package tools

import (
	"encoding/json"
	"fmt"
	"reflect"
	"strings"

	"gitea.d-ma.be/mathias/gitea-mcp/internal/gitea"
	"gitea.d-ma.be/mathias/gitea-mcp/internal/registry"
)

// Tool implements registry.Tool.
type Tool = registry.Tool

func textOK(v any) (json.RawMessage, error) {
	return json.Marshal(v)
}

func parseArgs(raw json.RawMessage, dst any) error {
	if len(raw) == 0 {
		if err := json.Unmarshal([]byte("{}"), dst); err != nil {
			return err
		}
	} else if err := json.Unmarshal(normalizeAliases(raw), dst); err != nil {
		return err
	}
	return validateRequiredIdentifiers(dst)
}

// validateRequiredIdentifiers rejects an empty repo identifier at the tool layer
// before it reaches the client, where it would build a trailing-empty path
// segment (`/api/v1/repos/{owner}/`) and leak gitea's bare 404 (#37). `repo` and
// `name` are always required where present — the per-repo identifier tools and
// the two create tools respectively; `owner` is already enforced by the
// allowlist check. Returns a typed ErrValidation naming the missing field.
func validateRequiredIdentifiers(dst any) error {
	v := reflect.ValueOf(dst)
	if v.Kind() != reflect.Ptr || v.IsNil() {
		return nil
	}
	v = v.Elem()
	if v.Kind() != reflect.Struct {
		return nil
	}
	t := v.Type()
	for i := 0; i < t.NumField(); i++ {
		base, opts, _ := strings.Cut(t.Field(i).Tag.Get("json"), ",")
		if base != "repo" && base != "name" {
			continue
		}
		// An optional identifier (e.g. code_search's `repo`, empty => owner-wide
		// fan-out) opts out by carrying `,omitempty`.
		if strings.Contains(opts, "omitempty") {
			continue
		}
		if v.Field(i).Kind() == reflect.String && v.Field(i).String() == "" {
			return fmt.Errorf("%q is required: %w", base, gitea.ErrValidation)
		}
	}
	return nil
}

// normalizeAliases reconciles the two spellings of the repo identifier so a tool
// works whichever the caller sends. `repo` is the canonical, idiomatic name that
// identifier tools now advertise (#38); `name` is kept as a back-compat alias.
// The mapping is bidirectional: `name`->`repo` fills the new canonical for old
// callers, and `repo`->`name` still fills the two create tools (repo_create,
// create_project_from_template) whose `name` legitimately means "name of the new
// repo". `index`->`number` is kept for the issue tools whose canonical is
// `number`. An explicit canonical value always wins over its alias.
func normalizeAliases(raw json.RawMessage) json.RawMessage {
	var m map[string]json.RawMessage
	if err := json.Unmarshal(raw, &m); err != nil {
		return raw // not a JSON object — leave untouched
	}
	changed := aliasInto(m, "name", "repo")
	changed = aliasInto(m, "repo", "name") || changed
	changed = aliasInto(m, "number", "index") || changed
	if !changed {
		return raw
	}
	if patched, err := json.Marshal(m); err == nil {
		return patched
	}
	return raw
}

// aliasInto copies m[alias] into m[canonical] when canonical is absent or an
// empty/zero JSON value and alias carries a usable one. An explicit canonical
// value always wins. Returns true if it wrote canonical.
func aliasInto(m map[string]json.RawMessage, canonical, alias string) bool {
	av, ok := m[alias]
	if !ok || isEmptyJSON(av) {
		return false
	}
	if cv, ok := m[canonical]; ok && !isEmptyJSON(cv) {
		return false
	}
	m[canonical] = av
	return true
}

func isEmptyJSON(v json.RawMessage) bool {
	switch strings.TrimSpace(string(v)) {
	case "", `""`, "null", "0":
		return true
	default:
		return false
	}
}

// capLimit returns a sane page size: 0 or negative → def, > 50 → 50.
func capLimit(in, def int) int {
	if in <= 0 {
		return def
	}
	if in > 50 {
		return 50
	}
	return in
}