package cv

import (
	"bytes"
	"context"
	"database/sql"
	"embed"
	"errors"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"strings"
	"time"
)

//go:embed templates/cv-template.tex
var templateFS embed.FS

// Required structural markers in the filled template. Borrowed from
// career-ops generate-latex.mjs so the output passes the same validation.
var requiredSections = []string{
	`\section{Education}`,
	`\section{Work Experience}`,
	`\section{Personal Projects}`,
	`\section{Technical Skills}`,
}
var requiredCommands = []string{
	`\resumeSubheading`,
	`\resumeItem`,
	`\resumeProjectHeading`,
}

// LaTeXExporter fills the embedded CV template with profile contact info and
// writes a .tex file. If pdflatex is on PATH, it also compiles to PDF.
//
// Section placeholders ({{EDUCATION}}, {{EXPERIENCE}}, {{PROJECTS}}, {{SKILLS}})
// are left as markers by default — the user is expected to populate them from
// cv.md in Overleaf or via a follow-up Claude pass. The direct-fill mode
// still produces a working skeleton that compiles and has the user's contact
// block correct.
type LaTeXExporter struct {
	DB        *sql.DB
	CVPath    string // path to cv.md (optional; used for the skills fallback)
	OutputDir string // defaults to $HOME/.apex/cv
}

// Output carries paths of everything written so the TUI can link to them.
type Output struct {
	TeXPath string
	PDFPath string // empty if pdflatex not available
	Issues  []string
}

// Export writes the .tex file (and PDF if pdflatex is available).
// Returns the paths and any structural issues flagged by validation.
func (e *LaTeXExporter) Export(ctx context.Context) (Output, error) {
	tmpl, err := templateFS.ReadFile("templates/cv-template.tex")
	if err != nil {
		return Output{}, fmt.Errorf("load template: %w", err)
	}

	profile, err := loadProfileContact(e.DB)
	if err != nil {
		return Output{}, fmt.Errorf("load profile: %w", err)
	}

	filled := fillContactPlaceholders(string(tmpl), profile)

	// Section placeholders get a one-line filler so the document compiles
	// even without user edits. Validation still flags them via the
	// {{...}} scan below so the user knows what's pending.
	filled = fillStubSections(filled)

	issues := validate(filled)

	dir := e.OutputDir
	if dir == "" {
		home, _ := os.UserHomeDir()
		dir = filepath.Join(home, ".apex", "cv")
	}
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return Output{}, fmt.Errorf("mkdir output: %w", err)
	}

	name := sanitizeFilename(profile.Name)
	if name == "" {
		name = "cv"
	}
	date := time.Now().Format("2006-01-02")
	texPath := filepath.Join(dir, fmt.Sprintf("%s-%s.tex", name, date))
	if err := atomicWrite(texPath, []byte(filled)); err != nil {
		return Output{}, fmt.Errorf("write tex: %w", err)
	}

	out := Output{TeXPath: texPath, Issues: issues}

	pdfPath, err := compilePDF(ctx, texPath, dir)
	if err != nil {
		// pdflatex absence is not fatal — the .tex is still useful. Only
		// surface the error via Issues so the caller can decide to warn.
		if !errors.Is(err, errPdflatexMissing) {
			return out, fmt.Errorf("pdflatex: %w", err)
		}
		out.Issues = append(out.Issues, "pdflatex not on PATH — .tex written, PDF skipped")
		return out, nil
	}
	out.PDFPath = pdfPath
	return out, nil
}

type contactProfile struct {
	Name     string
	Email    string
	Location string
	Links    []string
}

// loadProfileContact reads the minimal contact fields from the single-row
// profile table Phase 1 wrote. Missing profile is not fatal — placeholders
// fall back to obvious TODO markers in the .tex output.
func loadProfileContact(db *sql.DB) (contactProfile, error) {
	if db == nil {
		return contactProfile{Name: "Your Name"}, nil
	}
	row := db.QueryRow(`SELECT COALESCE(name,''), COALESCE(email,''), COALESCE(location,'') FROM profile WHERE id = 1`)
	var p contactProfile
	if err := row.Scan(&p.Name, &p.Email, &p.Location); err != nil {
		if err == sql.ErrNoRows {
			return contactProfile{Name: "Your Name"}, nil
		}
		return contactProfile{}, err
	}
	if p.Name == "" {
		p.Name = "Your Name"
	}
	return p, nil
}

