
	return lines
}