package approval

import (
	"bytes"
	"encoding/json"
	"fmt"
	"math"
	"sort"
	"strconv"
	"strings"
	"unicode/utf8"

	"git.novox.be/novox/mesh-contracts/operator-and-conversation/go/clients/operatorchannelclient"
	"git.novox.be/novox/mesh-sdk/go/outward"
)

// Call is one call the runner serves, as the gate judges it: a module's tool, or a seat verb its module serves.
type Call struct {
	// Address is the address as called: `<module>.<tool>` or `<seat>.<verb>`.
	Address string
	// Module is the module whose bundle serves it; Seat the seat of a verb, empty for a tool; Name the tool or the verb.
	Module, Seat, Name string
	// Fingerprint is the build the bundle serves, from its composed environment (§5).
	Fingerprint string
	// Caller is the caller the bus proved.
	Caller string
	// Args are the call's arguments, a JSON object.
	Args json.RawMessage
	// Description is the tool's or verb's own description, whose first line the ask explains it by.
	Description string
	// Own says it is one of the runner's own tools served under the module's name (its ledger repairs), not its bundle's.
	Own bool
}

// MostArguments is the most a marked call's arguments may hold: more is refused, asking nothing (§9).
const MostArguments = 16 * 1024

// arguments are a call's arguments by name; a body that is not an object is refused.
func arguments(raw json.RawMessage) (map[string]json.RawMessage, error) {
	args := map[string]json.RawMessage{}
	if len(bytes.TrimSpace(raw)) == 0 || string(bytes.TrimSpace(raw)) == "null" {
		return args, nil
	}
	if err := json.Unmarshal(raw, &args); err != nil {
		return nil, fmt.Errorf("its arguments are not a JSON object: %v", err)
	}
	return args, nil
}

// refusedUnasked says why a marked call is refused at once, asking nothing (§9): its arguments hold a secret's shape, or are
// more than MostArguments.
func refusedUnasked(raw json.RawMessage) string {
	if len(raw) > MostArguments {
		return fmt.Sprintf("its arguments are %d bytes, more than the %d a call that needs the operator's approval may carry", len(raw), MostArguments)
	}
	if r, ok := outward.CheckSecret(string(raw)); !ok {
		return fmt.Sprintf("its arguments hold %s, which no ask may carry", r.What)
	}
	return ""
}

// ActOf is the act a marked call binds (§8): `address`, `node`, `module` and `tool` or `seat` and `verb`, `build`, and
// `arg.<name>` for each argument given, a string as itself and any other value as its JSON in RFC 8785's canonical form.
func ActOf(c Call, node string) (operatorchannelclient.Act, error) {
	act := operatorchannelclient.Act{"address": c.Address, "node": node, "build": c.Fingerprint}
	if c.Seat == "" {
		act["module"], act["tool"] = c.Module, c.Name
	} else {
		act["seat"], act["verb"] = c.Seat, c.Name
	}
	args, err := arguments(c.Args)
	if err != nil {
		return nil, err
	}
	for name, raw := range args {
		var s string
		if json.Unmarshal(raw, &s) == nil {
			act["arg."+name] = s
			continue
		}
		canon, err := Canonical(raw)
		if err != nil {
			return nil, fmt.Errorf("the argument %s cannot be put in canonical form: %v", name, err)
		}
		act["arg."+name] = canon
	}
	return act, nil
}

// Canonical is a JSON value in RFC 8785's canonical form: no white space, an object's members sorted by their names' UTF-16
// code units, a number as ECMAScript writes a double, a string with only the escapes the RFC names.
func Canonical(raw json.RawMessage) (string, error) {
	dec := json.NewDecoder(bytes.NewReader(raw))
	dec.UseNumber()
	var v any
	if err := dec.Decode(&v); err != nil {
		return "", err
	}
	var b strings.Builder
	if err := canonicalValue(&b, v); err != nil {
		return "", err
	}
	return b.String(), nil
}

func canonicalValue(b *strings.Builder, v any) error {
	switch x := v.(type) {
	case nil:
		b.WriteString("null")
	case bool:
		b.WriteString(strconv.FormatBool(x))
	case json.Number:
		f, err := strconv.ParseFloat(string(x), 64)
		if err != nil || math.IsInf(f, 0) || math.IsNaN(f) {
			return fmt.Errorf("the number %s is not a double", x)
		}
		b.WriteString(es6Number(f))
	case string:
		canonicalString(b, x)
	case []any:
		b.WriteByte('[')
		for i, e := range x {
			if i > 0 {
				b.WriteByte(',')
			}
			if err := canonicalValue(b, e); err != nil {
				return err
			}
		}
		b.WriteByte(']')
	case map[string]any:
		names := make([]string, 0, len(x))
		for k := range x {
			names = append(names, k)
		}
		sort.Slice(names, func(i, j int) bool { return utf16Less(names[i], names[j]) })
		b.WriteByte('{')
		for i, k := range names {
			if i > 0 {
				b.WriteByte(',')
			}
			canonicalString(b, k)
			b.WriteByte(':')
			if err := canonicalValue(b, x[k]); err != nil {
				return err
			}
		}
		b.WriteByte('}')
	default:
		return fmt.Errorf("a value of type %T", v)
	}
	return nil
}