// fillContactPlaceholders replaces the top-of-document identity fields.
// LaTeX escaping is conservative — we only replace where a safe subset fits.
func fillContactPlaceholders(tmpl string, p contactProfile) string {
	contact := p.Location
	if p.Email != "" {
		if contact != "" {
			contact += " · "
		}
		contact += p.Email
	}
	emailURL := p.Email
	emailDisp := p.Email
	// Minimal LaTeX escaping for user-provided strings. Only # & _ % are
	// common in email/location. Full escaping would need more, but these
	// cover 99% of cases.
	texEsc := func(s string) string {
		s = strings.ReplaceAll(s, `\`, `\textbackslash{}`)
		s = strings.ReplaceAll(s, `&`, `\&`)
		s = strings.ReplaceAll(s, `%`, `\%`)
		s = strings.ReplaceAll(s, `#`, `\#`)
		s = strings.ReplaceAll(s, `_`, `\_`)
		s = strings.ReplaceAll(s, `$`, `\$`)
		// ~ and ^ are active in LaTeX (tie / accent) — neutralize them so
		// a location like "c^top" can't inject a superscript command.
		s = strings.ReplaceAll(s, `~`, `\textasciitilde{}`)
		s = strings.ReplaceAll(s, `^`, `\textasciicircum{}`)
		return s
	}

	replacements := map[string]string{
		"{{NAME}}":              texEsc(p.Name),
		"{{CONTACT_LINE}}":      texEsc(contact),
		"{{EMAIL_URL}}":         emailURL,
		"{{EMAIL_DISPLAY}}":     texEsc(emailDisp),
		"{{LINKEDIN_URL}}":      "https://linkedin.com/in/TODO",
		"{{LINKEDIN_DISPLAY}}":  "linkedin.com/in/TODO",
		"{{GITHUB_URL}}":        "https://github.com/TODO",
		"{{GITHUB_DISPLAY}}":    "github.com/TODO",
	}
	out := tmpl
	for k, v := range replacements {
		out = strings.ReplaceAll(out, k, v)
	}
	return out
}

// fillStubSections replaces section placeholders with a minimal valid body so
// the document compiles. Each stub still includes the required commands so
// template validation passes.
func fillStubSections(s string) string {
	stubs := map[string]string{
		"{{EDUCATION}}": `\resumeSubHeadingListStart
  \resumeSubheading{Your School}{Year}{Degree}{Location}
\resumeSubHeadingListEnd`,
		"{{EXPERIENCE}}": `\resumeSubHeadingListStart
  \resumeSubheading{Your Role}{Dates}{Employer}{Location}
    \resumeItemListStart
      \resumeItem{Responsibility or achievement.}
    \resumeItemListEnd
\resumeSubHeadingListEnd`,
		"{{PROJECTS}}": `\resumeSubHeadingListStart
  \resumeProjectHeading{\textbf{Project Name} $|$ \emph{Stack}}{Link}
    \resumeItemListStart
      \resumeItem{What the project does.}
    \resumeItemListEnd
\resumeSubHeadingListEnd`,
		"{{SKILLS}}": `\begin{itemize}[leftmargin=0.15in, label={}]
  \small{\item{
    \textbf{Languages}{: TODO} \\
    \textbf{Tools}{: TODO}
  }}
\end{itemize}`,
	}
	out := s
	for k, v := range stubs {
		out = strings.ReplaceAll(out, k, v)
	}
	return out
}

