package cli

import (
	"flag"
	"fmt"
	"io"
	"os"
	"strings"
	"text/tabwriter"
	"text/template"
	"time"

	"werkdock/internal/store"
)

// imagesCmd lists images. Without flags it prints one reference per
// line in the short form (":latest" omitted): machine-usable, and what
// Werkator matches lines against. `--format` takes docker's Go
// template over .Repository .Tag .ID .CreatedAt .CreatedSince .Size,
// with `table` (optionally followed by a template) for docker's
// column layout; `-q` prints IDs; a REPOSITORY[:TAG] argument filters,
// as `docker images alpine` does.
func imagesCmd(args []string) int {
	fs := flag.NewFlagSet("images", flag.ContinueOnError)
	fs.SetOutput(io.Discard)
	var format string
	var quiet bool
	fs.StringVar(&format, "format", "", "Go template, or 'table [TEMPLATE]' for docker's columns")
	fs.BoolVar(&quiet, "q", false, "print image IDs only")
	fs.BoolVar(&quiet, "quiet", false, "print image IDs only")
	if err := fs.Parse(args); err != nil {
		return fail(err)
	}
	if len(fs.Args()) > 1 {
		return fail(fmt.Errorf("unexpected argument %q", fs.Args()[1]))
	}
	var filter *store.Reference
	if len(fs.Args()) == 1 {
		ref, err := store.ParseReference(fs.Args()[0])
		if err != nil {
			return fail(err)
		}
		filter = &ref
		if !strings.Contains(fs.Args()[0], ":") {
			filter.Tag = "" // a bare repository matches every tag
		}
	}
	st, err := store.Default()
	if err != nil {
		return fail(err)
	}
	names, err := st.List()
	if err != nil {
		return fail(err)
	}
	var rows []imageRow
	for _, name := range names {
		ref, _ := store.ParseReference(name)
		if filter != nil && (ref.Repository != filter.Repository || (filter.Tag != "" && ref.Tag != filter.Tag)) {
			continue
		}
		rows = append(rows, imageRow{st: st, ref: ref})
	}
	switch {
	case quiet:
		for _, row := range rows {
			fmt.Println(row.ID())
		}
	case format != "":
		var any []interface{}
		for i := range rows {
			any = append(any, &rows[i])
		}
		if err := printFormatted(os.Stdout, format, imageColumns, any); err != nil {
			return fail(err)
		}
	default:
		for _, row := range rows {
			fmt.Println(row.ref.Short())
		}
	}
	return 0
}

// imageRow is one image as a template sees it; the fields docker's
// `images --format` offers, computed on demand because Size walks the
// rootfs.
type imageRow struct {
	st   store.Store
	ref  store.Reference
	meta *store.ImageMeta
}

func (r *imageRow) load() store.ImageMeta {
	if r.meta == nil {
		meta, _ := r.st.Meta(r.ref.String())
		r.meta = &meta
	}
	return *r.meta
}

func (r *imageRow) Repository() string { return r.ref.Repository }
func (r *imageRow) Tag() string        { return r.ref.Tag }
func (r *imageRow) ID() string         { return r.load().ID() }
func (r *imageRow) CreatedAt() string {
	return r.load().CreatedAt.Local().Format("2006-01-02 15:04:05 -0700 MST")
}
func (r *imageRow) CreatedSince() string {
	return humanDuration(time.Since(r.load().CreatedAt)) + " ago"
}
func (r *imageRow) Size() string {
	n, err := r.st.Size(r.ref.String())
	if err != nil {
		return "?"
	}
	return humanSize(n)
}

// column is one cell of a docker-style table: the header, and the
// template that fills it.
type column struct{ header, cell string }

// imageColumns is `docker images` default table.
var imageColumns = []column{
	{"REPOSITORY", "{{.Repository}}"},
	{"TAG", "{{.Tag}}"},
	{"IMAGE ID", "{{.ID}}"},
	{"CREATED", "{{.CreatedSince}}"},
	{"SIZE", "{{.Size}}"},
}

// printFormatted renders rows through docker's --format: a Go
// template per row, or "table [TEMPLATE]" with a header line and
// aligned columns (columns is the default table and names the headers).
func printFormatted(w io.Writer, format string, columns []column, rows []interface{}) error {
	table := false
	if rest, ok := strings.CutPrefix(format, "table"); ok && (rest == "" || rest[0] == ' ' || rest[0] == '\t') {
		table = true
		format = strings.TrimSpace(rest)
		if format == "" {
			var cells []string
			for _, c := range columns {
				cells = append(cells, c.cell)
			}
			format = strings.Join(cells, "\t")
		}
	}
	// docker accepts \t and \n spelled out in the format string.
	format = strings.NewReplacer(`\t`, "\t", `\n`, "\n").Replace(format)
	tmpl, err := template.New("images").Parse(format)
	if err != nil {
		return fmt.Errorf("--format: %w", err)
	}
	out := w
	if table {
		tw := tabwriter.NewWriter(w, 0, 0, 3, ' ', 0)
		defer tw.Flush()
		out = tw
		fmt.Fprintln(tw, tableHeader(format, columns))
	}
	for _, row := range rows {
		if err := tmpl.Execute(out, row); err != nil {
			return fmt.Errorf("--format: %w", err)
		}
		fmt.Fprintln(out)
	}
	return nil
}

// tableHeader turns a cell template into docker's header line:
// "{{.Repository}}\t{{.ID}}" becomes "REPOSITORY\tIMAGE ID".
func tableHeader(format string, columns []column) string {
	header := format
	for _, c := range columns {
		header = strings.ReplaceAll(header, c.cell, c.header)
	}
	header = strings.ReplaceAll(header, "{{.CreatedAt}}", "CREATED AT")
	return strings.ReplaceAll(header, "{{.RunningFor}}", "CREATED")
}

func humanSize(n int64) string {
	const unit = 1000.0
	value := float64(n)
	for _, suffix := range []string{"B", "kB", "MB", "GB"} {
		if value < unit || suffix == "GB" {
			if suffix == "B" {
				return fmt.Sprintf("%d%s", n, suffix)
			}
			return fmt.Sprintf("%.3g%s", value, suffix)
		}
		value /= unit
	}
	return ""
}

func humanDuration(d time.Duration) string {
	switch {
	case d < time.Minute:
		return fmt.Sprintf("%d seconds", int(d.Seconds()))
	case d < 2*time.Minute:
		return "About a minute"
	case d < time.Hour:
		return fmt.Sprintf("%d minutes", int(d.Minutes()))
	case d < 2*time.Hour:
		return "About an hour"
	case d < 48*time.Hour:
		return fmt.Sprintf("%d hours", int(d.Hours()))
	case d < 14*24*time.Hour:
		return fmt.Sprintf("%d days", int(d.Hours()/24))
	case d < 60*24*time.Hour:
		return fmt.Sprintf("%d weeks", int(d.Hours()/24/7))
	case d < 2*365*24*time.Hour:
		return fmt.Sprintf("%d months", int(d.Hours()/24/30))
	default:
		return fmt.Sprintf("%d years", int(d.Hours()/24/365))
	}
}