package tools

import (
	"context"
	"fmt"
	"sort"
	"strings"

	"code.nochebuena.dev/einherjar/mcp/internal/envspec"
	"code.nochebuena.dev/einherjar/mcp/internal/index"
	"github.com/modelcontextprotocol/go-sdk/mcp"
)

type checkEnvInput struct {
	Env      string   `json:"env" jsonschema:"the .env or .env.example contents to check (KEY=value lines; comments and blanks ignored)."`
	Modules  []string `json:"modules,omitempty" jsonschema:"module-granularity: the framework modules whose component configs the app composes, e.g. [\"db-postgres\",\"web\"]. Every env var in the module counts as composed. Convenient but coarse — a module can declare more than one config struct."`
	Composes []string `json:"composes,omitempty" jsonschema:"struct-granularity (preferred when precise): the exact config structs the app composes, as module/subpackage/Struct selectors, e.g. [\"web/server/Config\",\"db-postgres/Config\",\"core/logz/Config\"]. Use module/Struct when the config is at the module root. This catches struct-level dead vars, e.g. flagging EINHERJAR_SERVER_CORS_ORIGINS (which lives on web.Config, not web/server/Config)."`
}

type envFinding struct {
	Severity string `json:"severity"` // error | warning | info
	Kind     string `json:"kind"`     // unknown-var | missing-required | not-composed
	Var      string `json:"var"`
	Message  string `json:"message"`
	Hint     string `json:"hint,omitempty"`
}

type checkEnvOutput struct {
	Findings []envFinding `json:"findings"`
	OK       bool         `json:"ok"`
	Summary  string       `json:"summary"`
}

func registerCheckEnv(s *mcp.Server, idx *index.Index) {
	mcp.AddTool(s, &mcp.Tool{
		Name: "check_env",
		Description: "Check a .env / .env.example against the framework's real env vars. Flags EINHERJAR_* names that don't exist (invented or misspelled, e.g. EINHERJAR_PG_DATABASE), " +
			"and — when you declare what the app composes (via `modules` for coarse or `composes` for exact struct selectors) — required vars that are missing, plus framework vars that nothing composed reads (dead vars). " +
			"Prefer `composes` (e.g. web/server/Config) for precision; it catches struct-level dead vars that module granularity can't. " +
			"This is the enforcement half of building a correct global config: get_scaffold emits an accurate .env.example, get_config_env lists the truth, and check_env catches drift in an existing file.",
	}, func(ctx context.Context, req *mcp.CallToolRequest, args checkEnvInput) (*mcp.CallToolResult, checkEnvOutput, error) {
		findings, err := checkEnvVars(idx, args.Env, args.Modules, args.Composes)
		if err != nil {
			return errorResult(err.Error()), checkEnvOutput{}, nil
		}
		ok := true
		for _, f := range findings {
			if f.Severity == "error" {
				ok = false
			}
		}
		out := checkEnvOutput{Findings: findings, OK: ok, Summary: summariseEnvCheck(findings, ok)}
		return jsonText(out), out, nil
	})
}

// checkEnvVars is the pure core of check_env: given the framework index, an env
// file body, the modules the app composes (coarse), and the exact config structs
// it composes (precise selectors), it returns the drift findings. A var counts as
// "composed" when it is declared by any listed module or any listed struct.
func checkEnvVars(idx *index.Index, env string, modules, composes []string) ([]envFinding, error) {
	present := parseEnvKeys(env)
	known := envspec.KnownNames(idx)

	// The set of composed env vars (name -> Var), unioned from module-granularity
	// and struct-granularity selectors. Its keyset is the "what this app reads" set.
	expected := map[string]envspec.Var{}
	scoped := false
	for _, mod := range modules {
		mod = strings.TrimSpace(mod)
		if mod == "" {
			continue
		}
		if idx.FindModule(mod) == nil {
			return nil, fmt.Errorf("module not found: %s", mod)
		}
		scoped = true
		for _, v := range envspec.ForModule(idx, mod) {
			expected[v.Name] = v
		}
	}
	for _, sel := range composes {
		sel = strings.TrimSpace(sel)
		if sel == "" {
			continue
		}
		mod, sub, name, err := parseStructSelector(sel)
		if err != nil {
			return nil, err
		}
		if idx.FindModule(mod) == nil {
			return nil, fmt.Errorf("module not found in selector %q: %s", sel, mod)
		}
		vars := envspec.FindStruct(idx, mod, sub, name)
		if vars == nil {
			return nil, fmt.Errorf("struct not found for selector %q (want an existing module/subpackage/Struct)", sel)
		}
		scoped = true
		for _, v := range vars {
			expected[v.Name] = v
		}
	}