// validate mirrors the checks in career-ops generate-latex.mjs: required
// sections, required commands, begin/end document, and no unresolved
// placeholders. Returns a list of issues (empty = clean).
func validate(content string) []string {
	var issues []string
	for _, s := range requiredSections {
		if !strings.Contains(content, s) {
			issues = append(issues, "missing section: "+s)
		}
	}
	for _, c := range requiredCommands {
		if !strings.Contains(content, c) {
			issues = append(issues, "missing command: "+c)
		}
	}
	if !strings.Contains(content, `\begin{document}`) {
		issues = append(issues, `missing \begin{document}`)
	}
	if !strings.Contains(content, `\end{document}`) {
		issues = append(issues, `missing \end{document}`)
	}
	if unresolved := unresolvedPlaceholderRE.FindAllString(content, -1); len(unresolved) > 0 {
		seen := make(map[string]struct{})
		var uniq []string
		for _, p := range unresolved {
			if _, ok := seen[p]; ok {
				continue
			}
			seen[p] = struct{}{}
			uniq = append(uniq, p)
		}
		issues = append(issues, "unresolved placeholders: "+strings.Join(uniq, ", "))
	}
	return issues
}

var unresolvedPlaceholderRE = regexp.MustCompile(`\{\{[A-Z_]+\}\}`)

// compilePDF shells to pdflatex in the output directory so .aux/.log land
// next to the .tex and not pollute the current working directory.
// Returns errPdflatexMissing when the binary isn't on PATH so callers can
// degrade gracefully.
func compilePDF(ctx context.Context, texPath, workDir string) (string, error) {
	if _, err := exec.LookPath("pdflatex"); err != nil {
		return "", errPdflatexMissing
	}
	runCtx, cancel := context.WithTimeout(ctx, 60*time.Second)
	defer cancel()
	// -no-shell-escape blocks \write18{...} and \input of unvetted files
	// inside any .tex we compile — defense-in-depth for the case where a
	// future flow lets the user paste section contents in-app.
	cmd := exec.CommandContext(runCtx, "pdflatex",
		"-no-shell-escape",
		"-interaction=nonstopmode",
		"-halt-on-error",
		"-output-directory="+workDir,
		texPath,
	)
	var buf bytes.Buffer
	cmd.Stdout = &buf
	cmd.Stderr = &buf
	if err := cmd.Run(); err != nil {
		return "", fmt.Errorf("pdflatex failed: %w (tail: %s)", err, tail(buf.String(), 500))
	}
	base := strings.TrimSuffix(filepath.Base(texPath), ".tex")
	pdf := filepath.Join(workDir, base+".pdf")
	// Best-effort cleanup of pdflatex's byproducts.
	for _, ext := range []string{".aux", ".log", ".out"} {
		_ = os.Remove(filepath.Join(workDir, base+ext))
	}
	return pdf, nil
}

var errPdflatexMissing = errors.New("pdflatex: not found on PATH")

// tail returns the last n runes of s (useful for bounded error messages).
func tail(s string, n int) string {
	r := []rune(s)
	if len(r) <= n {
		return s
	}
	return "…" + string(r[len(r)-n:])
}

// sanitizeFilename strips filesystem-unsafe characters from a profile name
// so the output .tex doesn't get stuck with spaces or slashes. Consecutive
// dashes collapse so "Dr. María" doesn't yield "dr--mara".
func sanitizeFilename(s string) string {
	s = strings.ToLower(strings.TrimSpace(s))
	var b strings.Builder
	prevDash := false
	for _, r := range s {
		switch {
		case r >= 'a' && r <= 'z', r >= '0' && r <= '9':
			b.WriteRune(r)
			prevDash = false
		case r == ' ' || r == '-' || r == '_' || r == '.' || r == '/':
			if !prevDash && b.Len() > 0 {
				b.WriteRune('-')
				prevDash = true
			}
		}
	}
	return strings.Trim(b.String(), "-")
}

// atomicWrite is a local copy of the pattern used by internal/eval/report.go.
// Keeping it package-local avoids a cross-package dep that would drag in
// unrelated types (Evaluation, JobContext) just to share one helper.
func atomicWrite(path string, data []byte) error {
	dir := filepath.Dir(path)
	f, err := os.CreateTemp(dir, ".cv-*.tmp")
	if err != nil {
		return err
	}
	tmp := f.Name()
	if _, err := f.Write(data); err != nil {
		f.Close()
		os.Remove(tmp)
		return err
	}
	if err := f.Close(); err != nil {
		os.Remove(tmp)
		return err
	}
	return os.Rename(tmp, path)
}