package builder;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Objects;

public final class HttpRequest {

    // All fields are final: the object is immutable after build() returns.
    private final String url;
    private final String method;
    private final String body;
    private final Map<String, String> headers;
    private final int timeoutMs;
    private final int maxRetries;

    // Private: the only path to an HttpRequest is through Builder.build()
    private HttpRequest(Builder builder) {
        this.url        = Objects.requireNonNull(builder.url, "URL is required");
        this.method     = builder.method;
        this.body       = builder.body;
        this.headers    = Collections.unmodifiableMap(new HashMap<>(builder.headers));
        this.timeoutMs  = builder.timeoutMs;
        this.maxRetries = builder.maxRetries;
    }

    // Getters only — no setters, enforcing immutability
    public String getUrl()          { return url; }
    public String getMethod()       { return method; }
    public String getBody()         { return body; }
    public Map<String, String> getHeaders() { return headers; }
    public int getTimeoutMs()       { return timeoutMs; }
    public int getMaxRetries()      { return maxRetries; }

    @Override
    public String toString() {
        return String.format("%s %s (timeout=%dms, retries=%d, headers=%s, body=%s)",
            method, url, timeoutMs, maxRetries, headers, body);
    }

    // -----------------------------------------------------------------------
    // THE BUILDER — static inner class so it can call the private constructor
    // -----------------------------------------------------------------------
    public static class Builder {

        // Required field — no default, must be set
        private String url;

        // Optional fields with sensible defaults
        private String method     = "GET";
        private String body       = null;
        private Map<String, String> headers = new HashMap<>();
        private int timeoutMs     = 30_000;  // 30 seconds
        private int maxRetries    = 0;

        // Fluent methods: each returns 'this' so calls can be chained
        public Builder url(String url)              { this.url = url; return this; }
        public Builder method(String method)        { this.method = method; return this; }
        public Builder body(String body)            { this.body = body; return this; }
        public Builder header(String key, String v) { headers.put(key, v); return this; }
        public Builder timeoutMs(int ms)            { this.timeoutMs = ms; return this; }
        public Builder maxRetries(int n)            { this.maxRetries = n; return this; }

        // Terminal method: validates and creates the immutable HttpRequest
        public HttpRequest build() {
            if (url == null || url.isBlank()) {
                throw new IllegalStateException("url() is required before calling build()");
            }
            if (maxRetries < 0) {
                throw new IllegalStateException("maxRetries must be >= 0");
            }
            return new HttpRequest(this);  // calls the private constructor
        }
    }
}