	varModule := map[string]string{}
	for _, v := range envspec.All(idx) {
		varModule[v.Name] = v.Module
	}

	var findings []envFinding

	// 1. EINHERJAR_* present in the file that is not a real framework var.
	for name := range present {
		if !strings.HasPrefix(name, "EINHERJAR_") {
			continue
		}
		if _, real := known[name]; real {
			continue
		}
		findings = append(findings, envFinding{
			Severity: "error", Kind: "unknown-var", Var: name,
			Message: name + " is not a real Einherjar env var",
			Hint:    "Confirm the exact name with get_config_env; e.g. the db name is EINHERJAR_PG_NAME (not _DATABASE) and the server bind is EINHERJAR_SERVER_HOST/_PORT (not _ADDR).",
		})
	}

	// 2. Required vars of a composed module that the file never sets.
	for name, v := range expected {
		if !v.Required {
			continue
		}
		if _, ok := present[name]; !ok {
			findings = append(findings, envFinding{
				Severity: "error", Kind: "missing-required", Var: name,
				Message: name + " is required by " + v.Module + "." + v.Struct + " but is absent from the file",
				Hint:    "Add " + name + "= to the file; a required var with no default fails config.Load() at boot.",
			})
		}
	}

	// 3. A real framework var set in the file that nothing composed reads → dead.
	//    With struct selectors this catches struct-level dead vars (a var whose
	//    module is partly composed but whose specific struct is not).
	if scoped {
		for name := range present {
			mod, real := varModule[name]
			if !real {
				continue
			}
			if _, composed := expected[name]; composed {
				continue
			}
			findings = append(findings, envFinding{
				Severity: "info", Kind: "not-composed", Var: name,
				Message: name + " is a real " + mod + " var, but none of the composed configs read it — it will be ignored",
				Hint:    "Compose the config that declares it, or drop the var. (E.g. EINHERJAR_SERVER_CORS_ORIGINS lives on web.Config; it is dead if you compose web/server/Config instead.)",
			})
		}
	}

	sort.Slice(findings, func(i, j int) bool {
		if findings[i].Kind != findings[j].Kind {
			return findings[i].Kind < findings[j].Kind
		}
		return findings[i].Var < findings[j].Var
	})
	if findings == nil {
		findings = []envFinding{}
	}
	return findings, nil
}

// parseStructSelector splits a "module/Struct" or "module/subpackage/Struct"
// selector. The struct name is always the last segment; a two-part selector
// targets a module-root config (empty sub-package).
func parseStructSelector(sel string) (module, subPackage, name string, err error) {
	parts := strings.Split(sel, "/")
	switch len(parts) {
	case 2:
		return parts[0], "", parts[1], nil
	case 3:
		return parts[0], parts[1], parts[2], nil
	default:
		return "", "", "", fmt.Errorf("invalid struct selector %q (want module/Struct or module/subpackage/Struct)", sel)
	}
}

// parseEnvKeys returns the set of assigned variable names in an env file body,
// tolerating `export KEY=`, leading whitespace, comments, and blank lines.
func parseEnvKeys(body string) map[string]bool {
	keys := map[string]bool{}
	for _, line := range strings.Split(body, "\n") {
		line = strings.TrimSpace(line)
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		line = strings.TrimPrefix(line, "export ")
		eq := strings.IndexByte(line, '=')
		if eq <= 0 {
			continue
		}
		key := strings.TrimSpace(line[:eq])
		if key != "" {
			keys[key] = true
		}
	}
	return keys
}

func summariseEnvCheck(fs []envFinding, ok bool) string {
	if len(fs) == 0 {
		return "No issues — every EINHERJAR_* name is real and all required vars are present."
	}
	var errs, infos int
	for _, f := range fs {
		if f.Severity == "error" {
			errs++
		} else {
			infos++
		}
	}
	status := "OK"
	if !ok {
		status = "FAILED"
	}
	return status + ": " + itoa(errs) + " error(s), " + itoa(infos) + " note(s)."
}