package common

import (
	"encoding/json"
	"os"
	"regexp"
	"strings"

	"github.com/spf13/afero"

	"github.com/lukaszraczylo/harness-sync/internal/canonical"
	"github.com/lukaszraczylo/harness-sync/internal/fsx"
)

// ReadIfExistsFS returns the file body or empty string when missing, using fs.
func ReadIfExistsFS(fs fsx.FS, path string) (string, error) {
	b, err := afero.ReadFile(fs, path)
	if os.IsNotExist(err) {
		return "", nil
	}
	if err != nil {
		return "", err
	}
	return string(b), nil
}

// ReadIfExists returns the file body or empty string when missing.
func ReadIfExists(path string) (string, error) {
	return ReadIfExistsFS(fsx.OS(), path)
}

// ReadExistingFile returns the file body or (nil, nil) when missing.
// Other errors (permission denied, I/O failure) are returned verbatim so
// read-modify-write callers can distinguish a fresh first-run state from a
// broken read. Treating every error as "file is empty" silently overwrites
// the user's on-disk edits during apply.
func ReadExistingFile(path string) ([]byte, error) {
	b, err := os.ReadFile(path) //nolint:gosec // caller-controlled path
	if err != nil && os.IsNotExist(err) {
		return nil, nil
	}
	return b, err
}

// DirExistsFS reports whether path is an existing directory on fs.
func DirExistsFS(fs fsx.FS, path string) bool {
	info, err := fs.Stat(path)
	return err == nil && info.IsDir()
}

// DirExists reports whether path is an existing directory.
func DirExists(path string) bool {
	return DirExistsFS(fsx.OS(), path)
}

var trailingComma = regexp.MustCompile(`,(\s*[}\]])`)

// StripJSONComments converts JSONC to standard JSON by:
//   - removing // line comments (only outside string literals)
//   - removing /* */ block comments (only outside string literals)
//   - removing trailing commas before } or ]
//
// It is string-aware so it won't mangle // inside URL values like "https://...".
func StripJSONComments(s string) string {
	result := make([]byte, 0, len(s))
	i, n := 0, len(s)
	for i < n {
		switch {
		case s[i] == '"': // string literal — copy verbatim including escape sequences
			result = append(result, s[i])
			i++
			for i < n {
				c := s[i]
				result = append(result, c)
				i++
				if c == '\\' && i < n {
					result = append(result, s[i])
					i++
				} else if c == '"' {
					break
				}
			}
		case i+1 < n && s[i] == '/' && s[i+1] == '*': // /* block comment */
			i += 2
			for i+1 < n && (s[i] != '*' || s[i+1] != '/') {
				i++
			}
			i += 2
		case i+1 < n && s[i] == '/' && s[i+1] == '/': // // line comment
			i += 2
			for i < n && s[i] != '\n' {
				i++
			}
		default:
			result = append(result, s[i])
			i++
		}
	}
	out := trailingComma.ReplaceAllString(string(result), "$1")
	return strings.TrimSpace(out)
}

// ImportMCPFromJSONFileFS reads a JSON file from fs and extracts an MCP server
// map nested under the given top-level key. Returns nil with no error when missing.
func ImportMCPFromJSONFileFS(fs fsx.FS, path, key string) ([]canonical.MCPServer, error) {
	body, err := afero.ReadFile(fs, path)
	if os.IsNotExist(err) {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	return ParseMCPFromJSON(body, key)
}

// ImportMCPFromJSONFile reads a JSON file and extracts an MCP server map
// nested under the given top-level key (e.g. "mcpServers", "mcp").
// Returns nil with no error when the file is missing.
func ImportMCPFromJSONFile(path, key string) ([]canonical.MCPServer, error) {
	return ImportMCPFromJSONFileFS(fsx.OS(), path, key)
}

// ParseMCPFromJSON extracts MCP servers from a JSON body. The body may be
// raw JSON or JSONC (comments are stripped first). Tolerates the dialect
// differences across harnesses:
//   - claude / crush: command is a string, transport key is "type"
//   - kilo / opencode: command is a []string (first element is the binary)
//   - some configs: env appears as "env", others as "environment"
//   - some configs: transport appears as "type", others as "transport"
func ParseMCPFromJSON(body []byte, key string) ([]canonical.MCPServer, error) {
	// Try plain JSON first — StripJSONComments eats // inside URL strings.
	var raw map[string]json.RawMessage
	if err := json.Unmarshal(body, &raw); err != nil {
		clean := StripJSONComments(string(body))
		if err := json.Unmarshal([]byte(clean), &raw); err != nil {
			return nil, nil
		}
	}
	nested, ok := raw[key]
	if !ok {
		return nil, nil
	}
	var entries map[string]json.RawMessage
	if err := json.Unmarshal(nested, &entries); err != nil {
		return nil, nil
	}
	out := make([]canonical.MCPServer, 0, len(entries))
	for n, raw := range entries {
		srv, ok := parseMCPEntry(n, raw)
		if !ok {
			continue
		}
		// Skip extension-managed entries: they have no command and no url
		// (e.g. zed extensions providing their own MCP). Nothing to propagate.
		if srv.Command == "" && srv.URL == "" {
			continue
		}
		out = append(out, srv)
	}
	return out, nil
}

func parseMCPEntry(name string, raw json.RawMessage) (canonical.MCPServer, bool) {
	var e struct { //nolint:govet // fieldalignment: dialect-tolerant entry, irreducible
		Type        string            `json:"type"`
		Transport   string            `json:"transport"`
		Command     json.RawMessage   `json:"command"`
		Cmd         json.RawMessage   `json:"cmd"`
		Args        []string          `json:"args"`
		URL         string            `json:"url"`
		Headers     map[string]string `json:"headers"`
		Env         map[string]string `json:"env"`
		Environment map[string]string `json:"environment"`
	}
	if err := json.Unmarshal(raw, &e); err != nil {
		return canonical.MCPServer{}, false
	}

	cmdRaw := e.Command
	if len(cmdRaw) == 0 {
		cmdRaw = e.Cmd
	}
	cmd, args := splitCommand(cmdRaw)
	args = append(args, e.Args...)

	env := e.Env
	if len(env) == 0 {
		env = e.Environment
	}

	transport := e.Type
	if transport == "" {
		transport = e.Transport
	}

	return canonical.MCPServer{
		Name:      name,
		Command:   cmd,
		Args:      args,
		URL:       e.URL,
		Transport: transport,
		Headers:   e.Headers,
		Env:       env,
	}, true
}

// splitCommand accepts a JSON value that may be a string ("foo") or a
// string array (["foo","--bar"]). Returns (head, tail).
func splitCommand(raw json.RawMessage) (string, []string) {
	if len(raw) == 0 {
		return "", nil
	}
	var s string
	if err := json.Unmarshal(raw, &s); err == nil {
		return s, nil
	}
	var arr []string
	if err := json.Unmarshal(raw, &arr); err == nil && len(arr) > 0 {
		return arr[0], arr[1:]
	}
	return "", nil
}