// es6Number is a double as ECMAScript's Number.prototype.toString writes it (RFC 8785 §3.2.2.3).
func es6Number(f float64) string {
	if f == 0 {
		return "0"
	}
	abs := math.Abs(f)
	if abs >= 1e-6 && abs < 1e21 {
		return strconv.FormatFloat(f, 'f', -1, 64)
	}
	s := strconv.FormatFloat(f, 'e', -1, 64) // 1e+21, 1.5e-07
	mant, exp, _ := strings.Cut(s, "e")
	sign, digits := exp[:1], strings.TrimLeft(exp[1:], "0")
	return mant + "e" + sign + digits
}

func canonicalString(b *strings.Builder, s string) {
	b.WriteByte('"')
	for _, r := range s {
		switch {
		case r == '"':
			b.WriteString(`\"`)
		case r == '\\':
			b.WriteString(`\\`)
		case r == '\b':
			b.WriteString(`\b`)
		case r == '\f':
			b.WriteString(`\f`)
		case r == '\n':
			b.WriteString(`\n`)
		case r == '\r':
			b.WriteString(`\r`)
		case r == '\t':
			b.WriteString(`\t`)
		case r < 0x20:
			fmt.Fprintf(b, `\u%04x`, r)
		default:
			b.WriteRune(r)
		}
	}
	b.WriteByte('"')
}

func utf16Less(a, b string) bool {
	ua, ub := utf16Of(a), utf16Of(b)
	for i := 0; i < len(ua) && i < len(ub); i++ {
		if ua[i] != ub[i] {
			return ua[i] < ub[i]
		}
	}
	return len(ua) < len(ub)
}

func utf16Of(s string) []uint16 {
	out := make([]uint16, 0, utf8.RuneCountInString(s))
	for _, r := range s {
		if r >= 0x10000 {
			r -= 0x10000
			out = append(out, uint16(0xD800+(r>>10)), uint16(0xDC00+(r&0x3FF)))
		} else {
			out = append(out, uint16(r))
		}
	}
	return out
}

// Fingerprint is how an act is shown: its digest's first 24 hexadecimal digits in groups of four (§10).
func Fingerprint(digest string) string {
	hex := strings.TrimPrefix(digest, "sha256:")
	if len(hex) > 24 {
		hex = hex[:24]
	}
	var groups []string
	for len(hex) > 4 {
		groups, hex = append(groups, hex[:4]), hex[4:]
	}
	return strings.Join(append(groups, hex), " ")
}

// The bounds of the arguments shown in an ask (§11).
const (
	ShownBytes, ShownLines = 2000, 40
	PartBytes, PartLines   = 1200, 20
)

// shown is a call's arguments as an ask shows them (§11), one per line as "name: value", and whether all were shown whole:
// an argument whole where outward.Check passes it, else its shape, ‹path›, ‹address› or ‹withheld›; the whole when it is at
// most ShownBytes and ShownLines, else its first PartLines lines and PartBytes bytes, marked NOT SHOWN IN FULL.
func shown(raw json.RawMessage) (string, bool) {
	args, _ := arguments(raw)
	names := make([]string, 0, len(args))
	for n := range args {
		names = append(names, n)
	}
	sort.Strings(names)
	whole := true
	var lines []string
	for _, n := range names {
		var value string
		if json.Unmarshal(args[n], &value) != nil {
			value = string(args[n])
		}
		if r, ok := outward.Check(value); !ok {
			value, whole = shapeOf(r), false
		}
		lines = append(lines, n+": "+value)
	}
	text := strings.Join(lines, "\n")
	if all := strings.Split(text, "\n"); len(text) > ShownBytes || len(all) > ShownLines {
		if len(all) > PartLines {
			all = all[:PartLines]
		}
		text = strings.Join(all, "\n")
		if len(text) > PartBytes {
			text = cutBytes(text, PartBytes)
		}
		text += "\nNOT SHOWN IN FULL"
		whole = false
	}
	return text, whole
}

// shapeOf is what an argument outward.Check refuses is shown as.
func shapeOf(r outward.Refusal) string {
	switch r.Class {
	case "path":
		return "‹path›"
	case "address":
		return "‹address›"
	}
	return "‹withheld›"
}

// cutBytes is s at most n bytes, cut at a character's end.
func cutBytes(s string, n int) string {
	for n > 0 && !utf8.RuneStart(s[n]) {
		n--
	}
	return s[:n]
}